Highly superporous cholesterol-modified poly(2-hydroxyethyl methacrylate) scaffolds for spinal cord injury repair

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with cholesterol and the introduction of large pores have been developed to create highly superporous hydrogels that promote cell-surface interactions and that can serve as a permissive scaffold for spinal cord injury (SCI) treatment. Highly superporous cholesterol-modified PHEMA scaffolds have been prepared by the bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), cholesterol methacrylate (CHLMA), and ethylene dimethacrylate (EDMA) cross-linking agent in the presence of ammonium oxalate crystals to establish interconnected pores in the scaffold. Moreover, 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA) was incorporated in the polymerization recipe and hydrolyzed, thus introducing carboxyl groups in the hydrogel to control its swelling and softness. The hydrogels supported the in vitro adhesion and proliferation of rat mesenchymal stem cells. In an in vivo study of acute rat SCI, hydrogels were implanted to bridge a hemisection cavity. Histological evaluation was done 4 weeks after implantation and revealed the good incorporation of the implanted hydrogels into the surrounding tissue, the progressive infiltration of connective tissue and the ingrowth of neurofilaments, Schwann cells, and blood vessels into the hydrogel pores. The results show that highly superporous cholesterol-modified PHEMA hydrogels have bioadhesive properties and are able to bridge a spinal cord lesion.     

Cholesterol-modified superporous poly(2-hydroxyethyl methacrylate) scaffolds for tissue engineering

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with cholesterol and laminin have been developed to design scaffolds that promote cell–surface interaction. Cholesterol-modified superporous PHEMA scaffolds have been prepared by the bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), cholesterol methacrylate (CHLMA) and the cross-linking agent ethylene dimethacrylate (EDMA) in the presence of ammonium oxalate crystals to introduce interconnected superpores in the matrix. With the aim of immobilizing laminin (LN), carboxyl groups were also introduced to the scaffold by the copolymerization of the above monomers with 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA). Subsequently, the MCMEMA moiety in the resulting hydrogel was hydrolyzed to [2-(methacryloyloxy)ethoxy]acetic acid (MOEAA), and laminin was immobilized via carbodiimide and N-hydroxysulfosuccinimide chemistry. The attachment, viability and morphology of mesenchymal stem cells (MSCs) were evaluated on both nonporous and superporous laminin-modified as well as laminin-unmodified PHEMA and poly(2-hydroxyethyl methacrylate-co-cholesterol methacrylate) P(HEMA–CHLMA) hydrogels. Neat PHEMA and laminin-modified PHEMA (LN–PHEMA) scaffolds facilitated MSC attachment, but did not support cell spreading and proliferation; the viability of the attached cells decreased with time of cultivation. In contrast, MSCs spread and proliferated on P(HEMA–CHLMA) and LN-P(HEMA–CHLMA) hydrogels.     

Presence of pores and hydrogel composition influence tensile properties of scaffolds fabricated from well-defined sphere templates

Sphere templating is an attractive method to produce porous polymeric scaffolds with well-defined and uniform pore structures for applications in tissue engineering. While high porosity is desired to facilitate cell seeding and enhance nutrient transport, the incorporation of pores will impact gross mechanical properties of tissue scaffolds and will likely be dependent on pore size. The goals of this study were to evaluate the effect of pores, pore diameter, and polymer composition on gross mechanical properties of hydrogels prepared from crosslinked poly(ethylene glycol) (PEG) and poly(2-hydroxyethyl methacrylate) (pHEMA). Sphere templates were fabricated from uncrosslinked poly(methyl methacrylate) spheres sieved between 53-63 and 150-180 μm. Incorporating pores into hydrogels significantly decreased the quasi-static modulus and ultimate tensile stress, but increased the ultimate tensile strain. For pHEMA, decreases in gel crosslinking density and increases in pore diameters followed similar trends. Interestingly, the mechanical properties of porous PEG hydrogels were less sensitive to changes in pore diameter for a given polymer composition. Additionally, pore diameter was shown to affect skeletal myoblast adhesion whereby many cells cultured in porous hydrogels with smaller pores were seen spanning across multiple pores, but lined the inside of larger pores. In summary, incorporation of pores and changes in pore diameter significantly affect the gross mechanical properties, but in a manner that is dependent on gel chemistry, structure, and composition. Together, these findings will help to design better hydrogel scaffolds for applications where gross mechanical properties and porosity are critical.     

