Accurate Control of Microspheres by Surface Acoustic Waves for Quantitative Force Characterization and Cell Mechanics Measurement.
The mechanical properties of cells are critical indicators of cellular physiological state and function. However, existing technologies still face challenges in achieving non-contact, force-calibrated, and precisely controlled single-probe measurements of single-cell mechanical properties. A phase-programmable surface acoustic wave (SAW) platform is presented, in which orthogonally arranged interdigitated transducers (IDTs) generate controllable acoustic fields for deterministic two-dimensional manipulation of microspheres. Dynamic phase modulation of the SAW fields enables high-precision microsphere steering while producing tunable acoustic radiation forces in the piconewton-nanonewton range. To enable direct quantitative characterization of acoustic forces, a calibrated microneedle-microsphere force probe is integrated into the platform. This configuration establishes an experimental phase-force relationship, enabling in situ calibration of acoustic radiation forces without relying on theoretical models or indirect calculation. Based on this experimentally calibrated acoustic force framework, SAW-driven 5 μm microspheres are employed as localized single probes to perform controlled acoustic indentation of adherent C2C12 myoblasts. The apparent Young's modulus is determined to be 1.63 ± 0.21 kPa using Hertzian contact mechanics and shows agreement with AFM-based measurements under comparable experimental conditions. c Overall, this work establishes a calibrated acoustic radiation force measurement and single-cell apparent Young's modulus characterization approach. This approach may have potential significance for non-contact mechanophenotyping and lab-on-chip based cell mechanics studies. STATEMENT OF SIGNIFICANCE: R2: Accurate single-cell mechanical characterization is limited by the lack of direct force calibration and controllable acoustic loading in SAW-based techniques. In this work, we implemented a phase-programmable SAW platform that enables deterministic microsphere manipulation and controllable acoustic force generation. By integrating a calibrated microneedle-microsphere probe, we established a direct phase-force relationship, enabling in situ and direct measurement of acoustic radiation forces and overcoming reliance on theoretical or indirect force estimation. This calibrated acoustic manipulation framework further enables controlled probe-based indentation of adherent cells and quantitative determination of their apparent Young's modulus. The proposed work may advance acoustic force-based mechanophenotyping and provide a promising pathway toward scalable, chip-integrated single-cell mechanical analysis.