Angiogenic competency of biodegradable hydrogels fabricated from polyethylene glycol-crosslinked tyrosine-derived polycarbonates.

Synthetic biomaterials can be used as instructive biological milieus to guide cellular behaviour and function. To further realize this application, we synthesized a series of structurally similar hydrogels and tested their ability to modulate angiogenesis. Hydrogels were synthesized from poly(DTE-co-x% DT carbonate) crosslinked by y% poly(ethylene glycol) (PEG). Hydrogel desaminotyrosyl tyrosine (DT) contents (x%) ranged from 10-100%, and crosslink densities (y% PEG-crosslinker) ranged from 5-80%. The hydrogels were fashioned into porous scaffolds with highly interconnected macro- and micro-pore (>100 and 10 mm in diameter, respectively) architecture using poly(DTE-co-10%DT carbonate% crosslinked with 8% PEG. Under physiological conditions (in vitro), the hydrogels degraded into three major products: desaminotyrosyl-tyrosine ethyl ester (DTE), desaminotyrosyl tyrosine (DT), and poly(ethylene glycol)-di-DT-hydrazide (PEG-di-DT hydrazide). Increasing either DT content or crosslink density brought quickened degradation. Because DT and DTE, two of the three major degradation products, have not demonstrated any noticeable cytotoxicity or angiogenic effect in previous studies, we measured the cytotoxicity of PEG-di-DT hydrazide, the third major degradation product. We found that PEG-di-DT hydrazide only displayed significant cytotoxicity at the high concentration of 100 mg/mL. Interestingly, PEG-di-DT hydrazide and its further degradation product PEG-dihydrazide stimulated in vitro endothelial cell migration and tubulogenesis, which is comparable to results found with FGF-beta treatment. Subcutaneous implantation of the PEG-crosslinked poly(DTE-co-10%DT carbonate) scaffolds into the backs of rats elicited greater tissue growth over time and superior vascularization than poly(DTE carbonate) implantation. These results show that this new class of biomaterials has a strong potential to modulate angiogenesis.