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Correlation between Morphology, Mechanical Properties and Microdeformation Behavior of Electrospun Scaffolds Based on a Biobased Polymer Blend and Biogenic Nano-Hydroxyapatite
Abstract
For the investigations, scaffolds for bone regeneration (in the form of non-woven mats) were fabricated based on a polymer blend based on polycaprolactone, poly-L-lactic acid and gelatin by electrospinning which were partly modified using vitamin D3 and reinforced with 0 – 12 % nano-hydroxyapatite (nano-HAp extracted from ostrich bones) to improve both biocompatibility and mechanical performance. Electron microscopic approaches were applied to analyse the fiber microstructure due to phase separation and the microdeformation mechanisms after testing, as well as the fiber diameter as a function of the nano-HAp fraction. From uniaxial tensile testing it has been found that incorporation of nano-HAp into the blend triggers the mechanical properties of the scaffolds to a high degree, which results in an increase in tensile strength from 0.7 MPa to 5.6 MPa and an increase in strain at break from 2 % to 37 %. The transition from the very brittle behavior of the neat blend fiber mats to the highly ductile behavior of the blend fiber mats containing 12 % nano-HAp is related to a change in the microdeformation behavior of the nano- or micro-sized fibers. Whereas at lower nano-HAp content, crazing inside the fibers is prominent, thin-layer yielding becomes dominant at higher nano-HAp content.
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The incorporation of hydroxyapatite (HAP) into poly-l-lactic acid (PLLA) matrix serving as bone scaffold is expected to exhibit bioactivity and osteoconductivity to those of the living bone. While too low degradation rate of HAP/PLLA scaffold hinders the activity because the embedded HAP in the PLLA matrix is difficult to contact and exchange ions with body fluid. In this study, biodegradable polymer poly (glycolic acid) (PGA) was blended into the HAP/PLLA scaffold fabricated by laser 3D printing to accelerate the degradation. The results indicated that the incorporation of PGA enhanced the degradation rate of scaffold as indicated by the weight loss increasing from 3.3% to 25.0% after immersion for 28 days, owing to the degradation of high hydrophilic PGA and the subsequent accelerated hydrolysis of PLLA chains. Moreover, a lot of pores produced by the degradation of the scaffold promoted the exposure of HAP from the matrix, which not only activated the deposition of bone like apatite on scaffold but also accelerated apatite growth. Cytocompatibility tests exhibited a good osteoblast adhesion, spreading and proliferation, suggesting the scaffold provided a suitable environment for cell cultivation. Furthermore, the scaffold displayed excellent bone defect repair capacity with the formation of abundant new bone tissue and blood vessel tissue, and both ends of defect region were bridged after 8 weeks of implantation.
A novel natural hydroxyapatite (HAp) bioceramic was extracted from the ostrich cortical bone by the thermal decomposition method. HAp was characterized by different analytical tools such as thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). Removal of organic impurities from the bone powder was confirmed by TGA analysis. FTIR spectra of HAp confirmed the presence of the major functional groups such as phosphate (PO43−), hydroxyl (OH−), and carbonate (CO32−) in the bioceramic. The XRD data revealed that the HAp was the crystalline phase obtained by calcination of the bone powder at 950°C, and the SEM analyses confirmed the typical plate-like texture of the nanosized HAp crystals.
In article number 1903279, Jin Zhang, Jianlin Zuo, Jun Zou, Jianxun Ding, and co‐workers summarize the advances in the preparation, composition, and characteristics of polymer fibers, as well as their applications in bone and cartilage tissue engineering, and propose potential challenges and opportunities.
