Photoinduced Dual Shape Programmability of Covalent Adaptable Networks with Remarkable Mechanical Properties.

As classic shape memory polymers featuring shape reconfiguration of temporary state, covalent adaptable networks containing reversible bonds can enable permanent-state reconfigurability through topological rearrangement via dynamic bond exchange. Yet, such an attractive dual shape programmability is limited by the actuation mode of direct heat transfer and poor mechanical properties, restricting its control precision and functionality. Herein, we presented a method to create nanocomposites with photomodulated dual shape programmability and remarkable mechanical properties leading the fields of covalent adaptable networks. MXene, whose photothermal efficiency was revealed to be regulated by the etching method and delamination, was introduced into polyurethane networks. Upon adjusting the light intensity, the dual shape programmability of both permanent and temporary states could be accomplished, which exhibited potential in information recognition, photowriting paper, etc. Furthermore, owing to the dynamic transcarbamoylation at elevated temperatures, such a phototriggered dual shape programmability could be maintained after the self-healing and reprocessing.

Biomimetic Hydrogel Composites for Soil Stabilization and Contaminant Mitigation.

We have developed a novel method to synthesize a hyper-branched biomimetic hydrogel network across a soil matrix to improve the mechanical strength of the loose soil and simultaneously mitigate potential contamination due to excessive ammonium. This method successfully yielded a hierarchical structure that possesses the water retention, ion absorption, and soil aggregation capabilities of plant root systems in a chemically controllable manner. Inspired by the robust organic-inorganic composites found in many living organisms, we have combined this hydrogel network with a calcite biomineralization process to stabilize soil. Our experiments demonstrate that poly(acrylic acid) (PAA) can work synergistically with enzyme-induced carbonate precipitation (EICP) to render a versatile, high-performance soil stabilization method. PAA-enhanced EICP provides multiple benefits including lengthening of water supply time, localization of cementation reactions, reduction of harmful byproduct ammonium, and achievement of ultrahigh soil strength. Soil crusts we have obtained can sustain up to 4.8 × 103 kPa pressure, a level comparable to cementitious materials. An ammonium removal rate of 96% has also been achieved. These results demonstrate the potential for hydrogel-assisted EICP to provide effective soil improvement and ammonium mitigation for wind erosion control and other applications.

Bubble-Channeling Electrophoresis of Honeycomb-Like Chitosan Composites.

A chitosan composite with a vertical array of pore channels is fabricated via an electrophoretic deposition (EPD) technique. The composite consists of chitosan and polyethylene glycol, as well as nanoparticles of silver oxide and silver. The formation of hydrogen bubbles during EPD renders a localized increase of hydroxyl ions that engenders the precipitation of chitosan. In addition, chemical interactions among the constituents facilitate the establishment of vertical channels occupied by hydrogen bubbles that leads to the unique honeycomb-like microstructure; a composite with a porosity of 84%, channel diameter of 488 µm, and channel length of 2 mm. The chitosan composite demonstrates an impressive water uptake of 2100% and a two-stage slow release of silver. In mass transport analysis, both Disperse Red 13 and ZnO powders show a much enhanced transport rate over that of commercial gauze. Due to its excellent structural integrity and channel independence, the chitosan composite is evaluated in a passive suction mode for an adhesive force of 9.8 N (0.56 N cm-2 ). The chitosan composite is flexible and is able to maintain sufficient adhesive force toward objects with different surface curvatures.

Formation of nanopatterned polymer blends in photovoltaic devices.

In this paper, we demonstrate a double nanoimprinting process that allows the formation of nanostructured polymer heterojunctions of composition and morphology that can be selected independently. We fabricated photovoltaic (PV) devices with extremely high densities (10(14)/mm(2)) of interpenetrating nanoscale columnar features in the active polymer blend layer. The smallest feature sizes are as small as 25 nm on a 50 nm pitch, which results in a spacing of heterojunctions at or below the exciton diffusion length. Photovoltaic devices based on double-imprinted poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (F8TBT)/ poly(3-hexylthiophene) (P3HT) films are among the best polymer-polymer blend devices reported to date with a power conversion efficiency (PCE, eta(e)) of 1.9%.

A 'smart' aptamer-functionalized continuous label-free cell catch-transport-release system.

Label-free cell sorting devices are of great significance for biomedical research and clinical therapeutics. However, current platforms for label-free cell sorting cannot achieve continuity and selectivity simultaneously, resulting in complex steps and limited reliability. Here, an immunoaffinity-based cell catch-transport-release thermo-chemo-mechanical coupling hydrogel (iCatch) device is reported. It contains a temperature-responsive hydrogel that can generate spatial movement synergically with the reversible binding of affinity handle modified. The functionalized hydrogel is embedded inside a biphasic microfluidic platform to enable cell transportation between the flows. The cell sorting capability and biocompatibility of the iCatch device were validated with CCRF-CEM cells as a proof-of-concept, and CCRF-CEM-specific aptamers with thermo-responsive affinity as well as a hydrogel with temperature-dependent volume were employed accordingly. A cell catching efficiency of ∼40% and a recovery rate of ∼70% were achieved. The iCatch device provides a high-throughput (∼900 cells mm-1 s-1) platform for cell sorting and is ultimately valuable for downstream biomedical applications.

