Publications (17) View all
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Article: Elasticity, thermal stability and bioactivity of polyhedral oligomeric silsesquioxanes reinforced chitosan-based microfibres.
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ABSTRACT: A wet-spinning approach was used to extrude ribbon-like micrometer-thick fibres comprising chitosan with 1, 3, 5, 7 and 9% (w/w) polyhedral oligomeric silsesquioxanes (POSS). ANOVA reveals significant variations in the maximum stress (σ), stiffness (E), elastic energy storage (u') and fracture toughness (u) of the microfibres with respect to POSS concentration: σ, u' and u peak at 7% (w/w) but POSS concentration has no effect on E. Scanning electron microscopy of the ruptured microfibres reveals fracture and detachment of POSS precipitates from the chitosan matrix. Bioactivity test using simulated body fluids reveals a net gain in mass (by day 4) and grossly distorted morphology caused by apatite deposition on the microfibre surface. Fourier transform infrared spectroscopy reveals that chitin is partially deacetylated into chitosan and it further shows the presence of POSS in the microfibres. Thermogravimetric analysis shows that the microfibres are thermally stable up to 240°C in a nitrogen atmosphere.Journal of Materials Science Materials in Medicine 06/2011; 22(6):1365-74. · 2.32 Impact Factor -
Article: On defect interactions in axially loaded single-walled carbon nanotubes
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ABSTRACT: Despite the unparalleled mechanical properties of carbon nanotubes (CNTs), experiments have revealed large scattering which could be attributed to structural defects. How two neighboring defects may interact and influence the mechanical properties of CNTs is still unclear. Here, interactions between a Stone-Wales (SW) defect pair in axially loaded single-walled carbon nanotubes (SWCNTs) are systematically studied using molecular mechanics. The defect-defect interaction is quantified by the bond with the highest energy, E, which varies in magnitude with respect to the interdefect distance, D. Defect pairs, corresponding to combinations of two types of SW defects (namely, the SW defect of A and B modes) with a different relative orientation angle, ϕ, embedded in SWCNTs of different size and chirality were studied. It is shown from the results that, in general, E varies according to defect pair, and converges to a constant at large D. It is found that the magnitude of E is regulated by the type of defect pair, and the profile of E vs D is modulated by ϕ. In addition, E is also influenced by the tube size and chirality. From all of the cases studied, the largest indifference length, D0, beyond which two neighboring defects do not feel the existence of each other, is found to be approximately 30 Å.Journal of Applied Physics 03/2008; 103(5):054306-054306-7. · 2.17 Impact Factor -
Article: Nano-Fibre Critical Length Depends on Shape
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ABSTRACT: Nano-fibres in composite materials may not be cylindrical. A theoretical analysis shows that non-cylindrical nano-fibres have longer critical lengths leading, to composites with different mechanical properties requiring a]lower volume of reinforcing materialAdvanced Composites Letters 01/2008; 17(4):131-133. · 0.43 Impact Factor -
Article: Stress transfer in collagen fibrils reinforcing connective tissues: effects of collagen fibril slenderness and relative stiffness.
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ABSTRACT: Unlike engineering fibre composite materials which comprise of fibres that are uniform cylindrical in shape, collagen fibrils reinforcing the proteoglycan-rich (PG) gel in the extra-cellular matrices (ECMs) of connective tissues are taper-ended (paraboloidal in shape). In an earlier paper we have discussed how taper of a fibril leads to an axial stress up-take which differs from that of a uniform cylindrical fibre and implications for fibril fracture. The present paper focuses on the influence of fibre aspect ratio, q (slenderness), and Young's modulus (stiffness), relative to that of the gel phase, E(R), on the magnitude of the axial tensile stresses generated within a fibril and wider implications on failure at tissue level. Fibre composite models were evaluated using finite element (FE) and mathematical analyses. When the applied force is low, there is elastic stress transfer between the PG gel and a fibril. FE modelling shows that the stress in a fibril increases with E(R) and q. At higher applied forces, there is plastic stress transfer. Mathematical modelling predicts that the stress in a fibril increases linearly with q. For small q values, fibrils may be regarded as fillers with little ability to provide tensile reinforcement. Large q values lead to high stress in a fibril. Such high stresses are beneficial provided they do not exceed the fracture stress of collagen. Modulus difference regulates the strain energy release density, u, for interfacial rupture; large E(R) not only leads to high stress in a fibril but also insures against interfacial rupture by raising the value of u.Journal of Theoretical Biology 04/2007; 245(2):305-11. · 2.21 Impact Factor -
Article: Analysis of collagen fibril diameter distribution in connective tissues using small-angle X-ray scattering.
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ABSTRACT: Analysis of the diameters of collagen fibrils provides insight into the structure and physical processes occurring in the tissue. This paper describes a method for analyzing the frequency distribution of the diameters of collagen fibrils from small-angle X-ray scattering (SAXS) patterns. Frequency values of fibril diameters were input into a mathematical model of the form factor to calculate the equatorial intensity which best fits the experimentally derived data from SAXS patterns. A minimization algorithm utilizing simulated annealing (SA) was used in the fitting procedure. The SA algorithm allowed for random sampling of the frequency values, and was run iteratively to build up an optimized frequency distribution of fibril diameters. Results were obtained for collagen samples from sheep spine ligaments. The mean fibril diameter value obtained from this data-fitting method was 73 nm+/-20 nm (S.D.). From scanning transmission electron microscopy, the mean diameter was found to be 69 nm+/-14 nm (S.D.). The good agreement between the two methods demonstrates the reliability of the SAXS method for the tissue examined. The non-destructive nature of this technique, as well as its statistical robusticity and capacity for large sampling, means that this method is both quick and effective.Biochimica et Biophysica Acta 04/2005; 1722(2):183-8. · 4.66 Impact Factor
