Hydrogel composed of acrylic coumarin and acrylic Pluronic F-127 and its photo- and thermo-responsive release property

Hydrogels comprising acrylic coumarin (AC) and acrylic Pluronic F-127 (APF) were prepared by a free radical reaction and its photo- and thermal-responsive release property was investigated using methylene blue as a solute. AC and APF were prepared successfully, confirmed by ¹H NMR spectroscopy. The molar ratio of Pluronic F-127 chain to vinyl group of APF was 1:1.3, suggesting that diacrylic Pluronic F-127 which could act as a cross-linker for the formation of polymer networks was produced. The coumaryl groups of AC were dimerized as much as 60.1% by 2 h-UV irradiation. On the DSC thermogram, APF exhibited its melting point around 55.4°C, about 0.9°C lower than the melting point of Pluronic F-127. The gelling temperature of Pluronic F-127 solution (25% (w/v)) was about 40°C, determined by a viscometric method. The swelling ratio of the hydrogels increased up to greater than 8 in 30 min. The maximum release degree at 23 and 50°C of dye loaded in the hydrogels was suppressed by UV irradiation, possibly because of the photo-dimerization of coumaryl groups. The release degree at 50°C of dye loaded in the UV-treated hydrogels was lower as the content of APF was higher, possibly because the thermally induced gelation of the polymer chains could suppress the payload release from the hydrogels.     

Temperature-sensitive pluronic/poly(ethylenimine) nanocapsules for thermally triggered disruption of intracellular endosomal compartment

Pluronic hydrogel nanoparticles cross-linked with poly(ethylenimine) (PEI) were synthesized by a modified emulsification/solvent evaporation method. Pluronic F-127 preactivated at the terminal group with p-nitrophenyl chloroformate was dissolved in dichloromethane, and the organic solution was emulsified in deionized water containing PEI by sonication. Primary amine groups of PEI in the aqueous phase were conjugated and/or cross-linked with activated Pluronic F-127 in the vicinity of the water/dichloromethane interface, resulting in the formation of shell-cross-linked Pluronic/PEI nanocapsules. Pluronic/PEI nanocapsules exhibited a volume transition behavior over a temperature range of 24-33 degrees C. The thermally reversible swelling/deswelling of Pluronic/PEI nanocapsules was caused by temperature-dependent hydrophobic interaction of cross-linked and/or grafted Pluronic polymer chains in the nanocapsules. Pluronic/PEI nanocapsules were utilized to break up intracellular endosomal compartments by swelling-induced destabilization of the endosomal membrane triggered by a cold-shock treatment.     

Utilizing temperature-sensitive association of Pluronic F-127 with lipid bilayers to control liposome-cell adhesion

The temperature sensitive properties of Pluronic F-127 (MW ∼12?600, PEO₉₈-PPO₆₇-PEO₉₈), a block co-polymer or poloxamer, was used to control liposome-cell adhesion. When associated with liposomes, the PEO moiety of the block co-polymer is expected to inhibit liposome-cell adhesion. Liposomes were made using egg phosphatidylcholine and different mole% of Pluronic F-127. Size measurement of the liposomes at different temperatures, in the presence and absence of Pluronic F-127, shows significant reduction in the size of multilamellar vesicles, at higher temperatures, by the Pluronic molecules. Negative stain electron microscopy study showed the presence of individual molecules and micelles of Pluronic, respectively at temperatures below and above the critical micellar temperature (CMT). Measurement of the surface associated Pluronics indicated that they associated with liposomes when the sample was heated above the Pluronic CMT, and dissociated from liposomes when cooled below the CMT. Attachment of the Pluronic containing liposomes to CHO cells was inhibited at temperatures above the CMT, but not at temperatures below CMT, indicating that temperature-sensitive control of liposome-cell adhesion is achieved.     

