Hydrophilic sponges based on 2-hydroxyethyl methacrylate. I. effect of monomer mixture composition on the pore size

Antiswelling Photochromic Hydrogels for Underwater Optically Camouflageable Flexible Electronic Devices

Optical camouflage offers an effective strategy for enhancing the survival chances of underwater flexible electronic devices akin to underwater organisms. Photochromism is one of the most effective methods to achieve optical camouflage. In this study, antiswelling hydrogels with photochromic properties were prepared using a two-step solvent replacement strategy and explored as underwater optically camouflaged flexible electronic devices. The hydrophobic network formed upon polymerization of hydroxyethyl methacrylate (HEMA) ensured that the hydrogels possessed outstanding antiswelling properties. Internetwork hydrogen bonding interactions allowed the hydrogels to exhibit tissue-adaptable mechanical properties and excellent self-bonding capabilities. The introduction of polyoxometalates further enhanced the hydrogels' mechanical and self-bonding properties while imparting photochromic capability. The hydrogels could be rapidly and reversibly colored under 365 nm UV irradiation. The bleaching rate of the colored hydrogels increased with temperature, bleaching within 12 h at 60 °C but maintaining the color for more than 5 days at room temperature. The self-bonding and photochromic properties enabled the hydrogels to be easily assembled into optically camouflaged underwater flexible electronic devices for underwater motion sensing and wireless information transmission. An optically camouflaged strain sensor was first assembled for underwater limb motion sensing. Additionally, an underwater optically camouflaged wireless information exchange device was assembled to enable wireless communication with a smartphone. This work provided an effective strategy for the optical camouflage of underwater flexible electronic devices, presenting opportunities for next-generation underwater hydrogel-based flexible devices.

Easy-to-Prepare Flexible Multifunctional Sensors Assembled with Anti-Swelling Hydrogels

Recent years have witnessed the development of flexible electronic materials. Flexible electronic devices based on hydrogels are promising but face the limitations of having no resistance to swelling and a lack of functional integration. Herein, we fabricated a hydrogel using a solvent replacement strategy and explored it as a flexible electronic material. This hydrogel was obtained by polymerizing 2-hydroxyethyl methacrylate (HEMA) in ethylene glycol and then immersing it in water. The synergistic effect of hydrogen bonding and hydrophobic interactions endows this hydrogel with anti-swelling properties in water, and it also exhibits enhanced mechanical properties and outstanding self-bonding properties. Moreover, the modulus of the hydrogel is tissue-adaptable. These properties allowed the hydrogel to be simply assembled with a liquid metal (LM) to create a series of structurally complex and functionally integrated flexible sensors. The hydrogel was used to assemble resistive and capacitive sensors to sense one-, two-, and three-dimensional strains and finger touches by employing specific structural designs. In addition, a multifunctional flexible sensor integrating strain sensing, temperature sensing, and conductance sensing was assembled via simple multilayer stacking to enable the simultaneous monitoring of underwater motion, water temperature, and water quality. This work demonstrates a simple strategy for assembling functionally integrated flexible electronics, which should open opportunities in next-generation electronic skins and hydrogel machines for various applications, especially underwater applications.

Tuning the softness of poly(2-hydroxyethyl methacrylate) nanocomposite hydrogels through the addition of PEG coated nanoparticles

HYPOTHESIS

In nanocomposites, several factors govern the enhancement of properties when a nanofiller is added into a polymer matrix. Previously, our group have demonstrated that stabilizing nanoparticles improves the dispersion of nanoparticles in a hydrogel, but their effect on viscoelastic properties remain unclear. We hypothesized that coating the nanoparticles will block matrix-nanoparticle interactions, which would then affect the transfer of stress when the hydrogel is subjected to stress.

EXPERIMENT

To this end, we investigated the effects that nanofillers coated with polyethylene glycol (PEG) of variable molar mass have on the properties of physical hydrogels made from poly(2-hydroxyethyl methacrylate). PEG with molar masses of 6, 20, and 35 kDa were used at different concentrations and the viscoelastic properties of the resulting hydrogels were studied and compared with control hydrogels with and without nanofillers.

