Kyung Sik Oh

Antimicrobial Effects of Ag Doped Hydroxyapatite Synthesized from Co-Precipitation Route

Co-precipitation route was adopted to synthesize Ag doped hydroxyapatite (HAp) to achieve the homogenous distribution of silver. The washing of the precipitate, which is essential in stabilizing HAp but accompanies inevitable loss of Ag, was avoided and the reaction was carried out under off-stoichiometric Ca excess environment. The co-precipitation route enabled successful synthesis of HAp with the incorporation of silver as high as ~ 4%. The minimum inhibitory concentrations (MIC) against E.Coli. and S.Aureus were found to decrease with the increase of silver contents. The in vitro antimicrobial effect was not as strong as ion-exchanged Ag-HAp with similar silver contents, which was ascribed to the relative shortage of silver release in the initial period.

Effect of Fabrication Processes on the Antimicrobial Properties of Silver Doped Nano-Sized HAp

In fabrication of antimicrobial hydroxyapatite (HAp) doped with s ilver, the influences of particle size and drying route were investigated and discussed in relation with silver contents. Stronger antibiotics require as much silver as possible to be doped in HAp. In the introduction of silver ion through ion-exchange process, there were two critical experimental steps for the increase of silver content. By eliminating the supernatant solution through sublim ation route, the formation of agglomerates was minimized. And fine nano-particles were obtaine d by rapid stirring during precipitation. These two steps contributed to the great surface are a of HAp and as a result, 4.87% of silver was introduced. The corresponding antimicrobial properties were also found to be the strongest in this work.

Cytotoxicity and Antimicrobial Effect of Ag Doped Hydroxyapatite

In the synthesis of antimicrobial hydroxyapatite doped with silver, the amount of silver is the critical element affecting its properties. And also depending on the synthesis route, not only the amount of silver but also the release behavior was found to be altered. The cytotoxicity, antimicrobial effects and stability of effects were observed with Ag doped hydroxyapatite fabricated through various routes. The results suggested that the optimal antimicrobial property with none or mild cytotoxicity may be produced by modulating not only the doped silver amount but also their shape and synthesis route.

Functional scaffolds of bicontinuous, thermoresponsive L3-phase silica/hydroxyapatite nanocomposites

Silicified L3-poly(N-isopropylacrylamide)/hydroxyapatite nanocomposites have been prepared by the integration of a thermosensitive polymer and heterogeneous continuity in a 3-D interconnected porous structure for highly controlled drug release without initial burst release during step-wise temperature changes, and the in-vitro cytotoxicity test for biocompatibility is demonstrated.

Effect of Ag-Doped Hydroxyapatite as a Bone Filler for Inflamed Bone Defects

Silver (Ag)-doped hydroxyapatite (HAp) agglomerates containing 0.15%, 1.5% and 4.3% mole % of silver among total cations, respectively, were evaluated in vitro and in vivo to explore their potential application as a bone filler with antibacterial properties. The 0.15% Ag-doped HAp was mildly cytotoxic, whereas the 1.5% and 4.3% Ag-doped HAps were moderately cytotoxic in the standard agar overlay cytotoxicity assay. The in vivo test was carried out by implanting Ag-HAps in artificial bone defects at the periapical area of both mandibular 1 molar of rats and no remarkable cytotoxicity was found unlike what was observed in the in vitro data. All of the implanted Ag-doped HAp particles, regardless of their Ag contents, allowed appropriated cellular proliferation and favorable bone repair without remarkable inflammatory reaction through 3 week healing periods, in spite of the mild delay in organization of fibrin and inflammatory reaction with the 4.3% Ag-doped HAp at the early healing phase. They supported well new bone formation with osteointegrative and osteoconductive properties. The results suggest that HAps doped with Ag up to 4.3 % of total cations can be applied for repair of infection-associated bony defects.

Nano Magnetite Particles Prepared under the Combined Addition of Urea and Ammonia

Magnetite (Fe3O4) particles were prepared for biomedical application through three different routes. Each route had the difference in the selection of pH controlling agents. Ammonia, Urea and combined use of ammonia and urea were tested in the synthesis through co-precipitation. With the combined use of urea and ammonia, the size of particles could be reduced as small as 10 nm while effectively suppressing the agglomeration among particles. The surface charge measured at physiological condition explained the good dispersion behavior of nano-magnetite particles. The superparamagnetism observed in nano magnetite particles was expected to be useful for biomedical application in the respect of magnetic localization and dispersion.

Preparation and In Vivo Studies of β-TCP Based Bone Cement Containing Polyphosphate

b-Ca3(PO4)2 (TCP) based cement combined with polyphosphate was investigated. In the bone cement composed of b-TCP, monocalcium monophosphate (MCPM) and calcium sulfate hemihydrate (CSH), effect of the amount of setting agent on workability, setting time, temperature rise and compressive strength was evaluated. The polyphosphate, which was selected as a growth enhancer, could be introduced without affecting the properties of cement. The polyphosphate containing cement was introduced at the calvarial defect in a rabbit. After three months, the defect was covered with newly formed bone, in contrast with the case of polyphosphate free bone cement. These results suggest that the bone cement containing inorganic polyphosphate can be used as effective bone filler with considerable potential of bone regeneration for bony defects.

