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With the development of robotics, ground robots are no longer limited to planar motion. Passive height variation due to complex terrain and active height control provided by special structures on robots require a more general navigation planning framework beyond 2D. Existing methods rarely considers both simultaneously, limiting the capabilities and applications of ground robots. In this paper, we proposed an optimization-based planning framework for ground robots considering both active and passive height changes on the z-axis. The proposed planner first constructs a penalty field for chassis motion constraints defined in R3 such that the optimal solution space of the trajectory is continuous, resulting in a high-quality smooth chassis trajectory. Also, by constructing custom constraints in the z-axis direction, it is possible to plan trajectories for different types of ground robots which have z-axis degree of freedom. We performed simulations and realworld experiments to verify the efficiency and trajectory quality of our algorithm.

Buckling and post-buckling analysis of thin films is significant for the design, optimization and fabrication of stretchable electronic devices based on compression buckling. Aiming to achieve a more accurate and reliable way for the dynamic stability analysis of stiff films considering geometric nonlinearity, an implicit dynamic element-free Galerkin method based on the Strain-Rotation decomposition theorem is developed in this paper to investigate the dynamic buckling behavior of stiff films. Convergence and comparison studies are conducted to validate the numerical stability and accuracy of the proposed numerical method. The influences of compression loading rate and thickness to length ratio on the buckling/post-buckling of stiff thin films subjected to dynamic load are numerically analyzed and discussed in parametric studies. This work provides an effective way for the engineering computation of flexible electronic technology.

Microstructured flexible pressure sensors featured with good mechanical properties, boosting a variety of sophisticated application scenarios, including electronic skin (e‐skin), soft robotics, wearable electronics, etc. This review is very focusing on the recent research progress of microstructured flexible pressure sensors. For better understanding the corresponding devices, different mechanisms, materials, preparation methods are briefly introduced at the beginning. And with highlighting the significance of microstructure for device performance, the microstructures of different configurations (e.g., pyramid, pillar, hemisphere) are introduced and discussed in detail through analyzing the influence of configuration characteristics and material properties. Finally, according to the existing problems in the application, the research directions of flexible pressure sensor are prospected. Currently, catering to the explosive and ineluctable growth of this intelligent world, considerable microstructured flexible pressure sensors have emerged but their development is still at very first stage. In this review, some guidelines and tunable methods are suggested for the microstructured flexible pressure sensors of wide practical use in the future.

Skin-integrated electronics, also known as electronic skin (e-skin), are rapidly developing and are gradually being adopted in biomedical fields as well as in our daily lives. E-skin capable of providing sensitive and high-resolution tactile sensations and haptic feedback to the human body would open a new e-skin paradigm for closed-loop human–machine interfaces. Here, we report a class of materials and mechanical designs for the miniaturization of mechanical actuators and strategies for their integration into thin, soft e-skin for haptic interfaces. The mechanical actuators exhibit small dimensions of 5 mm diameter and 1.45 mm thickness and work in an electromagnetically driven vibrotactile mode with resonance frequency overlapping the most sensitive frequency of human skin. Nine mini actuators can be integrated simultaneously in a small area of 2 cm × 2 cm to form a 3 × 3 haptic feedback array, which is small and compact enough to mount on a thumb tip. Furthermore, the thin, soft haptic interface exhibits good mechanical properties that work properly during stretching, bending, and twisting and therefore can conformally fit onto various parts of the human body to afford programmable tactile enhancement and Braille recognition with an accuracy rate over 85%.

