Wearable 3D-Printed Microneedle Sensor for Intradermal Temperature Monitoring

Accurate temperature monitoring plays a crucial role in understanding the physiological status of patients and the early diagnosis of diseases commonly associated with local and global infections. Intradermal temperature measurement is, in principle, more precise than skin surface detection, as it prevents interference from environmental temperature changes and skin secretions. However, to date, precise and reliable intradermal temperature monitoring in a real-time and continuous manner remains a challenge. We propose herein high-resolution 3D printing to fabricate a mechanically robust and biocompatible hollow microneedle, filled with a temperature-responsive conducting polymer (poly(3,4-ethylenedioxythiophene): polystyrenesulfonate, PEDOT:PSS) to develop a microneedle temperature sensor (T-MN). The significance is 2-fold: rational design of robust MNs with high resolution in the micrometer domain and the implementation of a conducting polymer in a MN format for temperature sensing. The analytical performance of the developed T-MN is in vitro evaluated under mimicked intradermal conditions, demonstrating good sensitivity (-0.74%° C^-1), resolution (0.2 °C), repeatability (RSD = 2%), reproducibility (RSD = 2%), reversibility, and medium-term stability. On-body temperature monitoring is performed on six euthanized rats for 80 min. The results presented good agreement with those obtained using a commercial optical temperature probe, which was intradermally inserted into the rat skin. The reliability of utilizing the T-MN for precise and continuous intradermal temperature monitoring was successfully demonstrated, noting its potential use for patient monitoring in the near future but also temperature compensation for MN (bio)sensors that may need it.