Electronic devices with engineered three-dimensional (3D) architectures are indispensable for frictional-force sensing, wide-field optical imaging, and flow velocity measurement. Recent advances in mechanically guided assembly established deterministic routes to 3D structures in high-performance materials, through controlled rolling/folding/buckling deformations. The resulting 3D structures are, however, mostly formed on planar substrates and cannot be transferred directly onto another curved substrate. Here, we introduce an ordered assembly strategy to allow transformation of 2D thin films into sophisticated 3D structures on diverse curved surfaces. The strategy leverages predefined mechanical loadings that deform curved elastomer substrates into flat/cylindrical configurations, followed by an additional uniaxial/biaxial prestretch to drive buckling-guided assembly. Release of predefined loadings results in an ordered assembly that can be accurately captured by mechanics modeling, as illustrated by dozens of complex 3D structures assembled on curved substrates. Demonstrated applications include tunable dipole antennas, flow sensors inside a tube, and integrated electronic systems capable of conformal integration with the heart.

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microsystem technologies integrated with the human body for health monitoring [8][9][10][11][12][13][14] and disease treating, [15][16][17][18][19][20][21][22][23] to soft systems for low-power radio communication, [24] efficient energy harvesting/ storage, [25][26][27][28] high-capacity memory technologies, [29,30] and seed-inspired electronic micro-fliers. [31,32] An important class of these deformable electronic devices relies on novel structural designs of the device layout and hybrid integration with the soft elastomer substrate to achieve a high elastic stretchability in devices made of inorganic electronic components. [33][34][35][36][37][38][39][40] Herein, the elastic stretchability refers to the value of elongation of the device as elastically stretched to a strain level, below which the device can reversibly return to the load-free state, even after thousands of cycles without material failure, for example, fatigue failure of ductile materials, fracture of brittle materials and delamination at adhesive interfaces. Among various structural designs of stretchable inorganic electronics, [41][42][43][44][45][46][47][48][49][50][51][52][53] the "island-bridge" design represents a widely used strategy, where the bridge-like deformable interconnects in the intermediate regions (i.e., trenches) between the island-like non-stretchable elements (e.g., commercial chips) provide the stretchability, due Island-bridge architectures represent a widely used structural design in stretchable inorganic electronics, where deformable interconnects that form the bridge provide system stretchability, and functional components that reside on the islands undergo negligible deformations. These device systems usually experience a common strain concentration phenomenon, i.e., "island effect", because of the modulus mismatch between the soft elastomer substrate and its on-top rigid components. Such an island effect can significantly raise the surrounding local strain, therefore increasing the risk of material failure for the interconnects in the vicinity of the islands. In this work, a systematic study of such an island effect through combined theoretical analysis, numerical simulations and experimental measurements is presented. To relieve the island effect, a buffer layer strategy is proposed as a generic route to enhanced stretchabilities of deformable interconnects. Both experimental and numerical results illustrate the applicability of this strategy to 2D serpentine and 3D helical interconnects, as evidenced by the increased stretchabilities (e.g., by 1.5 times with a simple buffer layer, and 2 times with a ring buffer layer, both for serpentine interconnects). The application of the patterned buffer layer strategy in a stretchable light emitting diodes system suggests promising potentials for uses in other functional device systems.

Recently developed buckling-guided assembly methods provide a unique route to the design and manufacture of 3D mesostructures and microelectronic devices with superior performances and unusual functions. Combined with loading-path controlled strategies and/or active materials designs, reconfigurable 3D mesostructures with multiple stable 3D geometries can be formed, with promising applications in tunable antennas and multimodal actuators. The existing strategies are, however, limited by the applicable range of material types or requirements for switching between various complicated loading paths. Here, we present an electroadhesion-mediated strategy to achieve controlled adhesion of the 3D mesostructure to the substrate during the buckling-guided assembly. This strategy allows an active control of the delamination behavior in the film/substrate system, such that a variety of reconfigurable 3D mesostructures can be accessed by designing the electrode layout and strain-dependent voltage. An electromechanical model is developed to capture the delamination behavior of the film/substrate system under combined compression and voltage loadings, which is in excellent agreements with experimental measurements. Based on this model, an equivalent interface energy is proposed to quantify the contributions of the electroadhesion and van der Waals' interactions, which also facilitates simulations of the interface delamination with cohesive models in finite element analyses (FEA). Furthermore, a variety of reconfigurable 3D mesostructures are demonstrated experimentally, which agree well with FEA predictions using the concept of equivalent interface energy.

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Vibration of micro-electromechanical systems (MEMS) are of growing interest for applications in vibration measurements, vibration energy harvesters, and vibration sensors. Among the structures and devices reported, a class of 3D structures formed by mechanically-guided assembly are showing promising potentials, owing to the ability of controlled vibration behaviors (e.g., modes and natural frequencies) by reversibly changing the compressive strain. In addition, serpentine structures are good candidates for MEMS due to their ultra-low natural frequencies. Hence, we present a study on the vibration of the mechanically-assembled 3D serpentine structures. A theoretical model is established to capture the vibration mechanism, and therefore, a simple analytical expression for the natural frequency is derived. On this basis, the influence of material/geometry parameters on the natural frequency are systematically discussed. The developed analytical model would provide a better understanding of vibration mechanism in mechanically-assembled 3D structures.