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Search Results: 1 - 10 of 126579 matches for " Mingzhong Li "
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Gelation of Antheraea pernyi Silk Fibroin Accelerated by Shearing  [PDF]
Yu Liu, Siyong Xiong, Renchuan You, Mingzhong Li
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.46047

The rapid manufacture of silk fibroin gels in mild conditions is an important subject in the field of silk-based biomaterials. In this study, the gelation of Antheraea pernyi silk fibroin (ASF) aqueous solution was induced by shearing, without chemical cross-linking agents. Simple shearing controlled and accomplished the steady and rapid conformational transition to β-sheets with ease. The conformational transformation and rapid gelation mechanisms of ASF induced by shearing were tracked and analyzed by circular dichroism spectrometry, Fourier transform infrared spectroscopy and X-ray diffractometry, then compared with Bombyx mori silk fibroin (BSF). ASF quickly formed hydrogels within 24 - 48 h after shearing under different shearing rates for 30 - 90 min, resulting in sol-gel transformation when the β-sheet content reached nearly 50%, which is the minimum content needed to maintain a stable hydrogel system in ASF. The gel structures remained stable once formed. The rapid gelation of ASF through shearing compared with BSF was achieved because of ASF’s alternating polyalanine-containing units, which tend to form α-helix structures spontaneously. Further, the entropic cost during the conformational transition from the α-helix to the β-sheet structure is less than the cost of the transition from the random coil

The degradation behavior of silk fibroin derived from different ionic liquid solvents  [PDF]
Renchuan You, Ying Zhang, Yu Liu, Guiyang Liu, Mingzhong Li
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.56A002

Establishing an appropriate degradation rate is critical for tissue engineering scaffolds. In this study, the degradation rate of silk fibroin three-dimensional scaffolds was regulated by changing the molecular weight (MW) of the silk fibroin. The solubility of silk fibroin depends primarily on the ionic ability of the slovent to dissolve silk fibroin, therefore, we regulated the MW of the silk fibroin using LiBr, Ca(NO3)2 and CaCl2 to dissolve the silk fibers. SDS-PAGE analysis showed that the MW of the CaCl2-derived silk fibroin was lower than the MW produced using LiBr and Ca(NO3)2. In vitro and in vivo degradation results showed that the scaffolds prepared by low-MW silk fibroin were more rapidly degraded. Furthermore, FTIR and amino acid analysis suggested that the amorphous regions were preferentially degraded by Collagenase IA, while the SDS-PAGE and amino acid analysis indicated that the scaffolds were degraded into polypeptides (mainly at 10-30 kDa) and amino acids. Because the CaCl2-derived scaffolds contained abundant low MW polypeptides, inter-intramolecular entanglement and traversing of molecular chains in the crystallites reduced, which resulted in rapid degradation. The in vivo degradation results suggested that the degradation rate of the CaCl2-derived scaffolds was better matched to dermis regeneration, indicating that the degradation rate of silk fibroin can be effectively regulated by changing the MW to achieve a suitable dermal tissue regeneration rate.

Silk Fibroin Based Porous Materials
Qiang Zhang,Shuqin Yan,Mingzhong Li
Materials , 2009, DOI: 10.3390/ma2042276
Abstract: Silk from the Bombyx mori silkworm is a protein-based fiber. Bombyx mori silk fibroin (SF) is one of the most important candidates for biomedical porous material based on its superior machinability, biocompatibility, biodegradation, bioresorbability, and so on. In this paper, we have reviewed the key features of SF. Moreover we have focused on the morphous, technical processing, and biocompatibility of SF porous materials, followed by the application research. Finally, we provide a perspective the potential and problems of SF porous materials.
Preparation of Silk Fibroin Microspheres and Its Cytocompatibility  [PDF]
Jing Qu, Lu Wang, Yongpei Hu, Lingshuang Wang, Renchuan You, Mingzhong Li
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2013, DOI: 10.4236/jbnb.2013.41011
Abstract: The goal of this proof-of-concept study was the fabrication of porous silk fibroin (SF) microspheres which could be used as cell culture carriers under very mild processing conditions. The SF solution was differentiated into droplets which were induced by a syringe needle in the high-voltage electrostatic field. They were collected and frozen in liquid nitrogen and water in droplets formed ice crystals which sublimated during lyophilization and a great quantity of micropores shaped in SF microspheres. Finally, the microspheres were treated in ethanol so as to transfer the molecular conformation into β-sheet and then they were insoluble in water. SF particles were spherical in shape with diameters in the range of 208.4 μm to 727.3 μm, while the pore size on the surface altered from 0.3 μm to 10.7 μm. In vitro, the performances of SF microspheres were assessed by culturing L-929 fibroblasts cells. Cells were observed to be tightly adhered and fully extended; also a large number of connections were established between cells. After 5-day culture, it could be observed under a confocal laser scanning microscope that the porous microenvironment offered by SF particles accelerated proliferation of cells significantly. Furthermore, porous SF particles with smaller diameters (200 - 300 μm) might promote cell growth better. These new porous SF microspheres hold a great potential for cell culture carriers and issue engineering scaffolds.
The Cytocompatibility of Genipin-Crosslinked Silk Fibroin Films  [PDF]
Lingshuang Wang, Yiyu Wang, Jing Qu, Yongpei Hu, Renchuan You, Mingzhong Li
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2013, DOI: 10.4236/jbnb.2013.43026