FINDINGS

The coated nanofiller resulted in enhanced dispersion stabilization as the molar mass and concentration of the PEG increased. However, there were noticeable changes in viscoelastic properties. In general, the nanocomposite hydrogels exhibited reduced shear modulus, greater creep, and more accentuated shear thinning behaviour. These effects were attributed to hindered matrix-nanoparticle interactions because of the PEG coating, an increased slippage of the PHEMA chains as well as a plasticizing effect.

Heparin-functionalized hydrogels as growth factor-signaling substrates

Tuneable, bioactive hydrogels present an attractive option as cell-instructive substrates for tissue regeneration. Properties mimicking the extracellular matrix at the site of injury are sought after, in particular the ability to regulate growth factors that are key to the regeneration process. This study demonstrates the successful formation of hydrogels with heparin functionalities and fibroblast growth factor-2 (FGF-2). Poly(2-hydroxyethyl methacrylate)-heparin hydrogels were capable of retaining FGF-2 by specific binding to heparin and subsequently showed sustained presentation of the growth factor to mesenchymal stromal cells (MSC). Heparin acted as stable anchoring molecules for FGF-2 on the substrate and the synergistic effect of the ensuing heparin-FGF-2 complex was evident in supporting long term cell growth. The presence of heparin during 3D scaffold formation was also found to introduce surface roughness and microporosity to the resulting hydrogels. While FGF-2 has been known to encourage MSC growth and maintain their multilineage potential, other heparin-binding ligands such as bone morphogenetic proteins are potent differentiation stimuli for MSC. Therefore preserving MSC multipotency or a push toward a differentiation pathway may be pursued by the choice of ligand applied to and bound by the heparin functionalities on the current substrate.

Amphipathic Substrates Based on Crosslinker-Free Poly(ε-Caprolactone):Poly(2-Hydroxyethyl Methacrylate) Semi-Interpenetrated Networks Promote Serum Protein Adsorption

A simple procedure has been developed to synthesize uncrosslinked soluble poly(hydroxyethyl methacrylate) (PHEMA) gels, ready for use in a subsequent fabrication stage. The presence of 75 wt % methanol (MetOH) or dimethylformamide (DMF) impedes lateral hydroxyl–hydroxyl hydrogen bonds between PHEMA macromers to form during their solution polymerization at 60 °C, up to 24 h. These gels remain soluble when properly stored in closed containers under cold conditions and, when needed, yield by solvent evaporation spontaneous physically-crosslinked PHEMA adapted to the mould used. Moreover, this two-step procedure allows obtaining multicomponent systems where a stable and water-affine PHEMA network would be of interest. In particular, amphiphilic polycaprolactone (PCL):PHEMA semi-interpenetrated (sIPN) substrates have been developed, from quaternary metastable solutions in chloroform (CHCl₃):MetOH 3:1 wt. and PCL ranging from 50 to 90 wt % in the polymer fraction (thus determining the composition of the solution). The coexistence of these countered molecules, uniformly distributed at the nanoscale, has proven to enhance the number and interactions of serum protein adsorbed from the acellular medium as compared to the homopolymers, the sIPN containing 80 wt % PCL showing an outstanding development. In accordance to the quaternary diagram presented, this protocol can be adapted for the development of polymer substrates, coatings or scaffolds for biomedical applications, not relying upon phase separation, such as the electrospun mats here proposed herein (12 wt % polymer solutions were used for this purpose, with PCL ranging from 50% to 100% in the polymer fraction).