Synthesis and Properties of Bone Cement Containing Dense ß-TCP Granules

Effort was made to enhance the compressive strength and to suppres temperature rise during setting of β-Ca3(PO4)2 (TCP) based cement through the control of powder to liquid ratio. To increase the powder to liquid ratio, highly dense granules of β-TCP with the size around 300 μm were prepared and blended with monocalcium monophosphate (MCPM) and calc ium sulfate hemihydrate (CSH). Due to the decrease of the liquid necessary f or setting, compressive strength was remarkably increased from 3.9 to 20.6 MPa. The use of granular β-TCP was also affirmative in heat evolution, since temperature rise was virtually negligible during sett ing. Introduction Calcium phosphate bone cements have merits of excellent biocompatibili ty and mild heat evolution compared with the conventional polymer based cement like PMMA. Among t he various compositions of calcium phosphate cements, β-TCP based bone cement is unique in absorbability due to the metastable end product. For the number of calcium phosphate ce ments based particularly on α-TCP and tetracalcium phosphate (TeCP), hydroxyapatite (HAp) i s the end product with the variation in the degree of crystallinity and carbonation [1,2]. Since H Ap is the least soluble in most physiological conditions among calcium phosphates, it is hardly resorb ed and replaced with natural bone. On the contrary, hydroxyapatite does not participate during sett ing of β-TCP based cement and the chronic side effects can be prevented. A shortcoming of β-TCP based cement is relatively poor compressive strength around 5 MPa [3], while that of α-TCP or TTCP based cement is ranged near 50 MPa [1]. The increase of strength can be effectively a chieved through the decrease in porosity, since theoretical prediction indicates that strength is proportional to the inverse of porosity [4]. Less liquid as possible should be used to decrease the porosity. I n this work, highly dense and coarse (~300 μm) granules of β-TCP were prepared and introduced to decrease the volume of liquid necessary for setting. Difficulty in obtaining dense β-TCP is the limitation of sintering temperature. Densification should be completed below the transformation temperature to α-TCP, since intervention of α-TCP is not desirable due to its chemical reactivity and fragi lity. Therefore dense green body is desirable to be sintered under this limited sintering temperature. Colloidal sedimentation was adopted to prepare such a dense green body. Materials and Methods β−TCP (Ca3(PO4)2) powder was synthesized based on the N. Kirvak’s recipe [5]. 0.4 M of Ca(NO3)2 and 0.14 M of (NH4)2HPO4 solutions were reacted at 40 C. The volumes of solutions were prepared so that molar ratio of Ca/P is 1.4. The precipitate was separated from supernatant and dried in the oven. Through the calcinations at 900 C for 1 h, the precipitate transformed to β−TCP. The slurry was prepared through dispersion of β−TCP powder in distilled water with 0.2 ml of Darvan C per gram of powder. Cloudy state of the slurry was verifi ed to ensure dense settling of sediments. Decomposable net was introduced during sedimentation for the ease of breakdown after sintering. After drying, the sediment was fired at 1000 C for preliminary consolidation. The fired sediments were crushed and sieved to obtain granules of sizes betwe en 300~450 μm. The collected granules were fired again at 1180 C for further densification. 41.7 g of dense β-TCP granules were Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 237-240 doi:10.4028/www.scientific.net/KEM.254-256.237

Effect of Storage Conditions Prior to Mixing of β-TCP Based Bone Cement on the Reaction Products and the Setting

β-tricalcium phosphate (β-TCP) based cement features unique biodegradability and mild temperature rise as a material for bone reconstruction. However, the bone cement often raises a shelf life issue and therefore study was made focusing on the temperature and humidity during storage. With the increase of storing days, the density and compressive strength of hardened cement were found to drastically decrease for the cement powder stored in a mixed state. In addition, the setting property was finally lost at the same time. Such a degradation was more evident at higher temperature and was the result of the formation of dicalcium phosphate anhydrous (DCP) instead of dicalcium phosphate dehydrate (DCPD) during the storage. On the contrary, for the cement stored in an unmixed state, very slight changes were detected in density, compressive strength and setting time with the increase of storing days even if the powders were kept in a humid environment. In the unmixed ones, DCP was not precipitated regardless of the storing temperature. Discussion was made on the condition for precipitating either DCPD or DCP in terms of the amount of water supplied during setting. Practically the work suggested that the β-TCP based cement needs to be conserved at lower temperature and in dry environment as possible to effectively increase the shelf life.

Base-Coated Zirconia Brackets for Orthodontics

Yttria and iron co-doped tetragonal zirconia polycrystals ((Y, Fe)-TZPs) were investigated to evaluate the feasibility for the ceramic bracket application. Presintered the (Y,Fe)-TZPs brackets were machined, abraded and coated with granule spray containing 10~50 wt% of flux. Finally, the base-coated brackets were sintered. Roughness of the coated surface was decreased to 13 um and 10 um when the flux content was 30 wt% and 50 wt%, respectively. It may be due to the fusion and the collapse of the granules as a result of the high amount of flux. Better adhesion to the base surface of the brackets and irregular shape were observed by raising the amount of flux in the slurries. Wetting angle of ethylene glycol droplet on the (Y,Fe)-TZP bare surface was determined to be 41.85°, however, the angle became 0° after the granule spraying treatments. The (Y,Fe)-TZP brackets exhibited uniform embossed base and good wetting. The newly developed base-coated bracket could be highly applicable to enhance retention and to reduce adhesive resin remnant during the bracket debonding.