Thermoresponsive hydrogels from alginate-based graft copolymers

Three samples of sodium alginate grafted by amino-terminated PNIPAM (low and high molecular weight poly(N-isopropylacrylamide)) and a random P(NIPAM-co-NtBAM) (NtBAM: N-tertiary butyl acrylamide) copolymer, were synthesized via the carbodiimide chemistry and their temperature-induced hydrogelation capability was evaluated by rheology. All the samples showed thermothickening behaviour depending on concentration, ionic strength and hydrophobic comonomer content, incorporated to the PNIPAM thermo-sensitive pendant chains. The main result of this study was that a slight hydrophobic enrichment (just 15 mol% NtBAM) of PNIPAM was sufficient to shift the gelation temperature well below the physiological temperature at 32 °C and at the lowest polymer concentration studied (i.e. 10 wt%). The consequence of that was that the ALG-g-P(NIPAM-co-NtBAM) graft copolymer hydrogel exhibited the best rheological thermo-responsive properties and might be used as injectable hydrogel for potential applications in biomedicine.