Synthesis and evaluation of novel biodegradable hydrogels based on poly(ethylene glycol) and sebacic acid as tissue engineering scaffolds

Novel biodegradable poly(ethylene glycol) (PEG) based hydrogels, namely, PEG sebacate diacrylate (PEGSDA) were synthesized, and their properties were evaluated. Chemical structures of these polymers were confirmed by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR) spectroscopy. After photopolymerization, the dynamic shear modulus of the hydrogels was up to 0.2 MPa for 50% PEGSDA hydrogel, significantly higher than conventional hydrogels such as PEG diacrylate (PEGDA). The swelling ratios of these macromers were significantly lower than PEGDA. The in vitro degradation study demonstrated that these hydrogels were biodegradable with weight losses about 66% and 32% for 25% and 50% PEGSDA after 8 weeks of incubation in phosphate-buffered saline at 37 degrees C. In vitro biocompatibility was assessed using cultured rat bone marrow stromal cells (MSCs) in the presence of unreacted monomers or degradation products. Unlike conventional PEGDA hydrogels, PEGSDA hydrogel without RGD peptide modification induced MSC cell adhesion similar to tissue culture polystyrene. Finally, complex three-dimensional structures of PEGSDA hydrogels using solid free form technique were fabricated and their structure integrity was better maintained than PEGDA hydrogels. These hydrogels may find use as scaffolds for tissue engineering applications.     

Biomimetic poly(ethylene glycol)-based hydrogels as scaffolds for inducing endothelial adhesion and capillary-like network formation

The extracellular matrix (ECM) is an attractive model for designing synthetic scaffolds with a desirable environment for tissue engineering. Here, we report on the synthesis of ECM-mimetic poly(ethylene glycol) (PEG) hydrogels for inducing endothelial cell (EC) adhesion and capillary-like network formation. A collagen type I-derived peptide GPQGIAGQ (GIA)-containing PEGDA (GIA-PEGDA) was synthesized with the collagenase-sensitive GIA sequence attached in the middle of the PEGDA chain, which was then copolymerized with RGD capped-PEG monoacrylate (RGD-PEGMA) to form biomimetic hydrogels. The hydrogels degraded in vitro with the rate dependent on the concentration of collagenase and also supported the adhesion of human umbilical vein ECs (HUVECs). Biomimetic RGD/GIA-PEGDA hydrogels with incorporation of 1% RGD-PEGDA into GIA-PEGDA hydrogels induced capillary-like organization when HUVECs were seeded on the hydrogel surface, while RGD/PEGDA and GIA-PEGDA hydrogels did not. These results indicate that both cell adhesion and biodegradability of scaffolds play important roles in the formation of capillary-like networks.     

Synthesis and degradation test of hyaluronic acid hydrogels

Hyaluronic acid (HA) hydrogels prepared with three different crosslinking reagents were assessed by in vitro and in vivo degradation tests for various tissue engineering applications. Adipic acid dihydrazide grafted HA (HA-ADH) was synthesized and used for the preparation of methacrylated HA (HA-MA) with methacrylic anhydride and thiolated HA (HA-SH) with Traut's reagent (imminothiolane). (1)H NMR analysis showed that the degrees of HA-ADH, HA-MA, and HA-SH modification were 69, 29, and 56 mol%, respectively. HA-ADH hydrogel was prepared by the crosslinking with bis(sulfosuccinimidyl) suberate (BS(3)), HA-MA hydrogel with dithiothreitol (DTT) by Michael addition, and HA-SH hydrogel with sodium tetrathionate by disulfide bond formation. According to in vitro degradation tests, HA-SH hydrogel was degraded very fast, compared to HA-ADH and HA-MA hydrogels. HA-ADH hydrogel was degraded slightly faster than HA-MA hydrogel. Based on these results, HA-MA hydrogels and HA-SH hydrogels were implanted in the back of SD rats and their degradation was assessed according to the pre-determined time schedule. As expected from the in vitro degradation test results, HA-SH hydrogel was in vivo degraded completely only in 2 weeks, whereas HA-MA hydrogels were degraded only partially even in 29 days. The degradation rate of HA hydrogels were thought to be controlled by changing the crosslinking reagents and the functional group of HA derivatives. In addition, the state of HA hydrogel was another factor in controlling the degradation rate. Dried HA hydrogel at 37 degrees C for a day resulted in relatively slow degradation compared to the bulk HA hydrogel. There was no adverse effect during the in vivo tests.     

