Xiaohu Zhou

Liquid metal droplets with high elasticity, mobility and mechanical robustness

Non-stick, ultra-elastic liquid metal droplets were fabricated by coating polytetrafluoroethylene (PTFE) particles onto the surface of NaOH-treated liquid metal droplets. The liquid metal droplets consisted of a liquid metal core, a thin anti-oxidation layer to maintain the high surface tension of the liquid metal and a particle-interpenetrated shell to enhance the mobility of the droplet.

Hydrophilic Sponges for Leaf-Inspired Continuous Pumping of Liquids

A bio‐inspired, leaf‐like pumping strategy by mimicking the transpiration process through leaves is developed for autonomous and continuous liquid transport enabled by durable hydrophilic sponges. Without any external power sources, flows are continuously generated ascribed to the combination of capillary wicking and evaporation of water. To validate this method, durable hydrophilic polydimethylsiloxane sponges modified with polyvinyl alcohol via a “dip‐coat‐dry” method have been fabricated, which maintains hydrophilicity more than 2 months. The as‐made sponges are further applied to achieve stable laminar flow patterns, chemical gradients, and “stop‐flow” manipulation of the flow in microfluidic devices. More importantly, the ease‐of‐operation and excellent pumping capacity have also been verified with over 24 hs pumping and quasi‐stable high flow rates up to 15 µL min−1. The present strategy can be easily integrated to other miniaturized systems requiring pressure‐driven flow and should have potential applications, such as cell culture, micromixing, and continuous flow reaction.

Microfluidic Patterning of Metal Structures for Flexible Conductors by In Situ Polymer‐Assisted Electroless Deposition

A low‐cost, solution‐processed, versatile, microfluidic approach is developed for patterning structures of highly conductive metals (e.g., copper, silver, and nickel) on chemically modified flexible polyethylene terephthalate thin films by in situ polymer‐assisted electroless metal deposition. This method has significantly lowered the consumption of catalyst as well as the metal plating solution.

Rational Fabrication of Anti‐Freezing, Non‐Drying Tough Organohydrogels by One‐Pot Solvent Displacement

Tough hydrogels, polymeric network structures with excellent mechanical properties (such as high stretchability and toughness), are emerging soft materials. Despite their remarkably mechanical features, tough hydrogels exhibit two flaws (freezing around the icing temperatures of water and drying under arid conditions). Inspired by cryoprotectants (CPAs) used in the inhibition of the icing of water in biological samples, a versatile and straightforward method is reported to fabricate extreme anti-freezing, non-drying CPA-based organohydrogels with long-term stability by partially displacing water molecules within the pre-fabricated hydrogels. CPA-based Ca-alginate/polyacrylamide (PAAm) tough hydrogels were successfully fabricated with glycerol, glycol, and sorbitol. The CPA-based organohydrogels remain unfrozen and mechanically flexible even up to -70 °C and are stable under ambient conditions or even vacuum.

Mechanochemical Regulated Origami with Tough Hydrogels by Ion Transfer Printing

Stimuli-responsive hydrogels that undergo programmable shape deformation are of great importance for a wide variety of applications spanning from soft robotics and biomedical devices to tissue engineering and drug delivery. To guide shape morphing, anisotropic elements need to be encoded into the hydrogels during fabrication, which are extremely difficult to alter afterward. This study reports a simple and reliable mechanochemical regulation strategy to postengineer the hydrogels by encoding structures of high stiffness locally into prestretched tough hydrogels through ion transfer printing with a paper-cut. During printing, trivalent ions (Fe3+) were patterned and diffused into the prestretched tough gels, which dramatically increased the local stiffness by forming the second trivalent ionically cross-linked network. By removing the applied stretching force, the stiff anisotropy-encoded prestretched tough hydrogels underwent programmable shape morphing into complex three-dimensional origami structures due to the stiffness mismatch.

