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Interfacial properties of hydrophilized poly(lactic-co-glycolic acid) layers with various thicknesses
Abstract
Biodegradable polyesters such as poly(lactic-co-glycolic acid) copolymers (PLGA) are preferred materials for drug carrier systems although their surface hydrophobicity greatly limits their use in controlled drug delivery. PLGA thin films on a solid support blended with PEG-containing compound (Pluronic) were used as model systems to study the interfacial interactions with aqueous media. Degree of surface hydrophilization was assessed by wettability, and X-ray photoelectron spectroscopy (XPS) measurements. Protein adsorption behavior was investigated by in situ spectroscopic ellipsometry. The degree of protein adsorption showed a good correlation with the hydrophilicity, and surface composition. Unexpectedly, the layer thickness was found to have a great impact on the interfacial characteristics of the polymer films in the investigated regime (20-200 nm). Thick layers presented higher hydrophilicity and great resistance to protein adsorption. That special behavior was explained as the result of the swelling of the polymer film combined with the partial dissolution of Pluronic from the layer. This finding might promote the rational design of surface modified biocompatible nanoparticles.
... Poly(lactic-co-glycolic acid) (PLGA) nano-and microparticles have been described as convenient platforms to carry drug molecules in the body [15,16,17]. Surface modification of these biodegradable particles with polyethylene oxide containing molecules has been shown to increase the biocompatibility of these systems [18,19,20,21]. Interfacial interactions play an essential role in drug delivery as drug carrier particles have to pass several interfaces in the body before they reach the site of action. ...
... Solvent residues were removed by heating the samples to 60 °C above the glass transition temperature of the polymers. This also promotes the accumulation of Pluronic in the upper layers of the polymer mixture as was shown previously [19,32]. Prior to contact angle measurements the samples were equilibrated in water for 1 h to approximate the state of the polymers to those on the nanoparticle sols. ...
Hypothesis:
Adsorption and localization of nanoparticles at fluid interfaces are key factors in processes like transport through membranes or emulsion stabilization. Adsorption of poly(lactic-co-glycolic acid) (PLGA) and Pluronic coated PLGA nanoparticles (NPs) were studied at three different fluid interfaces. The effect of particle surface modification and type of interface was investigated with the aim of fine tuning interfacial interaction of the nanoparticles.
Experiments:
Surface tension measurements were carried out to determine the surface activity and adsorption kinetics of the particles. Particles layers at the air/water interface were further studied using the Langmuir balance technique by recording the surface pressure-area isotherms. Interfacial rheological measurements were performed to characterize the structural properties of the nanoparticle interfacial films.
Findings:
Interfacial adsorption and its kinetics were explained by the diffusion controlled adsorption theory and considering the energy barrier of particle transport to the interface. Surface modification by Pluronic increased the interfacial activity of nanoparticles at all interfaces. Surface activity of PLGA-Pluronic particles could be described by the contributions of both the PLGA NPs and the effective portion of their Pluronic shell. Both particle films present mainly elastic dilatational properties suggesting that particles are in kinetically separated state.
... These examples-among others-draw attention to the importance of understanding the adhesive properties of amyloids. Adsorption of a dissolved component at solid/liquid interface can be qualitatively/quantitatively characterized by several complementary analytical techniques, such as atomic force microscopy (AFM) [10], total internal reflection fluorescence microscope (TIRF) [11,12], in situ label-free optical techniques [13][14][15], polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) [16] and quartz crystal microbalance (QCM) [17,18]. ...
The adhesive properties of amyloid fibers are thought to play a crucial role in various negative and positive aggregation processes, the study of which might help in their understanding and control. Amyloids have been prepared from two proteins, lysozyme and β-lactoglobulin, as well as an Exendin-4 derivative miniprotein (E5). Thermal treatment was applied to form amyloids and their structure was verified by thioflavin T (ThT), 8-Anilino-1-naphthalenesulfonic acid (ANS) dye tests and electronic circular dichroism spectroscopy (ECD). Adsorption properties of the native and amyloid forms of the three proteins were investigated and compared using the mass-sensitive quartz crystal microbalance (QCM) technique. Due to the possible electrostatic and hydrophobic interactions, similar adsorbed amounts were found for the native or amyloid forms, while the structures of the adsorbed layers differed significantly. Native proteins formed smooth and dense adsorption layers. On the contrary, a viscoelastic, highly loose layer was formed in the presence of the amyloid forms, shown by increased motional resistance values determined by the QCM technique and also indicated by atomic force microscopy (AFM) and wettability measurements. The elongated structure and increased hydrophobicity of amyloids might contribute to this kind of aggregation.
... Based on these findings, it can be estimated that the core of the polymer particles is in a non-hydrated state alongside the aqueous medium, slowly penetrating into the matrix. Even though both polymers are considered hydrophobic ones, it is well known that a limited swelling by water can occur [21,22,[55][56][57][58]. ...
Biocompatible and biodegradable polymers such as poly(lactic-co-glycolic acid), PLGA and polycaprolactone, PCL nanoparticles (NPs) have been used successfully as drug carriers in controlled drug release. The main weakness is the generally low drug loading (1–-5%) of the NPs. An option to enhance the drug content of NPs is to find the optimum matrix for a given drug molecule. To reveal the influence of matrix and drug polarity on the favoured encapsulation, polymeric NPs loaded with a series of alkyl-4-hydroxybenzoate (paraben) with increasing alkyl chain length (C1-C8) as model drugs were prepared by nanoprecipitation method. The paraben series represents the drugs with various polarities while the selected matrix polymers show increased hydrophobicity: PLGA with 50% lactic acid content (PLGA50) < PLGA with 75% lactic acid content (PLGA75) < PCL. The drug content of the PLGA NPs was found to significantly increase up to 10% with the hydrophobicity of the parabens, while encapsulation was further boosted by applying PCL. To find the proper fit between drug and matrix and finely tune the polarity of the NPs, as a novel approach, blends of PLGA50 and PCL were applied as matrix polymers. The drug loading of the NPs was proved to be dependent on the systematically changed blend composition. Furthermore, the introduction of PCL into the PLGA50 matrix improves the release kinetics of the active component.
... Regarding CTAB-containing films, it has already been described that a higher presence of CTAB in polymeric samples increases the surface hydrophilicity [17]. This increase in wettability with the surfactant accumulation on the film surface was already observed by Gyulai et al. [21] using XPS analysis and working with different surfactant concentrations. Their study concluded that as the surface became richer in surfactant, it became more hydrophilic. ...
