Browsing by Author "Liu, DM"

Now showing 1 - 9 of 9

Electrophoretic deposition forming of porous alumina membranes
(1999-07-09)
Chen, CY
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
An electrophoretic deposition (EPD) technique is used to prepare porous alumina membranes. The deposition kinetics which are conventionally derived based on a mass conservation law have been modified in terms of the thickness of the deposited layer. This modification allows the porosity evolution of the membrane to be predicted under a variety of EPD processes. A transition in deposition from linear to parabolic kinetics is observed which has been further verified by a subsequent microstructure examination. The deposited layers are increasingly uniform and dense in structure with increasing deposition time over the parabolic kinetic regime; whilst a more porous packing is observed during the initial deposition time period, corresponding to the linear kinetic regime. The microstructural evolution of the EPD membranes appears to agree well with the porosity equations derived based on an analytical combination of both experimentally-derived formula and the corresponding kinetic model. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
Influence of the aspect ratio of bioactive nanofillers on rheological behavior of PMMA-based orthopedic materials
(2004-10-15)
Liu, TY
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this investigation, calcium-deficient hydroxyapatite (CDHA) nanocrystals with needle-like geometry were synthesized and incorporated with Poly(methyl methacrylate), PMMA, to form CDHA-PMMA nanocomposites. Rheological behaviors of the PMMA-CDHA melting suspensions were systematically investigated in terms of solid loading and aspect ratio of the CDHA nanoparticles. The maximum solid loadings of nano-CDHA particles with aspect ratios of 7.2, 10.4, and 17 were determined to be 28, 31, and 57%, respectively. An increase in solid concentrations causes pronounced shear-thinning behavior. This result suggests that a strong interaction, including Van der Waals attraction and mechanical interlocking, between the nano-CDHA particles makes the nanocomposite mixture more non-Newtonian. Furthermore, it was found that packing efficiency and yield strength in the suspension were strongly influenced by the aspect ratio, especially above the critical value of 8.8. The obtained critical aspect ratio and solid content provide not only appropriate design in the PMMA-CDHA polymeric suspension for fabrication process but also optimal conditions for the fabrication of orthopedic devices via injection molding or extrusion. (C) 2004 Wiley Periodicals, Inc.
Manipulation of nanoneedle and nanosphere apatite/poly(acrylic acid) nanocomposites
(2005-04-01)
Liou, SC
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Colloidal apatitic nanosphere of 2-5 nm in diameter was synthesized in the presence of poly(acrylic acid), PAA. PAA, which has long been recognized as an inhibitor in the synthesis of hydroxyapatite, is used as a structure-directing agent for the synthesis of calcium-deficient apatite (CDHA) in this study. Experimental observation suggests a critical amount of the low-molecular-weight PAA, above which morphological evolution of CDHA nanoparticles from needle to sphere was observed. This reveals that the PAA acts as an inhibitor for the growth of CDHA crystals. Further incorporation of PAA of high molecular weight formed a highly optically transparent nanocomposite, even with the nanospherical apatite loading up to 35 wt%, suggesting no agglomeration. This was further justified through transmission electron microscopy (TEM), where the CDHA nanospheres were uniformly distributed in the PAA-CDHA nanocomposites. No interfacial crevices were visually observed, indicating a highly compatible interface between the inorganic CDHA and organic PAA phase. (c) 2005 Wiley Periodicals, Inc.
On the study of BSA-loaded calcium-deficient hydroxyapatite nano-carriers for controlled drug delivery
(2005-09-20)
Liu, TY
;
Chen, SY
;
Liu, DM
;
Liou, SC
;
材料科學與工程學系
Calcium-deficient hydroxyapatite (CDHA) nano-crystals incorporated with bovine serum albumin (BSA) to form BSA-loaded nano-carriers were synthesized via both in-situ and ex-situ processes. Amount of BSA uptake by the CDHA nanocrystals and subsequent release behaviors of the BSA-loaded nano-carriers were investigated. The amount of BSA uptake by CDHA decreases with increasing pH but a larger amount was observed in the ex-situ compared to in-situ process above pH = 8.0. The release profile showed a bursting behavior for the nano-carrier prepared via the ex-situ process, which is probably due to the desorption of BSA molecules. In contrast, for the sample synthesized via the in-situ process at a higher pH level, a slower release profile without bursting behavior due to the dissolution of the BSA-incorporated CDHA crystal is seen from high solution TEM that indicates different extent of interaction between BSA and CDHA. On the other hand, for the nano-carriers prepared via the same process at lower pH level, a two-stage release profile was detected. An initial bursting release is due to the desorption of BSA from the CDHA surface, followed by a slow release as a result of the dissolution of the BSA-incorporated nano-crystals along its c-axis direction. (c) 2005 Elsevier B.V. All rights reserved.
