Fibre reinforced bioresorbable composites for spinal surgery

Area of Science:

• Biomaterials Science
• Orthopedic Engineering
• Materials Science

Background:

• Spinal fusion implants require biomaterials with specific mechanical and degradation properties.
• Poly-lactide (PLA) composites offer potential for bone regeneration and load-bearing applications.
• Beta-tricalcium phosphate (beta-TCP) is a bioactive ceramic often incorporated into bone void fillers and scaffolds.

Purpose of the Study:

• To evaluate the feasibility of using poly-lactide (PLA70) matrix composites, with varying beta-tricalcium phosphate (beta-TCP) content and poly-lactide (PLA96) fiber reinforcement, for spinal fusion implants.
• To assess the mechanical properties, including compressive yield and impact strength, of these composite materials.
• To investigate the in vitro degradation behavior and strength retention of the composites over a 24-week period in simulated body fluid.

Main Methods:

• Composites were fabricated with different weight percentages of beta-TCP in a PLA70 matrix, with and without PLA96 fiber reinforcement.
• Compressive yield strength was measured parallel and perpendicular to the composite's laminated structure.
• Impact strength was assessed using notched and un-notched specimens.
• In vitro degradation studies were conducted over 24 weeks in simulated body fluid, with mechanical testing at intervals.

Main Results:

• Compressive yield strength varied with beta-TCP content and direction of testing; higher beta-TCP decreased strength parallel but increased it perpendicular to the laminate.
• Fiber reinforcement did not significantly affect compressive yield strength but substantially increased impact strength.
• In vitro testing showed a decrease in compressive yield strength over 24 weeks, with greater loss in higher beta-TCP content samples.
• Composites retained 66-99% of initial compressive strength after 12 weeks, and 51-94% after 24 weeks, depending on composition.
• Calcium phosphate precipitation was observed on the material surfaces after in vitro incubation.

Conclusions:

• The initial compressive strengths of the beta-TCP/PLA composites are comparable to existing spinal fusion materials.
• Further investigation into the long-term strength retention and degradation profile is necessary to confirm suitability for clinical spinal fusion applications.
• The observed in vitro degradation and precipitation suggest potential for bioactivity but require correlation with in vivo performance.