Dynamic mechanical characterisation of hydroxyapatite reinforced biomedical composites

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Multiscale structural evolution of citrate-triggered intrafibrillar and interfibrillar mineralization in dense collagen gels

The mineralized extracellular matrix of bone is an organic?inorganic nanocomposite consisting primarily of carbonated hydroxyapatite, fibrous type I collagen, noncollagenous proteins, proteoglycans, and diverse biomolecules such as pyrophosphate and citrate. While much is now known about the mineralization-regulating role of pyrophosphate, less is known about the function of citrate. In order to assess the effect of negatively charged citrate on collagen mineralization, citrate-functionalized, bone osteoid-mimicking dense collagen gels were exposed to simulated body fluid for up to 7 days to examine the multiscale evolution of intra- and interfibrillar collagen mineralization. Here, we show by increases in methylene blue staining that the net negative charge of collagen can be substantially augmented through citrate functionalization. Structural and compositional analyses by transmission and scanning electron microscopy (including X-ray microanalysis and electron diffraction), and atomic force microscopy, all demonstrated that citrate-functionalized collagen fibrils underwent extensive intrafibrillar mineralization within 12 h in simulated body fluid. Time-resolved, high-resolution transmission electron microscopy confirmed the temporal evolution of intrafibrillar mineralization of single collagen fibrils. Longer exposure to simulated body fluid resulted in additional interfibrillar mineralization, all through an amorphous-to-crystalline transformation towards apatite (assessed by X-ray diffraction and attenuated total reflection-Fourier-transform infrared spectroscopy). Calcium deposition assays indicated a citrate concentration-dependent temporal increase in mineralization, and micro-computed tomography confirmed that >80 vol% of the collagen in the gels was mineralized by day 7. In conclusion, citrate effectively induces mesoscale intra- and interfibrillar collagen mineralization, a finding that advances our understanding of the role of citrate in mineralized tissuesScopu

Effect of phosphate-based glass fibre surface properties on thermally produced poly(lactic acid) matrix composites

Incorporation of soluble bioactive glass fibres into biodegradable polymers is an interesting approach for bone repair and regeneration. However, the glass composition and its surface properties significantly affect the nature of the fibre-matrix interface and composite properties. Herein, the effect of Si and Fe on the surface properties of calcium containing phosphate based glasses (PGs) in the system (50P 2O 5-40CaO-(10-x)SiO 2-xFe 2O 3, where x = 0, 5 and 10 mol.%) were investigated. Contact angle measurements revealed a higher surface energy, and surface polarity as well as increased hydrophilicity for Si doped PG which may account for the presence of surface hydroxyl groups. Two PG formulations, 50P 2O 5-40CaO-10Fe 2O 3 (Fe10) and 50P 2O 5-40CaO-5Fe 2O 3-5SiO 2 (Fe5Si5), were melt drawn into fibres and randomly incorporated into poly(lactic acid) (PLA) produced by melt processing. The ageing in deionised water (DW), mechanical property changes in phosphate buffered saline (PBS) and cytocompatibility properties of these composites were investigated. In contrast to Fe10 and as a consequence of the higher surface energy and polarity of Fe5Si5, its incorporation into PLA led to increased inorganic/organic interaction indicated by a reduction in the carbonyl group of the matrix. PLA chain scission was confirmed by a greater reduction in its molecular weight in PLA-Fe5Si5 composites. In DW, the dissolution rate of PLA-Fe5Si5 was significantly higher than that of PLA-Fe10. Dissolution of the glass fibres resulted in the formation of channels within the matrix. Initial flexural strength was significantly increased through PGF incorporation. After PBS ageing, the reduction in mechanical properties was greater for PLA-Fe5Si5 compared to PLA-Fe10. MC3T3-E1 preosteoblasts seeded onto PG discs, PLA and PLA-PGF composites were evaluated for up to 7 days indicating that the materials were generally cytocompatible. In addition, cell alignment along the PGF orientation was observed showing cell preference towards PGF. \ua9 2011 Springer Science+Business Media, LLC.Peer reviewed: YesNRC publication: Ye

Incorporation of vitamin E in poly(3hydroxybutyrate)/Bioglass composite films: effect on surface properties and cell attachment

This study investigated the possibility of incorporating α-tocopherol (vitamin E) into poly(3hydroxybutyrate) (P(3HB))/Bioglass composites, which are being developed for bone tissue engineering matrices. P(3HB) films with 20 wt% Bioglass and 10 wt% vitamin E were prepared using the solvent casting technique. Addition of vitamin E significantly improved the hydrophilicity of the composites along with increasing the total protein adsorption. The presence of protein adsorbed on the composite surface was further confirmed using X-ray photoelectron spectroscopy analysis. Preliminary cell culture studies using MG-63 human osteoblasts showed that the addition of vitamin E in the P(3HB)/20 wt% Bioglass films significantly increased cell proliferation. The results achieved in this study confirmed the possibility of incorporating vitamin E as a suitable additive in P(3HB)/Bioglass composites to engineer the surface of the composites by promoting higher protein adsorption and increasing the hydrophilicity

