In this work, we describe a straightforward approach to produce monodisperse Janus and core-shell particles by using organic solvent free single emulsion droplet-based microfluidic device combining with off-chip polymerization. To accomplish this, methyl methacrylate (MMA) was used as both the oil phase and solvent to dissolve a polymerizable PEGbased macromolecular surfactant, instead of traditional surfactant, and the photo-initiator. Janus particles can be easily obtained by off-chip UV polymerization due to polymerization induced phase separation between PEG and the formed poly(methyl methacrylate). At the same time, core-shell particles can also be easily attained by inverting the original collecting tube several times and then exposing to UV light. These results may extend the scope of microfluidic technology and the studies on polymerization induced self-assembly/phase-separation into easy fabrication of various new functional materials.

Up to now, fabrication of strong and stimuli-responsive supramolecular hydrogels via an easy molecular design and synthesis procedure is still a big challenge. In this work, a series of hydrophobically modified linear polyurethane–urea copolymers and one polyurethane copolymer were prepared via a greatly simplified one-pot approach to investigate the synergistic effect between hydrogen-bonding and hydrophobic effects. FT-IR and various mechanical performance studies show that not only a longer hydrophobic spacer (C12) but also a stronger hydrogen-bonding unit (urea) is necessary for their synergistic effect to yield high water containing, transparent, stretchy and tough supramolecular hydrogels. Moreover, these supramolecular materials also show nice cyclic shape-memory behaviours which can be realized under mild conditions, e.g. in air and water at room temperature. The non-covalent interaction's synergistic effect and stimuli-responsive character are expected to dramatically expand the design and choice of tough and smart supramolecular hydrogels/materials for biomaterials.

Various supramolecular materials, especially hydrogels, based on host–guest interactions have been widely studied due to their attractive properties and potential applications. However, many of their practical uses are still severely limited by their poor mechanical performance. In this report, we present a novel kind of supramolecular hydrogel showing extremely ductile, notch and stab resistant properties as well as excellent self-healing behavior. These supramolecular hydrogels are prepared by simple free-radical copolymerization of acrylamide and adamantane monomers which were preloaded on low molecular weight poly(AOI-β-cyclodextrin) (pAOI-β-CD). We attribute the hydrogel's exceptional mechanical performance to the synergy effect of the supramolecular imprint and movable multi-valent supramolecular crosslinker characters of pAOI-β-CD in forming reversible crosslinking before and after polymerization, respectively. The findings of this work provide the basis for the molecular design of supramolecular soft materials with distinguished mechanical performance, and will expand the scope of host–guest supramolecular hydrogel applications.

A strong and highly stretchable supramolecular hydrogel with a shear modulus of 200 kPa, an elongation at break of 770% at 4 MPa stress and a water-responsive shape-memory property is developed. The whole shape-memory procedure including shape deformation, fixing and recovery can be realized under mild and green conditions, i.e. in air and water.

Highly stretchable hydrogels based on the micellar copolymerization technique often dissolve in water; they may also become fragile or not exhibit their initially good mechanical performance when submerged in large amounts of water. In addition, the shape-deformation and shape-recovery processes of most reported shape-memory hydrogels need to be carried out at high temperatures. As yet, there have been no published reports on hydrogels which are both highly resilient and have water-responsive shape-memory properties. In this work, a novel, highly elastic polyacrylamide-based hydrogel was developed based on the micellar copolymerization technique using a polymerizable macromolecular micelle with hydrophobic cores locked by hydrogen bonds as a multifunctional crosslinker. The equilibrium water-swelling micelle crosslinked hydrogels still showed highly stretchable behaviour (elongation at break >700%) and even better resilience (almost no hysteresis and residual strains) than the as-prepared hydrogels. Together with the advantages of the highly elastic properties of the hydrogels and the dehydration-induced glass transition of the polyacrylamide network, the hydrogels also have a water-responsive shape-memory behaviour, which can be realized under mild and “green” conditions, i.e., in air and water at room temperature.