The Influence of Modified Pluronic F127 Copolymers with Higher Phase Transition Temperature on Arsenic Trioxide-Releasing Properties and Toxicity in a Subcutaneous Model of Rats

Pluronic F127 (PF-127) shows thermoreversible property, which is of the utmost interest in optimizing drug formulation and delivery. However, its hitherto unresolved drawback of a low phase transition temperature (T (tr)) has limited its application in injectable drug delivery systems. We have recently synthesized a new type of PF-127 copolymers with higher T (tr) using a simple oxidative method. Here, we have investigated the drug-releasing feature of oxidized PF-127 and oxidized PF-127-containing silver nanoparticles (SNPs), carrying arsenic trioxide (ATO), in a subcutaneous model of rats. Injectable hydrogels prepared with oxidized PF-127s were less viscous and easier to inject, at the same concentration, than their precursor. Addition of SNPs further elevated T (tr), resulting in even lower viscosity of the injectable hydrogel prepared from SNP-containing oxidized PF-127. The oxidized PF-127 copolymers did not differ significantly in ATO-releasing ability, compared with parental PF-127, but the addition of SNPs altered the ATO-releasing feature of oxidized PF-127 to some extent. ATO-carrying oxidized PF-127s had similar toxicity, but the addition of SNPs enhanced the hepatotoxicity of ATO, as evidenced by elevated serum levels of alanine aminotransferase and aspartate aminotransferase and histological alterations, compared to parental PF-127. The results presented herein warrant further investigation of the modified PF-127 copolymers to deliver ATO or other drugs in the form of injectable hydrogels.     

In vitro and in vivo release of albumin using a biodegradable MPEG-PCL diblock copolymer as an in situ gel-forming carrier

An MPEG-PCL diblock copolymer was synthesized as an in situ gel carrier, and its phase transition behavior in aqueous solutions was examined. For comparison, aqueous solutions of Pluronic F-127, a widely used injectable gel-forming solution, were also studied. Both MPEG-PCL copolymer and Pluronic aqueous solutions were sols at room temperature. As the temperature was increased above room temperature, the diblock copolymer and Pluronic solutions underwent a sol-to-gel phase transition, which manifested as an increase in viscosity indicative of the formation of a gel. All of the copolymer solutions became gels at body temperature, although the gel viscosity increased with the increasing concentration of the MPEG-PCL diblock copolymer in the solution. In in vitro experiments, in which the gels were exposed to PBS, the MPEG-PCL gels maintained their structural integrity for more than 28 days, whereas the Pluronic gel disappeared within 2 days. The same results were observed when the polymer solutions were subcutaneously injected into rats. The MPEG-PCL gels maintained their structural integrity longer than 30 days, while the Pluronic gel could not be observed after 2 days. The ability of the gels as drug carriers was studied by measuring the release of fluorescein isothiocyanate-labeled bovine serum albumin (BSA-FITC) from MPEG-PCL diblock copolymer gels in vitro as well as in vivo. In vitro, BSA release was sustained above 20 days, with a greater release at lower diblock copolymer concentration; by contrast, Pluronic gels exhibited almost complete release of BSA-FITC within 1 day. When the BSA-FITC-loaded diblock copolymer and Pluronic solutions were subcutaneously injected into rats, they immediately transformed into a gel. In vivo, sustained release of BSA-FITC over 30 days was observed from the MPEG-PCL gel, whereas BSA-FITC release from the Pluronic gel ceased within 3 days. Collectively, the present findings show that MPEG-PCL diblock copolymer solutions are thermo-responsive and maintain their structural integrity under physiological conditions, indicating that they are suitable for use as injectable drug carriers.     

In situ gelable interpenetrating double network hydrogel formulated from binary components: thiolated chitosan and oxidized dextran

In situ gelable interpenetrating double-network hydrogels composed of thiolated chitosan (Chitosan-NAC) and oxidized dextran (Odex), completely devoid of potentially cytotoxic small molecule cross-linkers and that do not require complex maneuvers or catalysis, have been formulated. The interpenetrating network structure is created by Schiff base formations and disulfide bond inter-cross-linkings through exploiting the disparity of their reaction times. Compared with the autogelable thiolated chitosan hydrogels that typically require a relatively long time span for gelation to occur, the Odex/Chitosan-NAC composition solidifies rapidly and forms a well-developed 3D network in a short time span. Compared with typical hydrogels derived from natural materials, the Odex/Chitosan-NAC hydrogels are mechanically strong and resist degradation. The cytotoxicity potential of the hydrogels was determined by an in vitro viability assay using fibroblast as a model cell, and the results reveal that the hydrogels are noncytotoxic. In parallel, in vivo results from subdermal implantation in mice models demonstrate that this hydrogel is not only highly resistant to degradation but also induces very mild tissue response.     

