Ismail Ab Rahman

Synthesis of silica nanoparticles by sol-gel: size-dependent properties, surface modification, and applications in silica-polymer nanocomposites — a review

Application of silica nanoparticles as fillers in the preparation of nanocomposite of polymers has drawnmuch attention, due to the increased demand for new materials with improved thermal, mechanical, physical, and chemical properties. Recent developments in the synthesis of monodispersed, narrow-size distribution of nanoparticles by sol-gel method provide significant boost to development of silica-polymer nanocomposites. This paper is written by emphasizing on the synthesis of silica nanoparticles, characterization on size-dependent properties, and surface modification for the preparation of homogeneous nanocomposites, generally by sol-gel technique. The effect of nanosilica on the properties of various types of silica-polymer composites is also summarized.

Biogenic silver nanoparticles using Rhinacanthus nasutus leaf extract: synthesis, spectral analysis, and antimicrobial studies

Nanotechnology is gaining momentum due to its ability to transform metals into nanoparticles. The synthesis, characterization, and applications of biologically synthesized nanomaterials have become an important branch of nanotechnology. Plant extracts are a cost-effective, ecologically friendly, and efficient alternative for the large-scale synthesis of nanoparticles. In this study, silver nanoparticles (AgNps) were synthesized using Rhinacanthus nasutus leaf extract. After exposing the silver ions to the leaf extract, the rapid reduction of silver ions led to the formation of AgNps in solution. The synthesis was confirmed by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. The in vitro antimicrobial activity of the AgNps synthesized using R. nasutus leaf extract was investigated against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia, Escherichia coli, Aspergillus niger, and Aspergillus flavus using a disc diffusion method. The AgNps showed potential activity against all of the bacterial strains and fungal colonies, indicating that R. nasutus has the potential to be used in the development of value-added products in the biomedical and nanotechnology-based industries.

Water sorption characteristics of restorative dental composites immersed in acidic drinks

OBJECTIVES To determine the diffusion coefficient, water sorption and solubility of various types of restorative dental composites and to evaluate the effect of acidic media (orange juice and coke) on their characteristics. METHODS Resin composite specimens (Filtek™ Z350, Spectrum(®) TPH(®)3 and Durafill(®) VS) were prepared in a stainless steel mold of 1mm thickness and 10mm diameter (n=5) and light-cured. All samples were dried at 37°C, immersed in media (distilled water, orange and coke) at 37°C and weighed at suitable time intervals (15, 35, 155, 320, 785, etc.min) until 40 days of immersion and then were dried again for 40 days. Diffusion coefficient (m(2)s(-1)) was determined according to Ficks second law while water sorption and solubility (μg/mm(3)) were calculated based on BS EN ISO 4049:2000. Data of water sorption and solubility were analyzed with One-Way ANOVA and post hoc Scheffe test at p=0.05. RESULTS The experimental data obtained were obeyed and nearly fitted to the diffusion theoretical data plot. The highest values of diffusion coefficients were presented by Durafill(®) VS (32.23-45.25×10(-13)m(2)s(-1)). Diffusion coefficients of Filtek™ Z350 and Spectrum(®) TPH(®)3 were the highest when immersed in coke media followed by distilled water and orange juice. The water sorption of most composites was significantly increased after immersion in coke and orange (p<0.05). Meanwhile only Spectrum(®) TPH(®)3 showed an increase in solubility when immersed in coke media. Z350 presented the highest water sorption after immersion in distilled water and coke (16.13 and 18.22μg/mm(3)) while Durafill(®) VS presented the highest solubility (7.20-9.27μg/mm(3)). SIGNIFICANCE The exposure of restorative dental composites to acidic drinks can cause an increase in diffusion coefficient, water sorption and solubility parameters which may accelerate the degradation process and thus reduce the life span of composite restoration.

