[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to investigate bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid (SBF). Calcium phosphates were electrodeposited on commercially pure titanium substrates in the modified SBF at 60 °C for 1 h maintaining the cathodic potentials of −1.5 V, −2 V, and −2.5 V (vs. SCE). Subsequently, the calcium phosphate coatings were transformed into apatites during immersion in the SBF at 36.5 °C for 5 days. The apatites consisted of needle-shaped crystallites distributed irregularly with different grain sizes. As the coatings were electrodeposited at higher cathodic potential, the crystallite of the apatites got denser and the grain sizes of the apatites became bigger during subsequent immersion in the SBF. However, as the coatings were electrodeposited at higher cathodic potential, the coatings were transformed into apatites with lower crystallinity and the Ca/P atomic ratio of the apatites got higher than 1.67, that of stoichiometric hydroxyapatite, after subsequent immersion in the SBF. In addition, CO32− ions contained in the modified SBF were incorporated in the calcium phosphate coating during electrodeposition and had an influence on transforming the calcium phosphate into bonelike apatite during subsequent immersion in the SBF showing that CO32− incorporated in the apatites disturbed crystallization of the apatites. These results revealed that the coating electrodeposited at −2.0 V (vs. SCE) in the modified SBF containing CO32− ions was the most bioactive showing transformation into carbonate apatite similar to bone apatite.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to develop a novel artificial nerve conduit and to evaluate its efficiency based on the promotion of peripheral nerve regeneration in rabbits.
The nerve conduit was made of a poly (l-lactide-co-glycolic acid)-coated collagen tube filled with collagen gel. The conduits were implanted into a 15 mm gap in the peroneal nerves of five rabbits. On the contralateral side, the defects were bridged with collagen-filled vein grafts.
Twelve weeks postoperatively nerve regeneration was superior to the vein graft in the PLGA-coated collagen tube, both morphologically and electrophysiologically.
The results indicate the superiority of the PLGA-coated collagen tube over vein grafts. Furthermore, they show that entubulation repair with this type of tube can support nerve regeneration over a nerve gap distance of at least 15 mm.
Preview · Article · Feb 2006 · Journal of Cranio-Maxillofacial Surgery
[Show abstract][Hide abstract] ABSTRACT: The aim of this in vitro study was to evaluate the suitability of using chitosan, poly (lactide-co-glycolide) (PLGA), and polymethyl methacrylate (PMMA) to control the release of chlorhexidine digluconate (CHX) from a prototype of controlled release drug device for root canal disinfection.
Four different prototypes with different formulations were prepared. Group A (n = 12): the device (absorbent paper point) was loaded with CHX as control. Group B (n = 12): same as group A, but the device was coated with chitosan (Texan MedTech). In Groups C and D, the device was treated in the same way as group A and then coated 3 times with 5% PMMA (Group C, n = 12, Aldrich), or coated 3 times with 3% PLGA (Group D, n = 12, Sigma). The devices were randomly allocated to experimental groups of 12 each. All the prototypes of controlled release drug device were soaked in 3 mL distilled water. The concentrations of CHX were determined using a UV spectrophotometer. The surface characteristics of each prototype were observed using a scanning electron microscope.
The result showed that release rate of CHX was the greatest in the noncoated group, followed by the chitosan-coated group, the PLGA-coated group, and the PMMA-coated group (P < 0.05). Pores were observed on the surface of the prototypes that were coated with PLGA and PMMA. When the pore size was smaller, the release rate was lower.
These data indicate that polymer coating can control the release rate of CHX from the prototypes of controlled release drug device.
[Show abstract][Hide abstract] ABSTRACT: The size and shape of magnetic chitosan particles were found to be dependent on both the barium ferrite/chitosan (BF/C) ratio and viscosity of a chitosan solution. The saturation magnetization of magnetic chitosan particles varied directly with the BF/C ratio, while coercivity remained almost constant. Notably, incorporated chitosan was shown to exert substantial activity with regard to low cytotoxicity and high heating rate.
Full-text · Article · May 2005 · Journal of Magnetism and Magnetic Materials
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to prepare the magnetic polymer composite particles with high ferrite content by encapsulating barium ferrite powders with alginate and investigate their physical and biological properties. The magnetic Ca-alginate composite particles were manufactured by adding barium ferrite-alginate slurry dropwise to a CaCl<sub>2</sub> solution. The final product was then completely cleaned and dried. Average size (0.1∼1 mm in diameter) of magnetic composite particles was dependent on the ratio of barium ferrite to alginate. The degree of swelling of magnetic Ca-alginate particles was increased as pH increased in aqueous media. The magnetic polymer composite particle was found to maintain high coercivity. The saturation magnetization for the magnetic Ca-alginate composites increased with the increase in the barium ferrite/alginate ratio. The self-heating induced by hysteresis loss under an alternating magnetic field was measured as a function of barium ferrite/alginate ratio in distilled water. The agar overlay test indicated a relatively high cell viability for the L929 cell line upon contact with the magnetic composite particles.