Polylactic acid (PLA) is a good candidate for the manufacture of polymeric biodegradable biomaterials. The inclusion of metallic particles and surfactants solves its mechanical limitations and improves its wettability, respectively. In this work, cetyltrimethylammonium bromide (CTAB) and magnesium particles have been incorporated into PLA films to evaluate the changes produced in the polymeric matrix cast on glass and silicone substrates. For this purpose, the surface of the films has been characterized by means of contact angle measurements and ToF-SIMS. Depth profiles and SEM images of the cross sections of the films have also been obtained to study their morphology. The results show that the CTAB in the polymer matrix with and without magnesium improves the wettability of the films, making them more suitable for cell adhesion. The higher the hydrophilicity, the higher the surfactant concentration. The depth profiles show, for the first time, that, depending on the surfactant concentration and the presence of Mg, there is a layer-like distribution near the surface where, in addition to the CTAB + PLA mixture, a surfactant exclusion zone can be seen. This new structure could be relevant in in vitro/in vivo situations when the degradation processes remove the film components in a sequential form.
... Where, the lipophilic PPO chains are embedded into the polymeric matrix resulting in the reduction of drug adsorption and enhancement of system biocompatibility. The hydrophilic PEO ends are diffused into the external medium, hence producing a diffusion barrier (Figure 7) (Gyulai et al. 2011). 7. Mechanism of drug release from polymeric PLGA-ISFI systems ...
As a result of the low oral bioavailability of several drugs, there is a renewed interest for parenteral administration to target their absorption directly into the blood bypassing the long gastrointestinal route and hepatic metabolism. In order to address the potential side effects of frequent injections, sustained release systems are the most popular approaches for achieving controlled long-acting drug delivery. Injectable in-situ forming implants (ISFIs) have gained greater popularity in comparison to other sustained systems. Their significant positive aspects are attributed to easier production, acceptable administration route, reduced dosing frequency and patient compliance achievement. ISFI systems, comprising biodegradable polymers such as poly (lactide-co-glycolide) (PLGA) based on solvent exchange mechanisms, are emerged as liquid formulations that develop solid or semisolid depots after injection and deliver drugs over extended periods. The drug release from ISFI systems is generally characterized by an initial burst during the matrix solidification, followed by diffusion processes and finally polymeric degradation and erosion. The choice of suitable solvent with satisfactory viscosity, miscibility and biocompatibility along with considerable PLGA hydrophobicity and molecular weights is fundamental for optimizing the drug release. This overview gives a particular emphasis on evaluations and the wide ranges of requirements needed to achieve reasonable physicochemical characteristics of ISFIs.
... Egy másik eljárás, a keverékképzés során megállapítottuk, hogy a Pluronic adalék nagymértékben dúsul a politejsav (PLA), politejsav/glikolsav polimerek (PLGA) felületi rétegében, ezáltal így is megvalósítható a felületmódosítás. 10 A polimer felület hidrofilizálásának mértéke követhetõ volt a nedvesedés méréssel, míg a felületi réteg pontos kémiai összetételének meghatározására röntgen sugár-fotoelektron spektroszkópiát használtunk. Azt találtuk, hogy a módosított felület hidrofil jellege az alkalmazott Pluronic összetételétõl, valamint mennyiségétõl függ, így ezekkel szabályozható. ...
Two aspects of biorelevant interfacial phenomena, the surface biocompatibility and membrane affinity of polymeric biomaterials were discussed in the present paper. Surface modifications of biodegradable polyesters, poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) were developed by forming poly(ethylene oxid), PEO-containing layer. Different polymer layers were studied by XPS and ellipsometry measurements to determine the effect of Pluronic component on bovine serum albumin (BSA) adsorption. Significant increase in surface hydrophilicity was achieved leading to reduced protein adsorption which contributes to enhanced biocompatibility.
Applying surface modifications to polymeric drug delivery nanoparticles (NPs) the macromolecular coverage offers the steric stabilization of the colloidal drug loaded particles. Meanwhile, the tuning of surface properties by changing the chemical composition can improve the membrane affinity of the drug carrier particles. Additionally, providing that significant number of functional groups is available in the surface layer that allows further chemical coupling of various ligands to accomplish targeted drug delivery.
To characterize the membrane affinity of a colloidal drug carrier, Langmuir-balance measurement using lipid monomolecular layers were carried out. These nanocarriers with diameter of 100-150 nm probably show different molecular interactions and transport route than the molecular construction. The adhesion to the membrane surface however, is a first crucial step in the process which is tested in the penetration ability measurement. With the aim to increase the membrane affinity and potential of targeted drug delivery the end group derivative of Pluronics was synthesized in a straightforward way to obtain Pluronic-amines. This method allows modulation of the charge character of the NPs’ surface and provides functional groups for chemical reactions useful for targeting while retaining the aggregation stability of the system. Presence of the positively charged end groups was detectable with electrophoretic mobility measurements. The Pluronic-amine coated NPs showed the highest membrane affinity into the DPPC layer while controllable properties of the surface layer can be achieved by combined application of the Pluronics with different compositions.
Adhesion/adsorption of the biodegradable PLGA NPs were studied at another model cell membrane (SLB) composed of lipid bilayer formed on a solid support. The influence of NPs’ surface properties on the interfacial interactions was evaluated comparing various amphiphilic block copolymers (Pluronics) as well as amphiphilic monoalkyl hyperbranched polyglycerols (Cn-HbPGs). Cn-HbPGs were successfully applied as surface modifiers and stabilizers in the preparation of PLGA NPs with outstanding colloidal stability due to the orienting interaction of the hydrophobic alkyl segment. The Pluronic- and C18-HbPG coated NPs were applied to SLB obtained on quartz crystal microbalance (QCM) sensor surface by liposome spreading. Degree and type of adhesion of NPs were determined by nanogravimetric measurements in combination with the visual analysis of the surfaces using atomic force microscopy (AFM). Comparison of different Pluronic surface coatings led to the conclusion that the length of the PEO chains in the Pluronic molecules has marked effect on the stability of the NPs and their interactions with lipid systems. Stabilization of NPs by C18-HbPG resulted in the highest membrane affinity which is an initial requirement for cellular uptake, followed by Pluronic105 with medium polarity within the Pluronic series applied here.
In parallel to the characterization of the drug carrier nanoparticles, the membrane affinity of various bioactive compounds has also been studied. Using both of the mono- and bilayer lipid model membrane measurements large number of drug candidates were managed to screen and promising compounds were selected acting against Mycobacterium tuberculosis, the pathogen of tuberculosis.
These types of model experiments have also proved useful in the assessment of amphiphilic cationic polymers applied as antibacterial coating on various textile materials. On the basis of the membrane affinity results the chemical structure involving conformational properties of the alkyl chain grafted poly(ethylene imine) derivatives was found to be important in the molecular interactions playing role in antibacterial behaviour of amphipathic cationic polyelectrolytes.
... The C\ \H signal at 284.9 eV originates from the methyl groups of the lactide units of the PLGA. The signals at 289.1 eV and 286.9 eV were assigned to the carbon in the carboxylic group of the PLGA (C_OO) and the neighboring carbon in the chain (C\ \O), respectively [36]. Fig. 3D shows the Ag 3d XPS spectra for the sample. ...