Morphable three-dimensional (3D) structures capable of reversible shape changes between distinct geometric configurations have widespread applications in many important engineering areas. Recent advances in mechanically-guided 3D assembly provided a powerful approach to achieve morphable 3D mesostructures in a broad set of high-performance materials, over length scales from several micrometers to tens of centimeters. This approach relies on prestrained elastomer substrates released with different sequences to trigger the stabilization of distinct 3D buckling modes in specially engineered 2D precursor structures. Many of the reported 2D precursor structures are constructed with ribbon components that incorporate creases with reduced stiffness at strategic locations. The design of crease geometries and crease locations is essential to the structural bistability through this loading-path approach, which requires the development of a theory to serve as the design basis. This paper presents a finite-deformation model to analyze the stability of different buckling modes induced during the simultaneous and sequential compressions of structures with cross-shaped ribbon geometries, a very representative class of precursor patterns. By introducing a perturbation method to obtain an analytic solution to the deformed configuration of a uniform beam, a theoretical model is developed to predict the postbuckling deformations in cross-shaped ribbon structures with a prescribed number of creases. Based on the analyses of the strain-energy landscape, a stability coefficient is proposed to evaluate the bistability of cross-shaped ribbon structures. The developed model is validated by finite element analyses (FEA) and experimental measurements of structures with a broad range of cross-shaped geometries. This model allows the construction of design diagrams to identify the bistability for a variety of geometric parameters, including the normalized width and location of each crease in the cross-shaped patterns. These results elucidate how to select the various design parameters to achieve bistable 3D structures through the loading-path approach. Furthermore, the developed model is extended to the bistability analyses of precursor structures with generalized cross patterns and cross-shaped patterns consisting of locally stiffened elements. This study offers a theoretical reference for the design of ribbon-shaped mesostructures to achieve diverse morphable microelectronic devices.

Stretchable electronic systems based on controllable compressive buckling can be further endowed with superior compliance and stretchability. However, such systems are usually restrained by the interference from different loads in practical applications, so it is desirable to study their dynamic behaviors. In this article, an analytical model is developed on the linear free vibrations of a buckled thin film attached to a flexible substrate, whose results can be verified by the finite element analysis (FEA). In the model, the film is considered as an Euler–Bernoulli beam, and the substrate is assumed as a Pasternak foundation with Kelvin viscoelasticity. The natural frequencies and their corresponding vibration modes of the buckled film with the substrate are obtained. The results indicate that the increases of stiffness and damping of the substrate have negative effects on the natural frequencies. The damping influences the low-order modes a lot but not the high-order modes. This study may provide some suggestions for the dynamic design of buckled thin films on flexible substrates. For example, the controllable vibration attenuation can be achieved by choosing the substrate with appropriate viscoelasticity.

Background: Heart failure (HF) has become a serious global public health issue due to its high incidence, high mortality and extremely low quality of life. According to several clinical trials, Qishen Yiqi Dripping pills (QSYQ) combined with routine western medicine treatment can further enhance the curative effect of HF patients. However, most of the trials are small in sample size and poor in quality, which can only provide limited evidence-based medicine. The existing systematic reviews of efficacy and safety has provided evidence for the clinical application of QSYQ to a certain extent, but there are still 3 major defects. Here, we will perform a systematic review and meta-analysis that include the randomized clinical trial (RCT) of CACT-IHF, apply meta-regression and subgroup analysis to cope with multiple confounding factors, and add the clinical efficacy standards of TCM, all-cause death and readmission rates as reliable efficacy evaluation indicators. The purpose of this study was to rigorously evaluate the clinical efficacy and safety of QSYQ in the complementary treatment of HF with a well-designed systematic review and meta-analysis. Methods: Following the strict search strategy, 9 databases will be searched to ensure a comprehensive search. We search the database from the establishment until November 30, 2020. This study will include RCTs of QSYQ in HF patients’ complementary treatment. Two searchers will independently draft and carry out the search strategy, and the third member will further complete it. Two members independently screen literature, extract data and cross-check, and solve different opinions through discussion or negotiation with the third member. The risk bias will be evaluated based on Cochrane tool of risk of bias. Meta-regression and subgroup analysis are used to check and deal with the heterogeneity. The data analysis will be conducted by the statistical software Stata 16.0. Results: The results of this research will be delivered in a peer-reviewed journal. Conclusion: This study expects to provide credible and scientific evidence for the efficacy and safety of QSYQ in HF's complementary treatment, and at the same time provide a convenient and effective choice for decision-makers and patients. Protocol registration number: INPLASY 2020120106. Ethical approval: Since this study is on the basis of published or registered RCTs, ethical approval and informed consent of patients are not required.