Injectable in situ physically and chemically crosslinkable gellan hydrogel

An injectable, in situ physically and chemically crosslinkable gellan hydrogel is synthesized via gellan thiolation. The thiolation does not alter the gellan's unique 3-D conformation, but leads to a lower phase transition temperature under physiological conditions and stable chemical crosslinking. The synthesis and hydrogels are characterized by (1)H NMR, FT-IR, CD, or rheology measurements. The injectability and the tissue culture cell viability is also tested. The thiolated gellan hydrogel exhibits merits, such as ease for injection, quick gelation, lower gelling temperature, stable structure, and nontoxicity, which make it promising in biomedicine and bioengineering as an injectable hydrogel.     

Smart hydrogels for in situ generated implants

The objective of this study was to explore the use of reverse thermo-responsive (RTG) polymers for generating implants at their site of performance, following minimally invasive surgical procedures. Aiming at combining syringability and enhanced mechanical properties, a new family of injectable RTG-displaying polymers that exhibit improved mechanical properties was created, following two different strategies: (1) to synthesize high-molecular-weight polymers by covalenty joining poly(ethylene glycol) and poly(propylene glycol) chains using phosgene as the coupling molecule and (2) to cross-link poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblocks after end-capping them with triethoxysilane or methacrylate reactive groups. While the methacrylates cross-linked rapidly, the triethoxysilane groups enabled the system to cross-link gradually over time. The chain-extended PEO/PPO copolymers had molecular weights in the 39 000-54 000 interval and exhibited improved mechanical properties. Reverse thermo-responsive systems displaying gradually increasing mechanical properties were generated by cross-linking triethoxysilane-capped (EO)(99)-(PO)(67)-(EO)(99) (F127) triblocks. Over time, the ethoxysilane groups hydrolyzed and created silanol moieties that subsequently condensated. With the aim of further improving their mechanical behavior, F127 triblocks were reacted with methacryloyl chloride and the resulting dimethacrylate was subsequently cross-linked in an aqueous solution at 37 degrees C. The effect of the concentration of the F127 dimethacrylate on the mechanical properties and the porous structure of the cross-linked matrixes produced was assessed. Rheometric studies revealed that the cross-linked hydrogels attained remarkable mechanical properties and allowed the engineering of robust macroscopic constructs, such as large tubular structures. The microporosity of the matrixes produced was studied by scanning electron microscopy. Monolayered conduits as well as structures comprising two and three layers were engineered in vitro, and their compliance and burst strength were determined.     

Mechanical properties of biomimetic tissue adhesive based on the microbial transglutaminase-catalyzed crosslinking of gelatin

Fibrin sealants are a type of soft tissue adhesive that employs biochemical reactions from the late stages of the blood coagulation cascade. Intrinsic to these adhesives are a structural protein and a transglutaminase crosslinking enzyme. We are investigating an alternative biomimetic adhesive based on gelatin and a calcium-independent microbial transglutaminase (mTG). Rheological measurements show that mTG catalyzes the conversion of gelatin solutions into hydrogels, and gel times are on the order of minutes depending on the gelatin type and concentration. Tensile static and dynamic loading of the adhesive hydrogels in bulk form demonstrated that the Young's modulus ranged from 15 to 120 kPa, and these bulk properties were comparable to those reported for hydrogels obtained from fibrin-based sealants. Lap-shear adhesion tests of porcine tissue were performed using a newly published American Society for Testing and Materials (ASTM) standard for tissue adhesives. The gelatin-mTG adhesive bound the opposing tissues together with ultimate adhesive strengths of 12-23 kPa which were significantly higher than the strength observed for fibrin sealants. Even after failure, strands of the gelatin-mTG adhesive remained attached to both of the opposing tissues. These results suggest that gelatin-mTG adhesives may offer the benefits of fibrin sealants without the need for blood products.     

