Recreating the sensation of softness

04 September 2019

Researchers develop materials that could recreate the sensation of softness.

Tiffany Hionas

Researchers from the University of California San Diego interested in the different factors that affect how humans perceive softness, have designed materials that replicate various levels of perceived softness.

While doing so, the group of researchers composed of a team of engineers and psychologists, have realised that this is a stepping stone into designing tactile materials and haptic interfaces which can be applied to technologies such as electronic skin, prostheses and medical robotics.

Co-leader of the study, Charles Dhong, an Assistant Professor in Biomedical Engineering at the University of Delaware and former Postdoctoral Fellow at UC San Diego comments that ‘we provide a formula to recreate a spectrum of softness,’ and ‘in doing so, we are helping close the gap in understanding what it takes to recreate some aspects of touch.’

Firstly, two parameters used to measure a material’s softness were examined; the indentation depth (how deep a finger can press into a material) as well as the contact area between material and fingertip. These two parameters normally change when a fingertip presses into an object.

The team created nine elastomeric slabs, and each elastomeric slab had its own ratio of indentation depth to contact area, differing in the amount of surface micropatterning, thickness and stiffness (Young’s modulus). They then carried out assessments, testing the slabs on human participants.

‘By creating these micropatterned surface structures, we produce discontinuous regions of contact where the finger presses in that are much smaller than the shadow it would cast on the surface,’ stated Darren Lipomi, a professor of Nanoengineering at UC San Diego.

As part of the experiment, 15 human participants were firstly instructed to identify the softer slab, and secondly, they were asked to rank the nine slabs from softest to hardest.Based on these results, it is revealed that the slabs which were perceived as softer were thicker, had little to no micropatterning and a low Young’s modulus.

Furthermore, the experiment revealed that the perception of softness is not made up from a mix of sensations, but instead, the perception of softness is a basic sensation.

Lipomi concludes that ‘this means softness is a primary ingredient of the human sense of touch. It's like how we have RGB for color displays. If we can find the other 'pixels of touch,' can we combine them to make any tactile image we want? These are the fundamental things we would like to know going forward.’

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