Kwang-Bum Park

Healing of rabbit calvarial bone defects using biphasic calcium phosphate ceramics made of submicron-sized grains with a hierarchical pore structure

OBJECTIVES This study investigated the efficacy of new bone graft substitutes - biphasic calcium phosphates (BCP) made of submicron-sized grains with fully interconnected wide-range micron-scale pores in two different macrodesigns: donut shaped with a 300-400 microm central macropore (n-BCP-1) or rod-shaped (n-BCP-2)--in the healing of rabbit calvarial defects, and compared their bone-healing properties with those of various commercial bone substitutes, which included substitutes with similar BCP composition (MBCP and Osteon), anorganic bovine bone (Bio-Oss), and beta-TCP (Cerasorb). MATERIAL AND METHODS The surface morphology of the bone substitutes was investigated using scanning electron microscopy (SEM). Defects 8 mm in diameter were created in the calvaria of 30 adult male New Zealand White rabbits and were filled with six types of bone substitutes. The percentage of newly formed bone (NB%) was evaluated histomorphometrically 4 and 8 weeks after implantation. RESULTS SEM observation showed submicron-sized grains with fully interconnected micropore structures in the n-BCP-1 and n-BCP-2 groups; these groups also showed considerable new bone formation in inner micropores as well as on the outer surfaces. The n-BCP-1 group exhibited enhanced new bone formation and direct ingrowth of bone tissue with blood vessels into central pores. Histomorphometric analysis showed significantly greater NB% in the n-BCP-1 group when compared with the other groups at 4 and 8 weeks (P<0.05). CONCLUSION A new BCP ceramics made of submicron-sized grains with a hierarchical pore structure was an effective osteoconductive material for the treatment of osseous defects of rabbit calvaria.

The cytocompatibility and osseointegration of the Ti implants with XPEED® surfaces

OBJECTIVES This study evaluated cytocompatibility and osseointegration of the titanium (Ti) implants with resorbable blast media (RBM) surfaces produced by grit-blasting or XPEED(®) surfaces by coating of the nanostructured calcium. MATERIAL AND METHODS Ti implants with XPEED(®) surfaces were hydrothermally prepared from Ti implants with RBM surfaces in a solution containing alkaline calcium. The surface characteristics were evaluated by using a scanning electron microscope (SEM) and surface roughness measuring system. Apatite formation was measured with SEM after immersion in modified-simulated body fluid and the amount of calcium released was measured by inductively coupled plasma optical emission. The cell proliferation was investigated by MTT assay and the cell attachment was evaluated by SEM in MC3T3-E1 pre-osteoblast cells. Thirty implants with RBM surfaces and 30 implants with XPEED(®) surfaces were placed in the proximal tibiae and in the femoral condyles of 10 New Zealand White rabbits. The osseointegration was evaluated by a removal torque test in the proximal tibiae and by histomorphometric analysis in the femoral condyles 4 weeks after implantation. RESULTS The Ti implants with XPEED(®) surfaces showed a similar surface morphology and surface roughness to those of the Ti implants with RBM surfaces. The amount of calcium ions released from the surface of the Ti implants with XPEED(®) surfaces was much more than the Ti implants with RBM surfaces (P < 0.05). The cell proliferation and cell attachment of the Ti implants showed a similar pattern to those of the Ti implants with RBM surfaces (P > 0.1). Apatite deposition significantly increased in all surfaces of the Ti implants with XPEED(®) surfaces. The removable torque value (P = 0.038) and percentage of bone-to-implant contact (BIC%) (P = 0.03) was enhanced in the Ti implants with XPEED(®) surfaces. CONCLUSION The Ti implants with XPEED(®) surfaces significantly enhanced apatite formation, removal torque value, and the BIC%. The Ti implants with XPEED(®) surfaces may induce strong bone integration by improving osseointegration of grit-blasted Ti implants in areas of poor quality bone.

