Shuanhong Ma

Molecularly Engineered Dual-Crosslinked Hydrogel with Ultrahigh Mechanical Strength, Toughness, and Good Self-Recovery

A molecularly engineered dual-crosslinked hydrogel with extraordinary mechanical properties is reported. The hydrogel network is formed with both chemical crosslinking and acrylic-Fe(III) coordination; these, respectively, impart the elasticity and enhance the mechanical properties by effectively dissipating energy. The optimal hydrogel achieves a tensile stress of ca. 6 MPa at a large elongation ratio (>7 times), a toughness of 27 MJ m(-3) , and a stiffness of ca. 2 MPa, and has good self-recovery properties.

Gecko-inspired but chemically switched friction and adhesion on nanofibrillar surfaces.

Chemically switched friction nano-fibrillar surfaces (SiNWAs-PSPMA & SiNWAs-PMAA arrays) can be constructed by finely decorating ordered Si nanowire arrays with responsive polymer brushes. As expected, these surfaces sense humidity or pH smartly and show reversible friction switching, based on swelling and shrinking of the polymer brushes, which is successfully monitored by AFM in liquid media.

Astringent Mouthfeel as a Consequence of Lubrication Failure

Herein, we systematically investigate the origin of astringent mouthfeel when we eat unripe fruits, drink coffee or tea, from the perspective of lubrication by simulating the dynamic weak interaction on the tongue with model protein (mucoprotein, MP) and polyphenolic compounds (tannic acid, TA). Astringency was due to the protein-mediated lubrication failure when encountering polyphenolic molecules that normally exist, for example in unripe fruits, coffee, tea. The underlying molecular mechanism of oral tribology is widely present in nature and enables us to engineer a tongue-like polyacrylamide composite hydrogel that exhibits high TA sensitivity and to develop a scientific strategy for catching slippery fish using TA-containing gloves. These results provide novel and useful insights into the failure of biological boundary lubrication on soft tissue surface with the adsorbed proteins.

Bio-Inspired Design and Fabrication of Micro/Nano-Brush Dual Structural Surfaces for Switchable Oil Adhesion and Antifouling

The underwater superoleophobic surfaces play a significant role in anti-oil contamination, marine antifouling, etc. Inspired by the Geckos feet and its self-cleaning property, a hierarchical structure composed of poly (acrylic acid) gel micro-brushes is designed by the liquid-infused method. This surface exhibits underwater superoleophobicity with very low oil adhesion. It is then modified with stimuli-responsive polymer nano-brushes via surface-initiated atom transfer radical polymerization from the embedded initiator. The micro/nano-brush dual structural surfaces can switch the underwater oil adhesion between low and high while keeping the superoleophobicity. The antifouling properties against algae attachment under different mediums are also investigated to show a strong link between oleophobicity and antibiofouling property. The model surface will be very useful in directing the design of marine self-cleaning coatings to both living and non-living species.

A facile route to fabricate a biodegradable hydrogel for controlled pesticide release

Avermectins are widely used to control weeds, insects, and plant diseases. We have prepared a controllable avermectin release system based on a hydrazone bond inducing hydrogel, which presents good release properties of avermectin triggered by temperature and pH stimuli. This strategy embarks on controllable pesticide release using an environmentally friendly hydrogel.

UV‐Triggered Surface‐Initiated Polymerization from Colorless Green Tea Polyphenol‐Coated Surfaces

A facile and versatile approach to constructing colorless surface coatings based on green tea polyphenols is reported, which can further act as a photoinitiating layer to initiate radical polymerization. These colorless green tea polyphenol coatings are capable of successfully photografting polymer brushes, and the resulting polymer brush patterns show spatial shape adjustability by masked UV irradiation. Both surface modifications and photografted polymer brushes do not alter the original color of the substrates. This method could be promising for the development of surface modifications.

