Browsing by Author "Liou, SC"

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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.
Structural characterization of nano-sized calcium deficient apatite powders
(2004-01-01)
Liou, SC
;
Chen, SY
;
Lee, HY
;
Bow, JS
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材料科學與工程學系
Nano-sized calcium-deficient apatitic (CDHA) crystals with Ca/P ratios from 1.5 to 1.67 were synthesized using wet chemical method and of needle-like shape with 5-10 nm in diameter and 40-50 nm in length was observed. The structural environment of the Ca atoms in all the CDHA nano-crystals has been investigated using EXAFS, XANES and EELS. The results reveal that a maximum Fourier transform amplitude occurs at the apatite with a Ca/P ratio of 1.67 and the structural disorder increase following the sequence of 1.67 > 1.5 > 1.6 > 1.55. A similar phenomenon is also observed in both K-edge XANES and L-2,L-3-edge ELNES in the Ca atom. The structural analysis further demonstrates that different chemical and biological properties among these CDHA nano-crystals with Ca/P ratio from 1.5 to 1.67 are primarily due to the effect of stoichiometry and non-stoichiometry as compared to the structural order-disorder. (C) 2003 Elsevier Ltd. All rights reserved.
Structural characterization of room-temperature synthesized nano-sized beta-tricalcium phosphate
(2004-07-01)
Bow, JS
;
Liou, SC
;
Chen, SY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A simple route for synthesizing nano-sized beta-tricalcium phosphate (beta-TCP) at room temperature has been developed in methanol solvent. The phase evolution from CaHPO4, intermediate amorphous calcium phosphate (ACP) phases (including ACP1 and ACP2 with different structures) to final beta-TCP with increasing aging time was observed. The formation of beta-TCP phase is favored due to the incorporation of carbonate which can suppress the transformation of ACPI phase. High-resolution transmission electron microscopy image along [1-100] zone axis of beta-TCP reveals two types of lattice fringes (straight and wavy fringes) in beta-TCP structure due to structural imperfection. Furthermore, the observations of abnormal diffraction intensity and superlattice diffraction in selected-area diffraction patterns further confirm the chemical order-disorder characteristics in beta-TCP structure and can be used to elucidate the resorbability of beta-TCP in either in vivo or in vitro environment due to the imperfection in beta-TCP crystal. (C) 2003 Elsevier Ltd. 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.
Transformation mechanism of different chemically precipitated apatitic precursors into beta-tricalcium phosphate upon calcination
(2002-12-01)
Liou, SC
;
Chen, SY
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材料科學與工程學系
;
Department of Materials Science and Engineering
The Ca-deficient apatite (CDHA) was prepared from the precursors of (CH3COO)(2)Ca - xH(2)O, Ca(NO3)(2).4H(2)O and H3PO4, (NH4)H2PO4 to investigate the transformation mechanism of beta-tricalcium phosphate (beta-TCP). X-ray diffraction analysis shows that the development of beta-TCP is not via direct reaction between Ca and P for all the different combinations between Ca and P precursors. The activation energy of beta-TCP formation with (NH4)H2PO4 as precursor was higher than that with H3PO4. Following the Johnson-Mehl-Avrami equation, the reaction kinetics of beta-TCP phase formation is found one-dimension growth with interface-controlled and diffusion controlled growth depending on the annealing temperature. There exists a transition between 750 degreesC and 825 degreesC, and the transition rate from interface-controlled to diffusion-controlled growth is precursor-dependent. (C) 2002 Elsevier Science Ltd. All rights reserved.
Tunable growth of ZnO nanorods synthesized in aqueous solutions at low temperatures
(2006-01-01)
Hsiao, CS
;
Peng, CH
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Chen, SY
;
Liou, SC
;
材料科學與工程學系
Highly arrayed ZnO nanorods were fabricated on the Si substrate buffered with patterned ZnO film (ZnOf/Si) via wet-chemical process. The growth behavior and morphology of single-crystal ZnO nanorods (ZNs) were investigated in terms of the annealing temperatures of the sputtered ZnO film. We found that the growth morphology of ZnO nanorods is strongly dominated by the grain size of the ZnO film on the Si substrate. The ZnOf/Si substrate was annealed at above a critical temperature to promote the crystallization of ZnO phase, and high-resolution transmission electron microscopy demonstrated that both ZNs and ZnOf on Si substrate are coherent. Furthermore, the ZNs seem to nucleate from the concave tip near the grain boundary between two ZnO grains in the ZnO film because of higher surface energy. However, a higher annealing temperature may lead to the formation of a larger ZnO crystal due to the coplanar coalescence behavior of several individual ZnO nanorods. (c) 2006 American Vacuum Society.