There is an increasing demand for crosslinking methods of silk fibroin (SF) scaffolds in biomedical applications that could maintain the biocompatibility, bioactivity as well as improve the water resistance and mechanical properties of SF materials. In this study, SF was crosslinked effectively with genipin which is a naturally occurring iridoid glucoside and the crosslinking mechanism was investigated through FTIR and amino acid analysis. The results showed that genipin could react with the -NH2 groups on the side chains of SF macromolecules and to form inter- and intra-molecular covalent bonds, and improved the stability of SF materials significantly. In vitro, the performances of genipin-crosslinked SF films were assessed by seeding L929 cells and compared with ethanol-processed SF films, glutaraldehyde and polyethylene glycol diglycidyl ether crosslinked ones. The genipin-crosslinked SF films showed a similar affinity to cells as ethanol-processed ones, and a higher bioactivity in promoting cell growth and proliferation, inhibition of cell apoptosis, and maintenance of normal cell cycle compared with glutaraldehyde and polyethylene glycol diglycidyl ether crosslinked SF films. These features, combined with the decrease of brittleness of SF films crosslinked with chemical methods, substantiated genipin as an effective and biocompatible agent for the manufacturing of bioactive SF materials which used as tissue engineering scaffolds and drug delivery carriers.

Influence of Sodium Lauryl Sulfate and Tween 80 on Carbamazepine–Nicotinamide Cocrystal Solubility and Dissolution Behaviour
Mingzhong Li,Ning Qiao,Ke Wang
Pharmaceutics , 2013, DOI: 10.3390/pharmaceutics5040508
Abstract: The influence of the surfactants of sodium lauryl sulfate (SLS) and Tween 80 on carbamazepine–nicotinamide (CBZ–NIC) cocrystal solubility and dissolution behaviour has been studied in this work. The solubility of the CBZ–NIC cocrystal was determined by measuring the eutectic concentrations of the drug and the coformer. Evolution of the intrinsic dissolution rate (IDR) of the CBZ–NIC cocrystal was monitored by the UV imaging dissolution system during dissolution. Experimental results indicated that SLS and Tween 80 had little influence upon the solubility of the CBZ–NIC cocrystal but they had totally opposite effects on the IDR of the CBZ–NIC cocrystal during dissolution. SLS significantly increased the IDR of the CBZ–NIC cocrystal while Tween 80 decreased its IDR.
HIV Vulnerability in Out-of-School Adolescents and Youth in Yunnan, China  [PDF]
Jianghong Li, Lijun Yang, Zhouyang Ren, Chongbin Mo, Dingwen Chen, Fuqiang Dai, Mingzhong Jiang, Zhijie Tang, Peter Jacoby
World Journal of AIDS (WJA) , 2012, DOI: 10.4236/wja.2012.22007
Abstract: This study investigated multiple aspects of vulnerability to HIV in out-of-school adolescents and youth in Yunnan Province, a high HIV risk region in China. The findings show that socially disadvantaged adolescents and youth were overrepresented in the out-of-school young people in Yunnan. The out-of-school young people in Yunnan exhibited 1) limited knowledge about HIV transmission and prevention, 2) a high prevalence of unprotected sexual activity, 3) high exposure to illicit drugs and alcohol use and a high prevalence of drug use in themselves, and 4) limited access to health services. There is an indication of higher exposure to risk behaviours in the younger age group. The study population used multiple media, particularly television, internet and radio, to obtain information about HIV transmission and prevention, particularly in the younger age group. These media may be an effective way of reaching this population in future HIV education and prevention programs in the region.
Comparison of Gelation Time and Polyalcohol Effect on Hydrogels from Domestic and Wild Silk Fibroins
Huijing Zhao,Siyong Xiong,Mingzhong Li,Qiang Zhang,Guiyang Liu
Advances in Materials Science and Engineering , 2012, DOI: 10.1155/2012/819464
Abstract: Silk fibroin (SF) hydrogels were obtained from both domestic (Bombyx mori) and wild (Antheraea pernyi) silkworms from aqueous silk fibroin solutions at room temperature. The gelation time of the Antheraea pernyi (A. pernyi) SF solution was significantly shorter than that of the Bombyx mori (B. mori) SF solution. The secondary structures of the two kinds of hydrogels were also compared. In order to further reduce the gelation time, various amounts of polyethylene glycol (PEG) were blended with the silk fibroins of A. pernyi and B. mori. The gelation time of both A. pernyi SF and B. mori SF decreased with the increased amount of PEG. After freeze-drying, the hydrogels were characterized through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Results showed that the addition of polyalcohol did not change the main secondary structure of the hydrogels. However, the addition of polyalcohol did reduce the gelation time and triggered additional formation of β-sheets. 