Tannic Acid-Grafted P(NIPAm-<i>co</i>-BioAcc) Copolymeric Flexible Hydrogels with Tunable Functional Properties

Poly(N-isopropylacrylamide) (PNIPAm)/biopolymer systems with responsive features are widely used multifunctional applications. In this article, an approach to study the macro-cross-linking effect of methacrylated tannic acid (ATA) in preparing N,N′-methylenebis(acrylamide) (MBA)-free dual-responsive (thermo and pH) PNIPAm hydrogel is presented. Being a derivative of plant oil, acrylated epoxidized linseed oil (AELO) assists in cross-linking as well as plasticizing the hydrogel in order to maintain structural integrity. The effects of both ATA and AELO on the physical, antioxidant, and antibacterial properties of the hydrogels were investigated. The lower critical solution temperature (LCST) transition of cross-linked PNIPAm hydrogels was tuned to the precise range 30–35 °C in the current hydrogel system. Phenolic hydroxyl groups present in ATA serve as pH-responsive moieties and present a maximum swelling ratio of 17 g/g in alkaline media for the hydrogel containing 3% AELO. The macro-cross-linking ability of ATA resulted in a porous honeycomb microstructure of the hydrogels. The increase in the tensile strength from 3% AELO to 7% AELO in hydrogels suggests that the covalent bonding of AELO with PNIPAm plays an important role in the stability of the hydrogels. ATA cross-linked system presented a substantial increase in antimicrobial activity, antioxidant capacity (>80%), and improved biocompatibility. The PNIPAm-based hydrogel at 7% AELO loading unveiled ∼40 and 35.5% biofilm inhibition against Escherichia coli and Staphylococcus aureus, respectively. Notably, all of the hydrogels have shown remarkable cell proliferation ability and cytocompatibility toward neuronal cell lines. Distinct fluorescence intensity was monitored from FDA staining assay after incubating with hydrogels inferring comparable cell proliferation and cell viability. In summary, dual-responsive PNIPAm-ATA-AELO hydrogels may serve as medical patches for potential biomedical applications.