Study In Vivo Intraocular Biocompatibility of In Situ Gelation Hydrogels: Poly(2-Ethyl Oxazoline)-Block-Poly(ε-Caprolactone)-Block-Poly(2-Ethyl Oxazoline) Copolymer,Matrigel and Pluronic F127

The long term in vivo biocompatibility is an essential feature for the design and development of sustained drug release carriers. In the recent intraocular drug delivery studies, hydrogels were suggested as sustained release carriers. The biocompatibility test for these hydrogels, however, was commonly performed only through in vitro cell culture examination, which is insufficient before the clinical applications. We compared three thermosensitive hydrogels that have been suggested as the carriers for drugs by their gel-solution phase-change properties. A new block terpolymer (PEOz-PCL-PEOz, ECE) and two commercial products (Matrigel® and Pluronic F127) were studied. The results demonstrated that the ocular media remained translucent for ECE and Pluronic F127 in the first 2 weeks, but cataract formation for Matrigel occurred in 2 weeks and for Pluronic F127 in 1 month, while turbid media was observed for both Matrigel and Pluronic F127 in 2 months. The electrophysiology examinations showed significant neuroretinal toxicity of Matrigel and Pluronic F127 but good biocompatibility of ECE. The neuroretinal toxicity of Matrigel and Pluronic F127 and superior biocompatibility of ECE hydrogel suggests ECE as more appropriate biomaterial for use in research and potentially in intraocular application.     

Rapid cross-linking of elastin-like polypeptides with (hydroxymethyl)phosphines in aqueous solution

In situ gelation of injectable polypeptide-based materials is attractive for minimally invasive in vivo implantation of biomaterials and tissue engineering scaffolds. We demonstrate that chemically cross-linked elastin-like polypeptide (ELP) hydrogels can be rapidly formed in aqueous solution by reacting lysine-containing ELPs with an organophosphorous cross-linker, beta-[tris(hydroxymethyl)phosphino]propionic acid (THPP) under physiological conditions. The mechanical properties of the cross-linked ELP hydrogels were largely modulated by the molar concentration of lysine residues in the ELP and the pH at which the cross-linking reaction was carried out. Fibroblasts embedded in ELP hydrogels survived the cross-linking process and were viable after in vitro culture for 3 days. DNA quantification of ELP hydrogels with encapsulated fibroblasts indicated that there was no significant difference in DNA content between day 0 and day 3 when ELP hydrogels were formed with an equimolar ratio of THPP and lysine residues of the ELPs. These results suggest that THPP cross-linking may be a biocompatible strategy for the in situ formation of cross-linked hydrogels.     

Preparation of <Emphasis Type="Italic">in situ</Emphasis> Injectable Chitosan/Gelatin Hydrogel Using an Acid-tolerant Tyrosinase

An in situ injectable chitosan/gelatin hydrogel was formed under slightly acidic conditions (pH 4.0 ~ 4.5) using an acid-tolerant tyrosinase, tyrosinase-CNK. A homogeneous chitosan/tyrosinase-CNK solution was prepared in one part of a dual-barrel syringe, and highly soluble gelatin in distilled water was prepared in the other part of the syringe without any additional crosslinking materials. Chitosan/gelatin hydrogel was formed in situ by simple injection of the solutions at room temperature followed by curing at 37°C. However, conventional mushroom tyrosinase did not catalyze this permanent gel formation. Tyrosinase- CNK-catalyzed glycol chitosan/gelatin hydrogel was similarly formed by this in situ injection approach. The hydrogels exhibited a high swelling ratio of 20-fold their own weight, interconnected micropores with an average diameter of approximately 260 μm and in vitro biodegradability suitable for tissue engineering and drug delivery applications. These results showed that tyrosinase-CNK-mediated chitosan/gelatin hydrogel formation has remarkable potential for the development of novel formulations for in situ injectable gel-forming systems.     