Synthesis and characterization of dendron cross-linked PEG hydrogels as corneal adhesives

In pursuit of a wound-specific corneal adhesive, hydrogels formed by the reaction of propionaldehyde, butyraldehyde, or 2-oxoethyl succinate-functionalized poly(ethylene glycol) (PEG) with a peptide-based dendritic cross-linker (Lys(3)Cys(4)) were characterized. These macromers react within minutes of mixing to form transparent and elastic hydrogels with in vitro degradation times that range from hours to months based on the type of bonds formed during the cross-linking reaction, either thiazolidine or pseudoproline. The mechanical properties of these materials, determined via parallel plate rheology, were dependent on the polymer concentration, as was the hydrogel adhesive strength, which was determined by lap shear adhesive testing. In addition, these hydrogels were efficacious in closing ex vivo 4.1 mm central corneal lacerations: wounds closed with these hydrogel adhesives were able to withstand intraocular pressure values equivalent to, or in excess of, those obtained by closing the wounds with suturing.     

Enzymatically degradable mussel-inspired adhesive hydrogel

Mussel-inspired adhesive hydrogels represent innovative candidate medical sealants or glues. In the present work, we describe an enzyme-degradable mussel-inspired adhesive hydrogel formulation, achieved by incorporating minimal elastase substrate peptide Ala-Ala into the branched poly(ethylene glycol) (PEG) macromonomer structure. The system takes advantage of neutrophil elastase expression upregulation and secretion from neutrophils upon recruitment to wounded or inflamed tissue. By integrating adhesive degradation behaviors that respond to cellular cues, we expand the functional range of our mussel-inspired adhesive hydrogel platforms. Rapid (<1 min) and simultaneous gelation and adhesion of the proteolytically active, catechol-terminated precursor macromonomer was achieved by addition of sodium periodate oxidant. Rheological analysis and equilibrium swelling studies demonstrated that the hydrogel is appropriate for soft tissue-contacting applications. Notably, hydrogel storage modulus (G') achieved values on the order of 10 kPa, and strain at failure exceeded 200% strain. Lap shear testing confirmed the material's adhesive behavior (shear strength: 30.4 ± 3.39 kPa). Although adhesive hydrogel degradation was not observed during short-term (27 h) in vitro treatment with neutrophil elastase, in vivo degradation proceeded over several months following dorsal subcutaneous implantation in mice. This work represents the first example of an enzymatically degradable mussel-inspired adhesive and expands the potential biomedical applications of this family of materials.     

Development of a temperature-sensitive composite hydrogel for drug delivery applications

To develop materials with improved controllability and specificity, we have investigated composite hydrogels with temperature-sensitive properties using photo cross-linking. Specifically, our novel composite materials are composed of nanoparticles made of poly(N-isopropylacrylamide) (PNIPAAm), temperature-sensitive hydrogels, and a photo cross-linker, poly(ethylene glycol) diacrylate (PEGDA). PNIPAAm particles were synthesized by emulsion polymerization and by varying concentration of four main factors: monomers (N-isopropylacrylamide), cross-linkers (N,N'-methylenebisacrylamide), surfactants (sodium dodecyl sulfate, SDS), and initiators (potassium persulfate). We found that the surfactant, SDS, was the most important factor affecting the particle size using the factorial design analysis. Additionally, both nano- and micro-PNIPAAm particles had excellent loading efficiency (>80% of the incubated bovine serum albumin (BSA)), and their release kinetics expressed an initial burst effect followed by a sustained release over time. Furthermore, BSA-loaded PNIPAAm nanoparticles were used to form three-dimensional gel networks by means of a photocuring process using a photo cross-linker, PEGDA, and a photoinitiator, Irgacure-2959 (I-2959). Results from scanning electron microscopy and in vitro BSA release studies from these hydrogels demonstrated that PNIPAAm nanoparticles were embedded inside the PEG polymeric matrix and the composite material was able to release BSA in response to changes in temperature. These PNIPAAm nanoparticle hydrogel networks may have advantages in applications of controlled drug delivery systems because of their temperature sensitivity and their ability of in situ photopolymerization to localize at the specific region in the body.     

