Variations in astrocyte and fibroblast response due to biomaterial particulates in vitro

The possible involvement of orthopedic biomaterial particles such as cobalt-chrome alloy (Co-Cr), ultrahigh molecular weight polyethylene (UHMWPE), titanium alloy (Ti-6Al-4V), and polymethyl methacrylate (PMMA) in the formation of glial and meningeal scars was investigated using an in vitro system. Cell lines were used as models for astrocytes and meningeal fibroblasts. They were incubated with varying concentrations of particle suspensions, after which proliferative and cytotoxic responses were quantified using MTT assay and Live/Dead microscopy. It was determined that relative particulate toxicity (arranged in decreasing order) to astrocytes is Co-Cr > Ti-6Al-4V > PMMA > UHMWPE, and toxicity to fibroblasts is PMMA > Co-Cr > Ti-6Al-4V > UHMWPE. Cell death caused by PMMA was mainly due to necrosis, while the rest of the particles induced apoptosis. Low quantities of Co-Cr and Ti-6Al-4V stimulate increased astrocyte proliferation rate. However, only the cells treated with titanium alloy caused upregulated transcription of reactive astrocyte markers such as glial fibrillary acidic protein, vimentin, nestin, and type IV collagen, suggesting the potential of titanium alloy alone to trigger glial scarring. None of the biomaterials tested promoted proliferation in fibroblasts implying that biomaterial particles are not directly involved in meningeal scar development.