Hybrid and Passive Tissue-Anchoring Mechanism for Ingestible Resident Devices

This work presents a hybrid tissue-anchoring mechanism that combines a pre-compressed microspring for autonomous actuation and a barbed microneedle (MN) for robust tissue anchoring with minimized preloading. The spring-microneedle unit (SMU) allows facile integration with potential ingestible resident systems to enable prolonged operation in the gastrointestinal (GI) tract (e.g. biomarker monitoring and therapeutic drug delivery). Utilizing high-precision direct laser writing (DLW), the SMU is directly fabricated on a flexible polyimide substrate, which that can be conveniently attached onto the exterior packages of ingestible devices to reduce the form factor and therefore to save room for multifunctional system components. The 3-D printed microspring can be compressed and embedded within a thin layer of dissolvable polymer (polyethylene glycol) and autonomously actuated with a ~140- \mu \text{m} displacement upon polymer dissolution in aqueous media at 37°C. Mechanical calibration of the SMU demonstrated an average release force of 8 mN for a 100- \mu \text{m} actuation. According to our previous research into barbed MNs, this actuation force provides a large enough preload for a MN to achieve robust tissue-anchoring. Above all, the novel and effective tissue-anchoring mechanism has a great potential for enabling long-term operation of miniature biosensing and drug delivery systems. [2020-0169]