Cross-linking and degradation of step-growth hydrogels formed by thiol-ene photoclick chemistry

Thiol-ene photoclick hydrogels have been used for a variety of tissue engineering and controlled release applications. In this step-growth photopolymerization scheme, four-arm poly(ethylene glycol) norbornene (PEG4NB) was cross-linked with dithiol containing cross-linkers to form chemically cross-linked hydrogels. While the mechanism of thiol-ene gelation was well described in the literature, its network ideality and degradation behaviors are not well-characterized. Here, we compared the network cross-linking of thiol-ene hydrogels to Michael-type addition hydrogels and found thiol-ene hydrogels formed with faster gel points and higher degree of cross-linking. However, thiol-ene hydrogels still contained significant network nonideality, demonstrated by a high dependency of hydrogel swelling on macromer contents. In addition, the presence of ester bonds within the PEG-norbornene macromer rendered thiol-ene hydrogels hydrolytically degradable. Through validating model predictions with experimental results, we found that the hydrolytic degradation of thiol-ene hydrogels was not only governed by ester bond hydrolysis, but also affected by the degree of network cross-linking. In an attempt to manipulate network cross-linking and degradation of thiol-ene hydrogels, we incorporated peptide cross-linkers with different sequences and characterized the hydrolytic degradation of these PEG-peptide hydrogels. In addition, we incorporated a chymotrypsin-sensitive peptide as part of the cross-linkers to tune the mode of gel degradation from bulk degradation to surface erosion.     

An approach to modulate degradation and mesenchymal stem cell behavior in poly(ethylene glycol) networks

A simple, sequential approach for creation of hydrolytically degradable poly(ethylene glycol) (PEG) hydrogels has been developed and characterized. The chemistry involves an initial step growth polymerization reaction between PEG-diacrylate and dithiothreitol (DTT) to form acrylate-terminated (-PEG-DTT-)n PEG chains, followed by photocross-linking to form a hydrogel network. Varying the extent of step growth polymerization prior to photocross-linking allowed for control over the equilibrium swelling ratio, degradation, and erosion of PEG hydrogels. Hydrogel degradability had a significant effect on behavior of human mesenchymal stem cells (hMSCs) encapsulated within PEG hydrogels, both in the presence and absence of an RGDSP cell adhesion ligand. In particular, enhanced network degradability resulted in enhanced hMSC viability and spreading during in vitro culture. Comparison of degradable and nondegradable hydrogels with similar physical properties (e.g., equilibrium swelling ratio) demonstrated that hMSC viability and spreading were dependent on network degradability. This study demonstrates that hydrolytically degradable PEG hydrogels can be formed via a sequential step growth polymerization and photocross-linking process and the resulting materials may serve as promising matrices for 3-dimensional stem cell culture and tissue engineering applications.     

Characterization of protein release from hydrolytically degradable poly(ethylene glycol) hydrogels

We present a novel fully hydrophilic, hydrolytically degradable poly(ethylene glycol) (PEG) hydrogel suitable for soft tissue engineering and delivery of protein drugs. The gels were designed to overcome drawbacks associated with current PEG hydrogels (i.e., reaction mechanisms or degradation products that compromise protein stability): the highly selective and mild cross‐linking reaction allowed for encapsulating proteins prior to gelation without altering their secondary structure as shown by circular dichroism experiments. Further, hydrogel degradation and structure, represented by mesh size, were correlated to protein release. It was determined that polymer density had the most profound effect on protein diffusivity, followed by the polymer molecular weight, and finally by the specific chemical structure of the cross‐linker. By examining the diffusion of several model proteins, we confirmed that the protein diffusivity was dependent on protein size as smaller proteins (e.g., lysozyme) diffused faster than larger proteins (e.g., Ig). Furthermore, we demonstrated that the protein physical state was preserved upon encapsulation and subsequent release from the PEG hydrogels and contained negligible aggregation or protein–polymer adducts. These initial studies indicate that the developed PEG hydrogels are suitable for release of stable proteins in drug delivery and tissue engineering applications. Biotechnol. Bioeng. 2011; 108:197–206. © 2010 Wiley Periodicals, Inc.     

