Cytocompatible\nHydrogels\nwith Tunable Mechanical Strength\nand Adjustable Swelling Properties through Photo-Cross-Linking of\nPoly(vinylphosphonates)

Herein, the synthesis,\ncharacterization, and application\nof a novel\nsynthetic hydrogel based on the photoinitiated cross-linking of poly(vinylphosphonates)\nis presented. First, statistical copolymers with adjustable ratios\nof the monomers diallyl vinylphosphonate (DAlVP) and diethyl vinylphosphonate\n(DEVP), as well as different molecular weights, were obtained via\nrare earth metal-mediated group-transfer polymerization (REM-GTP)\nwhile maintaining narrow polydispersities. The copolymers were cross-linked\nby applying photoinitiated thiol–ene click chemistry (λ\n= 365 nm). The network formation was monitored via oscillatory rheology\ncoupled with UV-irradiation, revealing the high spatiotemporal control\nof the reaction. Moreover, the equilibrium storage moduli of poly(vinylphosphonate)-based\nhydrogels increased with a growing number of DAlVP units and upon\napplication of a different cross-linker, which was additionally confirmed\nby nanoindentation experiments. In contrast, the water uptake of hydrogels\ndecreased with higher DAlVP amounts in the corresponding hydrogels\ndue to lower chain mobility and an overall increase in the hydrophobicity\nof the samples. Upon successful functionalization of P(DEVP-<i>stat</i>-DAlVP) copolymers with sodium 3-mercaptopropane-1-sulfonate,\nas indicated via <sup>1</sup>H DOSY NMR, the respective cross-linked\nmaterials displayed a remarkable increase in the water uptake; thus,\npresenting highly hydrophilic gels with an apparent interplay between\nwater uptake, cross-linking density, and functionalization degree.\nFinally, the purified hydrogels showed cytocompatibility and enabled\ncell adhesion of human umbilical artery smooth muscle cells (HUASMCs)\nafter direct seeding. The materials further allowed the adhesion and\ngrowth of an endothelial layer, triggered no pro-inflammatory response\nas evidenced by cytokine release of M0 macrophages, and exhibited\nantibacterial properties toward <i>S. aureus</i> and <i>E. coli</i>.