We report a dual ionic cross-linking approach for the preparation of double-network hydrogels with robustness, high strength, and toughness, sodium alginate/poly(acrylamide- co-acrylic acid)/Fe (SA/P(AAm- co-AAc)/Fe), in a facile "one-step" dual ionic cross-linking method. We take advantage of the abundant carboxyl groups on alginate molecules and the copolymer chains and their high coordination capacity with multivalent metal ions to obtain hydrogels with high strength and toughness. The optimal SA/P(AAm- co-AAc)/Fe (SA 2 wt % and AAc 5 mol %) hydrogels showed a remarkable mechanical performance with 3.24 MPa tensile strength and 1228% strain, both of which remained stable with 76% water content and were highly swelling resistant in an aqueous environment. The hydrogels possessed high fatigue resistance, self-recovery, pH-triggered healing capability, shape memory, and reversible gel-sol transition facilitated by pH regulation. Moreover, they show three-dimensional (3D) printing processability by properly adjusting the solution viscosity. The approach may provide a convenient way of obtaining hydrogels having high strength and toughness with a number of desirable properties for a broad range of biomedical applications.

Water-soluble fluorescent copper, silver and gold nanoclusters with quantum yields of 2.2, 6.8 and 5.3%, respectively, are prepared by a robust photoreduction of their inorganic precursors in the presence of poly (methacrylic acid) functionalized with pentaerythritol tetrakis 3-mercaptopropionate.

No abstract

As research continues, the control on the polymorph and morphology of calcium carbonate (CaCO 3 ) becomes a hot topic because its application is limited by these parameters. The polymorph and morphology control of CaCO 3 was successfully achieved via temperature and PEG (M w = 6000) during the decomposition of Ca(HCO 3 ) 2 , which has rarely been employed to prepare precipitated CaCO 3 . As-prepared CaCO 3 was characterized using XRD and SEM. In the case of no PEG, rhombohedra calcite, lamellar vaterite, rod-and needlelike aragonite are observed, and calcite is the major phase at all samples and it increases with temperature, whereas vaterite and aragonite decrease with temperature. The addition of PEG restrains the formation of vaterite and promotes the emergence of needlelike aragonite particles at 70°C, and prevents the generation of calcite and encourages the production of rodlike aragonite particles at 80°C and 90°C. This work not only provides a new way on the preparation of CaCO 3 powder but also presents the feasible control method in this route.

With the deepening of research on high-strength hydrogels, the multi-functional study of hydrogels has become a hot spot. In this paper, a dual cross-linked physical high-strength hydrogels is prepared by a relatively simple method. 2-Vinyl- 4,6-Diamino-2-vinyl-1,3,5-triazine (VDT) induces the formation of the first cross-linking points through the interaction of hydrogen bonds with poly(acrylamide-co-acrylic acid) (PAm-co-Ac) chains, then the secondary physical cross-linkers Fe that introduce ionic coordinates between Fe and -COO groups. Due to the synergistic effect of hydrogen bonding and ionic coordination, hydrogels possess high tensile strength (approx. 4.34 MPa), large elongation (approx. 17.64 times), and good healing properties under alkali solution after cutting into two pieces. Meanwhile, VDT contains diaminotriazine functional groups that easily form hydrogen bonds so that the polymer of hydrogels could absorb 5-fluorouridine. In addition, the contribution of ionic polymer segments enables pH to be sensitive to hydrogels and facilitates the adsorption of a large number of ionic monomers to form ionic conductive networks, the prepared hydrogel capacitor device has very high sensitivity to pressure and deformation, and can detect the movement behavior of the human body. The dual-physical cross-linked hydrogels had a selective adsorption to biological small molecules and could be assembled into a flexible wearable device with high sensitivity.