Device-tissue Interface Evaluation and Mitigation

Interface Evaluation

Immunohistochemically labeled section of tissue with an indwelling device (from Woolley et al. Journal of Neuroscience Methods 2011).

Device-Capture Histology of Ex Vivo Tissue

We developed a technique, device-capture histology (DCHist), enabling evaluation of the intact device-tissue interface. Using this technique we have shown the extent and variability of the brain’s reaction to the implant.

Close-up view of wired probe implanted at a shallow angle covered with a glass window for imaging (unpublished).

In Vivo Imaging of Device-Tissue Interface
Using transgenic animals we are able to study the device-tissue interface in vivo. This allows the study of the dynamics of the interface as the brain evolves it’s response to the implantation.

Mitigation of Tissue Responses to Neural Implants

Normalized Release of the Protein Bovine Serum Albumen from coating paradigms of Tetramethyl Orthosilicate (from McDermott et al. Conference Proceedings of the IEEE Conference on Neural Engineering 2015).

Coatings & Drug Delivery
After implantation of microelectrode arrays (MEAs) into the brain, the foreign body response (FBR) is activated, ultimately leading to microglial activation, astrocyte migration, and inflammation. This response is expected to have an effect upon device performance, decreasing signal to noise and increasing impedance. Research in the field has been conducted to mitigate this response, either by drug delivery or altering the MEA brain interface. For these methods to work, drug release must be controlled, without “burst release”, and the coating must not drastically increase the device footprint. Tetramethyl orthosilicate shows promise in that regard. Deposition of TMOS does not negatively impact MEA performance and has been shown capable of controlled release. However, the functionality of this polymer to mitigate the FBR depends on the ability to tune drug delivery without increasing the device footprint. In this study, novel coating paradigms were used to ascertain the ability of TMOS for tunable delivery, and the effect of these multiple coatings upon device footprint.

Device Design Approach
We have shown that a simple alteration to the site geometry of the electrode sites can enhance their longevity. We further propose to study the efficacy of using mechanically adaptive polymers as the substrate material for reducing the effect of shear stress and micromotion.
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