J.H.G. Rocha

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

UNLABELLEDnSi-hydroxyapatite (Si-HAP) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute.nnnOBJECTIVEnThe 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.nnnMETHODSnSilicon-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.nnnRESULTSnSingle-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.nnnSIGNIFICANCEnThe 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.

Hydroxyapatite scaffolds hydrothermally grown from aragonitic cuttlefish bones

Scaffolds of pure AB-type carbonated hydroxyapatite (HA) were successfully produced via hydrothermal transformation (HT) of aragonitic cuttlefish bones at 200 °C. Beyond low production cost, worldwide availability and natural biological origin of raw materials, the produced scaffolds preserved the initial structure of the cuttlefish bone, featuring pore size of ∼80 µm in width and ∼100 µm in height. The transformation was complete after 9 h and no intermediate products were registered. The kinetics were fast, since, HA was the dominant crystalline phase after only 1 h of HT. The HA crystallites formed had a size of nanoscale (∼20–50 nm) and were randomly oriented.

Synthesis and thermal stability of sodium, magnesium co-substituted hydroxyapatites

Sodium and magnesium co-substituted hydroxyapatite (Hap) and β-tricalcium phosphate mixtures were prepared through an aqueous precipitation method. Characterization results from XRD, FT-IR and thermal analysis have indicated the influence of additives (Na and Mg) on the thermal stability of the apatites. The elemental analyses have also confirmed the presence of Na+ and Mg2+ ions in the apatite structure. Calculated lattice parameters for the combined substitution of elements on the apatite structure were found to have contraction of the a-axis and expansion of the c-axis as well as of the unit cell volume with respect to that of pure Hap.

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.

A Method for Simultaneously Precipitating and Dispersing Nano-Sized Calcium Phosphate Suspensions

Stable and relatively concentrated aqueous suspensions of nano-sized stoichiometric hydroxyapatite could be prepared by a precipitation method in the presence of suitable surface active agent (SAA). The method includes the precipitation, vacuum filtration and washing of the precipitated powders, followed by re-dispersion. It could be concluded that the added amount of the SAA should be enough to cover the primary particles surface, and that washing should be better carried out using a SAA solution. The method developed enables the precipitation of the powders and the preparation of suspensions, while significantly shortening the overall time required for colloidal processing consuming.

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.