The concept of subcutaneous monitoring dates back to the 1950s with early research on glucose sensing, but practical clinical devices emerged in the late 1990s. The first approved continuous glucose monitoring system for diabetes management, the Medtronic CGM, was released in 2003. Since then, a range of sensors has undergone regulatory approval worldwide, including the Abbott FreeStyle Libre and Dexcom G6 products.
Technically, most underhudssensorer operate with electrochemical or optical transduction methods. Electrochemical sensors measure ion or molecule concentrations through redox reactions, while optical sensors use fluorescence or absorbance changes. Calibration procedures vary, with some devices requiring periodic blood sample confirmation and others employing algorithmic self‑calibration. Biological drift and tissue encapsulation remain primary long‑term challenges, prompting research into antifouling coatings and nanostructured electrodes.
Clinical applications extend beyond diabetes. Subcutaneous lactate sensors help in critical care to monitor tissue hypoxia, and pressure sensors are used for early detection of pressure ulcers in immobilized patients. In sports medicine, metabolic sensors provide insight into training load and metabolic fatigue. Wearable integration allows professionals to adjust therapy or training protocols in near real‑time, potentially improving outcomes and reducing healthcare costs.
Future directions include multi‑analyte platforms that can simultaneously monitor several biomarkers, and fully implantable sensors with autonomous power sources such as bio‑fuel cells. Advances in flexible electronics and 3D printing promise smaller devices with longer operational lifespans. Continued collaboration between materials scientists, engineers, and clinicians is essential to address biocompatibility, data security, and ethical considerations surrounding lifelong physiological monitoring.