Nichola J. Coleman

Bacteriostatic action of a novel four‐component bioactive glass

Bacterial adhesion to biomaterials causing biomaterial-centered infection and poor tissue integration is a problem that limits the extensive use of many biomaterial devices in clinical applications. Bioactive materials are those biomaterials that form a compliant, mechanically stable bond with host tissue. Sol-gel-derived glasses in the three-component system SiO(2)-CaO-P(2)O(5) exhibit bioactivity that is dependent on composition and texture (i.e., specific surface area, pore size, structure, and distribution). The in vitro bioactivity and antibacterial action of a novel sol-gel-derived glass, AgBG, in the system SiO(2)-CaO-P(2)O(5)-Ag(2)O are compared with those of its three-component counterpart, BG. The incorporation of 3-wt % Ag(2)O conferred antimicrobial properties to the glass without compromising its bioactivity. AgBG exhibited a marked bacteriostatic effect on E. coli MG1655 with a minimum inhibiting concentration of 0.2 mg (biomaterial)/mL (culture solution), above which bacterial growth was reduced to 0.01% of that of the control culture. In comparison, BG did not possess antimicrobial properties over the concentration range investigated (0.1-40.0 mg/mL).

Modulated temperature differential scanning calorimetry: A novel approach to pharmaceutical thermal analysis

Modulated temperature differential scanning calorimetry (MTDSC) is a novel thermoanalytical technique which involves the application of a sinusoidal heating programme to a sample and the resolution of the response into reversing and non-reversing signals, thereby enabling the deconvolution of complex and overlapping thermal processes. This represents an important advance on conventional differential scanning calorimetry (DSC), which involves the use of a linear heating programme, and does not allow the separation of the signal into component responses. In this review, the principles and current uses of conventional DSC will be discussed and compared to those of MTDSC, particularly with a view to emphasising the comparative advantages of the new technique with respect to existing methods. A discussion will be given of how this technique may be applicable to a range of pharmaceutical systems.

Aspects of the pore solution chemistry of hydrated cement pastes containing metakaolin

The hydroxide ion concentrations of expressed pore solutions of Ordinary Portland cement pastes containing 0, 10 and 20% of metakaolin by weight of cement were determined at various stages of hydration. Effects produced by two types of metakaolin, differing in degree of purity, were compared and, in each case, incorporation of metakaolin into the pastes was found to cause a long-term reduction in pore solution hydroxide ion concentration. The presence of metakaolin was also found to result in an increase in the extent to which chloride ions, introduced via the mix water, were excluded from the pore solution phase. The significance of these results in relation to the ability of hydrated cement matrices containing metakaolin to provide corrosion protection to embedded steel is considered.

Synthesis of Al-substituted 11 A tobermorite from newsprint recycling residue: a feasibility study

Newsprint recycling is responsible for significant volumes of secondary waste material for which further reprocessing and market development would be beneficial. In response to this problem, a layer lattice, ion exchange material, Al-substituted 11 Angstrom tobermorite, has been synthesised from newsprint recycling residue comprising gehlenite (Ca2Al2SiO7) akermanite (Ca2MgSi2O7), beta-dicalcium silicate (Ca2SiO4) and anorthite (CaAl2Si2O8) under hydrothermal conditions at 100 degreesC in the presence of NaOH. The hydrogamet phase, katoite (Ca3Al2SiO12H8), was also formed. Similar treatment regimes in the presence of LiOH and KOH did not yield significant quantities of Al-substituted 11 Angstrom tobermorite. A batch sorption study confirmed that the Al-substituted 11 Angstrom tobermorite-bearing product was effective in the exclusion of Cd2+, Pb2+ and Zn2+ from acidified aqueous media. The potential to enhance the yield of Al-substituted 11 Angstrom tobermorite relative to that of katoite and thus optimise the ion exchange efficiency of the product is discussed with respect to its application to heavy metal-contaminated wastewater treatment.

A gel-derived mesoporous silica reference material for surface analysis by gas sorption 1. Textural features

Current interest in monolithic mesoporous matrices requiring carefully tailored architectures has dictated the requirement for a new generation of standard materials for textural analysis. Accordingly, the textural characteristics of a mesoporous gel-derived silica monolith have been investigated by nitrogen sorption. Specific surface area (165.5±1.5 m2 g−1), specific pore volume (0.986±0.020 cm3 g−1), average pore size (119.2±2.7 A) and distribution are reported. The properties of the mesoporous silica were found to compare favourably with those of commercially available certified reference materials for BET surface area and pore size analysis. The primary advantage of the gel-silica monolith in this application is the elimination of errors associated with powder sampling.

Tensile properties of bioactive fibers for tissue engineering applications.

