Plant-Based Matrix for Bone Apatite Biomineralization: In Vitro Bioactivity, Biocompatibility, and Degradability of...

Plant-derived biomaterials offer safer and ethically acceptable alternatives to animal-based implants for bone regeneration. Lignin, an abundant aromatic biopolymer, is attractive due to its durability and antioxidant and antibacterial properties; however, its structural heterogeneity remains a major limitation. Here, we investigate the bioactivity, degradability, and cytocompatibility of two structurally distinct lignins extracted from sorghum stems and their lignin-silica composites. Hydroxyapatite (HAP) mineralization was evaluated in simulated body fluid (SBF), and degradation was assessed in Tris-HCl buffer. Cytocompatibility and cell proliferation were tested using MC3T3-E1 pre-osteoblast cells. Lignin with a higher phenolic hydroxyl content promoted Ca²⁺-mediated HAP nucleation, showing mineralization after 14 days that further increased by 28 days. A∼17% lignin mass loss was measured after 21 days. Cell culture studies revealed enhanced proliferation when grown with 25-50 μg/mL lignin, whereas higher concentrations (>500 μg/mL) reduced cell viability, indicating a concentration-dependent response. Lignin-silica composites (75:25 wt %) exhibited higher mass loss (>20%) while maintaining good cytocompatibility even at elevated concentrations. These findings indicate that phenolic hydroxyl groups play a critical role in promoting mineralization and enabling controlled degradation. Importantly, lignin-silica composites combine bioactivity with favorable cytocompatibility, supporting their potential use as a bioactive matrix for bone regeneration.