Regulation of Mineralization and Compressive Properties in Silk Protein Porous Scaffolds to Enhance Osteogenic Differentiation

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Abstract Mineralization capacity is an indispensable and critical property for bone tissue engineering (BTE) scaffolds. Silk protein (silk fibroin, SF; silk sericin, SS) possesses satisfactory mineralization potential. In this study, we employed silk protein as the primary material to develop in situ BTE scaffolds. Three scaffold materials were designed: a pure SF obtained via Na2CO3 degumming (SFN) or aqueous solvent degumming (SFF) and an SF/SS composite via adjusting aqueous solvent degumming. We investigated the effects of composition and pore structure on both mineralization behavior and compressive properties of these BTE scaffolds. Results indicated that a greater amount of hydroxyapatite-like nanocrystals grew on the pore walls within the SF/SS scaffold. During mineralization, hydroxyapatite nanorods initially formed, gradually grew into sheet-like crystals, and eventually assembled into flower-like crystalline structures. Notably, scaffolds with regular, elongated pore channels exhibited a denser mineral deposition, attributed to enhanced fluid permeation of simulated body fluid. The compressive strength and modulus of the scaffolds were effectively modulated by both SS incorporation and mineralization, following the trend of SF/SS > SFF > SFN. All scaffolds supported the high proliferative activity of bone marrow mesenchymal stem cells (BMSCs), and the incorporation of SS enhanced BMSC osteogenic differentiation. Most notably, the combination of an elongated pore structure with pre-mineralization realistically mimicked native bone ultrastructure, thereby synergistically promoting osteogenic differentiation and alkaline phosphatase expression. These findings reveal the interrelationship between pore architecture and osteogenic performance of silk-based BTE scaffolds, providing valuable design strategies to optimize mineralization, osteogenic differentiation, and mechanical support.

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