No abstract

For a hydrogel coating on a substrate to be stable, covalent bonds polymerize monomer units into polymer chains, crosslink the polymer chains into a polymer network, and interlink the polymer network to the substrate. In existing methods of hydrogel coating, the three processespolymerization, crosslinking, and interlinking-usually concur. This concurrency is unnecessary and hinders the widespread applications. In particular, many hydrogels are made by free-radical polymerization, involving toxic monomers, toxic initiators, and oxygen-free environment. For example, in the free-radical polymerization of a covalently crosslinked polyacrylamide hydrogel, when subject to UV light, the vinyl groups of acrylamide monomer and N,N′-methylenebisacrylamide crosslinker are activated concurrently. The former results in polyacrylamide chains and the latter results in a polyacrylamide network. When the substrate is involved, polymerization of monomers, crosslinking of poly mer chains, and interlinking between the hydrogel and substrate proceed concurrently. Since free radical polymerization is sensitive to oxygen, molding is usually required. Besides, molding is also used to control the shape and thickness of hydrogel coating. Depending on the geometry of the substrate, coating can be technically challenging for highly curved surfaces (e.g., 1D structures), or even impossible for hollow or cage structures. Furthermore, the monomers (e.g., acrylamide, acrylic acid, etc.) are usually toxic. Consequently, free-radical polymerization is unsuitable for everyday operation.For a hydrogel coating on a substrate to be stable, covalent bonds poly merize monomer units into polymer chains, crosslink the polymer chains into a polymer network, and interlink the polymer network to the substrate. The three processes-polymerization, crosslinking, and interlinking-usually concur. This concurrency hinders widespread applications of hydrogel coatings. Here a principle is described to create hydrogel paints that decouple polymerization from crosslinking and interlinking. Like a common paint, a hydrogel paint divides the labor between the paint maker and the paint user. The paint maker formulates the hydrogel paint by copolymerizing monomer units and coupling agents into polymer chains, but does not crosslink them. The paint user applies the paint on various materials (elastomer, plastic, glass, ceramic, or metal), and by various operations (brush, cast, dip, spin, or spray). During cure, the coupling agents crosslink the polymer chains into a network and interlink the polymer network to the substrate. As an example, hydrogels with thickness in the range of 2-20 µm are dip coated on medical nitinol wires. The coated wires reduce friction by eightfold, and remain stable over 50 test cycles. Also demonstrated are several proofofconcept applica tions, including stimuliresponsive structures and antifouling model boats.A hydrogel-coated substrate unites the superior properties of the substrate (e.g., strength, stiffness, and toughness) and the superior p...

Three Ligularia species (L. tongolensis, L. cymbulifera, and L. atroviolacea) were examined with respect to the chemical composition and nucleotide sequence. Furanoeremophilanes were found to be produced in the root of all samples of the three species collected in northwest Yunnan and southwest Sichuan. Eight furanoeremophilanes were identified, two of which were new. Most of the identified furanoeremophilanes were oxygenated at 3, 6, and 15-positions. The nucleotide sequence of the atpB-rbcL intergenic region was found to be essentially the same in the three species. These similarities imply that the three Ligularia species, all belonging to the section Corymbosae, are close to one another. The intra-specific diversity in the two widely distributed species in the Hengduan Mountains area, L. tongolensis and L. cymbulifera, were in contrast. Four out of 19 L. tongolensis samples contained a strongly Ehrlich-positive compound besides a number of positive compounds, and five variants of the atpB-rbcL sequence were found in these samples. In contrast, no variation was observed in 13 L. cymbulifera samples with respect to the furanoeremophilane composition or the atpB-rbcL sequence. The lack of diversity in L. cymbulifera probably resulted from the uniformity of its habitat.

Cycads represent one of the most ancient lineages of living seed plants. Identifying genomic features uniquely shared by cycads and other extant seed plants, but not non-seed-producing plants, may shed light on the origin of key innovations, as well as the early diversification of seed plants. Here, we report the 10.5-Gb reference genome of Cycas panzhihuaensis, complemented by the transcriptomes of 339 cycad species. Nuclear and plastid phylogenomic analyses strongly suggest that cycads and Ginkgo form a clade sister to all other living gymnosperms, in contrast to mitochondrial data, which place cycads alone in this position. We found evidence for an ancient whole-genome duplication in the common ancestor of extant gymnosperms. The Cycas genome contains four homologues of the fitD gene family that were likely acquired via horizontal gene transfer from fungi, and these genes confer herbivore resistance in cycads. The male-specific region of the Y chromosome of C. panzhihuaensis contains a MADS-box transcription factor expressed exclusively in male cones that is similar to a system reported in Ginkgo, suggesting that a sex determination mechanism controlled by MADS-box genes may have originated in the common ancestor of cycads and Ginkgo. The C. panzhihuaensis genome provides an important new resource of broad utility for biologists.