Towards an analytical model of soft biological tissues

In the past years, soft-tissue modelling research has seen substantial developments, a significant part of which can be ascribed to the refinement of numerical techniques, such as Finite Element analysis. A large class of physico-mechanical properties can be effectively simulated and predictions can be made for a variety of phenomena. However, there is still much that can be conceptually explored by means of fundamental theoretical analysis. In the past few years, driven by our interest in articular cartilage mechanics, we have developed theoretical microstructural models for linear elasticity and permeability that accounted for the presence and arrangement of collagen fibres in cartilage. In this paper, we investigate analytically the non-linear elasticity of soft tissues with collagen fibres arranged according to a given distribution of orientation, a problem that, aside from the case of fibres aligned in a finite number of distinct directions, has been treated exclusively numerically in the literature. We show that, for the case of a tissue with complex fibre arrangement, such as articular cartilage, the theoretical framework commonly used leads to an integral expression of the elastic strain energy potential. The present model is a first attempt in the development of a unified analytical microstructural model for non-linear elasticity and permeability of hydrated, fibre-reinforced soft tissues.     

Common protozoans as an uncommon cause of respiratory ailments in HIV-associated immunodeficiency

Opportunistic infections (OIs) are the leading cause of mortality and morbidity among HIV-positive subjects. The breadth of reports of the rare occurrence of OIs in HIV/AIDS has been increasing over the years and more recent studies have outlined the changing trends in the emergence of newer pathogens. Recent reports of the association of certain protozoans that normally do not infect sites other than their normal sites of localization have generated huge interest among scientists. The complete depression of the immune system, followed by the onset of OIs, especially due to protozoans, i.e. toxoplasmosis, isosporiasis, leishmaniasis, cyclosporosis, microsporidiosis and cryptosporidiosis, is not uncommon in AIDS. The immunologic and pathologic basis behind the susceptibility of immunodepressed individuals to these 'non-site-specific parasites' is likely to have a huge impact on HIV disease progression. Certain possible shortcomings in the immunologic armory of immunodeficient subjects, their failure to contain the establishment of these 'uncommon' agents in the human host and their significance in HIV disease progression are discussed.     

Irradiation-induced hypoxia in bones and soft tissues: an experimental study

Bone marrow and subcutaneous tissue pO2 and pCO2 were measured by means of implanted tissue tonometers in irradiated and nonirradiated rabbit hind limbs. The x-ray dose was 500, 1000, 1500, 2000, and 3000 rads. Tissue gas tensions were measured 1 day and 5 and 11 weeks after radiation. The pCO2 changes in both tissues were slight but not statistically significant. The subcutaneous tissue pO2 decreased during the acute phase of irradiation injury, and the effect of irradiation was dose-dependent. Later on, irradiation had no significant effects on the subcutaneous pO2, although light microscopy of the affected tissues showed fibrosis and blood vessel changes. The response of the subcutaneous pO2 to systemic hyperoxia also increased in the chronic phase of irradiation injury as a sign of improved microcirculation. The bone marrow showed a high radiosensitivity. Irradiation caused a rapid dose-dependent decrease of the marrow pO2, and the marrow pO2 decreased with time during the chronic phase of irradiation injury. The marrow pO2 responded slowly and marginally to an increment of arterial pO2 during breathing 100% oxygen as further evidence of impaired vascular pattern. The results showed that irradiation causes only a transient impairment of tissue perfusion in the skin. However, irradiation-damaged marrow was characterized by progressive tissue hypoxia.     

Wolff-Parkinson-White syndrome and rheumatic mitral stenosis: an uncommon coincidence that can cause severe hemodynamic disturbance

The combination of rheumatic mitral stenosis and Wolff-Parkinson-White syndrome is a rare situation. In this case, we are reporting an 72-year-old man presenting with multi-organ failure due to the this combination and successfully treated with radiofrequency ablation during preexcitated atrial fibrillation.     

Anisotropic material behaviours of soft tissues in human trachea: an experimental study

BackgroundHuman trachea is a multi-component structure composed of cartilage, trachealis muscle, mucosa and submucosa membrane and adventitial membrane. Its mechanical properties are essential for an accurate prediction of tracheal deformation, which has a significant clinic relevance. Efforts have been made in quantifying the material behaviour of tracheal cartilage and trachealis muscle. However, the material behaviours of other components have been least investigated.MethodsThree human cadaveric trachea specimens were used in this study. Trachealis muscle, mucosa and submucosa membrane and adventitia membrane were excised to perform the uniaxial test in axial and circumferential directions. In total, 72 tissue strips were prepared and tested. Tangent modulus was used to quantified the stiffness of each tissue strip at various stretch levels.ResultsThe obtained results indicated that all types of tracheal soft tissues were highly non-linear and anisotropic. Trachealis muscle in the circumferential direction had the most excellent extensibility; and the adventitial collagen membrane in the circumferential direction was the stiffest.ConclusionThis study is helpful in understanding the material behaviour of trachea. Obtained results can be used for computational and analytic modelling to quantify the tracheal deformation.     

Occurrence of uncommon polyamines in cultured tissues of maize

Summary The uncommon polyamines, norspermidine and norspermine, were detected in maizein vitro cultures of three different genotypes. The common polyamines, spermidine and spermine, along with the diamine, putrescine, were also observed. The total amounts of the uncommon polyamines, norspermidine and norspermine, were comparable to the total amounts of the common polyamines, spermidine and spermine, in the maize tissues. The titer for norspermidine was 6- to 15-fold greater than that of its common counterpart (spermidine) in the three genotypes. Norspermidine was the predominant polyamine among all triamines and tetramines detected in cell cultures of two of the three genotypes of maize examined and was predominant along with spermine in the third genotype. Enzyme assays performed with extracts from callus of one of the genotypes suggested a likely mechanism to account for the biosynthesis of the uncommon polyamines in cultured maize cells, through the actions of putrescine aminopropyltransferase, polyamine oxidase, and Schiff-base reductase/decarboxylase enzyme activities. This is the first report of the detection of uncommon polyamines in maize tissues, as well as the first report of these uncommon polyamines in a monocotyledonous plant.     

Inverse analysis of constitutive models: biological soft tissues

The paper describes a procedure for estimating the material parameters of biological soft tissue by fitting model prediction to experimental load-deformation data. This procedure minimizes the error between data and theoretical model prediction through systematically adjusting the parameters in the latter. The procedure uses commercially available software and is not specific to any particular model; nevertheless, for illustration purposes, we employ a six parameter fibril-reinforced poroelastic cartilage model. We are able to estimate any and all of these parameters by the procedure. Convergence of the parameters and convergence of the arbitrary initial stress relaxation to the data was demonstrated in all cases. Though we illustrate the optimization procedure here for unconfined compression only, it can be adapted easily to other experimental configurations such as confined compression, indentation and tensile test. Furthermore, the procedure can be applied in other areas of biomechanics where material parameters need to be extracted from experimental data.