Poly(lactic-co-glycolic acid)/Ag/ZnO nanorods coating were successfully prepared on the surface of Ti metallic implants using a hydrothermal method and subsequent spin-coating of mixtures of poly(lactic-co-glycolic acid) and silver nanoparticles. The poly(lactic-co-glycolic acid)/Ag/ZnO nanorods coating exhibited excellent antibacterial efficacy of over 96% against both Staphylococcus aureus and Escherichia coli when the initial content of Ag nanoparticles was over 3 wt%. In addition, the release of both silver and zinc could last for over a hundred days due to the enwrapping of poly(lactic-co-glycolic acid). Proliferation of mouse calvarial cells exhibited minimal cytotoxicity on the poly(lactic-co-glycolic acid)/Ag/ZnO coating with an initial content of Ag nanoparticles of 1 wt% and 3 wt%, while it inhibited cell proliferation once this value was increased to 6 wt%. The results revealed that this poly(lactic-co-glycolic acid)/Ag/ZnO composite could provide a long-lasting antibacterial approach and good cytocompatibility, thus exhibiting considerable potential for biomedical application in orthopedic and dental implants with excellent self-antibacterial activity and good biocompatibility.
... Using these techniques a wide range of applications, e.g. high-sensitivity characterization of protein layer formation [11][12][13], cell adhesion [14,15], monitoring of bacteria [14], interfaces [16] and substrate stability [17], has already been reported. Optical waveguide sensors provide high sensitivity, but only within the exponentially decaying region of the evanescent field, of which penetration depth is typically a few hundred nanometers. ...
Two surface-sensitive label-free optical methods, grating coupled interferometry (GCI) and spectroscopic ellipsometry (SE) were integrated into a single instrument. The new tool combines the high sensitivity of GCI with the spectroscopic capabilities of SE. This approach allows quantification with complex optical models supported by SE and accurate measurements with the evanescent field of GCI. A flow cell was developed to perform combined and simultaneous investigations on the same sensor area in liquid (or gas) environments. The capabilities of the instrument were demonstrated in simple refractometry and protein adsorption experiments.
... A comprehensive discussion of waveguide sensors is available in the review article of P. Kozma et al [21].The combination of ellipsometry with QCM has also been demonstrated [22]. The typical in situ ellipsometry configuration utilizes a flow cell equipped with glass windows for the input and output light [15,[23][24][25][26][27][28], in which not only the effect of the window and the absorption of the water, but also the fixed angle of incidence puts constraints. The so called Kretschmann configuration couples the light into the substrate using prisms [29][30][31][32][33][34], providing the illumination from the substrate, and measuring at the close proximity of the surface with the evanescent field, similar to OWLS and GCI. ...
Plasmon-enhanced in situ spectroscopic ellipsometry was realized using the Kretschmann geometry. A 10-μL flow cell was designed for multi-channel measurements using a semi-cylindrical lens. Dual-channel monitoring of the layer formation of different organic structures has been demonstrated on titania nanoparticle thin films supported by gold. Complex modeling capabilities as well as a sensitivity of ~40 pg/mm² with a time resolution of 1 s was achieved. The surface adsorption was enhanced by the titania nanoparticles due to the larger specific surface and nanoroughness, which is consistent with our previous results on titanate nanotubes.
... In most cases the drug is encapsulated into the polymeric particle and released in a controlled way by diffusion and erosion of the polymeric matrix891011. It was found however, that the hydrophobic character of the PLGA triggers the nonspecific adsorption of plasma proteins leading to the uptake of the particles by the mononuclear phagocyte system and hence their fast clearance from the body121314 . This undesirable process can be prevented by forming a poly(ethylene oxide), PEO corona on the particle to improve its surface biocom- patibility15161718. ...
Biodegradable poly(lactic-co-glycolic acid) copolymer, PLGA nanoparticles (NPs) with a surface layer of poly (ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers, Pluronics, are promising drug carrier systems. With the aim to increase the potential of targeted drug delivery the end group derivative of Pluronics was synthesized in a straightforward way to obtain Pluronic-amines. The formation of functional amine groups was confirmed by fluorescamine method and NMR analysis of their N-(tert-Butoxycarbonyl)-L-phenylalanine (Boc-Phe-OH) and N-(9-Fluorenylmethoxycarbonyl)- L-phenylalanine (Fmoc-Phe-OH) conjugates. Pluronic and Pluronic-amine stabilized PLGA NPs prepared by nanoprecipitation were characterized by dynamic light scattering and zeta potential measurements. All of the systems showed high colloidal stability checked by electrolyte induced aggregation, although the presence of Pluronicamine on the surface decreased the zeta potential in some extent. The introduction of reactive primary amine groups into the surface layer of PLGA NPs while preserving the aggregation stability, provides a possibility for coupling of various ligands allowing targeted delivery and also contributes to the improved membrane affinity of NPs.
... Although in certain cases, the reduction or even, if achievable, the prevention of protein and cellular adhesion is desirable, e.g., for antifouling surfaces and medical devices implanted into the bloodstream [13,[20][21][22][23][24], in most cases, such as medical implants designed to become assimilated with their host tissue, the http://dx.doi.org/10.1016/j.colsurfb.2014.07.015 0927-7765/© 2014 Elsevier B.V. All rights reserved. enhancement of surface adhesion is advantageous [2,13,25]. ...
... The activation and chemical coupling [9,10] yields a stable layer but is accompanied by partial degradation of the polyester. The PEG-containing triblock copolymer (Pluronic) proved to be an efficient surface modifier which can be applied in a blend form since it is miscible with PLGA in a certain concentration range depending on their composition [11][12][13]. The adsorption of Pluronic is however, the most simple and straightforward method to coat PLGA nanoparticles [5]. ...
... The hydrophobic PPO chains are anchored into the polymer matrix, while the hydrophilic PEO ends deploy into the surrounding aqueous environment, both at the implant surface or into the pores. The resulting hydrophilic coating of the surface might improve the biocompatibility of the system and hinder protein adsorption as proposed elsewhere [88]. At the same time, PEO segments can fill the pores thereby creating a diffusion barrier. ...
In situ forming implants (ISI) based on phase separation by solvent exchange represent an attractive alternative to conventional preformed implants and microparticles for parenteral applications. They are indeed easier to manufacture and their administration do not require surgery, therefore improving patient compliance. They consist of polymeric solutions precipitating at the site of injection and thus forming a drug eluting depot. Drug release from ISI is typically divided into three phases: burst during precipitation of the depot, diffusion of drug through the polymeric matrix and finally drug release by system degradation. This review gives a comprehensive overview on (i) the theoretical bases of these three phases, (ii) the parameters influencing them and (iii) the remaining drawbacks which have to be addressed to enlarge their commercial opportunities. Indeed, although some of them are already commercialized, ISI still suffer from limitations: mainly lack of reproducibility in depot shape, burst during solidification and potential toxicity. Nevertheless, depending on the targeted therapeutic application, these shortcomings may be transformed into advantages. As a result, keys are given in order to tailor these formulations in view of the desired application so that ISI could gain further clinical importance in the following years.
