Bacterial colonisation of bioceramic surfaces

Abstract

Hydroxyapatite (HAp – Ca₁₀(PO₄)₆(OH)₂) and tricalcium phosphate (TCP – Ca₃(PO₄)₂) are bioceramic materials of special interest with regards to bone surgery, in particular the repair of bone tissue defects. These materials are highly biocompatible with bone and soft tissue; they are bioactive, osteoconductive and resistant to sterilisation processes. In comparison with other biomaterials, particularly metallic materials, bioceramic surfaces exhibit high resistance to bacterial colonisation. This is currently considered to be one of the most important issues concerning materials used in medicine, due to the fact that bacterial biofilm is difficult to combat or remove and can be responsible for recurrent infections.

The aim of the present study was to evaluate bacterial colonisation on the surface of different calcium phosphate based materials.     

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Abstract

Deoxidation, desulphurisation and inclusion modification are some of the essential features in secondary steel refining through injection of calcium alloy in the form of a cored wire. It is imperative that the filling material must be consumed by the melt to the maximum extent in order to make this cored wire alloy addition cost effective and efficient. In this connection study of calcium recovery is an important issue, which may provide guidelines to select the optimum operating parameters from a fundamental basis. The present study is based on plant data from Tata Steel, Jamshedpur, India. The results demonstrate that maximum calcium recovery is achievable at an optimum speed of the cored wire. Dimensional analysis was carried out to analyse the plant data and the calcium recovery was found to correlate well with physically sound dimensionless numbers such as Biot number, the dimensionless bath temperature and the relative rate of silicon to sulphur transfer from/to the added calcium silicide in the melt. A correlation has also been obtained between the calcium recovery and various dimensionless parameters. The efficacy of calcium addition is also assessed through characterisation of inclusions by scanning electron microscopy and energy dispersive X-ray spectroscopy.     

Influence of Filler Size on Impact Properties of PP/Elastomer/Filler Ternary Composites

Influence of filler size on impact properties for polypropylene (PP)/elastomer/filler ternary composites was investigated. Calcium carbonate (CaCO₃) particles with a diameter in the range from 120 to 1200 nm were used as a filler and polystyrene-block-poly(ethylene-butene)-block-polystyrene triblock copolymer (SEBS) was used as an elastomer. In the PP/SEBS/CaCO₃ ternary composite, CaCO₃ particles and SEBS particles were dispersed in the PP matrix separately. In the case that SEBS elastomer volume fraction was below 0.12, the impact strength improved gradually with a decrease of CaCO₃ mean diameter from 1200 to 160 nm. In the case that SEBS volume fraction was above 0.17, the impact strength improved significantly by the incorporation of CaCO₃ particles with a mean diameter in the range from 120 to 900 nm. However, the impact strength hardly improved by the incorporation of CaCO₃ particles with a mean diameter of 1200 nm.     

Structural characteristics of poly(vinyl alcohol)–calcium carbonate composites prepared by sequential method

Abstract

Composites of poly(vinyl alcohol) (PVA) and calcium carbonate (CaCO₃) were prepared by a sequential method involving first in situ synthesis of CaCO₃ in PVA solution, then physical crosslinking of synthetic suspension and subsequently washing of resultant elastic gel followed by consolidation. The phase and composition, mechanical properties and microstructure of the composites and possible molecular interactions between both components were evaluated. X-ray diffraction analysis revealed that calcium carbonate was mainly composed of aragonite and calcite. Compression tests confirmed the composites prepared by this sequential method had good mechanical properties and that the compressive strength of the composites increased with higher content of calcium carbonate. PVA formed an interconnected network and needle-like CaCO₃ crystals together with some fine grains were well compatible with PVA. In situ synthesis induced a spectral shift of hydroxyl groups and C–O bonds of PVA and the suppression of the characteristic adsorption of calcite was also observed, according to Fourier transform infrared spectroscopy measurements.     

