Assessing the effects of cellulose-inorganic nanofillers on thermo/pH-dual responsive hydrogels

The incorporation of renewable bio-based materials/eco-friendly inorganic nanofillers into stimuli-responsive hydrogels meets the need for biocompatible and non-toxic functional materials. However, it remains challenging to build a three-dimensional network with enhanced mechanical properties and desired stimuli-responsive performances. In this study, dual stimuli-responsive hydrogels with interpenetrating polymer network structure are fabricated by the crosslinking of N-isopropylacrylamide (NIPAM)(1) and sodium alginate (SA)(2). 2,2,6,6-tetramethyl-piperidine-1-oxyl-oxidized cellulose nanofibers (TOCNF)(3) derived from energycane bagasse serves as a carrier material for nanosilicas (NS)(4) and nanoclays (NC)(5) and the effects of TOCNF, TOCNF/NS and TOCNF/NC on the hydrogels are thoroughly explored. Among these hydrogels, PNIPAM/SA-TOCNF-NS possesses the largest compressive strength of 66.7 kPa and it is 5.65 times higher than that of PNIPAM/SA. The thermo-sensitivity and pH-sensitivity of hydrogels are evidenced by swelling behaviors, optical properties, contact angle measurements and fluorescence tests. PNIPAM/SA-TOCNF exhibits the largest contact angle and the swelling processes for all the hydrogels are well fitted by pseudo-second-order swelling kinetic model. In addition, after incorporating carbon quantum dots, all the hydrogels display temperature dependent on-off fluorescence properties and this process are fully reversible with the heating and cooling cycles. These novel hydrogels with pH and temperature responsive characteristics and remarkable mechanical properties will open the door for interesting applications in smart sensors etc.