Evaluation of the sintering temperature on the mechanical behavior of ß-tricalcium phosphate/calcium silicate scaffolds obtained by gelcasting method.

Scaffolds have been studied during the last decades as an alternative method to repair tissues. They are porous structures that act as a substrate for cellular growth, proliferation and differentiation. In this study, scaffolds of ß-tricalcium phosphate with calcium silicate fibers were prepared by gel casting method in order to be characterized and validated as a better choice for bone tissue treatment. Gel-casting led to scaffolds with high porosity (84%) and pores sizes varying from 160 to 500 µm, which is an important factor for the neovascularization of the growing tissue. Biocompatible and bioactive calcium silicate fibers, which can be successfully produced by molten salt method, were added into the scaffolds as a manner to improve its mechanical resistance and bioactivity. The addition of 5 wt% of calcium silicate fibers associated with a higher sintering temperature (1300 °C) increased by 64.6% the compressive strength of the scaffold and it has also led to the formation of a dense and uniform apatite layer after biomineralization assessment.

Addition of Wollastonite Fibers to Calcium Phosphate Cement Increases Cell Viability and Stimulates Differentiation of Osteoblast-Like Cells.

Calcium phosphate cement (CPC) that is based on α-tricalcium phosphate (α-TCP) is considered desirable for bone tissue engineering because of its relatively rapid degradation properties. However, such cement is relatively weak, restricting its use to areas of low mechanical stress. Wollastonite fibers (WF) have been used to improve the mechanical strength of biomaterials. However, the biological properties of WF remain poorly understood. Here, we tested the response of osteoblast-like cells to being cultured on CPC reinforced with 5% of WF (CPC-WF). We found that both types of cement studied achieved an ion balance for calcium and phosphate after 3 days of immersion in culture medium and this allowed subsequent long-term cell culture. CPC-WF increased cell viability and stimulated cell differentiation, compared to nonreinforced CPC. We hypothesize that late silicon release by CPC-WF induces increased cell proliferation and differentiation. Based on our findings, we propose that CPC-WF is a promising material for bone tissue engineering applications.

Influence of Si substitution on the reactivity of α-tricalcium phosphate.

Silicon substituted calcium phosphates have been widely studied over the last ten years due to their enhanced osteogenic properties. Notwithstanding, the role of silicon on α-TCP reactivity is not clear yet. Therefore, the aim of this work was to evaluate the reactivity and the properties of Si-α-TCP in comparison to α-TCP. Precursor powders have similar properties regarding purity, particle size distribution and specific surface area, which allowed a better comparison of the Si effects on their reactivity and cements properties. Both Si-α-TCP and α-TCP hydrolyzed to a calcium-deficient hydroxyapatite when mixed with water but their conversion rates were different. Si-α-TCP exhibited a slower setting rate than α-TCP, i.e. kSSA for Si-TCP (0.021g·m-2·h-1) was almost four times lower than for α-TCP (0.072g·m-2·h-1). On the other hand, the compressive strength of the CPC resulting from fully reacted Si-α-TCP was significantly higher (12.80±0.38MPa) than that of α-TCP (11.44±0.54MPa), due to the smaller size of the entangled precipitated apatite crystals.

Hierarchical structures of ß-TCP/45S5 bioglass hybrid scaffolds prepared by gelcasting.

This paper investigates the microstructure and the mechanical properties of ß-tricalcium phosphate (ß-TCP) three-dimensional (3D) porous materials reinforced with 45S5 bioactive glass (BG). ß-TCP and ß-TCP/x%-BG scaffolds with interconnected pores networks, suitable for bone regeneration, were fabricated by gel-casting method. Mechanical properties, porosity, and morphological characteristics were evaluated by compressive strength test, scanning electron microscopy (SEM) and X-ray microtomography analysis, whereas the structures were fully explored by XRD, and Raman spectroscopy. To the best of our knowledge, this is the first time where the mechanism for understanding the effect of bioglass on the mechanical properties and microstruture of ß-TCP/45S5-BG scaffolds has been systematically studied. The findings showed that ionic product lixiviated from 45S5 bioactive glass, rich in silicon species and sodium ion, catalyzes a phase transition from ß-TCP to Si-TCP by replacement of phosphorus for silicon and contributes to the improvement of scaffolds mechanical properties. The compressive strength of ß-TCP/5%-BG and ß-TCP/7.5%-BG was improved around 200% in comparison to pure ß-TCP. Osteoblast-like cells (MG 63) were exposed to the materials for 24h through the use of medium conditioned by ß-tricalcium phosphate/bioactive glass. Cell viability was measured by MTT assay in the cells and the data obtained were submitted to ANOVA, Tukey׳s multiple comparison (p<0.05). The ß-TCP/7.5-BG promoted an increase of cell proliferation. The results suggest that compositions and processing method studied may provide appropriate materials for tissue engineering.

Apatite bone cement reinforced with calcium silicate fibers.

Several research efforts have been made in the attempt to reinforce calcium phosphate cements (CPCs) with polymeric and carbon fibers. Due to their low compatibility with the cement matrix, results were not satisfactory. In this context, calcium silicate fibers (CaSiO3) may be an alternative material to overcome the main drawback of reinforced CPCs since, despite of their good mechanical properties, they may interact chemically with the CPC matrix. In this work CaSiO3 fibers, with aspect ratio of 9.6, were synthesized by a reactive molten salt synthesis and used as reinforcement in apatite cement. 5 wt.% of reinforcement addition has increased the compressive strength of the CPC by 250% (from 14.5 to 50.4 MPa) without preventing the cement to set. Ca and Si release in samples containing fibers could be explained by CaSiO3 partial hydrolysis which leads to a quick increase in Ca concentration and in silica gel precipitation. The latter may be responsible for apatite precipitation in needle like form during cement setting reaction. The material developed presents potential properties to be employed in bone repair treatment.

Study of in vitro degradation of brushite cements scaffolds.

An interest path to fabricate supports for tissue engineering is to foam calcium phosphate cement's pastes leading to an increase on material's total porosity and interconnectivity which facilitates cells' adhesion, proliferation and differentiation. The aim of this work is to develop scaffolds of brushite cement and to evaluate its in vitro degradation rate. Macroporosity was obtained by foaming the liquid phase with different non-ionic surfactants (Tween 80 and Lutensol ON-110). The foam stability was achieved by adding chitosan. The scaffolds were immersed in Ringers(®) solution during 7, 14, 21 and 28 days and samples' microstructure, weight loss, mechanical resistance and apparent porosity were evaluated. Both scaffolds presented interconnected macropores with sizes ranging from 100 to 360 µm and total porosities higher than 60%. These properties could facilitate cell infiltration, bone growth and vascularization. The scaffolds obtained in this work should be considered as promising materials for application in bone tissue engineering.