The effect of the thread depth on the mechanical properties of the dental implant

PURPOSE This study aimed to evaluate the effect of implant thread depth on primary stability in low density bone. MATERIALS AND METHODS The insertion torque was measured by inserting Ti implants with different thread depths into solid rigid polyurethane blocks (Sawbones) with three different bone densities (0.16 g/cm3, 0.24 g/cm3, and 0.32 g/cm3). The insertion torque value was evaluated with a surgical engine. The static compressive strength was measured with a universal testing machine (UTM) and the Ti implants were aligned at 30° against the loading direction of the UTM. After the static compressive strength test, the Ti implants were analyzed with a Measurescope. RESULTS The Ti implants with deeper thread depth showed statistically higher mean insertion torque values (P<.001). Groups A and group B had similar maximum static compressive strengths, as did groups C and D (P>.05). After the static compressive strength, the thread shape of the Ti implants with deeper thread depth did not show any breakage but did show deformation of the implant body and abutment. CONCLUSION The implants with deeper thread depth had higher mean insertion torque values but not lower compressive strength. The deep threads had a mechanical stability. Implants with deeper thread depth may increase the primary stability in areas of poor quality bone without decreasing mechanical strength.

Increase of BM-MSC proliferation using L-DOPA on titanium surface in vitro.

In order to increase biocompatibility, many dental implants have been studied by immobilization of biomolecules on biomaterials. We used l-3,4-dihydroxyphenylalanine (L-DOPA) as a biomolecule for surface-modified titanium. Water contact angles of nontreated titanium discs (negative control), etched titanium discs (positive control), and titanium discs treated with L-DOPA following the etching process (experimental group) were 82.4 ± 5.7°, 67.1 ± 0.56°, and 44.15 ± 0.91°, respectively. Using atomic force microscopy images, we were able to find L-DOPA, which adhered to the titanium surface. The number of human bone marrow mesenchymal stem cells (BM-MSCs) in the experimental group was much higher than that of cells in any other group. Quantification values of amine groups in the positive control and experimental groups were approximately 3 and 7.5 µg, respectively. Therefore, findings from our research suggested the possibility of a causal link between increased L-DOPA content and cell proliferation in BM-MSCs. Moreover, coating of the discs with L-DOPA can result in greater hydrophilicity of the titanium surface and enhancement of cell adhesion and mitochondrial activity.

Effects of Collagen Grafting on Cell Behaviors in BCP Scaffold with Interconnected Pore Structure

BackgroundThis study was to investigate the effect of collagen grafted porous biphasic calcium phosphate (BCP) on cell attachment, proliferation, and differentiation. Porous BCP scaffolds with interconnected micropore structure were prepared with were prepared and then grafted with a collagen type I. The hydroxyapatite (HA) and β-tricalcium phosphate (TCP) ratio of the TCP scaffolds was about 60/40 and the collagen was crosslinked on the TCP scaffold surface (collagen-TCP).ResultsThe sintered BCP scaffolds showed fully interconnected micropore structures with submicron-sized grains. The collagen crosslinking in the scaffolds was conducted using the the N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (NHS) crosslinking method. The cell proliferation of collagen-BCP scaffolds showed a similar result to that of the BCP scaffolds. However, osteoblastic differentiation and cell attachment increased in the collagen-BCP scaffolds.ConclusionsCollagen-BCP scaffold improved the cell attachment ability in early phase and osteoblastic differentiation.

Repair of Cranial Bone Defects Using rhBMP2 and Submicron Particle of Biphasic Calcium Phosphate Ceramics with Through-Hole.

Recently a submicron particle of biphasic calcium phosphate ceramic (BCP) with through-hole (donut-shaped BCP (d-BCP)) was developed for improving the osteoconductivity. This study was performed to examine the usefulness of d-BCP for the delivery of osteoinductive rhBMP2 and the effectiveness on cranial bone regeneration. The d-BCP was soaked in rhBMP2 solution and then freeze-dried. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy analyses confirmed that rhBMP2 was well delivered onto the d-BCP surface and the through-hole. The bioactivity of the rhBMP2/d-BCP composite was validated in MC3T3-E1 cells as an in vitro model and in critical-sized cranial defects in C57BL/6 mice. When freeze-dried d-BCPs with rhBMP2 were placed in transwell inserts and suspended above MC3T3-E1, alkaline phosphatase activity and osteoblast-specific gene expression were increased compared to non-rhBMP2-containing d-BCPs. For evaluating in vivo effectiveness, freeze-dried d-BCPs with or without rhBMP2 were implanted into critical-sized cranial defects. Microcomputed tomography and histologic analysis showed that rhBMP2-containing d-BCPs significantly enhanced cranial bone regeneration compared to non-rhBMP2-containing control. These results suggest that a combination of d-BCP and rhBMP2 can accelerate bone regeneration, and this could be used to develop therapeutic strategies in hard tissue healing.