Two phase refinements of the structures of α-Si3N4 and β-Si3N4 made from rice husk by Rietveld analysis

Abstract The crystalline structures of α-Si3N4 and β-Si3N4 made from rice husk were obtained at room temperature (300 K) from X-ray powder diffraction with CuKα radiation using Rietveld analysis for the two phase mixture. For α-Si3N4 at 300 K, crystal data: Mr = 140.285, the rhombohedral system, P31c, a = 7.7650(4) A, c = 5.6275(2) A, V = 293.85(2) A3, Z = 4, Dx = 3.1709 g cm−3, μ = 133.474 cm−1 (λ = 1.5406 A), F(000) = 280.0, the structure was refined with 29 parameters to Rb = 2.42%, Rf = 1.78% for 243 peaks. For β-Si3N4 at 300 K, crystal data: Mr = 140.285, the hexagonal system, P63/m, a = 7.6093(8) A, c = 2.9079(2) A, V = 145.81(2) A3, Z = 2, Dx = 3.1951 g cm−3, μ = 134.492 cm−1 (λ = 1.5406 A), F(000) = 140.0, the structure was refined with 17 parameters to Rb = 3.02%, Rf = 1.88% for 145 peaks. The whole diffraction was fitted and refined with 46 parameters to Rwp = 6.98%, Rp = 5.33% for 3301 step intensities and ‘goodness of fit’ S = 3.50.

Assessment of DNA damage caused by locally produced hydroxyapatite-silica nanocomposite using Comet assay on human lung fibroblast cell line

The growing interest of nanotechnology in dentistry has sparked various applications of biomaterials in nanoscale to be developed. The aim of this study was to evaluate the genotoxicity effect of locally produced hydroxyapatite-silica nanocomposite (School of Dental Sciences, Universiti Sains Malaysia, Malaysia) using Comet assay on human lung fibroblast cell line, MRC-5. Extraction of this test material was prepared and the concentrations which produced IC10, IC25 and IC50 in cytotoxicity tests (MTT assay) were recorded. Three specific concentrations, 0.00005 g/mL, 0.0009 g/mL and 0.1 g/mL for IC10, 1C25 and IC50 respectively were further used to evaluate the genotoxicity effect along with concurrent positive (hydrogen peroxide) and negative (Eagle’s Minimum Essential Medium) controls. There was no significant difference in the tail moments between negative control and treatment groups (0.00005 g/mL). Dose-dependent relationship was observed, where significant difference was noticed in the tail moments between 0.0009 g/mL and 0.1 g/mL groups with that of the negative control. However, since the values were still less than 5, it can be considered as non-genotoxic. The tail moments between different concentrations of hydroxyapatite-silica nanocomposite and positive control differed significantly (P/0.05). This concludes that the locally produced HAsilica nanocomposite is non-genotoxic by Comet assay under the present test conditions.

One-pot synthesis of hydroxyapatite–silica nanopowder composite for hardness enhancement of glass ionomer cement (GIC)

Hydroxyapatite–silica nanopowder composite was prepared using one-pot sol–gel technique. The morphology of the powder consists of a mixture of spherical silica particles (∼30 nm) embedded within the elongated hydroxyapatite (∼103 nm). The synthesized nanoparticles were incorporated into commercial glass ionomer cement (GIC) and Vickers hardness was evaluated. Results shown that the addition of the nanopowder composite gave ∼73% increment in the hardness compared to the pure GIC. Higher content of hydroxyapatite–silica nanopowder resulted in dense cement and produced a stronger GIC and the application of this material with improved hardness property might lead to extend the clinical indications, especially in stress bearing areas.

The Synthesis and Characterization of Cobalt-Rice Husk Silica Nanoparticles

Spherical and needle-like cobalt nanoparticles incorporated on rice husk silica was synthesized by a simple, rapid and eco-friendly sol-gel route at room temperature. This was achieved by direct mixing of 20 wt.% Co 2+ with so- dium silicate from rice husk under ambient conditions to form RH-20Co. The cobalt was found to be isomorphously sub- stituted in the silica matrix. A good dispersion of cobalt nanoparticles was evidenced from X-ray diffraction. Transmis- sion electron microscopy confirmed the formation of well-dispersed and spherical cobalt nanoparticles with an average particle size of 5.6 nm. The magnetic properties of this material were measured with vibrating magnetometer. The satura- tion magnetization, Ms and coercive force, Hc was found to be 0.245 emu/g and 304.09 Oe respectively.