Quantitative evaluation of rat lymphocyte adsorption on microdomain structured surfaces of poly(2-hydroxyethyl methacrylate)/polyamine

The adsorption behaviour of rat lymphocytes on poly(2-hydroxyethyl methacrylate)-graft-polyamine (HA) copolymers was evaluated using a newly developed chromatographic method. The quantity of lymphocyte adsorption can be varied by regulating the polyamine content in the HA copolymer. A remarkable depression in lymphocyte adsorption was observed on the surface of HA copolymer, consisting of 7 wt% of polyamine graft and 93 wt% of poly(2-hydroxyethyl methacrylate) (pHEMA) backbone. Further introduction of a polyamine graft on pHEMA resulted in the increase of lymphocyte retention on the copolymer surfaces. Lymphocytes adsorbed on HA copolymer surface retained their original round shape. Detailed analysis of the chromatogram showed that interaction of lymphocytes with HA copolymer was very much weaker than that with homopolymer of pHEMA or polyamine.     

Superporous hydrogels containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan interpenetrating polymer networks

Superporous hydrogels containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan interpenetrating polymer networks (SPH-IPNs) were prepared by cross-linking O-carboxymethyl chitosan (O-CMC) with glutaraldehyde (GA) after superporous hydrogel (SPH) was synthesized. The structures of the SPH-IPNs were characterized with FT-IR, 13C-NMR and DSC. SEM, CLSM and light images revealed that the SPH-IPNs possessed both the IPN network and large numbers of pores and the cross-linked O-CMC molecules were located on the peripheries of these pores. The swelling behavior of SPH-IPNs was dependent on the O-CMC content, GA amount and cross-linking time. Due to the cross-linked O-CMC network, in vitro muco-adhesive force and mechanical properties, including compression and tensile modulus, of the SPH-IPN were greatly improved when compared with the CSPH. An enhanced loading capacity for insulin could be obtained by the SPH-IPNs as compared to non-porous hydrogel and CSPH, and more than 90% of the insulin was released within 1 h. With the improved mechanical properties, in vitro muco-adhesive force and loading capacities, the SPH-IPN may be used as a potential muco-adhesive system for peroral delivery of peptide and protein drugs.     

Dual-functional electrospun poly(2-hydroxyethyl methacrylate)

Poly(2-hydroxyethyl methacrylate) (pHEMA) has been widely used in many biomedical applications due to its well-known biocompatibility. For tissue engineering applications, porous scaffolds that mimic fibrous structures of natural extracellular matrix and possess high surface-area-to-volume ratios are highly desirable. So far, a systematic approach to control diameter and morphology of pHEMA fibers has not been reported and potential applications of pHEMA fibers have barely been explored. In this work, pHEMA was synthesized and processed into fibrous scaffolds using an electrospinning approach. Fiber diameters from 270 nm to 3.6 μm were achieved by controlling polymer solution concentration and electrospinning flow rate. Post-electrospinning thermal treatment significantly improves integrity of the electrospun membranes in water. The pHEMA microfibrous membranes exhibited water absorption up to 280% (w/w), whereas the pHEMA hydrogel only absorbed 70% water. Fibrinogen adsorption experiments demonstrate that the electrospun pHEMA fibers highly resist nonspecific protein adsorption. Hydroxyl groups on electrospun pHEMA fibers were further activated for protein immobilization. A bovine serum albumin (BSA) binding capacity as high as 120 mg BSA/g membrane was realized at an intermediate fiber diameter. The pHEMA fibrous scaffolds functionalized with collagen I significantly promoted fibroblast adhesion, spreading, and proliferation. We conclude that the electrospun pHEMA fibers are dual functional, that is, they resist nonspecific protein adsorption meanwhile abundant hydroxyl groups on fibers allow effective conjugation of biomolecules in a nonfouling background. High water absorption and dual functionality of the electrospun pHEMA fibers may lead to a number of potential applications such as wound dressings, tissue scaffolds, and affinity membranes.     

