Superhydrophobic and Environmentally Robust Flexible Piezoresistive Sensors Based on a Ceramic Fiber Network of Hydroxyapatite Nanowires/Aluminum Silicate Fibers

Abstract

Flexible piezoresistive sensors for wearable applications often suffer from poor environmental stability against sweat, humidity, corrosive media, and mechanical fatigue. Herein, a superhydrophobic and robust flexible composite film is designed that integrates an inorganic fibrous network of hydroxyapatite nanowires (HAPNWs) and aluminum silicate fibers (ASF) with carbon black (CB) as a conductive phase. By optimizing CB content (2.5–15 wt.%), a uniform, continuous three-dimensional percolation network along the HAPNWs/ASF scaffold is obtained, avoiding incomplete pathways at lower loadings and severe agglomeration at higher loadings. The optimized CB-10% composite exhibits a balanced piezoresistive response (423 ± 18 ms/426 ± 22 ms response/recovery time at 90° bending) and stable signal output over a wide bending angle range (30°–120°). The polydimethylsiloxane (PDMS) modification imparts superhydrophobicity with self-cleaning capability. The coating withstands 14 tape-peeling cycles, 14 abrasion cycles, 3000 bending cycles, and 11 water-impact cycles while maintaining stable conductivity. Moreover, the film retains electrical performance after immersion in pH 3–11 solutions, UV irradiation, or heat treatment up to 250°C, demonstrating a clear decoupling of surface wettability degradation from core electrical function. When attached to human joints (finger, wrist, elbow, knee), the sensor reliably monitors real-time motion with distinct signal patterns. This work provides a design strategy for durable, environment-tolerant flexible piezoresistive sensors.

Graphical Abstract