Chang Kuk You

Hydroxyapatite Coated Porous Alumina as a New Orbital Implant

Abstract. A synthetic hydroxyapatite coated porous alumina ocular orbital impla nt w s developed by polymeric sponge method in order to overcome shortcoming of current corall ine HA implant and to obtain secure attachment of extraocular muscles and fibrovascular i n-growth. It allows porous alumina skeletal to be a load bearing member and synthetic HA coat ing l yer to provide biocompatibility and long-term stability in an eye. It was found that slower heating rate of < 1°C/min at 280°C400°Cwas effective to achieve a dense porous alumina skeletal, and defects on as-sintered alumina skeletal was considerably decreased by the second coating of alumina slurry and sintering. The thickness of coated HA layer was about 20 μm with relatively good bonding to alumina skeletal. From in-vivo study, fibrovascularization was noted at periphery of the implant 2 we eks after implantation in all of the three groups, and to the center of the impla nt 4 and 12 weeks after implantation. This fibrovascularization was most predominant in 500 μm por e-sized group compared to the rest two groups. It is believed that HA coated porous alumina w ill be a good candidate for an artificial orbital implant with improved biocompatibility and long-term stabil ity.

Comparative Study of the Degradation Behavior of Mechanically Mixed and Chemically Precipitated Biphasic Calcium Phosphates

Surface morphology and degradation behavior of mechanically mixed and chemically precipitated biphasic calcium phosphate (M-BCP and P-BCP) were compared. For the M-BCP powder, commercial HA and TCP powders were used. In order to prepare P-BCP powder, precipitation method was used. The particle size of P-BCP was smaller than that of M-BCP. The disk-type specimens of each powder were prepared for the morphology comparison and degradation test. The surface morphology of sintered samples was porous in M-BCP and dense in P-BCP. The degradation test was conducted in the revised simulated body fluid (R-SBF) for 1, 7, and 21 days. Surface morphology and degradation rate of two samples were different. The weight gain in both samples increased linearly with immersion period due to apatite-like layer formation. However, the weight gain in M-BCP was much higher than that in P-BCP. The weight gain was related to the surface morphology and degradation with immersion period.

Evaluation of 5% Na2O-Incorporated Calcium Metaphosphate as a Scaffold for Tissue-Engineered Bone Regeneration

As a part of the effort to develop a suitable scaffold for tissue-engineered bone regeneration, we modified calcium metaphosphate (CMP) ceramic with Na20 and evaluated its efficiency as a scaffold. We incorporate 5% Na20 into pure CMP and prepare for an average pore size of 250 or 450 µm average pore sizes. The incorporation of 5% Na2O caused reduced compressive strength and there was no change in biodegradability. The in vitro cellular attachment and proliferation rate, however, were slightly improved. The 5% Na2O-incorporated macroporous CMP ceramic-cell constructs treated with Emdogain induced ectopic bone formation more effectively than those without Emdogain treatment. These results suggest that the incorporation of 5% Na2O into pure CMP is not effective for improving the physical characteristics of pure CMP but it is positive for improving the cellular reaction and osteogenic effect with the addition of Emdogain.

Evaluation of Hydroxyl Groups on Hydroxyapatite and Calcium Metaphosphate by Grafting TEOS and APTES

OH groups on hydroxyapatite (HA) and calcium metaphosphate (CMP) were evaluated by grafting tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethyloxysilane (3-APTES) which can bond covalently with OH group of ceramic biomaterials. The prepared HA and CMP disks were soaked in pH 2 and 5 of acidic water and ethanol solution respectively, where pH change of each solution was measured during soaking of samples. After grafting TEOS and 3-APTES on HA and CMP disks, samples were ultrasonically cleaned in distilled water and soaked in pH 5 of ethanol solution, and pH measurement was carried out in the same manner. The pH value of HA and CMP in aqueous solution at pH 2 increased with time continuously, resulting from dissolution of HA and CMP by acidic condition on surface. At pH 5 in aqueous solution, it was the same though the pH increase was smaller. In case of ethanol at pH 5 with HA, though pH value went up slightly, the curve became saturated with time, while there was no change in pH with CMP. After grafting TEOS and 3-APTES, pH values were stabilized with few changes, indicating that there was no direct chemical reaction between the acidic media and the surface of samples due to covalently grafted TEOS and 3-APTES layer. In conclusion, it was confirmed that OH group on the surface of HA was crystallographic and chemical one rather than physically adsorbed one by grafting TEOS or 3-APTES and it will serve an effective binding site for calcium and phosphate ions, or minerals.