Enhanced adhesion of dopamine methacrylamide elastomers via viscoelasticity tuning

We present a study on the effects of cross-linking on the adhesive properties of bio-inspired 3,4-dihydroxyphenylalanine (DOPA). DOPA has a unique catechol moiety found in adhesive proteins in marine organisms, such as mussels and polychaete, which results in strong adhesion in aquatic conditions. Incorporation of this functional group in synthetic polymers provides the basis for pressure-sensitive adhesives for use in a broad range of environments. A series of cross-linked DOPA-containing polymers were prepared by adding divinyl cross-linking agent ethylene glycol dimethacrylate (EGDMA) to monomer mixtures of dopamine methacrylamide (DMA) and 2-methoxyethyl acrylate (MEA). Samples were prepared using a solvent-free microwave-assisted polymerization reaction and compared to a similar series of cross-linked MEA materials. Cross-linking with EGDMA tunes the viscoelastic properties of the adhesive material and has the advantage of not reacting with the catechol group that is responsible for the excellent adhesive performance of this material. Adhesion strength was measured by uniaxial indentation tests, which indicated that 0.001 mol % of EGDMA-cross-linked copolymer showed the highest work of adhesion in dry conditions, but non-cross-linked DMA was the highest in wet conditions. The results suggest that there is an optimal cross-linking degree that displays the highest adhesion by balancing viscous and elastic behaviors of the polymer but this appears to depend on the conditions. This concentration of cross-linker is well below the theoretical percolation threshold, and we propose that subtle changes in polymer viscoelastic properties can result in significant improvements in adhesion of DOPA-based materials. The properties of lightly cross-linked poly(DMA-co-MEA) were investigated by measurement of the frequency dependence of the storage modulus (G') and loss modulus (G'). The frequency-dependence of G' and magnitude of G' showed gradual decreases with the fraction of EGDMA. Loosely cross-linked DMA copolymers, containing 0% and 0.001 mol % of EGDMA-cross-linked copolymers, displayed rheological behavior appropriate for pressure-sensitive adhesives characterized by a higher G' at high frequencies and lower G' at low frequencies. Our results indicate that dimethacrylate cross-linking of DMA copolymers can be used to enhance the adhesive properties of this unique material.     

In vitro cytotoxicity of unsaturated oligo[poly(ethylene glycol) fumarate] macromers and their cross-linked hydrogels

Currently, oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels are being investigated as an injectable and biodegradable system for tissue engineering applications. In this study, cytotoxicity of each component of the OPF hydrogel formulation and the resulting cross-linked network was examined. Specifically, OPF synthesized with poly(ethylene glycol) (PEG) of different molecular weights (MW), the cross-linking agent [PEG-diacrylate (PEG-DA)], and the redox initiator pair [ammonium persulfate (APS) and ascorbic acid (AA)] were evaluated for cytotoxicity at 2 and 24 h using marrow stromal cells (MSCs) as model cells. The effect of leachable byproducts of OPF hydrogels on cytotoxicity was also investigated. Upon exposure to various concentrations of OPF for 2 h, greater than 50% of the MSCs were viable, regardless of OPF molecular weight or concentration in the media. After 24 h, the MSCs maintained more than 75% viability except for OPF concentrations higher than 25% (w/v). When examining the cross-linking agent, PEG-DA of higher MW (3400) demonstrated significantly higher viability compared to PEG-DA with MW 575 at all concentrations tested. Considering initiators, when MSCs were exposed to AA and APS, as well as the combination of AA and APS, higher viability was observed at lower concentrations. Once cross-linked, the leachable products from the OPF hydrogels had minimal adverse effects on the viability of MSCs (percentage of live cells was higher than 90% regardless of hydrogel types). The results suggest that, after optimization of cross-linking parameters, OPF-based hydrogels hold promise as novel injectable scaffolds or cell carriers in tissue engineering.     