Poly(vinyl alcohol) Hydrogels with Broad-Range Tunable Mechanical Properties via the Hofmeister Effect.

Hydrogels, exhibiting wide applications in soft robotics, tissue engineering, implantable electronics, etc., often require sophisticately tailoring of the hydrogel mechanical properties to meet specific demands. For examples, soft robotics necessitates tough hydrogels; stem cell culturing demands various tissue-matching modulus; and neuron probes desire dynamically tunable modulus. Herein, a strategy to broadly alter the mechanical properties of hydrogels reversibly via tuning the aggregation states of the polymer chains by ions based on the Hofmeister effect is reported. An ultratough poly(vinyl alcohol) (PVA) hydrogel as an exemplary material (toughness 150 ± 20 MJ m-3 ), which surpasses synthetic polymers like poly(dimethylsiloxane), synthetic rubber, and natural spider silk is fabricated. With various ions, the hydrogel's various mechanical properties are continuously and reversibly in situ modulated over a large window: tensile strength from 50 ± 9 kPa to 15 ± 1 MPa, toughness from 0.0167 ± 0.003 to 150 ± 20 MJ m-3 , elongation from 300 ± 100% to 2100 ± 300%, and modulus from 24 ± 2 to 2500 ± 140 kPa. Importantly, the ions serve as gelation triggers and property modulators only, not necessarily required to remain in the gel, maintaining the high biocompatibility of PVA without excess ions. This strategy, enabling high mechanical performance and broad dynamic tunability, presents a universal platform for broad applications from biomedicine to wearable electronics.

Somatosensory actuator based on stretchable conductive photothermally responsive hydrogel.

Mimicking biological neuromuscular systems' sensory motion requires the unification of sensing and actuation in a singular artificial muscle material, which must not only actuate but also sense their own motions. These functionalities would be of great value for soft robotics that seek to achieve multifunctionality and local sensing capabilities approaching natural organisms. Here, we report a soft somatosensitive actuating material using an electrically conductive and photothermally responsive hydrogel, which combines the functions of piezoresistive strain/pressure sensing and photo/thermal actuation into a single material. Synthesized through an unconventional ice-templated ultraviolet-cryo-polymerization technique, the homogenous tough conductive hydrogel exhibited a densified conducting network and highly porous microstructure, achieving a unique combination of ultrahigh conductivity (36.8 milisiemens per centimeter, 103-fold enhancement) and mechanical robustness, featuring high stretchability (170%), large volume shrinkage (49%), and 30-fold faster response than conventional hydrogels. With the unique compositional homogeneity of the monolithic material, our hydrogels overcame a limitation of conventional physically integrated sensory actuator systems with interface constraints and predefined functions. The two-in-one functional hydrogel demonstrated both exteroception to perceive the environment and proprioception to kinesthetically sense its deformations in real time, while actuating with near-infinite degrees of freedom. We have demonstrated a variety of light-driven locomotion including contraction, bending, shape recognition, object grasping, and transporting with simultaneous self-monitoring. When connected to a control circuit, the muscle-like material achieved closed-loop feedback controlled, reversible step motion. This material design can also be applied to liquid crystal elastomers.

Exploiting the superior protein resistance of polymer brushes to control single cell adhesion and polarisation at the micron scale.

The control of the cell microenvironment on model patterned substrates allows the systematic study of cell biology in well defined conditions, potentially using automated systems. The extreme protein resistance of poly(oligo(ethylene glycol methacrylate)) (POEGMA) brushes is exploited to achieve high fidelity patterning of single cells. These coatings can be patterned by soft lithography on large areas (a microscope slide) and scale (substrates were typically prepared in batches of 200). The present protocol relies on the adsorption of extra-cellular matrix (ECM) proteins on unprotected areas using simple incubation and washing steps. The stability of POEGMA brushes, as examined via ellipsometry and SPR, is found to be excellent, both during storage and cell culture. The impact of substrate treatment, brush thickness and incubation protocol on ECM deposition, both for ultra-thin gold and glass substrates, is investigated via fluorescence microscopy and AFM. Optimised conditions result in high quality ECM patterns at the micron scale, even on glass substrates, that are suitable for controlling cell spreading and polarisation. These patterns are compatible with state-of-the-art technologies (fluorescence microscopy, FRET) used for live cell imaging. This technology, combined with single cell analysis methods, provides a platform for exploring the mechanisms that regulate cell behaviour.