Evaluation of Physical and Mechanical Properties of Porous Poly (Ethylene Glycol)-co-(L-Lactic Acid) Hydrogels during Degradation

Porous hydrogels of poly(ethylene glycol) (PEG) have been shown to facilitate vascularized tissue formation. However, PEG hydrogels exhibit limited degradation under physiological conditions which hinders their ultimate applicability for tissue engineering therapies. Introduction of poly(_L-lactic acid) (PLLA) chains into the PEG backbone results in copolymers that exhibit degradation via hydrolysis that can be controlled, in part, by the copolymer conditions. In this study, porous, PEG-PLLA hydrogels were generated by solvent casting/particulate leaching and photopolymerization. The influence of polymer conditions on hydrogel architecture, degradation and mechanical properties was investigated. Autofluorescence exhibited by the hydrogels allowed for three-dimensional, non-destructive monitoring of hydrogel structure under fully swelled conditions. The initial pore size depended on particulate size but not polymer concentration, while degradation time was dependent on polymer concentration. Compressive modulus was a function of polymer concentration and decreased as the hydrogels degraded. Interestingly, pore size did not vary during degradation contrary to what has been observed in other polymer systems. These results provide a technique for generating porous, degradable PEG-PLLA hydrogels and insight into how the degradation, structure, and mechanical properties depend on synthesis conditions.     

Lubricin is expressed in chondrocytes derived from osteoarthritic cartilage encapsulated in poly (ethylene glycol) diacrylate scaffold

Osteoarthritis (OA) is characterized by degenerative changes within joints that involved quantitative and/or qualitative alterations of cartilage and synovial fluid lubricin, a mucinous glycoprotein secreted by synovial fibroblasts and chondrocytes. Modern therapeutic methods, including tissue-engineering techniques, have been used to treat mechanical damage of the articular cartilage but to date there is no specific and effective treatment. This study aimed at investigating lubricin immunohistochemical expression in cartilage explant from normal and OA patients and in cartilage constructions formed by Poly (ethylene glycol) (PEG) based hydrogels (PEG-DA) encapsulated OA chondrocytes. The expression levels of lubricin were studied by immunohistochemistry: i) in tissue explanted from OA and normal human cartilage; ii) in chondrocytes encapsulated in hydrogel PEGDA from OA and normal human cartilage. Moreover, immunocytochemical and western blot analysis were performed in monolayer cells from OA and normal cartilage. The results showed an increased expression of lubricin in explanted tissue and in monolayer cells from normal cartilage, and a decreased expression of lubricin in OA cartilage. The chondrocytes from OA cartilage after 5 weeks of culture in hydrogels (PEGDA) showed an increased expression of lubricin compared with the control cartilage. The present study demonstrated that OA chondrocytes encapsulated in PEGDA, grown in the scaffold and were able to restore lubricin biosynthesis. Thus our results suggest the possibility of applying autologous cell transplantation in conjunction with scaffold materials for repairing cartilage lesions in patients with OA to reduce at least the progression of the disease.     

Polysaccharide-poly(ethylene glycol) star copolymer as a scaffold for the production of bioactive hydrogels

The production of polysaccharide-derivatized surfaces, polymers, and biomaterials has been shown to be a useful strategy for mediating the biological properties of materials, owing to the importance of polysaccharides for the sequestration and protection of bioactive proteins in vivo. We have therefore sought to combine the benefits of polysaccharide derivatization of polymers with unique opportunities to use these polymers for the production of bioactive, noncovalently assembled hydrogels. Accordingly, we report the synthesis of a heparin-modified poly(ethylene glycol) (PEG) star copolymer that can be used in the assembly of bioactive hydrogel networks via multiple strategies and that is also competent for the delivery of bioactive growth factors. A heparin-decorated polymer, synthesized by the reaction of thiol end-terminated four-arm star PEG (M(n) = 10 000) with maleimide functionalized low molecular weight heparin (LMWH, M(r) = 3000), has been characterized via (1)H NMR spectroscopy and size-exclusion chromatography; results indicate attachment of the LMWH with at least 73% efficiency. Both covalently and noncovalently assembled hydrogels can be produced from the PEG-LMWH conjugate. Viscoelastic noncovalently assembled hydrogels have been formed on the basis of the interaction of the PEG-LMWH with a PEG polymer bearing multiple heparin-binding peptide motifs. The binding and release of therapeutically important proteins from the assembled hydrogels have also been demonstrated via immunochemical assays, which demonstrate the slow release of basic fibroblast growth factor (bFGF) as a function of matrix erosion. The combination of these results suggests the opportunities for producing polymer-polysaccharide conjugates that can assemble into novel hydrogel networks on the basis of peptide-saccharide interactions and for employing these materials in delivery applications.     