Phase development and structural characterization of calcium phosphate ceramics-polyacrylic acid nanocomposites at room temperature in water-methanol mixtures
(2004-12-01)
Liou, SZC
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Calcium phosphate ceramics (CPCs) were prepared via an in-situ formation in the presence of polyacrylic acid (PAA) polymer under water-methanol (WM) mixture at room temperature. The PAA polymer was employed as both structure-directing agent and crystallization retardant to manipulate the development of resulting CPCs nano-crystallites which are observed to show a core-shell configuration with a thin layer of PAA molecules. A resulting phase evolution map with respect to the developing phases of calcium-deficient hydroxyapatite (CDHA), beta-tricalcium phosphate (beta-TCP), and an intermediate amorphous calcium phoshate (ACP) that were structurally and spectroscopically identified, was constructed in terms of fractions of water-to-methanol proportions and concentration of PAA. It is found that for the solutions in both water-rich and methanol-rich regions, pure CDHA and beta-TCP instead of intermediate ACP phase can be developed irrespective of the concentration of PAA, respectively. For conditions in between, i.e., with methanol fractions of 15%-90%, ACP appeared only when the PAA fell in a limited concentration range. (C) 2004 Kluwer Academic Publishers.
Preferential growth of thin rutile TiO2 films upon thermal oxidation of sputtered Ti films
(2002-01-01)
Ting, CC
;
Chen, SY
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Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Thin rutile TiO2 films with (200) preferred orientation were fabricated by thermal oxidation of sputtered Ti metal films on a fused silica substrate. Experimental results indicate that the preferential crystal growth of (200)-oriented TiO2 is determined by the competition between surface free energy and strain energy. The highly crystalline Ti film with (002) orientation has a greater tendency to promote the growth of (200)-oriented TiO2 However, for the amorphous and low crystalline Ti films, orientation of the crystallites evolved in the resulting TiO2, film tends to be randomly distributed. The extent of preferential crystal growth of TiO2 (200) plane can be enhanced by decreasing the annealing temperature or the thickness of Ti film. (C) 2002 Elsevier Science B.V All rights reserved.
Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films
(2000-10-15)
Ting, CC
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A dense rutile TiO2 thin film was synthesized by the thermal oxidation of a sputtered titanium metal film in ambient air. The effects on optical properties of TiO2 films of the crystal structure and microstructural evolution at various oxidation temperatures were investigated. The Ti films transformed into single-phase rutile TiO2 at temperatures greater than or equal to 550 degrees C without going through an anatase-to-rutile transformation. Instead, an additional crystalline Ti2O phase was detected at 550 degrees C only. An increase in the oxidation temperatures ranging between 700 and 900 degrees C led to an increase in both the refractive index and absorption coefficient, but a decrease in the band gap energy (E-g). According to the coherent potential approximation model, the band gap evolution of the oxidized films was primarily attributed to the electronic disorder due to oxygen deficiency at a higher oxidation temperature rather than the presence of an amorphous component in the prepared films. (C) 2000 American Institute of Physics. [S0021-8979(00)07920-2].
Study on drug release behaviour of CDHA/chitosan nanocomposites-Effect of CDHA nanoparticles
(2006-05-01)
Liu, TY
;
Chen, SY
;
Li, JH
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Liu, DM
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材料科學與工程學系
To explore the effect of nanofiller-polymer interaction on the drug release behaviour from a monolithic membrane prepared by Ca-deficient hydroxyapatite (CDHA)/chitosan nanocomposite, release kinetics was investigated in terms of different synthetic processes, i.e. in situ and ex situ routes, and various amounts of CDHA. It was found that a higher value of diffusion exponent (n) was obtained for the membranes in situ synthesized compared with those ex situ prepared. In addition, the it value of the membranes in situ synthesized increased with increasing CDHA amount, which remained in the range below 10wt.%. However, as CDHA content exceeded 30%, the n value remained constant. It indicates that the drug diffusion mechanism is altered by the CDHA-chitosan interaction which is strongly influenced by both the synthesis process and the concentration of the CDHA nanofiller in the membrane. On the other hand, a lower permeability (P) value of the membranes was observed for those prepared via the in situ process. Furthermore, P value decreased and increased with increasing CDHA amount in the range below and above 10 wi.%, respectively. It demonstrates that CDHA nanofillers act either diffusion barrier or diffusion enhancer for the CDHA/chitosan membranes, which is determined by the concentration of CDHA nanofiller and the synthesis route of nanocomposite. (c) 2006 Elsevier B.V All rights reserved.
Synthesis and characterization of needlelike apatitic nanocomposite with controlled aspect ratios
(2003-10-01)
Liou, SC
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Calcium-deficient apatitic (cd-HA) crystals with core-shell nanostructure with needlelike shape, 5-10nm in diameter and 2080 nm in length. were prepared via an in situ formation in the presence of polyacrylic acid (PAA) under aqueous solution of different pH values. ranging from 9 to 11. Nanostructure of the resulting crystals showing a core-shell configuration with a thin layer of PAA shell of about I rim thickness was investigated. Aspect ratio (AR) of the needlelike composite was found to depend on the concentration of the PAA and solution pH. At lower solution pH crystal growth was inhibited, i.e., leading to a decreased AR, with increase of PAA concentration. while an increased AR was detected at higher solution pH, suggesting a preferential growth of the cd-HA nanocrystals. Mechanism of such preferential growth was tentatively proposed and is suggested to correct PAA adsorption alone the long axis of the needlelike nanoparticles. (C) 2003 Elsevier Science Ltd. All rights reserved.