Characterization of Lubricant-Infused Surface Coatings Using a Label-Free Microwave Sensor.

Lubricant-infused surfaces (LIS) provide critical advantages for biomedical applications, including reduced biofouling and enhanced device performance. However, monitoring lubricant stability and depletion in real-time remains challenging due to limitations in existing characterization methods. This study presents a novel, noninvasive, label-free microwave sensing platform utilizing a coplanar ultrawideband (UWB) slot antenna coupled with a complementary split-ring resonator (CSRR)-based multisurface passive tag to accurately assess the stability and evaporation dynamics of fluorocarbon-based lubricants, perfluorodecalin (Lub A) and perfluoroperhydrophenanthrene (Lub B), infused onto polytetrafluoroethylene (PTFE) substrates. Experimental data demonstrated a direct correlation between lubricant evaporation and shifts in sensor resonance frequency, enabling precise tracking of lubricant stability under various conditions. Lub A exhibited significant evaporation rates in open-air (20 kHz/min) compared to closed-air environments (3 kHz/min). In contrast, Lub B showed improved stability, with lower evaporation rates of 4.8 kHz/min (open-air) and 1.71 kHz/min (closed-air). Under phosphate-buffered saline (PBS), periodic frequency fluctuations indicated gas bubble formation and lubricant replacement by PBS, affirming the sensor's capability to detect complex interactions. Additionally, real-time detection of the LIS self-healing mechanism via lubricant redistribution was confirmed through distinct resonance frequency shifts. These findings highlight the sensor's effectiveness for robust, real-time evaluation of LIS performance, underscoring its potential for enhancing predictive maintenance and reliability of biomedical implants.