Microribbon‐Like Elastomers for Fabricating Macroporous and Highly Flexible Scaffolds that Support Cell Proliferation in 3D

Hydrogel‐based scaffolds are widely used for culturing cells in three dimensions due to their tissue‐like water content and tunable biochemical and physical properties. Most conventional hydrogels lack the macroporosity desirable for efficient cell proliferation and migration and have limited flexibility when subject to mechanical load. Here microribbon‐like elastomers that, when photocrosslinked, can form macroporous and highly flexible scaffolds that support cell proliferation in 3D are developed. These microribbons are produced by wet‐spinning gelatin solution into microfibers, followed by drying in acetone, which causes asymmetrical collapse of microfibers to form microribbon‐like structures. Gelatin microribbons are then modified using methacrylate anhydride to allow further photocrosslinking into 3D scaffolds. The macroporosity and mechanical properties of the microribbon‐based scaffold may be tuned by varying wet‐spinning rate, drying temperature, choice of drying agent, level of glutaraldehyde crosslinking, and microribbon density. When encapsulated in the microribbon‐based scaffold, human adipose‐derived stromal cells proliferated up to 30‐fold within 3 weeks. Furthermore, microribbons‐based scaffold demonstrate great flexibility and can sustain up to 90% strain and 3 MPa stress without failing. The unique mechanical properties of microribbon‐based scaffolds make them promising tools for engineering shock‐absorbing tissues such as cartilage and intervertebral discs.     

Additive Manufacturing of 3D Aerogels and Porous Scaffolds: A Review

Aerogels are highly porous structures produced by replacing the liquid solvent of a gel with air without causing a collapse in the solid network. Unlike conventional fabrication methods, additive manufacturing (AM) has been applied to fabricate 3D aerogels with customized geometries specific to their applications, designed pore morphologies, multimaterial structures, etc. To date, three major AM technologies (extrusion, inkjet, and stereolithography) followed by a drying process have been proposed to additively manufacture 3D functional aerogels. 3D-printed aerogels and porous scaffolds showed great promise for a variety of applications, including tissue engineering, electrochemical energy storage, controlled drug delivery, sensing, and soft robotics. In this review, the details of steps included in the AM of aerogels and porous scaffolds are discussed, and a general frame is provided for AM of those. Then, the different postprinting processes are addressed to achieve the porosity (after drying); and mechanical strength, functionality, or both (after postdrying thermal or chemical treatments) are provided. Furthermore, the applications of the 3D-printed aerogels/porous scaffolds made from a variety of materials are also highlighted. The review is concluded with the current challenges and an outlook for the next generation of 3D-printed aerogels and porous scaffolds.     

Programmed Shape‐Morphing Scaffolds Enabling Facile 3D Endothelialization

Rapid formation of a confluent endothelial monolayer is the key to the success of small‐diameter vascular grafts, which is significantly important for treating dangerous and even sometimes deadly vascular disorders. However, the difficulty to homogenously locate endothelial cells onto the lumen of small‐diameter tubular scaffolds makes 3D endothelialization greatly challenging. Here, novel shape‐morphing scaffolds enabling programmed deformation from planar shapes to small‐diameter tubular shapes are designed and developed by combining biocompatible shape memory polymer and electrospun nanofibrous membrane. Endothelial cells can be conveniently seeded and attached on the 2D surface of the scaffolds and subsequently self‐rolled into 3D organization at physiological temperature. Endothelial cell responses and functions are varied on the shape‐morphing scaffolds with different nanofibrous electrospun membranes as the inner layer, arisen from the inducement of scaffolds with different morphological, physical, and biochemical characteristics. Owing to excellent properties of the nanofibrous membrane fabricated by the coelectrospinning of poly‐ε‐caprolactone (PCL) and gelatin methacrylate (GelMA), the shape‐morphing scaffolds with a nanofibrous PCL/GelMA inner layer support desirable homogeneous endothelial cell attachment as well as the rapid formation of biomimetic cell–scaffold interaction and cell–cell interaction under the 3D cell culture condition, therefore offering a visible approach for facile 3D endothelialization.     

Molecularly‐Engineered, 4D‐Printed Liquid Crystal Elastomer Actuators

Three‐dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual thiol‐ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo‐responsive structures that sequentially and reversibly undergo multiple shape changes.     