Biomimetic modification of dual porosity poly(2-hydroxyethyl methacrylate) hydrogel scaffolds-porosity and stem cell growth evaluation

The macroporous synthetic poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels as 3D cellular scaffolds with specific internal morphology, so called dual pore size, were designed and studied. The morphological microstructure of hydrogels was characterized in the gel swollen state and the susceptibility of gels for stem cells was evaluated. The effect of specific chemical groups covalently bound in the hydrogel network by copolymerization on cell adhesion and growth, followed by effect of laminin coating were investigated. The evaluated gels contained either carboxyl groups of the methacrylic acid or quaternary ammonium groups brought by polymerizable ammonium salt or their combinations. The morphology of swollen gel was visualized using the laser scanning confocal microscopy. All hydrogels had very similar porous structures - their matrices contained large pores (up to 10² μm) surrounded with gel walls with small pores (10⁰ μm). The total pore volume in hydrogels swollen in buffer solution ranged between 69 and 86 vol%. Prior to the seeding of the mouse embryonal stem cells, the gels were coated with laminin. The hydrogel with quaternary ammonium groups (with or without laminin) stimulated the cell growth the most. The laminin coating lead to a significant and quaternary ammonium groups. The gel chemical modification influenced also the topology of cell coverage that ranged from individual cell clusters to well dispersed multi cellular structures. Findings in this study point out the laser scanning confocal microscopy as an irreplaceable method for a precise and quick assessment of the hydrogel morphology. In addition, these findings help to optimize the chemical composition of the hydrogel scaffold through the combination of chemical and biological factors leading to intensive cell attachment and proliferation.

Synthesis and Examination of Nanocomposites Based on Poly(2-hydroxyethyl methacrylate) for Medicinal Use

Preparation of poly(2-hydroxyethyl methacrylate) (PHEMA) based nanocomposites using different approaches such as synthesis with water as the porogen, filling of polymer matrix by silica and formation of interpenetrating polymer networks with polyurethane was demonstrated. Incorporation of various biologically active compounds (BAC) such as metronidazole, decamethoxin, zinc sulphate, silver nitrate or amino acids glycine and tryptophan into nanocomposites was achieved. BAC were introduced into the polymer matrix either (1) directly, or (2) with a solution of colloidal silica, or (3) through immobilization on silica (sol-densil). Morphology of prepared materials was investigated by laser scanning microscopy and low-vacuum scanning electron microscopy. In vacuum freeze-drying, prior imaging was proposed for improving visualization of the porous structure of composites. The interaction between PHEMA matrix and silica filler was investigated by IR spectroscopy. Adsorption of 2-hydroxyethyl methacrylate and BAC from aqueous solution on the silica surface was also examined. Phase composition and thermal stability of composites were studied by the differential thermogravimetry/differential thermal analysis. Release of BAC into water medium from prepared composites were shown to depend on the synthetic method and differed significantly. Obtained PHEMA-base materials which are characterized by controlled release of BAC have a strong potential for application in manufacturing of different surgical devices like implants, catheters and drainages.

Systematic evaluation of pH and thermoresponsive poly(n-isopropylacrylamide-chitosan-fluorescein) microgel

The interesting properties of stimuli-responsive polymers lead to a wide range of possibilities in design and engineering of functional material for the biomedical application. A systematic approach focused on the evaluation of the physical properties of multiresponse (pH and temperature) PNIPAM was reported in this work. The effect of three different molar ratios of poly(n-isopropylacrylamide): chitosan (1:49, 1:99 and 1:198) were evaluated and labeled correspondingly as PC1F, PC2F, and PC3F. An increase in the lower critical solution temperature (LCST) of sample PC1F (34°C) was observed by differential scanning calorimetry (DSC). The presence of low molecular weight chitosan (LMWC) full-interpenetrating polymer (Full-IPN) segments in poly(n-isopropylacrylamide) was confirmed by Fourier-transform infrared spectroscopy (FT-IR). The hydrogel’s water capture was analyzed by two models of swelling, the power law model and a model that considers the relaxation of polymeric chains of the hydrogel, finding good correlations with experimental data in both cases. Sample PC3F resulted with higher swellability, increasing the weight of the hydrogel around seven times. Hydrogel pH-sensibility was confirmed placing the samples at different pH environments, with an apparent increase in swellability for acidic conditions, confirming the highest swellability for sample PC3F, due to hydrogen bonds boosted by chitosan high molar ratio. Based on these results, the hydrogel obtained has potential as a thermo-pH triggered hydrogel in drug delivery applications.