Cell transplantation using biocompatible, biodegradable scaffolds offers the possibility of creating or regenerating tissue to replace organ function when deficiency arises. The role of these temporary substrates is to support and guide the expanding cell culture until it becomes structurally integrated with the host tissue. 45S5 Bioglass(R) is a 4-component, melt-derived bioactive glass, which has been approved for human clinical use by the Food and Drug Administration. The biocompatibility and biodegradability of 45S5 Bioglass(R) are long established, whereas research into its performance as an extracellular scaffold is currently underway. In this study the tensile strengths (93 +/- 8 and 82 +/- 14 MPa), elongation to fracture (0.7 +/- 0.05%) and Weibulls moduli (3.0 and 3.5) of 45S5 Bioglass(R) fibers (mean diameters 193 and 280 microm) for tissue engineering applications are reported. The tensile strengths of the fibers are compared with those of bulk 45S5 Bioglass(R) and a range of biodegradable polymer materials currently used in the field of tissue engineering. Aspects of glass and fiber technology relevant to the design and manufacture of extracellular ceramic scaffolds are also discussed.

The solid state chemistry of metakaolin-blended ordinary Portland cement

The hydration of ordinary Portland cement (OPC) pastes containing 0 and 20% metakaolin was monitored by differential thermal analysis (DTA) and solid state magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The presence of hydrated gehlenite and a relative reduction in calcium hydroxide content of the metakaolin-blended OPC pastes observed by DTA are indicative of the pozzolanic reaction of metakaolin. An increase in the capacity of metakaolin-blended OPC pastes to exclude chloride ions from the pore electrolyte phase, via solid phase binding, has been reported. It is proposed that this increase in chloride binding capacity could be attributed to the participation of calcium aluminate species in the formation of Friedels salt which would otherwise be engaged in the formation of hydrated gehlenite and other AFm phases. The accelerating effect of replacement additions of metakaolin has been shown by 29Si NMR and was denoted by a comparative increase in the intensity of resonances arising from Q1 and Q2 species compared with that of Q0 species for metakaolin-blended specimens. The primary reactive centres of the pozzolan have been shown to be the 5-coordinate aluminium and amorphous silica. The spreading of the Q4 resonance of the amorphous silica of metakaolin through the Q3 and into the Q2 and Q1 regions of the NMR spectrum during pozzolanic reaction has been observed.

Aspects of the in vitro bioactivity of hydraulic calcium (alumino)silicate cement

In response to a burgeoning interest in the prospective clinical applications of hydraulic calcium (alumino)silicate cements, the in vitro bioactivity and dissolution characteristics of a white Portland cement have been investigated. The formation of an apatite layer within 6 h of contact with simulated body fluid was attributed to the rapid dissolution of calcium hydroxide from the cement matrix and to the abundance of pre-existing Si--OH nucleation sites presented by the calcium silicate hydrate phase. A simple kinetic model has been used to describe the rate of apatite formation and an apparent pseudo-second-order rate constant for the removal of HPO4(2-) ions from solution has been calculated (k(2) = 5.8 x10(-4) g mg(-1) min(-1)). Aspects of the chemistry of hydraulic cements are also discussed with respect to their potential use in the remedial treatment of living tissue.

Bioactivity and biocompatibility of a chitosan-tobermorite composite membrane for guided tissue regeneration

A polymer-mineral composite membrane of the mucopolysaccharide derivative, chitosan, and calcium silicate hydrate phase, tobermorite, was prepared by solvent casting and characterised by scanning electron microscopy (SEM) and Fourier Transform infrared spectroscopy (FTIR). The bioactivity and biocompatibility of the chitosan-tobermorite composite were evaluated in vitro with respect to its potential for use as a biodegradable guided tissue regeneration (GTR) membrane. The in vitro bioactivity of the composite was confirmed by the formation of crystalline substituted hydroxyapatite on the surface of the embedded tobermorite particles in simulated body fluid. The presence of the composite membrane was found to enhance the growth of MG63 human osteosarcoma cells by up to 30%. The findings of this initial study have indicated that this novel chitosan-tobermorite composite may be a suitable material for GTR applications.

Interfacial Properties of Three Different Bioactive Dentine Substitutes

Three different bioactive materials suitable as dentine substitutes in tooth repair have been studied: glass-ionomer cement, particulate bioglass, and calcium-silicate cement. On 15 permanent human molars, Class V cavities were prepared and the bottom of each cavity was de-mineralized by an artificial caries gel. After the de-mineralization, the teeth were restored with: (1) Bioglass®45S5 and ChemFil® Superior; (2) Biodentine™ and ChemFil® Superior; and (3) ChemFil® Superior for a complete repair. The teeth were stored for 6 weeks in artificial saliva, then cut in half along the longitudinal axis: the first half was imaged in a scanning electron microscope (SEM) and the other half was embedded in resin and analyzed by SEM using energy-dispersive X-ray analysis. The glass-ionomer and the bioglass underwent ion exchange with the surrounding tooth tissue, confirming their bioactivity. However, the particle size of the bioglass meant that cavity adaptation was poor. It is concluded that smaller particle size bioglasses may give more acceptable results. In contrast, both the glass-ionomer and the calcium-silicate cements performed well as dentine substitutes. The glass-ionomer showed ion exchange properties, whereas the calcium silicate gave an excellent seal resulting from its micromechanical attachment.