Hydrothermal synthesis of lithium silicate (Li2SiO3) from waste glass: a preliminary study

Current environmental directives to conserve resources and to divert waste streams have generated significant interest in mineral recycling. In this respect, this preliminary study has demonstrated that lithium metasilicate can be prepared by hydrothermal reaction between waste container glass and lithium hydroxide solutions at 100 °C. Minor proportions of calcium hydroxide, calcite, lithium carbonate and tobermorite were also produced during the reaction. Percentage crystallinity and proportion of lithium metasilicate in the reaction product were found to increase as functions of lithium hydroxide concentration (between 1 and 4 M). This research has also shown that the lithium metasilicate phase can take up 6.4 mmol/g of Zn2+ ions after 24 h during batch sorption. Further work to optimise the yield and to appraise the antimicrobial properties of Zn2+-bearing lithium metasilicate is now warranted

Enamael Protection by Hydroxyapatite Toothpaste

Tooth enamel comprises ∼90% substituted hydroxyapatite (Ca10(PO4)6(OH)2), HAP, which is continually subjected to consecutive cycles of dissolution and recrystallisation. Initial dental caries is denoted by non-cavitated white spot lesions (WSLs) when net demineralisation occurs. Commercial products such as toothpastes, mouthwashes and chewing gums that release bioavailable calcium, phosphate and/or fluoride species have been shown to facilitate the remineralisation and repair of initial WSLs. In this respect, synthetic HAP particles can be incorporated into toothpastes to exploit both their abrasive and remineralising properties. The present study investigates the potential of a toothpaste containing micron-sized HAP particles (mirasensitive hap+®, Hager Werken, Germany) to repair WSLs in human enamel under optimum pH-neutral conditions and to protect the enamel exposed to an aggressive acid-challenge regime in vitro

Enamael Remineralisation by Arginine-Calcium Carbonate Toothpaste

White spot lesions (WSLs) are the first visual indication that the dynamic processes that maintain healthy tooth enamel have shifted in favour of demineralisation. It is possible to reverse this early stage of enamel caries with good oral hygiene and home-use products that enhance the bioavailability of salivary calcium, phosphate and fluoride species. Arginine (C6H14N4O2), a conditionally essential α-amino acid, is metabolised by oral bacteria to generate ammonia which protects enamel from acid-erosion. It also forms complexes with Ca2+ ions which increase the bioavailability of calcium and promote remineralisation. The present in vitro study investigates the potential of a commercial arginine- and calcium carbonate-bearing toothpaste (Colgate Sensitive Pro-Relief, Colgate-Palmolive (UK) Limited) to repair WSLs in human enamel under optimum and aggressive acid-challenge conditions

Bioactivity and antimicrobial properties of chitosan-tobermorite membranes

Tobermorite (Ca5Si6O16(OH)2.4H2O) is a layered calcium silicate hydrate phase whose bioactivity and biocompatibility with respect to bone and dental tissues are documented. Chitosan is a biodegradable mucopolysaccharide derivative that has been evaluated as a tissue scaffold material for the in situ regeneration of bone and periodontal structures. Recent studies have shown that tobermorite-chitosan composites are potential candidates for use as biodegradable guided tissue regeneration (GTR) membranes [2,3]. During the GTR process, a membrane is used to isolate the exposed root surface from invasive epithelial and gingival tissues in order to enable the slow-growing periodontal ligament and hard tissues to regenerate. Resistance to potentially pathogenic oral bacteria is a highly desirable property of GTR membranes which are prone to biomaterial-centred infection. Silver (Ag+), copper (Cu2+) and gallium (Ga3+) ions are reported to confer antimicrobial activity when incorporated into bioactive materials [1,4,5]. In the present study, tobermorite was synthesised and ion-exchanged with Ag+, Cu2+ or Ga3+ ions. The in vitro bioactivity and antibacterial properties of solvent-cast tobermorite-chitosan composite membranes were then evaluated with respect to their potential use as GTR membranes to repair damaged periodontal structures

Textural and structural properties of bioactive glasses in the system CaO-SiO2

Gel-derived CaO-SiO2 binary glasses of CaO mole fractions 0. 2, 0.3 and 0. 4 have been prepared and characterised. Pore diameter specific pore volume, skeletal density and porosity were found to increase with increasing CaO-content, whereas a concomitant decrease in specific surface area was observed. Si-29 NMR indicated that the 0.2 CaO mole fraction glass consisted of higly polymerized Q(4) and Q(3) silicate species, with some Q(2) units. With increasing CaO mole fraction, these silicate species became progressively depolymerised such that isolated SiO4 tetrahedra were detected within the 0.4 CaO glass matrix. Unusually, the glasses retained a proportion of Q(4) and Q(3) species as the CaO mole fraction was increased. All glass formulations exhibited in vitro bioactivity. The rate of hydroxyapatite precipitation followed the order 0.2 CaO > 0.4 CaO > > 0.3 CaO, an effect that is attributed to differences in the rate of dissolution of calcium from these glasses. This, in turn, appears to be dependent upon the proportion of Ca 21 participating in the formation of the glassy network

