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Scission of electrospun polymer fibres by ultrasonication
Abstract
In this work we show that sonication alone can be used to scission bulk electrospun membranes into short fibres. The mechanism of such scission events is bubble cavitation stimulated by the ultrasonic probe, followed by bubble implosion. The tendency of polymer nanofibres to undergo failure by such a scission process appears to primarily depend on the ductility of the polymer, with brittle, electrospun polymer membranes such as poly(styrene) and poly(methyl methacrylate) readily producing short fibres of approximately 10 μm length. More ductile polymers such as poly(l-lactide) or poly(acrylonitrile) require additional processing after electrospinning and before sonication, to make them conducive to such sonication-based scission. Both the initial diameter of the fibres and the degree of nanofibre alignment of the electrospun membrane influence the final length of the resultant short fibres. It was found that the chemical and physical properties of the short nanofibres were unaltered by the sonication process. We are thus able to demonstrate that sonication is a promising method to produce significant quantities of short fibres of nanometre diameter and microns in length.
... Greenfeld and collaborators observed the appearance of discrete short fibres up to a length of 1 mm when electrospinning low molecular weight polymethyl-methacrylate (PMMA) (15 kDa) [26]. In a recent work, Sawawi and co-workers described the use of ultrasonication as a method for the scission of polystyrene and PMMA fibres down to 10 μm in length [27]. They have also shown the application of this method for the milling of UV/ozone pretreated Poly-L-Lactic Acid (PLLA) fibres. ...
... Indeed, when using water, which exhibits a static contact angle of 134°± 4 on the PLLA meshes, the dispersion and fragmentation efficiencies were very low. This is possibly due to the fibre-fibre adhesion being energetically more favourable than the fibre-water interaction [27]. Since with each sonication cycle the membranes are folded up, less water penetrates into the membrane, leading to a lack of cavitation bubble formation. ...
... Since with each sonication cycle the membranes are folded up, less water penetrates into the membrane, leading to a lack of cavitation bubble formation. It is possible that the ozone/UV exposure used as pre-treatment to cut PLLA fibres previously reported by Sawawi et al. [27] introduced \OH groups on the surface of the PLLA fibres, increasing their wettability with respect to water. This pre-treatment, however, irreversibly degrades PLLA fibres by oxidizing the ester bonds of the polymer, leading to a reduction of molecular weight and a significant reduction of the mechanical properties of the polymer. ...
... This dependency on the object length L also explains the decrease of cutting speed with shorter objects and the existence of a terminal object length, which is approached after long sonication times, both observed by different researchers. 114,115,116,120 The shorter the objects become, the lower is the drag force F. If F becomes smaller than the force needed for rupture, the object cannot be shortened any further, which means, that the terminal object length is reached. 115 This in turn means that from a given terminal length the minimum force needed for rupture being released by cavity collapse in more viscous media. ...
... The temperature of the dispersion during sonication is another factor known to possibly affect results achieved by ultrasonic treatment of dispersions. 114 To examine this factor's impact on the ultrasonic cutting of BTA fibers, a 1000 ppm dispersion of BTA 5 in anisole was sonicated at a power amplitude of 50% applying cooling bath temperatures of -30, -15 and 20 °C. For each temperature, temporal evolution of fiber dimensions is shown in Figure 59. ...
... In literature, this effect is attributed to lower energy release upon collapse of cavities, which had been formed by ultrasound beforehand, in warmer media. 114 Summarizing, it can be stated that the temperature of the medium cooling the sonicated dispersion plays a minor role in the ultrasonic cutting of BTA 5, at least in the temperature window investigated. At higher temperatures, additional effects due to partial dissolution of the BTA would expectantly have to be taken into account. ...
Supramolecular chemistry is supposed to become one of the significant research fields in material science of the 21st century. This is attributed to the manifold self-assembly processes resulting in distinct supramolecular architectures with specific functionalities. However, several issues are still not easy to solve. For example, tailoring supramolecular architectures with precise dimensions via bottom-up approaches remains challenging. Therefore, this work is dedicated to self-assembly, dimensional control and application of supramolecular 1D- and 2D- nanomaterials based on 1,4-bisamides and 1,3,5-trisamides. The first part addresses the self-assembly of 1,4-benzene- or 1,4-cyclohexanebisamides into 2D-nanoobjects. These novel 1,4-bisamides are designed with different fluorocarbon or tertbutyl substituents resulting in symmetrical or asymmetrical substitution patterns. Within each substitution pattern, the length of the fluorocarbons was varied from C3F7 over C5F11 to C7F15. A symmetric 1,4-bisamide with tert-butyl groups was used as reference. All bisamides proved to feature sufficient thermal stability allowing self-assembly experiments at elevated temperatures. In this context, an important aspect was the structural elucidation by X-ray diffraction, solid-state NMR and IR spectroscopy, as these methods reveal the H-bonding pattern, which typically reflects the shape of nano-objects on the mesoscale. In cooperation with the department of Inorganic Chemistry III at the University of Bayreuth, it was shown that bisamides without tert-butyl substituents form rows of molecules connected by H-bonds. These rows align into layers, which stack to form platelets. By contrast, bisamides comprising at least one tert-butyl substituent connect to four neighbors to form layers, which also stack into platelets. Based on this finding, a reference bisamide was used to evaluate different self-assembly processes and to tune self-assembly conditions to obtain thinner nano-platelets. Transferring and further optimizing these results to the symmetric and asymmetric 1,4-bisamides with fluorocarbon substituents it was found that an asymmetric bisamide formed the thinnest platelets, featuring an average thickness of around 32 nm, which equals 15 layers. In addition, a reduction of platelet thickness with longer fluorocarbon chains was revealed. Moreover, contact angle measurements of two fluorocarbon substituted bisamides revealed that the surfaces of their 2D-objects are highly hydrophobic. The second part focuses on dimensional control of supramolecular fibers of 1,3,5-benzene-trisamides via a top-down approach. In particular, length control of such fibers was addressed via ultrasound. For this, supramolecular submicron fibers of 1,3,5-benzene-trisamide were produced in large amounts by self-assembly upon cooling of solutions in high-boiling hydrocarbons. For later systematic sonication experiments, several dispersion media for supramolecular submicron fibers such as n-hexane, methyl cyclohexane and anisole were explored. A systematic screening of sonication parameters such as sonication time, ultrasonic power amplitude, medium, cooling bath temperature and concentration of BTA fibers revealed their influence on the final fiber dimensions. For instance, the applied ultrasonic energy is the major factor for the length of the obtained fibers. By contrast, raising the concentration or lowering the temperature gave only slightly shorter submicron fibers. Remarkably, the used medium during sonication altered fibers’ length as well as their aspect ratio. This way, it was possible to vary the aspect ratio from 3.7 to 6.8 and the fiber length from 0.66 to 0.98 μm. In this context, the fiber lengths were successfully correlated with the viscosity of the media revealing shorter fibers in more viscous media even after a long sonication time demonstrating the control over the fibers’ dimensions. In the third part, supramolecular nanofibers were applied to improve the foam morphology and mechanical properties of extruded polypropylene foams. This work was realized in cooperation with the department of Polymer Engineering at the University of Bayreuth. Conceptually, the homogeneously dissolved BTAs self-assemble during cooling in the extrusion process into solid nanofibers, which act as finely dispersed nucleation sites for the foam cells and consequently control the foam morphology. To realize this, three different BTAs at different concentrations were compounded into an isotactic polypropylene (i-PP) grade and injection molded. The specimens were thoroughly investigated and, based on these results, compounds comprising different concentrations of the three BTAs were chosen for foam extrusion. Talc at different concentrations was used as reference. Foam extrusion was realized in a tandem extrusion line using CO2 as physical blowing agent. It was found that the density and the morphology of extruded foams can be significantly altered by the presence of BTAs. With BTAs, the foam density is strongly reduced by more than 40% to 0.09 g/cm3 compared to neat i-PP. Also, the average foam cell diameter was reduced by more than 40%, reaching an optimum diameter of 27 μm. Such homogenous foams with small cell sizes could not be achieved with the talc reference foams. Moreover, it was demonstrated that the specific compression moduli of foams with BTA could lead to an improvement of more than 100% compared to neat i-PP and more than 65% compared to the talc reference foam. This finding is attributed to a reinforcing effect of BTA fibers.
... To overcome these drawbacks, the ES process should be modified to produce 3D thick structures with adequate porosity and appropriate Correspondence to: H. Mirzadeh; e-mail: mirzadeh@aut.ac.Ir pore dimensions to allow for cell infiltration and growth in a 3D biomimetic nanofibrous environment. Many attempts have been made to reach this aim including stacking electrospun layers and membrane, [23][24][25][26][27][28][29] combination of micro and nanofibers, [30][31][32] assembly of spinned nanofibers, [33][34][35][36] post-processing the electrospun mats with laser, ultrasonic vibration or mechanical expansion, [37][38][39][40][41] rolling or folding the fibers, [42][43][44] accelerated solidification, 45 variation in surface resistivity of spinning fibers, 46,47 alteration of the electric field, 48 changing the solution properties, 49 using liquid flow in the spinning fiber path, 21,50,51 and using sacrificing components. [52][53][54][55] In spite of the wide range of studies performed on preparation of highly porous 3D scaffolds by electrospinning, 21, structures with adequate porosity and proper pore size for cell infiltration in the millimeter scale have not been reported yet. ...
... On the contrary, in the literature articles, there is no exact control over the porosity and pore size enhancement of 3D electrospun structures. 21,[38][39][40][41]45,50,51 Besides, many works on fabrication of 3D scaffolds lack the possibility of easy cell diffusion, such as in post-assembly or stacking of conventional electrospun layers [23][24][25][26][27][28][29][33][34][35][36][42][43][44] . In the introduced technique, micro-thickness of each individual inner layer along the entire thickness of the scaffold and formation of the 3D pores that directly affect the facility of cellular movement and diffusion between layers can be adjusted by the variation in the thickness of the spring side wires (Fig. 3). ...
... The obtained mechanical properties of 3D helicaldesigned scaffold exhibited higher values when compared to other reported 3D nanofibrous structures, 21,[37][38][39][40][41]46,47,[50][51][52][53][54][55] or even other 3D scaffolds fabricated by other methods. 69,71 The obtained results can be attributed to the special design of this innovative three dimentional electrospun structure. ...
Adequate porosity, appropriate pore size and 3D-thick shape are crucial parameters in the design of scaffolds, as they should provide the right space for cell adhesion, spreading, migration and growth. In this work, a novel design for fabricating a 3D nanostructured scaffold by electrospinning was taken into account. Helical spring-shaped collector was purposely designed and used for electrospinning PCL fibers. Improved morphological properties and more uniform diameter distribution of collected nanofibers on the turns of helical spring-shaped collector are confirmed by SEM analysis. SEM images elaboration showed 3D pores with average diameter of 4 and 5.5 micrometer in x-y plane and z-direction, respectively. Prepared 3D scaffold possessed 99.98% porosity which led to the increased water uptake behavior in PBS at 37°C up to 10 days, and higher degradation rate compared to 2D flat structure. Uniaxial compression test on 3D scaffolds revealed an elastic modulus of 7 MPa and a stiffness of 10(2) MPa, together with very low hysteresis area and residual strain. In vitro cytocompatibility test with MG-63 osteoblast-like cells using AlamarBlue(TM) colorimetric assay, indicated a continuous increase in cell viability for the 3D structure over the test duration. SEM observation showed enhanced cells spreading and diffusion into the underneath layers for 3D scaffold. Accelerated calcium deposition in 3D substrate was confirmed by EDX analysis. Obtained morphological, physical and mechanical properties together with in vitro cytocompatibility results, suggest this novel technique as a proper method for the fabrication of 3D nanofibrous scaffolds for the regeneration of critical-size load bearing defects. This article is protected by copyright. All rights reserved.
... Wet electrospinning is a simple method to fabricate 3 dimensional nanober structures that provide the controlling of ber density, but the obtained bers are continuous, long and spongiform. 28 Various mechanical approaches such as grinding, 29 milling, 30 cutting with a razor blade under liquid nitrogen 31 and ultrasonication 30 have been also utilized to breakdown the electropun nanobers, though they are predominately appropriate for electrospun mats that are adequately brittle under mechanical loading to break. Grinding and milling methods have limited control over ber length. ...
