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This study presents a highly sensitive 3D force sensor based on a piezoresistive cantilever with stress concentration. The sensor achieves precise 3D force detection by integrating a polydimethylsiloxane (PDMS) cap with pyramid microstructures and silicon chip containing four piezoresistive cantilevers with a micro-hole at their root. Finite element simulation validates the superior performance of the micro-hole in enhancing the sensitivity of the force sensor. Compared to a traditional sensor based on a piezoresistive cantilever, the microhole design increases strain in the piezoresistive region of the cantilever by 2 times and the stress by 2.72 times. The proposed sensor exhibits promising potential for applications in various fields, including medical devices, robotics, industrial automation, and others.

Polydimethylsiloxane (PDMS) has attracted great attention in various fields due to its excellent properties, but its inherent hydrophobicity presents challenges in many applications that require controlled wettability. The purpose of this review is to provide a comprehensive overview of some key strategies for modifying the wettability of PDMS surfaces by providing the main traditional methods for this modification and the results of altering the contact angle and other characteristics associated with this property. Four main technologies are discussed, namely, oxygen plasma treatment, surfactant addition, UV-ozone treatment, and the incorporation of nanomaterials, as these traditional methods are commonly selected due to the greater availability of information, their lower complexity compared to the new techniques, and the lower cost associated with them. Oxygen plasma treatment is a widely used method for improving the hydrophilicity of PDMS surfaces by introducing polar functional groups through oxidation reactions. The addition of surfactants provides a versatile method for altering the wettability of PDMS, where the selection and concentration of the surfactant play an important role in achieving the desired surface properties. UV-ozone treatment is an effective method for increasing the surface energy of PDMS, inducing oxidation, and generating hydrophilic functional groups. Furthermore, the incorporation of nanomaterials into PDMS matrices represents a promising route for modifying wettability, providing adjustable surface properties through controlled dispersion and interfacial interactions. The synergistic effect of nanomaterials, such as nanoparticles and nanotubes, helps to improve wetting behaviour and surface energy. The present review discusses recent advances of each technique and highlights their underlying mechanisms, advantages, and limitations. Additionally, promising trends and future prospects for surface modification of PDMS are discussed, and the importance of tailoring wettability for applications ranging from microfluidics to biomedical devices is highlighted. Traditional methods are often chosen to modify the wettability of the PDMS surface because they have more information available in the literature, are less complex than new techniques, and are also less expensive.

Facile and efficient radiative daytime cooling technology is still a huge challenge. In this paper, we proposed an eco-friendly, facile, efficient superhydrophobic radiative daytime cooling film composed of polydimethylsiloxane, nano TiO 2 , and nano SiO 2 . This radiative daytime cooling film could have about 15°C cooling of Al sheet, 9°C cooling for the building model on a sunny summer day, and 8°C cooling for the building model on a cloudy summer day, respectively. This method is promising to be used in building cooling fields.

Skin wounds are common in accidental injuries, and the intricacies of wound repair are closely linked to endogenous electric fields. Electrical stimulation plays a pivotal role in the restorative processes of skin injuries, encompassing collagen deposition, angiogenesis, inflammation, and re-epithelialization. Employing electrical stimulation therapy replicates and enhances the effects of endogenous wound electric fields by applying an external electric field to the wound site, thereby promoting skin wound healing. In this study, we developed a self-powered repetitive mechanical impacts-electrical stimulation (RMI-ES) system utilizing a BaTiO 3 /polydimethylsiloxane (PDMS) piezoelectric composite film. Compared to conventional electrical stimulation devices, the fabricated piezoelectric composite film efficiently harvests energy from the pressure applied by the stimulation device and the tensile force occurring during natural rat activities. The results demonstrated that piezoelectric stimulation generated by the composite membrane expedited the cell cycle, promoting fibroblast proliferation. Additionally, piezoelectric stimulation induced favorable changes in fibroblast gene expression, including increased expression of transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), collagen 1, collagen 3, vascular endothelial growth factor (VEGF), and alpha-smooth muscle actin (α-SMA), while reducing interleukin-6 (IL-6) expression. Transcriptome analysis revealed that piezoelectric stimulation may induce fibroblast migration, proliferation, and collagen expression by influencing PI3K/AKT serine/threonine kinase (AKT) pathways. Further confirmation through the addition of the PI3K inhibitor LY294002 validated that piezoelectric stimulation can regulate the repair process after skin injury through the pathway. Importantly, in vivo results demonstrated that the electric field at the wound site effectively promoted wound healing, reduced inflammation, and stimulated collagen deposition and neovascularization. This study emphasizes the role of the piezoelectric membrane as an effective, safe, and battery-free electrical stimulator crucial for skin wound healing.