Strain hardening and high resilience are two unique mechanical characteristics of many soft biological hydrogels. However, these properties, especially the strain hardening behaviour, are generally not seen in synthetic polymer hydrogels. Here, hydrogels are prepared by free-radical copolymerization of acrylamide and chain-extended vinyl-modified pseudo-polyrotaxane, which acts as a multifunctional crosslinker. The reactive pseudo-polyrotaxane is based on a β-cyclodextrin monomer and amine-terminated PEG–PPG–PEG (Pluronic F127). The obtained hydrogels can be stretched from 10 to more than 26 times their original length before breaking and withstand a compression strain of 95% and even 98% without fracture. Tensile stretching tests show obvious strain hardening behaviours in high stretching and compression deformation regimes. The strain hardening behaviour in stretching deformation is considered to be the orientation and aggregation of the movable crosslinkers along the axial polymer backbone. Moreover, the formation of a second supramolecular network due to the chain-extension effect may also be responsible for it. Highly resilient behaviours with almost no hysteresis and residual strains are also observed even with a maximum strain of λ = 12 because of the inherent freely movable character of the crosslinkers.

Mechanically strong hydrogels have attracted much interest as a result of their potential applications as biomaterials. However, it is still a challenge to produce mechanically strong supramolecular hydrogels because of the inherently weak characteristics of non-covalent interactions. A novel polyurethane–urea supramolecular hydrogel with excellent mechanical properties was developed in our laboratory by chance during the preparation of a water-borne dispersion of polyurethane with an excess amount of –NCO groups. Subsequent studies showed that this mechanical strength was because of the slow formation of multi-urea linkages and further chain extension because of the reaction of water with the excess –NCO groups in the isocyanate prepolymer chains or the free diisocyanate, or both. The mechanical properties of the polyurethane–urea supramolecular hydrogels obtained can be adjusted by simply altering the diisocyanate content. The following ranges of properties were obtained: shear modulus, 0.2–0.8 MPa; elongation at breakage, 970–2420%; tensile strength, 3.3–34 MPa; and compression stress, up to 38 MPa. Further analysis showed that the elongation ratio and tensile stress at breakage linearly decreased and increased, respectively, with an increase in the ratio of the hard segment.

In order to overcome the poor mechanical property of classic hydrogels, many methods have been explored to prepare hydrogels with excellent performance during the last few decades. In this paper, we developed a novel micellar cross-linking copolymerization method without small molecular surfactants to prepare highly stretchable and resilient hydrogels. The polymerization is based on free-radical copolymerization of water soluble acrylamide and a polymerizable macromolecular surfactant (i.e., amphiphilic polyurethane (PU) macromonomer) which can self-assemble into micelles acting as multifunctional cross-linkers. The mechanical properties, such as breaking elongation ratio, modulus and fracture toughness can be easily adjusted by varying the concentration of the polymerizable macromolecular surfactants. In addition, the mechanical energy storage efficiency (also known as resilience) is more than 96% at a strain up to 400%. The high resilience of the obtained hydrogels is due to the reversible assembly of the hydrogen-bonded hydrophobe, which contributes to the dissipation of the crack energy along the hydrogel sample, inside the micelles within the gel network.

Up to now, fabrication of strong and stimuli-responsive supramolecular hydrogels via an easy molecular design and synthesis procedure is still a big challenge. In this work, a series of hydrophobically modified linear polyurethane–urea copolymers and one polyurethane copolymer were prepared via a greatly simplified one-pot approach to investigate the synergistic effect between hydrogen-bonding and hydrophobic effects. FT-IR and various mechanical performance studies show that not only a longer hydrophobic spacer (C12) but also a stronger hydrogen-bonding unit (urea) is necessary for their synergistic effect to yield high water containing, transparent, stretchy and tough supramolecular hydrogels. Moreover, these supramolecular materials also show nice cyclic shape-memory behaviours which can be realized under mild conditions, e.g. in air and water at room temperature. The non-covalent interaction's synergistic effect and stimuli-responsive character are expected to dramatically expand the design and choice of tough and smart supramolecular hydrogels/materials for biomaterials.

A strong and highly stretchable supramolecular hydrogel with a shear modulus of 200 kPa, an elongation at break of 770% at 4 MPa stress and a water-responsive shape-memory property is developed. The whole shape-memory procedure including shape deformation, fixing and recovery can be realized under mild and green conditions, i.e. in air and water.