Engineering Antioxidant and Oxygen-Releasing Lignin Composites to Promote Wound Healing

The application of engineered biomaterials for wound healing has been pursued since the beginning of tissue engineering. Here, we attempt to apply functionalized lignin to confer antioxidation to the extracellular microenvironments of wounds and to deliver oxygen from the dissociation of calcium peroxide for enhanced vascularization and healing responses without eliciting inflammatory responses. Elemental analysis showed 17 times higher quantity of calcium in the oxygen releasing nanoparticles. Lignin composites including the oxygen releasing nanoparticles released around 500 ppm oxygen per day at least for 7 days. By modulating the concentration of the methacrylated gelatin, we were able to maintain the injectability of lignin composite precursors and the stiffness of lignin composites suitable for wound healing after photo-crosslinking. In situ formation of lignin composites with the oxygen releasing nanoparticles enhanced the rate of tissue granulation, the formation of blood vessels and the infiltration of α-smooth muscle actin+ fibroblasts into the wounds over 7 days. At 30 days after surgery, the lignin composite with oxygen generating nanoparticles remodeled the collagen architecture resembling to the reticular pattern of unwounded collagen with minimal scar formation. Thus, our study shows the potential of functionalized lignin for wound healing applications requiring balanced antioxidation and controlled release of oxygen for enhanced tissue granulation, vascularization and maturation of collagens. ### Competing Interest Statement The authors have declared no competing interest. * ANOVA : analysis of variance AUC : area under curve DLS : dynamic light scattering ECs : endothelial cells ECM : extracellular matrix FBs : fibroblasts FFPE : formalin fixed paraffin embedded HPF : high powered field hdFBs : human dermal fibroblasts iNOS : inducible nitric oxide synthase LAP : lithium phenyl-2,4,6-trimethylbenzoylphosphinate GelMA : methacrylated gelatin MPs : microparticles myoFB : myofibroblasts NPs : nanoparticles PIXE : particle-induced x-ray emission PLGA : poly(lactic-co-glycolic) acid PDMS : polydimethylsiloxane PFO : pseudo-first order PZO : pseudo-zero order ROS : reactive oxygen species SLS : sodium lignosulfonate TLS : thiolated lignosulfonate TCEP HCl : tris(2-carboxyethyl)phosphine hydrochloride WT : wildtype