Water-dependent Interfacial Transition Zone in Resin-modified Glass-ionomer Cement/Dentin Interfaces

The function of the interfacial transition zone (absorption layer) in resin-modified glass-ionomer cements bonded to deep dentin remains obscure. This study tested the hypotheses that the absorption layer is formed only in the presence of water derived from hydrated dentin and allows for better bonding of resin-modified glass-ionomer cements to dentin. Ten percent polyacrylic acid-conditioned, hydrated, and dehydrated deep dentin specimens were bonded with 2 resin-modified glass-ionomer cements and sealed with resins to prevent environmental water gain or loss. A non-particulate absorption layer was identified over hydrated dentin only, and was clearly discernible from the hybrid layer when bonded interfaces were examined with transmission electron microscopy. This layer was relatively more resistant to dehydration stresses, and remained intact over the dentin surface after tensile testing. The absorption layer mediates better bonding of resin-modified glass-ionomer cements to deep dentin, and functions as a stress-relieving layer to reduce stresses induced by desiccation and shrinkage.

The influence of intrinsic water permeation on different dentin bonded interfaces formation

OBJECTIVES

To determine the effects of intrinsic wetness on the formation of dentin bonding interfaces of four resin cement systems bonded to dentin under different pulpal pressures.

METHODS

Thirty-six freshly extracted third molars were selected and processed for dentin μTBS. The teeth were randomly assigned into 12 experimental groups, according to the adhesive luting system [Adper Single Bond Plus (3M ESPE) combined with two luting agents RelyX ARC (3M ESPE) and heated Filtek Z250 Universal Restorative (3M ESPE), Clearfil CD Bond (Kuraray) combined with Clearfil Esthetic Cement (Kuraray), and RelyX Unicem 2 Automix (3M ESPE)] and pulpal pressure (0, 5, and 20 cm of simulated pulpal pressure). Leucite-reinforced glass-ceramic slabs (IPS Empress CAD, Ivoclar Vivadent) of 3mm thickness were bonded to dentin. The samples were stored in distilled water for 24h and then sectioned in X/Y directions across the adhesive interface to obtain specimens with a cross section of 0.8 ± 0.2mm(2). All sticks were fractured by tension at a crosshead speed of 1.0mm/min and the data were submitted to Kruskal-Wallis and Mann-Whitney Tests (α=0.05). Ultrastructural analysis of the interfaces was performed using Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM).

RESULTS

The statistical analyses showed that pulpal pressure decreased μTBS for all groups. Significantly higher μTBS values were obtained in heated Z250 group restored without any pulpal pressure. CLSM showed that the uptake of water through the dentin tubuli and their anastomosis of lateral branches during the adhesive luting procedures prevented adequate formation of the dentin bonding interfaces. SEM showed that the luting film created is material- dependent and all adhesive failure occurred at the resin-dentin interface.

CONCLUSION

The constant intrinsic wetness replenishment prevents adequate formation of the hybrid layer.

CLINICAL SIGNIFICANCE

Intrinsic moisture during adhesive luting procedures significantly affects the interaction between luting materials and dentin subtract and decreases the quality and bonding strength of the resin-dentin bond.

Microdynamics mechanism of D2O absorption of the poly(2-hydroxyethyl methacrylate)-based contact lens hydrogel studied by two-dimensional correlation ATR-FTIR spectroscopy

