Refinement and Validation of Primary Myelinating Neural Cell Cultures for In Vitro Assessment of Neural Interface Materials

Abstract

Intracortical electrodes for neuromodulation within the cortex rely on intimate contact with tissues for recording signals and stimulating neurons. In vivo approaches for evaluating responses to intracortical devices are resource intensive and complex, making statistically significant, high throughput data difficult to obtain. In vitro models provide an alternative to in vivo studies; however, existing approaches have limitations which restrict the translation of the cellular reactions to the implant scenario. Most notably, there is no current model that includes the four principle cell types critical to the health and function of the central nervous system (CNS). Initially, the utility and limitations of a clonal cell and a primary dissociated mixed myelinating cell (DMMC) cultures were investigated in direct contact with electrode materials common to bionic devices. The DMMC model, developed for neurobiology investigations, was chosen as it contained biologically relevant ratios of astrocytes, microglia, neurons and oligodendrocytes. Whilst, the DMMC was a significant improvement over the clonal PC12 cells and was able to yield some insight into relevant cell-material interactions, the culture was not robust. To improve the reliability and relevance of the DMMC for recapitulating CNS wound healing, a co-culture model using mature mixed glial cells (MGC) was proposed. It was shown that the MGC improved the attachment and differentiation of the DMMC. The co-culture revealed clear material specific cellular reactions to the materials. The co-culture was further refined to reduce time and resources, with characterisation of cell interactions, comparing a layered and single-step combined co-culture methodology. These two models were evaluated for their ability to model the mature CNS. The combined approach was then further analysed for its ability to model acute implant injury. The combined co-culture showed the most similarity to the CNS and underwent several changes characteristic of the acute implant reactions. To gain understanding of the subtle differences in these cultures a combination of genomic and morphological analysis was required. Future work will focus on assessing the combined co-cultures acute and chronic interactions with biomaterials, and further developing the analysis paradigm to increase the translation of the cell responses to the in vivo implant scenario.