... 29,32 Moreover, plastic deformation of bers may occur during cryogenic milling method and a combination of bers and akes was produced in milled electrospun bers. 30 Razor blade cutting under liquid nitrogen provides better control of length but is not efficient. 31 Some pre-treatment is needed for ultrasonic breaking of less brittle polymers such as UV-ozone irradiation that can be used to induce sites of fracture on the PLA mat and facilitate the ultrasonic breaking, yet nanober surfaces became rougher and more pitted aer sonication. ...
... 31 Some pre-treatment is needed for ultrasonic breaking of less brittle polymers such as UV-ozone irradiation that can be used to induce sites of fracture on the PLA mat and facilitate the ultrasonic breaking, yet nanober surfaces became rougher and more pitted aer sonication. 30 However, ultrasonication of PLA nanobers without any pretreatment could only enlarge the porosity of electrospun mat and produce 3 dimensional structure with long and continuous bers that enhanced cell inltration. 33 In comparison to above methods, chemical fragmentation of PLA nanobers through aminolysis reaction has some advantages including: producing discrete and short nanober with a uniform morphology, enabling control of ber length by varying reaction parameters, 20 reducing the hydrophobicity of bers, increasing ber-cell interaction, 34 decreasing the inammation reaction to implanted scaffold due to neutralizing the acidic products of scaffold degradation 35 and being useful for both aligned and non-aligned mats without any additional processing. ...
Electrospun fiber–hydrogel composites have been recently utilised to mimic the native extracellular matrix (ECM), in order to overcome the poor mechanical properties of hydrogels as well as restricted cell infiltration of electrospun fibers. In this study, poly(lactic acid) (PLA) fibers were firstly prepared via electrospinning method and then fragmented through aminolysis reaction. Next, hyaluronic acid (HA) was chemically grafted to the alginate (Alg) backbone by esterification reaction. Composite scaffolds were constructed with incorporation of fragmented nanofibers into alginate-graft-hyaluronate (Alg-g-HA) solution in 1 : 1 and 1 : 2 ratios and then gelation occurred by calcium chloride solution (102 mM). Scanning electron microscopy (SEM) images showed the formation of continuous and uniform PLA nanofibers without beads. The diameter and length of fragmented nanofibers were measured which were 0.568 ± 0.254 μm and 7.060 ± 4.963 μm (mean ± SD), respectively. Grafting of HA onto the Alg backbone was confirmed by nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. Incorporation of fragmented nanofibers into the alginate–hyaluronic acid hydrogel increased the compressive modulus by around 81% compared to the nanofiber-free hydrogel scaffold control and decreased water uptake. The cytocompatibility of the scaffolds was confirmed by using the MTT assay and acridine orange/propidium iodide (AO/PI) staining. SEM images revealed that chondrocytes maintained their spherical morphology in the composites. Hematoxylin and eosin (H&E) staining illustrated localization of the chondrocytes into lacuna with a round morphology and a uniform distribution within the scaffolds. Alcian blue staining also showed that the chondrocytes could produce a cartilage specific matrix within the composites. Therefore, it could be concluded that PLA nanofiber/Alg–HA hydrogel composites can provide a suitable microenvironment for chondrocytes during cartilage repair.
... An alternative to the chemical methods is mechanical (physical) ones. In this field, motor-driven blade cutting under liquid nitrogen [19,20], cryo-micro cutting [21], UV cutting with the presence of masks with a defined size of slits [22], laser cutting [23] and ultrasonication [24,25] might be distinguished. Ultrasonication is one of the methods used, among others, for electrospun fibrous scaffold disintegration and their pore size expansion. ...
... Additional use involves short electrospun fibers fabrication. The fibers fragmentation J o u r n a l P r e -p r o o f mechanism assumes bubble cavitation and implosion, followed with releasing energy and subsequent fibers fracture and fragmentation [24]. It allows obtaining short fibers from brittle materials in a very fast and simple manner [24]. ...
... The fibers fragmentation J o u r n a l P r e -p r o o f mechanism assumes bubble cavitation and implosion, followed with releasing energy and subsequent fibers fracture and fragmentation [24]. It allows obtaining short fibers from brittle materials in a very fast and simple manner [24]. However, similarly to most of the mechanical methods, it results in broad nanofibers' length distribution, consequently limiting the scope of their applications [21]. ...
This research work is aimed at studying the effect of ultrasounds on the effectiveness of fiber fragmentation by taking into account the type of sonication medium, processing time, and various PLLA molecular weights. Fragmentation was followed by an appropriate filtration in order to decrease fibers length distribution. It was evidenced by fiber length determination using SEM that the fibers are shortened after ultrasonic treatment, and the effectiveness of shortening depends on the two out of three investigated parameters, mostly on the sonication medium, and processing time. The gel permeation chromatography (GPC) confirmed that such ultrasonic treatment does not change the polymers' molecular weight.
Our results allowed to optimize the ultrasonic fragmentation procedure of electrospun fibers while preliminary viscosity measurements of fibers loaded into hydrogel confirmed their potential in further use as fillers for injectable hydrogels for regenerative medicine applications.
... In contrary to continuous fibers obtained by electrospinning, short fibers have not gained much attention. There are fewer studies about fabricating short fibers than long fibers (Sawawi, Wang, Nisbet, & Simon, 2013 F I G U R E 8 Cell viability and proliferation on the composite scaffolds on Day 7. (a-d) Representative live/dead staining images of cell seeded composite scaffolds without (a-b) and with (c-d) PCL nanofibers (50 wt%). (e-f) Representative immunostaining images of cell seeded scaffolds, cytoskeleton, and nucleus staining with phalloidin (green) and DAPI (blue), respectively. ...
... Thus, to make a balance between the fiber morphology and mechanical properties, a duration of 4 hr of UV irradiation was selected as pretreatment prior to ultrasonication. Plasma treatment has been also employed to improve the wettability of PCL fibers, which affects cell adhesion and proliferation (Jing, Mi, Peng, Peng, & Turng, 2015 predicted the minimum length of short fibers fabricated by sonication (Sawawi et al., 2013). This minimum length was reported to be a function of the tensile strength of the filament, its diameter, the solvent viscosity and cavitation parameters (Sawawi et al., 2013). ...
... Plasma treatment has been also employed to improve the wettability of PCL fibers, which affects cell adhesion and proliferation (Jing, Mi, Peng, Peng, & Turng, 2015 predicted the minimum length of short fibers fabricated by sonication (Sawawi et al., 2013). This minimum length was reported to be a function of the tensile strength of the filament, its diameter, the solvent viscosity and cavitation parameters (Sawawi et al., 2013). In this study, the ultimate fiber length was demonstrated to be proportional to the diameter of fiber, which was consistent with Huang's conclusion (Huang et al., 2009). ...
From a structural perspective, an ideal scaffold ought to possess interconnected macro pores with sizes from tens to hundreds of micrometers to facilitate cell infiltration and tissue formation, as well as similar topography to the natural extra cellular matrix (ECM) which would have an impact on cell behavior such as cell adhesion and gene expression. For that purpose, here we developed a fabrication process to incorporate electrospun short fibers within freeze‐dried scaffolds for tissue engineering applications. Briefly, PCL short fibers were first produced from electrospun fibers with ultrasonication method. They were then evenly dispersed in gelatin solution and freeze‐dried to obtain fiber incorporated scaffolds. The resulting scaffolds exhibited hierarchical structure including major pores with sizes ranging from 50‐150 μm and the short fibers dispersed in the thin walls of major pores, mimicking the fibrous feature of natural ECM. The short fibers were proven to modify the mechanical properties of scaffold and to facilitate cell adhesion and proliferation on the scaffold. As a promising scaffold for tissue engineering and regenerative medicine, the fiber incorporated scaffold may have further biomedical applications, in which the short fibers can act as drug release vehicles for growth factors or other biomolecules to promote vascularization. This article is protected by copyright. All rights reserved.
... Using electrospun fibers as nanoadditives has been explored primarily in polymerbased composites through film-stacking [3] or solution impregnation [4]. Short electrospun fiber reinforcement has been attempted through mechanical cutting [5] or ultrasonication [6] of electrospun nonwovens. However, these methods have not given full scope to the advantages of electrospun fibers. ...
... The compact nature of the non-woven mat obtained from traditional electrospinning substantially diminishes the flexibility of electrospun fibers, and the fibers cannot be dispersed inside the matrix. Meanwhile, the short electrospun fiber generation raises strict requirements in experiment devices and protocols and sometimes yields limited dispersibility [6]. ...
We propose a novel approach of wet electrospinning to yield fiber-reinforced polymer ceramic composites, where a reactive ceramic precursor gel is used as a collector. We illustrate our approach by generating polyethylene oxide (PEO) fibers in a potassium silicate gel; the gel is later activated using metakaolin to yield a ceramic-0.5 wt% PEO fiber composite. An increase of 29% and 22% is recorded for the fabricated polymer ceramic composites in terms of indentation modulus and indentation hardness respectively. Our initial findings demonstrate the process viability and might lead to a potentially scalable manufacturing approach for fiber-reinforced polymer ceramic composites.
... However, their applications in situ are still limited due to the lack of injection properties. Contrastively, short nanofibers (SNFs), which were prepared by ultrasonication [38], UV cutting [39], or cyrocutting [40,41] from electrospun nanofiber sheets, have been recently regarded as an advanced injectable material for various applications such as cytokines delivery [42] and oral infection ablation [43]. Especially, magneto-responsive SNFs have been further developed to induce the unidirectional growth of nerve cells within hydrogel [41]. ...
... Subsequently, the core-shell nanofiber sheets were cut into short core-shell sheets using the cryocutting method and then dispersed with ultrasonic treatment to remove the sacrificial PEO shell to obtain MSNFs (Fig. 2). Although some previous studies also used various methods to prepare the electrospun short fibers, it remains challenging to obtain the SNFs with controllable length and excellent dispersity [38,42]. To overcome this drawback, in this study we used the coaxial electrospinning technique to prepare the core-shell nanofiber, where the water-soluble polymer PEO was served as the sacrificial shell (Fig. 2a). ...
Developing an injectable anisotropic scaffold with precisely topographic cues to induce 3D cellular organization plays a critical role in volumetric muscle loss (VML) repair in vivo. However, controlling aligned myofiber regeneration in vivo based on previous injectable scaffolds continues to prove challenging, especially in a 3D configuration. Herein, we prepare the monodisperse remote magnetic controlled short nanofibers (MSNFs) with a high yield using an advanced coaxial electrospinning-cyrocutting method. An injectable anisotropic MSNF/Gel nanofiber/hydrogel scaffold based on MSNFs within photocurable hydrogel is further designed, showing the ability to guide 3D cellular alignment and organization by the precise microarchitecture control via a remote magnetic field. MSNF/Gel anisotropic scaffolds were able to recreate the macroscale and microscale topographical features of orbicular muscle and bipennate muscle mimicking their anatomical locations. Furthermore, the resultant MSNF/Gel anisotropic scaffolds significantly enhanced aligned myofiber formation in vivo and improved functional recovery of injured muscles in animal VML models. In summary, this approach offers a new promising tissue engineering strategy not only for the aligned myofiber formation for enhancing skeletal muscle regeneration in vivo but also for other biofabrication of living constructs containing complex anisotropy in vitro.
... Ultrasonication of PLAf was hypothesized to cause the PLA polymers on the fibril surface to undergo mechanically induced cleavage, which is known to happen for dissolved polymers (Caruso et al. 2009) and for some electro-spun polymer membranes (Sawawi et al. 2013) subjected to ultrasonication. This cleavage could result in the presence of additional hydroxyl and carboxylic acid groups on the fibril surface, similarly to what happens to PLA under base-catalyzed hydrolysis (Guo et al. 2015). ...
... This hypothesis was based on two previous research findings. First, it has been shown that PLA can undergo chain scission when exposed to ultrasonication (Caruso et al. 2009, Sawawi et al. 2013. Second, chain scission of PLA by hydrolysis has been shown to form new OH and COOH groups, which increase the PLA surface's hydrophilicity (Guo et al. 2015). ...