A good understanding of the microdynamics of the water absorption of poly(2-hydroxyethyl methacrylate) (PHEMA)-based contact lens is significant for scientific investigation and commercial applications. In this study, time-dependent ATR-FTIR spectroscopy combined with the perturbation correlation moving-window two-dimensional (PCMW2D) technique and 2D correlation analysis was used to study the microdynamics mechanism. PCMW2D revealed that D2O took 3.4 min to penetrate into the contact lens. PCMW2D also found the PHEMA-based contact lens underwent two processes (I and II) during D2O absorption, and the time regions of processes I and II are 3.4-12.4 min and 12.4-57.0 min. According to 2D correlation analysis, it was proved that process I has 5 steps, and process II has 3 steps. For process I, the first step is D2O hydrogen-bonding with "free" C[double bond, length as m-dash]O in the side chains. The second step is the hydrogen bond generation of the O-HO-D structure between D2O and "free" O-H groups in the side chain ends. The third step is the hydrogen bond generation of D2O and the "free" C[double bond, length as m-dash]O groups close to the crosslinking points in the contact lens. The fourth and the fifth steps are the hydration of -CH3 and -CH2- groups by D2O, respectively. For process II, the first step is the same as that of process I. The second step is the hydrogen bonds breaking of bonded O-H groups and the deuterium exchange between D2O and O-H groups in the side chain ends. The third step is also related to the deuterium exchange, which is the hydrogen bonds regeneration between the dissociated C[double bond, length as m-dash]O groups and the new O-D.

A Stiff Injectable Biodegradable Elastomer

Injectable materials often have shortcomings in mechanical and drug-eluting properties that are attributable to their high water contents. A water-free, liquid four-armed PEG modified with dopamine end groups is described which changed from liquid to elastic solid by reaction with a small volume of Fe3+ solution. The elastic modulus and degradation times increased with increasing Fe3+ concentrations. Both the free base and the water-soluble form of lidocaine could be dissolved in the PEG4-dopamine and released in a sustained manner from the cross-linked matrix. PEG4-dopamine was retained in the subcutaneous space in vivo for up to 3 weeks with minimal inflammation. This material's tailorable mechanical properties, biocompatibility, ability to incorporate hydrophilic and hydrophobic drugs and release them slowly are desirable traits for drug delivery and other biomedical applications.

Synthesis of Poly(2-Hydroxyethyl Methacrylate) Sponges via Activators Regenerated by Electron-transfer Atom-transfer Radical Polymerization

Activators regenerated by electron-transfer atom-transfer radical polymerization, catalyzed by tris(2-pyridylmethyl)amine/CuBr2 and Na{Cu(Gly3)}, was used to synthesize poly(2-hydroxyethyl methacrylate) sponges from 80 : 20 H2O/2-hydroxyethyl methacrylate mixtures. Polymerization-induced phase separations resulted in sponges having morphologies based on agglomerated polymer droplets. During the synthesis of poly(2-hydroxyethyl methacrylate) sponges, first-order kinetics were observed up to a maximum of ~50 % conversion regardless of the catalyst used. The morphologies of the sponges were dependent on the rate of polymerization, slower polymerization rates resulting in polymers with larger morphological features (pores and polymer droplets).

Biodegradation of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly{(2-hydroxyethyl methacrylate)-co-[poly(ethylene glycol) methyl ether methacrylate]} hydrogels containing peptide-based cross-linking agents

PHEMA-peptide and P[HEMA-co-(MeO-PEGMA)]-peptide conjugate hydrogels [where PHEMA = poly(2-hydroxyethyl methacrylate; PEGMA = poly(ethylene glycol) methacrylate] were readily prepared via photoinitiated free-radical polymerization in water. The PHEMA-peptide hydrogels were opaque and had a heterogeneous morphology of interconnected polymer droplets, characteristic of polymers that separate from the aqueous phase during the polymerization experiment. The P[HEMA-co-(MeO-PEGMA)]-peptide conjugates were transparent gels with a homogeneous morphology when formed in water, but when formed in aqueous NaCl solutions the P[HEMA-co-(MeO-PEGMA)]-peptide conjugates were also opaque and exhibited the heterogeneous morphology of interconnected polymer droplets. When incubated in solutions containing activated papain, P[HEMA-co-(MeO-PEGMA)]-peptide conjugates underwent degradation that was characterized by macroscopic changes to sample shape and size, sample weight, and microscopic structure. PHEMA-peptide conjugates did not undergo any significant degradation when incubated with papain, although ninhydrin-staining experiments suggested that some peptide cross-linker groups were cleaved during the incubation. The difference in degradation behavior of PHEMA-peptide and P[HEMA-co-(MeO-PEGMA)]-peptide conjugates is attributed to differences in aqueous solubility of PHEMA and P[HEMA-co-(MeO-PEGMA)].

