Schiff base crosslinked hyaluronic acid hydrogels with tunable and cell instructive time-dependent mechanical properties.

The dynamic interplay between cells and their native extracellular matrix (ECM) influences cellular behavior, imposing a challenge in biomaterial design. Dynamic covalent hydrogels are viscoelastic and show self-healing ability, making them a potential scaffold for recapitulating native ECM properties. We aimed to implement kinetically and thermodynamically distinct crosslinkers to prepare self-healing dynamic hydrogels to explore the arising properties and their effects on cellular behavior. To do so, aldehyde-substituted hyaluronic acid (HA) was synthesized to generate imine, hydrazone, and oxime crosslinked dynamic covalent hydrogels. Differences in equilibrium constants of these bonds yielded distinct properties including stiffness, stress relaxation, and self-healing ability. The effects of degree of substitution (DS), polymer concentration, crosslinker to aldehyde ratio, and crosslinker functionality on hydrogel properties were evaluated. The self-healing ability of hydrogels was investigated on samples of the same and different crosslinkers and DS to obtain hydrogels with gradient properties. Subsequently, human dermal fibroblasts were cultured in 2D and 3D to assess the cellular response considering the dynamic properties of the hydrogels. Moreover, assessing cell spreading and morphology on hydrogels having similar modulus but different stress relaxation rates showed the effects of matrix viscoelasticity with higher cell spreading in slower relaxing hydrogels.

May agricultural terraces induce gully erosion? A case study from the Black Soil Region of Northeast China.

Terracing of hillslopes is usually regarded as an effective measure to control soil erosion. Although it is often stressed that proper terrace construction and regular terrace maintenance are of great significance to prevent erosion on terraced hillslopes, examples of terrace-induced gully erosion are scarce. Field observations on terraced and partly abandoned hillslopes in the Black Soil Region of Northeast China, a region heavily affected by gully erosion since the middle of the 20th century, indicated that gully formation might be caused by terraces. In order to understand the impact of terracing on gully erosion, we selected several gullies to investigate the cause and timing of their triggering. We used a combination of field mapping, high-resolution digital terrain models, multi-temporal aerial photograph interpretation and interviews with local farmers. Our results showed that several gullies developed after terracing. Improper terrace design caused runoff concentration along terraces and ridges with mean inclination of 3.8%, which resulted in gully incision due to overtopping of terraces at low spots or due to the uncontrolled release of concentrated flow to adjoining unterraced hillslopes. The same processes are responsible for the persistent gully activity after abandonment and vegetation recovery. Furthermore, we showed how terraces affected gully morphology. Finally, we suggested appropriate countermeasures to stop further soil loss and land degradation on abandoned terraced hillslopes in NE China. Our findings are important as they demonstrate how poorly designed terraces may not only be ineffective but may even aggravate gully erosion.

Facile Construction of All-Solid-State Z-Scheme g-C3N4/TiO2 Thin Film for the Efficient Visible-Light Degradation of Organic Pollutant.

The increasing discharge of dyes and antibiotic pollutants in water has brought serious environmental problems. However, it is difficult to remove such pollutants effectively by traditional sewage treatment technologies. Semiconductor photocatalysis is a new environment-friendly technique and is widely used in aqueous pollution control. TiO2 is one of the most investigated photocatalysts; however, it still faces the main drawbacks of a poor visible-light response and a low charge-separation efficiency. Moreover, powder photocatalyst is difficult to be recovered, which is another obstacle limiting the practical application. In this article, g-C3N4/TiO2 heterojunction is simply immobilized on a glass substrate to form an all-solid-state Z-scheme heterojunction. The obtained thin-film photocatalyst was characterized and applied in the visible-light photodegradation of colored rhodamine B and tetracycline hydrochloride. The photocatalytic performance is related to the deposited layers, and the sample with five layers shows the best photocatalytic efficiency. The thin-film photocatalyst is easy to be recovered with stability. The active component responsible for the photodegradation is identified and a Z-scheme mechanism is proposed.

[Variations of Stable Isotope in Precipitation and Its Atmospheric Circulation Effect in Chongqing].

Variations of hydrogen and oxygen in stable isotopes and deuterium excess in precipitation as well as their relationship with precipitation,temperature and ENSO (El Niño/La Niño-Southern Oscilation) were analyzed by using 100 daily precipitation stable isotope data from April to October, 2015. The result showed that:① The equation of local meteoric water line (LMWL) was established:δD=8.28δ18O+12.34, the intercept and slope of which were greater than the global meteoric water 1ine (GMWL) but was similar to most of the southern China monsoon region.② Both stable isotopes and deuterium excess in precipitation indicated obvious seasonal variation in the monsoon region, high in summer and low in winter. This was attributed to the difference in moisture sources in different seasons. ③ In addition, no significant correlation was detected between δ18O values in precipitation with temperature and precipitation (r=0.03; r=0.12). But it was sensitive to atmospheric circulation effect, and was positively correlated with ENSO.δ18O values in precipitation and deuterium excess in precipitation clearly recorded the La Niño and El Niño conversion process between 2014 and 2015. During the El Niño event, the δ18O and d values became obvious on the high side, and the changes were the opposite during La Niño.