Smart hydrogels based on semi-interpenetrating polymeric networks of collagen-polyurethane-alginate for soft/hard tissue healing,drug delivery devices,and anticancer therapies

In this work, hydrogels based on semi-interpenetrating polymeric networks (semi-IPN) based on collagen-polyurethane-alginate were studied physicochemically and from different approaches for biomedical application. It was determined that the matrices in the hydrogel state are crosslinked by the formation of urea and amide bonds between the biopolymer chains and the polyurethane crosslinker. The increment in alginate content (0–40 wt%) significantly increases the swelling capacity, generating semi-crystalline granular structures with improved storage modulus and resistance to thermal, hydrolytic, and proteolytic degradation. The in vitro bioactivity results indicated that the composition of these novel hydrogels stimulates the metabolic activity of monocytes and fibroblasts, benefiting their proliferation; while in cancer cell lines, it was determined that the composition of these biomaterials decreases the metabolic activity of breast cancer cells after 48 h of stimulation, and for colon cancer cells their metabolic activity decreases after 72 h of contact for the hydrogel with 40 wt% alginate. The matrices show a behavior of multidose release of ketorolac, and a higher concentration of analgesic is released in the semi-IPN matrix. The inhibition capacity of Escherichia coli is higher if the polysaccharide concentration is low (10 wt%). The in vitro wound closure test (scratch test) results indicate that the hydrogel with 20 wt% alginate shows an improvement in wound closure at 15 days of contact. Finally, the bioactivity of mineralization was evaluated to demonstrate that these hydrogels can induce the formation of carbonated apatite on their surface. The engineered hydrogels show biomedical multifunctionality and they could be applied in soft and hard tissue healing strategies, anticancer therapies, and drug release devices.     

Development of macroporous poly(ethylene glycol) hydrogel arrays within microfluidic channels

The mass transport of solutes through hydrogels is an important design consideration in materials used for tissue engineering, drug delivery, and protein arrays used to quantify protein concentration and activity. We investigated the use of poly(ethylene glycol) (PEG) as a porogen to enhance diffusion of macromolecules into the interior of polyacrylamide and PEG hydrogel posts photopatterned within microfluidic channels. The diffusion of GST-GFP and dextran-FITC into hydrogels was monitored and effective diffusion coefficients were determined by fitting to the Fickian diffusion equations. PEG-diacrylate (M(r) 700) with porogen formed a macroporous structure and permitted significant penetration of 250 kDa dextran. Proteins copolymerized in these macroporous hydrogels retained activity and were more accessible to antibody binding than proteins copolymerized in nonporous gels. These results suggest that hydrogel macroporosity can be tuned to regulate macromolecular transport in applications such as tissue engineering and protein arrays.     

Synthesis and characterization of novel thiol-reactive poly(ethylene glycol) cross-linkers for extracellular-matrix-mimetic biomaterials

Synthetic extracellular matrix hydrogels can be used for three-dimensional cell culture, wound repair, and tissue engineering. Using the bifunctional electrophile poly(ethylene glycol) diacrylate (PEGDA), thiol-modified glycosaminoglycans and polypeptides can be cross-linked into biocompatible materials in the presence of cells or tissues. However, the rate of in situ cross-linking with PEGDA under physiological conditions may occur too slowly for clinical applications requiring a fast-curing preparation. To explore a wider range of cross-linking time courses, five homo-bifunctional PEG derivatives were synthesized and examined as cross-linking agents for thiol-modified derivatives of hyaluronan (HA). Thiol reaction rate constants were measured over a pH range of 7.4 to 8.6. The order of reactivity for the functional groups used was determined to be maleimide > iodoacetate > bromoacetate > iodoacetamide > acrylate > bromoacetamide, with rates increasing exponentially with increasing pH. The range of gelation times at physiological pH varied from less than 1 min to over 2 h. Addition of the cross-linkers to cell culture medium showed minimal cytotoxicity toward primary human dermal fibroblasts at concentrations anticipated during in situ cross-linking. Moreover, hydrogels prepared from thiol-modified gelatin and thiol-modified HA were biocompatible and supported attachment and proliferation of fibroblasts and hepatocytes.     

Porphyrin-cross-linked hydrogel for fluorescence-guided monitoring and surgical resection

We demonstrate that porphyrins can be used as efficient cross-linkers to generate a new class of hydrogels with enabling optical properties. Tetracarboxylic acid porphyrins reacted with PEG diamines to form a condensation polyamide in a range of appropriate conditions, with respect to reaction time, diisopropylethylamine initiator concentration, porphyrin-to-PEG ratio, porphyrin concentration, and PEG size. The network structure of the hydrogel maintained a porphyrin spacing that prevented excessive fluorescence self-quenching despite high porphyrin density. The near-infrared properties readily enabled low background, noninvasive fluorescence monitoring of the implanted hydrogel in vivo, as well as its image-guided surgical removal in real time using a low-cost fluorescence camera prototype. Emission could be tuned by incorporating copper metalloporphyrins into the network. The approach of creating hydrogels using cross-linking porphyrin comonomers creates opportunities for new polymer designs with strong optical character.     