Polylactic acid fibrils (PLAf) were employed as a fiber component in papermaking. The addition of 5 wt % of PLAf to bleached kraft birch pulp increased the tensile index of the resulting 100 g/m ² paper sheets by 20 % in comparison to sheets produced without PLAf. By heat-treating the paper sheets containing 5 wt % PLAf, a 35 % higher tensile index in comparison to sheets produced without PLAf was achieved. SEM imaging showed that the heat-treatment caused the PLAf to melt, which formed a film on the fiber web. The PLAf was ultrasonicated in an attempt to make its surface more hydrophilic and anionic and thus more compatible with cellulose. Chemical additives (cationic polyacrylamide, polyethylene imine and polyethylene glycol) were added to the PLAf/cellulose pulp mixture in order to increase the binding between the ultrasonicated PLAf and cellulose. Ultrasonication caused the PLAf length to decrease and the PLAf surface charge changed by 36 %, indicating that the PLAf became significantly more anionic. Neither ultrasonication of PLAf nor the chemical additives improved the paper sheets’ stretchability. Polyethyleneimine as an additive in an amount of 1 % increased the tensile index of heat-treated sheets made with 5 wt % of PLAf by 19 %.
... One possible issue with this method is fiber aggregation and entanglement during processing even under diluted conditions, which results in a relative high fiber aspect ratio compared with grinding. Other cutting methods include ultrasonication [111,112], in which electrospun fibers were processed in liquid media using ultrasonic excitation. Ultrasonication generates bubble cavitation followed by bubble implosion. ...
... (a) SEM image of short electrospun carbon nanofibers by grinding (adapted from[108]); (b) SEM image of short PS fibers made by ultrasonication aligned electrospun PS fibers in water (adapted from[112]); (c) SEM image of electrospun PPTA fibers from PPTA/sulfuric acid solution at concentration of 7 wt% (adapted from[116]); (d) SEM image of short PLA fiber by mechanical stirring electrospun fibers in organic medium (adapted from[103]). ...
Electrospun fibers have received significant interests for various application areas such as filtration, composites and biomedical products due to their large surface area, good continuity, high porosity and many other unique properties. In bio-related applications, electrospun fibers have been used for in-situ drug delivery, tissue engineering scaffolds and wound dressing. In more recent years, there has been a drive toward novel electrospun fibers with added functionalities. Nanoengineering of electrospun fibers has introduced many of such novel properties. Through this review, researchers are provided with a state of the art overview of nanoenhanced electrospun fibers with added functionalities. Examples of some nanoengineered fibers include; surface functionalization, multi-component fibers, porous nanofibers, the creation of surface nano-topographies, and the incorporation of nanoparticles to create hierarchical fibrous structures for tailoring of physicochemical properties with a special focus on biomedical applications.
... Fibres are continuous and smooth with no obvious defects (such as beads) observed (see Fig. 3 a1 and a2). A number of methods have been reported for the cutting of electrospun fibres, including ultrasonication [32,33], UV cutting [34], cryogenic-cutting [20,35], direct spinning by tuning concentration and voltage [36], spinning with nanoparticles [37] or the use of a specific electrospinning setup [38]. Cryo-cutting is an up-scalable method of fibre cutting however we found PLA fibres remained relatively ductile even at low temperature, making the cutting difficult. ...
... The method proved successful for the cutting of carbon nanotubes [39], however, its effectiveness is significantly reduced when using ductile polymer fibres. Hence, fibre pre-treatment such as irradiation have been used to generate weak points before ultrasonication in order to promote cutting [33]. In our work, we used a media composed of toluene and petroleum ether to facilitate the fragmentation of electrospun fibres. ...
Polylactide (PLA) fibre reinforced poly(trimethylene carbonate) (PTMC) composites were prepared by incorporating electrospun fibres in tri-functional methacrylate-terminated PTMC macromer solutions and cured by UV irradiation. Short electrospun fibres with average length of 50–700 μm were prepared by solvent assisted mechanical stirring and different amounts of short fibres were loaded into PTMC composites. The reinforcement effect of short PLA fibres at different concentrations and continuous fibre were assessed by tensile tests and micromechanical models. With the incorporation of continuous electrospun PLA fibres, the Young’s modulus of PTMC was increased from 2.7 to 310 MPa; while tensile strength and toughness were also improved significantly. The addition of small amounts (5 wt%) of short PLA fibres increased the Young’s modulus and tensile strength three-fold without compromising the ductility of PTMC. The potential to tailor the mechanical performance and dimensional stability of these nontoxic and degradable PTMC/fibre composites makes them interesting candidates for tissue engineering applications.
... Nowadays, sonication is widely used in the dispersion of nano-and mesoscale particles and filaments. In addition, it can also break carbon nanotubes [18e21], cylindrical micelles [22e24], and polymer fibers [25,26]. It is generally accepted that the destructive force is caused by ultrafast shear flow of the solvent created by cavitation, which involves the nucleation, growth, and collapse of microbubbles in solution. ...
... In other words, the bottlebrush dynamics undergoes a transition from non-draining (Zimm) to draining (Rouse) regime as the bottlebrushes become shorter. At the initial stages of sonication, long bottlebrushes (_ ε < t À1 Z ) may behave like solid cylindrically shaped objects, similar to carbon nanotubes, nanowires, polymeric fibrils [18,19,25,27,28]; while at the later stages, the backbone scission is controlled by solvent draining, which differentiates short bottlebrushes (_ ε > t À1 Z ) from solid cylindrical objects. Besides, the critical force for cleavage for solid cylindrically shaped objects depends on their cross-sectional area, in contrast to its independence on diameter (DP of side chains) for bottlebrushes and that it is determined by the strength of backbone bonds. ...
... [8] However, long, continuous fibers from electrospinning are not excretable as they are too large for phagocytosis by Kupffer cells. Numerous techniques, such as grinding, [19] cutting, [20] ultrasonication, [21] and homogenizers, [22] have been utilized in attempts to fragment electrospun nanofibers. Ultrasonication is reported to be the most efficient method in terms of simplicity and uniformity, however, its utility is limited to highly brittle polymers. ...
... Ultrasonication is reported to be the most efficient method in terms of simplicity and uniformity, however, its utility is limited to highly brittle polymers. [21] In this study, we aimed to develop a facile method for producing uniform-sized fragments from electrospun nanofibers, universally applicable for various polymers regardless of their mechanical properties. We utilized the colloid electrospinning of polymer and sacrificial nanoparticles to create a beads-on-a-string structure and subsequent chemical removal of the nanoparticles to introduce mechanical weak points along the fibers. ...
Electrospinning is a versatile method for synthesizing nanofibrous structures from nearly all polymers, offering a solution for the industrial‐scale mass production of nanomaterials in a wide range of applications. However, the continuous non‐woven structure intrinsic to electrospun fibers limits their applications, where a smaller length scale is desired. Here, we present a novel method to synthesize polymeric nanofiber‐fragments based on colloid electrospinning of polymer and sacrificial silica nanoparticles, followed by mechanical fracturing with ultrasonication. The size and hydrophobicity of silica nanoparticles are optimized for their improved integration within the polymer matrix, and the controllability of nanofiber‐fragment length by the amount of silica nanoparticle loading, down to 2 µm in length for poly(vinylidene fluoride‐trifluoroethylene) nanofibers with an average fiber diameter of approximately 100 nm, is shown. The resultant nanofiber‐fragments are shown to maintain their material properties including piezoelectric coefficients and their enhanced injectability for drug delivery application is demonstrated with an animal model. Colloid electrospinning of polymer and sacrificial silica nanoparticles is utilized to synthesize polymeric nanofiber‐fragments. The resultant nanofiber‐fragments are shown to maintain their material properties and their enhanced injectability for drug delivery application is demonstrated.
... Ultrasonication, which stimulates bubble cavitation and implosion, offers another approach for cutting off electrospun membranes into short fibers. Similarly, ultrasonication-assisted scission primarily depends on the ductility of polymers [42]. Brittle polymer-based electrospun membranes such as poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) are readily to break into short fibers with approximately 10 μm long upon sonication of 60 s for PS and 40 s for PMMA. ...
... High-yield production Nonuniformity; more effective for brittle fibers rather than ductile fibers [42] Ultrasonication with NaCl nanoparticle encapsulation ...
Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.
... The reason behind this is not fully understood. Surface roughness of electro-spun fibres has been addressed widely (Milleret et al., 2012;Sawawi et al., 2013) and ascribed to process conditions during electro-spinning such as humidity, polymer concentration, and the type of solvent used (Casper et al., 2003;Pai et al., 2009). Increase in the surface roughness of the fibres after onset of degradation in PBS solution at 37 1C has been reported for electro-spun poly(lactic-co-glycolic acid) (Duan et al., 2007) and DegraPol s (Henry et al., 2007) scaffolds. ...
Electro-spun biodegradable polymer fibrous structures exhibit anisotropic mechanical properties dependent on the degree of fibre alignment. Degradation and mechanical anisotropy need to be captured in a constitutive formulation when computational modelling is used in the development and design optimisation of such scaffolds. Biodegradable polyester-urethane scaffolds were electro-spun and underwent uniaxial tensile testing in and transverse to the direction of predominant fibre alignment before and after in vitro degradation of up to 28 days. A microstructurally-based transversely isotropic hyperelastic continuum constitutive formulation was developed and its parameters were identified from the experimental stress-strain data of the scaffolds at various stages of degradation. During scaffold degradation, maximum stress and strain in circumferential direction decreased from 1.02±0.23MPa to 0.38±0.004MPa and from 46±11% to 12±2%, respectively. In longitudinal direction, maximum stress and strain decreased from 0.071±0.016MPa to 0.010±0.007MPa and from 69±24% to 8±2%, respectively. The constitutive parameters were identified for both directions of the non-degraded and degraded scaffold for strain range varying between 0% and 16% with coefficients of determination r(2)>0.871. The six-parameter constitutive formulation proved versatile enough to capture the varying non-linear transversely isotropic behaviour of the fibrous scaffold throughout various stages of degradation.
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... [24e27] including adverse effects [28]. The method of sonication is also applied when the process of electrospinning is completed as for instance for the synthesis of nanoparticles [29], pore size and thickness of nanofibrous mats [30], production of short elongated nanofibres [31], yielding of anisometric particles [32]. ...
... homogeneous distribution of particles in polymer solutions), or it contributes to desirable alterations (e.g. obtaining polymer fractions of different molecular weights of xanthan gum [9] or scission of the polymer nanofibres [10]). ...
In order to fabricate a magnetic nanofibrous membrane by electrospinning, it is necessary to follow a suitable method for incorporating nanoparticles into a polymer solution. Ultrasound treatment represents a very effective technique for distributing magnetic nanoparticles within polymer solutions. Adverse effects caused by sonication over time on the given nanofibrous membrane (polymer degradation and appearance of defects) were evaluated by using rotational (magneto)rheometry, transmission and scanning electron microscopy, and magnetometry. A magnetorheological approach was selected to estimate the optimal duration of sonication, and findings were experimentally verified. It was concluded that the processed nanofibrous membrane showed promise as an advanced magnetoactive device.
... In contrast to this, the surface of the ultrasonicated samples is porous and fluffy ( Figure S3). Sawawi et al. reported an interesting phenomenon that ultrasonication can be used to scission electrospun membranes into short fibers [51]. They have found, that brittle electrospun polymers such as poly(styrene) and poly(methyl methacrylate) can be easily broken by the bubble cavitation. ...
The aim of tissue engineering is to develop methods to restore, maintain or improve tissue functions. To imitate the fibrous structure of the native extracellular matrix, the electrospinning technique is widely used. However, the dense packing of fibers results in small pores and hereby the inhibition of cellular penetration.
In this study, we used biocompatible and biodegradable poly(aspartic acid) based fibrous hydrogel scaffolds to enhance the cell infiltration using ultrasonication (US). The US can enlarge the space between the fibers in the scaffold and create a 3D structure based on the thickness increase of the samples. To prevent the scaffolds from degradation and create an easy-to-store sample beyond the US treatment, a freeze-drying process was also introduced in this work. After all these treatments, the scaffold’s specific load capacity was 0.11 ± 0.01 Nm²/g which did not change after a rehydration cycle and the elongation break became almost two times higher than before the US treatment. The cytotoxicity results demonstrated that the cellular viability did not show any significant decrease compared to the control groups for none of the samples. The cellular penetration was visualized by multiphoton microscopy.
