Crack-Resistant and Tissue-Like Artificial Muscles with Low Temperature Activation and High Power Density

Constructing soft robotics with safe human-machine interactions requires low-modulus, high-power-density artificial muscles that are sensitive to gentle stimuli. In addition, the ability to resist crack propagation during long-term actuation cycles is essential for a long service life. Herein, a material design is proposed to combine all these desirable attributes in a single artificial muscle platform. The design involves the molecular engineering of a liquid crystalline network with crystallizable segments and an ethylene glycol flexible spacer. A high degree of crystallinity can be afforded by utilizing aza-Michael chemistry to produce a low covalent crosslinking density, resulting in crack-insensitivity with a high fracture energy of 33 720 J m-2 and a high fatigue threshold of 2250 J m-2. Such crack-resistant artificial muscle with tissue-matched modulus of 0.7 MPa can generate a high power density of 450 W kg-1 at a low temperature of 40 °C. Notably, because of the presence of crystalline domains in the actuated state, no crack propagation is observed after 500 heating-cooling actuation cycles under a static load of 220 kPa. This study points to a pathway for the creation of artificial muscles merging seemingly disparate, but desirable properties, broadening their application potential in smart devices.

Functional silicone oils and elastomers: new routes lead to new properties

Silicones are mostly utilized for their stability to a range of vigorous environmental conditions, which arises, in part, from the lack of functionality in finished products. The commonly used functional groups in silicones, e.g., SiH, SiCHCH2, are mostly consumed during final product synthesis. Organic functional groups may also be found in silicone products, including organic alcohols, amines, polyethers, etc., that deliver functionality not achieved by traditional organic polymers (e.g., aminosilicones, softening of fabrics; silicone polyethers, superwetting agricultural adjuvants). However, relatively little organic chemistry is practiced in commercial silicones, limiting the types of desirable functionality that can be attained. We report the utilization of a series of simple-to-practice organic reactions that take place efficiently on silicone oils to allow the preparation of a wide variety of functional silicones. The silicone oil starting materials typically act as both solvent and educt to allow many of the newer reactions, such as Click processes, to be used to tune the properties of both silicone oil and elastomer products. The review considers the concept of 'functionality' to include: the reactive groups used to enable synthesis of more complicated structures; and separately, the functional properties of the product silicones. One such property that is considered throughout is degradability at end-of-life, which is related to the sustainability of silicones.

Facile Synthesis of Sulfur-Containing Functionalized Disiloxanes with Nonconventional Fluorescence by Thiol-Epoxy Click Reaction

Herein, a series of novel sulfur-containing functionalized disiloxanes based on a low-cost and commercially available material, i.e., 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane, and various thiol compounds were prepared by thiol-epoxy click reaction. It was found that both lithium hydroxide (LiOH) and tetrabutylammonium fluoride (TBAF) have high catalytic activity after optimizing the reaction condition, and the reaction can be carried out with high yields, excellent regioselectivity, mild reaction condition, and good tolerance of functional groups. These compounds exhibit excellent nonconventional fluorescence due to the formation of coordination bonds between Si atoms and heteroatoms (e.g., S or N) and can emit blue fluorescence upon ultraviolet (UV) irradiation. These results demonstrate that the thiol-epoxy click reaction could promisingly act as an efficient organosilicon synthetic methodology to construct various organosilicon materials with novel structures and functionality, and thus their application scope will be significantly expanded.

Tris(2,4,6-trimethoxyphenyl)phosphine – a Lewis base able to compete with phosphazene bases in catalysing oxa-Michael reactions

The performance of the fairly airstable and commercially available “Lewis base beast” TTMPP in catalysing oxa-Michael reactions and the control of its activity by dilution and solvent choice are disclosed.

Taking advantage of β-hydroxy amine enhanced reactivity and functionality for the synthesis of dual covalent adaptable networks

This study highlights the potential of β-hydroxy amines as building blocks for aza-Michael CANs.