1. Introduction Hydrogels can maintain a distinct three-dimensional porous structure with mechanical and structural properties similar to that of many natural tissues and extracellular matrices (ECMs) and can be delivered in a minimally invasive manner [1]. Therefore, hydrogels are of interest for many biomedical applications such as tissue engineering scaffolds, controlled drug release devices, and biosensors [2]. Hydrogels can be made of either synthetic materials or naturally derived materials [3]. Among naturally derived materials, it is agreed that silkworm silk fibroin (SF) is one of the most promising biomaterials because of its excellent biocompatibility, biosafety, controllable biodegradation rates, processability, and mechanical properties [4]. Silkworm silk fibroin is excreted by domestic (B. mori) and wild (A. pernyi) silkworms. Domestic SF hydrogels are of interest for use as bone-filling biomaterials, wound dressing, and so on and have proved to be promising for healing efficacy [5–10]. Compared with B. mori SF, A. pernyi SF, the most familiar wild SF, has more advantages in terms of chemical activity and high-affinity interactions with mammalian cells [11]. A. pernyi SF is rich in amino acids having polarity and ionogenic pendant groups, which are the potential reactive sites of chemical reactions. In terms of amino acids, A. pernyi SF has more Ala, Asp, and Arg and less Gly than does B. mori. Further, A. pernyi SF also has abundant alkaline amino acids (Arg and His) and the tripeptide sequence Arg-Gly-Asp (RGD), which is known to be
The Relationship between Secondary Structure and Biodegradation Behavior of Silk Fibroin Scaffolds
Yongpei Hu,Qin Zhang,Renchuan You,Lingshuang Wang,Mingzhong Li
Advances in Materials Science and Engineering , 2012, DOI: 10.1155/2012/185905
Abstract: Silk fibroin has a unique and useful combination of properties, including good biocompatibility and excellent mechanical performance. These features provided early clues to the utility of regenerated silk fibroin as a scaffold/matrix for tissue engineering. The silk fibroin scaffolds used for tissue engineering should degrade at a rate that matches the tissue growth rate. The relationship between secondary structure and biodegradation behavior of silk fibroin scaffolds was investigated in this study. Scaffolds with different secondary structure were prepared by controlling the freezing temperature and by treatment with carbodiimide or ethanol. The quantitative proportions of each secondary structure were obtained by Fourier transform infrared spectroscopy (FTIR), and each sample was then degraded in vitro with collagenase IA for 18 days. The results show that a high content of β-sheet structure leads to a low degradation rate. The random coil region in the silk fibroin material is degraded, whereas the crystal region remains stable and the amount of β-sheet structure increases during incubation. The results demonstrate that it is possible to control the degradation rate of a silk fibroin scaffold by controlling the content of β-sheet structure. 1. Introduction Silk fibroin is a natural protein produced by the domestic silkworm Bombyx mori, which is composed of a heavy-chain (H-chain, 350?kDa), light-chain (L-chain, 25?kDa), and an accessory protein (30?kDa). The amino acid composition of silk fibroin from Bombyx mori consists primarily of glycine, alanine, and serine [1, 2]. The three simple amino acids form the crystalline regions of silk fibroin, while the amino acids with bulky and polar side chains form the amorphous regions [3]. The silk polymorphs include silk I, silk II, and an air/water assembled interfacial silk III [1, 4]. The molecular conformation of silk II is antiparallel β-sheet structure. Silk fibroin has been used for centuries in production of textiles and clinical sutures [5]. Silk fibroin materials can support the attachment, proliferation, and differentiation of primary cells and cell lines [6–8] and is easily prepared as films [9], porous scaffolds [10], gels [11], and mats [12]. The impressive cytocompatibility and malleability of SF materials make silk a popular starting material for tissue engineering scaffolds used in skin, bone, blood vessel, ligament, and nerve tissue regeneration [13–15]. An ideal tissue engineering scaffold is nonimmunogenic and nontoxic but is biocompatible and supports cell adhesion, proliferation, and

WANG Fuli,LI Mingzhong,

自动化学报 , 1999,
Abstract: 1多层前向神经网络建模考虑如下的多输入多输出系统y(k)=f(y(k-1)T,y(k-2)T,…,y(k-p)T,u(k-1)T,u(k-2)T,…,u(k-q)T).(1)上式中u(k)∈Rm,y(k)∈Rn分别为系统的输入输出;p,q为系统的阶次...
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