Biomimetic Macroporous Hydrogels: Protein Ligand Distribution and Cell Response to the Ligand Architecture in the Scaffold

Macroporous hydrogels (MHs), cryogels, are a new type of biomaterials for tissue engineering that can be produced from any natural or synthetic polymer that forms a gel. Synthetic MHs are rendered bioactive by surface or bulk modifications with extracellular matrix components. In this study, cell response to the architecture of protein ligands, bovine type-I collagen (CG) and human fibrinogen (Fg), immobilised using different methods on poly(2-hydroxyethyl methacrylate) (pHEMA) macroporous hydrogels (MHs) was analysed. Bulk modification was performed by cross-linking cryo-co-polymerisation of HEMA and poly(ethylene glycol)diacrylate (PEGA) in the presence of proteins (CG/pHEMA and Fg/pHEMA MHs). The polymer surface was modified by covalent immobilisation of the proteins to the active epoxy (ep) groups present on pHEMA after hydrogel fabrication (CG–epHEMA and Fg–epHEMA MHs). The concentration of proteins in protein/pHEMA and protein–epHEMA MHs was 80–85 and 130–140 μg/ml hydrogel, respectively. It was demonstrated by immunostaining and confocal laser scanning microscopy that bulk modification resulted in spreading of CG in the polymer matrix and spot-like distribution of Fg. On the contrary, surface modification resulted in spot-like distribution of CG and uniform spreading of Fg, which evenly coated the surface. Proliferation rate of fibroblasts was higher on MHs with even distribution of the ligands, i.e., on Fg–epHEMA and CG/pHEMA. After 30 days of growth, fibroblasts formed several monolayers and deposited extracellular matrix filling the pores of these MHs. The best result in terms of cell proliferation was obtained on Fg–epHEMA. The ligands displayed on surface of these scaffolds were in native conformation, while in bulk-modified CG/pHEMA MHs most of the proteins were buried inside the polymer matrix and were less accessible for interactions with specific antibodies and cells. The method used for MH modification with bioligands strongly affects spatial distribution, density and conformation of the ligand on the scaffold surface, which, in turn, influence cell–surface interactions. The optimal type of modification varies depending on intrinsic properties of proteins and MHs.     

The Competing Effects of Hyaluronic and Methacrylic Acid in Model Contact Lenses

The aim of this study was to determine the influence of hyaluronic acid (HA) on lysozyme sorption in model contact lenses containing varying amounts of methacrylic acid (MAA). One model conventional hydrogel (poly(2-hydroxyethyl methacrylate) (pHEMA)) and two model silicone hydrogels (pHEMA, methacryloxypropyltris(trimethylsiloxy)silane (pHEMA TRIS) and N,N-dimethylacrylamide, TRIS (DMAA TRIS)) lens materials were prepared with and without MAA at two different concentrations (1.7 and 5%). HA, along with dendrimers, was loaded into these model contact lens materials and then cross-linked with 1-ethyl-3-(3-dimethylamino propyl)-carbodiimide (EDC). Equilibrium water content (EWC), advancing water contact angle and lysozyme sorption on these lens materials were investigated. In the HA-containing materials, the presence (P < 0.05) and amount (P < 0.05) of MAA increased the EWC of the materials. For most materials, addition of MAA reduced the advancing contact angles (P < 0.05) and for all the materials, the addition of HA further improved hydrophilicity (P < 0.05). For the non-HA containing hydrogels, the presence (P < 0.05) and amount (P < 0.05) of MAA increased lysozyme sorption. The presence of HA decreased lysozyme sorption for all materials (P < 0.05). MAA appears to work synergistically with HA to increase the EWC in addition to improving the hydrophilicity of model pHEMA-based and silicone hydrogel contact lens materials. Hydrogel materials that contain HA have tremendous potential as hydrophilic, protein-resistant contact lens materials.     

Reversible immobilization of drugs on a hydrogel matrix, 2. Diffusion of free chloramphenicol from poly(2-hydroxyethyl methacrylate) hydrogels

The diffusional behaviour of chloramphenicol

1 D -(–)-threo-N-[2-hydroxyl-1-hydroxymethyl-2-(4-nitrophenyl)ethyl]dichloroacetamide.

( 1 ) from poly( 2 -hydroxyethyl methacrylate) (pHEMA) hydrogels is reported. The drug was trapped in the matrix cross-linked with various amounts of ethylene dimethacrylate (0,5–18 mol-%), and the diffusion was followed from disc-shaped slabs at swelling equilibrium in water (phosphate buffer, pH 7) at 37°C. The diffusion obeys the second Fick law and is rapid (D ≈ 10^?8 cm² s^?1) in the case of the slightly crosslinked hydrogels used for corneal lenses. The diffusion coefficients decrease almost exponentially with increasing cross-linking ratio, and the process appears predominantly controlled by the free volume contribution of the diluent rather than by the sieving of the network.     