Results of the studies dealing with the toughness of polylactic acid/polycaprolactone (PLA/PCL) blends are analyzed with respect to the PCL particle size, PLA matrix crystallinity, and presence of a compatibilizer. It is shown that a high toughness or even “super-toughness” of PLA/PCL blends without a compatibilizer can be achieved for blends with the proper size of PCL particles. Nevertheless, the window for obtaining the super-tough PLA/PCL blends is quite narrow, as the final impact strength is very sensitive to multiple parameters: namely the blend composition, PLA matrix crystallinity, and PCL particle size. Available literature data suggest that the optimal composition for PLA/PCL blends is around 80/20 (w/w). The PLA/PCL(80/20) blends keep high stiffness of PLA matrix and the concentration of PCL particles is sufficient to achieve high toughness. The PLA/PCL(80/20) blends with low-crystallinity PLA matrix (below ca 10%) exhibit the highest toughness for bigger PCL particles (weight average diameter above 1 μm), while the blends with high-crystallinity PLA matrix (above ca 30%) exhibit the highest toughness for smaller PCL particles (weight average diameter below 0.5 μm). The addition of a compatibilizer may improve the toughness only on condition that it helps to achieve a suitable particle size. The toughness of both non-compatibilized and compatibilized PLA/PCL blends with optimized morphology can be more than 15 times higher in comparison with neat PLA.
Fabricating a bioartificial bone graft possessing structural, mechanical and biological properties mimicking the real bone matrix is a major challenge in bone tissue engineering. Moreover, the developed materials are prone to microbial invasion leading to biomaterial centered infections which might limit their clinical translation. In the present study, biomimetic nanofibrous scaffolds of Poly ɛ-caprolactone (PCL)/nano-hydroxyapatite (nHA) were electrospun with 1wt%, 5wt%, 10wt%, 15wt% and 30wt% of zinc oxide (ZnO) nanoparticles in order to understand the optimal concentration range of (ZnO) nanoparticles balancing both biocompatibility and osteoregeneration. The developed nanofibrous scaffolds were successfully characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), contact angle, fourier transform infrared spectroscopy (FTIR), wide-angle X-Ray diffraction (WAXD), brunaueremmett Teller (BET) surface area and tensile testing. Biocompatibility of the developed scaffolds at in vitro level was evaluated by culturing MG-63 cells and investigating the impact on cell viability, proliferation, protein adsorption, alkaline phosphatase (ALP) activity and biomineralization. The PCL/nHA scaffolds exhibited a 1.2-fold increase in cell viability and proliferation, while incorporation of ZnO nanoparticles to PCL/nHA imparted antimicrobial activity to the scaffolds with a progressive increase in the antimicrobial efficacy with increasing ZnO concentration. The results of cell viability were supported by ALP activity and mineralization assay, wherein, PCL/nHA/ZnO scaffolds showed higher ALP activity and better mineralization capacity as compared to pristine PCL. Although, the PCL/nHA/ZnO scaffolds with 10, 15 and 30wt% of ZnO particles exhibited superior antimicrobial efficacy against both gram-negative (E. coli) and gram-positive (S. aureus) bacteria, a significant decrease in the cell viability and mechanical properties was observed at higher concentrations of ZnO namely 15 and 30%. Amongst the various ZnO concentrations studied optimal cell viability, antimicrobial effect and mechanical strength were observed at 10wt.% ZnO concentration. Thus, the present study revealed that the biomimetic tri-component PCL/nHA/ZnO scaffolds with ZnO concentration range of ≤ 10% could be ideal for achieving optimal biocompatibility (cell proliferation, biomineralization, and antimicrobial capacity) and mechanical stability thus making it a promising biomaterial substrate for bone tissue regeneration.
Spectroscopy, National Research Center (Egypt). His main research interests are
development of new biomaterials to be used as scaffold in
nanoparticles (Au NPs). The biocomposite solution mixture was electrospun
at a potential of about 20 kV. The results indicate that HA and Au
NPs was uniformly distributed in the PVA nanoibers, which have diameter
in the range of 100−150 nm for pure PVA and 300−400 nm with
HA respectively. The thermal behavior of the composite was studied
by TG and the morphology of the electrospun ibers were investigated
by means of SEM technique. Tensile strength and elastic modulus conirmed
that the mechanical characteristics of the PVA/HA nanoibrous
mat were merely altered after Au additions. The formation of apatite
like structure on ibers surface during the in-vitro test was conirmed by
EDX analysis. The micro-porous ibers can have many potential uses in
the repair and treatment of defected bone, and bone tissue engineering.
