Preparation and performance study of strontium-carboxymethyl chitosan/silk fibroin/gelatin composite cartilage scaffolds

Abstract

Objective: Articular cartilage exhibits extremely poor self-repair capacity, often leading to osteoarthritis. This study aims to develop a strontium-containing porous composite cartilage scaffold (CMCS-Sr-Gel-SF) that combines bioactivity with mechanical support for cartilage injury repair. Methods: First, the carboxymethyl chitosan strontium (CMCS-Sr) composite was synthesized via a solution reaction method and characterized using EDS, XRD, and FTIR. Subsequently, pure scaffolds were prepared using CMCS-Sr at different concentrations, and their microstructure, mechanical properties, and cytotoxicity were evaluated via scanning electron microscopy (SEM), universal testing machine, and MTT assay. Based on this, CMCS-Sr at the optimal bioactive concentration (300 μg/mL) was selected and combined with silk fibroin (SF) and gelatin (Gel) to construct four three-dimensional porous scaffolds using vacuum freeze-drying technology. These scaffolds underwent a series of physicochemical characterizations, including SEM, XRD, FTIR, swelling rate, porosity, in vitro degradation rate, and mechanical properties. Cell proliferation during co-culture with chondrocytes was assessed using the CCK-8 assay to evaluate their biocompatibility. Results: Characterization results confirm that strontium ions successfully coordinate with CMCS to form stable CMCS-Sr complexes. While the pure CMCS-Sr scaffold exhibits excellent porosity (average pore size 167 ± 43.58 μm) and chondrocyte proliferation-promoting activity, its mechanical strength (compressive modulus of 185.82 kPa at 9% concentration) falls significantly short of natural cartilage requirements. The composite scaffold CMCS-Sr-Gel-SF demonstrated balanced comprehensive properties: an appropriate three-dimensional porous structure (pore size 167 ± 53.68 μm, porosity 81.62 ± 3.65%), excellent water absorption and swelling rate (2007 ± 157.3%), controllable degradation rate (53.33 ± 4.16% degradation at 28 days), and significantly enhanced compressive modulus (approximately 0.63 MPa). In vitro cell experiments demonstrate that the CMCS-Sr-Gel-SF scaffold effectively supports chondrocyte adhesion and proliferation, with cells maintaining vigorous growth activity throughout the 10-days culture period. Conclusion: The CMCS-Sr-Gel-SF scaffold successfully mimics the structure of natural extracellular matrix, enabling sustained release of strontium ions while creating a microenvironment that promotes cartilage tissue regeneration.