Fiber templating of poly(2-hydroxyethyl methacrylate) for neural tissue engineering

We have developed a method to create longitudinally oriented channels within poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels for neural tissue engineering applications. Incorporated into an entubulation strategy, these scaffolds have the potential to enhance nerve regeneration after transection injuries of either the spinal cord or the peripheral nerve by increasing the available surface area and providing guidance to extending axons and invading cells. The fabrication process is straightforward and the resultant scaffolds are highly reproducible. Polycaprolactone (PCL) fibers were extruded and embedded in transparent, crosslinked pHEMA gels. Sonication of the pHEMA/PCL composite in acetone resulted in the complete dissolution of the PCL, leaving longitudinally oriented, fiber-free channels in the pHEMA gel. Regulating the size and quantity of the PCL fibers allowed us to control the diameter and number of channels. Small and large channel scaffolds were fabricated and thoroughly characterized. The small channel scaffolds had 142+/-7 channels, with approximately 75% of the channels in the 100-200 micro m size range. The large channel scaffolds had 37+/-1 channels, with approximately 77% of the channels in the 300-400 micro m range. The equilibrium water content (EWC), porosity and compressive modulus were measured for each of the structures. Small and large channel scaffolds had, respectively, EWCs of 55.0+/-1.2% and 56.2+/-2.9%, porosities of 35+/-1% and 40+/-1% and compressive moduli of 191+/-7 and 182+/-4kPa.     

Stiffness and adhesivity control aortic valve interstitial cell behavior within hyaluronic acid based hydrogels

Bioactive and biodegradable hydrogels that mimic the extracellular matrix and regulate valve interstitial cells (VIC) behavior are of great interest as three-dimensional (3-D) model systems for understanding mechanisms of valvular heart disease pathogenesis in vitro and the basis for regenerative templates for tissue engineering. However, the role of stiffness and adhesivity of hydrogels in VIC behavior remains poorly understood. This study reports the synthesis of methacrylated hyaluronic acid (Me-HA) and oxidized and methacrylated hyaluronic acid, and the subsequent development of hybrid hydrogels based on modified HA and methacrylated gelatin (Me-Gel) for VIC encapsulation. The mechanical stiffness and swelling ratio of the hydrogels were tunable with the molecular weight of the HA and the concentration/composition of the precursor solution. The encapsulated VIC in pure HA hydrogels with lower mechanical stiffness showed a more spreading morphology compared to their stiffer counterparts and dramatically up-regulated alpha smooth muscle actin expression, indicating more activated myofibroblast properties. The addition of Me-Gel in Me-HA facilitated cell spreading, proliferation and VIC migration from encapsulated spheroids and better maintained the VIC fibroblastic phenotype. The VIC phenotype transition during migration from encapsulated spheroids in both Me-HA and Me-HA/Me-Gel hydrogel matrixes was also observed. These findings are important for the rational design of hydrogels for controlling the VIC morphology, and for regulating the VIC phenotype and function. The Me-HA/Me-Gel hybrid hydrogels accommodated with VIC are promising as valve tissue engineering scaffolds and 3-D models for understanding valvular pathobiology.     

Photo-cured hyaluronic acid-based hydrogels containing simvastatin as a bone tissue regeneration scaffold

We describe in this study the positive influences on in vitro and in vivo osteogenesis of photo-cured hyaluronic acid (HA) hydrogels loaded with simvastatin (SIM). Prior to loading SIM, we first characterized the HA hydrogels for their mechanical properties and swelling ratios. The results from this testing indicated that these two factors improved as the substitution degree of 2-aminoethyl methacrylate (AEMA) increased. MTT and live/dead assays showed that the HA hydrogels have good biocompatibility for use as scaffolds for bone tissue regeneration. Moreover, another MTT assay showed that the photo-cured HA hydrogels III fabricated with 30% AEMA (300 mg) conjugated HA (HA-AEMA iii) loaded with between 0.1 and 1 mg of SIM had a similar cytotoxicity as compared to the HA hydrogel III itself. The sustained release of SIM was observed to occur in the HA hydrogel III loaded with 1 mg of SIM. In vitro and in vivo experiments showed that the HA hydrogel III loaded with 1 mg of SIM had a significant influence on osteogenesis.     