It was demonstrated that the macro- and micromechanical behaviors of electrospun composite scaffolds based on PLA and HA can be simultaneously studied using 3D digital image correlation strain measurements coupled with an axial tensile test. It was proven that the addition of a small quantity (2%) of HA particles into PLA electrospun scaffolds decreased their mechanical properties by approximately 40 and 60% at the micro- and macroscales, respectively; nevertheless, when this amount was increased beyond 2% of HA, the composites recovered their stiffness, showing Young’s moduli ranging between 400 and 600 MPa. Hence, the mechanical responses of PLA–4% HA and PLA–6% HA electrospun scaffolds were conveniently enhanced with the addition of hydroxyapatite nanoparticles. The micromechanical measurements were able to capture the microstrain mechanism between electrospun nanofibers and the effect of HA nanoparticles on their mechanical response. This methodology could be a powerful tool for developing scaffolds for specific applications in tissue engineering.
Introduction:
In recent years there has been a steep increase in the number of orthopedic patients for many reasons. One major reason is osteomyelitis, caused by pyrogenic bacteria, with progressive infection of the bone or bone marrow and surrounding tissues. So antibiotics must be introduced during bone implantation to avoid prolonged infection.
Aim:
The objective of the study reported here was to prepare a composite film of nanocrystalline hydroxyapatite (HAp) and polycaprolactone (PCL) polymer loaded with ciprofloxacin, a frequently used antibiotic agent for bone infections.
Methods:
Nanocrystalline HAp was synthesized by precipitation method using the precursor obtained from eggshell. The nanocomposite film (HAp-PCL-ciprofloxacin) was prepared by solvent evaporation. Drug-release and biodegradation studies were undertaken by immersing the composite film in phosphate-buffered saline solution, while a cytotoxicity test was performed using the fibroblast cell line NIH-3T3 and osteoblast cell line MG-63.
Results:
The pure PCL film had quite a low dissolution rate after an initial sharp weight loss, whereas the ciprofloxacin-loaded HAp-PCL nanocomposite film had a large weight loss due to its fast drug release. The composite film had higher water absorption than the pure PCL, and increasing the concentration of the HAp increased the water absorption. The in vitro cell-line study showed a good biocompatibility and bioactivity of the developed nanocomposite film.
Conclusion:
The prepared film will act as a sustainable bone implant in addition to controlled drug delivery.
A missing cornerstone in the development of tough micro/nano fibre systems is an understanding of the fibre failure mechanisms, which stems from the limitation in observing the fracture of objects with dimensions one hundredth of the width of a hair strand. Tensile testing in the electron microscope is herein adopted to reveal the fracture behaviour of a novel type of toughened electrospun poly(methyl methacrylate)/poly(ethylene oxide) fibre mats for biomedical applications. These fibres showed a toughness more than two orders of magnitude greater than that of pristine PMMA fibres. The in-situ microscopy revealed that the toughness were not only dependent on the initial molecular alignment after spinning, but also on the polymer formulation that could promote further molecular orientation during the formation of micro/nano-necking. The true fibre strength was greater than 150 MPa, which was considerably higher than that of the unmodified PMMA (17 MPa). This necking phenomenon was prohibited by high aspect ratio cellulose nanocrystal fillers in the ultra–tough fibres, leading to a decrease in toughness by more than one order of magnitude. The reported necking mechanism may have broad implications also within more traditional melt–spinning research.
