Lignin-based Materials for Biomedical Applications: Basic Requirements and Properties

Abstract

The material selected for biomedical application must be biocompatible, stable against physiological media, non-toxic, non-carcinogenic, corrosion-resistant, bio-inert, and stimuli-responsive, and have a low wear rate. Lignin is the most abundant aromatic polymer on Earth with a complex, recalcitrant structure. A lot of knowledge is acquired on its pre-treatments and processing for biomedical uses in the forms of hydrogels, films, composite materials, nanoparticles, and aerogels. To avoid the potential toxicity and to control the cytotoxicity of lignin-based materials, it is necessary to increase the purity of the starting source materials and understand their reactivity. The poor water solubility, broad molecular weight (MW) distribution, and highly complex structure of lignin restrict its wider clinical applications. These limitations may be effectively improved by chemical modifications or by using lignin fractions with a narrow MW range. Antioxidant and antimicrobial properties allow lignin to be used in pharmaceuticals, drug delivery, and wound healing. It is also reported as a good candidate for composite materials intended for bone regeneration scaffolds in tissue engineering. Future challenges for lignin-based materials for biomedical applications include achieving a better understanding of the structure, isolation, and batch properties of lignin, as well as structure–function relationships in its applications.