Metal complexation-based gelation imparts load-bearing hydrogels with striking properties like reversibility, self-healing, and mechanical tunability. Using a bio-inspired metal−catechol complex, these properties have been introduced to a variety of polymer hydrogels, except hyaluronic acid, which is widely used in biological applications. In this research, we developed two different hyaluronic acid (HA) hydrogels by regulating the gelation kinetics of Fe 3+ and a catechol cross-linker, including Fe 3+ -induced covalent bonding and coordination bonding. Dual roles of Fe 3+ in catechol-modified HA (HA-CA), Fe 3+ −catechol coordination, and catechol oxidation followed by a coupling reaction were selectively applied for different gelations. Phase-changeable HA-CA gel was attributed to dominant Fe 3+ −catechol coordination with immediate pH control. Alternatively, allowing a curing time to form catechol coupling bonds resulted in color-changeable HA-CA gels with pH control. The gel structure is then preserved by dual cross-linking through covalent catechol-coupling-based coordinate bonds and electrostatic interactions between Fe 3+ and HA-CA. The hydrogels showed enhanced cohesiveness and shock-absorbing properties with increasing pH due to coordinate bonds inspired by marine mussel cuticles. The present gelation strategy is expected to expand the utility of HA hydrogels in biological applications, offering easy control over the phase, gel network, and viscoelastic properties.

No abstract

No abstract

Volatile chemical products (VCPs) have recently been identified as potentially important unconventional sources of secondary organic aerosol (SOA), in part due to the mitigation of conventional emissions such as vehicle exhaust. Here, we report measurements of SOA production in an oxidation flow reactor from a series of common VCPs containing oxygenated functional groups and at least one oxygen within the molecular backbone. These include two oxygenated aromatic species (phenoxyethanol and 1-phenoxy-2-propanol), two esters (butyl butyrate and butyl acetate), and four glycol ethers (carbitol, methyl carbitol, butyl carbitol, and hexyl carbitol). We measured gas- and particle-phase products with a suite of mass spectrometers and particle-sizing instruments. Only the aromatic VCPs produce SOA with substantial yields. For the acyclic VCPs, ether and ester functionality promotes fragmentation and hinders autoxidation, whereas aromatic rings drive SOA formation in spite of the presence of ether groups. Therefore, our results suggest that a potential strategy to reduce urban SOA from VCPs would be to reformulate consumer products to include less oxygenated aromatic compounds.

Erythritol is one of the most widely used low calorie sugar substitutes and has known inhibitory effects on the growth of Streptococcus mutans. However, the mechanism underlying this inhibition is poorly understood. Expression profiles of the glucosyltransferase (GTF) and fructosyltransferase (FTF) genes in S. mutans were evaluated in the presence of erythritol and other sweeteners. Adhesion of S. mutans to different carbohydrates was also determined across a range of concentrations. Erythritol significantly (p<0.05) inhibited adherence of S. mutans under multiple conditions, compared with sucrose. Erythritol significantly (p<0.05) inhibited expressions of gtfB, gtfC, gtfD, and ftf in the presence of various carbohydrates compared with sucrose. These findings were consistent with an anti-cariogenic effect of erythritol on S. mutans, and suggested mechanisms by which erythritol inhibits formation of dental caries.