Subtractive contact-patterning of molecular organic films

An array of optoelectronic applications requires micro- and nanoscale patterning of molecular organic films. A subtractive patterning technique is developed to define micron-sized features of nanometer range thickness on a variety of hole transporting and hole blocking materials. Lateral resolution of patterned features is controlled by micron-scale stamp shapes, while the removal of the patterned nanoscale film thicknesses (sub-10 nm to over 40 nm) is correlated to strength of interfacial and intermolecular forces. Using this process, a multi-color organic light-emitting device is fabricated, demonstrating the ability of contact patterning to manipulate organic molecular films on the micro- and nanoscales.     

Carbazole-Based Anion Ionic Water-Soluble Two-Photon Initiator for Achieving 3D Hydrogel Structures

3D hydrogel structures fabricated by two-photon polymerization (TPP) have become attractive in biomedical fields. Generally, conventional organic solvents are toxic and the residues left in the fabricated 3D structures are harmful to cells. Hence, anion ionic carbazole-based water-soluble two-photon initiator (TPI) 3,6-bis[2-(1-methylpyridinium)vinyl]-9-methylcarbazole ditosylate (BT) is proposed to construct arbitrary 3D hydrogel structures. Cucurbit[7]uril (CB7) and BT form a host-guest complex (CB7/BT) with a binding ratio of 1:1, which further improves the water solubility, biocompatibility and nonlinear absorption property of TPI. A water-soluble photoresist consisting of photoinitiator CB7/BT and monomer poly(ethylene glycol) diacrylate is prepared to explore the TPP fabrication capacity. The electron paramagnetic resonance measurement shows that CB7/BT initiates photopolymerization by alkyl radicals. The laser threshold power of the photoresist is 6.3 mW and the feature size is 127 nm in TPP at 780 nm. The initiator with p-toluenesulfonate anion exhibits higher binding energy, larger two-photon absorption cross-section and two-photon fabrication resolution compared with the previous work using iodide as an anion, indicating a promising way to improve the fabrication capacity of water-soluble TPI through changing the anion ionic group. The proposed strategy will provide high potential for the further application in the biomedical field.     

飞秒激光双光子聚合构建水溶性石墨烯-光刻胶的3D微结构

通过将水溶性石墨烯掺入至光引发剂2-苄基-2-二甲基氨基-1-（4-吗啉苯基）丁酮和季戊四醇三丙烯酸酯混合而成的光刻胶中,利用飞秒激光双光子聚合技术制作一系列平面图案及三维立体结构。利用亲水角测试表征混合物的浸润性,激光透过深度测试表征混合物的穿透性。实验结果证明,掺杂有水溶性石墨烯的混合液与玻璃仍具有较强结合力和一定激光穿透性。最后利用拉曼成像与扫描电子显微镜表征平面图案及三维结构。证实使用去离子水作为分散液可以将水溶性石墨烯掺杂进微结构中,并且掺杂有水溶性石墨烯的微结构在机械性能上比纯光刻胶微结构,结构更稳定且形貌更统一。     

Macroscopic Supramolecular Assembly to Fabricate 3D Ordered Structures: Towards Potential Tissue Scaffolds with Targeted Modification

3D ordered structures beyond microscale with targeted modification are catching increasing attention due to its application as tissue scaffolds. Especially scaffolds with necessary growth factors at designated locations are meaningful for induced cell differentiation and tissue formation. However, few fabrication methods can address the challenge of introducing bioactive species to the interior targeted places during the preparation process. Herein, for the first time macroscopic supramolecular assembly is applied to obtain such 3D ordered structures and established a proof‐of‐concept idea of complex scaffold with targeted modification. Taking strip‐like polydimethylsilicon building block as a model system, microscaled multilayered structures have been fabricated with parallel aligned building blocks in each layer. The morphology can be adjusted in a flexible way by tuning the number of layer, the space between two adjacent building blocks, and the position and orientation of each PDMS. The as‐prepared 3D structures are demonstrated biocompatible and potential as scaffolds for 3D cell culture. Moreover, bioactive species can be in situ incorporated into designated locations within the 3D structure precisely. In this way, a novel strategy is provided to address the current challenges in fabricating complex 3D tissue scaffolds with localized protein for future induced cell differentiation.     

