The conformal integration of electronic systems with irregular, soft objects is essential for many emerging technologies. We report the design of van der Waals thin films consisting of staggered two-dimensional nanosheets with bond-free van der Waals interfaces. The films feature sliding and rotation degrees of freedom among the staggered nanosheets to ensure mechanical stretchability and malleability, as well as a percolating network of nanochannels to endow permeability and breathability. With an excellent mechanical match to soft biological tissues, the freestanding films can naturally adapt to local surface topographies and seamlessly merge with living organisms with highly conformal interfaces, rendering living organisms with electronic functions, including leaf-gate and skin-gate transistors. On-skin transistors allow high-fidelity monitoring and local amplification of skin potentials and electrophysiological signals.
Soft neural electrode arrays that are mechanically matched between neural tissues and electrodes offer valuable opportunities for the development of disease diagnose and brain computer interface systems. Here, a thermal release transfer printing method for fabrication of stretchable bioelectronics, such as soft neural electrode arrays, is presented. Due to the large, switchable and irreversible change in adhesion strength of thermal release tape, a low‐cost, easy‐to‐operate, and temperature‐controlled transfer printing process can be achieved. The mechanism of this method is analyzed by experiments and fracture‐mechanics models. Using the thermal release transfer printing method, a stretchable neural electrode array is fabricated by a sacrificial‐layer‐free process. The ability of the as‐fabricated electrode array to conform different curvilinear surfaces is confirmed by experimental and theoretical studies. High‐quality electrocorticography signals of anesthetized rat are collected with the as‐fabricated electrode array, which proves good conformal interface between the electrodes and dura mater. The application of the as‐fabricated electrode array on detecting the steady‐state visual evoked potentials research is also demonstrated by in vivo experiments and the results are compared with those detected by stainless‐steel screw electrodes.
The application of
the serpentine mesh layout in stretchable electronics
provides a feasible method to achieve the desired stretchability by
structural design instead of modifying the intrinsic mechanical properties
of the applied materials. However, previous works using the serpentine
layout mainly focused on the optimization of structural stretchability.
In this paper, the serpentine mesh design concept is used to transform
the high-performance but hard-to-stretch piezoelectric film into a
stretchable form. The serpentine layout design strategies for the
piezoelectric film, which aim at not only desired stretchability but
also high utilization of the strain in the piezoelectric film during
deformation, are discussed with experimental and computational results.
A stretchable micromotion sensor with high sensitivity is realized
using the piezoelectric film with a serpentine layout. Human voice
recognition applications of the sensor, including speech pattern recognition
with machine learning, are demonstrated with the sensor integrated
with a wireless module. The stretchable micromotion sensor with a
serpentine layout illustrates the broader application of serpentine
layout design in the functional materials of stretchable electronics,
which can further extend the range of available functional materials
for novel stretchable electronic devices.
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