Island-bridge structures incorporated with kirigami membranes emerge as a novel design strategy for flexible/stretchable electronics, taking advantages of large stretchability, high-surface filling ratio and low resistance. However, it is hard to determine the mechanical properties of this design due to its complex geometries and nonlinear deformation configuration, thereby limiting its further applications. In this paper, we present a model for the postbuckling behavior of kirigami membranes through a combination of theoretical modeling, finite element analysis, and experiments. Scaling laws for elastic stretchability are developed, showing good agreement with numerical results and experimental images. Investigations on the critical height of post array are conducted to ensure the boundary condition of the kirigami membranes in the analytical model. These results can serve as design guidelines for kirigami structures and facilitate their applications in flexible/stretchable electronics.

A quaternary ammonium salt surfactant with tertiary amine groups (C16MIMBr) was prepared by the reaction of bromohexadecane with N, N, N, N-tetra methylpropane diamine, and the structure of the product was demonstrated by 1H NMR. A viscoelastic wormlike micellar system was constructed with C16MIMBr as the main agent and potassium bromide as the counterion salt, and the ratio of surfactant to counterion was optimized. It was shown that the viscosity of the system was maximum when the molar ratio of the C16MIMBr-KBr system was 1:4, and the rheological test also indicated that the viscoelasticity was best at 1:4. The pH-stimulated responsiveness and temperature-stimulated responsiveness of the C16MIMBr-KBr system were investigated by rheology and cryo-transmission electron microscopy, and the response mechanism was investigated and analyzed. It is shown that when the system is acidic, the positive charges on both sides of the surfactant lead to strong electrostatic repulsions within and between the surfactant molecules, resulting in a cone-like structure of the surfactant molecules and the formation of spherical micelles with very low viscosity. When the system is deprotonated under alkaline conditions, only one end of the surfactant head group is positively charged, and the inter-and intra-molecular electrostatic repulsive forces are greatly weakened, resulting in the intertwined growth of micelles and the formation of wormlike micelles. The temperature response mechanism analysis of the C16MIMBr-KBr system shows that at low temperature, only a small amount of cation can cross-mix with micelles to form a curved vesicle structure due to the low solubility of the system, resulting in a low viscosity of the system. As the temperature rises to 60 °C, the water solubility of the system is enhanced, and it desorbs from the vesicles into the solution. According to the equation of critical accumulation parameter, the critical accumulation parameter of the system decreases and the transition from vesicles to wormlike micelles occurs, leading to an increase in system viscosity.

This paper presents a ductility-centred analytical model for robustness assessment of axially restrained double-span steel beam systems further to sudden columns loss. The main benefit of the model is its ability of linking the response of semi-rigid beam-to-column joints to the load carrying capacity of the system, and in addition, the model supports the use of codified methods for joint response. The analytical model is first validated through comparisons against detailed double-span FE models, where it is found that the load-joint rotation responses of the axially restrained systems can be accurately captured by the analytical model, especially at catenary stages. Comparisons are also made against the FE results excluding the axial restraints. The axial restraints are shown to play a crucial role in the development of catenary action. Following the verification study, the analytical predictions of the double-span beam systems with varying parameters were further presented and discussed, and an illustrative design example was finally given to clearly demonstrate the practical use of the analytical model for robustness assessment of building frames. The analytical model is design effective and hand-calculable, and thus it brings convenience to robustness assessment of structures in practice. The proposed method may be considered as a feasible alternative method to detailed nonlinear dynamic analysis.