We report here a facile strategy to fabricate three-dimensional (3D) hydroxyapatite (HA) architectures with well-defined long continuous interconnected pores by using electrospinning and biomimetic mineralization. To this end, a polymeric nanofiber (NF) scaffold with well-defined architecture was fabricated by electrospinning, and bone morphogenetic protein 2 (BMP2) was then adsorbed onto the chemically modified NFs through bio-conjugation. The 3D nanoporous HA architecture was finally fabricated by biomimetic mineralization of NF-BMP2 hybrid in simulated body fluids and subsequent dissolution of NFs in hexafluoroisopropanol. The formation of NF-BMP2 hybrid was identified by confocal laser scanning microscopy analysis. The crystal structure of HA crystals formed on NFs was examined by X-ray diffraction. The chemical composition and interconnected porous structure of the created 3D HA architectures were measured by X-ray photoelectron spectroscopy, focused ion beam scanning electron microscopy, and transmission electron microscopy, respectively. This bottom-up strategy based on electrospinning and biomimetic mineralization opens up a new way to prepare diverse porous HA-based hybrid materials and show great potentials in drug delivery, gene transfer and tissue engineering.
For bone tissue engineering, nano‐hydroxyapatite (nano‐HAp) is a widely used bioceramic filler in polymer fibrous scaffolds that changes the morphology and micromechanical behavior of fibers. In this study, different volume fraction percentages of nano‐HAp and vitamin D3 (VD3) are incorporated into electrospun polymer blend fibrous scaffolds comprising polycaprolactone (PCL), poly‐L‐lactic acid (PLLA), and gelatin (GEL). Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and uniaxial tensile testing are used to characterize the chemical, morphological, and micromechanical properties of the scaffolds. The FTIR analysis showed the presence of functional groups of fillers and polymers and their molecular interactions in the fibers. In the microscopic analysis, the fillers are found to affect the fiber morphology (including diameter, phase separation, and texture) and the response of the fibers under tensile deformation. The addition of 3% by volume of filler suspension results in maximum diameter of 4.34 µm, and the addition of 6%–12% filler leads to an increase in tensile strength from 0.7 to 5.6 MPa and strain at break from 2% to 37% for the composite fibers compared to neat fibers. The crazing behavior of the fiber is more noticeable at a low filler content (0%), whereas thin‐layer yielding becomes predominant at a higher filler content (12%). Thus, the study shows that scaffold fibers undergo brittle‐to‐ductile transitions as the filler percentage in the polymer blend increases from 0% to 12%. It has been further found that morphogens used as growth factors can be easily released from hydroxyapatite after adsorption.
A scaffold that mimics the physicochemical structure of bone at the nanoscale level is an attractive alternative to conventional bone grafts, but its development remains a main challenge in bone tissue engineering today. This work describes the fabrication of a nanofibrous poly(vinyl alcohol)/chitosan/carbonated hydroxyapatite (PVA/CS/CHAp) scaffold. CHAp nanoparticles were synthesized using a co-precipitation method, and nanofibrous PVA/CS/CHAp scaffolds were fabricated by electrospinning using CHAp concentrations of 0, 5, 10, 15, and 20 wt%. The physicochemical properties of the scaffolds were evaluated by SEM, XRD, FTIR, and EDS, and the mechanical properties were determined by tensile strength tests. Swelling behavior, protein adsorption onto the scaffold surfaces, surface biomineralization, and cells viability were also evaluated in vitro. The addition of CHAp to the composite decreased the fiber diameter from ∼160 nm at 0 wt% to ∼139 nm at 15 wt% and great agglomerations were evident at 20 wt%. XRD, FTIR, and EDS showed effective incorporation of CHAp into the nanofibrous structure. This CHAp incorporation significantly increased the modulus of the scaffold at PVA/CS/CHAp 15 wt%, with an average 103.86 MPa, but tensile strength was not significantly altered. However, the elongation at break was decreased as the CHAp concentration increased. Swelling capacity of scaffold increases due to CHAp addition. Protein adsorption onto the scaffold increased 2.3fold at 20 wt% when compared to 0 wt%. The PVA/CS/CHAp 15 wt% showed a better bioactivity when compared to PVA/CS/CHAp 0 wt% after immersion of the scaffolds in a simulated body fluid solution for 7 days. Cell viability and cell morphology results reveal that PVA/CS/CHAp able to facilitate osteoblast cells to attach and proliferate. Introducing higher CHAp into the scaffold could increase the cell viability of the scaffold. PVA/CS/CHAp has potential to serve as an alternative scaffold material for bone tissue engineering.
