Nanostructured porous silicon scaffolds for enhanced biocompatibility of multichannel microelectrodes

Many different types of microelectrodes have been developed for use as a direct Brain-Machine Interface (BMI) to chronically record single- neuron action potentials from ensembles of neurons and control an effector. For example, a BMI device designed for human quadriplegic patients successfully used single neuron activity to move a cursor on a computer screen. However, these devices eventually failed. This failure was not due to failure of the microelectrodes, but more likely due to damage to surrounding tissue that results in the formation of a non-conductive glial scar. The use of nanostructured microelectrode surfaces to mimic the extracellular environment has been previously shown in vitro to positively affect neural survival and decrease glial cell proliferation. In this thesis, we tested whether nanostructured porous silicon would reduce glial activation around the microelectrode compared to smooth silicon. To accomplish this, we first designed a semi-automated process to quantify immunological staining around the microelectrode hole. We then examined the effect of implanting different surfaces for 1, 2, 4 and 6 weeks. Our immunohistochemical quantification process showed that porous surfaces decreased astrocytic up-regulation around the microelectrode insertion site, including less hypertrophied astrocytic cell bodies. Additionally, survival of neurons increased and recruitment of macrophages was decreased at one week post-insertion. Therefore, nanostructured porous silicon is more compatible with the brain environment than smooth silicon. In the long term, we hope that implementation of a nanostructured microelectrode surface will lead to a sustainable, chronically implantable microelectrode that can record from every recording site indefinitely. Once this goal has been achieved, BMI devices will be viable alternatives to patients who have lost normal motor function.