Soft, elastic and feather-light, yet tougher than steel, spider silk has long fascinated healers and engineers. Over centuries, this wonder material has been explored not only for clothing and body armour, but for sutures and bandages that gently aid wound healing. Today, spider silk’s structural secrets are also laying the ground for flexible, advanced electronic implants that can adapt to our body’s natural contours as they stimulate and monitor its living rhythms.
According to Huajian Gao, former Scientific Director at A*STAR’s Institute of High Performance Computing (IHPC), one hurdle in designing bioelectronic implants is getting them to sit comfortably around irregularly-shaped organs and tissues. Conventional heat-shrink films, like those used in packaging, are typically too stiff and can only be reshaped at temperatures far too high for human safety.
“The challenge is to create soft, stretchable interface materials that are stable under ambient conditions, and can significantly and rapidly contract in response to soft tissue-compatible stimuli,” said Gao.
An international team of researchers including Gao and colleagues from IHPC, A*STAR’s Institute of Materials Research and Engineering (IMRE) and Nanyang Technological University, Singapore; as well as the Chinese Academy of Sciences and Nanjing Medical University, China, posited that a material with a water-responsive quality, modelled after spider silk, could be used as enhanced bioelectronic interfaces. The concept leveraged ‘supercontraction’, a phenomenon where fibres in spider silk, when wetted, dramatically shrink.
To replicate these properties, the team developed a series of water-responsive, shape-adaptive polymer films. Dubbed WRAP films, these materials were synthesised from poly(ethylene oxide) and a poly(ethylene glycol)-α-cyclodextrin inclusion complex, then tested to assess their contractile response to water, mechanical properties, and compatibility with electronic devices.
The researchers found that on contact with water, the WRAP films shrunk by more than 50 percent of their original length in seconds, transforming into soft hydrogel-like films that could stretch up to 600 percent longer before breaking.
“This drastic change in material properties allows WRAP films to rapidly conform to soft tissue shapes when hydrated, making them ideal for biomedical uses where mechanical compatibility is crucial,” said Gao. “The films, when dry, also stayed exceptionally stable under ambient humidity and temperature, keeping their contractile properties even after months of storage or sterilisation treatments.”
Adding to these findings, the researchers also discovered that WRAP films had a unique microporous structure that allowed them to integrate the films seamlessly with electronic components when dry, forming shape-adaptive electrode arrays that can snugly wrap around living tissues on exposure to water.
When used in muscle stimulation tests in rats, these arrays were shown to outperform conventional gold elastomer electrodes. Moreover, the implanted WRAP electrodes did not trigger immune responses, suggesting an added degree of safety for future medical applications such as nerve repair, wound healing and electrophysiological signal recording.
The team is currently optimising the material properties and performance of their WRAP bioelectronic electrodes. “We aim to enable the use of WRAP films in applications such as creating artificial muscles and facilitating wound closure,” said Gao.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE) and Institute of High Performance Computing (IHPC).
