The Effect of Crosslinker Concentration on Drug Release Kinetics of Thermo-Responsive, Lignin-Based Soft Composites*

The use of lignin in soft composites has gained recent attention due to its various favorable qualities, such as biocompatibility, antimicrobial and antibacterial properties. Lignin, an abundant biopolymer, can be used in conjunction with stimuli-responsive materials, such as poly(N-isopropylacrylamide) (PNIPAm), as these materials are able to undergo a volume change at a temperature close to that of human physiological conditions. The fabrication of interpenetrating networks (IPNs) containing PNIPAm and other crosslinked polymers have been explored. However, traditional methods investigate the role of exclusively petroleum-based materials in the fabrication of these soft composites. In this study, we fabricated soft composites containing: (1) a thermo-responsive polymer, PNIPAm; (2) a hydrophilic polymer, poly(vinyl alcohol) (PVA); and (3) a sustainable biopolymer, lignin. The concentrations of crosslinkers glutaraldehyde and N,N’-methylenebisacrylamide were varied between 5 and 15 mass percent of their respective polymers. After fabrication, the drug-release kinetics of each soft composites were characterized. Specifically, the diffusion of caffeine through the network via ultraviolet-visible spectroscopy and the equilibrium water uptake were analyzed at room temperature and 40 °C. It was observed that the diffusion of caffeine into water was suppressed with the addition of lignin. Furthermore, the crosslinker concentration was also seen to impact the release kinetics.