In summary, we were able to overcome the major limitation of conventional electrospun scaffolds regarding their application in tissue engineering. We also improved the storing conditions of fibrous hydrogel scaffolds and extend their shelf life without degradation.
... This difference corresponded to ca. 33% decrease in the recovery efficiency of the MHNs, and indicated that the method of probe sonication led to the disconnection of some of the MHN network structure into either individual SCKs or polymer fibers, which were no longer covalently bound to the amine-IONs and, thus, remained in the water upon separation via magnetic action. The effects of probe sonication on the morphologies of the MHNs and SCKs are not surprising, since scission of covalent bonds in polymer fibers, 56 and molecular bottlebrushes 57 has been widely reported in the field of mechanochemistry. Additionally, the fractionation of non-crosslinked and crosslinked polymer micelles as a consequence of sonication has also been previously observed by our group, as well as others. ...
Magnetically-active hybrid networks (MHNs) are complex inorganic/organic composite materials that have been synthesized from the coupling of amine-functionalized iron oxide nanoparticles (amine-IONs) and pre-assembled shell crosslinked knedel-like (SCK) polymeric nanoconstructs. The intricate structure of these materials is composed of several inter-connected bundles of SCKs covalently bound to amine-IONs, which afford them magnetic responsivity. The MHNs were originally designed to sequester complex hydrocarbons from water; however, they have displayed a remarkable ability to form stable Pickering emulsions between organic solvents and water, upon mechanical stimulus. Two methods of emulsification, vortex and probe sonication, have been utilized to yield magnetically-active toluene-in-water and dodecane-in-water emulsions, which are stable for up to two months in the presence of the MHNs. A detailed study of the effect of the water-to-oil (W : O) volume ratio and the MHN concentration on the droplet size of the emulsions revealed that the smallest droplet size, and narrowest dispersity were obtained at a W : O = 3 : 1, for all conditions tested. Additionally, concentrations of MHNs as low as 1 mg mL(-1) and 1.5 mg mL(-1), for emulsions prepared via vortex and probe sonication, respectively, were sufficient to yield the smallest droplets and narrowest distributions. Furthermore, the oil droplets stabilized by the MHNs exhibited magnetic character, and could be manipulated with an external magnetic field.
... Figure 4 represents the r/e curves related to coral-free verses coral-loaded (1:1, 200 lm) roll. The specific structure of rolled nanofibrous mat led to obtaining high modulus and stiffness for CF-Roll scaffold compared to other reported nanofibrous structures (Shim et al. 2010;Nguyen et al. 2012;Jennes et al. 2012;Gu et al. 2013;Sawawi et al. 2013;Lee et al. 2011;Sun et al. 2012;Wulkersdorfer et al. 2010;Kim et al. 2014;Baker et al. 2012;Milleret et al. 2011). On the other hand, by the incorporation of stiff coral particles into the polymeric structure, the r/e curve moved up to higher stress values and the resultant compressive modulus and stiffness values Table 4. ...
In this work, an innovative and easy method for the fabrication of 3D scaffold from 2D electrospun structures is introduced. For this aim, coral microparticles were fixed inside the nanofibrous PCL/Gelatin mat and the obtained structure was post assembled into a cylindrical design. Scaffold fabrication procedure is described in detail and morphological properties, physical and mechanical characteristics and in vitro assessments of the prepared scaffold are reported. Presences of coral microparticles in the structure led to the formation of empty spaces (3D pores) between nanofibrous layers which in turn prevent the compact accumulation of nanofibers. Post-assembly of the obtained nanofibrous coral-loaded structures makes it possible to prepare a scaffold with any desired dimension (diameter and height). Existence of coral particles within the nanofibrous mats resulted in distant placement of layers toward each other in the assembling step, which in turn create vacancy in the structure for cellular migration and fluid and nutrients exchange of the scaffold with the surrounding environment. Cell morphology within the scaffolds is investigated and cytotoxicity and cytocompatibility of the structure is evaluated using Alamar blue assay. Enhancement in mineralization of the seeded cells within the prepared coral-loaded scaffolds is demonstrated by the use of SEM-EDX. Performed compression mechanical test revealed excellent modulus and stiffness values for the cylindrical samples which are comparable to those of natural bone tissue.
... [ 18 ] Hydrogels have been mixed with short fi bers for cardiac regeneration [ 19 ] and hydrogel reinforcement. [ 20 ] Beyond different reported techniques, such as ultrasonication, [ 21 ] homogenizing, [ 22 ] chemical treatment, [ 23 ] and patterned UV-crosslinking, [ 24 ] the electrospinning/microcutting method enables the production of quasi monodisperse short fi bers, [ 25 ] which is crucial to control and study cell-fi ber interactions. ...
To regenerate soft aligned tissues in living organisms, low invasive biomaterials are required to create 3D microenvironments with a structural complexity to mimic the tissue's native architecture. Here, a tunable injectable hydrogel is reported, which allows precise engineering of the construct's anisotropy in situ. This material is defined as an Anisogel, representing a new type of tissue regenerative therapy. The Anisogel comprises a soft hydrogel, surrounding magneto-responsive, cell adhesive, short fibers, which orient in situ in the direction of a low external magnetic field, before complete gelation of the matrix. The magnetic field can be removed after gelation of the biocompatible gel precursor, which fixes the aligned fibers and preserves the anisotropic structure of the Anisogel. Fibroblasts and nerve cells grow and extend unidirectionally within the Anisogels, in comparison to hydrogels without fibers or with randomly oriented fibers. The neurons inside the Anisogel show spontaneous electrical activity with calcium signals propagating along the anisotropy axis of the material. The reported system is simple and elegant and the short magneto-responsive fibers can be produced with an effective high-throughput method, ideal for a minimal invasive route for aligned tissue therapy.
... Further ultrasonication of nanofibers can result in scission and fragmentation resulting smaller sizes. These phenomena are observed in carbon nanotubes and some polymer nanofibers (Hennrich et al., 2007;Sawawi, Wang, Nisbet, & Simon, 2013). ...
... For tissue engineering applications particularly, where structural support is also a concern, electrospun nanofiber fragments and nanocarriers for drugs are a promising strategy. Electrospun scaffolds can be fragmented via ultrasonication [87] or microtome cutting [1b] into short nanofibers that retain the morphological benefits of electrospun materials and can be dispersed into hydrogels to form composite biomaterials. Natural collagen and poly-(3-caprolactone-co-d,l-lactide) have been fragmented via ultrasonication and dispersed within HAMC hydrogels without losing the desirable mechanical properties of the hydrogel. ...
... Ultrasonication, which stimulates bubble cavitation and implosion, offers another approach for cutting off electrospun membranes into short fibers. Similarly, ultrasonication-assisted scission primarily depends on the ductility of polymers [42]. ...
Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.
... Ultrasonication methods are also effective for cutting fibrous membranes into short polymer filaments. 127 Duan and co-workers 128 used a razor blade at a rotation of 5000 rpm for 45 seconds in 350 ml of dioxane for cutting nanofibres into short fibres of a length of 150 AE 30 mm. The length of the fibres was controlled by the volume of the short fibre dispersion and dioxane. ...
Over the past few decades, there has been a strong interest in the development of new micro- and nanomaterials for biomedical applications. Their use in form of capsules, particles or filaments suspended in body fluids is associated with conformational changes and hydrodynamic interactions responsible for their transport. The dynamics of fibres or other long objects in the Poiseuille flow is one of the fundamental problems in a variety of biomedical contexts, such mobility of proteins, dynamics of DNA or other biological polymers, cell movement, tissue engineering, and drug delivery. In this review, we discuss several important applications of micro and nanoobjects in this field and try to understand the problems of their transport in flow resulting from material-environment interactions in typical, crowded, and complex biological fluids. Our aim is to elucidate the relationship between the nano- and microscopic structures of elongated polymer particles and their flow properties, thus opening the possibility to design nanoobjects that can be efficiently transported by body fluids for targeted drug release or local tissue regeneration.
... A turbid sample scatters more light than a clear sample and therefore decreases the intensity of the transmitted light at a fixed wavelength, which depends on the size and the shape of the suspended particles [25,26]. The transmitted intensity of the PET NFs in water was found to be the lowest at 300 nm, indicating that the scattering was the highest at this wavelength. ...
The fouling of water filtration membranes by nano/microplastic fragments can result in the decline of the water flux across membranes, however, the impact of other types of nano/microplastics on filtration processes, such as nano/micro fibres, has not been well characterised. The flexibility and high aspect ratio of nano/micro fibres could favor their adsorption onto filtration membranes, hence the presence of such fibres in water streams constitutes a potential threat to membrane units. In this work, the fouling of ultrafiltration membranes by a mixed system of poly(ethylene terephthalate) nanofibres and organic contaminants commonly found in textile industry effluents was investigated before mitigation strategies based on periodic gas scouring were developed. The nanofibres were prepared by electrospinning and cryo-sectioning using a freezing agent containing the organic contaminants of interest, poly(ethylene glycol) and poly(vinyl alcohol). Results showed that the organic contaminants induced a water flux decline across the membranes of 50 % in less than an hour due to internal pore blocking whereas the adsorption of pure fibres as loose entanglements contributed to less than 10 % of the permeation loss observed due to low pore coverage. Although applying periodic gas scouring was not efficient to dislodge the organic contaminants from the pores, this cleaning procedure removed up to 75 % of the nanofibres from the surface of the membranes due to the shear forces generated by the gas bubbles. Hence, this study suggests that ultrafiltration membranes and gas scouring procedures could be successfully applied to control and limit the presence of fibres present in complex water streams.
... Thus, in our experiment, fragmentation of the mats started after 3 hours and they were completed within 4 hours. Therefore, the time of 4 hour was selected as a proper time for aminolysis and fragmentation of the PLLA nanofibers.In comparison to mechanical methods for chopping the electrospun nanofibers, like cutting with blades in liquid nitrogen28 and grinding,29 chemical fragmentation of PLLA nanofibers through aminolysis reaction has an efficient control over nanocylinders length.Besides, in comparison with ultrasonication, which has been used to breakdown brittle nanofibers or uses pretreatment such as UV-ozone irradiation for less brittle polymers,30 the aminolysis reaction does not F I G U R E 3 Morphology of the electrospun poly L-lactic acid nanofibers [Color figure can be viewed at wileyonlinelibrary.com] F I G U R E 4 Morphology of poly Llactic acid nanocylinders [Color figure can be viewed at wileyonlinelibrary.com] require pretreatment. ...
Nowadays, despite remarkable progress in developing bone tissue engineering products, the fabrication of an ideal scaffold that could meet the main criteria, such as providing mechanical properties and suitable biostability as well as mimicking the bone extracellular matrix, still seems challenging. In this regard, utilizing combinatorial approaches seems more beneficial. Here, we aim to reinforce the mechanical characteristics of gelatin hydrogel via a combination of Genipin‐based chemical cross‐linking and incorporation of the poly l‐lactic acid (PLLA) nanocylinders for application as bone scaffolds. Amine‐functionalized nanocylinders are prepared via the aminolysis procedure and incorporated in gelatin hydrogel. The nanocylinder content (0, 1, 2, 3, and 4 wt%) and cross‐linking density (0.1, 0.5, and 1 wt/vol%) are optimized to achieve suitable morphology, swelling ratio, degradation rate, and mechanical behaviors. The results indicate that hydrogel scaffold cross‐linking by 0.5 wt% of Genipin shows optimized morphological feathers with a pore size of around 300 to 500 μm as well as an average degradation rate (40.09% ± 3.08%) during 32 days. Besides, the incorporation of 3 wt% PLLA nanocylinders into the cross‐linked gelatin scaffold provides an optimized mechanical reinforcement as compressive modulus, and compressive strength show a 4‐ and 2.6‐fold increase, respectively. 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay indicates that the scaffold does not have any cytotoxicity effect. In conclusion, gelatin composite reinforced with 3 wt% PLLA nanocylinders cross‐linked via 0.5 wt/vol% Genipin is suggested as a potential scaffold for bone tissue engineering applications.
