Papers by Author: Racquel Z. LeGeros

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Authors: Racquel Z. LeGeros, Dindo Q. Mijares, J. Park, X.-F. Chang, I. Khairoun, Regina Kijkowska, Renata Dias, John P. LeGeros
Abstract: Our earlier studies showed that several ions inhibit the crystal growth of apatite and promote the formation of amorphous calcium phosphates (ACP). These ions include: magnesium (Mg), zinc (Zn), stannous (Sn), ferrous (Fe), carbonate (CO3), pyrophosphate (P2O7). The purpose of this study was to investigate the effect of combination of these ions (e.g., Mg & CO3, Mg & P2O7, Mg & Zn, etc) on the formation and stability of ACP. ACP compounds containing the different ions were prepared at 25 and 37oC according to the method we previously described. Chemical stability was investigated by suspending the different ACP preparations in solutions with or without inhibitory ions. Thermal stability was determined by sintering the ACP at different temperatures. Dissolution properties were determined in acidic buffer. The ACP before and after chemical or thermal treatment were analyzed using X-ray diffraction, infrared spectroscopy, and thermogravimetry. Results showed synergistic effects of inhibitory ions on the formation of ACP. ACP materials, regardless of their composition, remained amorphous even after heat treatment at 400oC. Transformation of ACP to other calcium phosphate phases depended on the pH and on the solution composition.
Authors: O.J. Aimanova, Racquel Z. LeGeros, V.A. Sinyayev
Abstract: The purpose of this study was to determine the microbiologic effect silver (Ag) when incorporated in amorphous calcium phosphate (ACP) prepared from solutions containing calcium, phosphate and pyrophosphate ions. The preparations were obtained from solutions with phosphate/pyrophosphate ratio, P/P2 = 7/3, and characterized as ACP using X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance and differential thermal analysis. The microbes tested were cultures of E. Coli, St. aureus, Ps aerogunosa, C. diphteroides and C. albicans in media alone (control), with ACP without Ag and with ACP containing different Ag concentrations. Results demonstrated the following: (1) Ag in ACP inhibited the growth of microorganisms in all five cultures, with ACP containing 3-6% Ag giving the greatest antimicrobial effect; (2) sensitivity to the antimicrobial action of Ag differed among the bacteria.
Authors: Min Chul Kim, Byung Hyun Lee, Kyoung Nam Kim, Kwang Mahn Kim, Seong Ho Choi, Chong Kwan Kim, Racquel Z. LeGeros, Yong Keun Lee
Abstract: A numerous techniques have been applied to fabricate three-dimensional scaffolds of high porosity and surface area. And X-ray micro computed tomography can be used studying the architecture of scaffold. In this study, we fabricated three-dimensional macroporous scaffold by polymeric sponge method using calcium phosphate glass. Calcium phosphate glass slurry was prepared by dissolving the glass powder in water polyvinyl alcohol, polyethylene glycol and dimethyl formamide. Reticulated polyurethane sponges were used as a template and were coated with the prepared slurry by infiltration technique several times. Sintering at 950oC exhibited dense microstructure as well as entire elimination of organic additives. By repeating the coating and sintering process, it was possible to decrease the pore size and be thick the strut of the structure. The unique feature of the micro computed tomography is that the three dimensions computed reconstruction can be sliced along any direction to gain accurate information on the internal geometric properties and structural parameters of scaffold. Porosity, surface area per unit volume and mean thickness of strut were evaluated through imaging and computer software of scaffold scan data.
Authors: Yasutaka Yamada, Atsuo Ito, Hiroko Kojima, Masataka Sakane, Shumpei Miyakawa, Toshimasa Uemura, Racquel Z. LeGeros
Abstract: Osteoclasts isolated from rabbits were cultured on zinc-containing tricalcium phosphate (ZnTCP) disks with zinc contents of 0.316 and 0.633 wt%, and on β-tricalcium phosphate (TCP) disks with nearly identical porosities, grain sizes and surface roughnesses. ZnTCPs directly suppressed the resorption activity of mature osteoclasts by enhancing apoptosis. We hypothesized that resorbing osteoclasts attached to ZnTCP locally accumulate zinc ions within the space defined by the clear zone during resorption, which in turn leads to apoptosis induction, even though the change in chemical composition of the culture medium is very small.
Authors: Byung Hyun Lee, Min Chul Kim, Kyoung Nam Kim, Kwang Mahn Kim, Seong Ho Choi, Chong Kwan Kim, Racquel Z. LeGeros, Yong Keun Lee
Abstract: In preliminary ageing test, the cement using only calcium phosphate glass as power phase cracked with 1 day in simulated body fluid because of high dissolution rate of the cement. We added 30 wt% of either β-TCP or HA to 70 wt% calcium phosphate glass as powder phase to control the dissolution rate of the cement and performed in vitro ageing test in simulated body fluid by dynamic protocol as well as static protocol to confirm the possibility of controlling. Adding either β-TCP or HA to the cement increases the setting time and decreases the compressive strength. In dynamic assay, the pH of extract is maintained over 7. However, pH decreased to around 5 in static assay. Therefore, weight loss by static protocol continuously increased for 14 days, while weight loss by dynamic protocol almost saturated. In XRD patterns of ageing cements, CaO peaks appeared. CaO peak was maximized most lately in dynamic assay of the cement adding HA and within 7 days, the cement adding HA showed higher weight loss. It is indicated that CaO formed in surface of the cement hinder the dissolution of the cement. In addition, compressive strength increased when the CaO peak was maximized.
Authors: Shu Jie Lin, Racquel Z. LeGeros, Ramin Rohanizadeh, Dindo Q. Mijares, John P. LeGeros
Authors: Toshiro Sakae, A. Ookubo, Racquel Z. LeGeros, R. Shimogoryou, Y. Sato, S. Lin, H. Yamamoto, Y. Kozawa
Authors: Seong Ho Choi, D.H. Baik, C.S. Kim, Chong Kwan Kim, Kyoung Nam Kim, Kwang Mahn Kim, Racquel Z. LeGeros, Yong Keun Lee
Abstract: The purpose of this study was to compare the bone regenerative effect of calcium phosphate glass and glass-ceramics in the system of CaO-CaF2-P2O5-MgO-ZnO, which is already reported that promoted the bone-like tissue formation in vitro and formed new bone in Sprague-Dawley rats. We prepared calcium phosphate glass and glass-ceramics with Ca/P ratio of 0.6 using the system CaO-CaF2-P2O5-MgO-ZnO and subsequently milled to 400 µm. 4×4 mm 1-wall intrabony defects of six beagle dogs were surgically created and used in this study. 8 weeks after transplantation of the prepared calcium phosphate glass and glass-ceramics in the experimental group 1 and 2, respectively, the animals were sacrificed. No root resorption or ankylosis were observed in all groups. It can be examined that the prepared glass-ceramics were more effective in alveolar bone regeneration with statistical signigicant difference. In cementum regeneration, both the prepared glass and glass-ceramics showed significantly different effect. However, there were no statistical significant difference neither in glass nor glass-ceramics in the amounts of junctional epithelium migration and connective tissue adhesion. Further study is required to control the flowability as well as reduce the absorption rate in vivo.
Authors: G. Daculsi, I. Khairoun, Racquel Z. LeGeros, Françoise Moreau, Paul Pilet, Xavier Bourges, Pierre Weiss, Olivier Gauthier
Authors: J. Peña, Racquel Z. LeGeros, Ramin Rohanizadeh, John P. LeGeros
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