The ever-growing overlap between stretchable electronic devices and wearable healthcare applications is igniting the discovery of novel biocompatible and skin-like materials for human-friendly stretchable electronics fabrication. Amongst all potential candidates, hydrogels with excellent biocompatibility and mechanical features close to human tissues are constituting a promising troop for realizing healthcare-oriented electronic functionalities. In this work, based on biocompatible and stretchable hydrogels, a simple paradigm to prototype stretchable electronics with an embedded three-dimensional (3D) helical conductive layout is proposed. Thanks to the 3D helical structure, the hydrogel electronics present satisfactory mechanical and electrical robustness under stretch. In addition, reusability of stretchable electronics is realized with the proposed scenario benefiting from the swelling property of hydrogel. Although losing water would induce structure shrinkage of the hydrogel network and further undermine the function of hydrogel in various applications, the worn-out hydrogel electronics can be reused by simply casting it in water. Through such a rehydration procedure, the dehydrated hydrogel can absorb water from the surrounding and then the hydrogel electronics can achieve resilience in mechanical stretchability and electronic functionality. Also, the ability to reflect pressure and strain changes has revealed the hydrogel electronics to be promising for advanced wearable sensing applications.

Droplet manipulation has found broad applications in various engineering and biomedical fields, such as biochemistry, microfluidic systems, drug delivery, and tissue engineering. Many methods have been developed to enhance the ability for manipulating droplets, among which magnetically actuated droplet manipulation has attracted widespread interests due to its remote, noninvasive manipulation ability and biocompatibility. This review summarizes the approaches and their principles that enable actuating the droplet magnetically. The potential biomedical applications of such a technique in bioassay, cell assembly, and tissue engineering are given.

Living cells respond to their mechanical microenvironments during development, healing, tissue remodeling and homeostasis attainment. However, this mechanosensitivity has not yet been established definitively for cells in three-dimensional (3D) culture environments, in part because of challenges associated with providing uniform and consistent 3D environments that can deliver a large range of physiological and pathophysiological strains to cells. Here, we report microscale magnetically actuated, cell-laden hydrogels (μMACs) for investigating the strain-induced cell response in 3D cultures. μMACs provide high-throughput arrays of defined 3D cellular microenvironments that undergo reversible, relatively homogeneous deformation following non-contact actuation under external magnetic fields. We present a technique that not only enables the application of these high strains (60%) to cells but also enables simplified microscopy of these specimens under tension. We apply the technique to reveal cellular strain-threshold and saturation behaviors that are substantially different from their 2D analogs, including spreading, proliferation, and differentiation. μMACs offer insights for mechanotransduction and may also provide a view of how cells respond to the extracellular matrix in a 3D manner.

A versatile method for spatially modulating hydrogel stiffness was proposed. The locally stiffened hydrogel presented tunable strain-shielding ability and thus aided to electronic components integration for wearable electronics.

Coniothyrium minitans is a potential biological control agent of the plant pathogenic fungus Sclerotinia sclerotiorum. In this research, T-DNA insertional transformation of strain ZS-1 of C. minitans mediated by Agrobacterium tumefaciens was obtained, with optimization of spore maturity for transformation. After confirmation by PCR, transformants were subjected to Southern blot analysis, and results showed that more than 82.7% of transformants had single T-DNA insertions, and 12.1% of transformants had two copies T-DNA insertions. The genomic DNA segments of transformants flanking the T-DNA could be amplified from both borders with TAIL-PCR. Four types of mutants were screened and identified from the T-DNA insertional library, which comprised sporulation deficient mutants, pathogenicity deficient mutants, pigment change mutants and antibiotic deficient mutant, and some of the mutants were described; the number and frequency of each type of mutant from the library were calculated, and the frequency of each type is 3.27 x 10(-3), 1.0 x 10(-4), 1.4 x 10(-4), 2.5 x 10(-4), respectively. The successful creation of the T-DNA insertional transformation library may help us to unravel the interaction between a parasite and its host at a molecular level, to clarify the differentiation and development of this fungus, and to analyze and clone functional genes from the biocontrol microorganism in tripartite associations.

Much effort has been made to engineer artificial fiber‐shaped cellular constructs that can be potentially used as muscle fibers or blood vessels. However, existing microfiber‐based approaches for culturing cells are still limited to 2D systems, compatible with a restricted number of polymers (e.g., alginate) and always lacking in situ mechanical stimulation. Here, a simple, facile, and high‐throughput technique is reported to fabricate 3D cell‐laden hydrogel microfibers (named hydrogel noodles), inspired by the fabrication approach for Chinese Hele noodle. A magnetically actuated and noncontact method to apply tensile stretch on hydrogel noodles has also been developed. With this method, it is found that cellular strain‐threshold and saturation behaviors in hydrogel noodles differ substantially from their 2D analogs, including proliferation, spreading, and alignment. Moreover, it is shown that these cell‐laden microfibers can induce muscle myofiber formation by tensile stretching alone. This easily adaptable platform holds great potential for the creation of functional tissue constructs and probing mechanobiology in three dimensions.

The graded mechanical properties (e.g., stiffness and stress/strain) of excellular matrix play an important role in guiding cellular alignment, as vital in tissue reconstruction with proper functions. Though various methods have been developed to engineer a graded mechanical environment to study its effect on cellular behaviors, most of them failed to distinguish stiffness effect from stress/strain effect during mechanical loading. Here, we construct a mechanical environment with programmable strain gradients by using a hydrogel of a linear elastic property. When seeding cells on such hydrogels, we demonstrate that the pattern of cellular alignment can be rather precisely tailored by substrate strains. The experiment is in consistency with a theoritical prediction when assuming that focal adhesions (FAs) would drive a cell to reorient to the directions where they are most stable. A fundamental theory has also been developed and is excellent in agreement with the complete temporal alignment of cells. This work not only provides important insights into the cellular response to the local mechanical microenvironment but can also be utilized to engineer patterned cellular alignment that can be critical in tissue remodeling and regenerative medicine applications.

The tissues of hollow organs can routinely stretch up to 2.5 times their length. Although significant pathology can arise if relatively large stretches are sustained, the responses of cells are not known at these levels of sustained strain. A key challenge is presenting cells with a realistic and well-defined three-dimensional (3D) culture environment that can sustain such strains. Here, we describe an in vitro system called microscale, magnetically-actuated synthetic tissues (micro-MASTs) to quantify these responses for cells within a 3D hydrogel matrix. Cellular strain-threshold and saturation behaviors were observed in hydrogel matrix, including strain-dependent proliferation, spreading, polarization, and differentiation, and matrix adhesion retained at strains sufficient for apoptosis. More broadly, the system shows promise for defining and controlling the effects of mechanical environment upon a broad range of cells.