Soft,Flexible Freestanding Neural Stimulation and Recording Electrodes Fabricated from Reduced Graphene Oxide

There is an urgent need for conductive neural interfacing materials that exhibit mechanically compliant properties, while also retaining high strength and durability under physiological conditions. Currently, implantable electrode systems designed to stimulate and record neural activity are composed of rigid materials such as crystalline silicon and noble metals. While these materials are strong and chemically stable, their intrinsic stiffness and density induce glial scarring and eventual loss of electrode function in vivo. Conductive composites, such as polymers and hydrogels, have excellent electrochemical and mechanical properties, but are electrodeposited onto rigid and dense metallic substrates. In the work described here, strong and conductive microfibers (40–50 μm diameter) wet‐spun from liquid crystalline dispersions of graphene oxide are fabricated into freestanding neural stimulation electrodes. The fibers are insulated with parylene‐C and laser‐treated, forming “brush” electrodes with diameters over 3.5 times that of the fiber shank. The fabrication method is fast, repeatable, and scalable for high‐density 3D array structures and does not require additional welding or attachment of larger electrodes to wires. The electrodes are characterized electrochemically and used to stimulate live retina in vitro. Additionally, the electrodes are coated in a water‐soluble sugar microneedle for implantation into, and subsequent recording from, visual cortex.     

Fabrication of silicon micro-mould for polymer replication using focused ion beam

Focused ion beam sputtering was used to fabricate microscale moulds of circular conical structures in silicon. As scan strategy, a continuous slicing method (CSM) modified from a two-dimensional (2D) slice-by-slice approach combined with a spiral scan was tested experimentally. With carefully chosen ion beam conditions and processing parameters, moulds were fabricated as a function of the ion dose for specific dwell times. Using the fabricated moulds, polymeric polydimethylsiloxane (PDMS) and polyurethane acrylate (PUA) microstructures were replicated and compared with the mould dimensions. Using PUA, the resolution of the polymer structure was examined on a nanoscale. In addition, mould-making failure due to both beam overlap and the field of view (FOV) is discussed. Finally, micro-lenses of different sizes were fabricated successfully.     

Biomimetic Ultralight,Highly Porous,Shape‐Adjustable,and Biocompatible 3D Graphene Minerals via Incorporation of Self‐Assembled Peptide Nanosheets

Hybrid nanomaterials with tailored functions, consisting of self‐assembled peptides, are intensively applied in nanotechnology, tissue engineering, and biomedical applications due to their unique structures and properties. Herein, a peptide‐mediated biomimetic strategy is adopted to create the multifunctional 3D graphene foam (GF)‐based hybrid minerals. First, 2D peptide nanosheets (PNSs), obtained by self‐assembling a motif‐specific peptide molecule (LLVFGAKMLPHHGA), are expected to exhibit biofunctionality, such as the biomimetic mineralization of hydroxyapatite (HA) minerals. Subsequently, the noncovalent conjugation of PNSs onto GF support is utilized to form 3D GF‐PNSs hybrid scaffolds, which are suitable for the growth of HA minerals. The fabricated biomimetic 3D GF‐PNSs‐HA minerals exhibit adjustable shape, superlow weight (0.017 g cm^?3), high porosity (5.17 m² g^?1), and excellent biocompatibility, proving potential applications in both bone tissue engineering and biomedical engineering. To the best of the authors' knowledge, it is the first time to combine 2D PNSs and GF to fabricate 3D organic–inorganic hybrid scaffold. Further development of these hybrid GF‐PNSs scaffolds can potentially lead to materials used as matrices for drug delivery or bone tissue engineering as proven via successful 3D scaffold formation exhibiting interconnected pore‐size structures suitable for vascularization and medium transport.     

Robotic Locomotion and Piezo1 Activity Controlled with Novel Liquid Marble-based Soft Actuators

A novel soft actuator is designed, fabricated, and optimized for applied use in soft robotics and biomedical applications. The soft actuator is powered by the expansion and contraction of a graphene-containing and encased liquid marble using the photothermal effect. Unfortunately, conventional liquid marbles are found to be too fragile and prone to cracking and failure for such applications. After experimentation, it is possible to remedy this problem by synthesizing liquid marbles encased with polymeric shells–polymerized in situ–for added mechanical strength and robustness. These marbles are shown to have intrinsic photothermal activity. They are then situated in bimorph-type soft actuators where one side of the actuator has a dramatically different Young's modulus than the other, leading to directional actuation which is successfully demonstrated in multistep walking soft robots. The soft actuators are shown to successfully activate the mechanosensitive Piezo protein in a transfected human cell line with high effectiveness and no toxicity. Overall, the liquid marble-powered soft actuators described here represent a new soft actuation methodology and a novel tool for mechanobiological studies, such as stem cell fate and organoid differentiation.     

