SonoPatch: Wearable Sonophoresis for On-Demand Physiological Modulation

Existing interfaces modulate user experience through visual, auditory, and haptic channels, but direct physiological modulation, which programmatically alters a user's internal state, remains largely underexplored. We present a wearable sonophoresis patch that uses low-frequency acoustic stimulation to deliver psychoactive substances transdermally, and evaluate its potential for programmable physiological modulation in HCI. We tested this in a double-blinded study (N=26) delivering 100 mg caffeine versus sham control, recording physiological signals during rest and a sustained attention task (SART). The planned comparison for heart rate standard deviation during rest was significant (HR-SD p=0.025, d=1.48), with the caffeine group showing suppressed HR~SD consistent with sympathetic activation. Mean heart rate at rest was not significant (p=0.365), but exploratory analyses during the cognitive task revealed significant cardiovascular divergence: heart rate (p=0.003) and heart rate standard deviation (p=0.027) both moved in directions consistent with systemic caffeine delivery, with effects emerging within minutes of device activation and a sustained group effect across all task rounds (p<0.001). These results provide indirect evidence that wearable sonophoresis can deliver substances to modulate user physiology, opening the design space for on-skin chemical interfaces that adapt delivery in real time to change the user's physiological state on demand.