Full-text · Article · Aug 2004 · IEEE Transactions on Magnetics
[Show abstract][Hide abstract] ABSTRACT: The goal of periodontal treatment is not only to arrest the progression of the disease but also to promote the functional, esthetic regeneration of the periodontium. Flap operation, bone graft, guided tissue regeneration, growth factors and bone morphogenetic protein have been used for this purpose. Among these techniques of regeneration, alloplastic graft, especially calcium phosphate is getting more attention recently.
[Show abstract][Hide abstract] ABSTRACT: This study examines the effect of non-ionic surfactants on surface hydrophilicity and detail reproducibility of die stone for hydrophilic polyvinyl siloxane impression materials. Hydrophilic polyvinyl siloxane impression materials were prepared with a polydimethylsiloxane composition and non-ionic surfactants. The surfactants used were nonylphenoxy poly(ethyleneoxy) ethanol homologs of varying ethyleneoxy chain length. These homologs are designated NP4, NP6, and NP10 according to the mole number of ethyleneoxy group of 4, 6, and 10, respectively. The contact angle, consistency, linear dimensional accuracy, and detail reproducibility for hydrophilic polyvinyl siloxane impression materials were tested. The non-ionic surfactants used in this study contain a silicone-loving group (nonylphenoxy group) which makes the surfactant dispersible in the silicone prepolymer. The dispersion size of these surfactants in polyvinyl siloxane prepolymers was dependent on the HLB of each surfactant. The more hydrophobic (silicone-loving) a surfactant is, the smaller the dispersion size is obtained. The incorporation of non-ionic surfactant into polyvinyl siloxanes enhanced their surface hydrophilicity and consequently led to significant reduction in contact angles. Significant differences in contact angle were found among the samples (P<0.05). The contact angle was lowest when NP4 was incorporated even though NP4 is less hydrophilic than NP6 and NP10. This implies that the exposed surfactant concentration on the surface was highest when NP4 was used. The consistency and linear dimensional accuracy of surfactant-modified silicone impression materials were not affected by the type of surfactants used in this study. However, NP4-modified polyvinyl siloxane impression material showed the highest quality reproduction of the thinnest line, indicating highest wettability with gypsum slurry among the samples. We concluded that the surface concentration of surfactant on the silicone impression material was a crucial factor in determining surface hydrophilicity. The surface hydrophilicity of surfactant-modified silicone impression materials was of major relevance for the detail reproduction of die stone.
No preview · Article · Nov 2003 · Colloids and Surfaces A Physicochemical and Engineering Aspects
[Show abstract][Hide abstract] ABSTRACT: The effect of interfacial crosslinking on miscibility behavior in blend systems of isocyanate-functionalized poly(Bu methacrylate) (PBMA) and a carboxylic alkali-sol. resin, poly(styrene/α-methylstyrene/acrylic acid) (SAA), was studied with different di-Me m-isopropenylbenzyl isocyanate (TMI) concns. For the blend films of pure PBMA and SAA, both theor. anal. and direct observation showed immiscibility between PBMA and SAA. For the blend systems of isocyanated PBMA and SAA, Fourier transform IR spectra and gel permeation chromatog. analyses qual. showed the crosslinking between the isocyanate group in isocyanated PBMA and the carboxylic group in SAA. Two tan δ peaks were shown in the blend system of SAA and isocyanated PBMA contg. low concns. of TMI (from 0 to 5 wt %), and the span of the two peaks became shorter as the TMI concn. increased. For a high TMI concn. (7 wt %), only one tan δ peaks was obsd. This result means the interfacial crosslinking between isocyanated PBMA and SAA occurred fully, and thus the miscibility between two polymers was significantly improved. As these results showed, the tensile strength of the blend film of isocyanated PBMA and SAA was higher than that of pure PBMA and SAA. [on SciFinder(R)]
No preview · Article · Oct 2003 · Journal of Applied Polymer Science
[Show abstract][Hide abstract] ABSTRACT: A styrene miniemulsion was prepd. using carboxylated polyurethane as the sole costabilizer and sodium dodecyl sulfate as the surfactant. The effects of the amt. of carboxylated polyurethane, the amt. of the initiator and surfactant, the presence of a water-phase inhibitor (sodium nitrite), and the reaction temp. on the kinetics of the miniemulsion polymn. were investigated. The evolution of the particle size during the polymn. was measured. The results show that the polymn. rate was proportional to the 0.21 power of the surfactant concn. and the 0.30 power of azobisisobutyronitrile. The droplet nucleation and homogeneous nucleation were found to be coexistent in the polymn. The hydrophilicity of the particle surface plays a key role in the nucleation of the particle and, therefore, has an important effect on the kinetics of the polymn. [on SciFinder(R)]
No preview · Article · Mar 2003 · Journal of Applied Polymer Science