Antibacterial activity of a chitosan-PVA-Ag+-Tobermorite composite for periodontal repair

A polymer-mineral composite was prepared by solvent casting a mixture of chitosan, poly(vinyl alcohol), and Ag+-exchanged tobermorite in dilute acetic acid and characterised by scanning electron microscopy and Fourier transform infrared spectroscopy. The in vitro bioactivity of the CPTAg membrane was confirmed by the formation of hydroxyapatite on its surface in simulated body fluid. The alkaline dissolution products of the tobermorite lattice buffered the acidic breakdown products of the chitosan polymer and the presence of silver ions resulted in marked antimicrobial action against S. aureus, P. aeruginosa, and E. coli. The in vitro cytocompatibility of the CPTAg membrane was confirmed using MG63 osteosarcoma cells. The findings of this preliminary study have indicated that chitosan-poly(vinyl alcohol)-Ag+-tobermorite composites may be suitable materials for guided tissue regeneration applications

Copper- and zinc-bearing composite membranes for periodontal repair

Periodontitis (inflammation and destruction of the tooth attachment apparatus) is one of the most widespread diseases in the world. Polymer-bioactive glass composite membranes can be used for the guided tissue regeneration (GTR) of diseased periodontal structures. GTR involves the placement of the membrane to exclude soft epithelial and gingival tissues from the exposed tooth in order to facilitate the regeneration of the more slow-growing periodontal ligament and hard tissues. Bioactive glasses incorporating antimicrobial ions such as silver, zinc and copper have been shown to resist biomaterial-centred infection; although, the presence of these metal ions is reported to reduce bioactivity in some instances. Chitosan, a biodegradable carbohydrate polymer, is a popular choice for GTR membranes as its structure resembles that of bone extracellular matrix. In the present study, copper- and/or zinc-bearing bioactive glasses were prepared by the sol-gel process and incorporated into chitosan membranes by solvent-casting. The in vitro bioactivity and degradation rates of the chitosan-bioactive glass membranes were evaluated with respect to their potential use as GTR membranes

Interactions of Cd2+, Co2+ and MoO42- ions with crushed concrete fines

Construction and demolition activities generate approximately two thirds of the world’s waste with concrete-based demolition material accounting for the largest proportion. Primary aggregates are recovered and reused, although the cement-rich fine fraction is underutilised. In this study, single metal batch sorption experiments confirmed that crushed concrete fines (CCF) are an effective sorbent for the maximum exclusion of 45.2 mg g-1 Cd2+, 38.4 mg g-1 Co2+ and 56.0 mg g-1 MoO42- ions from aqueous media. The principal mechanisms of sorption were determined, by scanning electron microscopy of the metal-laden CCF, to be co-precipitation with Ca2+ ions released from the cement to form solubility limiting phases. The removal of Co2+ and MoO42- ions followed a zero-order reaction and that of Cd2+ was best described by a pseudo-second-order model. The Langmuir model provided the most appropriate description of the steady state immobilisation of Cd2+ and Co2+, whereas the removal of MoO42- conformed to the Freundlich isotherm. Long equilibration times (>120 h), loose floc formation and high pH are likely to limit the use of CCF in many conventional wastewater treatment applications; although, these properties could be usefully exploited in reactive barriers for the management of contaminated soils, sediments and groundwater

Interaction of fluoride complexes derived from glass-ionomer cements with hydroxyapatite

A study has been undertaken of the interaction of complexed fluoride extracted from glass-ionomer dental cements with synthetic hydroxyapatite powder. Extracts were prepared from two commercial glass-ionomers (Fuji IX and ChemFlex) under both neutral and acidic conditions. They were analysed by ICP-OES and by fluoride-ion selective electrode with and without added TISAB to decomplex the fluoride. The pH of the acid extracts was 4, conditions under which fluoride complexes with protons as HF or HF2-, it also complexes with aluminium, which was found to be present in higher amounts in the acid extracts. Fluoride was found to be almost completely complexed in acid extracts, but not in neutral extracts, which contained free fluoride ions. Exposure of these extracts to synthetic hydroxyapatite powder showed that fluoride was taken up rapidly (within 5 minutes), whether or not it was complexed SEM (EDAX) study of recovered hydroxyapatite showed only minute traces of aluminium taken up under all conditions. This showed that aluminium interacts hardly at all with hydroxyapatite, and hence is probably not involved in the remineralisation process