Conformable Microneedle Interstitial Fluid Accessing Platform for Biochemical Sensing

Conformable sensing platforms are widely used as medical device platforms because of their ability to adapt well to complex biological structures. In particular, due to its flexibility and biocompatibility, it is used to measure bioelectrical signals in organs (eg brain, heart, muscle). In recent research, using this conformable sensing platform, many research groups are trying to access biofludics in various ways to measure biochemical signals as well as bioelectrical signals. As an example, there is a method using sweat to access biofludics. However, it has limitation to long-term monitoring of the disease, since it must be generated through electrical stimulation.<br/><br/>The microneedle platform is one candidate to access Interstitial fluid as penetration. To provide skin penetrability and conformability to skin simultaneously, the integrated substrate for this device must offer both a high Young’s modulus microneedle (10 ²~10 ³ μm) and a sub-micron-thick conformable substrate (~10 μm). A sub-micron-thick substrate can make high mechanical stress by wrinkling or crumpling, which causes damage to the interface between needle and substrate.<br/><br/>In the work reported here, we developed a novel multi-microneedle pH sensor array on soft substrates by integrating two siloxane-based polymers, each with a different Young’s modulus. The device could have two advantages through these integrated substrates, including skin penetrability of low Young’s modulus PDMS and conformability to the skin of high Young’s modulus epoxy siloxane, respectively. The medical applicability of these conformable microneedle pH sensors was demonstrated by measuring the pH distribution on the dermal layer of a peripheral-vascular-disease rat model. Furthermore, glucose sensing was also demonstrated.<br/><br/>Wonryung Lee et al., "Conformable Microneedle pH Sensors via the Integration of two Different Siloxane Polymers for Mapping Peripheral Artery Disease" <i>Science Advances</i> (2021).