| AVS 55th International Symposium & Exhibition | |
| BioMEMS Topical Conference | Tuesday Sessions |
| Session BM+BI+BO+NC-TuA |
| Session: | Microfluidics/Lab-on-a-Chip |
| Presenter: | A. Hess, Case Western Reserve University |
| Authors: | A. Hess, Case Western Reserve University J. Dunning, Louis Stokes VA Medical Center J. Harris, Case Western Reserve University J.R. Capadona, Louis Stokes VA Medical Center K. Shanmuganathan, Case Western Reserve University D. Tyler, Case Western Reserve University S. Rowan, Case Western Reserve University C. Weder, Case Western Reserve University C.A. Zorman, Case Western Reserve University |
| Correspondent: | Click to Email |
The development of advanced micromachining techniques for polymers has enabled the fabrication of mechanically flexible, MEMS-based neural probes from polyimide, PDMS, parylene and similar materials. The mechanical properties of these polymers can often be “tuned” during synthesis, but cannot be dynamically controlled once the material is formed. Members of our team have recently described the development of novel nanofiber-based polymer composites that exhibit reversible chemoresponsive mechanical behavior.1 These materials consist of a low modulus polymer that is reinforced by stiff cellulose fibrils. The stiffness of the nanocomposite is dependent on the interactions between these fibrils, which can be regulated chemically. Inspiration comes from the sea cucumber, which can modify the stiffness of its dermis by chemical regulation of collagen fibers. One of these nanocomposites, a poly(vinylacetate) (PVAc), exhibits a reduction in tensile modulus from 4.2 GPa to 1.6 MPa upon exposure to water, making it particularly well suited for penetrating neural probes that must be rigid during insertion and highly compliant during deployment. This paper describes the first effort to micromachine MEMS structures from such a material. The PVAc nanocomposite consisted of a dispersion of cellulose nanofibers (~16% v/v) extracted from sea creatures known as tunicates using the process described in Ref. 1. Neural probe designs similar to the well known “Michigan Probe” were selected for the first prototypes. These probes consist of a 50 μm-thick substrate micromachined into 280 um-wide by 3000 um-long shanks using a 50 W CO2 laser and a two-step process designed to minimize damage to the polymer. Both uncoated and Au-coated substrates were micromachined using this process. A process was developed to remove 300 nm of Au while only partially damaging the underlying PVAc nanocomposite, thereby enabling the fabrication of multi-electrode structures. No delamination of the Au films was observed throughout simple soak tests in PBS for 9 days. The presentation will detail the laser-based micromachining process and describe the challenges associated with PVAc micromachining, describe devices that incorporate parylene films to electrically insulate and passivate the electrodes, and review the performance of the neural probes.
1 J. R. Capadona, K. Shanmuganathan, D.J. Tyler, S.J. Rowan, and C. Weder, Science, 319, 1370 (2008).