Sporophytic control of tapetal development and pollen fertility by a mitogen-activated protein kinase cascade in rice.

Tapetum, the innermost layer of the anther wall, provides essential nutrients and materials for pollen development. Timely degradation of anther tapetal cells is a prerequisite for normal pollen development in flowering plants. Tapetal cells facilitate male gametogenesis by providing cellular contents after highly coordinated programmed cell death (PCD). Tapetal development is regulated by a transcriptional network. However, the signaling pathway(s) involved in this process are poorly understood. In this study, we report that a mitogen-activated protein kinase (MAPK) cascade composed of OsYDA1/OsYDA2-OsMKK4-OsMPK6 plays an important role in tapetal development and male gametophyte fertility. Loss of function of this MAPK cascade leads to anther indehiscence, enlarged tapetum, and aborted pollen grains. Tapetal cells in osmkk4 and osmpk6 mutants exhibit an increased presence of lipid body-like structures within the cytoplasm, which is accompanied by a delayed occurrence of PCD. Expression of a constitutively active version of OsMPK6 (CA-OsMPK6) can rescue the pollen defects in osmkk4 mutants, confirming that OsMPK6 functions downstream of OsMKK4 in this pathway. Genetic crosses also demonstrated that the MAPK cascade sporophyticly regulates pollen development. Our study reveals a novel function of rice MAPK cascade in plant male reproductive biology.

Study on the definition, mechanism and controllability of secondary bubbles based on the bubble nucleation model in injection foaming polypropylene.

The process of nucleation and growth of polypropylene foam was observed by using visualizations of the mold-opening foam injection molding (MOFIM) and free foaming (FREEF). The fitting of the mathematical model formula was used to supplement the judgment conditions of the secondary bubbles to explore the generation process and formation conditions of the secondary bubbles. The results of changes in blowing agent content and melt temperature proved the rationality of the judgment basis and the appearance of secondary bubbles started from the late stage of balanced-foaming. Then, the combined action of several nucleation mechanisms led to the emergence of secondary bubbles, which was observed utilizing glass fibers as nucleating agents and tracers. The data for the two foaming modes indicated that the formation of secondary bubbles is closely related to temperature and pressure drop. The bubble nucleation model was amended and validated by regulating the temperature variation in the mold cavity to control the number of secondary bubbles, which enabled the nucleation process of secondary bubbles to be fitted to an "S-shaped" curve. Finally, a controllable number of secondary bubbles was obtained from the bimodal bubble structure. Herein, this study enriches our understanding of the formation process of secondary bubbles, and provides theoretical guidance for fabricating high density, small size foam materials.

Synthesis of Porous Carbon Nitride Nanobelts for Efficient Photocatalytic Reduction of CO2.

Sustainable conversion of CO2 to fuels using solar energy is highly attractive for fuel production. This work focuses on the synthesis of porous graphitic carbon nitride nanobelt catalyst (PN-g-C3N4) and its capability of photocatalytic CO2 reduction. The surface area increased from 6.5 m2·g-1 (graphitic carbon nitride, g-C3N4) to 32.94 m2·g-1 (PN-g-C3N4). C≡N groups and vacant N2C were introduced on the surface. PN-g-C3N4 possessed higher absorbability of visible light and excellent photocatalytic activity, which was 5.7 and 6.3 times of g-C3N4 under visible light and simulated sunlight illumination, respectively. The enhanced photocatalytic activity may be owing to the porous nanobelt structure, enhanced absorbability of visible light, and surface vacant N-sites. It is expected that PN-g-C3N4 would be a promising candidate for CO2 photocatalytic conversion.

Robust Hydrogel Adhesive with Dual Hydrogen Bond Networks.

Hydrogel adhesives are attractive for applications in intelligent soft materials and tissue engineering, but conventional hydrogels usually have poor adhesion. In this study, we designed a strategy to synthesize a novel adhesive with a thin hydrogel adhesive layer integrated on a tough substrate hydrogel. The adhesive layer with positive charges of ammonium groups on the polymer backbones strongly bonds to a wide range of nonporous materials' surfaces. The substrate layer with a dual hydrogen bond system consists of (i) weak hydrogen bonds between N,N-dimethyl acrylamide (DMAA) and acrylic acid (AAc) units and (ii) strong multiple hydrogen bonds between 2-ureido-4[1H]-pyrimidinone (UPy) units. The dual hydrogen-bond network endowed the hydrogel adhesives with unique mechanical properties, e.g., toughness, highly stretchability, and insensitivity to notches. The hydrogel adhesion to four types of materials like glass, 316L stainless steel, aluminum, Al2O3 ceramic, and two biological tissues including pig skin and pig kidney was investigated. The hydrogel bonds strongly to dry solid surfaces and wet tissue, which is promising for biomedical applications.

Ultra-stretchable hydrogels with hierarchical hydrogen bonds.

Hydrogels are attractive for applications in intelligent soft materials and flexible electronics. Herein, we report a new hydrogel with a hierarchical hydrogen bond system consisting of (1) weak hydrogen bonds between N,N-dimethylacrylamides (DMAA) and acrylic acids (AAc) and (2) strong multiple hydrogen bonds between 2-ureido-4[1H]-pyrimidinone units. By optimizing the ratios of DMAA and AAc and the balance of weak and strong hydrogen bonds, the hydrogels have unique properties. The transparent hydrogels have tunable Young's modulus (70-1,250 kPa) and are highly stretchable (up to 4,340% strain), tough (fracture energies of 10.8 kJ/m2, matching natural rubber) and insensitive to notches when it is highly stretched (λ = 19.6).

