Bioresorbable Electronic Implants: History, Materials, Fabrication, Devices, and Clinical Applications

Abstract

Medical implants, either passive implants for structural support or implantable devices with active electronics, have been widely used for the diagnosis and treatment of various diseases and clinical issues. These implants offer various functions, including mechanical support of biological structures in orthopedic and dental applications, continuous electrophysiological monitoring and feedback of electrical stimulation in neuronal and cardiac applications, and controlled drug delivery while maintaining arterial structure in drug‐eluting stents. Although these implants exhibit long‐term biocompatibility, surgery for their retrieval is often required, which imposes physical, biological, and economical burdens on the patients. Therefore, as an alternative to such secondary surgeries, bioresorbable implants that disappear after a certain period of time inside the body, including bioresorbable active electronics, have been highlighted recently. This review first discusses the historical background of medical implants and briefly define related terminology. Representative examples of non‐degradable medical implants for passive structural support and/or for diagnosis and therapy with active electronics are also provided. Then, recent progress in bioresorbable active implants composed of biosignal sensors, actuators for therapeutics, wireless power supply components, and their integrated systems are reviewed. Finally, clinical applications of these bioresorbable electronic implants are exemplified with brief conclusion and future outlook.

Bioresorbable Materials on the Rise: From Electronic Components and Physical Sensors to In Vivo Monitoring Systems

“…[33] The authors investigated the dissolution rate of Si NMs (B-doped, 10 15 cm −3 , 200 nm thick) in PBS (1×) spiked with different concentrations of albumin (0.01-35 g L −1 ), Si(OH) 4 (0-300 mg L −1 ) and cations (Na + , Mg 2+ and Ca 2+ , 1 × 10 −3 m) at 37 °C. The increase of the protein concentration slowed down the dissolution rate due to augmented protein adsorption onto the NM surface; moreover, regardless of the concentration (and presence) of proteins, the dissolution rate reduced by increasing the concentration of Si(OH) 4 , consistently with the chemical equilibrium reported in Equation (1). Conversely, the presence of cations in the aqueous medium (i.e., PBS at pH 7.4, with 35 g L −1 of proteins at 37 °C) led to an accelerated dissolution rate, which was greater for divalent cations (namely, Ca 2+ and Mg 2+ ) with respect to monovalent cations (Na + ).…”

“…Bioresorbable materials that fully dissolve in the body with biologically benign byproducts provide a unique opportunity to engineer new electrical, optical, and sensing components into implantable biodegradable systems that eliminate any boundary with the human body, granting direct access to organs, tissues, and biofluids without the need of secondary device‐retrieving surgery that may cause tissue lesion or infection …”

Material‐Based Approaches for the Fabrication of Stretchable Electronics

“…Meanwhile, the intrinsically stretchable electronic system can be implanted to internal organs for biomedical purposes, such as continuous health monitoring for diagnosis, long-term therapy, and prosthetic implants. [166][167][168][169][170][171][172][173] Park et al [95] reported the fabrication of an epicardial bio-electronic system based on Ag NW/SBS conductive elastomer composite (Figure 10b). The intrinsic softness of the Ag NW/SBS composites and mesh structured electrodes were designed to conformally wrap around the heart, thereby facilitating the high-quality ECG signal recording and feedback stimulation therapy, without disturbing the movement of the heart.…”

Materials Strategies and Device Architectures of Emerging Power Supply Devices for Implantable Bioelectronics

“…Composite materials involving formation of networks of active materials in a biocompatible soft polymer matrix represent an alternative approach . If the implantable systems are designed for short or mid‐term application, biodegradable characteristics are desirable, so as to eliminate the need for a second surgery for device retrieval . Adopting biodegradable materials into the device systems will be critically important, including the metals and oxides acting as electrodes or interconnects (Mg, Mg alloy, Zn, iron (Fe), molybdenum (Mo), silicon dioxide (SiO 2 ), magnesium oxide (MgO), molybdenum trioxide (MoO 3 ), etc.…”

“…); and semiconductors (silicon (Si), silicon germanium alloy (SiGe), indium–gallium–zinc‐oxide (IGZO), etc.) which act as key components for diodes or transistors …”