Self-adaptive and configurable transfer printing of flexible electronics via rheology of liquid foam

Flexible electronics (FEs) have the potential to endow objects with the virtues and functionalities of electronics. The key is transferring manufactured FEs from original rigid substrates and printing onto targets. However, existing transfer printing accommodates limited circumstances due to immutable mechanical properties of either solid or liquid stamps. Here, a self-adaptive, configurable transfer printing method is developed based on the unique rheology of liquid foam that enables integration of ultrathin FEs onto arbitrary surfaces conformally, three-dimensionally and non-invasively. The liquid foam exhibits adaptive mechanical properties between solid and liquid, converting among elastic, plastic and dynamic behaviors spontaneously. We demonstrate liquid foam can support FEs with shape maintained prepared with no defect, transform FEs to irregular topographies in a stress-free manner, and extend the reach of FEs to inner surfaces of semi-closed objects i.e., cranial cavity, which were barely feasible before. This approach overcomes key bottlenecks of current technologies and opens numerous opportunities for FEs in wearables and brain-computer interfaces.