A low-profile electromechanical packaging system for soft-to-flexible bioelectronic interfaces

Abstract

Interfacing the human body with the next generation of electronics requires technological advancement in designing and producing bioelectronic circuits. These circuits must integrate electrical functionality while simultaneously addressing limitations in mechanical compliance and dynamics, biocompatibility, and consistent, scalable manufacturing. The combination of mechanically disparate materials ranging from elastomers to inorganic crystalline semiconductors calls for modular designs with reliable and scalable electromechanical connectors. Here, we report on a novel interconnection solution for soft-to-flexible bioelectronic interfaces using a patterned and machined flexible printed circuit board, which we term FlexComb, interfaced with soft transducing systems. Using a simple assembly process, arrays of protruding “fingers” bearing individual electrical terminals are laser-machined on a standard flexible printed circuit board to create a comb-like structure, namely, the FlexComb. A matching pattern is also machined in the soft system to host and interlock electromechanically the FlexComb connections via a soft electrically conducting composite. We examine the electrical and electromechanical properties of the interconnection and demonstrate the versatility and scalability of the method through various customized submillimetric designs. In a pilot in vivo study, we validate the stability and compatibility of the FlexComb technology in a subdural electrocorticography system implanted for 6 months on the auditory cortex of a minipig. The FlexComb provides a reliable and simple technique to bond and connect soft transducing systems with flexible or rigid electronic boards, which should find many implementations in soft robotics and wearable and implantable bioelectronics.

A soft, scalable and adaptable multi-contact cuff electrode for targeted peripheral nerve modulation

“…In addition, the selected technology can be considered suitable for applications in the highly dynamic nervous system, due to the minimal impact of strain on device functionality, as reported in previous work (2x impedance increase at 1 kHz with applied 45% strain) (Minev et al 2015a ). Electrical connection to external stimulation equipment is permitted by using a customized flexible printed circuit board (PCB), hereafter named “FlexComb” (Fallegger et al 2023 ) or a microfabricated polyimide-based equivalent system ( Supplementary materials and Methods) which is connected to the gold tracks through the same Pt-PDMS coating used at the electrode sites. The cuff is further comprised of a an adjustable fastener which is designed to pass across two slits, with the aid of a suture attached at the end of the belt.…”

“…The implant electrodes are coated with a platinum-silicone composite using screen-printing. Finally, a flexible PCB is aligned and connected to the pads, then covered with a silicone sealant as described previously (Fallegger et al 2023 ). After curing, the outline of the implant is defined using laser cutting and finally the cuff is released by dissolving the dextran layer in water.…”

An implantable biohybrid nerve model towards synaptic deep brain stimulation

“…Future iterations might benefit from using a flexible cable connector such as that used in Fallegger et al . [39] to increase the number of working electrodes. When performing the aging experiment, the impedance of the electrodes after being implanted in vivo increases, as expected and reported in different works [33, 27, 40].…”

“…The yield of working electrodes per device should be improved, but most of the non-working channels can be traced back to the interface between the omnetics connector and the Pt tracks. Future iterations might benefit from using a flexible cable connector such as that used in Fallegger et al [39] to increase the number of working electrodes. When performing the aging experiment, the impedance of the electrodes after being implanted in vivo increases, as expected and reported in different works [33,27,40].…”

Lifetime engineering of bioelectronic implants with mechanically reliable thin film encapsulations

“…The interface between the additional encapsulation material and device can also fail, leading to a short circuit between device channels (figure 5.5), which would appear as very low impedance or a very high leakage current. Designers may consider implementing wiring techniques more suitable for flexible electronics which mitigate these points of failure, such as the FlexComb system, which uses a flexible platinum-PDMS composite rather than a bonded or soldered wire [349], reducing the susceptibility of the joint to fatigue.…”