... Instead, the adoption of a liquid bath collector has been exploited to either expedite the coagulation of fibers [1] or obtain fibers with specific structures [2]. Using electrospun fibers as nanoadditives has been explored primarily in polymer-based composites [3] through film-stacking [4] or solution impregnation [5]. Short electrospun fiber reinforcement has been attempted through mechanical cutting [6] or ultrasonication [7] of electrospun nonwovens. ...
We propose a novel approach of wet electrospinning to yield fiber-reinforced polymer ceramic composites, where a reactive ceramic precursor gel is used as a collector. We illustrate our approach by generating polyethylene oxide (PEO) fibers in a potassium silicate gel; the gel is later activated using metakaolin to yield a ceramic-0.5 wt% PEO fiber composite. An increase of 29% and 22% is recorded for the fabricated polymer ceramic composites in terms of indentation modulus and indentation hardness respectively. Our initial findings demonstrate the process viability and might lead to a potentially scalable manufacturing approach for fiber-reinforced polymer ceramic composites.
... Although fragmented nanofibers have been prepared using various methods in past research, hydrolyzation has an advantage over other methods in terms of process efficiency and the uniformity of the size of the fragmented nanofibers. For example, the cryogenic milling method is limited by the elasticity of the fibers [44], while the grinding and milling method lacks fiber length control [45,46]. Similarly, though it affords better fiber length control, the liquid nitrogen method is inefficient [47]. ...
Composite hydrogels with electrospun nanofibers (NFs) have recently been used to mimic the native extracellular matrix. In this study, composite hydrogels of methacrylated hyaluronic acid containing fragmented polycaprolactone NFs were used for bone tissue engineering. The composite (NF/hydrogel) was crosslinked under ultraviolet (UV) light. The incorporation of fragmented polycaprolactone NFs increased the compression modulus from 1762.5 to 3122.5 Pa. Subsequently, adipose-derived stem cells incorporated into the composite hydrogel exhibited a more stretched and elongated morphology and osteogenic differentiation in the absence of external factors. The mRNA expressions of osteogenic biomarkers, including collagen 1 (Col1), alkaline phosphatase, and runt-related transcription factor 2, were 3-5-fold higher in the composite hydrogel than in the hydrogel alone. In addition, results of the protein expression of Col1 and alizarin red staining confirmed osteogenic differentiation. These findings suggest that our composite hydrogel provides a suitable microenvironment for bone tissue engineering.
... The human dermal fibroblast culture displayed a 1.4 times better proliferation rate on ultrasonicated chitosan nonwovens compared to the pristine one. Electrospun nanofibers were scissored onto short fibers by ultrasonic treatment by Sawawi et al. [50]. Ultrasound cavity bubble implosion caused the effect. ...
: Micro- and nanofibers are historically-known materials that are continuously reinvented due to their valuable properties. They display promise for applications in many fields, from tissue engineering to catalysis or sensors. In the first application, micro- and nanofibers are mainly produced from a limited library of biomaterials with properties that need alteration before use. Post-modification is a very effective method for attaining on-demand features and functions of nonwovens. This review summarizes and presents methods of functionalization of nonwovens produced by electrostatic means. The reviewed modifications are grouped into physical methods, chemical modification, and mixed methods.
... In comparison to mechanical methods of chopping the electrospun nanofibers, like cutting with blades in liquid nitrogen and grinding, PLA nanofibers chemical fragmentation through aminolysis reaction controls nanofibers' length efficiently [38,39] . In addition, compared with ultrasonication, used to breakdown brittle nanofibers or using UV-ozone irradiation for less brittle polymers' pretreatment, the aminolysis reaction not only does not require pretreatment but also it could be mentioned as a pretreatment itself for further surface treatments such as collagen grafting in our study [40] . Also, the increase in amino groups' amount on the chopped nanofibers during aminolysis, and thereby the rise in the nanofibers' hydrophilicity, may improve the interactions between cells and nanofibers, besides causing nanofibers' dispersity in aqueous media conceivably [35] . ...
Hydrogel/fiber composites (HFC) improved by bio-related modifications have emerged as compelling scaffolds for regenerative medicine. In this study, by adding collagen-grafted poly-L-lactic acid fibers and genipin as a chemical cross-linker to synthesize polypyrrole-chitosan precursor, conductive HFC scaffolds were prepared. Techniques, including microscopy, mechanical analysis, conductivity measurement, and cell culture studies, are used to assess fibers and HFC scaffolds’ structural, electrical, and functional performances. The scaffold is biocompatible according to the results of
MTT assay and attachment of PC-12 cells. In conclusion, polypyrrole-chitosan hydrogel reinforced by collagen-grafted PLA fibers is suggested to be a potential scaffold for electrically responsive tissue applications.
... Electrospun nonwovens in the form of separated fibers were incorporated by several authors and tested as injectable systems for spinal cord healing [24] or cartilage regeneration [25,26]. Nonwovens were cut into small pieces and disintegrated on single fibers under sonification conditions [27], aminolysis [28], or UV [29]. As a complement to this topic, the review of Bosworth et al. is highly recommended. ...
Development of hybrid scaffolds and their formation methods occupies an important place in tissue engineering. In this paper, a novel method of 3D hybrid scaffold formation is presented as well as an explanation of the differences in scaffold properties, which were a consequence of different crosslinking mechanisms. Scaffolds were formed from 3D freeze-dried gelatin and electrospun poly(lactide-co-glicolide) (PLGA) fibers in a ratio of 1:1 w/w. In order to enhance osteoblast proliferation, the fibers were coated with hydroxyapatite nanoparticles (HAp) using sonochemical processing. All scaffolds were crosslinked using an EDC/NHS solution. The scaffolds’ morphology was imaged using scanning electron microscopy (SEM). The chemical composition of the scaffolds was analyzed using several methods. Water absorption and mass loss investigations proved a higher crosslinking degree of the hybrid scaffolds than a pure gelatin scaffold, caused by additional interactions between gelatin, PLGA, and HAp. Additionally, mechanical properties of the 3D hybrid scaffolds were higher than traditional hydrogels. In vitro studies revealed that fibroblasts and osteoblasts proliferated and migrated well on the 3D hybrid scaffolds, and also penetrated their structure during the seven days of the experiment.
... [10] Normally, the short fibers obtained by using mechanical cutting devices, such as homogenizer, mixer, blender, grinder, exhibit uncontrollable length and broad length distribution represented by the high coefficient of variation (CV), [3,[24][25][26] which is defined as the ratio of the standard deviation to the mean length. Simultaneously, beyond several different reported methods, such as chemical treatment, [27] ultrasonication, [28] electric spark, [29] concentrated polymer brush, [30] and direct electrospinning, [31][32][33] the patterned UV-crosslinking [34] and microcutting method [35,36] based on highly aligned fibers enable the production of quasi-monodisperse short fibers. Short fiber dispersions with low CV have not been used to the best of our knowledge for the preparation of sponges. ...
Ultralight highly porous sponges made of short electrospun polymer fibers have gained significant attention for a variety of applications. According to the established procedures, short electrospun fibers are obtained by cutting or homogenization of electrospun fibers in suspension, which yield fibers with inhomogeneous fiber length. The role of the fiber length distribution and the fiber length in the mechanical compressibility of the sponges is unknown. Therefore, as a model study, sponges made from suspensions of short electrospun poly(acrylonitrile) (PAN) fibers with controlled fiber length distribution are investigated, and the role of the fiber length distribution in the compressibility of the sponges is analyzed quantitatively. These sponges are also compared to the ones prepared by established procedure as a benchmark. It is found that the compression stress and modulus of ultralight sponges with monodisperse short fibers are respectively 32% and 45% higher than that made with polydisperse short fibers. The study also shows that sponges made from longer fibers have higher modulus in comparison to the sponges made from shorter fibers. Ultralight highly porous sponges are obtained by freeze‐drying of suspensions of short fibers with well‐controlled length from electrospun yarn. The sponges with monodisperse short fibers show higher compression strength and modulus originating from short fiber dispersion with homogeneous fiber length.
Electrospun nanofibers are emerging reinforcing fillers with epoxy matrix owing to its high aspect ratio, surface area, and mechanical properties resulting in wider applications. Application of non‐woven configuration of nanofiber mats, collected from electrospinning has been traditionally confined to improve interlaminar responses of fiber reinforced composites. However, potential of short nanofiber in improving bulk matrix properties cannot be under estimated. This study adopts matrix modification approach by incorporating different concentration of nylon 6 short nanofiber in epoxy matrix to investigate its influence on tensile and viscoelastic properties of nanocomposite. Results showed a moderate improvement in modulus for nanocomposites despite to general drop in strength, however fracture energy and failure strain improved significantly at an optimum concentration of 0.1 wt% nanofiber. In addition, highest storage modulus as well as damping factor was recorded with decline in glass transition temperature for 0.1 wt% nanofiber content. Moreover, it was revealed that addition of nanofiber altered brittle fracture to neck‐featured ductile mode and effectively introduced energy absorbing interfaces making it well suit for diverse applications. Short electrospun nanofibers were prepared to reinforce epoxy. Tensile properties of nanocomposites with different nanofiber concentrations were investigated. Viscoelastic response of nanocomposites showed introduction of energy absorbing interfaces.
Short nanofibers have been of interest in preparing 3D porous structures, aerosol filters, and nanocomposites. These materials require nanofiber retrieval and application in short form with simultaneous control over aspect ratio. Electrospinning, conventionally, offers minimal control over short nanofiber yield as nonwoven mat is the default configuration of collected sample. High surface area to volume ratio nanofiber, however, can offer new vistas in material design if standardization of short nanofiber preparation practices, offering control over aspect ratio, can be attained. It will provide novel insights into design of tissue engineering scaffolds, filtration membranes, and nanocomposite properties. This work summarizes reported efforts to prepare short nanofiber through mechanical, chemical, material, and operational variables. It aims to provide comparative glance at attempts to control aspect ratio along with pros and cons of the adopted techniques. Lastly, discussion shares generalized conclusions and insights gathered while reviewing material and operational variables adopted for short nanofiber preparation.
The asbestos-containing waste management is a public health topic for countries which have used this mineral. Treatment of chrysotile (white asbestos), a phyllosilicate from serpentine, crocidolite (blue asbestos, first results on this kind of asbestos), one of the five asbestos varieties of amphibole family and asbestos-containing waste conversion process is proposed by using hydrothermal treatment in supercritical water. All samples were treated in an Inconel Batch Reactor. The treatment durations range is from 1 to 6 hours, temperatures range is from 400°C to 750°C, mass concentration range is from 0.02 to 170 mg. mL ⁻¹ and pressures are higher than 23 MPa. Ultrapure water is used for sample preparation. This ultrapure water is used to monitor mineral leaching on the aqueous phase and to avoid particle cross-contamination. Transmission electron microscopy analyses were carried out to check the presence or not of asbestos phase. According to these analyses, the best conditions of conversion were 1 hour and 0.02 mg. mL ⁻¹ for chrysotile, 3 hours and 0.02 mg. mL ⁻¹ for crocidolite and 1 hour and 20 mg. mL ⁻¹ for asbestos-containing waste, at T = 750°C. Supercritical water conditions were maintained during the whole treatment. The X-ray diffraction showed that the main phases present after treatments were riebeckite and magnetite (crocidolite), forsterite and enstatite (chrysotile), and calcite, spurrite and gehlenite (asbestos-containing waste). Finally, a scanning electron microscopy analysis was performed to monitor morphological fibre change. The elongated structure, partially fragmented, was found in all samples.
The significant impact of drug-loaded nanocarriers on cancer chemotherapy lies in the ability to specifically target to tumors with alleviated systemic toxicities. In the current study, a versatile and scalable method has been developed to construct fiber rods from electrospun fibers by ultrasonication using encapsulated NaCl nanoparticles as void-precursors. The shape effects of doxorubicin (DOX)-loaded fiber rods with an average diameter of around 500 nm and different lengths are determined on the blood circulation, tumor accumulation and cellular uptake. Compared with microspheres, fiber rods indicate an up to 4-fold higher accumulation in tumors and an up to 3-fold longer terminal half-life of plasma DOX levels after intravenous injection. Fiber rods with shorter lengths show a significantly higher in vitro cytotoxicity to tumor cells, a higher DOX accumulation and cell necrosis in tumors, and a significantly lower metastasis in lungs. Among fiber rods with different lengths, fiber rods with an average length of 2 μm induce significantly higher inhibition on tumor cell proliferation and induction of cell apoptosis, as wells as no detectable metastatic nodules in lung sections. Therefore, the shape effects of electrospun fiber rods hold great potential for enhancing systemic circulation and directing biodistribution to improve therapeutic outcomes.
