Shape-shifting electronics have potential for implants and movable medical sensors

The circuits are the result of a collaboration between the King Abdullah University of Science and Technology (KAUST) and the University of California, Berkeley and the team refers to them as "silicon honeycomb-serpentine reconfigurable electronic platforms". The primary reason for the research, which is described in Applied Physical Letters, was to devise systems that could conform to the changing shape of human bodies by stretching, bending and twisting.

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The team describes circuits that can assume three different shapes without affecting the connectivity between components: quatrefoils (a four-lobed shape), stars, and irregular forms. "Quatrefoils can be used for rectangular object-based operation, while stars are for more intricate architectures, and irregular-shaped ones are specifically for implanted bioelectronics," said Muhammad Hussain, co-author and a visiting professor at the University of California, Berkeley.

As with many engineering systems, the inspiration for the morphing circuits came from nature, Hussain explained. "Think of how flowers bloom. Based on the same principle, we gathered many videos of flowers blossoming, analysed their geometric pattern and used them for our first set of designs," he said. In particular, we analysed their stress distribution in an iterative manner, taking design architecture, materials and their properties into consideration. It's a tedious process to reach the optimal balance, but this is where engineering helps."

In particular, the team found that the reconfiguration capabilities of the circuits could be improved if they eliminated certain interconnects within the system. Optimisation of design was carried out on a macro scale version of the platform.

Unlike many attempts to make reconfigurable electronic circuits, Hussain and the team used silicon rather than conductive polymers to form the backbone of the system. This, they explained in their paper, is because over 90% of modern electronics are based on silicon platforms, so using the same material makes integration easier; moreover, silicon has superior semiconductor properties, thermal stability and electron mobility to even the best conductive polymers.

However, it also presents problems: rigidity, fragility and susceptibility to strain. The honeycomb shapes, circular islands for electronic components and serpentine interconnecting components from which their circuits are built are well-suited to maintaining connectivity while changing shape. “We integrate islands in the design to serve as a host for electronics, where the serpentine interconnects serve as mechanical support by absorbing the large deformation during stretching. They also serve as electrical interconnects between islands when they are sputtered by conductive materials,” the paper says.

Hussein explained that reconfiguration opens the door to making more versatile medical devices. Imagine that a lab-on-chip platform is implanted within your body to monitor the growth of a tumour in the shoulder area," he said. "While it is implanted, if we observe some abnormality in lung function, a platform that is equipped enough can change its shape and size, and relocate or expand to go monitor lung function."

The ultimate goal of the team is to produce an implantable device that would fit like a sleeve around the heart, both monitoring the organ's ability and with the capability of expanding and contracting to provide mechanical pumping assistance when necessary. "We still have a long way to go to integrate soft robotics with embedded high-performance flexible complementary metal-oxide semiconductor (CMOS) electronics on a variety of reconfigurable electronic platforms, which will be of immense importance," Hussain said. "It offers wonderful engineering challenges, requires true multidisciplinary efforts and has the ability to bind a variety of disciplines into applications that are simply not possible with the existing electronics infrastructure."