Background Lens opacity seriously affects the visual development of infants. Slit-illumination images play an irreplaceable role in lens opacity detection; however, these images exhibited varied phenotypes with severe heterogeneity and complexity, particularly among pediatric cataracts. Therefore, it is urgently needed to explore an effective computer-aided method to automatically diagnose heterogeneous lens opacity and to provide appropriate treatment recommendations in a timely manner. Methods We integrated three different deep learning networks and a cost-sensitive method into an ensemble learning architecture, and then proposed an effective model called CCNN-Ensemble [ensemble of cost-sensitive convolutional neural networks (CNNs)] for automatic lens opacity detection. A total of 470 slit-illumination images of pediatric cataracts were used for training and comparison between the CCNN-Ensemble model and conventional methods. Finally, we used two external datasets (132 independent test images and 79 Internet-based images) to further evaluate the model's generalizability and effectiveness. Results Experimental results and comparative analyses demonstrated that the proposed method was superior to conventional approaches and provided clinically meaningful performance in terms of three grading indices of lens opacity: area (specificity and sensitivity; 92.00% and 92.31%), density (93.85% and 91.43%) and opacity location (95.25% and 89.29%). Furthermore, the comparable performance on the independent testing dataset and the internet-based images verified the effectiveness and generalizability of the model. Finally, we developed and implemented a website-based automatic diagnosis software for pediatric cataract grading diagnosis in ophthalmology clinics. Conclusions The CCNN-Ensemble method demonstrates higher specificity and sensitivity than conventional methods on multi-source datasets. This study provides a practical strategy for heterogeneous lens opacity diagnosis and has the potential to be applied to the analysis of other medical images.

A viscosity reducer was prepared by using octadecyl methacrylate (SA) and styrene(S) as polymerization monomers and ethylene glycol dimethacrylate (EDMA) as branched monomers. When the dosage of viscosity reducer is 800 ppm, the viscosity reduction rate is more than 60%. By comparing the effect of different amount of viscosity reducer on the precipitation point, precipitation amount and asphalt particle diameter, it is found that the addition of viscosity reducer could increase the asphalt precipitation point and significouldtly decrease the precipitation’ amount and average particle size. In general, the addition of viscosity reducers could provide a good dispersion of asphaltene precipitation. The data from infrared spectroscopy, scouldning electron microscopy, XRD showed that the viscosity reducer could inhibit asphaltenes by changing the polarity of asphaltene molecules, causing hydrogen bonding, dispersing asphaltene molecules, adsorbing or embedding asphaltene molecular lamellae. And it has a good dispersion effect on asphaltene precipitation, which well inhibited asphaltene precipitation.

Lithographically defined interconnects with filamentary, serpentine configurations have been widely used in various forms of stretchable electronic devices, owing to the ultra-high stretchability that can be achieved and the relative simple geometry that facilitates the design and fabrication. Theoretical models of serpentine interconnects developed previously for predicting the performance of stretchability were mainly based on the theory of infinitesimal deformation. This assumption, however, does not hold for the interconnects that undergo large levels of deformations before the structural failure. Here, an analytic model of serpentine interconnects is developed starting from the finite deformation theory of planar, curved beams. Finite element analyses (FEA) of the serpentine interconnects with a wide range of geometric parameters were performed to validate the developed model. Comparisons of the predicted stretchability to the estimations of linear models provide quantitative insights into the effect of finite deformation. Both the theoretical and numerical results indicate that a considerable overestimation (e.g., > 50% relatively) of the stretchability can be induced by the linear model for many representative shapes of serpentine interconnects. Furthermore, a simplified analytic solution of the stretchability is obtained by using an approximate model to characterize the nonlinear effect. The developed models can be used to facilitate the designs of serpentine interconnects in future applications.

Buckling stability of thin films on compliant substrates is universal and essential in stretchable electronics. The dynamic behaviors of this special system are unavoidable when the stretchable electronics are in real applications. In this paper, an analytical model is established to investigate the vibration of post-buckled thin films on a compliant substrate by accounting for the substrate as an elastic foundation. The analytical predictions of natural frequencies and vibration modes of the system are systematically investigated. The results may serve as guidance for the dynamic design of the thin film on compliant substrates to avoid resonance in the noise environment.

