Bioceramics 17

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Authors: Regina Kijkowska, Racquel Z. LeGeros
Abstract: Lanthanide phosphates are known as slightly soluble salts with their solubility products ranging from 10-25 to 10-27. These phosphates can be obtained a) by precipitation from aqueous solutions of their salts using, for example, sodium or ammonium phosphates or b) by crystallization from boiling phosphoric acid solution. Application of crystallization in highly acidic solution instead of precipitation method yields highly crystalline solids of the composition of LnPO4.H2O (Ln: La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu and Y). This paper presents the effect of the acidity of the solution used for the crystallization process on crystallinity and morphology of EuPO4.H2O obtained: the higher the acidity of the solution the larger the crystals obtained. The morphology of the crystals changed from sphere-like particles crystallized in 2M H3PO4 to large hexagonal rods formed 2M H3PO4 with additional 0.4 M of HCl or HNO3.
Authors: Xiang Wei, Mufit Akinc
Abstract: Tricalcium phosphate modified by silicon and zinc was synthesized as a candidate for resorbable temporal bone implant having a controlled solubility and improved biocompatibility. Since Si and Zn are essential trace elements with stimulatory effects on bone formation, Si,Znmodified tricalcium phosphate can also promote bone formation. From XRD and ICP analyses, it was shown that up to 10 mol% Si and Zn can be incorporated in the tricalcium phosphate lattice without formation of a second phase. Changes in lattice parameters and unit volume of TCP as calculated by Rietveld refinement analysis indicate that Si and Zn substitute for P and Ca respectively.
Authors: Jian Sheng Wang, K.E. Tanner, Saba Abdulghani, Lars Lidgren
Abstract: Injectable bone substitutes (IBS) based on calcium phosphate (CaP) and/or calcium sulphate (CaS) are used as fillers in bone defects to stimulate bone integration and allow mechanical loading. Two types of IBS, IBS-1 is CaP+20%CaS and IBS-2 is CaS+40% hydroxyapatite, were investigated. The materials were injected into holes in the femur and tibia in rabbits. After 10 weeks the femora were subjected to indentation testing and tibiae were prepared for histology evaluation. IBS-1 lead to an higher indentation load compared to control, that is no material inserted, while IBS-2 showed no significant difference between material and control. Histology showed that with IBS-1, the bone penetrated into and integrated with the material in the defect. With IBS-2, new bone grew into the outer 0.5-1.0 mm. The materials could be used for different indications, such as to support fracture healing or in contained cavities.
Authors: Kyung Sik Oh, Young Keun Jeong, Jae Pil Yu, Soo-Kyung Chae, Hong Yeoul Kim, Ho Yeon Lee, Sin-Soo Jeun
Abstract: 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.
Authors: Koji Goto, Masami Hashimoto, Shunsuke Fujibayashi, Tadashi Kokubo, Takashi Nakamura
Abstract: Two types of new bioactive polymethylmethacrylate (PMMA)-based bone cements containing nano−sized titania (TiO2) particles were prepared and evaluated to assess the effect of TiO2 content on their mechanical properties and osteoconductivity. We prepared two types of bioactive bone cement, ST50c and ST60c, which contained 50 wt% silanized TiO2 and 60 wt% silanized TiO2, respectively. Commercially available PMMA cement (PMMAc) was used as a control. The cements were inserted into rat tibiae and solidified in situ. After 6 and 12 weeks, they were taken out for evaluation of osteoconductivity by scanning electron microscopy (SEM), contact microradiography (CMR) and Giemsa surface staining. SEM revealed that ST60c and ST50c apposed to bone directly while PMMAc did not. The affinity index of ST60c was significantly higher than for the other cements at each time interval. The results showed that ST60c was a promising material, but its mechanical strength should be improved before application in prosthesis fixation.