Hybrid composites combining two fibre types with distinctly different mechanical properties have the potential to surpass the stiffness-toughness dilemma, which is characteristic to standard (single fibre type) composite materials. The current work demonstrates this potential on the example of carbon fibre/self-reinforced polypropylene (SRPP) hybrids. The aim is to understand the transition from brittle to ductile behaviour under tensile and impact loadings and to identify the parameters affecting this transition. It was found that the volume fraction (Vf) of carbon fibres at which the transition occurs can be increased by using a dispersed layup with thinner layers. The use of a high adhesion matrix results in higher modulus and yield strength but lowers the transition Vf. The experimental program is supported by analytical models used to predict modulus, strength and energy absorption. Results indicate that pseudo-ductile carbon fibre/SRPP hybrids are competitive with composites produced from bulk and sheet moulding compounds.
PLA/PCL co-mingled nanofibrous mats were prepared via multi-jet electrospinning. The concentration of PLA and PCL in the co-mingled mats were controlled by changing the flow rate of the two polymer solutions. The amount of PLA and PCL in the co-mingled nanofibrous mats was monitored by UV–Vis measurements through a colored dye added to PLA and by FTIR-ATR analysis. Morphology and mechanical properties of the nanofibrous mats were respectively examined by scanning electron microscopy (SEM) and tensile tests. Water contact angles measurements were also carried out in order to investigate the wettability of the materials. Finally, the hydrolytic degradation of the mats in buffer solution at pH 4, pH 7 and pH 10 were studied up to 50 days.
In this study, hydroxyapatite (HAp) and gelatin (GEL) scaffolds were prepared to mimic the mineral and organic component of natural bone. The raw material was first compounded and resulting composite were molded into the petridishes. Using Solvent casting process, it is possible to produce scaffolds with mechanical and structural properties close to natural trabecular bone.The mechanical properties of composites were investigated by Thermo-mechanical analyzer (TMA), Vickers microhardness tester, Universal testing machine. It was observed that the composite has maximum tensile strength of 37.13MPa ( oven drying) and % elongation of 7.68 (Oven drying) and 2.04 (Natural drying) at 15% of Hap respectively. These results demonstrate that the prepared composite scaffold is a potential candidate for bone tissue engineering.Bangladesh J. Sci. Ind. Res. 50(1), 15-20, 2015
Enhancing matrix crystallization has been demonstrated to be an effective method to simultaneously improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) modified with flexible polymers, such as poly(ε-caprolactone) (PCL). Unfortunately, increasing PLLA matrix crystallinity alone cannot guarantee the enhancement of impact toughness in most cases, so other structural parameters should be considered. In this work, taking PLLA/PCL (80/20) blend as an example, the combined roles of matrix crystallization and impact modifier particle size in the toughening have been investigated. PLLA matrix crystallinity was controlled by adding a highly effective nucleating agent and PCL particle size was tailored by varying processing conditions while maintaining constant interfacial adhesion. It is interesting to find that toughening is efficient only if matrix crystallinity and particle size are well matched. With the significant increase of matrix crystallinity, an evident decrease of optimum particle size for toughening PLLA has been identified for the first time. Therefore, suitable particle size is the precondition for highly crystalline matrix to work effectively in the toughening because only small particles (0.3–0.5 μm) are effective in trigger shear yielding mechanism of the matrix needed for good toughness, whereas relatively large particles (0.7–1.1 μm) are only capable of toughening amorphous matrix effectively by initiating multiple crazing of the matrix. Importantly, our findings can be used to well explain the reason for the different roles of matrix crystallization in the toughening of different PLLA blends reported in the literature. Furthermore, the heat resistance of the blend with a highly crystalline matrix is much better than that of the blend with an amorphous one as expected. This work could not only provide a new insight into the synergistic roles of matrix crystallization and modifier particle size in the toughening of PLLA but also set up a universal framework for designing high-performance PLLA products with both good impact toughness and high heat resistance.