[Show abstract][Hide abstract] ABSTRACT: The effects of miscibility enhancement between polystyrene (PS) and poly(ethylene-co-acrylic acid) (EAA) on dynamic mech. properties, barrier property, and tensile strength were investigated. Ethylene-modified latexes were prepd. by the emulsion polymn. of styrene using EAA, [Mn: 18 800; acid no.: 140], as a polymeric emulsifier. The EAA-grafted-PS in-situ-formed during the emulsion polymn. lead to the improvement of miscibility between PS and EAA. The dynamic mech. properties of the ethylene-modified PS films exhibited a single glass transition temp. (Tg) value, thus conforming to the law of miscibility. The grafted and anchoring EAA mols. onto PS particles resulted in significant increase of chem. resistance. Addnl., the tensile strength property was improved for the ethylene-modified PS system due to the enhanced compatibility between PS and EAA, compared with simple blends. [on SciFinder(R)]
No preview · Article · Jul 2002 · Colloids and Surfaces A Physicochemical and Engineering Aspects
[Show abstract][Hide abstract] ABSTRACT: The mechanism of film formation of emulsifier-free monodisperse poly(n-butyl methacrylate) (PBMA) latex in the presence of postadded alkali-soluble resin (ASR), namely poly(styrene/alpha-methylstyrene/acrylic acid) (SAA) was followed using atomic force microscopy (AFM). The film morphology and peak-to-valley distance (Δz) of latex particles in the film was monitored at different annealing temperatures as a function of annealing duration. The Δz of the PBMA particles in films containing SAA was found to be higher than those in the pure PBMA films. The AFM results suggest very strongly the formation of a hard surface layer of SAA over the soft PBMA particle, and the migration of free SAA to the latex film surface during annealing. The SAA layer adsorbed on and surrounding each PBMA particle retards the viscoelastic flow of the PBMA particles and slows down the gradual coalescence of the particles in film formation. Annealing at high temperature, the PBMA particles fuse at a faster rate than the SAA due to its lower T(g) compared to that of SAA. The difference in the rates of fusion of the SAA and PBMA phases leads to the formation of indentations on individual particles at high annealing temperature and long annealing duration.
No preview · Article · Feb 2000 · Macromolecular Symposia
[Show abstract][Hide abstract] ABSTRACT: Ethylene-modified latexes were prepared by emulsion polymerization of styrene and n-butyl methacrylate using ethylene-acrylic acid (EAA), [M(n): 18,800, acid number: 140], as a polymeric emulsifier respectively. EAA containing 20% portion of acrylic acid could form aggregates like micelles and the solubilization ability of the aggregates were dependent on the electrolyte concentration above 100% degree of neutralization of EAA. The polystyrene (PS) latexes prepared using EAA showed small particle size and monodispersed particle size distribution in the presence of excess neutralizing agent or relatively high content of electrolyte. The EAA improved the barrier properties of ethylene-modified poly(n-butyl methacrylate) (PBMA) films.
No preview · Article · Feb 2000 · Macromolecular Symposia
[Show abstract][Hide abstract] ABSTRACT: Free-radical terpolymn. of α-methylstyrene/styrene/acrylic acid (AMS/ST/AA) in a continuous stirred tank reactor (CSTR) was studied theor. and exptl. A series of reactions were conducted to investigate the effect of the reaction temp., residence time, solvent contents, initiator concn., chain-transfer agent level, and different monomer compns. on the mol. wt. distribution (MWD). The math. model based on "the instantaneous property method (IPM)" and the pseudokinetic rate const. method was introduced and modified to predict the MWD of the bulk terpolymer produced in a CSTR. The effects of process variables were included in the math. model. Extensive comparisons were made between the theor. results and exptl. values. The rate of the free-radical terpolymn. of AMS/ST/AA was comparatively slow and it was found that the concn. of α-methylstyrene had a strong influence on the mol. wt. and polydispersity of the MWD. This presumably reflected the existence of a normal biomol. termination rate and a slow propagation rate due to steric hindrances at the doubly substituted vinyl carbon atom or transfer of the allylic hydrogen from the α-Me group. Good agreement was obtained between calcd. MWD and the exptl. one by assuming that the disproportionation termination of free radicals was the dominant chain-stoppage mechanism. [on SciFinder(R)]
No preview · Article · Jan 2000 · Journal of Applied Polymer Science
[Show abstract][Hide abstract] ABSTRACT: The effect of alkali-soluble resin (ASR) postadded to emulsifier-free monodisperse poly(n-butyl methacrylate) latexes (PBMA) on the surface properties of the latex films formed was investigated using the contact angle method. The contact angles of a probe liquid (containing 50:50 wt % ethylene glycol and water) on the film surface were determined as a function of the annealing temperature of the film and the annealing duration. The ASR, poly(styrene/α-methylstyrene/acrylic acid), was found to exude to the air/polymer interface after annealing, as monitored using FTIR−ATR. Thus the surface properties of the films were dependent on the concentration of the ASR employed, the annealing temperature, and the duration. Annealing the film at a temperature approximately equal to the Tg of ASR allows them (ASR) to undergo unrestricted migration to the film surface and also to expose the hydrophobic region of their chains to the surface. The more hydrophobic character of the film annealed at 150 °C with a higher contact angle as compared to that at 50 °C is a result of the change in chain conformation of the ASR at the surface brought about by annealing. Also, the results illustrate that the hydrophobic−hydrophilic character of the PBMA−SAA film surface can be changed readily by merely adjusting the annealing temperature.