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, we report a visible light mediated thiol-acrylate photopolymerization scheme to synthesize dually degradable PEG-peptide hydrogels with controllable crosslinking and degradability. We systematically evaluated the influence of immobilized mono-thiol pendant peptide on the crosslinking of these hydrogels. We further proposed methods to modulate hydrogel crosslinking, including adjusting concentration of co-monomer or altering the design of multifunctional peptide crosslinker. Due to the formation of thioether ester bonds, these hydrogels were hydrolytically degradable. If the di-thiol peptide linkers used were susceptible to protease cleavage, these thiol-acrylate hydrogels could be designed to undergo partial proteolysis. The differences between linear and multi-arm PEG-acrylate (i.e., PEGDA vs. PEG4A) were also evaluated. Finally, we explored the use of the mixed-mode thiol-acrylate PEG4A-peptide hydrogels 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 were studied using PEG4A-peptide hydrogels. This visible light polymerized thiol-acrylate hydrogel system represents an alternative to existing light-cured hydrogel platforms and should be useful in many biomedical applications.

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.

. (2016). In situ formation of silk-gelatin hybrid hydrogels for affinity-based growth factor sequestration and release. RSC Advances, 6(115), 114353-114360. http://dx.doi.org/10.1039/C6RA22908E 2 AbstractSilk fibroin (SF) and gelatin are natural polymers suitable for biomedical applications, including controlled protein release. SF offers high mechanical strength and slow enzymatic degradability, whereas gelatin contains bioactive motifs that can provide biomimicry to the resulting scaffolds.Owing to their complementary material properties, SF and gelatin are increasingly being used together to afford hybrid scaffolds with adjustable properties. Here, we report the use of in situ crosslinked SF/Gelatin hydrogels as a platform for tunable growth factor sequestration and delivery. We demonstrate that the physical assembly of SF into insoluble network could be accelerated by sonication even in the presence of gelatin. However, the processing conditions from which to prepare SF aqueous solution (e.g., heating duration and number of processing steps) drastically altered the resulting hydrogel physical properties. Furthermore, the stiffness of SF/Gelatin hybrid gels display temperature dependency. Specifically, incorporation of gelatin increased gel stiffness at 25°C but decreases hydrogel mechanical stability at 37°C. The thermostability of SF/Gelatin gels can be restored by using low concentration of genipin, a naturally derived chemical crosslinker. We also incorporate heparin-conjugated gelatin (GH) into the hydrogels to create a hybrid matrix capable of sequestering growth factors, such as basic fibroblast growth factor (bFGF). Both sonicated SF (SSF) and hybrid SSF-GH gels exhibit moderate bFGF sequestration, but only SSF-GH gels afford slow release of bFGF. On the other hand, genipin-stabilized network exhibited the highest retention and sustained release of bFGF, suggesting the suitability of this particular formulation as a scaffold for tissue engineering applications.3