Cyclodextrin-containing hydrogels for contact lenses as a platform for drug incorporation and release

Poly(2-hydroxyethyl methacrylate) hydrogels containing β-cyclodextrin (pHEMA/β-CD) have been investigated as a platform for sustained release of ophthalmic drugs. First of all, pHEMA/β-CD hydrogel membranes and contact lenses were prepared by photopolymerization of HEMA, mono-methacrylated β-CD (mono-MA-β-CD) and trimethylolpropane trimethacrylate using a cast molding process. The hydrogels were characterized by Fourier transform infrared spectroscopy, equilibrium swelling ratio (ESR) and tensile tester. The results showed that the incorporation of β-CD in the hydrogels increased the ESR and tensile strength. Then, puerarin was used as a model to evaluate drug loading and in vitro and in vivo release behavior of the pHEMA/β-CD hydrogels. It was revealed that puerarin loading and in vitro release rate were dependent on β-CD content in the pHEMA/β-CD hydrogels. In rabbit eyes the pHEMA/β-CD hydrogel contact lenses exhibited longer mean residence times (MRT_F) of puerarin in tear fluid than that of pHEMA contact lenses and 1% puerarin eye drops. The puerarin concentration in the aqueous humor of rabbit reached a maximum of 0.81 μg ml^?1 after wearing the pHEMA/β-CD contact lens, which had been presoaked in 0.802 mg ml^?1 puerarin solution for 4.81 h. Also, the pHEMA/β-CD contact lenses had a higher drug bioavailability in aqueous humor than puerarin eye drops. The data demonstrate that pHEMA/β-CD hydrogel contact lenses can effectively deliver puerarin through the cornea.     

Bioactive rosette nanotube-hydroxyapatite nanocomposites improve osteoblast functions

Inspired from biological systems, small synthetic organic molecules expressing the hydrogen bonding arrays of the DNA bases guanine and cytosine were prepared, and their self-assembly into rosette nanotubes (RNTs) was investigated. Due to their unique biological, physicochemical, and mechanical properties, RNTs could serve as the next generation of injectable orthopedic materials. In this study, a self-assembling module (termed twin base linkers or TBL) was synthesized, and the corresponding RNTs were used as bioactive components in composites of poly (2-hydroxyethyl methacrylate) (pHEMA) and hydroxyapatite (HA) nanoparticles (termed TBL/HA/pHEMA). The properties of these composites were characterized for solidification time, surface morphology, mechanical properties, and cytocompatibility. The experimental conditions were optimized to achieve solidification within 2-40?min, offering a range of properties for orthopedic applications. Composites with 20?wt% HA nanoparticles had a compressive strength (37.1?MPa) and an ultimate tensile stress (14.7?MPa) similar to that of a natural vertebral disc (5-30?MPa). Specifically, the TBL (0.01?mg/mL)/HA(20?wt%)/pHEMA composites improved long-term functions of osteoblasts (or bone-forming cells) in terms of collagen synthesis, alkaline phosphatase activity, and calcium deposition. Moreover, this composite inhibited fibroblast adhesion, thus decreasing the potential for undesirable fibrous tissue formation. In summary, this in vitro study provided evidence that TBL/HA/pHEMA composites are promising injectable orthopedic implant materials that warrant further mechanistic and in vivo studies.     

Biodegradability of poly (2-hydroxyethyl methacrylate) in the presence of the J774.2 macrophage cell line

The degradation of cross-linked and linear poly(2-hydroxyethyl methacrylate) (pHEMA), was examined in vitro with J774.2 cells. pHEMA microbeads were prepared with both types of polymers. Only cells in contact with the microbeads increased their production of lysosomal enzymes (TRAcP and ANAE) and released large amounts of reactive oxygen species with both types of pHEMA microbeads. Electron microscopy showed that macrophages were able to erode the surface of linear pHEMA but unable to erode the surface of the cross-linked polymer. Cells appeared wrapped by the linear pHEMA surface, but those cultured on the cross-linked polymer were only laying at the surface. After cell culture, the surface roughness of pHEMA slices was observed by atomic force microscopy (AFM). There was a significant increase in roughness (R(a)) of the surface of linear pHEMA slices cultured with J774.2 cells whereas no difference in R(a) between the surface of cross-linked pHEMA slices could be measured. AFM image of the hydrated materials were done: the surface of linear pHEMA swelled considerably in saline whereas the hydrated cross-linked polymer did not differ from the air-dried appearance. In conclusion, linear pHEMA swells in biological fluids, activates macrophages in close contact with the polymer and can be progressively eroded.     

