Green synthesis of covalent hybrid hydrogels containing PEG/PLA-based thermoreversible networks

A series of thermosensitive polyethylene glycol (PEG)-polylactic-acid (PLA)-based hydrogels were synthesized, through the Diels-Alder reaction, with tunable hydrophilicity and hydrophobicity. Polyethylene glycol (PEG) was end-functionalized with furan groups using a synthetic furanic diol prepared by thiol-ene reaction. Functional maleimide PLA was prepared from PLA-diol, glycerol, 4,4 '-methylenebis(cyclohexyl isocyanate) (H12MDI) and N-hydroxymethylmaleimide (HMM), by the isocyanate-alcohol condensation reaction. FTIR, H-1 NMR, DSC, and SEC studies of the prepared precursors were carried out. Then, an organic solvent-free environmentally friendly synthesis was used to obtain the cross-linked Diels-Alder adducts, by changing the feeding ratio of PEG/PLA. The rheological studies proved the success of using Diels-Alder reaction, confirming the formation of cross-linked networks and its thermal dependence. After proceeding with their characterizations, the obtained adducts were brought into contact with the water leading to the formation of hydrogels. Swelling measurements revealed that the chemical composition influenced the swelling and the water diffusion mechanism of hydrogels. Finally, we found that hydrolytic degradation was governed by ester bond hydrolysis that could be controlled by adjusting the composition ratio of PEG to PLA.