Development of Smart Memory Polymers for Implantable Devices

There is a growing body of research on the integration of sensing systems for measuring blood pressure by integrating sensors into vascular stents ^1–3. Using implantable sensors enables for continuous sensing of diseases such as hypertension, neurological disorders, diabetes, and other cardiovascular diseases situated <i>in vivo</i> will allow for better therapeutic management and diagnosis of patients. One such sensor has been developed by our team using polydimethylsiloxane (PDMS) and a capacitor electrode, however the sensor will need an invasive procedure for implantation, limiting its widespread uptake. Here we report on the development of an implantable blood pressure sensor that can be delivered using minimally invasive methods. The delivery of this sensor system is enabled through the use of a Smart Memory Polymer (SMP), which can change conformation on elevation to body temperature. Smart memory polymers (SMPs) were first introduced to biomedical engineering in 1988 with polyurethane based SMPs ⁴. The SMP reported here consists of a combination of PDMS and PCL⁵. When formed correctly, this SMP is soft at room temperature and then uncoils at 37 °C to enable deployment. Both PDMS and PCL are already used in the body and have an established safety profile. However, we have confirmed that the polymer blend system is non-toxic to cells <i>in </i>vitro, with <i>in vivo </i>experiments currently underway. We were able to deposit the sensor electrodes on the surface of the PDMS-PCL blend using photolithography ⁶. Using this polymer and deposition method, it was possible to miniaturise the current capacitor electrode design from 8x14 mm to 2x4 mm while maintaining sensor function.<br/><br/><br/>1. Oyunbaatar, N. E. & Lee, D. W. Foldable Polymer Stent Integrated with Wireless Pressure Sensor for Blood Pressure Monitoring. in <i>Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS)</i> vols 2023-January 61–64 (Institute of Electrical and Electronics Engineers Inc., 2023).<br/>2. Oyunbaatar, N. E., Kim, D. S., Prasad, G., Jeong, Y. J. & Lee, D. W. Self-rollable Polymer Stent Integrated with Wireless Pressure Sensor for Real-time Monitoring of Cardiovascular Pressure. <i>Sens Actuators A Phys</i> <b>346</b>, (2022).<br/>3. Cleven, N. J. <i>et al.</i> A novel fully implantable wireless sensor system for monitoring hypertension patients. <i>IEEE Trans Biomed Eng</i> <b>59</b>, 3124–3130 (2012).<br/>4. Hager, M. D., Bode, S., Weber, C. & Schubert, U. S. Shape memory polymers: Past, present and future developments. <i>Progress in Polymer Science</i> vols 49–50 3–33 Preprint at https://doi.org/10.1016/j.progpolymsci.2015.04.002 (2015).<br/>5. Kai, D. <i>et al.</i> Elastic poly( <i>ε</i> -caprolactone)-polydimethylsiloxane copolymer fibers with shape memory effect for bone tissue engineering. <i>Biomedical Materials</i> <b>11</b>, 015007 (2016).<br/>6. A regenerative microchannel neural interface for recording from and stimulating peripheral axons in vivo. (2012) doi:10.1088/1741-2560/9/2/029601.