Synthesis of superporous hydrogels: hydrogels with fast swelling and superabsorbent properties.

We have been interested in the synthesis of hydrogels with fast swelling kinetics and superabsorbent properties. To increase the water absorption rate, interconnected pores were introduced to the hydrogels. Since the pore size in the dried hydrogels is in the order of hundreds of micrometers, these hydrogels are called "superporous" hydrogels. Superporous hydrogels were synthesized by crosslinking polymerization of various vinyl monomers in the presence of gas bubbles formed by the chemical reaction of acid and NaHCO3. The polymerization process was optimized to capture the gas bubbles inside the synthesized hydrogels. The use of the NaHCO3/acid system allowed easy control of timing for gelation and foam formation. We found that PF127 was the best foam stabilizer for most of the monomer systems used in our study. Scanning electron microscope (SEM) pictures showed interconnected pores forming capillary channels. The capillary channels, which were critical for fast swelling, were preserved during drying by dehydrating water-swollen hydrogels with ethanol before drying. The ethanol-dehydrated superporous hydrogels reached equilibrium swelling within minutes. The equilibrium swelling time could be reduced to less than a minute with the use of a wetting agent. In our study, water moisture was used as a wetting agent since the amount of moisture content in the dried hydrogels easily could be controlled. Preparation of superporous hydrogels using the right blowing system, foam stabilizer, drying method, and wetting agent makes it possible to reduce the swelling time to less than a minute regardless of the size of the dried gels. The superporous hydrogels can be used where fast swelling and superabsorbent properties are critical.     

Poly(2-hydroxyethyl methacrylate) biomimetic coating to improve osseointegration of a PMMA/HA/glass composite implant: in vivo mechanical and histomorphometric assessments

Bone implants must simultaneously satisfy many requirements, even though the surface properties remain a crucial aspect in osseointegration success. Since a single material with a uniform structure cannot satisfy all of these requirements, composite materials specifically designed for orthopedic or dental implant application should be envisaged. Two poly(methylmethacrylate)/hydroxyapatite composites reinforced by E-glass fibres, uncoated (PMMA/HA/Glass) and poly(2-hydroxyethyl methacrylate) (PMMA/HA/Glass+pHEMA) coated by the biomimetic method, were mechanically (push-out test) and histomorphometrically (Affinity Index, AI) investigated in an in vivo rabbit model. Cylindrical implants (diameter 2 mm x 5 mm length) were inserted into rabbit femoral cortical (mid-diaphysis) and cancellous (distal epiphysis) bone, under general anesthesia. The highest values of push-out force and ultimate shear strength were observed for the PMMA/HA/Glass at 12 weeks, which significantly (p < 0.001) differed from those of PMMA/HA/Glass+pHEMA at the same experimental time and from those of PMMA/HA/Glass at 4 weeks. At both experimental times, significantly (p < 0.0005) lower values of AI were observed in the PMMA/HA/Glass+pHEMA versus PMMA/HA/Glass (distal femoral epiphysis: 4 weeks = 33%; 12 weeks = 19%; femoral diaphysis: 4 weeks = 15%; 12 weeks = 11%). The good mechanical and histomorphometric results obtained with PMMA/HA/Glass should be followed by further evaluation of bone remodeling processes and mechanical strength around loaded PMMA/HA/Glass implants at longer experimental times. Finally, the biomimetic method applied to pHEMA needs to be further investigated in order to improve the positive effect of SBF on pHEMA and to enhance the coating adhesion.     

