Biomedical subjects

Patrick Sharrock

Publications and source records attributed to Patrick Sharrock.

9 recordsLinked to original sources

PubMed2006

The role of acrylophosphonic acid monomers in the formation of hybrid layers based on self-etch adhesives.

UNLABELLED: The role of acrylophosphonic acid monomers in the formation of hybrid layers based on self-etch adhesives. OBJECTIVES: Our plan was to define the reaction products formed when an acrylophosphonic acid reacts with tooth hard tissue. Our aim was to describe the incorporation of the reaction products in the hybrid layer formed. METHODS: Potentiometric methods were used to measure acid dissociation constants and investigate calcium complex formation. Infrared spectroscopy and NMR were used to follow water contents and show transformation of phosphorous containing compounds. RESULTS: The acrylophosphonic acid contained in AdheSE (Ivoclar Vivadent, Schaan, Liechtenstein) is characterized by two acidities with pK(a1)=2.4 and pK(a2)=7.0, and interacts with calcium ions in a purely ionic fashion. When hydroxyapatite crystals are dissociated by the presence of AdheSE, brushite is formed together with a calcium cross-linked network of the phosphonate containing copolymer. CONCLUSION: The results give a new image of the hybrid layer where the adhesive behaves like an ionomer resin incorporating collagen but also minerals and salt bridges.

Acid Etching, Dental↗

PubMed2005

Physical and chemical characterisation of crude meat and bone meal combustion residue: "waste or raw material?".

As a result of the recent bovine spongiform encephalopathy (BSE) crisis in the European beef industry, the use of animal by-product is now severely controlled. Meat and bone meal (MBM) production can no longer be used to feed cattle and must be safely disposed of or transformed. Main disposal option is incineration, producing huge amounts of ashes the valorisation of which becomes a major concern. The aim of this work is to characterise MBM combustion residue in order to evaluate their physical and chemical properties to propose new valorisation avenues. The thermal behaviour of crude meat and bone meal was followed by thermogravimetric analysis (TGA) and (24 wt.%) inorganic residue was collected. The resulting ashes were characterised by powder X-ray diffraction (XRD), particle size distribution, specific surface area (BET), scanning electron microscopy (SEM) couple with energy disperse X-ray analysis (EDX). Elemental analysis revealed the presence of chloride, sodium, potassium, magnesium with high level of phosphate (56 wt.%) and calcium (31 wt.%), two major constituents of bone, mainly as a mixture of Ca10(PO4)6(OH)2 and Ca3(PO4)2 phases. The impact of combustion temperature (from 550 to 1000 degrees C) on the constitution of ashes was followed by TGA, XRD and specific surface measurements. We observed a strong decrease of surface area for the ashes with crystallisation of calcium phosphates phases without major changes of chemical composition.

Animals↗

PubMed2005

Lead electrocapture on hydroxyapatite coated electrodes.

Hydroxyapatite coated electrodes were made by a hydrolysis reaction involving silanes and hydroxyapatite particles on stainless steel. Aqueous lead ions were captured on the coatings with or without electromigration. Results depend on coating thickness, supporting electrolyte and the presence of the electric field. It was found that this new electrocapture method can remove lead from solutions down to ppb levels.

Durapatite↗

PubMed2005

Release of aqueous calcium and phosphate from human dental enamel following administration of self-etching adhesives.

Seven self-etching adhesives were studied on an experimental reconstituted human enamel model. The objective was to evaluate the acid dissociation step of the enamel minerals. The self-etching products were applied to the enamel specimens according to the manufacturers' instructions and then rinsed with distilled water. The aqueous calcium and phosphate released were analysed chemically by atomic absorption and ion chromatography, respectively. Results show widely varying concentrations related to pH, acid concentration and calcium binding capacity. All concentrations are less than reference values obtained with orthophosphoric acid. The effectiveness of self-etchants is discussed in terms of their ability to demineralise human enamel and incorporate the released ions in the subsequent HEMA co-polymer composing the hybrid layer.

Adhesives↗

PubMed2004

Stabilisation of heavy metal containing dusts by reaction with phosphoric acid: study of the reactivity of fly ash.

Water-washed fly ash was reacted with phosphoric acid in order to transform available heavy metals into insoluble metal phosphate compounds. The temperature, pH and concentration of free phosphate were monitored during the first 80 min of reaction. Phosphoric acid reacted rapidly with second order kinetics and an apparent rate constant of 0.015 l/(mol s m2). Analysis of the evolution of the concentrations of other major elements of fly ash shows that the reaction follows a dissolution-precipitation type mechanism. The solubility of trace heavy metals tends to increase at low pH values. Various heat and mass transfer coefficients are derived and help understand the phosphate stabilisation procedure and design industrial reactors for this purpose. Calcium phosphates are formed which can trap heavy metals in a stable apatite mineral structure.

Carbon↗

PubMed2004

Release of anthracyclines adsorbed on copper-treated hydroxylapatites.

