Orthogonal invariant sets of the diffusion tensor and the development of a curvilinear set suitable for low-anisotropy tissues.

We develop a curvilinear invariant set of the diffusion tensor which may be applied to Diffusion Tensor Imaging measurements on tissues and porous media. This new set is an alternative to the more common invariants such as fractional anisotropy and the diffusion mode. The alternative invariant set possesses a different structure to the other known invariant sets; the second and third members of the curvilinear set measure the degree of orthotropy and oblateness/prolateness, respectively. The proposed advantage of these invariants is that they may work well in situations of low diffusion anisotropy and isotropy, as is often observed in tissues such as cartilage. We also explore the other orthogonal invariant sets in terms of their geometry in relation to eigenvalue space; a cylindrical set, a spherical set (including fractional anisotropy and the mode), and a log-Euclidean set. These three sets have a common structure. The first invariant measures the magnitude of the diffusion, the second and third invariants capture aspects of the anisotropy; the magnitude of the anisotropy and the shape of the diffusion ellipsoid (the manner in which the anisotropy is realised). We also show a simple method to prove the orthogonality of the invariants within a set

Decellularization and Characterization of Porcine Superflexor Tendon: A Potential Anterior Cruciate Ligament Replacement

The porcine superflexor tendon (SFT) was identified as having appropriate structure and properties for development of a decellularised device for use in ACL reconstruction. SFTs were decellularised using a combination of freeze thaw and washes in hypotonic buffer and 0.1% (w/v) SDS in hypotonic buffer plus proteinase inhibitors followed by nuclease treatment and sterilisation using peracetic acid. The decellularised biological scaffold was devoid of cells and cell remnants and contained only 13 ng.mg-1 (dry weight) residual total DNA. Immunohistochemistry showed retention of collagens type I and III and tenascin-C. Quantitative analysis of sulphated sugar and hydroxyproline content revealed a loss of glycosaminoglycans compared to native tissue but no loss of collagen. The decellularised SFT was biocompatible in vitro and in vivo following implantation in a mouse subcutaneous model for 12 weeks. Uniaxial tensile testing to failure indicated that the gross material properties of decellularised SFT were not significantly different to native tissue. Decellularised SFTs had an ultimate tensile strength of 61.8 ± 10.3 MPa (± 95 % confidence limits), a failure strain of 0.29 ± 0.04 and a Young’s modulus of the collagen phase of 294.1 ± 61.9 MPa. Analysis of the presence of the alpha-Gal (galactose-α-1,3-galactose) epitope by immunohistochemistry, lectin binding and antibody absorption assay indicated that the epitope was reduced but still present post decellularisation. This is discussed in light of the potential role of non-cellular alpha-Gal in the acceleration of wound healing and tissue regeneration in the presence of antibodies to alpha-Gal

The effects of irradiation on the biological and biomechanical properties of an acellular porcine superflexor tendon graft for cruciate ligament repair

Acellular xenogeneic tissues have the potential to provide ‘off‐the‐shelf’ grafts for anterior cruciate ligament (ACL) repair. To ensure that such grafts are sterile following packaging, it is desirable to use terminal sterilization methods. Here, the effects of gamma and electron beam irradiation on the biological and biomechanical properties of a previously developed acellular porcine superflexor tendon (pSFT) were investigated. Irradiation following treatment with peracetic acid was compared to peracetic acid treatment alone and the stability of grafts following long‐term storage assessed. Irradiation did not affect total collagen content or biocompatibility (determined using a contact cytotoxicity assay) of the grafts, but slightly increased the amount of denatured collagen in and decreased the thermal denaturation temperature of the tissue in a dose dependant fashion. Biomechanical properties of the grafts were altered by irradiation (reduced ultimate tensile strength and Young's modulus, increased failure strain), but remained superior to reported properties of the native human ACL. Long term storage at 4°C had no negative effects on the grafts. Of all the conditions tested, a dose of minimum 25 kGy of gamma irradiation had least effect on the grafts, suggesting that this dose produces a biocompatible pSFT graft with adequate mechanical properties for ACL repair

Comparison of the biomechanical tensile and compressive properties of decellularised and natural porcine meniscus

