Polyacryloyl hydrazide based injectable & stimuli responsive hydrogels with tunable properties.

The synthesis and characterization of a series of injectable and stimuli responsive hydrogels based on polyacryloyl hydrazide have been accomplished using dimethyl 2,2'-thiodiacetate, acrylic acid (AA), diethyl malonate and polyethylene glycol diacrylate (PEGDA) as cross-linkers through a chemical or dual cross-linking pathway. The cross-linking reactions were carried out at room temperature or 70 °C to synthesize uniform and transparent gels. The swelling ratios ≈ 10-800% of the hydrogels depended on the type and concentration of the cross-linker, temperature and pH of the medium. A suitable combination of chemical and physical cross-linking was necessary to achieve optimum storage modulus of the gels. The yield stress of the gels synthesized using cross-linker concentrations up to 0.7 mol L was observed above 10% strain and the viscosity decreased by at least two orders of magnitude upon increasing the shear rate by 1000 times suggesting that the gels may be smoothly injected through the needle. The gels released up to 10-84% of the total encapsulated Rhodamine B in a controlled manner over a period of 120 h under physiological conditions. The gels prepared using cross-linker concentrations up to 1.3 mol L exhibited excellent water retention capacity (>95%) up to 40 days. Samples synthesized using AA and PEGDA as cross-linkers exhibited excellent cytocompatibility and are potential candidates for controlled delivery as well as non-evasive biomedical applications.