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Open AccessArticle

Modeling the Insertion Mechanics of Flexible Neural Probes Coated with Sacrificial Polymers for Optimizing Probe Design

Department of Biomedical Engineering, The State University of New Jersey, 599 Taylor Rd., Piscataway, NJ 08854, USA
New Jersey Center for Biomaterials, 145 Bevier Rd., Piscataway, NJ 08854, USA
Author to whom correspondence should be addressed.
Academic Editor: Patricia Broderick
Sensors 2016, 16(3), 330;
Received: 16 December 2015 / Revised: 18 February 2016 / Accepted: 29 February 2016 / Published: 4 March 2016
(This article belongs to the Section Chemical Sensors)
Single-unit recording neural probes have significant advantages towards improving signal-to-noise ratio and specificity for signal acquisition in brain-to-computer interface devices. Long-term effectiveness is unfortunately limited by the chronic injury response, which has been linked to the mechanical mismatch between rigid probes and compliant brain tissue. Small, flexible microelectrodes may overcome this limitation, but insertion of these probes without buckling requires supporting elements such as a stiff coating with a biodegradable polymer. For these coated probes, there is a design trade-off between the potential for successful insertion into brain tissue and the degree of trauma generated by the insertion. The objective of this study was to develop and validate a finite element model (FEM) to simulate insertion of coated neural probes of varying dimensions and material properties into brain tissue. Simulations were performed to predict the buckling and insertion forces during insertion of coated probes into a tissue phantom with material properties of brain. The simulations were validated with parallel experimental studies where probes were inserted into agarose tissue phantom, ex vivo chick embryonic brain tissue, and ex vivo rat brain tissue. Experiments were performed with uncoated copper wire and both uncoated and coated SU-8 photoresist and Parylene C probes. Model predictions were found to strongly agree with experimental results (<10% error). The ratio of the predicted buckling force-to-predicted insertion force, where a value greater than one would ideally be expected to result in successful insertion, was plotted against the actual success rate from experiments. A sigmoidal relationship was observed, with a ratio of 1.35 corresponding to equal probability of insertion and failure, and a ratio of 3.5 corresponding to a 100% success rate. This ratio was dubbed the “safety factor”, as it indicated the degree to which the coating should be over-designed to ensure successful insertion. Probability color maps were generated to visually compare the influence of design parameters. Statistical metrics derived from the color maps and multi-variable regression analysis confirmed that coating thickness and probe length were the most important features in influencing insertion potential. The model also revealed the effects of manufacturing flaws on insertion potential. View Full-Text
Keywords: brain-to-computer interface; neural electrode; probe; finite element model; biomechanics brain-to-computer interface; neural electrode; probe; finite element model; biomechanics
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Singh, S.; Lo, M.-C.; Damodaran, V.B.; Kaplan, H.M.; Kohn, J.; Zahn, J.D.; Shreiber, D.I. Modeling the Insertion Mechanics of Flexible Neural Probes Coated with Sacrificial Polymers for Optimizing Probe Design. Sensors 2016, 16, 330.

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