Surface modification of biomaterials is a strategy used to improve cellular and in vivo outcomes. However, most studies do not evaluate the lifetime of the introduced surface layer, which is an important aspect affecting how a biomaterial will interact with a cellular environment both in the short and in the long term. This study evaluated the surface layer stability in vitro in buffer solution of materials produced from poly(lactic-co-glycolic acid) (50:50) and polycaprolactone modified by hydrolysis and/or grafting of hydrophilic polymers using grafting from approaches. The data presented in this study highlight the shortcomings of using model substrates (e.g., spun-coated films) rather than disks, particles, and scaffolds. It also illustrates how similar surface modification strategies in some cases result in very different lifetimes of the surface layer, thus emphasizing the need for these studies as analogies cannot always be drawn.
Ellipsometry has a very high thin film sensitivity and can resolve sub-nm changes in the thickness of a protein film on a solid substrates. Being a technique based on photons in and photons out it can also be applied at solid-liquid interfaces. Ellipsometry has therefore found many in situ applications on protein layer dynamics but studies of protein layer structure are also frequent. Numerous ex situ applications on detection and quantification of protein layers are found and several biosensing concepts have been proposed. In this chapter, the use of ellipsometry in the above mentioned areas is reviewed and experimental methodology including cell design is briefly discussed. The classical ellipsometric challenge to determine both thickness and refractive index of a thin film is addressed and an overview of strategies to determine surface mass density is given. Included is also a discussion about spectral representations of optical properties of a protein layer in terms of a model dielectric function concept and its use for analysis of protein layer structure.
Amphiphilic hyperbranched polyglycerols (HbPG) were synthesized by dodecyl and octadecyl alcohols as direct initiators for the ring-opening multibranching polymerization of glycidol. These polymers possess molecular weight dependent surface activity, and are efficient surfactants and stabilizers for poly(lactic/glycolic acid) (PLGA) nanoparticles, opening new possibilities for functionalized drug carriers, targeting, imaging agents, etc.
Silicaatzirconiaatpoly(malic acid) nanocarriers of 110 nm mean diameter were designed, synthesized and characterized for the targeted delivery of diagnostic and therapeutic 99mTc to folate-overexpressing tumors. An important achievement was that a multifunctional l-(-)-malic-acid-based copolymer was formed in situ at the surface of the inorganic cores in a single synthetic step incorporating l-(-)-malic acid, β-cyclodextrin rings, folic acid moieties, and polyethylene glycol chains. Morphological and in-depth structural analysis of the particles proved their [email protected] structure. Stability experiments in aqueous media evidenced that stable suspensions can be obtained from the lyophilized powder in 10 mM phosphate buffer at pH 7.4. During 14-day degradation experiments, the nanoparticles were found to be slowly dissolving (including inorganic core) in saline and also in total cell medium. An in vitro toxicity assay on hepatocytes showed a concentration-dependent decrease of cell viability down to 63 ± 1% at the highest applied concentration (0.5 mg ml-1). Proof of concept experiments of technetium-99m radiolabelling and in vivo labelling stability are presented.
Ellipsometry has a very high thin film sensitivity and can resolve sub-nm changes in the thickness of a protein film on a solid substrates. Being a technique based on photons in and photons out it can also be applied at solid-liquid interfaces. Ellipsometry has therefore found many in situ applications on protein layer dynamics but studies of protein layer structure are also frequent. Numerous ex situ applications on detection and quantification of protein layers are found and several biosensing concepts have been proposed. In this chapter, the use of ellipsometry in the above mentioned areas is reviewed and experimental methodology including cell design is briefly discussed. The classical ellipsometric challenge to determine both thickness and refractive index of a thin film is addressed and an overview of strategies to determine surface mass density is given. Included is also a discussion about spectral representations of optical properties of a protein layer in terms of a model dielectric function concept and its use for analysis of protein layer structure.
Ellipsometry Applications in the Characterization of Polymer Blend Films Concluding Remarks Acknowledgments
Biodegradable polylactic/glycolic acid copolymers are widely used as colloidal drug delivery systems. PLGA nanoparticles were prepared using non-ionic, PEO-containing block copolymer (Pluronic) and charged polymeric (PEI) surface modifiers. Physicochemical properties such as size, size distribution, zeta potential, surface composition, and colloid stability were compared to their behavior at interfaces. Adhesion of the PLGA nanoparticles to solid surface, accumulation at water surface and their cell membrane affinity (using a Langmuir lipid monolayer as a model system) were characterized. Significant differences were observed in surface activity and adhesion as well as in membrane affinity of nanoparticles depending on their surface composition. The interplay of electrostatic and steric effects resulted in sufficient colloid stability and maximum membrane affinity for the system stabilized with the mixture of Pluronic and PEI.
Biodegradable PLGA is commonly employed for controlled drug release on the order of weeks to months. Hydrophobic drugs distribute homogeneously in PLGA, but their strong hydrophobic interaction typically results in narrow release profiles. In this study, three molecular weights (MW) and two different terminal end-groups of biodegradable PLGA were applied to broaden the range of drug release and vary the mechanical properties without the use of additives. Films knife-casted from PLGA polymers with terminal carboxylic acid end-groups were found to 1) absorb more water, 2) have higher rates of polymer mass loss, 3) increased hydrophobic drug release as compared to films knife casted from similar MW PLGA polymers with terminal ester end-groups. The highest drug release rates were obtained from low MW PLGA that had the densest surface concentration of terminal acid groups. An intermediate drug release profile was obtained with a blend of high and low MW PLGA. The various PLGA polymers (differing in MW, terminal groups, and combinations thereof) described herein could give rise to PLGA\PLGA blends that would allow independent tuning of drug release and mechanical properties without the inclusion of non-degradable additives with respect to hydrophobic, small molecule drugs.
The incorporation of low molecular weight drugs and therapeutic peptides into multilayer films assembled via the layer-by-layer technique can potentially provide means to deliver small molecules to target sites and to tune their release. This study describes the use of both hydrophobic and electrostatic interactions to incorporate a tridecapeptide antiinflammatory hormone, α-melanocyte stimulating hormone (α-MSH), as a building block at the base of a multilayer assembly of hyaluronic acid (HA) and chitosan (CS) on poly(lactic-co-glycolic acid) (PLGA) surfaces. A range of switching layers, including a neutral lipid, dioleylphosphatidylcholine (DOPC), a negatively charged lipid mixture DOPC/dioleylphosphatidylserine (DOPS) and a negatively charged polysaccharide, HA, were investigated for their ability to support subsequent HA and CS layers. Molecular dynamics simulations were performed to examine the structure and surface chemistry of α-MSH in solution and on surfaces to provide insights into the conditions most likely to support multilayer assembly. The multilayer assembly was stable at physiological pH and was successfully applied to particulate systems.