The design of 3D hydrogel constructs to elicit highly controlled cell response is a major field of interest in developing tissue engineering. The bioactivity of encapsulated cells inside pure alginate hydrogel is limited by its relatively inertness. Combining short nanofibers within a hydrogel serves as a promising method to develop a cell friendly environment mimicking the extracellular matrix. In this paper, we fabricated alginate hydrogels incorporating different magnetic short nanofibers (M.SNFs) content for olfactory ecto-mesenchymal stem cells (OE-MSCs) encapsulation. Wet-electrospun gelatin and superparamagnetic iron oxide nanoparticles (SPIONs) nanocomposite nanofibers were chopped using sonication under optimized conditions and subsequently embedded in alginate hydrogels. The storage modulus of hydrogel without M.SNFs as well as with 1 and 5 mg/mL of M.SNFs were in the range of nerve tissue. For cell encapsulation, OE-MSCs were used as a new hope for neuronal regeneration due to their neural crest origin. Resazurin analyses and LIVE/DEAD staining confirmed that the composite hydrogels containing M.SNFs can preserve the cell viability after 7 days. Moreover, the proliferation rate was enhanced in M.SNF/hydrogels compared to alginate hydrogel. The presence of SPIONs in the short nanofibers can accelerate neural-like differentiation of OE-MSCs rather than the sample without SPIONs.
L'électrofilage, une technique pour la fabrication électrostatique de fibres, a suscité un intérêt croissant ces dernières années en raison de sa polyvalence et de son potentiel d'application dans divers domaines, notamment en ingénierie tissulaire. Le polymère polycaprolactone (PCL) a été approuvé pour une application biomédicale et offre d'excellentes propriétés mécaniques et une biodégradation lente, ce qui en fait un matériau approprié pour une utilisation comme échafaudage pour l’ingénierie tissulaire. Des études antérieures réalisées dans notre laboratoire ontmontré que le greffage covalent (méthode "Grafting From") de polymères ou copolymères bioactifs permet de surmonter l'hydrophobicité du PCL et peut favoriser l'adhésion et la différenciation cellulaire sur les échafaudages. Différents échafaudages en fibres PCL avec différentes microstructures ont été préparés par électrofilage. Le greffage de polymères bioactifs sur ces échafaudages a été réalisé en utilisant deux techniques de "grafting from" ; (i) le greffage par voie thermique pendant 1 ou 3 h qui nécessite une activation de surface par ozonation comme référence et (ii) le greffage UV pendant 1 heure avec ou sans activation de surface. Nous avons comparé ces techniques de greffage en termes de modification de surface, d'effets du processus de greffage sur les propriétés intrinsèques du PCL. Des essais in vitro ont étéréalisés pour observer le comportement des cellules fibroblastiques sur divers échafaudages fonctionnalisés présentant différents degrés d'hydrophilie de surface et les comparer entre eux, ainsi qu’à des échafaudages non greffés. La réussite du greffage de polymères ioniques sur les échafaudages en fibres PCL a été démontrée à l'aide de diverses techniques de caractérisation de surface. Les modifications possibles des propriétés intrinsèques du PCL ont été étudiéespar caractérisation mécanique, chromatographie d'exclusion stérique (SEC) et calorimétrie différentielle à balayage (DSC). Enfin, la biodégradation de ces échafaudages, à différents temps, a été évaluée dans différents milieux. Cette étude montre l'élaboration de différents échafaudages en fibre PCL, leur fonctionnalisation par greffage polymères bioactifs et l'appréciation des changements mécaniques et microstructuraux. Les essais biologiques in vitro ont montré l’effet favorable du polymère greffé sur la réponse cellulaire et que selon le type de microstructure de l'échafaudage, sa fonctionnalisation de surface par des polymères bioactifs et son hydrophilie de surface, différents comportements cellulaires peuvent être observés.
Hybridized carbon nanofibers containing calcium phosphate nanoparticles (CNF/CaP) were investigated as osteocompatible nanofillers for epoxy resin. The CNF/CaP was produced by electrospinning mixture solution of polyacrylonitrile and CaP precursor sol–gel, followed by preoxidation and carbonization. The continuous and long CNF/CaP was ultrasonically chopped, mixed into epoxy resin and thermo-cured. Compared to pure CNFs with similar ultrasonication treatment, the shortened CNF/CaP reinforced composites demonstrated significant enhancement in flexural properties of epoxy composites, benefiting from the improved interfacial adhesion between CNF/CaP and resin matrix. The resulting composites also displayed good biocompatibility and sustained calcium ion release, which categorized them as promising materials for bone repairing.
Tailoring the fiber length of supramolecular fibers with a homogeneous length distribution is challenging. Typically, self‐assembly processes, a bottom‐up approach, allow controlling the supramolecular fiber diameter but not the fiber length. Therefore, in this study, a top‐down approach, namely ultrasonication, is applied to achieve dimensional control of the length of supramolecular fibers. As a supramolecular building block, the benzenetrisamide (BTA),1,3,5‐tris(2,2‐dimethylpropionylamino)benzene (t‐Bu‐BTA), is selected since it effectively forms rigid supramolecular submicron fibers from solution. The important ultrasonication processing parameters, such as sonication time, fiber concentration, dispersion medium, and dispersion temperature are systematically varied to determine their influence on the final fiber length and length distribution. Controlling the cutting into short submicron fibers is readily achieved by adjusting the applied sonication time and the viscosity of the dispersion medium. Based on these results, it is now possible to tailor the aspect ratio of supramolecular submicron fibers. Ultrasonication is applied to achieve dimensional control of the length of supramolecular submicron fibers based on benzenetrisamides. The sonication time, fiber concentration, dispersion medium, and dispersion temperature are systematically varied to determine their influence on the final fiber length and length distribution. Adjustable lengths are readily achieved by the applied sonication time and the viscosity of the medium.
In this work, poly(l-lactic acid) (PLLA) ultrafine fibers with different morphology and structure were fabricated by a novel linear-jet electrospinning method which relies on a conventional electrospinning set-up with continuous rotating drum. To control the morphology and structure of PLLA electrospun fibers, different solution systems and electrospinning conditions were investigated. Two PLLA solution systems (PLLA/DMF/CH2Cl2 and PLLA/CH2Cl2) with different concentration and conductivity were used for the electrospinning and their influences on the formation of the linear electrospinning jet were discussed. Two types of collecting patterns with aligned buckling and linear structure were achieved under the linear electrospinning jet. Highly aligned PLLA electrospun fibers with porous surface could be formed by using the highly volatile solvent CH2Cl2. Here, it should be emphasized that the diameter and surface porosity of such highly aligned PLLA electrospun fibers can be fine tuned by varying the winding velocity. The results of SEM images and polarized FTIR investigations verified that the as-spun PLLA porous surface fibers were highly aligned and molecularly oriented, leading to the enhanced mechanical performance as compared to the non-woven PLLA electrospun fibers.
The objective of this work is to investigate the nanoencapsulation of valuable bioactive compounds with the innovative electrohydrodynamic technology. More specifically, electrospraying, was applied for the encapsulation of three different active agents with lipolytic, anti-aging and antioxidant activity: Deoxycholic acid (DCA), olive leaves’ enzymatically modified extract and a hybrid of Deoxycholic acid-Hydroxytyrosol (DCA-HXT) in zein (ZN) biodegradable polymer. The resulting powders were evaluated regarding the system's: compositional and chemical characteristics, thermal stability and humidity effect, morphology, shape and size, encapsulation efficiency and release kinetics from the wall material. Encapsulation led to stable nanosystems, regarding the moisture and temperature effect, with high glass Transition Temperatures (Tg between 130-139 °C), and a mean particle size of 400-600 nm. Finally, high encapsulation efficiencies (DCA= 84.01%, DCA-HXT = 79.34% and modified extract =80.75%) and long-term release profiles (DCA=192 h, DCA-HXT=228 h and mod. extract=100 h) were measured for all three systems. Based on these results, we conclude that electrospraying process is an effective methodology for the development of bioactive agents’ nanosystems with excellent physicochemical properties and increased bioavailability; a crucial factor for the formation of high added-value products such as cosmetics.
An environmentally friendly non-woven nanotextile has been prepared using enantiomeric pairs of poly (lactic acid) PLA by electrospinning technique. Solution blending of synthesized high molecular weight (⁓10⁵ Da) poly (L-lactic acid) PLLA and poly (D-lactic acid), PDLA for prolonged time stirring produce solely stereocrystallites (sc). The high crosslinking effect of sc-PLA has played an important role, with multifunctional behaviour on the addition of anatase-TiO2 (a-TiO2) in three different ways (Case-I-III). The high crystallinity of a-TiO2 (~7.14 nm), has been confirmed from XRD and TEM studies as 98 %. The nanofinish as studied in (Case -III) by dipping and drying has decreased the water contact angle for the electrospun sc-PLA nanotextile from highly hydrophobic (132°) to superhydrophilicity after 8 min. An easy demonstration of high temperature treated nanofabric (at 100 °C) has proven to obtain an anti-shrinkage sc-PLA nanofabric. Even, the presence of a-TiO2 has improved the colour strength ability of sc-PLA as a dark dyed nanofabric. The loading of as-synthesized a-TiO2 nanoparticle has enhanced adsorbent dosages for 5TdipscPLA up to 1.44 mg/g of MB dosage, at contact time (8 h), and 68 % methylene blue (MB) removal efficiency under UV irradiation. Thereby, this a-TiO2 impregnated sc-PLA nanofabric tends to dye removal.
We report that a graphene sheet has an unusual mode of atomic-scale fracture owing to its structural peculiarity, i.e. singl sheet of atoms. Unlike conventional bond-breaking tensile fracture, a graphene sheet can be cut by in-plane compression, whic is able to eject a row of atoms out-of-plane. Our scale-bridging molecular dynamics simulations and experiments reveal tha this compressive atomic-sheet fracture is the critical precursor mechanism of cutting single-walled carbon nanotubes (SWCNTs by sonication. The atomic-sheet fracture typically occurs within 200 fs during the dynamic axial buckling of a SWCNT; th nanotube is loaded by local nanoscale flow drag of water molecules caused by the collapse of a microbubble during sonication.
This is on the contrary to common speculations that the nanotubes would be cut in tension, or by high-temperature chemica reactions in ultrasonication processes. The compressive fracture mechanism clarifies previously unexplainable diameter-dependen cutting of the SWCNTs under sonication.
In this study, polymeric nanofibrous composites containing anatase TiO2 short nanofibers (TiO2-SNF) were successfully produced via electrospinning. The fabrication of the nanofibrous composite structure includes two steps. First, anatase TiO2 nanofibers were obtained by calcination of electrospun PVP/TiO2 nanofibers and then crushed into short nanofibers ranging from few microns in length. Second, these TiO2-SNF were dispersed into polymer solutions and then electrospun into nanofibrous composites. We obtained nanofibers containing TiO2-SNF from different polymer types including PMMA, PAN, PET and PC. The SEM and TEM imaging indicated that some of the TiO2-SNF were fully covered by the polymeric matrix whereas some TiO2-SNF were partially covered and/or stick on the surface of the fibers. The photocatalytic activity of nanofibrous composites containing TiO2-SNF was evaluated by monitoring the photocatalytic decomposition of a model dye (rhodamine-6G) under UV irradiation.