Soft robots complement the existing efforts of miniaturizing conventional, rigid robots, and have the potential to revolutionize areas such as military equipment and biomedical devices. This type of system can accomplish tasks in complex and time-varying environments through geometric reconfiguration induced by diverse external stimuli, such as heat, solvent, light, electric field, magnetic field, and mechanical field. Approaches to achieve reconfigurable mesostructures are essential to the design and fabrication of soft robots. Existing studies mainly focus on four key aspects: reconfiguration mechanisms, fabrication schemes, deformation control principles, and practical applications. This review presents a detailed survey of methodologies for morphable mesostructures triggered by a wide range of stimuli, with a number of impressive examples, demonstrating high degrees of deformation complexities and varied multi-functionalities. The latest progress based on the development of new materials and unique design concepts is highlighted. An outlook on the remaining challenges and open opportunities is provided.

Assembly of 3D micro/nanostructures in advanced functional materials has important implications across broad areas of technology. Existing approaches are compatible, however, only with narrow classes of materials and/or 3D geometries. This paper introduces ideas for a form of Kirigami that allows precise, mechanically driven assembly of 3D mesostructures of diverse materials from 2D micro/nanomembranes with strategically designed geometries and patterns of cuts. Theoretical and experimental studies demonstrate applicability of the methods across length scales from macro to nano, in materials ranging from monocrystalline silicon to plastic, with levels of topographical complexity that significantly exceed those that can be achieved using other approaches. A broad set of examples includes 3D silicon mesostructures and hybrid nanomembrane-nanoribbon systems, including heterogeneous combinations with polymers and metals, with critical dimensions that range from 100 nm to 30 mm. A 3D mechanically tunable optical transmission window provides an application example of this Kirigami process, enabled by theoretically guided design.

Popping materials and devices from 2D into 3D Curved, thin, flexible complex three-dimensional (3D) structures can be very hard to manufacture at small length scales. Xu et al. develop an ingenious design strategy for the microfabrication of complex geometric 3D mesostructures that derive from the out-of-plane buckling of an originally planar structural layout (see the Perspective by Ye and Tsukruk). Finite element analysis of the mechanics makes it possible to design the two 2D patterns, which is then attached to a previously strained substrate at a number of points. Relaxing of the substrate causes the patterned material to bend and buckle, leading to its 3D shape. Science , this issue p. 154 ; see also p. 130

Stretchable electronics that require functional components with high areal coverages, antennas with small sizes and/or electrodes with invisibility under magnetic resonance imaging can benefit from the use of electrical wiring constructs that adopt fractal inspired layouts. Due to the complex and diverse microstructures inherent in high order interconnects/electrodes/antennas with such designs, traditional non-linear postbuckling analyses based on conventional finite element analyses (FEA) can be cumbersome and time-consuming. Here, we introduce a hierarchical computational model (HCM) based on the mechanism of ordered unraveling for postbuckling analysis of fractal inspired interconnects, in designs previously referred to as ‘self-similar’, under stretching. The model reduces the computational efforts of traditional approaches by many orders of magnitude, but with accurate predictions, as validated by experiments and FEA. As the fractal order increases from 1 to 4, the elastic stretchability can be enhanced by � 200 times, clearly illustrating the advantage of simple concepts in fractal design. These results, and the model in general, can be exploited in the development of optimal designs in wide ranging classes of stretchable electronics systems.

Three-dimensional (3D) structures capable of reversible transformations in their geometrical layouts have important applications across a broad range of areas. Most morphable 3D systems rely on concepts inspired by origami/kirigami or techniques of 3D printing with responsive materials. The development of schemes that can simultaneously apply across a wide range of size scales and with classes of advanced materials found in state-of-the-art microsystem technologies remains challenging. Here, we introduce a set of concepts for morphable 3D mesostructures in diverse materials and fully formed planar devices spanning length scales from micrometers to millimeters. The approaches rely on elastomer platforms deformed in different time sequences to elastically alter the 3D geometries of supported mesostructures via non-linear mechanical buckling. Over 20 examples have been experimentally and theoretically investigated, including mesostructures that can be reshaped between different geometries as well as those that can morph into three or more distinct states. An adaptive radio frequency circuit and a concealable electromagnetic device provide examples of functionally reconfigurable microelectronic devices.