Characterisation of monophasic and diphasic mullite precursors by solid state reaction study

Abstract

The characterisation by various spectroscopic techniques of amorphous mullite precursors formed from monophasic (SH) and diphasic (DG) gels is reviewed. In a new approach, both types of precursor have been heated with CaCO₃ and the crystalline phases formed during solid state reaction monitored using an X-ray powder diffraction technique. The formation of a calcium aluminosilicate phase (gehlenite) rather than calcium aluminate suggests that both precursors consist of an amorphous aluminosilicate phase of composition close to that of 3:2 mullite.     

Corrosion properties of anodic oxide coatings on Ti–6Al–4V in simulated body solution

Abstract

Anodic oxide coatings were synthesised on Ti–6Al–4V substrates using aqueous electrolytes containing dissolved calcium and phosphorus. Different coatings were produced by varying the time of synthesis. Inherent features of the coatings were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Uniform corrosion, electrochemical polarisation and ac impedance tests were performed in simulated body fluid (SBF). Small amounts of calcium and phosphorus are deposited from the electrolyte on to the coating and their levels increase with increasing duration of synthesis. Maximum values of porosity and thickness are obtained for oxides coated for 3 h. Coatings produced from shorter times showed very good resistance to the attack of SBF.     

Mg2+ content control of aragonite whisker synthesised from calcium hydroxide and carbon dioxide in presence of magnesium chloride

Abstract

This research is concerned with thermodynamic control of inorganic whisker synthesis in existence of some additives. The polymorphism and morphology control of calcium carbonate (CC) is an active research area because of wide applications of CC. Magnesium chloride has been used to improve the formation of aragonite whisker synthesised from Ca(OH)₂ and CO₂. However, the reaction kinetics and the purity of final products affected by MgCl₂ have not been theoretically studied. In the present research quantitative thermodynamic calculation showed that MgCl₂ can decrease relative supersaturation by several orders of magnitude and so is favourable to the formation of aragonite. High reactant ratio of MgCl₂/Ca(OH)₂ will give a marked decrease in pH within the transformation of Ca(OH)₂ into Mg(OH)₂, but a small decrease in pH in the following CaCO₃ formation, which is disadvantageous to the control of the synthesis with pH. Both solid Mg(OH)₂ and MgCO₃ may exist in aragonite product, but can be avoided by pH control. Maximum MgCO₃ content in aragonite product is <1·00 wt-% and MgCO₃ can be removed by slightly decreasing pH using excessive CO₂ adsorption, which will result in a negligible decrease in Ca²⁺ conversion and an increase in carbonate ion concentration. High carbonate ion concentration, unfortunately, is disadvantageous to the reuse of MgCl₂ solution. The present study gives a guidance of synthesising aragonite in the presence of inorganic salts such as MgCl₂.     

Influence of calcium phosphate on rheological properties of sanitaryware slip

Abstract

The aim of this work is to study the influence of calcium phosphate on sanitaryware suspension viscoelasticity. The specific interest was given to use of waste calcium phosphate instead of feldspar in a sanitaryware slip: the goal is to set up a new formulation of raw materials with the same rheological properties and related casting parameters of the traditional one. Above all, two suspensions parameters were studied: the calcium phosphate concentration and the aging effects. The most appropriate calcium phosphate concentration and aging time were found.     

Influence of calcium carbonate added to the SBS rubber formulation on the surface modifications produced by halogenation

To improve the adhesion properties of styrene–butadiene–styrene (SBS) rubber sole to polyurethane adhesive, surface treatments are required, of which halogenation with trichloroisocyanuric acid (TCI) solutions in organic solvents is the most commonly used treatment in the footwear industry. Calcium carbonate filler is commonly added to improve the mechanical properties and to reduce shining of SBS rubber formulations. The influence of the filler on the effectiveness of surface chlorination of SBS rubber had not been considered in the existing literature. Therefore, 10 wt% calcium carbonate filler was added to the SBS rubber formulation and the surface modifications and adhesion properties produced by treatment with TCI solutions were investigated. The resulting surface modifications and adhesion were compared to those obtained in unfilled SBS rubber. It is shown that the treatment with TCI solutions was less effective in the calcium-carbonate-filled SBS rubber and a lower peel strength to polyurethane adhesive was obtained; however, a cohesive failure in the rubber was always obtained.