A. Balamurugan

An in vitro biological and anti-bacterial study on a sol–gel derived silver-incorporated bioglass system

OBJECTIVES The purpose of this study was to evaluate the in vitro antibacterial and biological activity of silver-incorporated bioactive glass system SiO2-CaO-P2O5-Ag2O (AgBG). The bacteriostatic and bactericidal properties of this new quaternary glass system along with the ternary sol-gel glass system SiO2-CaO-P2O5 (BG) have been studied using Escherichia coli as a test micro-organism. The AGBG system thus appears to be a promising material for dental applications, since similar effects might be produced on a film of bacteria and mucous that grows on the teeth. METHODS The SiO2-CaO-P2O5-Ag2O and SiO2-CaO-P2O5 glass systems were synthesized by the sol-gel technique and characterized for their physicho-chemical properties. The antibacterial activity and biological properties were evaluated by determining the minimum inhibitory concentrations (MICs). Release of Ag+ into the culture medium was measured by inductively coupled plasma (ICP) analysis. RESULTS The in vitro antibacterial action of the SiO2-CaO-P2O5-Ag2O was compared with that of its ternary counterpart glass system. The concentrations of Ag-bioglass, in the range of 0.02-0.20 mg of Ag-bioglass per millilitre of culture medium, were found to inhibit the growth of these bacteria. The Ag-bioglass not only acts bacteriostatically but it also elicited a rapid bactericidal action. A complete bactericidal effect was elicited in the early stages of the incubation at Ag-bioglass concentration of 20 mg/ml and the ternary glass system had no effect on bacterial growth or viability. The antibacterial action of Ag-bioglass was exclusively attributed to the leaching of Ag+ ions from the glass matrix. SIGNIFICANCE One of the major advantages of incorporating silver ions into a gel glass system is that the porous glass matrix can allow for controlled sustained delivery of the antibacterial agent to dental material, used even under anaerobic conditions such as deep in the periodontal pocket. This glass system also provides long-term action required for systems which are constantly at risk of microbial contamination.

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.

Synthesis, bioactivity and preliminary biocompatibility studies of glasses in the system CaO–MgO–SiO2–Na2O–P2O5–CaF2

New compositions of bioactive glasses are proposed in the CaO–MgO–SiO2–Na2O–P2O5–CaF2 system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO4) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts’ cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).

Cryo‐X‐ray analysis—A novel tool to better understand the physicochemical reactions at the bioglass/biological fluid interface

The present study deals with the short‐term physicochemical reactions at the interface between bioactive glass particles [55SiO2‐20CaO‐9P2O5‐12Na2O‐4MgO. mol%] and biological fluid (Dulbecco Modified Eagles Medium (DMEM)). The physicochemical reactions within the interface are characterized by scanning transmission electron microscopy (TEM) (STEM) associated with Energy‐dispersive X‐ray spectroscopy (EDXS). Microanalysis of diffusible ions such as sodium, potassium, or oxygen requires a special care. In the present investigation the cryo‐technique was adopted as a suitable tool for the specimen preparation and characterization. Cryosectioning is essential for preserving the native distribution of ions so that meaningful information about the local concentrations can be obtained by elemental microanalysis. The bioglass particles immersed in biological fluid for 24 h revealed five reaction stages: (i) dealkalization of the surface by cationic exchange (Na+, Ca2+ with H+ or H3O+); (ii) loss of soluble silica in the form of Si(OH)4 to the solution resulting from the breakdown of SiOSi bonds (iii); repolymerization of Si(OH)4 leading to condensation of SiO2); (iv) migration of Ca2+ and PO43− to the surface through the SiO2‐rich layer to form CaO‐P2O5 film; (v) crystallization of the amorphous CaO‐P2O5 by incorporating OH or CO32− anions with the formation of three different surface layers on the bioactive glass periphery. The thickness of each layer is ≈300 nm and from the inner part to the periphery they consist of SiOH, which permits the diffusion of Ca2+ and PO43− ions and the formation of the middle CaP layer, and finally the outer layer composed of NaO, which acts as an ion exchange layer between Na+ ions and H+ or H3O+ from the solution. Microsc. Res. Tech., 2008.

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.