Injectable and biocompatible chitosan-alginic acid hydrogels.

Injectable and biocompatible polysaccharide hydrogels are ideal scaffolds for drug delivery and tissue engineering. Here, we report a new in situ forming hydrogels by self-crosslinking chitosan and a biocompatible polymeric crosslinker, oxidized alginic acid. The dialdehyde alginic acid was synthesized by the oxidant reaction of alginic acid with sodium periodate. The gel was formed in situ by the Schiff base reactions between their amine groups of chitosan and aldehyde groups of alginic acid. It deformed under stress and kept its shape integrity at the strain of 40%. Sustained cargo release including rhodamine and bovine serum albumin from the hydrogels was obtained. The hydrogels were degraded by chitosanase within 30 d and the pH values of the solution remained neutral. H9c2 cells proliferated the hydrogels and maintained their native state. These results suggested this hydrogel can be promising cell therapy scaffolds for tissue engineering.

Thermo-modulated Hela cell release from an elastic and biocompatible hydrogel.

Cell growth and release from the hydrogel scaffolds are critical steps in cell culture and cell therapies. Herein a double network hydrogel with one thermosensitive P(AEtMA-Cl-DEAEA) network and the other polyacrylamide network is reported. The diad hydrogel is elastic and maintains its structural integrity under large deformation. BSA is adsorbed onto the hydrogel at body temperature and subsequently released from the hydrogel at lower temperature. Hela cells proliferate on the hydrogel scaffolds at 37°C. When the scaffold is incubated at low temperature (20°C), 32.6% ± 6.4% of its population are detached from the scaffolds. The detached cells remain active in cell culture. This hydrogel with excellent mechanical properties and unique biological function has promising biomedical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1786-1791, 2019.

Controlled protein delivery from photosensitive nanoparticles.

Light provides a powerful approach for delivery of cargos and study of important biological events. This article reports a series of photosensitive and biocompatible delivery of nanoparticles which released proteins upon light irradiation. The nanoparticles were synthesized by emulsion copolymerization of 2-(dimethylamino) ethyl methacrylate with functional monomers and a photoliable o-nitrobenzyl diacrylate crosslinker. Upon mild UV irradiation (λ = 365 nm, 10 mJ/cm(2)), the photosensitive crosslinker underwent light-induced degradation and the sizes of the nanoparticles increased dramatically. The nanoparticles were uptaken by the cells which is confirmed by flow cytometry analysis. Bovine serum albumin and green fluorescent protein were loaded as model proteins into the nanoparticles and accelerated photo-triggered release were achieved.

Luminescent properties of CdTe quantum dots synthesized using 3-mercaptopropionic acid reduction of tellurium dioxide directly.

A facile one-step synthesis of CdTe quantum dots (QDs) in aqueous solution by atmospheric microwave reactor has been developed using 3-mercaptopropionic acid reduction of TeO2 directly. The obtained CdTe QDs were characterized by ultraviolet-visible spectroscopy, fluorescent spectroscopy, X-ray powder diffraction, multifunctional imaging electron spectrometer (XPS), and high-resolution transmission electron microscopy. Green- to red-emitting CdTe QDs with a maximum photoluminescence quantum yield of 56.68% were obtained.

Biodegradable thermogelling hydrogel of P(CL-GL)-PEG-P(CL-GL) triblock copolymer: degradation and drug release behavior.

Degradation and drug release behavior of thermogelling hydrogel of poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide) [P(CL-GL)-PEG-P(CL-GL) (1880-1540-1880)] triblock copolymer were investigated. The copolymer aqueous solution (25 wt%) underwent sol-gel transition at 35 degrees C as the temperature increased and formed a stable gel at body temperature. After incubation in PBS buffer solution (0.1 M) at 37 degrees C, the gel degraded completely into a viscous liquid at 14th week. Chemical microstructural analysis of the degraded samples by (1)H-NMR revealed the degradation occurring mainly on the glycolyl sequences of the copolymer. The pH value of the gel buffer solution maintained neutral during the initial 8 weeks, which may be beneficial for the preservation of activity of pH-sensitive drugs. Incorporation of drugs into the gel was formulated at room temperature without the use of any organic solvent. The gel formed a controlled release depot with delivery times of 12, 32, and 25 days for isoniazid, rifampicin and bovine serum albumin, respectively. Controlled release of hydrophobic rifampicin was achieved with insignificant burst effect due to the distribution of the drug mainly in the hydrophobic polyester regions of the gel.

Biodegradable and thermoreversible hydrogels of poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol) aqueous solutions.

The aqueous solutions of triblock copolymers of poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol) [PEG-P(CL-GA)-PEG] undergoing sol-gel transition as the temperature increases from 20 to 60 degrees C were successfully prepared. The thermogelling block copolymers were synthesized by subtle control of the hydrophilic/hydrophobic balance and the chain microstructures. The amphiphilic block copolymer formed micelles in aqueous solution, and the micelle aggregated as the temperature increased. The sol-gel transition of the copolymer aqueous solutions was studied focusing on the structure-property relationship. GA was incorporated into the polymer chain to prevent crystallization of PCL component and increase the polymer degradation. It is expected to be a promising long-term delivery system for pH-sensitive drugs, proteins, and genes.