Introduction: Surgical interventions for the treatment of chronic neck pain, which affects 330 million people globally, include fusion and recently cervical total disc replacement (CTDR). However, current CTDRs have been associated with issues similar to those affecting other joint replacement devices, including excessive wear and wear particle-related inflammation. Recently a new, highly wear-resistant biomaterial, silicon nitride, has been proposed, in the form of a surface engineered coating, for total joint replacement applications, including CTDRs. The aim of the study was to evaluate the effects of cobalt-chromium (CoCr) nanoparticles and silicon nitride (Si3N4) submicron and nanoparticles on murine fibroblasts (L929) and cells of the dura mater.
Materials and methods: Porcine fibroblasts isolated from the dura mater, seeded at the density of 5x103cells/well, and L929 murine fibroblasts cells, seeded at the density of 1x104 cells/well, were cultured with clinically-relevant CoCr nanoparticles and commercially available silicon nitride submicron and nanoparticles, at doses of up to 50:1µm3/cell and 500:1 µm3/cell, for CoCr and Si3N4, respectively. Cell viability was assessed using the ATP-Lite assay over 6 days period, at time-points of 0, 1, 3 and 6 days.
Results and discussion: The viability of L929 cells was significantly reduced by CoCr particles at densities of 50:1 µm3/cell at days 1, 3 and 6, as well as 5:1 µm3/cell at days 1 and 6. The highest particle seeding density (500:1µm3/cell) of Si3N4 nanoparticles also caused cytotoxic effects in L929 cells, but only at day 1. No reduction in cell viability of L929s, when cultured with sub-micron Si3N4 particles, was observed at any of the time-points. Only the highest doses of particles had a negative effect of the viability of dural fibroblasts. Only at the day 1 time-point, CoCr particles (50:1µm3/cell), submicron Si3N4 particles (500:1 and 50:1 µm3/cell), as well as nano-sized Si3N4 particle (500:1 µm3/cell) caused a significant reduction in cell viability in porcine dural fibroblasts. At days 3 and 6 no significant cytotoxic effects caused by any of the particles tested were observed.
Conclusions: The data suggested differences in the resistance of the murine L929 fibroblast cells and porcine dural fibroblasts to CoCr nanoparticles and Si3N4 submicron, and nanoparticles. The study showed that particles produced by the newly proposed biomaterial coating have little to no effect on the viability of L929s and porcine dural fibroblasts. Both types of cells showed a cytotoxic reaction, but only to the highest doses (500:1 and 50:1 µm3/cell) of Si3N4 particles at day 1, which was not presented at later time-points. Additionally, these preliminary findings showed that silicon nitride coating could be used for the application of CTDRs and potentially reduce adverse tissue reactions caused by wear particles, which have previously been seen in other total joint replacement devices.