Biomaterials-related infections pose serious problems in implant surgery, despite the development of non-adhesive coatings. Non-adhesive coatings, like polymer brush-coatings, have so far only been investigated with respect to preventing initial bacterial adhesion, but never with respect to effects on kinetics of bacterial growth. Here, we compare adhesion and 20 h growth of three bacterial strains (Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa) on pristine and brush-coated silicone rubber in a parallel plate flow chamber. Brush-coatings were made using a tri-block copolymer of polyethylene oxide (PEO) and polypropylene oxide (PPO). Brush-coatings prevented adhesion of staphylococci to below 5 x 10(5)cm(-2) after 30 min, which is a 10-fold reduction compared to pristine silicone rubber. Biofilms grew on both brush-coated and pristine silicone rubber, while the viability of biofilms on brush-coatings was higher than on pristine silicone rubber. However, biofilms on brush-coatings developed more slowly and detached almost fully by high fluid shear. Brush-coating remained non-adhesive after S. epidermidis biofilm formation and subsequent removal whereas a part of its functionality was lost after removal of S. aureus biofilms. Adhesion, growth and detachment of P. aeruginosa were not significantly different on brush-coatings as compared with pristine silicone rubber, although here too the viability of biofilms on brush-coatings was higher. We conclude that polymer brush-coatings strongly reduce initial adhesion of staphylococci and delay their biofilm growth. In addition, biofilms on brush-coatings are more viable and easily removed by the application of fluid shear.
Poly(ethylene glycol) (PEG)-modified poly(lactic acid) (PLA) systems were created by physically entrapping the modifying species at the PLA surface. The surface characterization and biological performance of these materials are described. This modification strategy is performed by reversible gelation of the PLA surface following exposure to a solvent/nonsolvent mixture. PEG is then able to diffuse into the swollen surface region, before it is collapsed by the addition of more nonsolvent. This results in the localized physical entrapment of the diffused material. We have demonstrated by high-resolution X-ray photoelectron spectroscopy that control over the PEG surface density may be achieved by using predetermined process conditions, such as a particular solvent/nonsolvent ratio or a set polymer treatment time, and that surface coverage of around 75% is possible. Cell adhesion studies have shown that even in serum-containing media PEG entrapment will prevent attachment, with a 95% reduction in cell number compared to unmodified PLA. This modification strategy was also used to coentrap both PEG and poly(l-lysine)-RGD within the PLA surface region. The attachment of cells to this material shows that the entrapment approach may be used to create highly selective biomaterial surfaces that are able to prevent unwanted cell or protein adhesion yet actively promote specific cellular interaction.
Differential subshell photoionisation cross-sections, relative to F1s = 1.00, are derived from new and previously reported XPS (Mg Kα) peak i
A new family of branched polymers was synthesized for different biomedical applications such as the preparation of targeted nanoparticulate drug carriers. They are new copolymers of hydroxy-acids and allyl glycidyl ether. The functional groups (allyl-, hydroxyl- and carboxyl-) to which various groups will be grafted are linked to the polymer backbone. The resulting polymers were characterized by 1H NMR, 13C NMR, size exclusion chromatography (SEC), elemental analysis and differential scanning calorimetry (DSC). In vitro cytotoxicity assays were also conducted to ensure biocompatibility of the polymers. In order to obtain some structural evidences, different molecules have been grafted on the pendant groups. The method allows a rapid and easy synthesis of allyl-, hydroxyl- and carboxyl-branched degradable polymers for grafting various bioactive molecules.
A series of copolymers are reported, synthesized via the random copolymerization of acetic acid 5-acetoxy-6-oxotetrahydropyran-2-yl methyl ester (1), and S,S-lactide. The copolymers are characterized by 1H NMR spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and static water contact angle measurements. Four different copolymer compositions are obtained with 1 (RP1), 6 (RP2), 11 (RP3), and 25 wt % (RP4) of ring-opened monomer 1 incorporated with ring-opened S,S-lactide, and these are compared with a sample of poly(S,S-lactide) (P-S,S-LA) of related number-averaged molecular weight. As the loading of ring-opened monomer 1 increases, the glass transition temperatures of the copolymers decrease, in line with the values calculated using the Fox equation. The glass transition temperatures can, therefore, be controlled within the range 55 °C (RP1)−46 °C (RP4). The copolymers are spin-coated onto glass or electrospun into fibers and the static water contact angles determined. The static water contact angles, measured for either the fibers or the films, depend on the loading of ring-opened monomer 1 in the copolymers. The contact angle for RP4 is 7° lower than that of P-S,S-LA. The degradation of the copolymers is studied using size exclusion chromatography (SEC) conducted using samples in phosphate buffered chloroform solutions, enabling determination of the degradation rate constant. The degradation experiments show that as the loading of ring-opened monomer 1 in the copolymers increases, the degradation rate constants increase; thus, RP4 degrades 4 times faster than P-S,S-LA or RP1. Electrospun fibers of the copolymers are used to assess cell viability and growth. The viability of human osteogenic sarcoma Saos-2 cells on RP4 electrospun fibers is significantly higher than that on RP1, RP2, and P-S,S-LA fibers (p < 0.05).
Poly(L-lactic acid-co-L-lysine) [OCH(CH 3 )COOCH(CH 3 )CO] m [OCH(CH 3 )CONHCH([CH 2 ] 4 NH 2 )CO] n was synthesized by ring opening copolymerization of L,L-lactide with an urethane-protected 2,5-morpholinedione monomer. The polymer films degraded to half their original M w in 5 weeks when exposed to pH 7.1 in phosphate-buffered saline at 37°C with agitation.
A program for quantitative evaluation of x-ray photoelectron spectra has been developed to serve as a practical tool for surface chemists. The program uses the ‘classic’ approach of quantification and requires as input the integrated intensities of the measured XPS lines. The usual correction methods and factors can be applied and controlled independently. All necessary basic data for calculations are integrated into the main library of the program. Besides the usual ‘infinitely thick homogeneous sample’ geometry model, the program is able to calculate models for layered structures, both on flat and curved surfaces. Calculation for several samples or experimental data sets can be done together. Results can be presented in several forms, such as atomic %, atomic ratio, oxide molar ratio, etc., and can be stored, printed and charted. Data can be labelled and annotated. XPS MultiQuant is equipped with a user-friendly interface, full text help system and a ‘wizard’ for easy set-up of calculations. Copyright © 2004 John Wiley & Sons, Ltd.
