Inorganic Polymers (Geopolymers) as Potential Bioactive Materials

<p>The primary aim of this project was to synthesise potassium activated geopolymer composites with bioactivity, and this was realised by adding 10wt% of calcium hydroxide, nano-structured calcium silicate or calcium phosphate to the geopolymer matrix. The synthesised samples were cured at 40'C then heated to 550'C and 600'C to reduce their alkalinity. Tensile strength was measured by diametral compression. The effect of exposure to simulated body fluid (SBF) was determined by x-ray diffractometry (XRD), 27Al, 29Si and 43Ca nuclear magnetic resonance spectroscopy with magic angle spinning (MAS NMR), pH measurements, inductively coupled plasma (ICP), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDS). XRD, 27Al and 29Si MAS NMR confirmed that all the samples retained their structural characteristics of a true aluminosilicate geopolymer, even after heating and exposure to SBF. EDS examination of the calcium-containing geopolymer composites showed that the calcium distribution was generally homogeneous. Exposure of the geopolymer composites to SBF at body temperature, was used to simulate the behaviour of the geopolymer composites in blood plasma. XRD and SEM/ EDS analysis showed that the geopolymers containing calcium hydroxide and calcium silicate formed hydroxyl apatite (HA) and carbonate hydroxyl apatite (HCA) after their exposure to SBF, indicating a degree of bioactivity. The absorption of calcium and phosphorus from the SBF and the observation of nano crystals rich in these elements provide some evidence of bioactive phases in the composite containing calcium phosphate and the reference geopolymer. The reference and the calcium phosphate geopolymer (both heated to 600XC) produced the lowest pH (ca.8) in the SBF. ICP analysis of the SBF after exposure shows that most of the aluminium remains in the geopolymer structure. The greatest release of aluminium (< 2.7 ppm after 168 hours) was found for the calcium hydroxide geopolymer (heated to 600'C). Diametral compression testing showed that the strength of the calcium phosphate-containing geopolymer heated to 550'C (4.17 MPa) is comparable with that of Bioglass(R)(5.56 MPa), currently used as a bio-material. Although none of the composites are ideal in all respects, they show sufficient promise to suggest that with further refinement, geopolymer materials may well be become candidates as bioactive ceramics.</p>

Inorganic Polymers (Geopolymers) as Potential Bioactive Materials

<p>The primary aim of this project was to synthesise potassium activated geopolymer composites with bioactivity, and this was realised by adding 10wt% of calcium hydroxide, nano-structured calcium silicate or calcium phosphate to the geopolymer matrix. The synthesised samples were cured at 40'C then heated to 550'C and 600'C to reduce their alkalinity. Tensile strength was measured by diametral compression. The effect of exposure to simulated body fluid (SBF) was determined by x-ray diffractometry (XRD), 27Al, 29Si and 43Ca nuclear magnetic resonance spectroscopy with magic angle spinning (MAS NMR), pH measurements, inductively coupled plasma (ICP), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDS). XRD, 27Al and 29Si MAS NMR confirmed that all the samples retained their structural characteristics of a true aluminosilicate geopolymer, even after heating and exposure to SBF. EDS examination of the calcium-containing geopolymer composites showed that the calcium distribution was generally homogeneous. Exposure of the geopolymer composites to SBF at body temperature, was used to simulate the behaviour of the geopolymer composites in blood plasma. XRD and SEM/ EDS analysis showed that the geopolymers containing calcium hydroxide and calcium silicate formed hydroxyl apatite (HA) and carbonate hydroxyl apatite (HCA) after their exposure to SBF, indicating a degree of bioactivity. The absorption of calcium and phosphorus from the SBF and the observation of nano crystals rich in these elements provide some evidence of bioactive phases in the composite containing calcium phosphate and the reference geopolymer. The reference and the calcium phosphate geopolymer (both heated to 600XC) produced the lowest pH (ca.8) in the SBF. ICP analysis of the SBF after exposure shows that most of the aluminium remains in the geopolymer structure. The greatest release of aluminium (< 2.7 ppm after 168 hours) was found for the calcium hydroxide geopolymer (heated to 600'C). Diametral compression testing showed that the strength of the calcium phosphate-containing geopolymer heated to 550'C (4.17 MPa) is comparable with that of Bioglass(R)(5.56 MPa), currently used as a bio-material. Although none of the composites are ideal in all respects, they show sufficient promise to suggest that with further refinement, geopolymer materials may well be become candidates as bioactive ceramics.</p>