Cell replacement therapy with multi-potent neural stem/progenitor cells (NSPCs) into the injured spinal cord is limited by poor survival and host tissue integration. An injectable and biocompatible polymeric cell delivery system serves as a promising strategy to facilitate cell delivery, promote cell survival and direct cell behaviour. We developed and characterized the use of a physical hydrogel blend of hyaluronan (HA) and methylcellulose (MC) for NSPC delivery, and incorporated electrospun fibers of either collagen or poly(ε-caprolactone-co-D,L-lactide) (P(CL:DLLA)) to promote cell–matrix interactions and influence cell behaviour. The shear-thinning and thermally reversible HAMC had a zero-shear viscosity of 1.2 Pa s at 25 °C, formed a weak gel at 37 °C with a yield stress of 0.5 Pa, and swelled to 115% of its original volume after one day. HAMC was both cytocompatible and allowed NSPC differentiation in vitro, similar to what one would observe in media. Interestingly, cells cultured in HAMC remained homogeneously dispersed over the 7 d culture period, unlike those cultured in media controls where significant cell aggregation was observed. Inclusion of electrospun fibers in the HAMC hydrogel further influenced cell behaviour. Composite systems of collagen fibers in HAMC resulted in reduced survival/proliferation and differentiation relative to HAMC itself whereas composites of P(CL:DLLA) fibers in HAMC maintained cell survival/proliferation and enhanced neuronal and oligodendrocytic differentiation similar to HAMC. In this study, the importance of the cell delivery vehicle to NSPC survival and cell fate was demonstrated in vitro and is being tested in on-going studies in vivo.
Electrospun polyacrylonitrile (PAN) fiber precursor-based carbon nanofiber (CNF) mats were produced and impregnated with epoxy resin. The mechanical properties of as-prepared nanofibers in the mat and short fiber filled epoxy nanocomposite forms were determined to demonstrate the effect of fiber aspect ratio on those properties. The experimental results reveal that epoxy nanocomposites containing electrospun carbon nanofibers (ECNF) with high fiber aspect ratio in the non-woven mat form yield better mechanical properties than those filled with short ECNFs. The ECNF mat in epoxy nanocomposites provides better homogeneity and easier preparation than short ECNFs. Mechanical properties of ECNF mat-epoxy nanocomposites, which were obtained using tensile and flexural tests, such as stiffness, increased, while toughness and flexural strength decreased, compared with the neat epoxy resin. Dynamic mechanical analysis results showed higher modulus for ECNF mat-epoxy nanocomposites, compared with those for neat epoxy resin and short ECNF-epoxy nanocomposites. The ECNF-epoxy nanocomposites had higher storage and Young's moduli with 1.23, 3.56 and 9.28 wt% ECNF mat loadings for the storage modulus and 0.98, 2.06% ECNF mat loadings for Young's modulus, even though the glass transition temperature (Tg), values dropped at all these extents of ECNF mat contents when compared with the neat epoxy resin.
Electrospinning has been applied to prepare uniaxially aligned nanofibers made of organic polymers, ceramics, and polymer/ceramic composites. The key to the success of this method was the use of a collector consisting of two pieces of electrically conductive substrates separated by a gap whose width could be varied from hundreds of micrometers to several centimeters. As driven by electrostatic interactions, the charged nanofibers were stretched to span across the gap and thus to become uniaxially aligned arrays over large areas. Because the nanofibers were suspended over the gap, they could be conveniently transferred onto the surfaces of other substrates for subsequent treatments and various applications. Materials that have been successfully incorporated into this procedure include conventional organic polymers, graphite carbon, and metal oxides. By controlling the parameters for electrospinning, we have also fabricated a number of simple device structures, for example, an individual nanofiber spanning across two electrodes, 2D arrays of crossbar junctions, and optical polarizers.
We review the current state of the polymer–carbon nanotube composites field. The article first covers key points in dispersion and stabilization of nanotubes in a polymer matrix, with particular attention paid to ultrasonic cavitation and shear mixing. We then focus on the emerging trends in nanocomposite actuators, in particular, photo-stimulated mechanical response. The magnitude and even the direction of this actuation critically depend on the degree of tube alignment in the matrix; in this context, we discuss the affine model predicting the upper bound of orientational order of nanotubes, induced by an imposed strain. We review how photo-actuation in nanocomposites depend on nanotube concentration, alignment and entanglement, and examine possible mechanisms that could lead to this effect. Finally, we discuss properties of pure carbon nanotube networks, in form of mats or fibers. These systems have no polymer matrix, yet demonstrate pronounced viscoelasticity and also the same photomechanical actuation as seen in polymer-based composites.
This article will begin with an introduction to acoustic cavitation, the physical phenomenon responsible for the chemical effects of ultrasound. Some recent applications of sonochemistry to the synthesis of nanophase and amorphous metals, as well as to heterogenous catalysis, will then be highlighted. Finally, we will examine the effects of ultrasound on metal powders in liquid-solid slurries.
The chemical effects of ultrasound do not come from a direct interaction of sound with molecular species. Ultrasound has frequencies from around 15 kilohertz to tens of megahertz. In liquids, this means wavelengths from centimeters down to microns, which are not molecular dimensions. Instead, when sound passes through a liquid, the formation, growth, and implosive collapse of bubbles can occur, as depicted in Figure 1. This process is called acoustic cavitation.
More specifically, sound passing through a liquid consists of expansion waves and compression waves. As sound passes through a liquid, if the expansion wave is intense enough (that is, if the sound is loud enough), it can pull the liquid apart and form a bubble (a cavity). The compression wave comes along and compresses this cavity, then another expansion wave re-expands it. So we have an oscillating bubble going back and forth, say, 20,000 times a second.
Assessment of axonal infiltration and guidance within neural tissue engineering scaffolds, along with the characterisation of the inflammatory response, is critical in determining these scaffolds' potential for facilitating neural repair. In this study, the extent of microglial and astrocytic response was measured following implantation of electrospun poly(epsilon-caprolactone) (PCL) scaffolds into the caudate putamen of the adult rat brain. The inflammation peaked at around 4 days (microglia) and 7 days (astrocytes) and subsided to homeostatic levels by 60 days. There was no evidence of microglial encapsulation and indeed neurites had infiltrated the implants, evidence of scaffold-neural integration. Whilst the inflammatory response was uninfluenced by the degree of PCL fibre alignment, the extent of neurite entry was. Large porosity, as was the case with the randomly orientated polymer fibres, enabled neurite infiltration and growth within the scaffold. However, neuronal processes could not penetrate scaffolds when fibres were partially aligned and instead, preferentially grew perpendicular to the direction of PCL fibre alignment at the implant-tissue interface i.e. perpendicular, not parallel, contact guidance was provided. This investigation shows that electrospun PCL fibres are compatible with brain tissue and provide preliminary insights regarding the influence of microglia and astrocytes in neural integration within such scaffolds.
The influence of the substitution of methanol in place of ethanol during the ultrasonic production of antimony sulfoiodide (SbSI) nanowires is presented. The new technology is faster and more efficient at temperatures greater than 314 K. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), optical diffuse reflection spectroscopy (DRS) and IR spectroscopy. The coexistence of Pna2(1) (ferroelectric) and Pnam (paraelectric) phases at 298 K was observed in the SbSI nanowires produced in methanol. The methanol decomposes during the sonication or due to the adsorption process on SbSI nanowires.
The magnetite nanoparticles were synthesized in an ethanol-water solution under ultrasonic irradiation from a Fe(OH)(2) precipitate. XRD, TEM, TG, IR, VSM and UV/vis absorption spectrum were used to characterize the magnetite nanoparticles. It was found that the formation of magnetite was accelerated in ethanol-water solution in the presence of ultrasonic irradiation, whereas, it was limited in ethanol-water solution under mechanical stirring. The monodispersibility of magnetite particles was improved significantly through the sonochemical synthesis in ethanol-water solution. The magnetic properties were improved for the samples synthesized under ultrasonic irradiation. This would be attributed to high Fe(2+) concentration in the magnetite cubic structure.
Electrospinning has been employed extensively in tissue engineering to generate nanofibrous scaffolds from either natural or synthetic biodegradable polymers to simulate the cellular microenvironment. Electrospinning rapidly produces fibers of the nanolength scale and the process offers many opportunities to tailor the physical, chemical, and biological properties of a material for specific applications and cellular environments. There is growing evidence that nanofibers amplify certain biological responses such as contact guidance and differentiation, however this has not been fully exploited in tissue engineering. This review addresses the cellular interactions with electrospun scaffolds, with particular focus on neural, bone, cartilage, and vascular tissue regeneration. Some aspects of scaffold design, including architectural properties, surface functionalization and materials selection are also addressed.
This chapter presents the photodegradation and radiolysis of poly(lactic acid) (PLA), based on the results of academic research carried out over the past decades. In addition to the initiators and additives used in the polymerization process, compounds produced during the molding process can become optical impurities that absorb the irradiated light and thus cause photodegradation. The degradation schemes in organic materials caused by absorption of such high‐energy radiation are very different from those produced by ultraviolet (UV) or visible photo‐irradiation. It was found that photodegradation of poly(l‐lactic acid) PLLA chains can occur at random even in the crystalline region of PLLA chains by UV irradiation. The photodegradability of PLA can be modified by blending PLA with other polymers. Composites with nanosilver particles greatly suppressed the photodegradation of PLA due to the effect of light absorption of polyvinylpyrrolidone and scattering of nanoparticles in the nanoparticle coating.
The research and development of nanofibers has gained much prominence in recent years due to the heightened awareness of its potential applications in the medical, engineering and defense fields. Among the most successful methods for producing nanofibers is the electrospinning process. In this timely book, the areas of electrospinning and nanofibers are covered for the first time in a single volume. The book can be broadly divided into two parts: the first comprises descriptions of the electrospinning process and modeling to obtain nanofibers while the second describes the characteristics and applications of nanofibers. The material is aimed at both newcomers and experienced researchers in the area. © 2010 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.
Single-wall fullerene nanotubes were converted from nearly endless, highly tangled ropes into short, open-ended pipes that
behave as individual macromolecules. Raw nanotube material was purified in large batches, and the ropes were cut into 100-
to 300-nanometer lengths. The resulting pieces formed a stable colloidal suspension in water with the help of surfactants.
These suspensions permit a variety of manipulations, such as sorting by length, derivatization, and tethering to gold surfaces.
Spherical and irregular microparticles both in the size of 5μm were put into the de-ionized water respectively to form different suspensions, and vibrating cavitation experiments were performed in the two kinds of suspensions. After the experiment, the damages on the specimen surfaces were measured and free radicals in suspensions were detected. It was found that suspensions with particles cause more severe cavitation erosion than those without particles. Compared with a spherical particle, the shape of the irregular particle has little effect on the number of the cavities, but it causes abrasion on the solid surface besides the cavitation erosion.
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
Epoxy/CNT nanocomposites were synthesized in various ways to examine the effects of dispersion methods on its tribological properties. The carbon nanotubes (CNTs) were pre-treated in three different ways: no pre-treatment, activation in HNO3, and activation in HNO3 plus application of a coupling agent. The dispersion and mixing methods used were: dual asymmetric centrifuge, sonication, hand mixing. The CNTs were mixed either into the hardener or the resin.The curing behaviour was studied via DSC, and the thermomecanical properties were determined using a DMA. The tribological properties were investigated in a ball-on-prism test rig under unidirectional continuous sliding against austenitic stainless steel.For the untreated CNTs, it seems that the wear resistance improves with increasing effort put into dispersion: sonication has a positive effect, sonication plus dual asymmetric centrifuge proves even better. A pre-treatment with HNO3 or a silane-coupling agent can improve the wear resistance of the composite. However, the pre-treated CNTs should be dispersed without the use of ultrasound, which seems to damage the pre-treated CNTs. The results showed that the wear resistance in general increases with improved dispersion and integrity of the CNTs.
A Kodak Ektapro Hs motion analyzer is applied to observe the ultrasonic effect on the mixing and breakage processes of agglomerated crystals suspended in ethanol. Mixing processes with stirring and with ultrasound are investigated by the dispersion of ink in the ethanol and by the motion of small crystals. The vessel is divided into several sections to investigate the local mixing process. Velocity variance is used to indicate the difference of turbulence when ultrasound and impeller stirring are applied respectively. The cavitation distribution in different sections is also recorded, and the effects on particles of different sizes are investigated.Observation of the breakage processes in different sections shows that both collisions between crystals and the vibration and implosion of cavitation bubbles contribute to the breakage process of agglomerated crystals. Finally, the effect of ultrasonic treatment is also compared with impeller stirring and with mechanical grinding.