Developing autonomous self-healing materials for applications in harsh conditions is challenging because the reconstruction of interaction in material for self-healing will experience significant resistance and fail. Herein, a universally self-healing and highly stretchable supramolecular elastomer is designed by synergistically incorporating multi-strength H-bonds and disulfide metathesis in polydimethylsiloxane polymers. The resultant elastomer exhibits high stretchability for both unnotched (14000%) and notched (1300%) samples. It achieves fast autonomous self-healing under universal conditions, including at room temperature (10 min for healing), ultralow temperature (−40 °C), underwater (93% healing efficiency), supercooled high-concentrated saltwater (30% NaCl solution at −10 °C, 89% efficiency), and strong acid/alkali environment (pH = 0 or 14, 88% or 84% efficiency). These properties are attributable to synergistic interaction of the dynamic strong and weak H-bonds and stronger disulfide bonds. A self-healing and stretchable conducting device built with the developed elastomer is demonstrated, thereby providing a direction for future e-skin applications. Developing autonomous self-healing materials for application under extreme conditions is challenging. Here, the authors design a highly stretchable elastomer by incorporation of H-bonds and disulphide methathesis, which shows efficient self-healing under extreme conditions.

We report a remarkable thickness-dependent wrinkling behavior of oxygen plasma-treated polydimethylsiloxane (PDMS) films, in which an energy barrier separates the wrinkling mechanics into two regimes. For thick films, the film wrinkles with a constant periodicity which can be precisely predicted by the classic nonlinear finite mechanics. Reducing the film thickness below 1 mm leads to nonuniform wrinkles with an increasing periodicity which gives rise to random scattering and transparency changes under mechanical strains. By tuning the film thickness, we were able to control both the quality and size of the periodic wrinkles and further design mechanochromic devices featuring brilliant structural colors and programmable colorimetric responses. This work sheds light on the fundamental understanding of the wrinkling mechanics of bilayer systems and their intriguing mechanochromic applications.

Ice accumulation causes various problems in our daily life for human society. The daunting challenges in ice prevention and removal call for novel efficient antiicing strategies. Recently, photothermal materials have gained attention for creating icephobic surfaces owing to their merits of energy conservation and environmental friendliness. However, it is always challenging to get an ideal photothermal material which is cheap, easily fabricating, and highly photothermally efficient. Here, we demonstrate a low-cost, high-efficiency superhydrophobic photothermal surface, uniquely based on inexpensive commonly seen candle soot. It consists of three components: candle soot, silica shell, and polydimethylsiloxane (PDMS) brushes. The candle soot provides hierarchical nano/microstructures and photothermal ability, the silica shell strengthens the hierarchical candle soot, and the grafted low-surface-energy PDMS brushes endow the surface with superhydrophobicity. Upon illumination under 1 sun, the surface temperature can increase by 53 °C, so that no ice can form at an environmental temperature as low as −50 °C and it can also rapidly melt the accumulated frost and ice in 300 s. The superhydrophobicity enables the melted water to slide away immediately, leaving a clean and dry surface. The surface can also self-clean, which further enhances its effectiveness by removing dust and other contaminants which absorb and scatter sunlight. In addition, after oxygen plasma treatment, the surface can restore superhydrophobicity with sunlight illumination. The presented icephobic surface shows great potential and broad impacts owing to its inexpensive component materials, simplicity, ecofriendliness, and high energy efficiency.