Heparin interacting protein mediated assembly of nano-fibrous hydrogel scaffolds for guided stem cell differentiation

A new methodology is developed to conjugate hyaluronic acid (HA) hydrogel with novel nano-fibrous architectures via non-covalent assembly that specifically allows for targeted adipose-derived stem cells (ASCs) differentiation and soft tissue engineering. The assembly of non-covalently associated hydrogel network produced via the interaction of a low molecular weight heparin (LMWH) modified HA derivative and heparin interacting protein (HIP). The multifunctional star poly(ethylene glycol) (PEG) and HIP copolymer has the capability to mediate the non-covalent assembly of nano-fibrous HA hydrogel networks via affinity interactions with LMWH. The effect of the HIP mediation on in vitro gelation, rheological characteristics, degradation, equilibrium swelling, adipose-derived stem cells (ASCs) proliferation and differentiation of nano-fibrous hydrogel is examined. The results suggest the potential utility of this unique design of the bioactive nano-fibrous HA hydrogel in directing the differentiation of ASCs and adipogenesis in ECM-mimetic scaffolds in vitro. These studies demonstrate that this nano-fibrous HA hydrogel can render the formulation of a therapeutically effective platform for in vitro adipogenesis applications.     

Highly extensible, tough, and elastomeric nanocomposite hydrogels from poly(ethylene glycol) and hydroxyapatite nanoparticles

Unique combinations of hard and soft components found in biological tissues have inspired researchers to design and develop synthetic nanocomposite gels and hydrogels with elastomeric properties. These elastic materials can potentially be used as synthetic mimics for diverse tissue engineering applications. Here we present a set of elastomeric nanocomposite hydrogels made from poly(ethylene glycol) (PEG) and hydroxyapatite nanoparticles (nHAp). The aqueous nanocomposite PEG-nHAp precursor solutions can be injected and then covalently cross-linked via photopolymerization. The resulting PEG-nHAp hydrogels have interconnected pore sizes ranging from 100 to 300 nm. They have higher extensibilities, fracture stresses, compressive strengths, and toughness when compared with conventional PEO hydrogels. The enhanced mechanical properties are a result of polymer nanoparticle interactions that interfere with the permanent cross-linking of PEG during photopolymerization. The effect of nHAp concentration and temperature on hydrogel swelling kinetics was evaluated under physiological conditions. An increase in nHAp concentration decreased the hydrogel saturated swelling degree. The combination of PEG and nHAp nanoparticles significantly improved the physical and chemical hydrogel properties as well as some biological characteristics such as osteoblast cell adhesion. Further development of these elastomeric materials can potentially lead to use as a matrix for drug delivery and tissue repair especially for orthopedic applications.     

Photo-cross-linked hydrogels with polysaccharide-poly(amino acid) structure: new biomaterials for pharmaceutical applications

The aim of this work has been the preparation and characterization of novel hydrogels with polysaccharide-poly(amino acid) structure having suitable physicochemical properties for pharmaceutical applications. In the first step, hyaluronic acid (HA) and alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) have been derivatized with methacrylic anhydride (AMA), thus obtaining HA-AMA and PHM derivatives, respectively. In the second step, aqueous solutions of both these derivatives have been irradiated at 313 nm to obtain chemical hydrogels. The hydrogel obtained by irradiating for 15 min an aqueous solution containing 4% w/v of HA-AMA and 4% w/v of PHM resulted in the highest yield. Its swelling ability was dependent on the pH and nature of the external medium. Besides, this hydrogel undergoes a partial hydrolysis, especially in the presence of enzymes, such as esterase or hyaluronidase, but the entity of this degradation is lower than that observed for a hydrogel based on HA-AMA alone. The ability of this hydrogel to entrap drug molecules has been evaluated by using thrombin as a model drug. In vitro release studies and a platelet aggregation test demonstrated that the HA-AMA/PHM hydrogel is able to release thrombin in the active form, thus suggesting its suitability for the treatment of hemorrhages.