Raúl García Carrodeguas

Bioactive composite bone cement based on α‐tricalcium phosphate/tricalcium silicate

Silicon compounds are known as bioactive materials that are able to bond to the living bone tissue by inducing an osteogenic response through the stimulation and activation of osteoblasts. To improve the bioactive and mechanical properties of an α-Ca(3)PO(4)-based cement, the effects of the addition of Ca(3 SiO(5) (C(3)S) on physical, chemical, mechanical, and biological properties after soaking in simulated body fluid (SBF) were studied. The morphological and structural changes of the material during immersion were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that it is possible to increase the compressive strength of the cement by adding 5% of C(3)S. Higher C(3)S contents enhance bioactivity and biocompatibility by the formation of a dense and homogeneous hydroxyapatite layer within 7 days; however, compressive strength decreases drastically as a consequence of delayed hydrolysis of α-Ca(3)(PO(4) (2). An increment in setting times and degradation rate of composites containing C(3)S was also observed.

Devitrification studies of wollastonite–tricalcium phosphate eutectic glass

The present paper describes and discusses the devitrification and crystallization process of wollastonite-tricalcium phosphate (W-TCP) eutectic glass. This process was studied in situ from room temperature up to 1375 degrees C, by neutron diffractometry in vacuum. The data obtained were combined and compared with those performed in ambient atmosphere by differential thermal analysis and with those of samples fired in air at selected temperatures, and then cooled down and subsequently studied by laboratory XRD and field emission scanning electron microscopy fitted with energy X-ray dispersive spectroscopy. The experimental evidence indicates that the devitrification of W-TCP eutectic glass begins at approximately 870 degrees C with the crystallization of a Ca-deficient apatite phase, followed by wollastonite-2M (CaSiO(3)) crystallization at approximately 1006 degrees C. At 1375 degrees C, the bio-glass-ceramic is composed of quasi-rounded colonies formed by a homogeneous mixture of pseudowollastonite (CaSiO(3)) and alpha-tricalcium phosphate (Ca(3)(PO(4))(2)). This microstructure corresponds to irregular eutectic structures. It was also found that it is possible to obtain from the eutectic composition of the wollastonite-tricalcium phosphate binary system a wide range of bio-glass-ceramics, with different crystalline phases present, through appropriate design of thermal treatments.

Effect of Mg and Si co-substitution on microstructure and strength of tricalcium phosphate ceramics

Magnesium and silicon co-doped tricalcium phosphate (TCP) ceramics with compositions corresponding to 0, 5 and 10wt% CaMg(SiO3)2 in the system Ca3(PO4)2-CaMg(SiO3)2 were obtained by conventional sintering of compacted mixtures of Ca3(PO4)2, MgO, SiO2 and CaCO3 powders at temperatures between 1100 and 1450°C. Microstructural analyses were performed by X-ray diffraction and field emission scanning electron microscopy with energy dispersive spectroscopy. Major phases in the obtained ceramics were β- or α+β-tricalcium phosphate containing Mg and Si in solid solution. Certain amounts of liquid were formed during sintering depending on composition and temperature. There were found significant differences in distributions of strength determined by the diametral compression of disc tests (DCDT). Failure strengths were controlled by microstructural defects associated with phase development. Mg and Si additions were found to be effective to improve densification and associated strength of TCP bioceramics due to the enhancement of sintering by the low viscosity liquids formed. The highest density and strength were obtained for the TCP ceramic containing 5wt% CaMg(SiO3)2 sintered at 1300°C. Cracking and porosity increased at higher temperatures due to grain growth and swelling.

α-Tricalcium phosphate cements modified with β-dicalcium silicate and tricalcium aluminate: Physicochemical characterization, in vitro bioactivity and cytotoxicity

Biocompatibility, injectability and in situ self-setting are characteristics of calcium phosphate cements which make them promising materials for a wide range of clinical applications in traumatology and maxillo-facial surgery. One of the main disadvantages is their relatively low strength which restricts their use to nonload-bearing applications. α-Tricalcium phosphate (α-C3P) cement sets into calcium-deficient hydroxyapatite (CDHA), which is biocompatible and plays an essential role in the formation, growth and maintenance of tissue-biomaterial interface. β-Dicalcium silicate (β-C2S) and tricalcium aluminate (C3A) are Portland cement components, these compounds react with water to form hydrated phases that enhance mechanical strength of the end products. In this study, setting time, compressive strength (CS) and in vitro bioactivity and biocompatibility were evaluated to determine the influence of addition of β-C2S and C3A to α-C3P-based cement. X-ray diffraction and scanning electron microscopy were used to investigate phase composition and morphological changes in cement samples. Addition of C3A resulted in cements having suitable setting times, but low CS, only partial conversion into CDHA and cytotoxicity. However, addition of β-C2S delayed the setting times but promoted total conversion into CDHA by soaking in simulated body fluid and strengthened the set cement over the limit strength of cancellous bone. The best properties were obtained for cement added with 10 wt % of β-C2S, which showed in vitro bioactivity and cytocompatibility, making it a suitable candidate as bone substitute.