Zwitterionic Silicone Materials Derived from Aza-Michael Reaction of Amino-Functional PDMS with Acrylic Acid

Supramolecular zwitterionic silicones are synthesized by aza-Michael reaction between acrylic acid and amine-functional polydimethylsiloxanes. The in-depth characterization of this chemistry, applied for the first time to silicones, is investigated first with model alkylamines (hexylamine, 2-ethylhexylamine and N-propylethylenediamine), a model oligosiloxane (3-aminopropylmethyl bis(trimethylsiloxy)silane), and finally various amino-polysiloxanes. It is shown that after a first acid-base reaction resulting in ionic pairing, aza-Michael addition proceeds smoothly in mild conditions (50 °C, 1-week reaction). Both monoadducts and di-adducts, together with residual amine, are observed by NMR. The supramolecular assembly of the thus-created zwitterionic moieties is highlighted by a concomitant increase in viscosity and phase separation, as observed by transmission electron microscopy, bringing an additional glass transition at -40 °C assigned to highly polar ionic clusters. Below the stoichiometry in acrylic acid, all zwitterionic silicones follow the same classical behavior of nonentangled polymers according to the Rouse model, whereas upon introducing an excess of acrylic acid to amino groups, an enhancement of the elasticity is observed. Finally, silicone elastomers with solid-like behavior and elastomeric mechanical properties are obtained using a high molar mass polymer bearing bifunctional N-(2-aminoethyl)-3-aminopropyl units that favor a high degree of physical crosslinking.

Organocatalytic Michael Addition as a Method for Polyisobutylene Chain-End Functionalization

Functionalization of polyolefins, in particular polyisobutylene, remains a relatively unexplored application for the Michael reaction. This work evaluates the potential of polyisobutylene acrylate (PIBA) chain-end modification via organocatalyzed thiol-Michael and aza-Michael additions. A series of chain-end functional polyisobutylene oligomers are prepared using "click" reactions of thiols or amines to PIBA in the presence of 0.02 equivalents of organocatalyst. Reaction kinetics and chain-end transformations are monitored using NMR spectroscopy and the macromolecular products are characterized by size exclusion chromatography. Further potential of this synthetic strategy is illustrated by thiol-Michael addition of thiols formed in situ via nucleophilic thiolactone ring opening. The obtained results provide an efficient method for the preparation of functional polyisobutylene oligomers that can be utilized in a broad range of potential applications.

Direct Conjugation of Streptavidin to Encoded Hydrogel Microparticles for Multiplex Biomolecule Detection with Rapid Probe-Set Modification

Encoded hydrogel microparticles synthesized via flow lithography have drawn attention for multiplex biomarker detection due to their high multiplex capability and solution-like hybridization kinetics. However, the current methods for preparing particles cannot achieve a flexible, rapid probe-set modification, which is necessary for the production of various combinations of target panels in clinical diagnosis. In order to accomplish the unmet needs, streptavidin was incorporated into the encoded hydrogel microparticles to take advantage of the rapid streptavidin–biotin interactions that can be used in probe-set modification. However, the existing methods suffer from low efficiency of streptavidin conjugation, cause undesirable deformation of particles, and impair the assay capability. Here, we present a simple and powerful method to conjugate streptavidin to the encoded hydrogel microparticles for better assay performance and rapid probe-set modification. Streptavidin was directly conjugated to the encoded hydrogel microparticles using the aza-Michael addition click reaction, which can proceed in mild, aqueous condition without catalysts. A highly flexible and sensitive assay was developed to quantify DNA and proteins using streptavidin-conjugated encoded hydrogel microparticles. We also validated the potential applications of our particles conducting multiplex detection of cancer-related miRNAs.

Simultaneously improved dielectric and mechanical properties of silicone elastomer by designing a dual crosslinking network

A homogenous silicone dielectric elastomer with simultaneously improved dielectric and mechanical properties is synthesized by designing a dual crosslinking network.

Synthesis of thermo- and photo-responsive polysiloxanes with tunable phase separationviaaza-Michael addition

Two kinds of thermo- and photo-dual-responsive polysiloxanes were synthesized through a facile, effective, and catalyst-free aza-Michael addition.