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The effect of sterilization on the structural integrity of the polydimethylsiloxane (PDMS) matrix composite reinforced with carbon fibers (CF) is investigated by nanoindentation test. We present the investigation of the influence of sterilization processes on fiber/matrix interphase properties. The effect of multiple widely-used steam sterilization processes on fibers/matrix interphase region properties was studied by modulus mapping test.

In this study we present the investigation of the influence of multiple sterilization processes on micromechanical properties carried out on a composite based on carbon fibers (CF) and polymer matrix composite polydimethylsiloxane (PDMS). The effect of widely-used steam sterilization process on fibers/matrix interphase region properties was studied by nanoindentation.

The stress gradient index (G(p)) is introduced for the assessment of dysplasia in human hip joint. The absolute value of G(p) is equal to the magnitude of the gradient of the contact stress at the lateral acetabular rim. The parameter G(p) normalized with respect to the body weight (W(B)) is determined from the standard anteroposterior radiographs of adult human hips and pelvises using the mathematical model. The average value of G(p)/W(B) was determined for the group of dysplastic hips and for the group of normal hips. In the group of normal hips the average value of G(p)/W(B) is smaller (-0.445x10(5) m(-3)) than in the group of dysplastic hips (+1.481x10(5) m(-3)). The difference is statistically significant P

The influence of surface corrosive defects on the remaining working ability of transit gas pipelines of big diameters is discussed. An analytical and a FEM-numerical approach to the problem are presented. Finally a comparison of some of the authors' experimental results (to verify the theoretical solutions) with ANSI/ASME Code recommendations is given.

Composite materials based on a polyamide fabric (aramid) and a polydymethylsiloxane (PDMS) matrix were designed for application in bone surgery. In order to increase the bioactivity, 2, 5, 10, 15, 20, and 25 vol.% of nano/micro hydroxyapatite (HA) and tricalcium phosphate (TCP) were added. We studied the effect of the additives on the biocompatibility of the composite. It appears that nano additives have a more favorable effect on mechanical properties than microparticles. 15 vol.% of nano hydroxyapatite additive is an optimum amount for final application of the composites as substitutes for bone tissue: in this case both the mechanical properties and the biological properties are optimized without distinct changes in the inner structure of the composite.

This report is about composites used for bone grafting. Targets the composites compact of organic chemical compounds (biopolymers) and anorganic chemical compounds (nanoparticles). These composites must be, among others, biocompatible, nontoxic for organism and their mechanical properties must be near to mechanical properties of bone. This report focused on biodegradable composites based on gelatine and nanopowder of hydroxyapatite in nanofiber and particle form.

Contact stress distribution in the articular surface of the hip is considered a factor in the development of osteoarthritis, a common complication in hips with aseptic necrosis of the femoral head. We present evidence supporting the hypothesis that osteoarthritis in hips with aseptic necrosis of the femoral head can be caused by elevated contact stress related to the reduced load-bearing ability of the necrotic bone. By using a previously validated mathematical model, we observed that hip contact stress may increase considerably if the load-bearing capacity of the necrotic lesion is decreased, if the size of the necrotic segment is increased, and if the necrotic segment is located more laterally. These effects are affected by the intrinsic shape of the hip. As the estimated values of stress in hips with osteonecrosis are in the range obtained by the same method in dysplastic hips, osteoarthritis in hips with osteonecrosis can be caused by elevated contact stress.

An analytical model has been used to simulate the effects of tissue aging on residual strain, constitutive relations and stiffness parameter in the main right and left (ramus circumflexus) human coronary arteries, based on experimental data. The experimental opening angle theta scatters considerably with age. The optimum angle theta(op) approximately equals 70 degrees, which makes the circumferential stress uniform in the arterial wall at a normal blood pressure, is approximately constant throughout aging. Above age of the 15 years the estimated and experimental values of theta are greater than theta(op) and therefore the mechanical load of the inner layers of the media and the intima decreases and the adventitia is overloaded. On the basis of nonlinear regression analysis, age-related constitutive laws of arterial wall circumferential stiffness have been determined. Above the age of 30, arterial wall hardening increases rapidly. The left coronary artery is stiffer than the right artery for groups from 35 to 45 years of age. Hyperelasticity theory has been used to identify age-related multiaxial stress through wall thickness. A theoretical model based on the reduced Green strain provides a very good representation of the coronary artery circumferential mechanical response and predicts its nearly isotropic behavior. Bio-composite material forms non-homogeneous stresses and, in the course of aging, it increases the adventitia loading. In groups aged from 10 to 15 years, whose coronary artery residual strains are low, the circumferential stress distribution has a classic form. Stiffness parameter beta gradually increases with age and this increase is significant above the age of 60. Parameter beta tends to decrease when the opening angle theta increases.

Hypothesis of regulation of proteosynthetic activity of chondrocytes is suggested. A deformation of the cartilage caused by contact hip joint stress and consequent deformation of the chondrocytes are considered as main factors that could influence the metabolism of the cartilage.

The limit carrying capacity of gas pipelines having corrosion defects were evaluated by means of an improved FEM analysis, together with the ANSI/ASME defect judgement and an experimental verification. When compared with our past presentation at the proceedings of the CAPE'93 Colloquium (dealing with reproduced defects), this paper evaluates the remaining lifetime of a pipeline having natural faults. The new improved analysis includes geometrical nonlinearities leading to a modification of limit state parameters and thus matching better with actuality. This presented work was initiated by the firm of Trans-Gas in Prague after having had a pipeline inspected proving some parts of it as being heavily corroded. The task in hand was to determine the remaining pipeline lifetime with the view to at least a two-year period.

The aim of the present work is to demonstrate of the influence of the adventitia on distribution of residual stresses in the human aorta. The biomaterial increase in media as well as in adventitia in the course of the aorta's growth is formed by an intussusceptive mechanism of growth. In children's aortas, formative elastin lamellae are wavy with high amplitude perpendicular to the aortic surface. In adults' aortas the waves become smoother (stepwise) towards the adventitia. Also introduced is the growth function, which characterizes the biomaterial growth and the interference between the media and adventitial layers. It is possible to expect an extraordinary variability in the formation of the aortic wall tissue in the course of its growth as a result of metabolic and humoral influences and magnitude of the residual stresses in the course of growth.