Marangoni microjet-photonic sintering synergy enables robust piezoresistive interfaces on methylated polysiloxanes for closed-loop proprioceptive exoskeletons

Abstract

Proprioceptive feedback enhances soft exoskeletons by improving actuation precision and enabling adaptive user–robot interaction for daily assistive tasks. While piezoresistive sensors are ideal for compact integration, their long-term robustness is compromised by interfacial delamination-induced signal attenuation on methylated polysiloxane substrates under intricate mechanical and environmental stresses. In this study, we present a novel in-situ deposition principle that leverages cavitation microjet and Marangoni flow effect to achieve facile, homogeneous, and surfactant-free immobilization of multiwalled carbon nanotubes (MWCNTs) onto geometrically diverse, chemically inert Ecoflex substrates. This work provides the first comprehensive mechanistic elucidation, demonstrating that Marangoni-assisted filler immobilization, driven by surface energy gradients, is the prerequisite for effective ultrasonic deposition. A physics-informed model, coupling Rayleigh–Plesset cavitation dynamics and Stokes number-based particle–fluid interaction theory, closely aligns with deposition outcomes. The ridge-groove microtopography of the piezoresistive interface, controlled via mold chemical vapor smoothing and reinforced through photonic sintering (PhS), yields encapsulation-free strain sensors with skin-like compliance, reliable sensing modalities, and exceptional resilience to environmental abrasion and humidity. The versatility of the strategy is further validated through hybrid co-deposition of MWCNT and silver nanowires (AgNWs). Integrated into our patented tendon-driven exoskeleton glove featuring dual slack-enabling mechanics and VR-guided object recognition, these sensors enable real-time proprioceptive feedback for adaptive grasping assistance. This work provides a scalable, cost-effective platform for next-generation wearable robotics and rehabilitation systems.