In vitro oxidative degradation of a spinal posterior dynamic stabilization device

Abstract

This study quantified the changes of the frequency-dependant viscoelastic properties of the BDyn (S14 Implants, Pessac, France) spinal posterior dynamic stabilization (PDS) device due to in vitro oxidation. Six polycarbonate urethane (PCU) rings and six silicone cushions were degraded using a 20% hydrogen peroxide/0.1 M 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 to 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 analyzing changes of viscoelastic properties of degraded biomaterials and medical devices into which they are incorporated, using a frequency sweep. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1237-1244, 2018.

Hyperspectral chemical imaging reveals spatially varied degradation of polycarbonate urethane (PCU) biomaterials

“…Both Trommsdorff et al [43] and Cipriani et al [17] stated that, as the degradation is limited to the surface layer, the functionality [43] and the mechanical properties [17] of the entire device are unlikely to be affected. However, Lawless et al [8] discovered that the viscous property, of the BDyn device's PCU component, was statistically different, at specific frequencies, after in vitro degradation [8].…”

“…Long-term implantable polymers are an important class of biomaterials, used in a variety of biomedical applications [5]. In particular, the polyurethane (PU) group, and more specifically polycarbonate urethanes (PCU), are used in vascular catheters [6,7] and orthopaedic [8][9][10][11] applications. Though PCU has been shown to be more biostable than polyether urethanes (PEU) [12,13], another polymer in the PU group used in cardiovascular applications [14], PCU components of explanted orthopaedic implants have been reported to degrade in the human body due to oxidation [9,15].…”

“…This oxidative degradation results in the cleavage of chemical bonds in a polymer [16] and has been shown to adversely affect the surface chemical structure of the PCU spacer of the Dynesys spinal stabilisation device (Zimmer, Warsaw, Indiana, USA) [15,[17][18][19]. To replicate and understand the effect of in vivo oxidation on chemical structure, an accelerated in vitro oxidation method to degrade PCU biomaterials has been reported [8,12,20]. This process produces hydroxyl radicals from the H 2 O 2 /CoCl 2 solution and is reported to be an appropriate model of the in vivo processes which produce oxygen radicals at the polymer/cell interface [21].…”

“…This process produces hydroxyl radicals from the H 2 O 2 /CoCl 2 solution and is reported to be an appropriate model of the in vivo processes which produce oxygen radicals at the polymer/cell interface [21]. By using this in vitro degradation method, it was shown that oxidative degradation also affects the viscoelastic properties of the BDyn spinal stabilisation device (S14 Implants, Pessac, France), and its components, at specific frequencies [8].…”

“…Fourier transform infra-red (FTIR) spectroscopy is one of the three recommended techniques to quantify the chemical structure of polymers according to the ISO standard 10993-18, in addition to nuclear magnetic resonance (NMR) spectroscopy and mass spectroscopy (MS). Attenuated total reflectance Fourier transform infra-red (ATR-FTIR) spectroscopy has been used to understand and characterise the chemical structure changes of films [20,[22][23][24][25], tubing [23], dumbbell or cylindrical specimen shapes [26][27][28][29][30], pacemaker or defibrillator leads [14,31] and orthopaedic devices [8,15,[17][18][19]. A major limitation of standard ATR-FTIR, as conventionally applied, is that spectra are usually acquired from a single point of a sample.…”