Selective deposition and preferential alignment of two-dimensional (2D) nanoparticles on complex and flexible three-dimensional (3D) substrates can tune material properties and enrich structural versatility for broad applications in wearable health monitoring, soft robotics, and human−machine interfaces. However, achieving precise and scalable control of the morphology of layer-structured nanomaterials is challenging, especially constructing hierarchical architectures consistent from nanoscale alignment to microscale patterning to complex macroscale landscapes. This work demonstrated a scalable and straightforward hybrid 3D printing method for orientational alignment and positional patterning of 2D MXene nanoparticles. This process involved (i) surface topology design via microcontinuous liquid interface production (μCLIP) and (ii) directed assembly of MXene flakes via capillarity-driven direct ink writing (DIW). With well-managed surface patterning geometry and printing ink quality control, the surface microchannels constrained MXene suspensions and leveraged microforces to facilitate preferential alignment of MXene sheets via layer-by-layer additive depositions. The printed devices displayed multifunctional properties, i.e., anisotropic conductivity and piezoresistive sensing with a wide sensing range, high sensitivity, fast response time, and mechanical durability. Our fabrication technique shows enormous potential for rapid, digital, scalable, and low-cost manufacturing of hierarchical structures, especially for micropatterning and aligning 2D nanoparticles not easily accessible through conventional processing methods.

Additive manufacturing (AM), also known as three-dimensional (3D) printing, is thriving as an effective and robust method in fabricating architected piezoelectric structures, yet most of the commonly adopted printing techniques often face the inherent speed-accuracy trade-off, limiting their speed in manufacturing sophisticated parts containing micro-/nanoscale features. Herein, stabilized, photo-curable resins comprising chemically functionalized piezoelectric nanoparticles (PiezoNPs) were formulated, from which microscale architected 3D piezoelectric structures were printed continuously via micro continuous liquid interface production (μCLIP) at speeds of up to ~60 μm s-1, which are more than 10 times faster than the previously reported stereolithography-based works. The 3D-printed functionalized barium titanate (f-BTO) composites reveal a bulk piezoelectric charge constant d33 of 27.70 pC N-1 with the 30 wt% f-BTO. Moreover, rationally designed lattice structures that manifested enhanced, tailorable piezoelectric sensing performance as well as mechanical flexibility were tested and explored in diverse flexible and wearable self-powered sensing applications, e.g., motion recognition and respiratory monitoring.

Conductive and self-healing (SH) hydrogels have been receiving continuous attention, which could broaden the design of ionotronic devices for health monitoring systems and soft robots with the ability to repair damage autonomously. So far, three-dimensional (3D) fabrication of such SH hydrogels is mainly limited to traditional molding/casting or extrusion-based 3D printing methods, which limits the formation of sophisticated structures with highresolution features. Furthermore, the need of external stimuli (e.g., water, heat, and pH change) to achieve SH behavior could restrict their wide application. Herein, we report an ion-conductive SH hydrogel suitable for a home-built highresolution and high-speed 3D printing process, micro continuous liquid interface production (μCLIP). This material system relies on interpenetrating polymer networks (IPN) hydrogel formed by physically cross-linked poly(vinyl alcohol) combined with chemically/ionically cross-linked poly(acrylic acid) and ferric chloride. By carefully optimizing the resin's composition, we can balance high-resolution printability and superb SH capability, at the same time manifesting sufficient ion conductivity. Specifically, complex 3D structures with microscale features (down to 100 μm) can be printed at speeds up to 16.5 μm s −1 . Upon damage occurs, hydrogen bonds within hydroxyl and carboxyl groups, as well as ionic bonds generated from ferric ions, contribute together to achieve fast and high efficiency SH, which can restore 90% (100%) of the original mechanical strength at room temperature within 4 h (8 h) without any external stimulus. In addition, both the as-printed and self-healed hydrogels manifest superior ion conductivity and stretchability. Therefore, the SH hydrogels can be rapidly printed and tailored as customized wearable sensors, and the sensing capabilities were quantitatively investigated and compared. In terms of applications, SH hydrogel-based knuckle sensors were prototyped to detect a finger's folding and unfolding motions.

Architected materials such as lattices are capable of demonstrating extraordinary mechanical performance. Lattices are often used for their stretch-dominated behavior, which gives them a high degree of stiffness at low-volume fractions. At the other end of the stiffness spectrum, bending-dominated lattices tend to be more compliant and are of interest for their energy absorption performance. Here, we report a class of ultra-compliant interwoven lattices that demonstrate up to an order of magnitude improvement in compliance over their traditional counterparts at similar volume fractions. This is achieved by selectively decoupling nodes and interweaving struts in bending-dominated lattices, inspired by observations of this structural principle in the lattice-like arrangement of the Venus flower basket sea sponge. By decoupling nodes in this manner, we demonstrate a simple and near-universal design strategy for modulating stiffness in lattice structures and achieve among the most compliant lattices reported in the literature.