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

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 (f_n), phase angle and impedance at resonance, and quality factor (Q_n) 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 (f_{air, low} = 38.1 kHz and f_{air, high} = 836.9 kHz). Various spectral features of the sensor's impedance response, including changes in f_n, phase angle, Q_n, 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.