Initial strength of highpressed extrusion poly-L-lactide screw.

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Materials Engineering

Background:

• Poly-L-lactide (PLLA) is a biodegradable polymer used in medical devices.
• Current PLLA screw manufacturing often employs a drawing technique.
• There is a need for improved PLLA materials with enhanced mechanical properties for orthopedic applications.

Purpose of the Study:

• To compare the initial strength of PLLA screws manufactured using high-pressed extrusion versus drawing techniques.
• To evaluate the safe torque for driving these screws in simulated clinical scenarios.
• To assess the mechanical performance of extrusion-strengthened PLLA screws under various bone conditions.

Main Methods:

• Development of PLLA material using a high-pressed extrusion technique.
• Manufacturing of PLLA screws based on AO screw design (4.5 mm cortical and 4.0 mm cancellous).
• Mechanical testing including pull-out and twisting tests.
• Simulated insertion into minipig cortical and cancellous bone models to assess screw integrity and failure modes.

Main Results:

• High-pressed extrusion-strengthened PLLA material demonstrated higher bending strength than drawing-strengthened PLLA.
• Extrusion-strengthened PLLA screws showed superior performance in pull-out and twisting tests compared to draw-strengthened screws.
• Simulations indicated specific failure locations for cortical screws based on bone thickness, while cancellous screws did not fracture.

Conclusions:

• The high-pressed extrusion technique significantly enhances the mechanical strength of PLLA screws.
• Extrusion-strengthened PLLA screws offer improved performance over traditional draw-strengthened screws for clinical use.
• Further investigation into screw-bone interactions is warranted to optimize clinical application and safety.