Self-Lubrication Mechanism of Surface-Textured Polymer-Matrix Composites under the Induction of Frictional Stress.

Polymer-matrix composites have been widely used in the manufacture of seals, bearings, electrical insulators, and self-lubricating films as engineering applications move toward lighter weight, higher strength, and corrosion resistance. However, the high-speed shear effect of the friction pairs in relative motion leads to localized heating of the polymer surface, resulting in deformation or softening of the device. Herein, acer mono maple and canna leaves were used as templates to construct polymer-matrix sulfonated polyether-etherketone/polytetrafluoro-wax (SPEEK/PFW) composites with a surface-textured structure. As the bionic texture reduces the level of direct contact between the friction pairs, the frictional thermosoftening of SPEEK occurs in the localized areas of the bumps and leads to the release of PFW stored in textures, resulting in the formation of a soft polymer sliding layer in the worn area and greatly enhancing the frictional stability. By investigation of the tribological properties of textured SPEEK/PFW composites under different loads and sliding speeds, the mechanisms from surface wear to matrix softening and spontaneous construction of a slipping layer are summarized. The results of scanning electron microscopy and three-dimensional profilometer characterization of the wear scars show the surface state of SPEEK/PFW after friction, revealing the friction-thermotropic deformation of the surface texture. The results of this study not only improve our understanding of the frictional heat-induced surface self-lubrication mechanism of textured polymer composites but also provide a reference for the development of multiphase hybrid polymer-matrix composites with excellent self-lubrication properties.

Effect of Graphene on the Performance of Silicon-Carbon Composite Anode Materials for Lithium-Ion Batteries.

(Si/graphite)@C and (Si/graphite/graphene)@C were synthesized by coating asphalt-cracked carbon on the surface of a Si-based precursor by spray drying, followed by heat treatment at 1000 °C under vacuum for 2h. The impact of graphene on the performance of silicon-carbon composite-based anode materials for lithium-ion batteries (LIBs) was investigated. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) images of (Si/graphite/graphene)@C showed that the nano-Si and graphene particles were dispersed on the surface of graphite, and thermogravimetric analysis (TGA) curves indicated that the content of silicon in the (Si/graphite/graphene)@C was 18.91%. More bituminous cracking carbon formed on the surface of the (Si/graphite/graphene)@C due to the large specific surface area of graphene. (Si/Graphite/Graphene)@C delivered first discharge and charge capacities of 860.4 and 782.1 mAh/g, respectively, initial coulombic efficiency (ICE) of 90.9%, and capacity retention of 74.5% after 200 cycles. The addition of graphene effectively improved the cycling performance of the Si-based anode materials, which can be attributed to the reduction of electrochemical polarization due to the good structural stability and high conductivity of graphene.

Sustainable cellulose foams for all-weather high-performance radiative cooling and building insulation.

Passive daytime radiative cooling (PDRC) as a zero-energy-consumption cooling technique offers rich opportunities in reducing global energy consumption and mitigating CO2 emissions. Developing high-performance PDRC coolers with practical applicability based on sustainable materials is of great significance, but remains a big challenge. Herein, polyvinyl alcohol (PVA) and esterified cellulose (EC) extracted from sawdust were used as raw materials to construct foams by using a dual-crosslinking assisted-unidirectional freeze-drying strategy followed by hydrophobic surface modification. The resultant PVA/EC (PEC) foams with ideal hierarchical macropore structure displayed various excellent features, such as low thermal conductivity (26.2 mW·m-1·K-1), high solar reflectance (95 %) and infrared emissivity (0.97), superhydrophobicity as well as high mechanical properties. The features allowed the PEC foams to be used as radiative coolers with excellent PDRC performance and thermal insulating materials. A maximum sub-ambient temperature drops of 10.2 °C could be achieved for optimal PEC foams. Building simulations indicated that PEC foams could save 55.8 % of the energy consumption for Xi'an. Our work would give inspiration for designing various types of PDRC coolers, including but certainly not limited to foams-based radiative coolers.

MicroRNAs can effectively induce formation of insulin-producing cells from mesenchymal stem cells.

MicroRNAs regulate insulin secretion, pancreatic development and beta cell differentiation. However, the function of microRNAs in the formation of insulin-producing cells (IPCs) from adult stem cells is poorly understood. We examine the microRNA expression profile in nestin-positive umbilical cord-derived mesenchymal stem cells (N-UCMSCs) and nestin-positive pancreatic mesenchymal stem cells using a deep sequencing approach. We also selected specific microRNAs for overexpression in N-UCMSCs and found that miR-375 and miR-26a induced IPCs differentiation from N-UCMSCs by downregulating target genes including mtpn, sox6, bhlhe22 and ccnd1. Small interfering RNAs were also used to knock down these genes in N-UCMSCs to induce the formation of IPCs. These results suggest that endogenous microRNAs involved in the formation of IPCs from adult stem cells show promise for advancing the development of an effective cell transplant therapy for diabetes. Copyright © 2017 John Wiley & Sons, Ltd.

Multi-lineage potential research of bone marrow mesenchymal stem cells from Bama miniature pig.

Bone marrow mesenchymal stem cells (BMSCs) are easy to obtain and thought to be ideal candidate cells for reconstruction of tissues and organs. Pigs are an appropriate animal model because their physiological structure, organ size, nutritional metabolism, and pathological reactions are similar to those of humans. In this study, bone marrow was collection from Bama miniature pigs to isolate BMSCs (B-BMSCs) by whole bone marrow culture method. We then examined their biological characteristics such as growth kinetics, surface antigen, and multi-lineage potential. B-BMSCs could be cultured for 36 passages in vitro. Growth kinetics and colony forming assay analyses indicated that B-BMSCs had a strong capacity for self-renewal in vitro and their proliferation rate appeared to decrease with passaging. These findings were supported by the animal cytophysiology in vitro. Surface antigen detection showed that B-BMSCs expressed CD29, CD44, CD71, CD73, and CD90, but not the endothelial cell marker CD31 or hematopoietic cell-specific marker CD34. This result was consistent with the characteristics of B-BMSCs. Furthermore, under appropriate conditions for multidirectional differentiation, B-BMSCs were induced to differentiate into adipocytes, osteoblasts, neuron-like cells, islet cells, liver-like cells, and endothelial cells as indicated by reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence. These results verified the differentiation potential of B-BMSCs. In this study, B-BMSCs were isolated from Bama miniature pigs, and the self-renewal ability and differential potential was evaluated in vitro. The present study has important bearing on the potential application of B-BMSCs as a stem cell source for regenerative therapies. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 671-685, 2015. © 2015 Wiley Periodicals, Inc.

Isolation and characterization of chicken dermis-derived mesenchymal stem/progenitor cells.

Dermis-derived mesenchymal stem/progenitor cells (DMS/PCs) were isolated from the skin tissue of 16-day-old chick embryos and then characterized by immunofluorescence and RT-PCR. We found that primary DMS/PCs could be expanded for 15 passages. Expression of ß -integrin, CD44, CD71, and CD73 was observed by immunofluorescence and RT-PCR. Passage 3 DMS/PCs were successfully induced to differentiate into osteoblasts, adipocytes, and neurocytes. The results indicate the potential for multilineage differentiation of DMS/PCs that may represent an ideal candidate for cellular transplantation therapy.