Formation of 3D mesostructures in advanced functional materials is of growing interest due to the widespread envisioned applications of devices that exploit 3D architectures. Mechanically guided assembly based on compressive buckling of 2D precursors represents a promising method, with applicability to a diverse set of geometries and materials, including inorganic semiconductors, metals, polymers, and their heterogeneous combinations. This paper introduces ideas that extend the levels of control and the range of 3D layouts that are achievable in this manner. Here, thin, patterned layers with well-defined residual stresses influence the process of 2D to 3D geometric transformation. Systematic studies through combined analytical modeling, numerical simulations, and experimental observations demonstrate the effectiveness of the proposed strategy through ≈20 example cases with a broad range of complex 3D topologies. The results elucidate the ability of these stressed layers to alter the energy landscape associated with the transformation process and, specifically, the energy barriers that separate different stable modes in the final 3D configurations. A demonstration in a mechanically tunable microbalance illustrates the utility of these ideas in a simple structure designed for mass measurement.

Electrical interconnects that adopt self-similar, serpentine layouts offer exceptional levels of stretchability in systems that consist of collections of small, non-stretchable active devices in the so-called island–bridge design. This paper develops analytical models of flexibility and elastic stretchability for such structures, and establishes recursive formulae at different orders of self-similarity. The analytic solutions agree well with finite element analysis, with both demonstrating that the elastic stretchability more than doubles when the order of the self-similar structure increases by one. Design optimization yields 90% and 50% elastic stretchability for systems with surface filling ratios of 50% and 70% of active devices, respectively.

Buckling-driven assembly of 3D mesostructures from releasable multilayers offers versatile design options for unique applications., Capabilities for assembly of three-dimensional (3D) micro/nanostructures in advanced materials have important implications across a broad range of application areas, reaching nearly every class of microsystem technology. Approaches that rely on the controlled, compressive buckling of 2D precursors are promising because of their demonstrated compatibility with the most sophisticated planar technologies, where materials include inorganic semiconductors, polymers, metals, and various heterogeneous combinations, spanning length scales from submicrometer to centimeter dimensions. We introduce a set of fabrication techniques and design concepts that bypass certain constraints set by the underlying physics and geometrical properties of the assembly processes associated with the original versions of these methods. In particular, the use of releasable, multilayer 2D precursors provides access to complex 3D topologies, including dense architectures with nested layouts, controlled points of entanglement, and other previously unobtainable layouts. Furthermore, the simultaneous, coordinated assembly of additional structures can enhance the structural stability and drive the motion of extended features in these systems. The resulting 3D mesostructures, demonstrated in a diverse set of more than 40 different examples with feature sizes from micrometers to centimeters, offer unique possibilities in device design. A 3D spiral inductor for near-field communication represents an example where these ideas enable enhanced quality (Q) factors and broader working angles compared to those of conventional 2D counterparts.

Formation of three-dimensional (3D) mesostructures in advanced functional materials is of growing interest due to the widepread envisioned applications of devices that exploit 3D architectures. Mechanically-guided assembly based on compressive buckling of 2D precursors represents a promising method, with applicability to a diverse set of geometries and materials, including inorganic semiconductors, metals, polymers and their heteogenous intergration. This paper introduces ideas that extend the levels of control and and the range of 3D layouts that are achievable in these systems. Here, thin, patterned layers with well-defined residual stresses influence the process of 2D to 3D geometric transformation. Systematic studies through combined analytical modeling, numerical simulations and experimental observations demonstrate the effectiveness of the proposed strategy through ~20 example cases with a broad range of complex 3D topologies. The results elucidate the ability of these stressed layers to alter the energy landscape associated with the transformation process and, specifically, the energy barriers that separate different stable modes in the final 3D configurations. A demonstration in a mechanically tunable micro-balance illustrates the utility of these ideas in a simple structure designed for mass measurement.