Degradable Hydrogels for Tissue Engineering – Part I: Synthesis by RAFT Polymerization and Characterization of PHEMA Containing Enzymatically Degradable Crosslinks

A nonapeptide, which is sensitive to enzymatic digestion by collagenase, was modified by the covalent attachment of an acrylamido group at the terminal positions. The functionalized peptide was used as a crosslinking agent during polymerization of 2-hydroxyethyl methacrylate (HEMA). Reversible addition-fragmentation chain transfer (RAFT) method was used to obtain a polymer (PHEMA) with an average theoretical molecular weight of 4000 Da, containing enzymatically labile peptide crosslinks. The functionalized peptide was analyzed in detail by 1H and 13C nuclear magnetic resonance (NMR) spectrometry. The polymerization reaction was monitored by near infrared spectrometry, while the resulting polymer was analyzed by size exclusion chromatography and solid NMR spectrometry. The peptide-crosslinked PHEMA was subjected to an in-vitro degradation assay in the presence of collagenase. At the highest concentration of enzyme used in the study, a weight loss of 35% was recorded after 60 days of incubation in the collagenolytic medium. This suggests that crosslinking with enzymatically degradable peptides is a valid method for inducing biodegradability in polymers that otherwise are not degradable.

Proliferation and differentiation of goat bone marrow stromal cells in 3D scaffolds with tunable hydrophilicity

We have synthesized methacrylate-endcapped caprolactone networks with tailored water sorption ability, poly(CLMA-co-HEA), in the form of three-dimensional (3D) scaffolds with the same architecture but exhibiting different hydrophilicity character (x(HEA)=0, 0.3, 0.5), and we investigated the interaction of goat bone marrow stromal cells (GBMSCs) with such structures. For this purpose, GBMSCs were seeded and cultured for 3, 7, 14, 21, and 28 days onto the developed scaffolds. Cells have proliferated throughout the whole scaffold volume. Cell adhesion and morphology were analyzed by SEM, whereas cell viability and proliferation was assessed by MTS test and DNA quantification concluding that numbers of cells increased as a function of the culturing time (until day 14) and also with the hydrophobic content in the samples (from 50 to 100% of CLMA). No significant difference between samples with 100% and 70% of CLMA were detected in some cases. Osteoblastic differentiation was followed by assessing the alkaline phosphatase activity of cells, as well as type I collagen and osteocalcin expressions levels until day 21. The three markers were positive at days 14 and 21 when cells were cultured in 100% CLMA substrates which suggests osteoblastic differentiation of mesenchymal stem cells within these scaffolds. On the other hand, when the CLMA content decreases (until 50%), type I collagen and osteocalcin were positive but ALP was negative indicating that the differentiation process is affected by hydrophilic content. We suggest that such system may be useful to extract information on the effect of materials' wettability on the corresponding biological performance in a 3D environment. Such general insights may be relevant in the context of biomaterials selection for tissue engineering strategies.

Future Design of a New Keratoprosthesis. Physical and Biological Analysis of Polymeric Substrates for Epithelial Cell Growth

