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171.
A novel process was developed to fabricate biodegradable polymer scaffolds for tissue engineering applications, without using organic solvents. Solvent residues in scaffolds fabricated by processes involving organic solvents may damage cells transplanted onto the scaffolds or tissue near the transplantation site. Poly(L-lactic acid) (PLLA) powder and NaCl particles in a mold were compressed and subsequently heated at 180 degrees C (near the PLLA melting temperature) for 3 min. The heat treatment caused the polymer particles to fuse and form a continuous matrix containing entrapped NaCl particles. After dissolving the NaCl salts, which served as a porogen, porous biodegradable PLLA scaffolds were formed. The scaffold porosity and pore size were controlled by adjusting the NaCl/PLLA weight ratio and the NaCl particle size. The characteristics of the scaffolds were compared to those of scaffolds fabricated using a conventional solvent casting/particulate leaching (SC/PL) process, in terms of pore structure, pore-size distribution, and mechanical properties. A scanning electron microscopic examination showed highly interconnected and open pore structures in the scaffolds fabricated using the thermal process, whereas the SC/PL process yielded scaffolds with less interconnected and closed pore structures. Mercury intrusion porosimetry revealed that the thermally produced scaffolds had a much more uniform distribution of pore sizes than the SC/PL process. The utility of the thermally produced scaffolds was demonstrated by engineering cartilaginous tissues in vivo. In summary, the thermal process developed in this study yields tissue-engineering scaffolds with more favorable characteristics, with respect to, freedom from organic solvents, pore structure, and size distribution than the SC/PL process. Moreover, the thermal process could also be used to fabricate scaffolds from polymers that are insoluble in organic solvents, such as poly(glycolic acid). Cartilage tissue regenerated from thermally produced PLLA scaffold. 相似文献
172.
173.
Recent progresses of molecular imprinting in metal oxide matrices were summarized. Application of the surface sol-gel process to mixtures of organic carboxylic acids and titanium alkoxide provides ultrathin layers of titania gel (10-20 nm thick), in which molecule-sized cavities are kept intact upon removal of the organic templates. The imprinted cavity reflects the structural and functional features of the template molecule, and the enantioselective imprinting of dipeptide isomers is observed. Robustness and flexibility of the ultrathin titania layer is demonstrated by the formation of interconnected titania hollow structures. Possible practical applications and unsolved problems of this technique are discussed. 相似文献
174.
175.
Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process 总被引:3,自引:0,他引:3
YANG Donghui* HE Deping*& YANG Shangrun* . Department of Materials Science Engineering Southeast University Nanjing China . Department of Chemistry Nanjing University Nanjing China 《中国科学B辑(英文版)》2004,47(6):512-520
Metal foams, now one of research foci, are a newclass of materials with low densities and novel physi-cal, mechanical, thermal, electrical and acoustic prop-erties[1—8]. Demands from high-tech make Al alloyfoam, which has much higher specific strength than ofpure Al foam, the new development focus[9—11]. Melt foaming process is one of the approaches tofabricate Al foam and Al alloy foam and their porestructure (pore diameter and porosity) has close rela-tionship with the thermal decompo… 相似文献
176.
Mariko Kusabe Hiromitsu Kozuka Satoru Abe Hiroshi Suzuki 《Journal of Sol-Gel Science and Technology》2007,44(2):111-118
Hydroxypropylcellulose (HPC)–titania hybrid thin films were prepared by sol–gel method where titanium tetraisopropoxide Ti(OC3H7
i
)4 was hydrolyzed under acidic conditions in the presence of HPC, followed by dip-coating and drying at 120 °C for 24 h. The
viscosity average molecular weight of HPC was 55,000–70,000 or 110,000–150,000, and the TiO2/(HPC + TiO2) mass ratio ranged from 0 to 1, which was calculated on the assumption that all Ti(OC3H7
i
)4 is converted into TiO2. The films were 0.35–1.0 μm thick, transparent in visible region and opaque in ultraviolet (UV) region, where the optical
absorption coefficient in UV region increased with increasing titania content. The refractive index increased with increasing
titania content, ranging from 1.6 to 1.8 for the hybrid thin films. The pencil hardness increased from 6B to 5H, the durability
in hot water significantly increased and the contact angle of water on films increased from 35° to 89° with increasing titania
content. Crack-free films could be deposited on organic polymer substrates irrespective of titania or HPC contents, where
cracking did not occur at higher HPC contents even when the substrate was bent. 相似文献
177.
In this paper are described the main characteristics of the plasma spraying process of alumina deposits, i.e., the temperature and flow field of the plasma jets obtained with the classical spraying torches, the injection of the particles into the plasma jet, the particle surface temperature and velocities in the plasma (measured for calibrated alumina particles), and the coating generation. The measurements on the alumina particles are compared with the predictions of a mathematical model. The experimental and computed particle velocities are in rather good agreement. However, this is not the case for the particle surface temperature. Possible reasons for the discrepancy are proposed (influence of the carrier gas, thermophoretic forces, and poor penetration of the particles into the plasma core even for an injection velocity twice that of the optimal calculated one, as shown by recent measurements). Finally the correlations between the particle velocities and surface temperature, and the properties of the alumina coating (porosity, crystal structure, mechanical properties) are studied. 相似文献
178.
A novel algorithm is proposed for the fixed-node quantum Monte Carlo (FNQMC) method.In contrast to previous procedures,its "guiding function" is not optimized prior to diffusion quantum Monte Carlo (DMC) computation but synchronistically in the diffusion process The new algorithm can not only save CPU time,but also make both of the optimization and diffusion carried out according to the same sampling fashion,reaching the goal to improve each other This new optimizing procedure converges super-linearly,and thus can accelerate the particle diffusion During the diffusion process,the node of the "guiding function" changes incessantly,which is conducible to reducing the "fixed-node error" The new algorithm has been used to calculate the total energies of states X3B1 and a1A1 of CH2 as well as π-X2B1 and λ-2A1 of NH2 The singlet-triplet energy splitting (λEsT) in CH2 and π energy splitting in NH2 obtained with this present method are (45 542±1.840) and (141.644±1.589) kJ/mol,respectively The calculated 相似文献
179.
D. Duracher F. Sauzedde A. Elaissari A. Perrin C. Pichot 《Colloid and polymer science》1998,276(3):219-231
Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization
of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride
as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly
homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering
(QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of
a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without
affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided
that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell
layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease
of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic
particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle
morphology information were inferred for discussion of the polymerization mechanism of this system.
Received: 21 August 1997 Accepted: 22 October 1997 相似文献
180.
This article examines the current status of Markov processes in single molecule fluorescence. For molecular dynamics to be described by a Markov process, the Markov process must include all states involved in the dynamics and the first-passage time (FPT) distributions out of those states must be describable by a simple exponential law. The observation of non-exponential FPT distributions or other evidence of non-Markovian dynamics is common in single molecule studies and offers an opportunity to expand the Markov model to include new dynamics or states that improve understanding of the system. 相似文献