Key Engineering Materials Vols. 396-398

Abstract: The incorporation of ions in the lattice of hydroxyapatite alters significantly its structure. Particularly, if anions such as trigonal borate units are accommodated in the lattice severe distortions must occur around the substitution site because of different geometric shape, electric charge and anion size. Solid-state NMR has been used to investigate this problem in detail for a hydroxyapatite sample synthesized by high temperature solid state reaction. The results clearly verify the existence of network distortions. Indeed, only about 1/3 of the total phosphate content forms crystalline hydroxyapatite (also found in XRD) whereas the residual amount is contained in two different phosphate sites with 31P chemical shifts of 5.5 ppm and 2.3 ppm, but broad resonances lines suggesting disorder. Furthermore, a novel proton signal at -0.6 ppm was found which is directly associated with the borate incorporation. No specific correlation of the two structurally different borate units with the two phosphate groups is found.

Abstract: We developed new calcium phosphate bone substitute material, amorphous calcium polyphosphate. The new material is synthesized by a cement-like slif-setting reaction with calcium phosphate glass, basic materials and water. In this study, we prepared with CPG, Na2CO3 and NaOH solution. When they are mixed together, amorphous phase was precipitated. The precipitated amorphous phase consisted of polyphosphate chains condensed with Na ions released from Na2CO3 and NaOH. When the amorphous calcium polyphosphate dissolves, inorganic polyphosphates are released into the medium. The inorganic polyphosphates as the dissolution product inducted the calcification of the osteoblast cells. Therefore, in animal test, the new bone formation in rat calvarial defects treated with the new material was significantly higher than sham-surgery control group, especially in the initial stage. The amorphous calcium polyphosphate was biocompatible and bioresorbable and promoted the new bone formation.

Abstract: The setting behaviour, the compressive strength and the porosity of four calcium alkali orthophosphate cements were examined under laboratory conditions (dry) and under conditions similar to those during clinical application (37°C, contact with body fluid). The results showed an increase of the setting times when specimens were covered with simulated body fluid. Especially, the final setting time (FHZ) was significantly higher for three of the four cements. Furthermore, when specimens were stored in SBF for 16h, an extensive decrease of the compressive strength was noted. The porosity was more than twice as high after 16h in SBF and this may be the cause for the great decrease of the compressive strength.

Abstract: Different types of bone grafts are available in Brazil due to the increase of use of biomaterials for hard tissue replacement. This study was designed to evaluate the scientific production of Brazilian research groups on safety and efficacy of calcium phosphate bone grafts of commercial use in Brazil. The calcium phosphate bone grafts approved for commercial use in Brazil were searched at the National Health Regulatory Agency’s database (ANVISA). The main leaders’ names of the Brazilian Research Groups on these health technologies were obtained by applying the search strategies to the National Council of Technological and Scientific Development’s database (CNPq). Afterwards, it was performed a systematic search of studies conducted by these leaders on calcium phosphate bone grafts and published from 2000 to May 2008 at the following databases: Medline, Lilacs and Scielo. Twenty-nine bone grafts composed by calcium phosphates were registered at Anvisa in May 2008. From those products, 17 and 12 were from imported and national origin respectively. There were twenty-four Brazilian research groups on calcium phosphate bone grafts whose scientific production consisted of 5 studies on bone grafts registered at Anvisa: 3 experiments conducted in animals on the Brazilian bovine bone graft Gen-Ox®, one prospective comparative study and one case report both evaluating the clinical performance of a national biomaterial composed by BMP, demineralized bovine bone, inorganic bovine bone and bovine collagen with the commercial name Gen-Tech® for dentistry applications and 6 months of follow-up. However, all the included studies had poor methodological quality and could not be used for further recommendations despite their good results. The scientific evidence produced by the Brazilian research groups on safety and efficacy of calcium phosphate bone grafts of commercial use in Brazil is still scant. Additional studies are necessary to evaluate these technologies.

Abstract: A material able to be used as bone implant for specific applications was developed. The proposed solution establishes that all implant surfaces should be bioactive since porous surfaces in contact with bone are extremely necessary for bone adhesion. The bioactive material composite with high mechanical strength designed with a PMMA functional structure gradient produced in this work has a dense core enveloped by a porous bioactive surface. Pore sizes and shapes as well their interconnectivity was analyzed by SEM tests; the cytotoxicity was investigated in vitro using Vero cell and bone conductivity and biocompatibility was investigated in vivo in rabbits. The implant porous bioactive part analyzed in vitro showed no toxicity and tests in vivo showed a remarkable biocompatibility and bone cell growth. Some samples with hydroxyapatite (HAp) were analyzed by EDX and SEM tests, the results showed a fair hydroxyapatite distribution in the implant pore surfaces as much as a part which was retained inside the PMMA inner porous. The average scaffold pore sizes obtained was around 250.0µm and the diameter shrinkage of 4.0% was observed in all samples. This study demonstrated that the functional gradient structure composite studied can be a good candidate for cranial bone implants due to its good bone conductivity and biocompatibility.