Shape‐Reconfigurable Aluminum–Air Batteries

The battery shape is a critical limiting factor affecting foreseeable energy storage applications. In particular, deformable metal–air battery systems can offer low cost, low flammability, and high capacity, but the fabrication of such metal–air batteries remains challenging. Here, it is shown that a shape‐reconfigurable‐material approach, in which the deformable components composed of micro‐ and nanoscale composites are assembled, is suitable for constructing polymorphic metal–air batteries. By employing an aluminum foil and an adhesive carbon composite placed on a cellulose scaffold as a substrate, an aluminum–air battery that can be deformed to an unprecedented high level, e.g., via expanding, folding, stacking, and crumpling, can be realized. This significant deformability results in a specific capacity of 128 mA h g^?1 (496 mA h g^?1 per cell; based on the mass of consumed aluminum) and a high output voltage (10.3 V) with 16 unit battery cells connected in series. The resulting battery can endure significant geometrical distortions such as 3D expanding and twisting, while the electrochemical performance is preserved. This work represents an advancement in deformable aluminum–air batteries using the shape‐reconfigurable‐material concept, thus establishing a paradigm for shape‐reconfigurable batteries with exceptional mechanical functionalities.     

A Unified View on Nanoscale Packing,Connectivity, and Conductivity of CNT Networks

The design of functional structures from primary building blocks requires a thorough understanding of how size, shape, and particle–particle interactions steer the assembly process. Specifically, for electrically conductive networks build from carbon nanotubes (CNTs) combining macroscopic characterization and simulations shows that the achievable conductivity is mainly governed by CNT aspect ratio, length dispersity and attractive interactions. However, a direct link between the actual 3D network topology that leads to the observed electrical conductivity has not been established yet due to a lack in nanoscale experimental approaches. Here it is shown experimentally for randomly packed (jammed) CNT networks that the CNT aspect ratio determines, as theoretically predicted, the contact number per CNT which in turn scales linearly with the resulting electrical conductivity of the CNT network. Furthermore, nanoscale packing density, contact areas, contact distribution in random and nonrandom configurations, and least resistance pathways are quantified. The results illustrate how complex nanoscale networks can be imaged and quantified in 3D to understand and model their functional properties in a bottom‐up fashion.     

Tunable Anisotropic Wettability of Rice Leaf‐Like Wavy Surfaces

Rice leaves can directionally shed water droplets along the longitudinal direction of the leaf. Inspired by the hierarchical structures of rice leaf surfaces, synthetic rice leaf‐like wavy surfaces are fabricated that display a tunable anisotropic wettability by using electrostatic layer‐by‐layer assembly on anisotropic microwrinkled substrates. The nanoscale roughness of the rice leaf‐like surfaces is controlled to yield tunable anisotropic wettability and hydrophobic properties that transitioned between the anisotropic/pinned, anisotropic/rollable, and isotropic/rollable water droplet behavior states. These remarkable changes result from discontinuities in the three‐phase (solid–liquid–gas) contact line due to the presence of air trapped beneath the liquid, which is controlled by the surface roughness of the hierarchical nanostructures. The mechanism underlying the directional water‐rolling properties of the rice leaf‐like surfaces provides insight into the development of a range of innovative applications that require control over directional flow.     

