Mechanism of Direct Acoustic Construction and Gradient Properties Tuning.

Despite the effectiveness of microstructured elastomers for force sensing, current fabrication methods struggle to precisely control the gradient properties of complex microstructures due to limited energy-field flexibility, resulting in uniform performance that hinders high-sensitivity sensing. Here, directed acoustic construction (DAC) technology is employed to fabricate fingerprint-inspired elastomeric microstructures with intra-layer gradient properties, and the underlying mechanisms of acoustic curing, particle reinforcement, and property tuning are revealed. The acoustic-induced curing of polydimethylsiloxane (PDMS) arises from synergistic physical, chemical, and mechanical effects. The incorporation of diamond particles into the PDMS matrix reinforces all three acoustic effects, thereby promoting polymerization and curing, which in turn broadens the tunable range of properties via acoustic waves. DAC enables omnidirectional patterning of microstructures and wide-range gradient modulation, with feature sizes of approximately 200 µm. The resulting microstructure exhibits distinct inner-outer mechanical responses, producing a linear contact area-pressure relationship that enhances sensitivity and linearity. Compared with those of the uniform microstructures, the force sensing sensitivity is improved by 52.06%. When integrated onto a robotic fingertip as a functional sensing layer, it can distinguish fine textures and detect multidirectional forces. DAC enables site-specific quantitative modulation and rapid fabrication (within 10 min), expanding its applications in micro/nanofabrication and flexible sensing.