Development of Polymer-Metal Screw System for Bone Fracture Repair: Combining Strength and Biocompatibility.

Area of Science:

• Biomaterials Engineering
• Orthopedic Surgery
• Medical Device Design

Background:

• Conventional metallic and polymeric bone screws present complications like tissue damage and inadequate stability.
• Existing orthopedic implants often lead to stress shielding and metallosis, necessitating improved designs.

Purpose of the Study:

• To develop and evaluate a novel polymer-metal screw system to address the shortcomings of current orthopedic fixation devices.
• To assess the mechanical properties and biological safety of a new screw combining a polymer outer shell with a titanium alloy inner core.

Main Methods:

• Manufactured polymer-metal screws using polylactic acid (PLA) or polyurethane (PU) with a titanium grade 5 (Ti6Al4V) insert.
• Evaluated screw performance through insertion torque, pullout force, static and fatigue bending tests.
• Assessed biocompatibility using in vitro cell culture and in vivo studies on Sprague-Dawley rats, following ISO 10993 standards.

Main Results:

• The polymer-metal screws exhibited optimal driving torque and pullout force.
• PLA screws with a metallic insert showed significantly enhanced bending strength (531.7 ± 32.5 MPa) compared to polymer-only screws.
• In vitro and in vivo studies confirmed excellent cytocompatibility and no systemic toxicity, with improved bone growth observed around implants.

Conclusions:

• The developed polymer-metal screw system effectively combines the benefits of polymers and metals, mitigating the drawbacks of conventional screws.
• This innovative screw design shows significant potential for improving fracture fixation and patient outcomes in orthopedic surgery.
• The system demonstrates robust mechanical performance and excellent biological safety, paving the way for clinical application.