Fabrication and characterization of biodegradable poly(3-hydroxybutyrate) composite containing bioglass

Bacterially derived poly(3-hydroxybutyrate) (P(3HB)) has been used to produce composite films by incorporating Bioglass particles (&lt;5 m) in 5 and 20 wt % concentrations. P(3HB) was produced using a large scale fermentation technique. The polymer was extracted using the Soxhlet technique and was found to have similar thermal and structural properties to the commercially available P(3HB). The effects of adding Bioglass on the microstructure surface and thermal and mechanical properties were examined using differential scanning calorimetry, dynamic mechanical analysis (DMA), X-ray diffraction, surface interferometry, electron microscopy, and nanoindentation. The addition of increasing concentrations of Bioglass in the polymer matrix reduced the degree of crystallinity of the polymer as well as caused an increase in the glass transition temperature as determined by DMA. The presence of Bioglass particulates reduced the Young's modulus of the composite. The storage modulus and the loss modulus, however, increased with the addition of 20 wt % Bioglass. A short period (28 days) in vitro bioactivity study in simulated body fluid confirmed the bioactivity of the composites, demonstrated by the formation of hydroxyapatite crystals on the composites' surface. <br/

Effect of Si and Fe doping on calcium phosphate glass fibre reinforced polycaprolactone bone analogous composites

Reinforcing biodegradable polymers with phosphate-based glass fibres (PGF) is of interest for bone repair and regeneration. In addition to increasing the mechanical properties, PGF can also release bioinorganics, as they are water soluble, a property that may be controllably translated into a fully degradable composite. Herein, the effect of Si and Fe on the solubility of calcium-containing phosphate-based glasses (PG) in the system (50P(2)O(5)-40CaO-(10 - x)SiO2-xFe(2)O(3), where x = 0, 5 and 10 mol.%) were investigated. On replacing SiO2 with Fe2O3, there was an increase in the glass transition temperature and density of the PG, suggesting greater crosslinking of the phosphate chains. This significantly reduced the dissolution rates of degradation and ion release. Two PG formulations, 50P(2)O(5)-40CaO-10Fe(2)O(3) (Fe10) and 50P(2)O(5)-40CaO-5Fe(2)O(3)-5SiO(2) (Fe5Si5), were melt drawn into fibres and randomly incorporated into polycaprolactone (PCL). Initially, the flexural strength and modulus significantly increased with PGF incorporation. In deionized water, PCL-Fe5Si5 displayed a significantly greater weight loss and ion release compared with PCL-Fe10. In simulated body fluid, brushite was formed only on the surface of PCL-Fe5Si5. Dynamic mechanical analysis in phosphate buffered saline (PBS) at 37 degrees C revealed that the PCL-Fe10 storage modulus (E') was unchanged up to day 7, whereas the onset of PCL-Fe5Si5 E' decrease occurred at day 4. At longer-term ageing in PBS, PCL-Fe5Si5 flexural strength and modulus decreased significantly. MC3T3-E1 preosteoblasts seeded onto PCL-PGF grew up to day 7 in culture. PGF can be used to control the properties of biodegradable composites for potential application as bone fracture fixation devices. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Fabrication and characterization of biodegradable poly(3-hydroxybutyrate) composite containing Bioglass

Bacterially derived poly(3-hydroxybutyrate) (P(3HB)) has been used to produce composite films by incorporating Bioglass particles (<5 m) in 5 and 20 wt % concentrations. P(3HB) was produced using a large scale fermentation technique. The polymer was extracted using the Soxhlet technique and was found to have similar thermal and structural properties to the commercially available P(3HB). The effects of adding Bioglass on the microstructure surface and thermal and mechanical properties were examined using differential scanning calorimetry, dynamic mechanical analysis (DMA), X-ray diffraction, surface interferometry, electron microscopy, and nanoindentation. The addition of increasing concentrations of Bioglass in the polymer matrix reduced the degree of crystallinity of the polymer as well as caused an increase in the glass transition temperature as determined by DMA. The presence of Bioglass particulates reduced the Young's modulus of the composite. The storage modulus and the loss modulus, however, increased with the addition of 20 wt % Bioglass. A short period (28 days) in vitro bioactivity study in simulated body fluid confirmed the bioactivity of the composites, demonstrated by the formation of hydroxyapatite crystals on the composites' surface