Resorption Mechanism of Hydroxyapatite and β-Tricalcium Phosphate Coating Layer

Beta-tricalcium phosphate(β-TCP) coating layer is known to be resorbed much faster than hydroxyapatite(HA), however, there has been no report to explain the exact reason of these results. Eighty titanium discs, coated with HA(n=40) or β-TCP(n=40) by dip and spin coating method, were divided into 2 subgroups respectively; Dissolution(D, n=20) and osteoclast culture(C, n=20). The coated discs in D group were immersed in the cell culture media for 5 days, whereas, in C group, osteoclasts were seeded on the specimens and cultured for 5 days. After simple dissolution test, β-TCP coating layer showed much more cracks and denudation as compared to HA. In osteoclast culture group, mean area fraction of resorption pits in HA-C group was 11.62%, which was significantly higher than that of 0.73% in β-TCP-C group(p=0.001). In conclusion, the resorption mechanisms of HA and β-TCP coating layers were different each other in vitro study. The coated β-TCP was degraded mainly by dissolution and separation from implant, on the other hand, the HA coating layer was resorbed by osteoclastic activity.

Fabrication of Macroporous Scaffold Using Calcium Phosphate Glass for Bone Regeneration

Numerous techniques have been applied to fabricate three-dimensional sc affold of high porosity and surface area. In this study, we fabricated three-dimens ional macroporous scaffold by polymeric sponge method using calcium phosphate glass in CaO-CaF 2-P2O5-MgO-ZnO. Calcium phosphate glass slurry was prepared by suspending the glass powder in w ater, polyvinyl alcohol, polyethylene glycol and dimethyl formamide. Reticulated polyurethane s ponges were used as a template and were coated with the prepared slurry by infiltration technique several times. Calcium phosphate glass slurry was homogenously thick coated when the amounts of c alcium phosphate glass powder and polyvinyl alcohol were 67 and 8 wt%, respectively. Addition of 10 wt % dimethyl formamide as a drying control chemical additive into a slurry succ essively prevented microcrack formation. Sintering at 850 C exhibited dense microstructures as well as entire eliminati on of organic additives. When the macroporous scaffolds were transplanted subcutaneously in the dorsal surface of mice, the vascularized mesenchymal stem cells were formed in the transplanted scaffolds and the regenerated connective tissue was also formed after 4 weeks. Thes e results of the present study suggested that the fabricated macroporous scaffold is expected to be useful scaffold material for osteogenic tissue development.

Preliminary Radiological In Vivo Study of Calcium Metaphosphate Coated Ti-Alloy Implants