The present work is a comparative evaluation of physical and biological properties of electrospun biodegradable fibrous scaffolds based on polycaprolactone (PCL) and its blend with polycaprolactone-polyethyleneglycol-polycaprolactone (CEC) with and without nanohydroxyapatite (nHAP) particles. The fiber morphology, porosity, surface wettability, and mechanical properties of electrospun PCL were distinctly influenced by the presence of both copolymer CEC and nHAP. The degradation in hydrolytic media affected both morphological and mechanical properties of the scaffolds and the tensile strength decreased by 58% for PCL, 83% for PCL/CEC, 36% for PCL/nHAP and 75% for PCL/CEC/nHAP in 90 days of PBS ageing. MTT assay using mouse fibroblast L929 cells proved all the scaffolds to be non-cytotoxic. An overall enhanced performance was shown by PCL/CEC/nHAP scaffold in cell viability (LPH) and proliferation (Picogreen). Simultaneously, ELF assay of ALP activity (bone marker) confirmed the presence of osteogenic-induced Rabbit adipose-derived mesenchymal stem cells (ADMSCs) on all the scaffolds. In comparison, the results reveal the potential of the cytocompatible PCL/CEC/nHAP scaffold for the fabrication of living bony constructs for tissue engineering applications.
In order to augment bone formation, a new biodegradable scaffold system was fabricated using different ratios of hydroxyapatite (HAp) blended with synthetic polymer polycaprolactone (PCL) and natural polymer gelatin (GE) followed by electrospinning method. Three different concentrations of HAp were used in PCL/GE to obtain a blend of 10, 30, and 50% (w/v) HAp-PCL/GE. These HAp-loaded PCL/GE blends were then compared with PCL/GE blends by different mechanical and biological in vitro and in vivo studies to understand the applicability of the system. Scanning electron microscopy, X-ray diffraction analysis, and tensile strength measurement were done to obtain physical properties. Fifty Percent HAp-PCL/GE blends possessed the highest mechanical strength. In vitro cytotoxicity and proliferation of osteoblast cells on the PCL/GE and HAp-PCL/GE scaffolds were examined and shown that addition of HAp in PCL/GE was beneficial by increasing cell viability (>85%) proliferation and cell-surface attachment. Expression of collagen and osteopontin was also found higher in 50% HAp-PCL/GE blends than the others. On the other hand, in vivo bone formation was examined using rat models and increased bone formation was observed in 50% HAp-PCL/GE blends within 6 weeks. Based on the combined results of this study, HAp-PCL/GE membranes were found to hold great promise for use in tissue engineering applications, especially in bone tissue engineering.
Biodegradable and biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a copolymer of microbial polyester, was fabricated as a nanofibrous film by electrospinning and composited with hydroxyapatite (HAp) by soaking in simulated body fluid. Compared with a PHBV cast (flat) film, the electrospun PHBV nanofibrous film was hydrophobic. However, after HAp deposition, both of the surfaces were extremely hydrophilic. The degradation rate of HAp/PHBV nanofibrous films in the presence of polyhydroxybutyrate depolymerase was very fast. Nanofiber formation increased the specific surface area and HAp enhanced the invasion of enzyme into the film by increasing surface hydrophilicity. The surface of the nanofibrous film showed enhanced cell adhesion over that of the flat film, although cell adhesion was not significantly affected by the combination with HAp.