In-vivo degradation of poly(carbonate-urethane) based spine implants

Area of Science:

• Biomaterials Science
• Spinal Device Engineering
• Materials Degradation

Background:

• Spinal stabilization devices are crucial for treating spinal pathologies.
• Dynesys® devices utilize poly(carbonate-urethane) (PCU) spacers and polyethylene-terephthalate (PET) cords.
• Understanding the in vivo biostability of these materials is essential for patient safety.

Purpose of the Study:

• To evaluate the biostability of explanted Dynesys® spinal devices.
• To assess physical and chemical alterations in PCU spacers and PET cords after implantation.
• To compare explanted devices with a non-implanted control.

Main Methods:

• Analysis of fourteen explanted Dynesys® devices and one control.
• Surface examination for physical alterations (abrasion, cracks).
• Chemical analysis using ATR-FTIR, DSC, GC/MS, and hardness measurements.
• Evaluation of fluid absorption and extractable components.

Main Results:

• PCU spacers showed surface abrasion, microscopic cracks, oxidation, and chain scission.
• PCU composition exhibited slight heterogeneity, with extractable polycarbonate segments detected.
• PET cords had adherent biological material (proteins) and trapped biological fluid residues (cholesterol derivatives, fatty acids).
• No significant chemical degradation was observed in PET cords.

Conclusions:

• Implantation causes superficial physical and chemical damage to PCU spacers in Dynesys® devices.
• PCU degradation mechanisms and the impact of byproducts require further investigation.
• PET cords demonstrated good biostability with minimal observed alterations.