Comparative study on the cellular activities of osteoblast-like cells and new bone formation of anorganic bone mineral coated with tetra-cell adhesion molecules and synthetic cell binding peptide

Purpose We have previously reported that tetra-cell adhesion molecule (T-CAM) markedly enhanced the differentiation of osteoblast-like cells grown on anorganic bone mineral (ABM). T-CAM comprises recombinant peptides containing the Arg-Gly-Asp (RGD) sequence in the tenth type III domain, Pro-His-Ser-Arg-Asn (PHSRN) sequence in the ninth type III domain of fibronectin (FN), and the Glu-Pro-Asp-Ilu-Met (EPDIM) and Tyr-His (YH) sequence in the fourth fas-1 domain of βig-h3. Therefore, the purpose of this study was to evaluate the cellular activity of osteoblast-like cells and the new bone formation on ABM coated with T-CAM, while comparing the results with those of synthetic cell binding peptide (PepGen P-15). Methods To analyze the cell viability, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was performed, andto analyze gene expression, northernblot was performed. Mineral nodule formations were evaluated using alizarin red stain. The new bone formations of each group were evaluated using histologic observation and histomorphometrc analysis. Results Expression of alkaline phosphatase mRNA was similar in all groups on days 10 and 20. The highest expression of osteopontin mRNA was observed in the group cultured with ABM/P-15, followed by those with ABM/T-CAM and ABM on days 20 and 30. Little difference was seen in the level of expression of collagen type I mRNA on the ABM, ABM/T-CAM, and ABM/P-15 cultured on day 20. There were similar growth and proliferation patterns for the ABM/T-CAM and ABM/P-15. The halo of red stain consistent with Ca2+ deposition was wider and denser around ABM/T-CAM and ABM/P-15 particles than around the ABM particles. The ABM/T-CAM group seemed to have bone forming bioactivity similar to that of ABM/P-15. A complete bony bridge was seen in two thirds of the defects in the ABM/T-CAM and ABM/P-15 groups. Conclusions ABM/T-CAM, which seemed to have bone forming bioactivity similar to ABM/P-15, was considered to serve as effective tissue-engineered bone graft material.

Characterization of Bioactive Glass-Ceramics Prepared by Sintering Mixed Glass Powders of Cerabone® A-W Type Glass/CaO-SiO2-B2O3 Glass

From our previous work, CaO-SiO 2-B2O3(CSB, CaO 45.8, SiO 2 45.8, B2O3 8.4mol%) glass-ceramic was proven to show fast dissolution rate in-vitro and in-vivo and Cerabone ® A-W (Cera) hardly degraded in SBF. To control the biodegradation rate, we prepared g l ss-ceramics by mixing glass powders of Cera and CSB. The glass-ceramics sint ered 800C for 2h showed dense microstructure and were composed of crystalline -wollastonite, apatite and a residual glass matrix. So mixing CSB with Cera enabled low temperature crystallizat ion of -wollastonite. In addition, as the amount of CSB glass powder increased, rate of dissolution and mecha nical properties increased, but bioactivity slightly decreased. Introduction Bioactive glass-ceramics have been extensively studied for bette ioactivity than hydroxyapatite or other calcium phosphate compounds[1-3]. Especially Kokubo et al. reported apati te–wollastonite containing glass-ceramics(Cerabone  A-W) with high mechanical strength and it has been widely used as bone replacement[4]. Recently, biodegradation of bioactive materials became important for bone substitutes. For complete new bone replacement, rate of bone ingrowth must be similar with that of dissolut ion f implant. So, biodegradation rate of ideal bone graft must be controlled. The present authors found that glass-ceramics in the CaO-SiO 2-B2O3 system were not only non-toxic, bioactive and biodegradable but also osteoconductive. However, the glass-ceramics presented so fast diss olu ion rate in-vitro and in-vivo that significant bone growth could not be anticipated[5]. In this study, novel biodegradation controllable glass-ceramics prepare d by sintering mixed glass powders of Cerabone  A-W type glass and CaO-SiO 2-B2O3 glass were investigated. Materials and Methods Table.1 The chemical compositions of Cerabone-AW  and CSB glass Sample Name CaO(wt%) SiO2(wt%) P2O5(wt%) B2O3(wt%) MgO(wt%) CaF2(wt%) Cera 44.9 34.2 16.3 4.6 0.5 CSB 43.4 46.6 10 Table. 2 Mixing ratios of prepared glass-ceramics Sample Name Cera(wt%) CSB(wt%) C3 75 25 CB 50 50 B3 25 75 Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 147-150 doi:10.4028/www.scientific.net/KEM.254-256.147

