Replicating fine tactile sense is one of robotics’ biggest challenges, with artificial grippers and prosthetics generally failing to replicate the delicate motor skills exhibited by people.
Led by Professor Nathan Lepora, the latest breakthrough saw the BRL team create a 3D-printed mesh of pin-like papillae on the underside of an artificial skin, mimicking the dermal papillae found between the outer epidermal and inner dermal layers of human tactile skin.
Fabricated using advanced 3D printers that mix soft and hard materials to create biomimetic structures, these artificial papillae produce digital signals analogous to the neural signals that humans exhibit when touching objects and establishing tactile spatial relationships.
“We found our 3D-printed tactile fingertip can produce artificial nerve signals that look like recordings from real, tactile neurons,” said Lepora, a professor from Bristol’s Department of Engineering Maths and based at BRL. “Those recordings are very complex with hills and dips over edges and ridges, and we saw the same pattern in our artificial tactile data.
“Human tactile nerves transmit signals from various nerve endings called mechanoreceptors, which can signal the pressure and shape of a contact. Classic work by Phillips and Johnson in 1981 first plotted electrical recordings from these nerves to study ‘tactile spatial resolution’ using a set of standard ridged shapes used by psychologists. In our work, we tested our 3D-printed artificial fingertip as it ‘felt’ those same ridged shapes and discovered a startlingly close match to the neural data.”
Although the historical tactile data was a close match, the artificial skin did not exhibit quite the same level of sensitivity as human touch. According to Professor Lepora, this is probably because the 3D-printed skin is thicker than real skin. His team at BRL is now exploring how to 3D-print structures on the microscopic scale of human skin, with the work having wide-ranging implications for areas like soft robotics and prosthetics.
“Our work helps uncover how the complex internal structure of human skin creates our human sense of touch,” said Prof Lepora. “This is an exciting development in the field of soft robotics - being able to 3D-print tactile skin could create robots that are more dexterous or significantly improve the performance of prosthetic hands by giving them an in-built sense of touch.
“Our aim is to make artificial skin as good – or even better - than real skin.”