Poly- l-lactic acid (PLLA), a biodegradable polymer used extensively in FDA-approved implants, has recently been found to exhibit piezoelectricity when appropriately processed ( 15– 17). However, commonly used piezoelectric materials such as lead zirconate titanate (PZT) and polyvinylidene difluoride (PVDF) contain toxic or nonbiodegradable components, respectively, and thus are not favorable for implantation inside the human body. Since piezoelectric materials can generate electricity from mechanical impact ( 14), they can serve as appealing sensing materials, alternative to the described passive semiconductors and capacitive polymers, for self-powered force sensors. The materials can even be fabricated into nano- and microstructures and interfaced with soft tissues to monitor biological forces ( 9, 12– 14). Piezoelectric materials are often used for force/pressure sensors, transducers, and generators ( 10, 11). Piezoelectricity is a phenomenon which allows materials to convert deformation into electricity and vice versa ( 9). Friction-induced triboelectric charges, while ideal for energy harvesting and some force-detecting applications, are often susceptible to noise from motion of the sensor ( 7), variation of force response due to the delay of charge dissipation in the sensor ( 8), and a limitation of miniaturization due to the requirement of a physical gap between triboelectric layers. Recently, triboelectric sensors fabricated with biodegradable polymers have been reported with the exciting ability for in vivo energy harvesting ( 6). Ideally, erodible devices for biointegration should only contain materials which have been extensively studied and used in Food and Drug Administration (FDA)-approved implants. However, for clinical applications, further improvements of these devices are still required to overcome some challenges including ( i) the use of electronic materials (e.g., silicon and silicon dioxide), which has not been confirmed to be completely bioerodible and safe for long-term use inside the human body, ( ii) the dependence on complex clean-room fabrication tools, and ( iii) the use of a battery to power passive materials. These sensors exhibit excellent performance in monitoring biological pressures, including intracranial, abdominal, and cardiac pressures. In this regard, there have been achievements in degradable force sensors, relying on silicon piezoresistive probes or capacitive biopolymers ( 4, 5). Therefore, the devices should be flexible and at the same time biodegradable to avoid an invasive removal surgery, which could damage directly interfaced tissues. Pressure sensors are often required to be implanted and directly integrated with native soft tissues and organs. The sensor can be integrated with tissues and organs, forming self-sensing bionic systems to enable many exciting applications in regenerative medicine, drug delivery, and medical devices. This piezoelectric sensor offers an appealing alternative to present biodegradable electronic devices for the monitoring of intraorgan pressures. We also demonstrate this PLLA piezoelectric sensor can be implanted inside the abdominal cavity of a mouse to monitor the pressure of diaphragmatic contraction. We show the sensor can precisely measure pressures in a wide range of 0–18 kPa and sustain a reliable performance for a period of 4 d in an aqueous environment. Here, we present a strategy for material processing, electromechanical analysis, device fabrication, and assessment of a piezoelectric Poly- l-lactide (PLLA) polymer to create a biodegradable, biocompatible piezoelectric force sensor, which only employs medical materials used commonly in Food and Drug Administration-approved implants, for the monitoring of biological forces. Despite recent achievements in degradable electronic devices, there is still a tremendous need to develop a force sensor which only relies on safe medical materials and requires no complex fabrication process to provide accurate information on important biophysiological forces. Therefore, the devices should be flexible and at the same time biodegradable to avoid invasive removal surgery that can damage directly interfaced tissues. Pressure sensors are often required to be implanted and directly integrated with native soft biological systems. Measuring vital physiological pressures is important for monitoring health status, preventing the buildup of dangerous internal forces in impaired organs, and enabling novel approaches of using mechanical stimulation for tissue regeneration.

Piezo sensor