Anthracyclines are antibiotics widely used for the treatment of leukemia and solid tumors. Perfusion is the standard clinical administration form. Unfortunately, this does not allow treatment of gastric cancers. A new galenic presentation, consisting of anthracyclines adsorbed onto hydroxylapatite granules, has been developed. It was found to be possible to modulate the release of the drug as a function of the pH by using copper(II) ions. At neutral pH, the drug remains on the mineral support, but at pH 3, the drug is released into solution. Further investigations demonstrate that copper-containing hydroxylapatite can retain a determined quantity of antibiotic by surface complexation. This result could contribute to new designs for drug carriers targeted for gastric cancers.

Adsorption↗

PubMed2003

Beneficial use of meat and bone meal combustion residue: "an efficient low cost material to remove lead from aqueous effluent".

Meat and bone meal (MBM) combustion residues, a natural apatite-rich substance, was evaluated as a low cost substitute for hydroxyapatite in lead sequestration from water effluents. The thermal behaviour of crude meat and bone meal was followed by TGA and 24% inorganic residue was collected. The resulting ashes were characterised by powder X-ray diffraction (XRD), particle size distribution, specific surface area (BET), and elemental analysis confirming apatite contents, with high level of phosphate (56.3%) and calcium (36.8%). Mechanism and kinetics of lead removal by this bioinorganic material were investigated and compared to mechanisms and kinetics involved with synthetic apatite. Batch metal removal experiments were carried out with 500 and 1500ppm (mg/kg) Pb(2+) solutions. Lead concentration, calcium and pH were monitored. We observed that the mechanism is similar to that occurring for pure apatite, and involved both surface complexation and calcium hydroyapatite (CaHA), Ca(10)(PO(4))(6)(OH)(2), dissolution followed by less soluble Pb(10)(PO(4))(6)(OH)(2) precipitation, as confirmed by XRD analysis of ashes after incubation with lead solution. Our results show that this natural apatite-rich material removes in a few minutes a large quantity of lead (275mg/g capacity) which remains however lower than the theoretical maximum capacity (if calcium were totally substituted by lead). Meat and bone meal combustion residues represent a valuable alternative apatite source for environmental application.

Abattoirs↗

PubMed2002

Characterization of sound human dentin particles of sub-millimeter size.

OBJECTIVES: To obtain small dentin particles to provide material for the characterization of dentin. To study the interaction of etchants with dentin not covered by a smear layer and bonding agents. METHODS: Sound human dentin particles of sub-millimeter sizes were obtained by room temperature high-pressure fragmentation. Smear-layer free particles of three different average sizes were obtained by sieving. Surface areas were measured by the BET method. Simultaneous thermogravimetric and differential thermal analysis was carried out on all specimens and etched samples. Densities were measured by helium pycnometry. RESULTS: On average, the water, organic and mineral contents show the expected proportions. The more dense particles tend to be in the smaller sized fractions. Thus dentin particles of average size 100 microm have a density of 2.482(0.002) g/ml which is statistically different from the 300 microm average sized particles with 2.306(0.002) g/ml. However, the respective measured specific surface areas of 2.54(0.01) and 2.50(0.02) m(2)/g are not found to be statistically different. The specific surface areas of dentin particles increase upon etching, the increase being related to acid strength. Thermal analysis of acid-etched 200 microm diameter particles shows up to 75% loss of carbonate and only 30% loss of phosphate. SIGNIFICANCE: Smear-layer free dentin particles which have not been exposed to heat by grinding can be obtained by room temperature high-pressure fragmentation. Such sub-millimeter sized dentin particles can be acid-etched to significantly increase their specific surface area. Thermogravimetry used to analyze carbonate and phosphate contents gives new insight to the buffering action of human dentin.

Acid Etching, Dental↗

PubMed2002

Calcium phosphate stabilization of fly ash with chloride extraction.

Municipal solid waste incinerator by products include fly ash and air pollution control residues. In order to transform these incinerator wastes into reusable mineral species, soluble alkali chlorides must be separated and toxic trace elements must be stabilized in insoluble form. We show that alkali chlorides can be extracted efficiently in an aqueous extraction step combining a calcium phosphate gel precipitation. In such a process, sodium and potassium chlorides are obtained free from calcium salts, and the trace metal ions are immobilized in the calcium phosphate matrix. Moderate calcination of the chemically treated fly ash leads to the formation of cristalline hydroxylapatite. Fly ash spiked with copper ions and treated by this process shows improved stability of metal ions. Leaching tests with water or EDTA reveal a significant drop in metal ion dissolution. Hydroxylapatite may trap toxic metals and also prevent their evaporation during thermal treatments. Incinerator fly ash together with air pollution control residues, treated by the combined chloride extraction and hydroxylapatite formation process may be considered safe to use as a mineral filler in value added products such as road base or cement blocks.

Air Pollutants↗