The application of ellipsometry of the study of the adsorption behavior of proteins and synthetic macromolecules at the air-water interface has been investigated. It is shown that for macromolecules the amount adsorbed per unit area, Γ, as determined by ellipsometry, only has a well-defined physical meaning if the refractive-index increment remains constant up to high concentrations present in the adsorbed layer. It has been found experimentally that this conditioned is fulfilled for proteins. The ellipsometric Γ values of some protein agree satisfactorily with those obtained by two independent techniques has been used to investigate the adsorption from solution of κ-casein, bovine serum albumin, and polyvinyl alcohol. For bovine serum albumin, Γ reaches a plateau value of 2.9 mg/m2 for concentrations ≥ 0.05 wt%. The thickness of the adsorbed molecules. For κ-casein, Γ steadily increases with increasing centration and multilayers are formed. The technique provides interesting information on conformational changes in adsorbed macromolecules, on the rate of the process, and on the conditions under which these occur.
Radio frequency (RF) plasma treatment in O2 was applied to modify the surface of poly (l-lactic acid) (PLLA) and poly (d,l-lactic acid-coglycolic acid) (PLGA) as biodegradable polymers. The surface structure, morphology, wettability and surface chemistry of treated films were characterized by water drop contact angle measurement, scanning electron microscope (SEM), optical invert microscope, differential scanning calorimetry (DSC) and ATIR–FTIR spectroscopy. The cell affinity of the oxygen plasma treated film was evaluated by nervous tissue B65 cell culture in stationary conditions. The results showed that the hydrophilicity increased greatly after O2 plasma treatment. The results showed that improved cell adhesion was attributed to the combination of surface chemistry and surface wettability during plasma treatment. Cell culture results showed that B65 nervous cell attachment and growth on the plasma treated PLLA was much higher than an unmodified sample and PLGA. Surface hydrophilicity and chemical functional groups with high polar component play an important role in enhancing cell attachment and growth.
An overview of recent advances in the surface modification of colloidal particles to oppose uptake by the mononuclear phagocyte system (MPS) is presented. First, we describe the colloidal particles and hydrophilic coating materials investigated, with particular focus on the literature concerning particles other than liposomes. Then the pharmacokinetics and biodistribution of these MPS-opposing systems are summarized. Finally, the mechanism behind the MPS-avoidance phenomenon is discussed in the light of the concept of steric stabilization. We conclude that the literature reviewed provides enough promise for anticipating therapeutic and diagnostic applications of surface-modified nanoparticles.
Poly(lactic acid) or polylactide (PLA) is the most extensively researched and utilized biodegradable and renewable thermoplastic polyester, with potential to replace conventional petrochemical-based polymers. In recent times, several PLA-based technologies have emerged with an emphasis on achieving chemical, mechanical, and biological properties equivalent or superior to conventional polymers. The frequent need for a chemical or physical modification of PLA to achieve suitable properties for its intended consumer and biomedical applications, however, has demanded significant attention in the last decade. In the first part of this review, we briefly discuss the advantages, limitations, production methods, and applications of unmodified PLA. The second part, the major objective of this paper, focuses on the various bulk and surface-modification strategies used to date and their basic principles, drawbacks, and achievements.
The relative intensities of photoelectron lines is discussed. The relationship of observed intensities to angle of observation is considered as are the errors introduced by ignoring the fact that different lines may have different angular distributions. Tables of theoretical results for the angular distribution asymmetry parameter, [beta], are presented for incident Al K[alpha], Mg K[alpha], and Zr M[zeta] radiation for all atomic ground state subshells of non-zero angular momentum. The application of these results to molecules is discussed.
Interaction of bovine serum albumin (BSA) with poly(lactic acid) (PLA) layers mixed with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers (Pluronic) at air/solution interfaces was studied by the Langmuir balance technique. Wettability of the mixed PLA-Pluronic system was characterized in the form of a transferred one-layer Langmuir-Blodgett film, and considerable hydrophilization was obtained for all of the Pluronics (6400, 6800, 10500, and 12700) applied here. The density of PEO chains in the monolayer and hence the coverage of PLA was controlled by the composition and the compression of the mixed monolayers. Tensiometric investigations revealed that a significant reduction of BSA adsorption/penetration was achieved by applying the Pluronic 6800 and 12700 with long PEO blocks for hydrophilization of PLA. Interaction of BSA with the modified PLA monolayer depended on the density and length of the PEO chains. The surface morphological characteristics of the films determined by atomic force microscopy were in good correlation with the results of BSA interaction. The average roughness of the polymer LB layer was high due to BSA penetration into the PLA film, while smooth surfaces with small roughness were obtained when the PLA layer was modified by Pluronic 6800.
Research on quantitative control of targeting effect for the drug delivery system of ligand-conjugated nanoparticles of biodegradable polymers is at the cutting edge in the design of drug delivery device. In this work, we developed a post-conjugation strategy, which makes the ligand conjugation after the preparation of the drug-loaded nanoparticles of two copolymers blend. We synthesized the PLGA-PEG copolymer with PEG functioning as the linker molecule needed for herceptin conjugation. Docetaxel-loaded nanoparticles of the PLGA-PEG/PLGA copolymer blend were prepared by the nanoprecipitation method. Anti-HER2 antibody (heceptin), which targets the breast cancer cells of HER2 receptor overexpression, was conjugated on the drug-loaded PLGA-PEG/PLGA nanoparticles for sustained, controlled and targeted delivery of docetaxel. We demonstrated that the targeting effect can be quantitatively controlled by two ways, i.e. (1) adjusting the copolymer blend ratio of the nanoparticle matrix, which showed within the range of 20% PLGA/PEG in the copolymer blend a linear relation with the ligand density on the nanoparticle surface, and (2) adjusting the herceptin feed molar ratio to NH2 in the linker molecules appearing on the nanoparticle surface, which also showed a linear relation. Compared with the pre-conjugation strategy developed recently in the literature, in which the ligand was firstly conjugated onto the PLGA-PEG copolymer before preparation of the nanoparticles of the PLGA-PEG/PLGA copolymer blend, the post-conjugation strategy provides more efficient use of the ligand and protects its bioactivity in the nanoparticle preparation process, thus resulting in much better performance in drug targeting, which was assessed in vitro with SK-BR-3 breast cancer cells of HER2 receptor overexpression and MCF7 breast cancer cells of HER2 receptors moderate expression.
Biodegradable polyesters such poly(lactic acid) and poly(lactic/glycolic acid) (PLGA) copolymers are preferred biomaterials and used among others as drug delivery systems, although their surface hydrophobicity limits their application. In this work, chemical modification of the PLGA surface was developed by coupling of either linear or starlike poly(ethylene glycol) (PEG) molecules via chemical bonds to the PLGA surface following amino functionalization as a first step to improve its biocompatibility. The chemical attachment was followed by detailed X-ray photoelectron spectroscopy (XPS) studies. It was shown that substantial modification can be achieved by linear PEG, but even higher surface coverage with hydrophilic groups can be obtained when the six-armed PEG is applied with the additional advantage of possible further functionalization via free amino groups available on the surface of the latter. As a final goal, a significant increase of water wettability together with reduced protein adsorption was achieved on PEG-coupled PLGA surfaces.