Abstract: The purpose of this study was to improve injectability and cohesiveness of original calcium carbonate-calcium phosphate mixed (CaCO3-CaP) self-setting paste for bone filling and repair. With this aim in view dry co-grinding was implemented on the solid phase (vaterite and dicalcium phosphate dihydrate) of this cement. A protocol designed to quantify paste injectability has been established and pointed out the synergistic positive effects of solid phase co-grinding treatment on injectability, cohesiveness and setting time of the paste. The improvement of these properties are related to close and homogeneous association of reactive powders and to the decrease of specific surface area favoring the powders hydration process enhancing setting reaction rate. In addition, the particle size decrease and morphology modification improved flowability of the paste which results in a low and constant (320 g) force level to extrude the paste.

Abstract: Compressive strength of apatite type bone cement was analyzed with respect to the concentration of setting agent and types of saline solution used for storage after setting. With the increase of the concentration to 2 M, the density of paste decreased. However, the compressive strength of cement was not necessarily correlated with the density and dependent on the type of saline solution used for storage after setting. One solution led rather porous paste and the strongest specimen from the series was obtained under the maximized amount of apatite within the paste. The other saline solution induced the more dense paste after setting. In this series, the strongest specimen was obtained under the coexistence of low crystalline apatite and dicalcium phosphate dihydrate. The difference between two saline solutions was explained in terms of the solidity of skeleton formed by apatite.

Abstract: Biphasic calcium phosphate foam consisting of core aTCP covered with carbonate apatite (CO3Ap) was fabricated based on the compositional transformation by exposing aTCP foam to (NH4)2HPO4 aqueous solution at 200 °C for 90min in order to understand the effect on bone formation rate and granule remaining ratio. The BCP foam was gently crushed and sieved to prepare foam granular. Bone defects made at the mandible of beagle dog were reconstructed with aTCP, BCP and CO3Ap foam granular. 3 months after surgery, bone reconstruction rate of the BCP and CO3Ap were 159.7±28.6% and 169.0±29.7% whereas those of aTCP and blood clot group were 89.5±14.7% and 85.2±13.2%, respectively, and no further increase was observed at 6 month. On the other hand, granular remaining ratio was 3.0±1.7%, 3.1±1.8%, 6.9±2.0% for BCP, aTCP and CO3Ap foam granular, respectivly. We concluded therefore, BCP foam granular could be an ideal bone substitute since it alllows large porosity, at least similar bone formation ratio to CO3Ap and faster replacement to bone.

Abstract: Bioceramics with different Ca/P ratio were prepared from a mechanical mixture of NaPO3, CaCO3, Ca(OH)2 and phosphate buffer solution and implanted in rats subcutaneous tissues. The cements were characterized by Thermogravimetric analysis (TG-TDA), X-ray diffraction and 31P-NMR. The implant sites were excised after 1, 4 and 16 weeks, fixed, dehydrated, included in paraffin wax for serial cutting and examined under the light transmitted microscope. They were biocompatible and biodegradable when implanted in rat subcutaneous. None of the materials induced ectopic osteogenesis. According to the results, the studied materials seem to be able for manufacturing reabsorbable bone implants.

Abstract: The effect of using Na2HPO4 solution as mixing liquid in the physicochemical and mechanical properties of calcium aluminate cement (CAC), with a view to a possible reinforcement additive of conventional α-TCP-based CPC was studied. The results showed that the degree of the hydration reaction of CaAl2O4 (CA) increased when Na2HPO4 solution was used as mixing liquid. The porosity of cement was also lower (37.9 ± 1.3 %) than for H2O (33.2 ± 3.6 %). The values of compressive strength for cements prepared with both mixing liquids were lower than 3 MPa due to the excessive L/P ratio employed and large porosity. After immersion in SBF, only the Al(OH)3 hydrate is observed and no other crystalline hydrated calcium aluminate nor calcium phosphate was formed in any of the cements. Both cements released Ca ions to, and removed P ions from SBF, being this effect more remarkable when Na2HPO4 was used. As for other CAC, no Al was released to the SBF and no potential toxicity due to this ion should be expected.