Submicron diameter fibers of polystyrene are electrospun from solutions in dimethylformamide (DMF). When electrospun in a high-humidity environment, the interior of these fibers was found to be highly porous rather than consolidated, despite the smooth and nonporous appearance of the fiber surfaces. The formation of interior porosity is attributed to the miscibility of water, a nonsolvent for the polymers in solution, with DMF. The resulting morphology is a consequence of the relatively rapid diffusion of water into the jet, leading to a liquid−liquid phase separation that precedes solidification due to evaporation of DMF from the jet. When electrospun in a low-humidity environment, the fibers exhibit a wrinkled morphology that can be explained by a buckling instability. Understanding which morphology forms under a given set of conditions is achieved through the comparison of three characteristic times: the drying time, the buckling time, and the phase separation time. The morphology has important consequences for the properties of the fibers such as their mechanical strength and stiffness.
Electrospinning is a technique used to produce micron to submicron diameter polymeric fibers. The surface of electrospun fibers is important when considering end-use applications. For example, the ability to introduce porous surface features of a known size is required if nanoparticles need to be deposited on the surface of the fiber or if drug molecules are to be incorporated for controlled release. Surface features, or pores, became evident when electrospinning in an atmosphere with more than 30% relative humidity. Increasing humidity causes an increase in the number, diameter, shape, and distribution of the pores. Increasing the molecular weight of the polystyrene (PS) results in larger, less uniform shaped pores. This work includes an investigation of how humidity and molecular weight affect the surface of electrospun PS fibers. The results of varying the humidity and molecular weight on the surface of electrospun PS fibers were studied using optical microscopy, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM) coupled with image analysis.
Carbon nanotubes are commonly dispersed in liquid solvents by means of sonication. This has the disadvantage, however, that it can induce the scission of the particles that are near imploding cavitation bubbles. Nanotube scission arises from the fluid friction at the surface of the nanotubes in the radial elongational flow field that forms around a cavitation bubble. An understanding of the kinetics of this phenomenon is of critical importance for controlling the length of the nantoubes in their applications yet remains elusive. We investigate this kinetics quantitatively in the present work. The strain rate of the elongational flow around a cavitation bubble is estimated experimentally using carbon microfibers of known mechanical properties. The average length L(t) of the nanotubes is measured by means of dynamic light scattering as a function of time t, and we observed that L(t) scales as t−n, with n 0.2. This scaling differs from the one predicted theoretically in the literature for the scission of flexible polymer chains. Possible origins of this difference are discussed. We believe that the reduced probability of a nanotube to be in the vicinity of a cavitation bubble if the sonication power is in some sense low and can slow down the kinetics of nanotube scission.
A study was conducted to demonstrate the controlled movement of short electrospun polymer microfibers containing superparamagnetic nanoparticles. The controlled movement of the electrospun polymer microfibers was demonstrated by the interconnection of hippocampal neurons that have potential therapeutic applications. MMA/Anth copolymer was selected as a polymer matrix for tracing the movement of these microfibers through fluorescence microscopy. Superparamagnetic nanoparticles were selected for magnetic modification, as magetization was achieved in the presence of a magnetic field. A solution of the fluorescent copolymer, with dispersed superparametric cobalt nanoparticles was electrospun on a rotating drum. Scanning electron microscopy examination of the resulting aligned composite fibers showed diameters of different ranges.
Biodegradable polymeric nanocylinders were fabricated by segmental degradation of electrospun nanofibers. P01Y(L-lactic acid) (PLA) was electrospun to produce non-crystalline nanofibers that were immediately treated with amino group-containing strong bases to fabricate semicrystalline PLA nanocylinders with tunable aspect ratio. The formation of PLA nanocylinders was attributed to two concurrent events occurring during the aminolysis reaction: (i) development of stacked lamellae and (ii) transversely oriented degradation and fragmentation of the amorphous gaps between lamellae, both responsible for -1, the fragmentation of PLA nanofibers into uniformly shaped nanocylinders. The aspect ratio of PLA nanocylinders was tunable by varying aminolysis time and controlling nanofiber diameter.
Introduction Mechanisms of Photodegradation Mechanism of Radiation Degradation Photodegradation of PLA Photosensitized Degradation of PLA Radiation Effects on PLA Modification of PLA by Irradiation References
Short electrospun fibers were obtained by using UV cutting method. Either polymers with double bonds with a photocross-linker (CL) and photoinitiator (PI) or known photochemistry of coumarin ([2 + 2] cycloaddition reaction) without the addition of CL and PI is utilized for making short electrospun fibers. The electrospun fibers were irradiated by UV light in the presence of a mask with a defined width of slits. The uncovered parts of fibers were cross-linked and therefore became insoluble. The non-crosslinked parts were removed by immersion of the fibers into an appropriate solvent. The length of obtained short fibers can be controlled by changing the width of the slits of the employed mask.
Composite multicellular spheroids composed of mesenchymal stem cells (MSCs) and synthetic biodegradable nanofilaments are fabricated. Extracellular-matrix-mimicking nanofilaments, prepared from transverse fragmentation of semicrystalline poly(L-lactic acid) nanofibers and subsequent surface modification with cell adhesive peptides, are used to form composite multicellular spheroids with MSCs by cellular self-assembly. The size of the composite spheroids could be readily controlled with the integrated amount of the nanofilaments. The composite spheroids show enhanced adipogenic potential compared to homotypic spheroids. The resultant spheroids are used as building blocks for 3D biohybrid construction with the assistance of a microstructured scaffold fabricated by a direct polymer melt deposition process. An angiogenic growth factor, basic fibroblast growth factor, is also locally delivered in a sustained fashion from the heparinized scaffold surface for facile neovascularization of adipogenic tissue. The produced multiscaled and multifunctional hybrid MSC construct enable the successful formation of vascularized adipose tissue in vivo.
Electrospinning with a collector consisting of two pieces of electrically conductive substrates separated by a gap has been used to prepare uniaxially aligned PAN nanofibers. Solution of 15 wt % of PAN/DMF was used tentatively for electrospinning. The effects of width of the gap and applied voltage on degree of alignment were investigated using image-processing technique by Fourier power spectrum method. The electrospinning conditions that gave the best alignment of nanofibers for 10–15 wt % solution concentrations were experimentally obtained. Bundles like multifilament yarns of uniaxially aligned nanofibers were prepared using a new simple method. After-treatments of these bundles were carried out in boiling water under tension. A comparison was made between the crystallinity and mechanical behavior of posttreated and untreated bundles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4350–4357, 2006
High power ultrasound (HPU) represents a non-thermal processing method that has been rapidly researched and used in the last 10 years. The application of power ultrasound offers the opportunity to modify and improve some technologically important compounds which are often used in food products. One of them is starch. The aim of this research was to examine the effect of the high power ultrasound of 24 kHz frequency on rheological and some physical properties of corn starch. Various ultrasound treatments were used; an ultrasound probe set with different intensities (34, 55, 73 W cm−2) and treatment times (15 and 30 min) and ultrasound bath of 2 W cm−2 intensity and treatment times (15 and 30 min). Rheological parameters, turbidity and swelling power of corn starch suspensions were determined for native and ultrasonically treated corn starch suspensions. Differential scanning calorimetry was used in order to examine the pasting properties of corn starch. The results have shown that the ultrasound treatment of corn starch distorts the crystalline region in starch granules. The results of differential scanning calorimetry measurements have shown a decrease in enthalpy of gelatinization. A significant decrease in consistency coefficient (k) has also been observed. The consistency coefficient decreases stepwise jointly with the increasing ultrasound power. The increase in the swelling power is associated with water absorption capacity and corn starch granules solubility, respectively.
Electrospun fibers were produced using a variety of solvents to investigate the influence of polymer/solvent properties on the fiber surface morphology. Electrospinning is a novel processing technique for the production of fibers with diameters in the range of a few nanometers to tens of micrometers. We have been able to produce polymeric fibers with a high surface area through the introduction of a micro-and nanostructured surface structure, which we refer to as a "porous" morphology. These features could be introduced in several different polymeric fibers increasing their range of application significantly. The pores vary from densely packed, well-formed nanopores with diameters in the range 20-350 nm to larger flat pores of about 1 µm. The increased surface area of polymeric fibers was correlated with high volatility solvents used in the electrospinning process. The effect of processing parameters on the fiber surface morphology was also investigated using optical microscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM).
The objective of this research was to show the reinforcing effects of nanofibers in an epoxy matrix and in a rubber matrix using electrospun nanofibers of PBI (polybenzimidazole). The average diameter of the electrospun fibers was around 300 nanometers, which is less than one tenth the diameter and 1/100 the cross sectional area of ordinary reinforcing fibers. The ultrafine fibers provide a very high ratio of surface area to volume. The nanofibers toughened the brittle epoxy resin. The fracture toughness and the modulus of the nanofiber (15 wt%)-reinforced epoxy composite were both higher than for an epoxy composite made with PBI fibrids (17 wt%), which are whisker-like particles. In an elastomeric matrix, The Young's modulus and tear strength of the chopped nanofiber-reinforced styrene-butadiene rubber (SBR) were higher than those of the pure SBR. Micrographs of the fracture surfaces were obtained by scanning electron microscopy (SEM).
In order to clarify the behavior of bubbles which is closely related to cavitation phenomena, the research of the dynamics
of bubbles has been intensively conducted and established the research field of bubble dynamics. In this review paper it is
intended to describe briefly studies on bubble dynamics including the history in conjunction with the shock wave dynamics.
The ultrasonic degradation of poly(ethylene oxide) (PEO) of different initial molecular weights was studied at a fixed temperature. The time variation of the number average molecular weight was determined using Gel Permeation Chromatography (GPC). The ultrasonic degradation rate, K, was assumed to be of the form, k = k(d)(x - x(lim))(lambda), where k(d) represents the rate coefficient, while x and x(lim), represent the molecular weight and limiting molecular weight, respectively. A continuous distribution model assuming midpoint chain scission and two different expressions for the rate coefficient was developed to satisfactorily model the experimental data. In the first method, the model was solved numerically and the values of k(d) and lambda were determined by fitting the model to the experimental data. However, when lambda is assumed to be unity, an analytical solution to the model was determined and fitted the experimental data for the degradation of PEO. To confirm this model, the effect of initial molecular weight on the degradation of other polymers (polyacrylamide (PAM), poly(butyl acrylate) (PBA), poly(methyl acrylate) (PMA)) was also investigated. The assumption of lambda = 1 fitted the experimental data for the ultrasonic degradation of these polymers indicating that this is a reasonable approximation for the ultrasonic degradation of polymers. The effect of various solvents on the degradation of poly(ethylene oxide) was also investigated. No degradation was observed when PEO was degraded in acetone, acetonitrile or methanol but degradation occurred in mixtures of water and the above solvents. Thus.. it was concluded that the degradation of PEO was dependent more on the vapor pressure of the solvent than on polymer-solvent interactions. (c) 2005 Elsevier Ltd. All rights reserved.
The ultrasonic degradation of poly(vinyl alcohol) was investigated at different pHs of the solvent, in different water/solvent binary mixtures, and at different polymer concentrations. The samples were analyzed with gel permeation chromatography. The degradation rate coefficients were determined with a continuous distribution model. A higher degradation rate was obtained at pH extremes, in better solvents, and at lower polymer concentrations. The results are explained and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4888–4892, 2006
Solutions of polystyrene in toluene have been studied as part of a comprehensive study of the parameters affecting the degradation of polymers under irradiation with high-intensity ultrasound. Results are reported which demonstrate the molecular weight dependence of the process and the effect of solution temperature, ultrasound intensity and the nature of dissolved gases on the rate and extent of degradation over a considerably wider range than previously studied. They demonstrate that the limiting molecular weight and polydispersity of the materials can be controlled by suitable manipulation of the experimental conditions. The effects are explained in terms of the influence that each of the parameters has on the shear gradients generated around cavitation bubbles in the solution. The possibility of using the ultrasound process in the control of polymer structure and for the preparation of block copolymers is discussed.
Powders of polyethylene, polypropylene, poly(vinyl chloride) and poly(methyl methacrylate) have been subjected to irradiation with high-intensity ultrasound while suspended in water. Changes in the particle sizes and the surface morphology were noted and the pattern of the results was correlated with the physical properties of the materials. In anticipation of sonochemically enhanced reactions at polymer surfaces, the effect on a polyethylene sheet was also examined. The implications of the results for preparative methods as well as surface reactions are discussed.