Triblock copolymers of polyethylene oxide (PEO) and polypropylene oxide (PPO), that is, PEOn-PPOm-PEOn, better known as Pluronic can adsorb to surfaces in either a pancake or a brushlike configuration. The brushlike configuration is advantageous in numerous applications, since it constitutes a surface repellent to proteins and microorganisms. The conformation of the adsorbed Pluronic layer depends on the hydrophobicity of the substratum surface, but the hydrophobicity threshold above which a brushlike conformation is adopted is unknown. Therefore, the aim of this study is to investigate Pluronic F-127 adsorption on surfaces with different hydrophobicities using a quartz crystal microbalance with dissipation. Adsorption in a brushlike conformation occurred on surfaces with a water contact angle above 80 degrees , as inferred from the thickness, viscosity, and elasticity of the adsorbed layer. The concentration of Pluronic F-127 in solution affected only the kinetics of adsorption and not the final layer thickness or conformation of adsorbed Pluronic molecules.
The adsorption of four different amphiphilic polymers to a model surface has been studied, and the effects of the adsorbed amphiphiles on the subsequent adsorption of fibrinogen (Fg) and human serum albumin (HSA) at the surfaces were investigated. The amphiphilic polymers were one commercially available ABA block copolymer, Pluronic PE9400 (PE94), composed of poly(ethylene oxide) (A-blocks) and poly(propylene oxide) (B-block), and three graft copolymers, two with backbones of poly(styrene-co-acrylamide) (STY) and one with a backbone of poly(methyl methacrylate-co-ethylhexyl methacrylate) (ACRY). The backbones carried poly(ethylene oxide) (PEO) grafts. The model surface was a hydrophobic methylated silica surface (HMS). The amphiphilic polymers were adsorbed at the HMS surface from an ethanol/water solution. The adsorption process was monitored by ellipsometry. After rinsing with phosphate buffered saline (PBS), protein was added and the continued adsorption measured by ellipsometry. Surfaces modified by adsorption of the amphiphilic polymers were also characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS). According to these measurements the amphiphilic polymers adsorbed in significant amounts at the HMS surface. A limited study by atomic force microscopy (AFM), as well as the XPS measurements, suggests that both single molecules and micellar aggregates adsorb at the surface. ACRY and PE94 gave the highest levels of adsorption. As compared to the Pluronic block copolymer the graft copolymers were more strongly attached to the HMS surface, as shown by less desorption on rinsing with solvent. The ellipsometric results show that the adsorption of HSA and Fg at HMS surfaces containing preadsorbed amphiphilic polymer was significantly reduced as compared to the bare HMS surface. ACRY and PE94 showed the largest effects. Both polymers gave more than a 20-fold reduction of the Fg adsorption and a 10-fold reduction of the HSA adsorption. The STY polymers reduced the protein adsorption by a factor of 2-3.
In accordance with earlier observations, a single intravenous injection of long circulatory poloxamine-908-coated polystyrene particles to rats dramatically affected the circulation half-life and body distribution of a second dose when administered 10 days later. Both liver and spleen macrophages recognised and cleared from the blood the majority of the second dose of poloxamine-908-coated particles. The second dose of poloxamine-908-coated particles, however, regained their long circulatory behaviour when administered 1-3 h after a bolus intravenous injection of 30 mg free poloxamine-908 or poloxamer-407 (in saline)/150 g body weight. When the interval between free copolymer and particle administration was increased to 24 h then macrophage-rich organs were able to extract poloxamine-coated beads from the blood. In contrast to poloxamine-908 and poloxamer-407, prior administration of poloxamer-188 and polyethyleneglycol-20000 also failed to restore the long circulatory behaviour of the second dose of poloxamine-908-coated particles. These observations are of interest in experimental drug delivery, particularly in experimental cancer therapy (diagnostic imaging and drug delivery), involving multiple injections of poloxamine-based long circulating nanosized vehicles.
The objective of this study was to investigate the efficiency of two treatments for poly(D,L-lactic acid) (PDLLA) surface modification using silk fibroin. one chemical treatment and one physical treatment: 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (WSC) and entrapment. The properties of control films, WSC-modified and entrapment-treated PDLLA films were investigated by water contact angle measurement and electron spectroscopy for chemical analysis (ESCA). The water-contact angle measurement indicated the change of hydrophilicity and the ESCA analysis suggested that the modified PDLLA film using silk fibroin became enriched with nitrogen atoms. The biocompatibility of PDLLA film might be altered, which in turn would affect the functions of cells that were seeded on it. Therefore, attachment and proliferation of osteoblasts that were seeded on modified PDLLA films and control films were examined. Cell viability was evaluated by the MTT assay and differentiated cell function was assessed by measuring alkaline phosphatase activity. These results suggested that silk fibroin was used to modify PDLLA surface via WSC and that entrapment could improve the interactions between osteoblasts and PDLLA films. The entrapment treatment was more effective thin WSC treatment to accomplish the goal of surface modification.
Surface properties of poly (D,L-lactide) (PDLLA) were modified by combining plasma treatment and collagen modification. The changes of surface properties were characterized by contact angles, surface energy, X-ray photoelectron spectra and scanning electron microscopy. The mouse 3T3 fibroblasts were used as model cells to evaluate the cell affinity of PDLLA before and after modification. Effects of different modification methods including plasma treatment, collagen coating and combining plasma treatment with collagen anchorage were investigated and compared. The results showed that the hydrophilicity and surface-free energy were improved and reduced, respectively, after each modification. Plasma pre-treatment could improve the roughness as it incorporated the polar groups and positively charged groups onto the sample surface; so the plasma pre-treated surface would benefit in anchoring more collagen tightly. As a result, cell affinity of PDLLA modified by combining plasma treatment with collagen anchorage was greatly improved. The modified materials could endure rinsing by PBS, which would facilitate further application when the modified materials were used as cells scaffold in tissue engineering.
The structure of the adsorbing layers of native and denatured proteins (fibrinogen, gamma-immunoglobulin, albumin, and lysozyme) was studied on hydrophilic TiO(2) and hydrophobic Teflon-AF surfaces using the quartz crystal microbalance with dissipation and optical waveguide lightmode spectroscopy techniques. The density and the refractive index of the adsorbing protein layers could be determined from the complementary information provided by the two in situ instruments. The observed density and refractive index changes during the protein-adsorption process indicated the presence of conformational changes (e.g., partial unfolding) in general, especially upon contact with the hydrophobic surface. The structure of the formed layers was found to depend on the size of the proteins and on the experimental conditions. On the TiO(2) surface smaller proteins formed a denser layer than larger ones and the layer of unfolded proteins was less dense than that adsorbed from the native conformation. The hydrophobic surface induced denaturation and resulted in the formation of thin compact protein films of albumin and lysozyme. A linear correlation was found between the quartz crystal microbalance measured dissipation factor and the total water content of the layer, suggesting the existence of a dissipative process that is related to the solvent molecules present inside the adsorbed protein layer. Our measurements indicated that water and solvent molecules not only influence the 3D structure of proteins in solution but also play a crucial role in their adsorption onto surfaces.