Effect of B2O3 on the Sintering Behavior and Phase Transition of Wollastonite Ceramics

By adding B2O3 powder into alpha wollastonite ceramics synthesized by solid-state reaction, the sintering temperature of wollastonite ceramics low ered by 300 C and temperature that exhibit maximum density decreased by about 400 C. In addition, we found that liquid-phase sintering observed in wollastonite-B 2O3(WB) ceramics is due to melting of calcium borate which is conf irmed by DTA measurement. Phase transition between alpha wollastonite and b ta wollastonite is observed in WB ceramics, while no phase transition is observed in alpha wollas tonite. In WB ceramics, beta wollatonite started to appear at 900 C, and above 950 C, phase transition from alpha phase to beta phase took place and only alpha wollastonite remained above 1100 C. Especially, the sample sintered at 950C was composed of almost beta wollastonite in the case of W5B. In a ddition, we observed abnormal grain growth due to liquid phase in the sintered sample. Introduction Since the discovery of Bioglass ® by Hench in 1972[1], various materials including glasses[2,3], sintered hydroxyapatite[4], glass ceramics[5,6], composite materia ls[7] have been studied for biomedical applications. Among them, wollastonite ceramics have been reported to have good bioactivity and biocompatibility [8]. Furthermore, because it has good me chanical property, there are possible applications of wollastonite ceramics for the manufacture of artificial bone and dental root. However in spite of its availability of as a biomaterial, its sintering temperature is very high. And study about two polymorphisms of wollastonite ceramics, alpha phase and bet phase, is not enough. In this study, to lower sintering temperature of wollastonite, B 2O3 was added to pure alpha wollastonite ceramics, and we studied the phase transition and the microstructure. Method To obtain pure alpha wollatonite ceramics, a mixture of CaCO 3 (99.99%, high purity chem., Japan) and SiO2(99.9% high purity chem., Japan) with a CaO/SiO 2 molar ratio equal to one was prepared by ball-milling for 24h in ethanol media and then the mixture was calci ned at 1300 oC for 12h in a Pt crucible. Calcined wollastonite powder was confirmed to be pure alpha pha se by XRD, and pulverized by additional ball milling for 24h. By adding 5 and 10wt% B 2O3 powder (99.9% high purity chem., Japan) to pure wollastonite powder and mixing them, W5B and W 10B were obtained. The compositions are presented in table 1. These three powders including p re wollastonite were granulated and compacted into pellets. The shrinkage behaviors of the pell ets w re observed using a dilatometry (DIL 402C, Netsch, German) and the crystalline behavior was observed by differential thermal analysis (DTA, SDT 2960, TA inst., USA). The pellets of WB ceramics were sintered at 800~1100 C for 2h, and those of wollastonite were sintered at 1000~1400 C for 2h. The bulk density and open porosity of sintered samples were determined using Archimedes ’ method. The phases of sintered samples were confirmed by XRD (M18XHF-SRA, Mac Sci., J apan) and their mirror-polished surfaces were observed by SEM (JSM-5600, Jeol, Japan). Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 151-154 doi:10.4028/www.scientific.net/KEM.254-256.151