Evaluation of n-Butyl Cyanoacrylate Adhesive in Rat Subcutaneous Tissue

Background Tissue adhesives have been widely used for wound closure, especially in children, because they are painless, fast, and easy to use and result in minimal scarring. Objective To analyze the biocompatibility of an adhesive based on n‐butyl‐cyanoacrylate in the subcutaneous tissue of rats. Materials and Methods Two surgical sites were prepared (approximately 3 cm apart): one on the left side of the animal and the other on the right side); polyethylene tubes were implanted in each surgical site. The tube on the left was filled with n‐butyl‐cyanoacrylate (treated group) and the tube on the right side was unfilled (control group). After 7, 30, and 120 days, the animals were killed, and the specimens were processed for histologic analysis. Results No significant inflammatory reaction occurred in the treated group, showing results similar to the control group. Conclusion This adhesive based on n‐butyl‐cyanoacrylate is biocompatible in the subcutaneous tissue of rats.

Preparation, characterization, and in vitro evaluation of nanostructured chitosan/apatite and chitosan/Si-doped apatite composites

Chitosan/apatite (CHI/Ap) composites are attracting great attention as biomaterials for bone repair and regeneration procedures. The reason is their unique set of properties: bioactivity and osteoconductivity provided by Ap and resorbability supplied by CHI among others. Thus, in this study, CHI/Ap and CHI/Si-doped Ap composites were prepared and characterized. Particle size, surface area, in vitro physiological stability, enzymatic biodegradation, and bioactivity were evaluated. Unimodal particle size distribution was obtained for composites with high CHI/Ap ratios while bimodal distribution was present in composites with low CHI/Ap ratio. Physiological stability decreased with Si doping and with the CHI content. Acetylation degree and molecular weight of CHI did not affect in vitro stability. Rate of enzymatic degradation increased with the CHI content in composites. Si-doped Ap composites also showed increased degradation with respect to non-doped ones. The bioactivity of the composites was evidenced by the deposition on their surface of a calcium phosphate layer with Ap morphology after immersion in simulated body fluid. Both, biodegradation and bioactivity were dependent on the molecular weight of the polymeric CHI matrix. These results suggest that the CHI/Ap composites obtained are promising materials for bone regeneration applications.

Effects of silica addition on the chemical, mechanical and biological properties of a new α-Tricalcium Phosphate/Tricalcium Silicate Cement

The addition of tricalcium silicate (C3S) to apatite cements results in an increase of bioactivity and improvement in the mechanical properties. However, adding large amounts raises the local pH at early stages, which retards the precipitation of hydroxyapatite and produces a loss of mechanical strength. The introduction of Pozzolanic materials in cement pastes could be an effective way to reduces basicity and enhance their mechanical resistance; thus, the effect of adding silica on the chemical, mechanical and biological properties of α-tricalcium phosphate/C3S cement was studied. Adding silica produces a reduction in the early pH and a decrease in setting times; nevertheless, the presence of more calcium silicate hydrate (C-S-H) delays the growth of hydroxyapatite crystals and consequently, reduces early compressive strength. The new formulations show a good bioactivity, but higher cytotoxicity than traditional cements and additions higher than 2.5% of SiO2 cause a lack of mechanical strength and an elevated degradability.

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.

Evaluación In Vitro de Composites Basados en Quitosana e Hidroxiapatita

The aim of the present work was to develop an in situ preparation of chitosan/apatite nanocomposites and evaluate their bioactivity, physiological stability and enzymatic biodegradation. Composites of different chitosan/hydroxyapatite ratios were prepared by wet chemistry using different kinds of chitosan. The method of preparation used to obtain composites in this work could be more attractive with respect to previous procedures because it allows more homogeneous systems and to control the composition and structure of the resulting materials. The bioactivity of the studied material was evidenced by the deposition in its surface of a calcium phosphate layer with apatite morphology after immersion in simulated body fluid (SBF). A higher biodegradation of composites with respect to apatite was obtained due to the presence of chitosan. Also the biodegradability of the composites increased with the chitosan content. Both, biodegradation and bioactivity could be controlled by the molecular weight of chitosan polymer matrix Along the different kinds of chitosan used, a better in vitro biological result was obtained using a chitosan with lower molecular weight. The in vitro biological characteristics of composites indicate that they are promising materials for bone substitution in guided bone regeneration.