Successful regeneration of the cranium in patients suffering from cranial bone defects is an integral step to restore craniofacial function. However, restoration of craniofacial structure has been challenging due to its complex geometry, limited donor site availability, and poor graft integration. To address these problems, we investigated the use of a thiol–acrylate hydrogel as a cell carrier to facilitate cranial regeneration. Thiol–acrylate hydrogels were formulated with 5–15 wt% poly(ethylene glycol)-diacrylate (PEGDA) and 1–9 mm dithiothreitol (DTT). The degradation rate, swelling ratio, and shear modulus of the resulting hydrogel were first characterized. Then, pre-osteoblast-like cells (MC3T3-E1) were encapsulated in the hydrogel and cultured for up to 21 d. Our results demonstrate that compared to samples formulated from 15 wt% PEGDA, 5 wt% PEGDA samples showed lower storage modulus at day 10 (0.7 kPa versus 8.3 kPa), 62.7% higher in weight change after soaking for 10 d. While the 5 wt% PEGDA group showed an 85% weight loss between day 10 and 21, the 15 wt% PEGDA group showed a 5% weight gain in the same time period. Cell viability with 15 wt% PEGDA and 5 mm DTT hydrogel decreased by 41.3% compared to 5 wt% PEGDA and 5mM DTT gel at day 7. However, histological analysis of cells after 21 d in culture revealed that they had pericellular mineral deposition indicating that the cells were differentiating into osteoblasts lineage in all experimental groups. This study shows that thiol–acrylate hydrogels can be tailored to achieve different degradation rates, in order to enhance cell viability and differentiation. Thus, the findings of this study provide a fundamental understanding for the application of thiol–acrylate hydrogels in cranial bone regeneration.

Hydrogels are crosslinked hydrophilic matrices for a variety of biomedical applications. Silk fibroin (SF), one of typical natural biomaterials, has been explored as base material for hydrogel. Photocrosslinked SF hydrogel containing poly(ethylene glycol) (PEG) was formulated through visible light initiated thiol-acrylate photopolymerization. The morphological, structural and thermal properties of SF . PEG hydrogel was investigated through scanning electron microscopy, X-ray diffractometry, thermogravimetry, and differential scanning calorimetry. The morphology of SF hydrogel showed dot and uneven surface with network cross-section. X-ray diffraction curves showed that the specific diffraction peaks of PEG were not changed by the intensity of the peaks were affected by sonication. Thermo-degradation behavior of SF . PEG hydrogel sonicated was significantly affected and became complex pattern compared to unsonicated ones. However, the melting endothermic temperature of SF-PEG hydrogel was not changed but the crystalline enthalpy was decreased by gelation and sonication.

Various polymerization mechanisms have been developed to prepare peptide-immobilized poly(ethylene glycol) (PEG) hydrogels, a class of biomaterials suitable for studying cell biology in vitro. Here, a visible light mediated thiol-acrylate photopolymerization scheme is reported to synthesize dually degradable PEG-peptide hydrogels with controllable crosslinking and degradability. The influence of immobilized monothiol pendant peptide is systematically evaluated on the crosslinking of these hydrogels. Further, methods are proposed to modulate hydrogel crosslinking, including adjusting concentration of comonomer or altering the design of multifunctional peptide crosslinker. Due to the formation of thioether ester bonds, these hydrogels are hydrolytically degradable. If the dithiol peptide linkers used are susceptible to protease cleavage, these thiol-acrylate hydrogels can be designed to undergo partial proteolysis. The differences between linear and multiarm PEG-acrylate (i.e., PEGDA vs PEG4A) are also evaluated. Finally, the use of the mixed-mode thiol-acrylate PEG4A-peptide hydrogels is explored for in situ encapsulation of hepatocellular carcinoma cells (Huh7). The effects of matrix stiffness and integrin binding motif (e.g., RGDS) on Huh7 cell growth and HIPPO pathway activation are studied using PEG4A-peptide hydrogels. This visible light poly-merized thiol-acrylate hydrogel system represents an alternative to existing light-cured hydrogel platforms and shall be useful in many biomedical applications.

Facile formation of silk fibroin/gelatin-heparin hybrid hydrogels for affinity-based growth factor sequestration and release.

Hydrogels fabricated from poly (ethylene glycol) (PEG) based macromers are ideal for drug delivery and tissue engineering applications. Recently, a new visible light-mediated photopolymerization scheme was developed to fabricate cytocompatible and degradable poly (ethylene glycol)-diacrylate (PEGDA) hydrogels. Co-polymerization of mono-cysteine peptides (e.g. CRGDS) with PEGDA offers the gels with cell adhesion property. However, this approach causes significant reduction in network crosslinking density, in part due to chain transfer of thiols to acrylates. The goal of the project is to improve the network cross-linking efficiency of this peptide-immobilized PEGDA hydrogel for cell culture. We hypothesized that the incorporation of bi-functional bis-cysteine peptides or silk fibroin will produce hydrogels with enhanced stiffness. The shear moduli of the gels were characterized via oscillatory rheometry in strain-sweep (0.1-5%) mode. Hydrolytic degradation of the gels as a function of time was also evaluated by rheometry. Cytocompatibility of the hydrogel system will be assessed by in situ encapsulation of 3T3 fibroblasts. Cell metabolic activity was determined by Alamar-Blue assay. We found that the bis-cysteine peptide enhanced gel crosslinking, as compared with mono-cysteine peptide. Incorporation of silk fibroin protein also exhibited enhancement in gel stiffness. However, the optimum concentration of incorporated silk fibroin presented an increased shear modulus compared to gels containing only the mono-cysteine peptide. Ongoing work is focused on fine-tuning gel formulations and degradation, as well as on evaluating the cytocompatibility of these visible-light cured thiol-acrylate hydrogels.

ABSTRACTA variety of polymers of synthetic origins (e.g., poly(ethylene glycol) or PEG) and macromolecules derived from natural resources (e.g., silk fibroin or SF) have been explored as the backbone materials for hydrogel crosslinking. Purely synthetic PEG‐based hydrogels are often chemically crosslinked to possess limited degradability, unless labile motifs are designed and integrated into the otherwise non‐degradable macromers. On the other hand, SF produced by Bombyx mori silkworm can be easily formulated into physical hydrogels. These physical gels, however, are less stable than the chemically crosslinked gels. Here, we present a simple strategy to prepare hybrid PEG‐SF hydrogels with chemically crosslinked PEG network and physically entrapped SF. Visible light irradiation initiated rapid thiol‐acrylate gelation to produce a network composed of non‐degradable poly(acrylate‐co‐NVP) chains, hydrolytically labile thioether ester bonds, and interpenetrating SF fibrils. We evaluated the effect of SF entrapment on the crosslinking efficiency and hydrolytic degradation of thiol‐acrylate PEG hydrogels. We further examined the effect of adding soluble SF or sonicated SF (S‐SF) on physical gelation of the hybrid materials. The impacts of SF or S‐SF inclusion on the properties of chemically crosslinked hybrid hydrogels were also studied, including gel points, gel fraction, equilibrium swelling ratio, and mesh size. We also quantified the fraction of SF retention in PEG hydrogels, as well as the influence of remaining SF on moduli and degradation of chemically crosslinked thiol‐acrylate PEG hydrogels. This simple hybrid hydrogel fabrication strategy should be highly useful in future drug delivery and tissue engineering applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43075.