The aim of the present work was the design of novel nanoparticle compositions based on poly(lactic acid/glycolic acid) (PLGA): poloxamer and PLGA: poloxamine blend matrices. For this purpose, we have applied a modified solvent diffusion technique that allows the preparation of the nanoparticles without the use of high energy sources. Nanoparticles have been prepared with different PLGA: poloxamer and PLGA: poloxamine ratios using PEO-derivatives with different molecular weights (Mw) and hydrophilia-lipophilia balance (HLB) values. Our results show that the physicochemical characteristics of the nanoparticles, such as size and zeta potential, are influenced by the type of PEO-derivative associated to the PLGA matrix. The 1H-NMR analysis of the different nanoparticle compositions showed that the extent of incorporation of the PEO-derivative depends strongly on its HLB and also on the nanoparticles preparation conditions. The capacity of these nanoparticles as drug delivery devices was evaluated using bovine insulin as a model drug. The insulin-encapsulation efficiency was shown to be dependent on the composition of the nanoparticles, those containing hydrophilic PEO-derivatives being the most effective in entrapping the drug molecules. The formation of the blend system displayed positive effects on the release characteristics of the nanoparticles. Nanoparticles exhibited a reduced initial burst and a nearly linear, constant release rate over a time period of two weeks.
Poly(lactic acid) (PLA) and poly(lactic/glycolic acid) copolymers (PLGA) are biodegradable drug carriers of great importance, although successful pharmaceutical application requires adjustment of the surface properties of the polymeric drug delivery system to be compatible with the biological environment. For that reason, reduction of the original hydrophobicity of the PLA or PLGA surfaces was performed by applying a hydrophilic polymer poly(ethylene oxide) (PEO) with the aim to improve biocompatibility of the original polymer. PEO-containing surfaces were prepared by incorporation of block copolymeric surfactants, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic), into the hydrophobic surface. Films of polymer blends from PLA or PLGA (with lactic/glycolic acid ratios of 75/25 and 50/50) and from Pluronics (PE6800, PE6400, and PE6100) were obtained by the solvent casting method, applying the Pluronics at different concentrations between 1 and 9.1% w/w. Wettability was measured to monitor the change in surface hydrophobicity, while X-ray photoelectron spectroscopy (XPS) was applied to determine the composition and chemical structure of the polymer surface and its change with surface modification. Substantial reduction of surface hydrophobicity was achieved on both the PLA homopolymer and the PLGA copolymers by applying the Pluronics at various concentrations. In accordance with the wettability changes the accumulation of Pluronics in the surface layer was greatly affected by the initial hydrophobicity of the polymer, namely, by the lactide content of the copolymer. The extent of surface modification was also found to be dependent on the type of blended Pluronics. Surface activity of the modifying Pluronic component was interpreted by using the solubility parameters.
While biodegradable, biocompatible polyesters such as poly (lactic-co-glycolic acid) (PLGA) are popular materials for the manufacture of tissue engineering scaffolds, their surface properties are not particularly suitable for directed tissue growth. Although a number of approaches to chemically modify the PLGA surface have been reported, their applicability to soft tissue scaffolds, which combine large volumes, complex shapes, and extremely fine structures, is questionable. In this paper, we describe two wet-chemical methods, base hydrolysis and aminolysis, to introduce useful levels of carboxylic acid or primary and secondary amine groups, respectively, onto the surface of PLGA with minimal degradation. The effects of temperature, concentration, pH, and solvent type on the kinetics of these reactions are studied by following changes in the wettability of the PLGA using contact angle measurements. In addition, the treated surfaces are studied using X-ray photoelectron spectroscopy (XPS) to determine the effect on the surface chemical structure. Furthermore, we show using XPS analysis that these carboxyl and amine groups are readily activated to allow the covalent attachment of biological macromolecules.
The present work focus on the adsorption of fibrinogen (Fgn) on to the semi-interpenetrating polymer networks (IPNs) of polyethylene glycol (PEG) and poly(2-hydroxyethyl methacrylate-co-acrylonitrile) and attempts to correlate the adsorption behaviour of proteins to the blood compatible aspects of the polymeric surfaces. The semi-IPNs were prepared by copolymerizing 2-hydroxyethyl methacrylate and acrylonitrile in the presence of PEG and a crosslinker ethyleneglycol dimethacrylate (EGDMA). The prepared spongy gels were characterized by FTIR and Environmental Scanning Electron Microscopy (ESEM) for structural and morphological analysis. The prepared semi IPNs were studied for their water sorption capacity and the data were utilized to evaluate network parameters such as average molecular weight between crosslinks (M(c)) and crosslink density (q). The adsorption of Fgn was carried out on to the prepared polymeric matrices and static and dynamic aspects of the adsorption process were investigated. The adsorption process was also studied as a function of pH and ionic strength of the protein solution and chemical architecture of the semi IPN. The antithrombogenic properties of the IPN's were also judged and correlated with water sorption and protein adsorption findings.
A clear understanding of the mechanisms responsible for the protein-resistant nature of end-tethered poly(ethylene oxide) (PEO) surfaces remains elusive. A barrier to improved understanding is the fact that many of the factors involved (chain length, chain density, hydration, conformation, and distal chemistry) are inherently correlated. We hypothesize that, by comparing systems of variable but precisely known chain density, it should be possible to gain additional insight into the effects of the other factors. To evaluate this hypothesis, chain-end-thiolated PEOs were chemisorbed to gold-coated silicon wafers such that a range of chain densities was obtained. Three different PEOs were investigated: hydroxy-terminated chains of molecular weight 600 (600-OH), methoxy-terminated chains of molecular weight 750 (750-OCH3), and methoxy-terminated chains of molecular weight 2000 (2000-OCH3). In situ null ellipsometry was used to determine PEO chemisorption kinetics, ultimate PEO chain densities, protein adsorption kinetics, and ultimate protein adsorbed quantities. With this approach, it was possible to ascertain the effects of PEO distal chemistry (-OH, -OCH3), chain length, and layer hydration on protein adsorption. The data obtained suggested that properties related to chain density (conformational freedom, hydration) were the main determinants of protein resistance at chain densities up to a critical value of approximately 0.5 chain/nm2; at this value, protein adsorption was a minimum for the methoxy-terminated PEOs. For the hydroxyl-terminated PEO, adsorption leveled off at the critical value. Thus distal chemistry appears to be a major determinant of protein resistance at chain densities greater than the critical value.
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