microneedle arrays (mna) on flexible substrate for neural recording and stimulation

Department: Electrical & Computer Engineering
Faculty Advisor(s): Shadi A. Dayeh

Primary Student
Name: Sang Heon Lee
Email: shl311@ucsd.edu
Phone: 858-534-6940
Grad Year: 2019

Technologies that enable single unit detection in clinical neurology are anticipated to revolutionize neuroprosthetics for restoring communication and motor control due to neurological injuries, and in neurotherapies for patients with epilepsy, movement disorders, and in neurodegenerative and neuropsychiatric disrupted cognitive processes. To record single units, it is important to develop (1) mechanically/biologically compliant probes for the brain interface, (2) probes that can sense at depth but not displacing large tissue volume to minimize biofouling response, (3) low tethering wire density, and (4) high-density probes capable of accurate spatiotemporal resolution in transducing brain activity. We developed next generation microneedle arrays (MNA) for use in human patients, with dense (>104/cm2) out-of-plane MNAs on thin (<10&#956;m thick) flexible substrates. The device preparation utilizes standard microfabrication techniques, thus the microscale electrochemical interface can be tailored to lower impedances and enlarge charge-injection capacities that are critical for the efficacy of next generation neuromodulation devices. MNA is composed of 32 Si-microneedles (100&#956;m length, diameter of 7&#956;m), built on <10&#956;m flexible polyimide substrates with monolithically embedded Cr/Pt metal lines, and coated with parylene-C except for their tips that are composed of platinum nanorods (PtNRs) for efficient transduction of brain activity (PtNR height ~400nm; PtNR diameter &#8804;100nm). Preliminary experiments validated that the devices can be implanted in agarose using standard pneumatic inserters from Blackrock microsystems without buckling or cracking. In comparison with Utah electrode arrays, MNA?s small fixed diameter suggests lower scarring and biofouling similar to the results of Kozai et al. obtained with a 7&#956;m carbon fiber. For electrochemical characteristics, the Utah electrodes are exposed to a length of ~100&#956;m, and their surface area is greater than that of a cone shaped tip of ~25416&#956;m2; their impedances is ~430158k&#937; compared to ~35586k&#937; for our devices for ~670 smaller surface area (38&#956;m2). The charge injection capacity (CIC) without applying a DC bias at open-circuit potential (which can further increase CIC) is 3.4mC/cm2 for our MNAs compared to 0.42mC/cm2 for the Utah electrodes. This is equivalent to ~210nC/phase which is greater than the 8-64nC/phase required for microstimulation. With the above characteristics, MNAs on flex are monolithic, scalable, have electrochemical properties exceeding that of existing clinically used iBCI electrodes, and have mechanical properties similar to recently published novel electrodes that induced negligible tissue scarring and biofouling. The flexibility in the fabrication permits engineering different probe dimensions potentially targeting different areas of the brain and different depths within one array.

Industry Application Area(s)
Life Sciences/Medical Devices & Instruments | Materials

Related Files:

  1. mna2.png

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