Ultrasound Delivery and Modulation of Chemical Haptic Stimuli
This paper introduces a novel system that uses ultrasound acoustophoresis for the contactless delivery of chemical stimulants to the skin to produce haptic sensations. The authors highlight the limitations of traditional methods like pads and propose ultrasound as a dynamic delivery and modulation mechanism.
Study
Figure. Illustration of the experimental setup, design, and results. (a) Experimental setup. The chemical was applied to the forearm using acoustic levitation. (b) Experimental protocol. Participants were asked to rate the perceived intensity of any given sensation for five minutes on a visual analogue scale (VAS, 0–10 cm), where 0 represented no intensity and 10 represented the maximum imaginable intensity (Højland et al., 2015). After reporting on their perception, participants selected a set of words that described sensations perceived during the five minutes. (c) Plots of the GAMM smooths of the perceived intensity of haptic sensations and 95\% pointwise confidence intervals for the smooth. The curve indicates the trend in the intensity data. (top) Perception of ethanol, capsaicin, cinnamal, and menthol; (middle) perception of cinnamal in combination with 50 Hz and 200 Hz acoustic stimulation. Smooth for the perception of cinnamal added for reference; and (bottom) perception of 50 Hz, and 200 Hz acoustic stimulation. (d) Frequency plots of the words participants selected to describe any sensation perceived during the study. (top) Words related to the perception of capsaicin, cinnamal, ethanol, and menthol; (middle) words related to the perception of cinnamal in combination with 50 Hz and 200 Hz ultrasound stimulation; and (bottom) words related to the perception of 50 Hz and 200 Hz ultrasound stimulation.
The research involved three human-subject studies with a total of 160 participants. The first study demonstrated that chemical stimulants such as menthol, capsaicin, cinnamal, and ethanol, delivered via ultrasound, are indeed perceivable on the skin. The second study showed that ultrasound stimulation applied to the same area can modulate the perceived intensity of a chemical stimulant (cinnamal), often increasing its perceived intensity and shortening the time to initial perception. The third study investigated the perception of ultrasound stimulation alone.
Findings
Figure. Time-intensity analysis for all three studies. (a) The maximal reported intensity. (b) The time in seconds at which the maximal intensity occurs. (c) The time in seconds at which the stimulant was initially perceived. (d) The time in seconds at which the stimulant was not perceived any more. (e) The number of seconds around the maximal intensity at which the reported intensity plateaued. (f) The rate of change before the maximal intensity occurred. (g) The rate of change after the maximal intensity occurred. (h) The area under the mean curve. (i) The area under the mean curve before the maximal intensity occurred. (j) The area under the mean curve after the maximal intensity occurred. Mean area with same letters indicate a significant difference at p<.05. Error bars represent standard errors of the means.
The key findings indicate that chemical stimulants can effectively induce haptic sensations when delivered via ultrasound, and that this perception can be modulated by simultaneous ultrasound stimulation. The combination of ultrasound and chemical delivery also shows potential for a faster onset and a more sustained sensation . The authors conclude that this new method of delivery offers opportunities for advanced haptic technologies and for gaining deeper insights into the interaction between chemical and mechanical senses. This approach allows for digital control of chemical stimulation, avoiding the confounding factor of physical contact associated with traditional delivery methods.
Video
Video. Setup and results of the presented study
Read the full paper here: 10.1038/s41598-025-94463-7.
Cite this work using the following:
@article{10.1038/s41598-025-94463-7,
title = {Ultrasound can deliver chemical stimulants to the skin and modulate their perception},
author = {Dalsgaard, Tor-Salve and Bhatia, Arpit and Gao, Lei and Hirayama, Ryuji and Subramanian, Sriram and Bergström, Joanna and Hornbæk, Kasper},
year = 2025,
month = {mar},
journal = {Scientific Reports},
publisher = {Nature Publishing Group},
volume = 15,
number = 1,
pages = 9,
doi = {10.1038/s41598-025-94463-7},
issn = {2045-2322},
}