Resistência a tração (por compressão diametral) em gessos odontológicos: influência da espessura dos corpos de prova

The influence of different specimen thicknesses on the tensile strenght (by diametral compression method 11) of dental stones has been studdied. It was observed that there was greater reproducibility os results as the thickness of the samples decreased. This leads us to recommend the latter type os samples when conducting diametral compression tensile strenght tests. A relationship between the compression strenght and tensile strenght was also studdied. It was found that the difference between the two strenghts decrenses as the thickness os the diametral compression strenght samples increases. The results were expressed in stress values.

Breakage Strength of Wood Sawdust Pellets: Measurements and Modelling

Wood pellets are an important source of renewable energy. Their mechanical strength is a crucial property. In this study, the tensile strength of pellets made from oak, pine, and birch sawdust with moisture contents of 8% and 20% compacted at 60 and 120 MPa was determined in a diametral compression test. The highest tensile strength was noted for oak and the lowest for birch pellets. For all materials, the tensile strength was the highest for a moisture content of 8% and 120 MPa. All pellets exhibited a ductile breakage mode characterised by a smooth and round stress–deformation relationship without any sudden drops. Discrete element method (DEM) simulations were performed to check for the possibility of numerical reproduction of pelletisation of the sawdust and then of the pellet deformation in the diametral compression test. The pellet breakage process was successfully simulated using the DEM implemented with the bonded particle model. The simulations reproduced the results of laboratory testing well and provided deeper insight into particle–particle bonding mechanisms. Cracks were initiated close to the centre of the pellet and, as the deformation progressed, they further developed in the direction of loading.

Stochastic finite element analysis of the diametral compression test of powder compacts and porous materials

This paper presents a stochastic finite element approach for modeling the mechanical behavior of powder compacts and porous materials under diametral compression test conditions. The main goal is assessing the validity of the diametral compression test as an indirect technique to estimate tensile strengths of brittle or quasi-brittle materials exhibiting porosity heterogeneity. Thus, the study seeks to predict the influence of porosity randomness on stress distributions and the spatial location of the highest tensile stress on thin disc-shaped specimens. The proposed formulation uses a stochastic framework that couples a random spatial field to the finite element analysis to include non-deterministic features. Two case studies consider comparable targets for the mean porosity but different coefficients of variations. For each case study, a total of 1000 realizations are conducted under identical loading and boundary conditions. The predicted stress distributions are compared to the ones from homogenous closed-form solutions from the literature. Then, the expected magnitude and location of the maximum tensile stress are evaluated by statistical means. Findings from the stochastic model show that porosity randomness induces stress concentration around less dense volumes and location deviation of the maximum tensile stress from the center of the discs. Likewise, porosity heterogeneity could affect the accuracy of experimental diametral compression tests even for small variance cases; and so, the reliability of the mechanical properties derived from models based exclusively on the classic assumption of material homogeneity.

Influence of Alumina Nanoparticles on the Mechanical Properties of a Bioresin Composite

The aim of this study is to characterize (wettability, surface roughness and gloss) and test (microhardness and diametral compression) four types of light-cured composite resins, one of which is commercial. The first lab-made composite is the reference, obtained by mechanical mixing of three monomers, in equal concentrations. The following two lab-made materials can be considered nanocomposites because they were mechanically mixed in the base solution (Bis-GMA/TEGDMA/Bis-EMA) with α-Al2O3 nanopowders, with a concentration of 5 wt.% for one solution and 10 wt.% for the other. The benchmark material comparison for these lab-made composite and nanocomposite resins is the bioresin system, Filtek™ Supreme Ultra Universal Restorative. Results were promising, especially for the 10 wt.% Al2O3/Bis-GMA/TEGDMA/Bis-EMA system, characterized by mechanical improvment in comparison with the reference composite.