A series of new aminomethylated derivatives of isoliquiritigenin was synthesized. The structures of the compounds were confirmed by IR, MS, NMR, 13C-NMR and elemental analyses. Cytotoxic activities of these derivatives towards the human prostatic cell line PC-3, human mammary cancer cell line MCF-7 and human oophoroma cell line HO-8910 in vitro were tested. The IC50 values showed cytotoxic activities of some of these new derivatives were relatively strong. Furthermore, tumor growth inhibition in vivo of aminomethylated derivatives of isoliquiritigenin 15 was superior to that of isoliquritigenin and reached inhibition rates of 71.68%. The detailed synthesis, spectroscopic data, biological and pharmacologicalactivities of the synthesized compounds were provided.

Lithographically defined electrical interconnects with thin, filamentary serpentine layouts have been widely explored for use in stretchable electronics supported by elastomeric substrates. We present a systematic and thorough study of buckling physics in such stretchable serpentine microstructures, and a strategic design of the serpentine layout for an ultra-stretchable electrode, via analytical models, finite element method (FEM) computations, and quantitative experiments. Both the onset of buckling and the postbuckling behaviors are examined, to determine scaling laws for the critical buckling strain and the limits of elastic behavior. Two buckling modes, namely the symmetric and anti-symmetric modes, are identified and analyzed, with experimental images and numerical results that show remarkable levels of agreement for the associated postbuckling processes. Based on these studies and an optimization of the design layout, we demonstrate routes for application of serpentine interconnects in an ultra-stretchable electrode that offer, simultaneously, an areal coverage as high as 81% and a biaxial stretchability as large as ∼170%.

Characterization of temperature and thermal transport properties of the skin can yield important information of relevance to both clinical medicine and basic research in skin physiology. Here we introduce an ultrathin, compliant skin-like, or 'epidermal', photonic device that combines colorimetric temperature indicators with wireless stretchable electronics for thermal measurements when softly laminated on the skin surface. The sensors exploit thermochromic liquid crystals patterned into large-scale, pixelated arrays on thin elastomeric substrates; the electronics provide means for controlled, local heating by radio frequency signals. Algorithms for extracting patterns of colour recorded from these devices with a digital camera and computational tools for relating the results to underlying thermal processes near the skin surface lend quantitative value to the resulting data. Application examples include non-invasive spatial mapping of skin temperature with milli-Kelvin precision (±50 mK) and sub-millimetre spatial resolution. Demonstrations in reactive hyperaemia assessments of blood flow and hydration analysis establish relevance to cardiovascular health and skin care, respectively.

When mounted on the skin, modern sensors, circuits, radios, and power supply systems have the potential to provide clinical-quality health monitoring capabilities for continuous use, beyond the confines of traditional hospital or laboratory facilities. The most well-developed component technologies are, however, broadly available only in hard, planar formats. As a result, existing options in system design are unable to effectively accommodate integration with the soft, textured, curvilinear, and time-dynamic surfaces of the skin. Here, we describe experimental and theoretical approaches for using ideas in soft microfluidics, structured adhesive surfaces, and controlled mechanical buckling to achieve ultralow modulus, highly stretchable systems that incorporate assemblies of high-modulus, rigid, state-of-the-art functional elements. The outcome is a thin, conformable device technology that can softly laminate onto the surface of the skin to enable advanced, multifunctional operation for physiological monitoring in a wireless mode.

Fractal-inspired designs for interconnects that join rigid, functional devices can ensure mechanical integrity in stretchable electronic systems under extreme deformations. The bonding configuration of such interconnects with the elastomer substrate is crucial to the resulting deformation modes, and therefore the stretchability of the entire system. In this study, both theoretical and experimental analyses are performed for postbuckling of fractal serpentine interconnects partially bonded to the substrate. The deformation behaviors and the elastic stretchability of such systems are systematically explored, and compared to counterparts that are not bonded at all to the substrate.

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