Tuning the Hydration and Lubrication of the Embedded Load-Bearing Hydrogel Fibers

One of the most prominent properties of hydrogels is their excellent hydrolubrication that derives from the strong hydration of the gel network. However, excessive hydration makes hydrogels exhibit a very poor mechanical property, which limits their practical applications. Here, we prepared a novel composite surface of hydrogel nanofibers embedded in an anodic aluminum oxide substrate which exhibited both excellent lubrication and a high load-bearing capacity. Through the copolymerization of acrylic acid and 3-sulfopropyl methacrylate potassium salt, the gel network swelled sufficiently in aqueous solution and caused high osmotic pressure repulsion to bear heavy loads and hence exhibited excellent aqueous lubrication (μ ≈ 0.01). Notably, the friction coefficient of gels showed no dependence on the load in the experiment, whereas it was strongly influenced by the sliding velocity. Additionally, both electrolyte solution and ionic surfactants affect the conformation of the polymer chains, which results in a significant impact on the friction properties of hydrogel fibers.

High Strength Astringent Hydrogels Using Protein as the Building Block for Physically Cross-linked Multi-Network

Integrating proteins into a hydrogel network enables its good bioactivity as an ECM environment in biorelative applications. Although extensive studies on preparing protein hydrogels have been carried out, the reported systems commonly present very low mechanical strength and weak water-rentention capacity. Learning from the astringent mouthfeel, we report here a protein engineered multinetwork physical hydrogel as TA-PVA/BSA. In a typical case, the BSA protein-integrated poly(vinyl alcohol) (PVA) solution is treated by the freeze-thaw method and forms the first hydrogel network, and tannic acid (TA) then cross-links with BSA proteins and PVA chains to form the secondary hydrogel network based on the noncovalent interaction (hydrogen bond and hydrophobic interaction). The as-prepared TA-PVA/BSA composite hydrogel is a pure physically cross-linking network and possesses ultrahigh tensile strength up to ∼9.5 MPa but is adjustable, relying on the concentration of TA and BSA. Moreover, its mechanical strength is further improved by prestretching induced anisotropy of mechanical performance. Because of its controllable and layered structure as skin, the composite hydrogel presents good water-retention capacity compared to traditional high strength hydrogels. This work demonstrates a novel method to design high mechanical strength but layered physical cross-linking hydrogels and enables us to realize their biorelative applications.

Promoting Lubricity and Antifouling Properties by Supramolecular-Recognition-Based Surface Grafting

In the supramolecular host-guest system, the host molecule selectively identifies the guest and forms the inclusion complex with the guest molecule. In this study, the physicochemical properties of solid surfaces were regulated by the interfacial supramolecular recognition. The host-guest interaction between β-cyclodextrin and guest molecules, including adamantaneacetic acid, sodium dodecyl sulfonate, and a copolymer of 2-methacryloyloxy-2-methyladamantane and 3-sulfopropyl methacrylate potassium salt, was introduced onto the silicon substrate to construct supramolecular composite surfaces. After the assembly of hydrophilic guest molecules on the host surface, the wettability, aqueous lubrication, and anti-algae cell adhesion properties of the supramolecular composite surfaces were improved. This strategy of host-guest interfacial supramolecular recognition provides a new route to prepare aqueous lubrication and antifouling materials.

Continuous Surface Polymerization via Fe(II)‐Mediated Redox Reaction for Thick Hydrogel Coatings on Versatile Substrates

The development of versatile generalized strategies for easy surface modification is of immense scientific interest. Herein, a novel mechanism to form functional hydrogel coatings on a wide variety of substrate materials including polymers, polymeric resins, ceramics, and intermetallic compounds, enabling easy change of the surface wettability and lubrication property, is reported. In situ polymerization and hydrogel coating formation is initiated by free radicals generated through the redox reaction between Fe2+ and S2 O8 2- at the solid-liquid interface, which shows controllable growth kinetics. Hydrogel modification is fast, controllable, and performed in mild conditions at room temperature. The chemical components, thickness, and network structure of the hydrogel coating can be well controlled. The surface catalytically initiated radical polymerization method allows reinitiation of the polymerization when the grafted hydrogel coating is polished away, and allows continuous surface polymerization to form multi-interpenetrating network hydrogel coatings. Interestingly, it is fully compatible with 3D-printing technology, and by using 3D-printed composites as the catalytic template, it demonstrates an extreme advantage for engineering 3D hollow hydrogel objects with various complex structures. The versatility of this method makes it generate potential applications in the field of surface/interface and biological engineering.