飞秒激光组装一维纳米材料及其应用

一维纳米材料具有众多优异的特性,是构建微纳米功能性器件的基石。实现一维纳米材料在二维和三维空间的高精度和高定向组装是充分发挥其应用潜力的关键,同时也是制造难点。在众多纳米材料组装技术中,飞秒激光直写诱导组装技术具有独特优势,可实现一维纳米材料在任意三维结构中的可设计、高定向及高精度的组装。首先简要介绍了一维纳米材料组装研究的背景,并总结了非激光直写组装技术的研究现状和存在的挑战,然后较详细介绍了飞秒激光直写技术在一维纳米材料组装研究中的进展,重点回顾了金属(包括Au和Ag纳米线)、半导体(包括CNTs和ZnO)一维纳米材料的飞秒激光直写组装及微纳光电子功能器件的制造。并讨论了诱导一维纳米材料定向排布的光学力和非光学力(包括剪切力、体积收缩应力和空间限制)的作用机理,理论计算和实验研究结果验证了飞秒激光诱导的非光学力作用是导致一维纳米材料定向排布的主要原因。最后探讨了目前飞秒激光组装技术面临的一些问题和未来在高精度纳米材料组装和三维功能器件集成方面的发展趋势。     

A biocompatible pressure sensor based on a 3D-printed scaffold functionalized with PEDOT:PSS for biomedical applications

Personalized health-care monitoring, such as human motion and gait, can provide valuable information useful for prevention and diagnosis of a variety of diseases and also in patients rehabilitation. By employing suitable biocompatible materials that possess tunable compression properties related to 3D structure and able to convert the strain stimuli into a detectable signal, pressure sensors for human motion monitoring can be developed. In this study, our purpose is to obtain a conductive and biocompatible scaffold able to transform the mechanical deformations caused by an applied pressure to an electrical resistance variations. In particular, the effect of a conductive biocompatible functionalization with PEDOT:PSS polymer on thermoplastic silicone polycarbonate polyurethane (CarboSil) scaffold presenting five different structures have been studied by mechanical and electrical tests. The scaffold stiffness depends on structures features but it is not affected by the PEDOT:PSS coating. The electrical tests show a linear response on a wide range of pressure loads with all the tested polymeric scaffolds. Two scaffolds show the higher conductivity respect to other samples. Therefore, the scaffold structure network influences the electrical sensor response. The possibility to exploit the 3D printing tecnology with CarboSil paves the way to a new class of customizable, easy to manufacture and biocompatible integrated devices for medical applications.     

Controlled Nanopatterning of a Polymerized Ionic Liquid in a Strong Electric Field

Nanolithography has become a driving force in advancements of the modern day's electronics, allowing for miniaturization of devices and a steady increase of the calculation, power, and storage densities. Among various nanofabrication approaches, scanning probe techniques, including atomic force microscopy (AFM), are versatile tools for creating nanoscale patterns utilizing a range of physical stimuli such as force, heat, or electric field confined to the nanoscale. In this study, the potential of using the electric field localized at the apex of an AFM tip to induce and control changes in the mechanical properties of an ion containing polymer—a polymerized ionic liquid (PolyIL)—on a very localized scale is explored. In particular, it is demonstrated that by means of AFM, one can form topographical features on the surface of PolyIL‐based thin films with a significantly lower electric potential and power consumption as compared to nonconductive polymer materials. Furthermore, by tuning the applied voltage and ambient air humidity, control over dimensions of the formed structures is reproducibly achieved.     

Reconfigurable Three-Dimensional Mesotructures of Spatially Programmed Liquid Crystal Elastomers and Their Ferromagnetic Composites

Reversible programming of 3D soft mesostructures is desired for many applications including soft robotics and biomedical devices. The large, reversible shape changes of liquid crystal elastomers (LCEs), which result from the coupling between the alignment of liquid crystal (LC) molecules and the macroscopic deformation of polymer networks, have attracted much attention for such applications. Here, a facile and versatile strategy is introduced to create reconfigurable, freestanding 3D mesostructures of LCEs and magnetic LCE composites that are inaccessible with existing techniques via spatially programming LC molecules through mechanical buckling. Demonstrations include experimental and theoretical results of more than 20 reconfigurable 3D LCE mesostructures of diverse configurations, from coils and spirals to structures that resemble fences and frameworks, with characteristic feature sizes and thicknesses ranging from micro to macro. The large, reversible shape-switching behaviors of these structures over multiple cycles are also demonstrated. An LCE gripper is shown to grab/release objects of both regular and irregular geometries. Furthermore, a robot of ferromagnetic LCE composites that simultaneously responds to magnetic and thermal stimuli for diverse biomimetic behaviors, especially crawling underneath a narrow crack, illustrates the integration of other functional materials to LCEs for multifunctional systems.