Flexible Parylene-Based 3-D Coiled Cable

Ray Huang1, Student Member, IEEE and Yu-Chong Tai, Fellow, IEEE

Caltech Micromachining Laboratory, California Institute of Technology, USA

Abstract- Prosthesis systems require reliable and flexible 1 connecting cables from the sensing/stimulating electrode sites to processing circuitries. However, the limitations on the fabrication materials and processes restrict the cables’ ability to stretch, resulting in breakage and failure of the implanted cabled device. Thus, a microfabricated and fully implantable 3-D parylene coiled cable for prosthesis application is presented. Compared to traditional flexible cables, this parylene coiled structure is able to be stretched by 100% of its original length and is also long-term biocompatible. In addition, the cable structure can be heat-formed in a mold to match muscle curvature and sharp turns in testing subjects and can also be directly integrated with flexible multi-electrodes arrays and neural probes.

Keywords: BioMEMS; flexible cable; parylene cable; neural prosthesis; interconnect

I. INTRODUCTION

Recent developments in neural prosthesis allow movement intention decoding by surgically implanting a sensing electrode array in the parietal cortex [1]. An insertion medium with flexible cable interconnect has been developed for this application [2], but along with several other state-of-the-art cable interconnect technologies [3-5], these wired interconnects are not able to accommodate the more physically active areas when implanted in testing subjects. Few researchers hypothesized that the extension, contraction and vibration of muscles groups often induce failures such as line fatigue, breakage and cable laceration during long term implantations. Thus, a biocompatible and stretchable alternative that is robust and reliable must be studied and developed.

In this work, we present the fabrication and testing results of a single metal layer parylene-based cable molded into a 3-D structure that is encapsulated with biocompatible silicone. Unlike previous versions of interconnects, this novel spiral structure provides ample room for the cable to be extended beyond its fabricated length and has the potential to overcome the aforementioned challenges. The fabrication process steps

This work was supported in part by National Science Foundation (award number H28927)

Contacting Author: Ray Huang is with the Caltech Micromachining Lab, California Institute of Technology, 1200 E. California Blvd, MC 136-93, Pasadena, CA 91125, USA. (Email: rhuang@caltech.edu; phone:+1-626-395-2227; fax:+1-626-584-9104)

described in this work are fully compatible with MEMS technology and are able to be integrated with other system components. We have chosen to use parylene-C (poly-para-xylylene C) due to its flexibility and mechanical strength (Young’s modulus ~4GPa, in between those of silicone and polyimide), insulation capability, its proven United States Pharmacopeia (USP) Class VI biocompatibility and its prior use in medical applications. In addition, parylene can be patterned using standard microfabrication techniques such as reactive ion etching.

I. DEVICES DESIGN

The fabricated parylene cables are 6 cm long and 0.9 mm wide. Each of these cables has 34 platinum trace lines that are 10 µm wide and 0.25 µm thick with 10 µm pitch embedded in two layers of parylene of equal thickness totaling 10 µm. The traditional cables provide little to no stress relief once implanted and fixed in the testing subject. In addition, the cables become more fragile after annealing treatment, which increase the chance of tearing and cracking which greatly reduces the life time of the cables. Our new proposed structure (Figure 1) consists of a heat-formed 3-D coil to alleviate these problems. After heat treatment the coils turns have diameters of ~1.1 mm and pitches of 2 mm. The number of turns and the diameters of the turns can be modified according to specification by changing the size of annealing rod. The cables are fabricated separately from the silicon probes and can be bonded together post-process (Figure 2). Both the silicon probe and the coiled cable structure provide metal bonding pads for electrical connection, which is satisfied by using commercially available conductive epoxy. Test cables with the above specifications are made in order to test the mechanical properties of this structure (Figure 3).

Figure 1. Close up view of the 3-D coiled parylene cable. The coil has 5 turns per centimeter and can be modified according to specification and surgery requirements. The cable can also be heat formed into other shapes and contours depending on the location of the implant.

317

Proceedings of the 2010 5th IEEE International Conference on Nano/Micro Engineered and Molecular Systems January 20-23, Xiamen, China

978-1-4244-6545-3/10/$26.00 ©2010 IEEE

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S. Musallam, Band R. A. ANeural Prosthe2004. R. Huang, C. Andersen, J. Silicon Probes2008, pp. 240-

W. Li, D. RodgPackaging,” inJ. F. Hetke, KInterconnects proc. TransducJ. Subbaroyanpolymer intercby intracorticavivo study”, in

ble Silic

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CONCLUS

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ACKOWLEDGE

uld also like toand other m

Laboratory at Ce assistance.

REFEREN

B. D. Corneil,Andersen, “Coetics,” Science

Pang, Y.C. TBurdick, “

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cone Filled Co

1.4 mm diam

2 cm

>0.4 cm>20%

0.6 N

>20 days

SION

onstrated the fstretchable thrable to be integable prostheticng test is prtesting in salinture for more t

results, this ect scheme to bsthetic system.ating of the cable.

EMENTS

o thank Mr. Tmembers of Caltech for th

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iled Cable

meter

m

s

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device showbe incorporatedFuture work ibiocompatible

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heir generous

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nn

edn

320