High-Fidelity Replica Molding of Glassy Liquid Crystalline Polymer Microstructures

Responsive Liquid Crystal Network Microstructures with Customized Shapes and Predetermined Morphing for Adaptive Soft Micro-Optics

Stimuli-responsive materials have garnered substantial interest in recent years, particularly liquid crystal networks (LCNs) with sophisticatedly designed structures and morphing capabilities. Extensive efforts have been devoted to LCN structural designs spanning from two-dimensional (2D) to three-dimensional (3D) configurations and their intricate morphing behaviors through designed alignment. However, achieving microscale structures and large-area preparation necessitates the development of novel techniques capable of facilely fabricating LCN microstructures with precise control over both overall shape and alignment, enabling a 3D-to-3D shape change. Herein, a simple and cost-effective in-cell soft lithography (ICSL) technique is proposed to create LCN microstructures with customized shapes and predesigned morphing. The ICSL technique involves two sequential steps: fabricating the desired microstructure as the template by using the photopolymerization-induced phase separation (PIPS) method and reproducing the LCN microstructures through templating. Meanwhile, surface anchoring is employed to design and achieve molecular alignment, accommodating different deformation modes. With the proposed ICSL technique, cylindrical and spherical microlens arrays (CMLAs and SMLAs) have been successfully fabricated with stimulus-driven polarization-dependent focusing effects. This technique offers distinct advantages including high customizability, large-area production, and cost-effectiveness, which pave a new avenue for extensive applications in different fields, exemplified by adaptive soft micro-optics and photonics.

A microneedle vaccine printer for thermostable COVID-19 mRNA vaccines

Decentralized manufacture of thermostable mRNA vaccines in a microneedle patch (MNP) format could enhance vaccine access in low-resource communities by eliminating the need for a cold chain and trained healthcare personnel. Here we describe an automated process for printing MNP Coronavirus Disease 2019 (COVID-19) mRNA vaccines in a standalone device. The vaccine ink is composed of lipid nanoparticles loaded with mRNA and a dissolvable polymer blend that was optimized for high bioactivity by screening formulations in vitro. We demonstrate that the resulting MNPs are shelf stable for at least 6 months at room temperature when assessed using a model mRNA construct. Vaccine loading efficiency and microneedle dissolution suggest that efficacious, microgram-scale doses of mRNA encapsulated in lipid nanoparticles could be delivered with a single patch. Immunizations in mice using manually produced MNPs with mRNA encoding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein receptor-binding domain stimulate long-term immune responses similar to those of intramuscular administration.

Switching between 3D Surface Topographies in Liquid Crystal Elastomer Coatings Using Two-Step Imprint Lithography

While dynamic surface topographies are fabricated using liquid crystal (LC) polymers, switching between two distinct 3D topographies remains challenging. In this work, two switchable 3D surface topographies are created in LC elastomer (LCE) coatings using a two-step imprint lithography process. A first imprinting creates a surface microstructure on the LCE coating which is polymerized by a base catalyzed partial thiol-acrylate crosslinking step. The structured coating is then imprinted with a second mold to program the second topography, which is subsequently fully polymerized by light. The resulting LCE coatings display reversible surface switching between the two programmed 3D states. By varying the molds used during the two imprinting steps, diverse dynamic topographies can be achieved. For example, by using grating and rough molds sequentially, switchable surface topographies between a random scatterer and an ordered diffractor are achieved. Additionally, by using negative and positive triangular prism molds consecutively, dynamic surface topographies switching between two 3D structural states are achieved, driven by differential order/disorder transitions in the different areas of the film. It is anticipated that this platform of dynamic 3D topological switching can be used for many applications, including antifouling and biomedical surfaces, switchable friction elements, tunable optics, and beyond.

The Bumpy Road to Stem Cell Therapies: Rational Design of Surface Topographies to Dictate Stem Cell Mechanotransduction and Fate

Cells sense and respond to a variety of physical cues from their surrounding microenvironment, and these are interpreted through mechanotransductive processes to inform their behavior. These mechanisms have particular relevance to stem cells, where control of stem cell proliferation, potency, and differentiation is key to their successful application in regenerative medicine. It is increasingly recognized that surface micro- and nanotopographies influence stem cell behavior and may represent a powerful tool with which to direct the morphology and fate of stem cells. Current progress toward this goal has been driven by combined advances in fabrication technologies and cell biology. Here, the capacity to generate precisely defined micro- and nanoscale topographies has facilitated the studies that provide knowledge of the mechanotransducive processes that govern the cellular response as well as knowledge of the specific features that can drive cells toward a defined differentiation outcome. However, the path forward is not fully defined, and the "bumpy road" that lays ahead must be crossed before the full potential of these approaches can be fully exploited. This review focuses on the challenges and opportunities in applying micro- and nanotopographies to dictate stem cell fate for regenerative medicine. Here, key techniques used to produce topographic features are reviewed, such as photolithography, block copolymer lithography, electron beam lithography, nanoimprint lithography, soft lithography, scanning probe lithography, colloidal lithography, electrospinning, and surface roughening, alongside their advantages and disadvantages. The biological impacts of surface topographies are then discussed, including the current understanding of the mechanotransductive mechanisms by which these cues are interpreted by the cells, as well as the specific effects of surface topographies on cell differentiation and fate. Finally, considerations in translating these technologies and their future prospects are evaluated.

