Hydrolytically degradable POSS-PEG hybrid hydrogels prepared in aqueous phase with tunable mechanical properties, swelling ratio and degradation rate

A series of hydrolytically degradable polyhedral oligomeric silsesquioxanes (POSS)-poly(ethylene glycol) (PEG) hybrid hydrogels were prepared by covalently grafting hydrophobic POSS onto hydrophilic 4-arm-PEG-maleimide to form an amphipathic precursor and further cross-linking with hydrolytically PEG-diester-dithiol via Michael-type addition. The process to form hydrogels was in aqueous phase completely, which is free of metal catalyst, UV irradiation, and organic solvents. In addition, POSS as enhanced agents, only small amounts are needed to cause significant changes in hydrogels properties due to the special surface properties and high mechanical stability of the nanosize particles. Experimental results showed that by increasing the mass fraction of POSS from 0% to 4%, the storage modulus (G′) of the hybrid hydrogels have observably increased from 250 Pa to 1800 Pa. Furthermore, the hybrid hydrogels exhibited a good water absorption capacity and they can be degraded by hydrolysis. The swelling ratio of the hybrid hydrogels decreased with the increase of the POSS content and the microstucture of hybrid hydrogels is also dominated by the POSS content. The degradation rate can be tuned by the POSS content, and a higher POSS content corresponds to a slower degradation rate.