Hyun Seung Ryu

Porous Beta-Calcium Pyrophosphate as a Bone Graft Substitute in a Canine Bone Defect Model

Hydroxyapatite(HA) has been used in various situations in which bone aug mentation and restoration are required. Porous HA has been used either alone or in conjugation with freez e dried or autogenous bone , with variable clinical success. However, it has a de fect that it is relatively bio-inert and remains in the host body for a long time. In this study, porous -calcium pyrophosphate( -CPP) has been compared with porous HA in an canine bone defect model to discover the possibility as a bone graft substitute replacing porous HA. Porous HA and porous -CPP were implanted in the proximal tibia of 5 dogs. 2 animals were sacrificed at 8 weeks a nd 3 animals were sacrificed at 20 weeks after surgery. Radiographs were obtained every 4 weeks and histologi c sections of the implant site were obtained at the time of sacrifice. By serial radi ography, both implants showed contraction of radio-opaque area, blurring of graft margin, and piecemeal patterned i ncorporation of surrounding new bone. But these changes were more prominent in porous -CPP compared with porous HA and showed more rapid resorbing features. Porous HA and porous -CPP were completely integrated into newly formed bone after partial degradation and bony tissue ingrowth wa s progressing during the study period. In the case of porous -CPP, the new bone growth was as vigorous as in HA, but the pore is larger and the wall of the scaffold is thinner and bone ingrow th in gaps between the implants was more evident than in HA, which suggest more rapid degradation of -CPP in vivo. Preliminary report of our experiment suggests that porous -CPP appears to provide an alternative graft material that is bioactive, more completely incorporated and more rapidly resorbable than porous HA .

Effects of Al2O3 Addition in Glass Composition on the Mechanical Properties of A/W Glass-Ceramic

The effect of Al 2O3 addition on the mechanical properties of CaO-SiO 2-P2O5 glass ceramic was investigated. By addition of Al 2O3, fracture toughness has been increased up to 3.34 MPa·m. Bending strength has been decreased compared to Cerabone® due to t oo low sintered density. Bioactivity of the glass also seem to be restrained due to th addition of Al 2O3. No bone-like apatite was formed after immersion in SBF(Simulated Body Fluid) even for 60 days. Introduction Natural bone is a composite in which an assembly of hydroxyapatite small crystal particles is effectively reinforced by organic collagen fibers. Kokubo et al. attempted to prepare a similar composite by a process of crystallization of glass in 1982 [1]. Thi s glass-ceramic was named Cerabone® A-W and showed higher mechanical strength than parent gla sses such as Bioglass®-type glasses and sintered hydroxyapatite. But, still it do not show proper mecha nical strength compared to human cortical bone. The purpose of this study is to increase the mechani cal properties of the bioglass, by addition Al 2O3. And the bioactivity of this bioceramic was discussed with in-vitro test. Materials and Method CaO 44.7 wt%, SiO2 34 wt%, P2O5 16.2 wt%, MgO 4.6 wt%, and CaF 2 0.5 wt% was ball milled with anhydrous methyl alcohol for 24 hours. After drying, it was a nd put into a Pt crucible, heated to 1500°C, and quenched in water. After drying the quenched glass, it was spex milled for 15 hours and then crushed into a fine powder 1.5μm in average size. Al 2O3 was added to prepared glass powder. The mixture was ball milled 24 hours with anhydrous methyl alcohol as a solvent. The mixture with 10, 20, and 30 vol% Al 2O3 will be called CA10, CA20, and CA30 respectively, in this documents. Powder was granulated first, then pressed under a pressure of 150 MPa and then went through Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 959-962 doi:10.4028/www.scientific.net/KEM.240-242.959

Characterization of CaO-SiO2-B2O3 Glass-Ceramics and Effect of Composition on Bioactivity

The sintering behavior, mechanical properties and bioactivity of (50-x/2) CaO⋅SiO2-xB2O3 (4.2≤x≤17.2) glass-ceramics was investigated. The glass-ceramics cons isted of three phases, monoclinic-wollastonite, calcium borate and an amorphous borosilicate mat rix. Some glass-ceramics sintered at 750-830 C for 2h, has produced a nearly pore-free microstructure. The mechanica l strength of the dense specimens was higher than that of other bioacti ve ceramics, compressive strength, 2813MPa and fracture toughness, 3.12MPa ⋅m 1/2 . Bioactivity of the glass-ceramics depends on the amount of CaB 2O4 and borosilicate glass matrix. The glass-ceramic with more CaB2O4 and borosilicate glass exhibited better bioactivity. It might be like ly that more soluble CaB 2O4 increases the supersaturation of Ca ions in the SBF solution and water-corrosive borosilicate glass forms Si-OH groups that act as nucleation sites for the hydroxycarbonate apatite (HCA) laye r. Introduction The creation of a bony union requires a hydroxy -carbonate (HCA) layer formation on a bioactive ceramic implant [1,2]. Bioactive glass and glass-ceramics must contain CaO and SiO 2. The mechanism of bioactivity has been reported that CaO was dissolved to raise supersaturation of Ca 2+ and SiO2 was hydrated to provide nucleation sites of HCA layer [3]. It is difficult to prepare pure CaO⋅SiO2 glass due to high melting temperature and rapid recrystallizat ion. In this study, we prepared (0.5-x)CaO·SiO2-xB2O3 glass and glass-ceramics. The addition of B 2O3 lowers melting temperature and viscosity and thus prohibits recrytallization. In this current work sintering, mechanical property and bioactivity of (0.5-x)CaO·SiO 2-xB2O3 glass-ceramics were investigated. Methods The glass compositions are presented in Table 1. The starting materials we e 99.99% CaCO3(high purity chem., Japan), 99.9% SiO 2 (high purity chem. Japan), and 99.9% B 2O3(high purity chem..Japan). The mixture of starting materials was melted in a Pt crucible at 1450-1550 C for 2h. The melt was poured to a stainless steel mold. The glasses wer pulverized to be 3-4 μm using pelenary mill. The glass powder was granulated and compacted into pel lets. The shrinkage of specimen was measured by a dilatometer. The pellets were als o sintered at 650~950 C for 2h. The bulk density and open porosity of sintered specimens were determined, using Archimedes method. The crystallization of glass was examined by DTA. Compressive s trength, hardness, 3-point bending strength and fracture toughness were measured. Bioactivity was inve stigat d by an in-vitro test. Mirror-polished specimens were soaked in simulated body fluid (SBF) s olution. Surface of specimens Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 261-264 doi:10.4028/www.scientific.net/KEM.240-242.261

