Sintese de cimento osseo a base de a-TCP e estudo da influencia do Mg e do Si em suas propriedades finais / a-TCP calcium phosphate cement and the influence of Mg and Si substitution on its final properties

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

The need for new biomaterials which could improve life quality of people who suffer from oldness diseases or who have any bone tissue injury due to accidents and diseases like obesity and cancer are resulting in a growing number of researches. In this context, the development of new orthopedics biomaterials based on calcium phosphates compounds is relevant once they present excellent bioactivity and biocompatibility due to its chemical composition similar to the mineral part of bone and teeth. Silicon substitution into some phosphorous sites of calcium phosphate bioceramics is a promising field on the development of new biomaterials for orthopedics applications due to the increased bioactivity and cell differentiation on the material’s surface which could be promoted by the presence of this element. In this manner, Si-α-TCP is receiving huge efforts since its employment as bone cement could be of great interest. Moreover, silicon is known to stabilize the α-TCP structure and to promote its formation at lower temperatures leading to a cost reduction of its processing. Thus, the major objective of this study is to investigate the influence of Si on the chemical, physical, mechanical, biocompatible and bioactive properties of the calcium phosphate cement once there is a lack of publication regarding this material. On the other hand, the synthesis of a pure α-tricalcium phosphate is not an easy task since all process conditions can change its final properties, or even inhibit its formation. The most limiting factor is the quality of the starting reagents which may preclude the formation of α-TCP at temperatures as high as 1600° C. Therefore, the reproducibility of α-TCP synthesis becomes very difficult and, in some cases, impossible. In this context, and together with the development of Si-α-TCP, high purity reagents were synthesized to eliminate the most important impurity which is an established stabilizer element of β-TCP, magnesium. It has been discovered that the standardization of the reagents properties guaranteed the reproducibility of α-TCP manufacturing process. Nevertheless, it was also observed that Si has a strong influence on the setting reaction of the cement by reducing by almost four times the TCP reactivity once this element stabilizes the α-TCP structure and the final material is less soluble. As a result, the mechanical strength of the cement at initial times was extremely low (0,81 ± 0,25 MPa) even though it has achieved similar values to the cement without silicon after 168 hours of setting (18 MPa for α-TCP e 15 MPa for Si-α-TCP). Nonetheless, the biocompatibility after in vivo study and the precipitation of an apatite layer after SBF immersion lead to the conclusion that Si has a positive interference on the bone regeneration process. It was possible to develop a new calcium phosphate cement based on Si-α-TCP obtained from laboratory synthesized reagents which lead to a considerable reduction on the production costs and in a high purity level of the final material. The synthesis of CaCO3, CaHPO4 and CaSiO3 with low contents of impurities was the most significant step to cost reduction due to the lower temperatures needed to synthesize Si-α-TCP (1200°C) and α-TCP (1300°C), the enhanced facility on milling and the improved bone cement bioactivity in Simulated Body Fluid. National technology was developed in order to guarantee the production of a bone cement which has a huge potential to clinical application and, certainly, it will be more accessible to Brazilian people.

ASSUNTO(S)

ion exchange biocompatibility biocompatibilidade chemical kinetics biomaterials biomateriais troca ionica calcium phosphate fosfato de calcio cinetica quimica

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