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The translation of many tissue engineering/regenerative medicine (TE/RM) therapies that demonstrate promise in vitro are delayed or abandoned due to reduced and inconsistent efficacy when implemented in more complex and clinically relevant preclinical in vivo models. Determining mechanistic reasons for impaired treatment efficacy is challenging after a regenerative therapy is implanted due to technical limitations in longitudinally measuring the progression of key environmental cues in vivo. The ability to acquire real-time measurements of environmental parameters of interest including strain, pressure, pH, temperature, oxygen tension, and specific biomarkers within the regenerative niche in situ would significantly enhance the information available to tissue engineers to monitor and evaluate mechanisms of functional healing or lack thereof. Continued advancements in material and fabrication technologies utilized by microelectromechanical systems (MEMSs) and the unique physical characteristics of passive magnetoelastic sensor platforms have created an opportunity to implant small, flexible, low-power sensors into preclinical in vivo models, and quantitatively measure environmental cues throughout healing. In this perspective article, we discuss the need for longitudinal measurements in TE/RM research, technical progress in MEMS and magnetoelastic approaches to implantable sensors, the potential application of implantable sensors to benefit preclinical TE/RM research, and the future directions of collaborative efforts at the intersection of these two important fields.

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Liquid electrolyte volume is a key driver in the lifetime and overall size of microfabricated biodegradable batteries. Harnessing liquid from the body to serve as the battery electrolyte may, therefore, be desirable; however, for stable operation, maintaining a constant environment inside the electrochemical cell is required even in the presence of changing body conditions. We report a biodegradable battery featuring a solid electrolyte of sodium chloride (NaCl) and polycaprolactone (PCL).This approach harnesses the body fluid that diffuses into the cell as an element of the electrolyte; however, the large excess of ionic material suspended in the PCL holds intracellular conditions constant. A constant discharge profile can then be achieved even in the presence of varying external aqueous conditions, enabling compact, stably-performing cells.

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