Antibacterial Peptide-Based Gel for Prevention of Medical Implanted-Device Infection

Implanted medical devices are prone to infection. Designing new strategies to reduce infection and implant rejection are an important challenge for modern medicine. To this end, in the last few years many hydrogels have been designed as matrices for antimicrobial molecules destined to fight frequent infection found in moist environments like the oral cavity. In this study, two types of original hydrogels containing the antimicrobial peptide Cateslytin have been designed. The first hydrogel is based on alginate modified with catechol moieties (AC gel). The choice of these catechol functional groups which derive from mussel’s catechol originates from their strong adhesion properties on various surfaces. The second type of gel we tested is a mixture of alginate catechol and thiol-terminated Pluronic (AC/PlubisSH), a polymer derived from Pluronic, a well-known biocompatible polymer. This PlubisSH polymer has been chosen for its capacity to enhance the cohesion of the composition. These two gels offer new clinical uses, as they can be injected and jellify in a few minutes. Moreover, we show these gels strongly adhere to implant surfaces and gingiva. Once gelled, they demonstrate a high level of rheological properties and stability. In particular, the dissipative energy of the (AC/PlubisSH) gel detachment reaches a high value on gingiva (10 J.m^-2) and on titanium alloys (4 J.m^-2), conferring a strong mechanical barrier. Moreover, the Cateslytin peptide in hydrogels exhibited potent antimicrobial activities against P. gingivalis, where a strong inhibition of bacterial metabolic activity and viability was observed, indicating reduced virulence. Gel biocompatibility tests indicate no signs of toxicity. In conclusion, these new hydrogels could be ideal candidates in the prevention and/or management of periimplant diseases.     

Reduction of the in vitro hemolytic activity of soybean lecithin liposomes by treatment with a block copolymer

The in vitro hemolytic activity of liposomes made of soybean L-alpha-lecithin towards diluted (0.0086 v/v) human erythrocytes was used to investigate the effect of surface coating on the interaction of liposomes with cells. The increase in apparent volume of the block copolymer of ethylene glycol and propylene glycol, Pluronic F-127, in the presence of liposomes supports the hypothesis of either adsorption or penetration of the copolymer at the surface of the liposomes. When the liposomes are pre-incubated with Pluronic F-127, their lytic activity towards fresh erythrocytes is significantly reduced while it remains unchanged towards erythrocytes aged in vitro. It is also found that aging the liposomes has little effect on their lytic activity while aging of the erythrocytes makes them more fragile towards the liposomes. The results are discussed in terms of steric hindrance.     

Rapidly photo-cross-linkable chitosan hydrogel for peripheral neurosurgeries

Restoring continuity to severed peripheral nerves is crucial to regeneration and enables functional recovery. However, the two most common agents for coaptation, sutures and fibrin glues, have drawbacks such as inflammation, pathogenesis, and dehiscence. Chitosan-based adhesives are a promising alternative, reported to have good cytocompatibility and favorable immunogenicity. A photo-cross-linkable hydrogel based on chitosan is proposed as a new adhesive for peripheral nerve anastomosis. Two Az-chitosans were synthesized by conjugating 4-azidobenzoic acid with low (LMW, 15 kDa) and high (HMW, 50-190 kDa) molecular weight chitosans. These solutions formed a hydrogel in less than 1 min under UV light. The LMW Az-chitosan was more tightly cross-linked than the HMW variant, undergoing significantly less swelling and possessing a higher rheological storage modulus, and both Az-chitosan gels were stiffer than commercial fibrin glue. Severed nerves repaired by Az-chitosan adhesives tolerated longitudinal forces comparable or superior to fibrin glue. Adhesive exposure to intact nerves and neural cell culture showed both Az-chitosans to be nontoxic in the acute (minutes) and chronic (days) time frames. These results demonstrate that Az-chitosan hydrogels are cytocompatible and mechanically suitable for use as bioadhesives in peripheral neurosurgeries.     

