In vitro oxidative degradation of a spinal posterior dynamic stabilisation device

This study quantified the changes of the frequency-dependant viscoelastic properties of the BDyn (S14 Implants, Pessac, France) spinal posterior dynamic stabilisation (PDS) device due to in vitro¬ oxidation. Six polycarbonate urethane (PCU) rings and six silicone cushions were degraded by using a 20% hydrogen peroxide / 0.1M cobalt (II) chloride hexahydrate, at 37°C, for 24 days. The viscoelastic properties of the individual components and the components assembled into the BDyn PDS device were determined using Dynamic Mechanical Analysis at frequencies from 0.01–30 Hz. Attenuated Total Reflectance Fourier Transform Infra-Red spectra demonstrated chemical structure changes, of the PCU, associated with oxidation while Scanning Electron Microscope images revealed surface pitting. No chemical structure or surface morphology changes were observed for the silicone cushion. The BDyn device storage and loss stiffness ranged between 84.46 N/mm to 99.36 N/mm and 8.13 N/mm to 21.99 N/mm, respectively. The storage and loss stiffness for the components and BDyn device increased logarithmically with respect to frequency. Viscoelastic properties, between normal and degraded components, were significantly different for specific frequencies only. This study demonstrates the importance of analysing changes of viscoelastic properties of degraded biomaterials and medical devices into which they are incorporated, using a frequency sweep.