Flexible wearable sensors are emerging as next-generation tools to collect information from the human body and surroundings in a smart, friendly, and real-time manner. A new class of such sensors with various functionality and amenability for the human body is essential for this goal. Unfortunately, the majority of the wearable sensors reported so far in the literature were of a single function (mostly strain sensors) and just a prototype without thinking of continuous mass production. In this paper, we report a series of multifunctional conductive hydrogel/ thermochromic elastomer hybrid fibers with core–shell segmental configuration and their application as flexible wearable strain and temperature sensors to monitor human motion and body/surrounding temperatures. Specifically, a conductive reduced-graphene-oxide-doped poly­(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylamide (rGO-poly­(AMPS-co-AAm)) hydrogel and a thermochromic elastomer containing silicon rubber and thermochromic microcapsules are chosen as strain-sensitive and thermosensitive materials, respectively. A core–shell segmental structure is realized by programming the extrusion of either conductive hydrogel precursor solution or a thermochromic elastomer prepolymer as a core layer via dual-core coaxial wet spinning. Depending on the assembly order and length of the conductive hydrogel and the thermochromic elastomer, the as-prepared hybrid fibers can be used for different purposes, i.e., human-motion monitoring, body or room temperature detection, and color decoration. The strategy described above, i.e., fabrication of core–shell segmental fibers via the wet-spinning method, is especially suitable for mass production in industry and can be further extended to fabricate flexible wearable devices with more components and more functions such as transistors, sensors, displays, and batteries.

In this paper, a novel bioinspired stem cell‐laden microgel and related in vivo cartilage repair strategy are proposed. In particular, herein the preparation of new stem cell‐laden microgels, which can be injected into the chondral defect site in a minimally invasive way, and more importantly, capable of in situ self‐assembly into 3D macroporous scaffold without external stimuli, is presented. Specifically, thiolated gelatin (Gel‐SH) and vinyl sulfonated hyaluronic acid (HA‐VS) are first synthesized, and then stem cell‐laden gelatin/hyaluronic acid hybrid microgels (Gel‐HA) are generated by mixing Gel‐SH, HA‐VS, and bone mesenchymal stem cells (BMSCs) together via droplet‐based microfluidic approach, followed by gelation through fast and efficient thiol‐Michael addition reaction. The encapsulated BMSCs show high viability, proliferation, and chondrogenic differentiation potential in the microgels. Moreover, the in vitro test proves that BMSC‐laden Gel‐HA microgels are injectable without sacrificing BMSC viability, and more importantly, can self‐assemble into cartilage‐like scaffolds via cell–cell interconnectivity. In vivo experiments further confirm that the self‐assembled microgels can inhibit vascularization and hypertrophy. The Gel‐HA microgels and relevant cartilage repair strategy, i.e., injecting BMSC‐laden microgels separately and reconstructing chondral defect structure by microgel self‐assembly, provides a simple and effective method for cartilage tissue engineering and regenerative medicine.

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Inspired by stimuli-tailored dynamic processes that spatiotemporally create structural and functional diversity in biology, a new hierarchical patterning strategy is proposed to induce the emergence of complex multidimensional structures via dynamic sacrificial printing of stimuli-responsive hydrogels. Using thermally responsive gelatin (Gel) and pH-responsive chitosan (Chit) as proof-of-concept materials, we demonstrate that the initially printed sacrificial material (Gel/Chit-H+ hydrogel with a single gelatin network) can be converted dynamically into non-sacrificial material (Gel/Chit-H+–Citr hydrogel with gelatin and an electrostatic citrate–chitosan dual network) under stimulus cues (citrate ions). Complex hierarchical structures and functions can be created by controlling either the printing patterns of citrate ink or the diffusion time of citrate ions into the Gel/Chit-H+ hydrogel. Specifically, mechanically anisotropic hydrogel film and cell patterning can be achieved via two-dimensional (2D) patterning; complex external and internal 3D structures can be fabricated in stimuli-responsive hydrogel and other hydrogels that are not stimuli-responsive under experimental conditions (also owing to the erasable properties of Gel/Chit-H+–Citr hydrogel) via 3D patterning; and an interconnected or segregated fluidic network can be constructed from the same initial 3D grid structure via 4D patterning. Our method is very simple, safe and generally reagentless, and the products/structures are often erasable, compatible and digestible, enabling advanced fabrication technologies (e.g. additive manufacturing) to be applied to a sustainable materials platform.