Programmable Liquid Crystal Defect Arrays via Electric Field Modulation for Mechanically Functional Liquid Crystal Networks

The arrangement of mesogenic units determines mechanical response of the liquid crystal polymer network (LCN) film to heat. Here, we show an interesting approach to programming three-dimensional patterns of the LCN films with periodic topological defects generated by applying an electric field. The mechanical properties of three representative patterned LCN films were investigated in terms of the arrangement of mesogenic units through tensile testing. Remarkably, it was determined that LCN films showed enhanced toughness and ductility as defects increased in a given area, which is related to the elastic modulus mismatch that mitigates crack propagation. Our platform can also be used to modulate the frictional force of the patterned LCN films by varying the temperature, which can provide insight into the multiplex mechanical properties of LCN films.

Design of Active Interfaces Using Responsive Molecular Components

Responsive interfaces are interfaces that show a defined and reversible change in physical properties in response to external stimuli. Typically, responsive interfaces result from the immobilization of responsive molecular components at the interface that translate a nanoscale signal into a macroscopic effect. Responsive interfaces can also be obtained if the topology of the interface can be reversibly changed using an external stimulus. As the surface of any material is its connection to the environment, responsive interfaces provide opportunities for interactive materials which are not only able to change properties upon demand, but also sense their environment and act autonomously. The application of responsive molecular components at interfaces, however, requires chemical and physical compatibility with the material surface of interest, posing a challenge not least in the retention of the responsive functionality. The state of the art in "active" interfaces which display responsive wettability, permeability, or adhesion is discussed, with a particular emphasis on microscale and nanoscale patterning since patterned interfaces can give rise to unique material properties. Finally, perspectives in the development of responsive interfaces, as well as promising approaches for bypassing the most prominent challenges are discussed.

Structure and Frictional Properties of the Leg Joint of the Beetle Pachnoda marginata (Scarabaeidae, Cetoniinae) as an Inspiration for Technical Joints

The efficient locomotion of insects is not only inspiring for control algorithms but also promises innovations for the reduction of friction in joints. After previous analysis of the leg kinematics and the topological characterization of the contacting joint surfaces in the beetle Pachnoda marginata, in the present paper, we report on the measurement of the coefficient of friction within the leg joints exhibiting an anisotropic frictional behavior in different sliding directions. In addition, the simulation of the mechanical behavior of a single microstructural element helped us to understand the interactions between the contact parts of this tribological system. These findings were partly transferred to a technical contact pair which is typical for such an application as joint connectors in the automotive field. This innovation helped to reduce the coefficient of friction under dry sliding conditions up to 17%.

Shape-Programmed Fabrication and Actuation of Magnetically Active Micropost Arrays

Micro- and nanotextured surfaces with reconfigurable textures can enable advancements in the control of wetting and heat transfer, directed assembly of complex materials, and reconfigurable optics, among many applications. However, reliable and programmable directional shape in large scale is significant for prescribed applications. Herein, we demonstrate the self-directed fabrication and actuation of large-area elastomer micropillar arrays, using magnetic fields to both program a shape-directed actuation response and rapidly and reversibly actuate the arrays. Specifically, alignment of magnetic microparticles during casting of micropost arrays with hemicylindrical shapes imparts a deterministic anisotropy that can be exploited to achieve the prescribed, large-deformation bending or twisting of the pillars. The actuation coincides with the finite element method, and we demonstrate reversible, noncontact magnetic actuation of arrays of tens of thousands of pillars over hundreds of cycles, with the bending and twisting angles of up to 72 and 61°, respectively. Moreover, we demonstrate the use of the surfaces to control anisotropic liquid spreading and show that the capillary self-assembly of actuated micropost arrays enables highly complex architectures to be fabricated. The present technique could be scaled to indefinite areas using cost-effective materials and casting techniques, and the principle of shape-directed pillar actuation can be applied to other active material systems.

Mechanically programmed 2D and 3D liquid crystal elastomers at macro- and microscale via two-step photocrosslinking

Liquid crystal elastomers (LCEs) are a unique class of active materials with the largest known reversible shape transformation in the solid state. The shape change of LCEs is directed by programming their molecular orientation, and therefore, several strategies to control LC alignment have been developed. Although mechanical alignment coupled with a two-step crosslinking is commonly adopted for uniaxially-aligned monodomain LCE synthesis, the fabrication of 3D-shaped LCEs at the macro- and microscale has been rarely accomplished. Here, we report a facile processing method for fabricating 2D and 3D-shaped LCEs at the macro- and microscales at room temperature by mechanically programming (i.e., stretching, pressing, embossing and UV-imprinting) the polydomain LCE, and subsequent photocrosslinking. The programmed LCEs exhibited a reversible shape change when exposed to thermal and chemical stimuli. Besides the programmed shape changes, the actuation strain can also be preprogrammed by adjusting the extent of elongation of a polydomain LCE. Furthermore, the LCE micropillar arrays prepared by UV-imprinting displayed a substantial change in pillar height in a reversible manner during thermal actuation. Our convenient method for fabricating reversible 2D and 3D-shaped LCEs from commercially available materials may expedite the potential applications of LCEs in actuators, soft robots, smart coatings, tunable optics and medicine.

Predicting the Conditions for Homeotropic Anchoring of Liquid Crystals at a Soft Surface. 4-n-Pentyl-4'-cyanobiphenyl on Alkylsilane Self-Assembled Monolayers

We have studied, using atomistic molecular dynamics simulations, the alignment of the nematic liquid-crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) on self-assembled monolayers (SAMs) formed from octadecyl- and/or hexyltrichlorosilane (OTS and HTS) attached to glassy silica. We find a planar alignment on OTS at full coverage and an intermediate situation at partial OTS coverage because of the penetration of 5CB molecules into the monolayer, which also removes the tilt of the OTS SAM. Binary mixtures of HTS and OTS SAMs instead induce homeotropic (i.e., perpendicular) alignment. A comparison with the existing experimental literature is provided.