Preparation and characterization of gelatin/hyaluronic acid cryogels for adipose tissue engineering: In vitro and in vivo studies

Macroporous elastic scaffolds containing gelatin (4% or 10%) and 0.25% hyaluronic acid (HA) were fabricated by cryogelation for application in adipose tissue engineering. These cryogels have interconnected pores (～200 μm), high porosity (>90%) and a high degree of cross-linking (>99%). The higher gelatin concentration reduced the pore size, porosity and swelling ratio of the cryogel but improved its swelling kinetics. Compressive mechanical testing of cryogel samples demonstrated non-linear stress–strain behavior and hysteresis loops during loading–unloading cycles, but total recovery from large strains. The presence of more gelatin increased the elastic modulus, toughness and storage modulus and yielded a cryogel that was highly elastic, with a loss tangent equal to 0.03. Porcine adipose-derived stem cells (ADSCs) were seeded in the cryogel scaffolds to assess their proliferation and differentiation. In vitro studies demonstrated a good proliferation rate and the adipogenic differentiation of the ADSCs in the cryogel scaffolds, as shown by their morphological change from a fibroblast-like shape to a spherical shape, decreased actin cytoskeleton content, growth arrest, secretion of the adipogenesis marker protein leptin, Oil Red O staining for triglycerides and expression of early (LPL and PPARγ) and late (aP2 and leptin) adipogenic marker genes. In vivo studies of ADSCs/cryogel constructs implanted in nude mice and pigs demonstrated adipose tissue and new capillary formation, the expression of PPARγ, leptin and CD31 in immunostained explants, and the continued expression of adipocyte-specific genes. Both the in vitro and in vivo studies indicated that the gelatin/HA cryogel provided a structural and chemical environment that enabled cell attachment and proliferation and supported the biological functions and adipogenesis of the ADSCs.     

Swelling and mechanical properties of glycol chitosan/poly(vinyl alcohol) IPN-type superporous hydrogels

Glycol chitosan/poly(vinyl alcohol) interpenetrating polymer network type superporous hydrogels were prepared using a gas foaming/freeze-drying method. The effect of the molecular weight of the strengthener, poly(vinyl alcohol) (PVA), on the swelling and mechanical behavior of the superporous hydrogels was investigated. The introduction of a small amount of high molecular weight PVA significantly enhanced the mechanical strength but slightly reduced the swelling capacity. The freezing/thawing (F/T) drying process had a significant effect on the physical properties of the glycol chitosan/PVA superporous hydrogels, because hydrogen bonds were formed between the PVA molecules as a result of the number of F/T cycles. The swelling ratio decreased but the mechanical strength increased with increasing freezing time. However, this effect was not as strong as the number of F/T cycles. The differential scanning calorimetry was used to examine how the thermal behavior associated with the hydrogen bond-induced crystalline structure was affected by the F/T process.     

Hydrogel based on interpenetrating polymer networks of dextran and gelatin for vascular tissue engineering

Hydrogel networks are highly desirable as three-dimensional (3-D) tissue engineering scaffolds for cell encapsulation due to the high water content and ability to mimick the native extracellular matrix. However, their application is limited by their nanometer-scale mesh size, which restricts the spreading and proliferation of encapsulated cells, and their poor mechanical properties. This study seeks to address both limitations through application of a novel cell-encapsulating hydrogel family based on the interpenetrating polymer network (IPN) of gelatin and dextran bifunctionalized with methacrylate (MA) and aldehyde (AD) (Dex-MA-AD). The chemical structure of the synthesized Dex-MA-AD was verified by (1)H-NMR and the degrees of substitution of MA and AD were found to be 14 and 13.9+/-1.3 respectively. The water contents in all these hydrogels were approximately 80%. Addition of 40 mg/ml to 60 mg/ml gelatin to neat Dex-MA-AD increased the compressive modulus from 15.4+/-3.0 kPa to around 51.9+/-0.1 kPa (about 3.4-fold). Further, our IPN hydrogels have higher dynamic storage moduli (i.e. on the order of 10(4)Pa) than polyethylene glycol-based hydrogels (around 10(2)-10(3)Pa) commonly used for smooth muscle cells (SMCs) encapsulation. Our dextran-based IPN hydrogels not only supported endothelial cells (ECs) adhesion and spreading on the surface, but also allowed encapsulated SMCs to proliferate and spread in the bulk interior of the hydrogel. These IPN hydrogels appear promising as 3-D scaffolds for vascular tissue engineering.