Laminin Peptide-Immobilized Hydrogels Modulate Valve Endothelial Cell Hemostatic Regulation

Valve endothelial cells (VEC) have unique phenotypic responses relative to other types of vascular endothelial cells and have highly sensitive hemostatic functions affected by changes in valve tissues. Furthermore, effects of environmental factors on VEC hemostatic function has not been characterized. This work used a poly(ethylene glycol) diacrylate (PEGDA) hydrogel platform to evaluate the effects of substrate stiffness and cell adhesive ligands on VEC phenotype and expression of hemostatic genes. Hydrogels of molecular weights (MWs) 3.4, 8, and 20 kDa were polymerized into platforms of different rigidities and thiol-modified cell adhesive peptides were covalently bound to acrylate groups on the hydrogel surfaces. The peptide RKRLQVQLSIRT (RKR) is a syndecan-1 binding ligand derived from laminin, a trimeric protein and a basement membrane matrix component. Conversely, RGDS is an integrin binding peptide found in many extracellular matrix (ECM) proteins including fibronectin, fibrinogen, and von Willebrand factor (VWF). VECs adhered to and formed a stable monolayer on all RKR-coated hydrogel-MW combinations. RGDS-coated platforms supported VEC adhesion and growth on RGDS-3.4 kDa and RGDS-8 kDa hydrogels. VECs cultured on the softer RKR-8 kDa and RKR-20 kDa hydrogel platforms had significantly higher gene expression for all anti-thrombotic (ADAMTS-13, tissue factor pathway inhibitor, and tissue plasminogen activator) and thrombotic (VWF, tissue factor, and P-selectin) proteins than VECs cultured on RGDS-coated hydrogels and tissue culture polystyrene controls. Stimulated VECs promoted greater platelet adhesion than non-stimulated VECs on their respective culture condition; yet stimulated VECs on RGDS-3.4 kDa gels were not as responsive to stimulation relative to the RKR-gel groups. Thus, the syndecan binding, laminin-derived peptide promoted stable VEC adhesion on the softer hydrogels and maintained VEC phenotype and natural hemostatic function. In conclusion, utilization of non-integrin adhesive peptide sequences derived from basement membrane ECM may recapitulate balanced VEC function and may benefit endothelialization of valve implants.     

Rheological study of genipin cross-linked chitosan hydrogels

This paper reports the rheological behavior of chitosan solutions that have been cross-linked with different amounts of genipin, at body temperature and physiological pH. The effect of the cross-linker loading on the rheological properties of hydrogels has been evaluated. The oscillatory time sweep method was used to monitor the dynamic viscoelastic parameters during in situ (i.e., in the rheometer) gelation experiments, enabling the determination of the gelation time. The stress and frequency sweeps were employed to measure G' of the cured hydrogels. It was found that the solutions of chitosan cross-linked with genipin, under physiological conditions, could form relatively strong elastic gels when compared to those of pure chitosan. Moreover, the gelation time obtained from the crossover of G' and G' was in excellent agreement with the value obtained from the Winter-Chambon criterion. A significant reduction on this parameter was achieved even at low genipin concentrations. This behavior suggests that these formulations are able to be produced in situ and thus constitute promising matrices for cells and bioactive molecule encapsulations.     

Swelling and mechanical properties of biopolymer hydrogels containing chitosan and bovine serum albumin

Experimental and theoretical investigations of the swelling and mechanical properties of hydrogels formed from chitosan, bovine serum albumin (BSA), and chitosan/BSA mixtures cross-linked with genipin were performed. The properties of cross-linked chitosan hydrogels were explained in terms of its polyelectrolyte behavior, which led to a gradual increase in swelling ratio below the pK value, but whereby its swelling ability was eliminated by the presence of salt that screened the charges. Comparison of theoretical and experimental calculations of the swelling ratio, however, indicated that complications arising from wastage of cross-links, and formation of polymerized genipin cross-links must be considered before quantitative prediction can be achieved. Cross-linked BSA hydrogels swelled even in the presence of salt, and a marked increase in swelling was observed below pH = 3 that was explained as the result of an acid induced denaturation of the protein that led to unfolding of the molecule. Swollen BSA hydrogels were mechanically weak, however. Composite gels made from a cross-linked mixture of chitosan and BSA exhibited the swelling behavior of BSA combined with the mechanical properties of chitosan and were therefore considered most suitable for use in a gastric environment.