Genotoxicity evaluation of dental restoration nanocomposite using comet assay and chromosome aberration test

Nanocomposite is used as a dental filling to restore the affected tooth, especially in dental caries. The dental nanocomposite (KelFil) for tooth restoration used in this study was produced by the School of Dental Sciences, Universiti Sains Malaysia, Malaysia and is incorporated with monodispersed, spherical nanosilica fillers. The aim of the study was to determine the genotoxic effect of KelFil using in vitro genotoxicity tests. The cytotoxicity and genotoxicity of KelFil was evaluated using MTT assay, comet assay and chromosome aberration tests with or without the addition of a metabolic activation system (S9 mix), using the human lung fibroblast cell line (MRC-5). Concurrent negative and positive controls were included. In the comet assay, no comet formation was found in the KelFil groups. There was a significant difference in tail moment between KelFil groups and positive control (p < 0.05). Similarly, no significant aberrations in chromosomes were noticed in KelFil groups. The mitotic indices of treatment groups and negative control were significantly different from positive controls. Hence, it can be concluded that the locally produced dental restoration nanocomposite (KelFil) is non-genotoxic under the present test conditions.

Preparation of low melting temperature, lead-free glaze by the sol–gel method

The sol–gel method was used to prepare low melting temperature, lead-free glaze based on the Na2O–K2O–CaO–ZnO–B2O3–Al2O3–SiO2 system. Tetraethoxysilane and aluminium sec-butoxide were used to replace silica and alumina, high melting constituents of the raw materials. A homogeneous gel was obtained through sequential hydrolysis by using 5 mol of water per mol of alkoxides, a mixture of ethanol and 2-butanol as solvent, and HCl as catalyst (pH ∼ 3). The remainder of the raw materials was processed to be coated by the gel. Gel as the coating layer was observed to be amorphous and homogeneously bonded around the raw materials particles and was very effective in lowering the melting temperature of the glaze by 30–130°C. This, however, depends on the amount of metal alkoxides used for replacement. TEM, SEM and porosimeter were used to characterize the glaze samples.

Effect of biphasic calcium phosphate scaffold porosities on odontogenic differentiation of human dental pulp cells

Calcium phosphates (CaP) of different porosities have been widely and successfully used as scaffolds with osteoblast cells for bone tissue regeneration. However, the effects of scaffold porosities on cell viability and differentiation of human dental pulp cells for dentin tissue regeneration are not well known. In this study, biphasic calcium phosphate (BCP) scaffolds of 20/80 hydroxyapatite to beta tricalcium phosphate ratio with a mean pore size of 300 μm were prepared into BCP1, BCP2, BCP3, and BCP4 of 25%, 50%, 65%, and 75% of total porosities, respectively. The extracts of these scaffolds were assessed with regard to cell viability, proliferation, and differentiation of human dental pulp cells. The high alkalinity, and more calcium and phosphate ions release that were exhibited by BCP3 and BCP4 decreased the viability and proliferation of human dental pulp cells as compared to BCP1 and BCP2. BCP2 significantly increased both cell viability and cell proliferation. However, the cells cultured with BCP3 extract revealed high alkaline phosphatase (ALP) activity and high expression of odontoblast related genes, collagen type I alpha 1, dentin matrix protein-1, and dentin sialophosphoprotein as compared to that cultured with BCP1, BCP2, and BCP4 extracts. The results highlight the effect of different scaffold porosities on the cell microenvironment and demonstrate that BCP3 scaffold of 65% porosity can support human dental pulp cells differentiation for dentin tissue regeneration.