Conformable Hybrid Systems for Implantable Bioelectronic Interfaces

Abstract

of Things (IoT) to wellness and medical technologies. In the past decade, significant efforts have been deployed to exploit these technologies to design and manufacture conformable bioelectronic interfaces.Mechanical compliance is a critical specification for the long-term integration of on-skin devices and implants with a biological host. The latter is largely composed of soft tissues, with Young's moduli E in the range from 100 Pa to 10 MPa (excluding bones and cartilage), [1] and sustains different physiological dynamic behaviors, e.g., repeated displacements of hundreds of micrometers at 1 Hz in the heart or brain, [2] volumetric changes up to 8% in the heart, [3] or large flexion and angular displacement in the skin or spinal cord. [4] In contrast, electronic materials are stiff, with the elastic modulus in the range of 1 GPa (organic materials) to 100 GPa (inorganic materials) and rigid, bearing little strain without displaying mechanical failure or defect generation. Interfaces between such disparate biological and man-made materials suffer therefore from a mechanical mismatch that hinders reliable and continued device function in the body. [1,5] Several approaches have been used to engineer mechanical compliance within an electronic device or circuit. [6] Outcomes of such conformable circuits include improved mitigation of foreign body reaction (FBR) in vivo compared to rigid interfaces, [7] access to so far unreachable regions, [8] and bidirectional communication with high spatiotemporal resolution with the biological host.Monolithic integration of electronic devices and circuits on semiconductor wafers offers extreme miniaturization and very high device density (e.g., >10 8 transistors mm −2 , Intel FinFET Technology nodes [9] ). Such large scale of integration cannot be achieved for electronics prepared on conformable carrier substrates, as this class of devices employs lower performance device materials and polymeric substrates with low chemical and/or thermal stability leading to limited lithographic resolution and large transistor sizes. These constraints typically worsen as the compliance of the substrate increases. Some of the highest device densities reported to date are >10 000 cm −2 on flexible substrate [10] and 347 cm −2 on stretchable carrier. [11] Conformable hybrid systems leverage the performance of standard complementary metal-oxide-semiconductor integrated circuits (ICs) and the compliance of discrete flexible or stretchable components and carriers, to effectively provide high-performance and mechanically compliant electronic circuits. They call for new Conformable bioelectronic systems are promising tools that may aid the understanding of diseases, alleviate pathological symptoms such as chronic pain, heart arrhythmia, and dysfunctions, and assist in reversing conditions such as deafness, blindness, and paralysis. Combining reduced invasiveness with advanced electronic functions, hybrid bioelectronic systems have evolved tremendously in the last decade, pushed by progress in materials ...

Skin-Integrated Wearable Systems and Implantable Biosensors: A Comprehensive Review

“…To modulate these body responses that affect the in vivo functionality and longevity of implantable devices, several strategies have been reported [72][73][74], either passively via physicochemical features, or actively with molecules or matrix. These studies have essentially focused on the use of biocompatible material coatings, chemical surface modification of the device, conformable bioelectronics, steroidal and nonsteroidal anti-inflammatory drugs and angiogenic drugs [71,75].…”

“…Conformable devices able to reduce the mechanical mismatches between the implant and the biological tissue have also been used as a strategy to overcome FBR in implantable biosensors [72]. For example, Wang et al [88] reported on functionalized multi-walled carbon nanotubes twisted into helical fiber bundles that mimic the hierarchical structure of muscle and allow the monitoring of multiple disease biomarkers in vivo.…”

Devising Materials Manufacturing Toward Lab‐to‐Fab Translation of Flexible Electronics

“…Requirements for encapsulation of flexible electronics can be more stringent than rigid counterparts, when close contact with human tissues occurs (on‐skin and implantable systems), liquid materials are enclosed (liquid metals, electrolytes, fluid for mechanical buffering [ 63 ] ), or harsh environmental conditions are commonplace during operation (building‐integrated devices, aerospace applications). From materials perspective, use of both conventional rigid encapsulation materials (e.g., SiN x , SiO x , SiC) and flexible polymeric encapsulation materials (e.g., polyimide, parylene‐C, silicones) [ 12,65 ] are necessary to harness the superior passivation properties of the former and mechanical flexibility and durability of the latter. Meanwhile, rational molecular design for new polymers with combined optimal properties should be explored [ 66 ] to overcome the current shortfall in barrier properties against moisture and other vapor molecules.…”

“…In addition, medical devices, especially implants, that incorporate flexible electronics although frequently reported in academic journals, are far from matured for real‐world application. [ 12 ]…”

A Chip Integrity Monitor for Evaluating Moisture/Ion Ingress in mm-Sized Single-Chip Implants

“…Block diagram of the implemented system showing the sensor array used for ion and moisture ingress experimentation and the measurement engine used for automatic control, readout, and transmission of the measurement results to off-chip for further processing. [27], [28] conformal coatings have been proposed which add minimally to the overall size and weight of the device and could make possible the realization of more flexible implants [29], [30], [31]. These protective coatings usually feature high barrier properties and aim at increasing the lifetime operation of the chip by blocking moisture and ions ingress.…”