In order to evaluate the bone-implant integration behavior of biodegradable c lcium metaphosphate (CMP, [Ca(PO 3)2]n) coated metallic implant, as-machined, blasted, and blasted /CMP-coated Ti6Al4V screw-type implants were prepared and asepti cally implanted into male New Zealand white rabbits. CMP sol was prepared by sol-gel process and coate on each substrate by dip and spin coating. The CMP coated layer was smooth and uniform with fine grai s, compared to that of as-machined and as-blasted specimens. Each specimen was inserted i nto the defects of bilateral intratibial metaphysis bone and then followed up for 1 and 6 weeks. From the radiographs at 1 and 6 weeks after implantation, all the implants were shown to be apparent ly well integrated with surrounding bone tissue without interfacial fracture, bony resorption, or ra di lucent lines. With the combination of histological results, CMP-coated group was noticed that bony bridges were extending from the endosteum onto the implants at 6 weeks after implantation, wi th the showing good osseo-intergration compared to other two groups. Introduction The development of a stable direct bonding between bone and implant surface (osteointegration) is the critical issue for the long-term success of orthopedic and denta l impl nts. The establishment and maintenance of osteointegration depends on wound healing, repairing and remodel ing f hard tissues. The tissue response to an implant involves physical factors such as i mplant design and surface topography, and chemical factors such as composition and structure of the material surface [1]. To improve the implant fixation to a host bone, several strategies have been developed focusing on the surface modification of materials. For example, the physical surf ace modification of implants in roughness by various techniques has been attracted, because it has been de monstrated that the osteoblastic cells tend to attach more easily to rough surface [ 4], consequently increasing the bone apposition [5]. Chemical surface modifications have been also realized by cova lent attachment of an organic monolayer anchored by a siloxane network [2], and immobilization of specific adhesive peptides like arginine-glycine-aspartic acid-serine (RGDS) [3]. In addition, the implants coated with different bioactive materials such as calcium phosphates, bioactive glasses [6], diamond-like carbon, and amorphous C-N film [7] enha nced the bonding to bone. However, it has been currently reported that the coating layer w s sometimes delaminated from the substrates. Therefore, as one of the alternatives to solve this proble m, the biodegradable material coating on implants, which may allow the organism to replace the for eign material by new bone tissue in a balanced time schedule, was conductd [8]. Calcium metaphosphate (CM P, [ a(PO3)2]n) is a Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 881-886 doi:10.4028/www.scientific.net/KEM.254-256.881

Stimulatory Effect of Nano-Sized Calcium Metaphosphate Particles on Proliferation and Osteoblastic Differentiation of Human Bone Marrow Mesenchymal Stem Cells

Recently, nanomaterials have received considerable attention because of their potential applications in the biomedical field. In the present study, we investigated the effects of nano-sized calcium metaphosphate (CMP) particles (50 nm) compared with micro-sized CMP particles (200-500 nm and 10 μm) on the proliferation and osteoblastic differentiation of human bone marrow stem cells (BMSCs). BMSCs were challenged with CMP particles with different sizes for 3, 5, and 7 days. An analysis of the proliferation revealed that the nano-sized CMP particles (50 nm) stimulated the proliferation of BMSCs up to 27.79% compared to the untreated control. This stimulatory effect of the nano-sized CMP particle was dose-dependent. CMP particles appeared to adhere on the surface of BMSCs but this did not cause distinguishable morphological changes. Moreover, all CMP particles (50 nm to 10 μm) were capable of stimulating an osteoblastic differentiation of BMSCs as accessed by alkaline phosphatase (ALP) and von Kossa stainings. Further molecular analysis revealed that all the CMP particles induced an expression of osteoblast-related genes such as osteocalcin (OC) and collagen I (Col I). Taken together, our data demonstrate that nano-sized CMP particles have the potential to stimulate the proliferation and osteoblastic differentiation of BMSCs.

In Vitro Study of HA and CMP Grit-Blasted and Acid Etched of Ti Surface

Grit-blasting using bioactive HA and biodegradable CMP followed by acid etching was done. The apatite formation of prepared Ti samples was evaluated by immersion in R-SBF. And cell viability, proliferation, and differentiation were conducted using MTT assay and ALP staining. In RSBF immersion tests, non-etched HA-blasted samples showed the faster apatite-like formation than other samples. Acid etched and non-etched HA-blasted samples showed better cell viability and proliferation compared to CMP-blasted samples after 1 and 3 days. And the cell differentiation of non-etched HA-blasted samples was better compared to etched ones, and etched and non-etched CMP-blasted samples.

Effect of Acid Etching on Surface Chemistry and Microstructure of HA and CMP Grit-Blasted Ti Surface

Grit blasting using bioactive HA and biodegradable CMP followed by acid etching has been done. HNO3 and H3PO4 were used for the etching solution by controlling the concentration and etching time to know the effect on the surface chemistry and morphology of the Ti implant. Characterization of samples was done by using SEM, EDX and surface profilometer. The contents of residues on Ti surface decreased with increasing acid concentration and etching time. It was observed that the acidic etching rate of HA grits on Ti surface was faster than that of CMP grits. And HNO3 etched more rapidly the HA and CMP grits on Ti surface, compared to H3PO4. Therefore, the surface roughness of dental implants can be controlled by having appropriate combination of acid concentration and etching time.