Authors: Aliassghar Tofighi, R. Palazzolo
Abstract: ACP (amorphous calcium phosphate) and DCPD (dicalcium phosphate dihydrate, or Brushite) powders were high energy dry ball milled at a 1:1 ratio for 1, 2, 3, 4, 10, or 24 hours to produce a variety of powders for use as calcium phosphate cements (CPC). A 1:1 blend of powders not subjected to milling was used as baseline material (control). Physicochemical and mechanical characterization was performed on the powder or cement at each milling time point and compared to control. The following changes were noted after 24 hours of milling: the crystallinity was reduced to a fully amorphous phase, the tap density increased by 89%, the specific surface area decreased by a factor of 7, and the total porosity of hardened cement decreased by 50%. Additionally, the compressive strength of hardened CPC increased from 2.6 MPa to a peak of 50 MPa after 10-h milling. The rate of paste hardening increased throughout the 24-h period. Full conversion of each milled material produced a similar composition low-crystalline calcium deficiency apatite with Ca/P atomic ratio of 1.45 and specific surface area around 195 m2/g. The specific structure of these CPC, with high surface area and reactivity of nano-crystals, is ideal for in vivo remodeling of new bone and controlled release of protein and growth factors.
Authors: Marie-Laure Fontaine, Christèle Combes, Thierry Sillam, Gérard Dechambre, Cristian Rey
Abstract: The feasibility of calcium carbonate-based cements involving the re-crystallization of metastable calcium carbonate varieties has been demonstrated. Two cement compositions were obtained by mixing either calcium carbonate phases (cement A) or a calcium carbonate and a calcium phosphate phase (cement B) with an aqueous media. These cements set and hardened after 30 minutes and 90 minutes respectively. The final composition of cement A was calcite and aragonite whereas cement B lead to a carbonated apatite analogous to bone mineral. Despite poor mechanical properties the presence of a high carbonate content in the final phase might be of interest to increase the cement resorption rate and to favour its replacement by bone tissue. First assays of implantation performed on fresh anatomical pieces (fresh cadavers) at 37°C revealed important advantages of such cement compositions: easiness of use, rapid setting, good adhesion to bone, very good homogeneity and stability of the cement.
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: The mixed pastes of binary calcium phosphate glass with Ca/P ratio of 0.6 and distilled water were set after about 4 hr, while never set when calcium phosphate glass with Ca/P lower than 0.5. Their compressive strength was ranged from 16.0 to 23.3 MPa. When Na2HPO4 solution was used instead of distilled water as liquid phase, the setting time became drastically much shorter. As the mole concentration of Na2HPO4 solution increased from 0.25 M to 2 M, setting time was shortened to 35 min from almost 3 hr, but compressive strength decreased from 28.8 MPa to 13.2 MPa. At constant mole concentration, as the mass ratio of a powder to liquid ratio increased, setting time was shortened and maximum compressive strength was measured when a powder/liquid ratio was 2.5. However, no crystallized phases were detected either during setting or after complete setting. The XRD , FT-IR and SEM examinations indicated that calcium phosphate glass dissolved and then glass phase precipitated again. We concluded, therefore, that Na2HPO4 just affected the kinetics of dissolution and precipitation of CPG. The mechanism of hardening has yet to be studied.
Authors: J.A. Shin, S.U. Im, S.E. Song, C.S. Kim, Se Young Choi, Yong Keun Lee, Kyoung Nam Kim, Chong Kwan Kim, Seong Ho Choi
Abstract: This present study was carried out to find out the effects of calcium aluminate cement(CaO·Al203, CAC), which has been developed with biocompatibility and mechanical properties, in biological environments. Two different particle sizes of CAC - 3.5 µm vs. 212-250 µm which is recommended in periodontal bone grafting procedures – were filled in 8mm calvarial defects in Sprague-Dawley rats. The specimens were examined histologically, especially the bone-cement interface and the response of surrounding tissues. The result of this study shows that when calvarial defects in white rats are filled with 212-250 µm calcium aluminate cement, the materials proved to be bio-compatible in growth and healing on the surrounding tissues. When further researches on direct bone adhesion and bone regeneration ability are fulfilled, CAC is expected to be applied to various fields of periodontology in the future.
Authors: Elisabeth Engel, L. Asin, J.A. Delgado, C. Aparicio, Josep A. Planell, M.P. Ginebra
Abstract: Calcium phosphate cements (CPC) are being applied as bone regeneration materials. New methods are being developed to create macroporosity, in order enhance the angiogenesis, bone colonization and biodegradation of the material. In this study the effect of the incorporation of albumen as foaming agent in an a-tricalcium phosphate (a-TCP) cement, in terms of the surface roughness and in vitro cell response, was studied. The addition of albumen to CPC cements increased the surface roughness of the cements. Cell cultures, using MG63 osteoblasts, were performed and showed that cell attachment was not affected by the presence of albumen. However, cell proliferation was significantly increased in the albumen-containing cements.

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