Meniscal repair is widely used as a treatment for meniscus injury. However, where meniscal damage has progressed such that repair is not possible, approaches for partial meniscus replacement are now being developed which have the potential to restore the functional role of the meniscus, in stabilising the knee joint, absorbing and distributing stress during loading, and prevent early degenerative joint disease. One attractive potential solution to the current lack of meniscal replacements is the use of decellularised natural biological scaffolds, derived from xenogeneic tissues, which are produced by treating the native tissue to remove the immunogenic cells. The current study investigated the effect of decellularisation on the biomechanical tensile and compressive (indentation and unconfined) properties of the porcine medial meniscus through an experimental-computational approach. The results showed that decellularised medial porcine meniscus maintained the tensile biomechanical properties of the native meniscus, but had lower tensile initial elastic modulus. In compression, decellularised medial porcine meniscus generally showed lower elastic modulus and higher permeability compared to that of the native meniscus. These changes in the biomechanical properties, which ranged from less than 1% to 40%, may be due to the reduction of glycosaminoglycans (GAG) content during the decellularisation process. The predicted biomechanical properties for the decellularised medial porcine meniscus were within the reported range for the human meniscus, making it an appropriate biological scaffold for consideration as a partial meniscus replacement

Influence of catalyst structure on PEM fuel cell performance – A numerical investigation

The effect of the catalyst microstructure on a 5 cm2 PEM fuel cell performance is numerically investigated. The catalyst layer composition and properties (i.e. ionomer volume fraction, platinum loading, particle radius, electrochemical active area and carbon support type), and the mass transport resistance due to the ionomer and liquid water surrounding the catalyst particles, are incorporated into the model. The effects of the above parameters are discussed in terms of the polarization curves and the local distributions of the key parameters. An optimum range of the ionomer volume fraction was found and a gain of 39% in the performance was achieved. As regards the platinum loading and catalyst particle radius, the results showed that a higher loading and a smaller radius leads to an increase in the PEMFC performance. Further, the influence of the electrochemical active area produces an overall increase of 22% in current density and this was due to the use of a new material developed as support for Pt particles, an iodine doped graphene, which has better electrical contacts and additional pathways for water removal. Using this parameter, the numerical model has been validated and good agreement with experimental data was achieved, thus giving confidence in the model as a design tool for future improvements of the catalyst structure

How to correct small quantum errors

The theory of quantum error correction is a cornerstone of quantum information processing. It shows that quantum data can be protected against decoherence effects, which otherwise would render many of the new quantum applications practically impossible. In this paper we give a self contained introduction to this theory and to the closely related concept of quantum channel capacities. We show, in particular, that it is possible (using appropriate error correcting schemes) to send a non-vanishing amount of quantum data undisturbed (in a certain asymptotic sense) through a noisy quantum channel T, provided the errors produced by T are small enough.Comment: LaTeX2e, 23 pages, 6 figures (3 eps, 3 pstricks

Decellularisation affects the strain rate dependent and dynamic mechanical properties of a xenogeneic tendon intended for anterior cruciate ligament replacement

Development of new replacement grafts for anterior cruciate ligament (ACL) repair requires mechanical testing to ensure they can provide joint stability following implantation. A decellularised porcine superflexor tendon (pSFT) has been developed previously as an alternative to current reconstruction methods and subjected to biomechanical analysis. The application of varied strain rates to biological tissues is known to alter their biomechanical properties, however the effects of decellularisation on strain rate dependent and dynamic mechanical behaviour of tissues have not been explored. This study utilised tensile testing to investigate the material properties of native and decellularised pSFTs at three different strain rates (1%.s−1, 10%.s−1 and 100%.s−1). In addition, dynamic mechanical analysis (DMA) was used to ascertain the relative contributions of the solid and fluid phase components of the tissues. Ultimate tensile strength was significantly reduced in decellularised compared with native untreated pSFTs but was unaffected by strain rate. In contrast, toe region moduli increased with increasing strain rate for native tissues, but this effect was not observed in decellularised pSFTs. Linear region moduli were unaffected by strain rate, but were significantly reduced in decellularised pSFT compared with native tissue. Following DMA, significant reductions in dynamic modulus, storage modulus and loss modulus were seen in decellularised compared with native pSFT. Interestingly, the damping ability of the tendons was unaffected by decellularisation, suggesting that solid and fluid phases of the tissue were affected equally. These results, alongside previous studies, suggest that decellularisation affects collagen crimp, tissue swelling and collagen fibre sliding. However, despite these findings, the biomechanical properties of decellularised pSFT remain sufficient to act as an off-the-shelf solution for ACL reconstruction

The Mersey Estuary : sediment geochemistry

This report describes a study of the geochemistry of the Mersey estuary carried out between April 2000 and December 2002. The study was the first in a new programme of surveys of the geochemistry of major British estuaries aimed at enhancing our knowledge and understanding of the distribution of contaminants in estuarine sediments. The report first summarises the physical setting, historical development, geology, hydrography and bathymetry of the Mersey estuary and its catchment. Details of the sampling and analytical programmes are then given followed by a discussion of the sedimentology and geochemistry. The chemistry of the water column and suspended particulate matter have not been studied, the chief concern being with the geochemistry of the surface and near-surface sediments of the Mersey estuary and an examination of their likely sources and present state of contamination