High‐Strength, Anisotropic Resorbable Screws via Mineralization of Chitin for Fracture Fixation

ABSTRACT The use of resorbable screws for fracture fixation offers significant advantages over traditional metal implants, including the elimination of secondary surgery and the reduction of stress shielding. However, current resorbable screws are clinically limited by inflammatory responses, inappropriate degradation rates, and insufficient osteogenic activity. Herein, inspired by natural bone tissue, high‐strength resorbable screws are developed through sequential pre‐stretching, solvent exchanging, air drying, and machining of mineralized chitin hydrogels. The amorphous calcium phosphate gradually transforms into a rod‐shaped hydroxyapatite in alkaline gel networks during the mineralization process. The anisotropic structure of the screws produced by pre‐stretching the chitin/HAP hydrogel significantly enhances their axial mechanical strength and radial swelling performance. This improvement enables the screws to function as “expansion screws”, facilitating fracture fixation in practical applications. The resulting chitin/HAP screws demonstrate excellent biocompatibility and enhanced osteogenic differentiation capability. The in vivo assessment in the rat femoral condyle indicates that the chitin/HAP screws are initially firmly fixed within the bone tunnel, then gradually degrade and are replaced by new bone without causing any inflammation. Our chitin/HAP screws exhibit appropriate biodegradability, excellent biocompatibility, and support normal bone remodeling, highlighting their potential applications in internal fracture fixation.