The advancement of laser-induced graphene (LIG) technology has streamlined the fabrications of flexible graphene devices. However, the ultrafast kinetics triggered by laser irradiation generates intrinsic amorphous characteristics, leading to high resistivity and compromised performance in electronic devices. Healing graphene defects in specific patterns is technologically challenging by conventional methods. Herein, we report the rapid rectification of LIG’s topological defects by flash Joule heating in milliseconds (referred to as F-LIG), whilst preserving its overall structure and porosity. The F-LIG exhibits a decreased I D / I G ratio from 0.84 – 0.33 and increased crystalline domain from Raman analysis, coupled with a 5-fold surge in conductivity. Pair distribution function and atomic-resolution imaging delineate a broader-range order of F-LIG with a shorter C-C bond of 1.425 Å. The improved crystallinity and conductivity of F-LIG with excellent flexibility enables its utilization in high-performance soft electronics and low-voltage disinfections. Notably, our F-LIG/polydimethylsiloxane strain sensor exhibits a gauge factor of 129.3 within 10% strain, which outperforms pristine LIG by 800%, showcasing significant potential for human-machine interfaces. Laser-induced graphene (LIG) can be obtained via a practically convenient approach, but its amorphous characteristics limit its applications. Here, the authors report a flash Joule heating strategy to improve the crystalline quality and conductivity of LIG, leading to strain sensors with enhanced sensitivity.

Ball milling is a representative mechanochemical strategy that uses the mechanical agitation-induced effects, defects, or extreme conditions to activate substrates. Here, we demonstrate that ball grinding could bring about contact-electro-catalysis (CEC) by using inert and conventional triboelectric materials. Exemplified by a liquid-assisted-grinding setup involving polytetrafluoroethylene (PTFE), reactive oxygen species (ROS) are produced, despite PTFE being generally considered as catalytically inert. The formation of ROS occurs with various polymers, such as polydimethylsiloxane (PDMS) and polypropylene (PP), and the amount of generated ROS aligns well with the polymers’ contact-electrification abilities. It is suggested that mechanical collision not only maximizes the overlap in electron wave functions across the interface, but also excites phonons that provide the energy for electron transition. We expect the utilization of triboelectric materials and their derived CEC could lead to a field of ball milling-assisted mechanochemistry using any universal triboelectric materials under mild conditions. Through contact-electro-catalysis (CEC), reactive oxygen species can be produced by chemically inert triboelectric materials in ball milling, enabling mechanoredox reactions with a broad selection of abundant triboelectric materials

Substantial research over the past two decades has established that extracellular matrix (ECM) elasticity, or stiffness, affects fundamental cellular processes, including spreading, growth, proliferation, migration, differentiation and organoid formation. Linearly elastic polyacrylamide hydrogels and polydimethylsiloxane (PDMS) elastomers coated with ECM proteins are widely used to assess the role of stiffness, and results from such experiments are often assumed to reproduce the effect of the mechanical environment experienced by cells in vivo. However, tissues and ECMs are not linearly elastic materials—they exhibit far more complex mechanical behaviours, including viscoelasticity (a time-dependent response to loading or deformation), as well as mechanical plasticity and nonlinear elasticity. Here we review the complex mechanical behaviours of tissues and ECMs, discuss the effect of ECM viscoelasticity on cells, and describe the potential use of viscoelastic biomaterials in regenerative medicine. Recent work has revealed that matrix viscoelasticity regulates these same fundamental cell processes, and can promote behaviours that are not observed with elastic hydrogels in both two- and three-dimensional culture microenvironments. These findings have provided insights into cell–matrix interactions and how these interactions differentially modulate mechano-sensitive molecular pathways in cells. Moreover, these results suggest design guidelines for the next generation of biomaterials, with the goal of matching tissue and ECM mechanics for in vitro tissue models and applications in regenerative medicine. This Review explores the role of viscoelasticity of tissues and extracellular matrices in cell–matrix interactions and mechanotransduction and the potential utility of viscoelastic biomaterials in regenerative medicine.