Implantable biodegradable electronic devices for medical applications offer the potential to provide therapeutic or monitoring functions for limited periods of time - weeks to months - degrading in register with the anticipated needs of the application and thus not requiring surgical removal. However, numerous technologies remain to be developed to enable practical biodegradable electronic systems. The goal of this R21 is to develop completely biodegradable radio frequency (RF) power generators and stimulating electrodes as novel platform technology for enabling a variety of surgically implantable biodegradable electronic devices. The generators and electrodes will be designed according to electrical specifications and forms that are compatible with their incorporation into a biodegradable spinal fusion stimulator as a paradigm application of this technology. Our novel approach will be to use RF coil circuits based on biocompatible and bioresorbable magnesium alloy conductive and resistive components, and also use this same alloy as the material for the electrodes. Using the electrical specifications of existing, non-degradable spinal fusion stimulators in clinical use for guidelines, we will design, fabricate, and test RF coil circuits and stimulating electrodes to deliver constant current stimulation. Stem cell proliferative and differentiative responses to the stimulating electrodes will be assessed in vitro and compared with responses to conventional non-degradable electrodes. Pilot experiments to assess electrode degradation and tissue compatibility will be assessed in vivo in a tethered hard-wired subcutaneous rat model. Functionality and coupling efficiency of the RF coil circuit will be assessed in vitro in simulated body fluid. Successful completion of these aims, as demonstrated by confirming predicted cellular responses and component functionalities over time, will establish the basis for follow-on research addressing component optimizations and complete system development, including integration with active electronics, and testing in an animal spinal fusion model.
The objective of this study to demonstrate feasibility of key components for implantable biodegradable electronic devices that need only function temporarily, such as an electrical stimulator for spinal fusion, or in more general terms, for stimulating repair and remodeling of tissue engineered constructs, fractures, or grafts. This technology would make electrical stimulation a more practical and acceptable therapeutic option by overcoming the barriers to clinical acceptance of permanent implants that only need to function for relatively short periods of time after implantation and may require surgical removal at the end of their service life.