Softening and Shape Morphing of Stiff Tough Hydrogels by Localized Unlocking of the Trivalent Ionically Cross-Linked Centers

The mechanical properties (e.g., stiffness, stretchability) of prefabricated hydrogels are of pivotal importance for diverse applications in tissue engineering, soft robotics, and medicine. This study reports a feasible method to fabricate ultrasoft and highly stretchable structures from stiff and tough hydrogels of low stretchability and the application of these switchable hydrogels in programmable shape-morphing systems. Stiff and tough hydrogel structures are first fabricated by the mechanical strengthening of Ca2+ -alginate/polyacrylamide tough hydrogels by addition of Fe3+ ions, which introduces Fe3+ ionically cross-linked centers into the Ca2+ divalent cross-linked hydrogel, forming an additional and much less flexible trivalent ionically cross-linked network. The resulting stiff and tough hydrogels are exposed to an L-ascorbic acid (vitamin C, VC) solution to rapidly reduce Fe3+ to Fe2+ . As a result, flexible divalent ionically cross-linked networks are formed, leading to swift softening of the stiff and tough hydrogels. Moreover, localized stiffness variation of the tough hydrogels can be realized by precise patterning of the VC solution. To validate this concept, sequential steps of VC patterning are carried out for local tuning of the stiffness of the hydrogels. With this strategy, localized softening, unfolding, and sequential folding of the tough hydrogels into complex 3D structures is demonstrated.

A pneumatic valve controlled microdevice for bioanalysis

This paper describes a pneumatic valve controlled microdevice for performing mixing and reaction. This microdevice combined the degassed polydimethylsiloxane (PDMS) pumping method with a syringe-actuated valve system to control the dispensing and mixing of nanoliter solutions. The syringe was used to manually generate vacuum and to open the valves. Upon the opening of the valve, the microchamber was filled with the solution, which was driven by the external atmosphere through the degassed PDMS microchannel. With this microdevice, the enzymatic kinetics of alkaline phosphatase converting the fluorescein diphosphate was studied, and the Michaelis-Menten kinetics was analyzed. The microdevice has the advantages of simplicity and low cost in fabrication and operation.

Tough protein organohydrogels

Tough protein organohydrogels were fabricated by applying a solvent displacement-induced toughening (SDIT) strategy. With SDIT, traditionally weak and brittle protein hydrogels were altered to protein organohydrogels with remarkably high performance in anti-freezing, non-drying, topological healing, thermal plasticizing, mechanical toughness and stretchability. The SDIT opens a reliable and straightforward path to develop novel biomimetic materials and artificial devices from abandunt protein-based sources.

Porous polydimethylsiloxane monolith for protein digestion

This paper reports the preparation of porous polydimethylsiloxane (PDMS) monolith and its application in protein digestion. Glass microbubbles were used as the template to prepare the porous PDMS monolith. The PDMS monolith presented the interconnected porous structure with a high specific surface area. The average pore size of the porous PDMS monolith was 51 μm with the interconnected pores of 15 μm. Trypsin was immobilized on the inner pore surface of the PDMS monolith with high stability and high density by using the polydopamine as the primer with the advantage of the mild and efficient immobilization condition. Compared with the 12 hour in-solution digestion, the porous PDMS monolith could digest the protein within 15.6 minutes. The high digestion efficiency by continuously flowing the model protein solutions through the porous PDMS monolith with immobilized trypsin demonstrated the value of the porous PDMS monolith as a solid support for enzyme microreactors.

Shape morphing of anisotropy-encoded tough hydrogels enabled by asymmetrically-induced swelling and site-specific mechanical strengthening

This communication reports a dual regulation strategy, i.e., swelling and stiffness mismatch, for the shape morphing of calcium-alginate/polyacrylamide (PAAm) tough hydrogels enabled by site-specific patterning of ferric ions. Complex 3D or even 4D folding of tough hydrogels is achieved by sequentially applying the dual regulation.