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Multi-layer embedded carbon fibres as highly compliant and stretchable interconnects

This paper describes a unique technique to manufacture highly stretchable and implantable interconnects. A possible application is presented, where the interconnects are intended to create a network of nodes sensing biological parameters in e.g. the bladder wall. The interconnects are fabricated by embedding nickel-plated carbon fibres bundles first in a thin polyurethane tube and then in a soft, elastic, polydimethylsiloxane matrix. The insulation barrier properties of the proposed packaging technique were verified by a leakage current measurement performed in body mimicking media. The use of multiple thin fibres increases the amount of bending cycles before mechanical failure occurs. Carbon fibres possess extraordinary fatigue resistance and can withstand more than 160 000 deformation cycles under normal operating conditions without failing and display minimal impedance change. Patterning the polymeric matrix in a meander shape, along with the conductors, allowed the fabrication of extremely compliant interconnects that can achieve large deformations in response to low tensile stress. Due to the carbon fibres’ strength, the only factor limiting the device’s ultimate elongation is the geometrical length of the meandering structure itself. Even when stretched to its maximum, beyond normal operating conditions, the completely assembled device survived 20 000 loading cycles before failure of the polymeric coating. The proposed interconnects can follow the extensive deformation of the biological structures they are attached to, and can be stretched to 200% of their original length with less than 0.1 N of applied force.