J.M.G. Ventura

Suitability evaluation of sol–gel derived Si-substituted hydroxyapatite for dental and maxillofacial applications through in vitro osteoblasts response

UNLABELLED Si-hydroxyapatite (Si-HAP) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute. OBJECTIVE The aim of this investigation was to study the effect of Si substitution into the hydroxyapatite matrices and evaluate the biocompatibility effects of Si-HAP material in vitro with human osteoblasts. METHODS Silicon-substituted hydroxyapatite (Si-HAP) bioceramic materials were prepared by incorporating small amounts of silicon into the structure of hydroxyapatite [Ca10(PO4)6(OH)2, HAP] through a sol-gel method. A series of silicon substitutions ranging from 0, 1, 3 and 5 mol%, which are comparable to the measured silicon contents in natural bone, were performed. RESULTS Single-phase Si-HAP was obtained upon calcining the as-prepared powders up to 800 degrees C since no secondary phases, such as tricalcium phosphate (TCP), tetracalcium phosphate (TeCP) or calcium oxide (CaO), were identified by X-ray diffraction analysis. The effects of silicon-substituted hydroxyapatite (Si-HAP) materials towards the responses of human osteoblast-like (HOB) cells were investigated and compared with pure hydroxyapatite. SIGNIFICANCE The Si-HAP indicated a significant increase in cell growth density with culture time irrespective of the amount of Si substituted in HAP. A high Si content (5 mol%) appears to promote rapid bone mineralization, since large amount of calcium phosphate minerals started to develop across the ECM by day 31 for a sample containing 5 mol% Si. On the other hand, a high Si content may result in fast dissolution of the material, owing to a decrease of HAP crystallite size, which might not be ideal for cell attachment for prolonged time periods. An optimum level of Si appears to exist at 3 mol%, which balances these effects.

3D chitosan–gelatin–chondroitin porous scaffold improves osteogenic differentiation of mesenchymal stem cells

A porous 3D scaffold was developed to support and enhance the differentiation process of mesenchymal stem cells (MSC) into osteoblasts in vitro. The 3D scaffold was made with chitosan, gelatin and chondroitin and it was crosslinked by EDAC. The scaffold physicochemical properties were evaluated. SEM revealed the high porosity and interconnection of pores in the scaffold; rheological measurements show that the scaffold exhibits a characteristic behavior of strong gels. The elastic modulus found in compressive tests of the crosslinked scaffold was about 50 times higher than the non-crosslinked one. After 21 days, the 3D matrix submitted to hydrolytic degradation loses above 40% of its weight. MSC were collected from rat bone marrow and seeded in chitosan-gelatin-chondroitin 3D scaffolds and in 2D culture plates as well. MSC were differentiated into osteoblasts for 21 days. Cell proliferation and alkaline phosphatase activity were followed weekly during the osteogenic process. The osteogenic differentiation of MSC was improved in 3D culture as shown by MTT assay and alkaline phosphatase activity. On the 21st day, bone markers, osteopontin and osteocalcin, were detected by the PCR analysis. This study shows that the chitosan-gelatin-chondroitin 3D structure provides a good environment for the osteogenic process and enhances cellular proliferation.

Method for Tailoring and Control the Morphology, Size and Porosity of Calcium Phosphate Granules

Hydroxyapatite (HA) is the calcium-phosphate material with composition closest to that of human bone, what makes it suitable for osseous implant purposes, namely as fillers, spacers and bone grafts substitutes. This study is aimed at the development of a method to produce porous spherical hydroxyapatite granules. The process involves the spraying of a suspension with different amounts of a setting agent to a setting media. The tailor and the control of the morphology, size and porosity of the granules were attained by adjusting the nozzle diameter, the pressure of air flow and the distance between the nozzle and the setting media.

Synthesis and Characterization of Sol Gel Derived Silicon Substituted Porous Hydroxyapatite Scaffolds - Effect of Siliconlevelontheinvitrobiocompatibilityof Si-Hap

Ceramics based on calcium phosphates are known to be perspective materials for biomedical applications. Noticeable attention has been paid to hydroxyapatite Ca10(PO4)6(OH)2 due to its affinity to a bone mineral, Hench et al [1]. It was recognised recently that Si-substituted HAP is a highly promising material in sense of bioactivity improvement, Patel et al [2]. In the frame of distinct research activity structured around this subject, some important problems are to be solved: (a) solubility of Si in the HAP lattice; (b) rationalization of Si effect on the sintering of HAP; (c) in vitro biocompatibility of the Si-HAP. The present work is focused on the sol gel synthesis of Si-HAP with Ca10(SixPO4)6-x(OH)2-x (x=0.56) nominal composition and evaluation of the effect of Si on HAP ceramics. The limit of Si solubility in HAP lattice was estimated to be not higher than x=0.56. The incorporation of Si influences the initial stages of sintering. The effect of Si on sintering behaviour can be viewed in terms of its segregation to grain boundaries, the phenomenon arising from lattice instability of Si-HAP due to the charge compensation in the course of aliovalent substitution, LeGeros [3]. The in vitro biocompatibility of the Si substituted HAP was tested on human osteoblasts. The cells were cultured on hydroxyapatite, and Si-substituted hydroxyapatite (Si-HAP) discs. However, an increase of the silicon content from 0.8 to 1.6 wt % leads to the polymerization of the silicate species at the surface. The in vitro bioactivity assays showed that the formation of an apatite-like layer onto the surface of silicon-containing substrates is strongly enhanced as compared with pure silicon-free hydroxyapatite, Jarcho [4]. The samples containing monomeric silicate species showed higher in vitro bioactivity than that of silicon-rich sample containing polymeric silicate species, Carlisle [5]. The influence of these substrates on cell behaviour in vitro was assessed by measuring total protein in the cell lysate and the production of several phenotypic markers: collagen type I (COL I), alkaline phosphatase (ALP), osteocalcin (OC), and the formation of bone mineral. There was a significantly higher production of ALP on Si-HAP at day 7 following which, the addition of hydrocortisone promoted the differentiation of cells. Mineral deposits were visualized on the surface of the materials at day 21. These deposits coincided with the areas of high cell density. At day 28, a larger number of deposits were observed (Fig. 1). No difference in the pattern or timing of mineralization was seen between the materials.