Biomechanical and Histomorphometric Study of the Bone-Screw Interface of Calcium Pyrophosphate Coated Titanium Screws

The purpose of this study is to compare the osseointegration of calcium pyrophosphate(CPP) coated screws with uncoated screws. CPP coating was prepared and coated by dipping method. CPP coated and uncoated screws were inserted into the mongrel dogs. The insertion torques, radiographs, histology, histomorphometric analysis, and extraction torques were evaluated at 2, 4, and 8 weeks after surgery. The insertion torque was not different between CPP coated and uncoated screws. The extraction torques of CPP coated screws at 2, 4, and 8 weeks(5.45±2.05, 7.62±1.51 and 6.60±2.80 cNM) were significantly higher than their insertion torques(2.74±1.13, 2.98±0.70, and 2.18±1.34 cNM)(p<0.0001, <0.0001 and 0.0005 respectively) and significantly higher than the extraction torques of uncoated screws(1.14±0.470, 2.57±1.36, and 3.18 ±0.499 cNM). The percentages of direct bone-screw contact of CPP coated screws were statistically higher than those of uncoated screws at 2, 4, and 8 weeks. These results suggest that CPP coating may improve the clinical results by allowing early motion exercises and early weight bearing.

Biomechanical, Radiomorphometric Evaluation of CaO-SiO2-B2O3 Glass-Ceramics in a Rabbit Lumbar Fusion Model

The purpose of our study is to compare the biodegradation and osteoconduction between CaO-SiO2-B2O3 glass-ceramics(CS10B) and hydroxyapatite(HA), tricalcium phosphate(TCP). Porous CS10B implants were prepared by polymer sponge method. Single-level posterolateral spinal fusions were performed on thirty rabbits. The animals were divided into three groups by implant material: HA, TCP and CS10B. Radiographs checked every two weeks. All animals were sacrificed 12 weeks after surgery. The proportion of the area occupied by ceramics in final radiography on the initial radiography was calculated. Uniaxial tensile strength was measured on 7 cases in each group. The proportion of the area of HA(88.7%±16.1) was significantly higher than those of the others(p<0.05), and the proportion of the area of CS10B(28.2%±9.3) was significantly lower than those of HA and TCP(37%±9.6)(p<0.05). The mean values of tensile strength of the HA(191.4±33.5 N) and CS10B(182.7±19.9 N) were significantly higher(p<0.05) than those of the TCP(141.1±28.2 N). CS10B showed the tensile strength of fusion masses similar to those of the HA, however, more rapid biodegradation than HA and TCP. These findings suggest that CS10B grafts have the possibility as a bone graft substitute.

Fabrication of CaO-SiO2-B2O3 Porous Glass-Ceramics by Self-Foaming Method

Porous bioceramics as bone filler have been fabricated by various me thods. In this study, the method that porous CaO-SiO 2-B2O3 bioactive glass-ceramics can be prepared by self-foaming was introduced, and the mechanism for this self-foaming was investig ated. Considering weight loss and thermal expansion, B 2O3 volatilization is the reason for this self-foaming. As the sinte ri g temperature increased, pore size and porosity(66~90%) was increased a nd interconnection between pores collapsed. Poor interconnetion can be improved by HCl treatment or s oaking in SBF. The skeleton consisted of 5 μm needle-shaped grains. The compressive strength of this porous glass-ceramics was 15.93+ 0.49 MPa. and this value was higher that that (0.5-2MPa) of other porous bioceramics fabricated by various methods. The stress-strain curves showed that this porous ceramics was elastic and flexible like bone. In-vitro test showed this porous glass-ceramics were bioactive and biodegradable. So, this porous glass-ceramic can be believed to be osteoc onductive and have good mechanical property. Introduction Since the discovery of Bioglass ® by Hench in 1972 [1], many investigations regarding bioactive glasses and glass-ceramics have been reported. Bioactive glass and glass-ceramics form a hydroxycarbonate apatite(HCA) layer on their surfaces in-vitro and in-vivo [2-3]. Porous biodegradable materials used as templates for tissue regenera tion h ve been fabricated by various methods. In the present study, the method that bioactive CaO-SiO 2-B2O3 glass[4] could be transformed into a porous glass-ceramic by a simple heat-treatment me thod, was introduced, and the mechanism for this self-foaming was investigated. In addition, their bioactivity and biodegradability were investigated.

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 uf6da 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 uf6da A-W type glass and CaO-SiO 2-B2O3 glass were investigated. Materials and Methods Table.1 The chemical compositions of Cerabone-AW uf6da 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