Real-time monitoring of hydrogel rheological property changes and gelation processes using high-order modes of cantilever sensors

Abstract

Here, we report that high-order modes of dynamic-mode piezoelectric cantilever sensors near 1 MHz persist in hydrogels and enable sensitive characterization of hydrogel viscoelastic properties and real-time monitoring of rheological property changes. Continuous tracking of the resonant frequency (fn), phase angle and impedance at resonance, and quality factor (Qn) of low- and high-order modes in piezoelectric-excited milli-cantilever (PEMC) sensors enabled the characterization of hydrogel viscoelastic properties and real-time monitoring of gelation processes (fair, low = 38.1 kHz and fair, high = 836.9 kHz). Various spectral features of the sensor's impedance response, including changes in fn, phase angle, Qn, and impedance, enabled sensing of changes in alginate and polyethylene glycol dimethacrylate (PEGDMA) hydrogel composition and low-frequency viscoelastic properties characterized by DMA across the 0.5–4 wt. % and 8–18 wt. % concentration ranges, respectively. The phase angle and impedance responses exhibited the highest sensitivities to changes in alginate and PEGDMA hydrogel storage modulus (E′) and loss factor [tan(δ)]. High-order modes exhibited an increased dynamic range upper limit (33.2 kPa) and reduced limit of detection (90 Pa) for the detection of changes in E′ relative to low-order modes (23.4 kPa and 230 Pa, respectively). This work suggests that high-order modes of PEMC sensors near 1 MHz compliment low-order modes in the 1–100 kHz frequency range for sensitive characterization and real-time monitoring of hydrogel rheological properties across a wide frequency range. Millimeter-scale piezoelectric cantilever sensors appear to be a promising characterization and processing tool for hydrogel materials research.