One of the main issues in the development of new biocolonizable materials is to understand the influence of the synthetic material on the biological response in terms of cellular adhesion, proliferation, and differentiation. In this study, we characterized different polymeric materials (with different hydrophobicity/hydrophilicity ratios and electrical charges) using dynamic-mechanical analysis, equilibrium water content, and surface energy. Cell adhesion, viability, morphology, and proliferation studies were conducted with these materials using a conjunctival epithelial cell line (IOBA-NHC). The biological data regarding physicochemical parameters of the materials were also correlated. When conjunctival epithelial cells were grown on poly(ethyl acrylate-co-hydroxyethyl acrylate) copolymers, P(EA-co-HEA), samples with up to 20% hydrophilic groups on their polymeric chain showed adhesion, viability, and proliferation, although these three factors decreased as the hydrophilic group content increased. The poly(ethyl acrylate-co-methacrylic acid) 90/10 copolymer, P(EA-co-MAAc) 90/10, showed better results than poly(ethyl acrylate-co-hydroxyethyl acrylate) copolymers and were even better than tissue control polystyrene (TCPS). This feature is explained by the presence of electrical charges on the surface of the poly(ethyl acrylate-co-methacrylic acid) 90/10 copolymer. The fact that the ionic groups are configured in domains structured in nanophases as happens in this copolymer improves cell adhesion even further.

Monoblocks in root canals: a hypothetical or a tangible goal

The term monoblock has become familiar in the endodontic literature with recent interest in the application of dentin adhesive technology to endodontics. Endodontic monoblocks have generated controversial discussions among academicians and clinicians as to whether they are able to improve the quality of seal in root fillings and to strengthen roots. This review attempts to provide a broader meaning to the term monoblock and to see how this definition may be applied to the materials that have been used in the past and present for rehabilitation of the root canal space. The potential of currently available bondable materials to achieve mechanically homogeneous units with root dentin is then discussed in relation to the classical concept in which the term monoblock was first employed in restorative dentistry and subsequently in endodontics.

Mechanical and morphological characterization of homogeneous and bilayered poly(2-hydroxyethyl methacrylate) scaffolds for use in CNS nerve regeneration

Homogeneous and bilayered macroporous poly(2-hydroxyethyl methacrylate), p(HEMA), hydrogel scaffolds were examined as possible matrices for nerve regeneration in the CNS. An important issue to consider for a CNS scaffold is that it must be able to closely mimic the natural tissue it is replacing, while remaining intact, and mechanically stable enough to allow for regenerating axons to elongate through it. Phase-separated homogeneous and bilayered p(HEMA) scaffolds were fabricated, by varying water, crosslinking, and initiating agents; all of which directly affected the mechanical properties of the polymer. An increase in water concentration resulted in a decrease in the modulus for a given crosslinking and initiating concentration for all homogenous scaffolds, but the same result was not evident in the bilayered scaffolds. The distinct regions within the bilayered scaffolds generate a matrix, containing both a highly porous region with modulus values representative of spinal cord tissue, as well as a nonporous region that provides overall mechanical stability to the entire implant. The overall result is a composite matrix for possible use in CNS nerve regeneration, which mimics the mechanical properties of spinal tissue, but can withstand the forces that it will be subjected to in the injury site.

Preparation and characterization of novel biocompatible cryogels of poly (vinyl alcohol) and egg-albumin and their water sorption study

Polyvinyl alcohol (PVA) and egg albumin are water-soluble, biocompatible and biodegradable polymers and have been widely employed in biomedical fields. In this paper, novel physically cross-linked hydrogels composed of poly (vinyl alcohol) and egg albumin were prepared by cyclic freezing/thawing processes of aqueous solutions containing PVA and egg albumin. The FTIR analysis of prepared cryogels indicated that egg albumin was successfully introduced into the formed hydrogel possibly via hydrogen bonds among hydroxyl groups, amide groups and amino groups present in PVA and egg albumin. The gels were also characterized thermally and morphologically by DSC and SEM-techniques, respectively. The prepared so called 'cryogels' were evaluated for their water uptake potential and influence of various factors such as chemical architecture of the spongy hydrogels, pH and temperature of the swelling bath were investigated on the degree of water sorption by the cryogels. The effect of salt solution and various simulated biological fluids on the swelling of cryogel was also studied. The in vitro biocompatibility of the prepared cryogel was also judged by methods such as protein (BSA) adsorption, blood clot formation and percentage hemolysis measurements.