Aahj Fons Sauren

Effects of placement and orientation of body-fixed accelerometers on the assessment of energy expenditure during walking

• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publishers website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.

Elastic and viscoelastic material behaviour of fresh and glutaraldehyde treated porcine aortic valve tissue

In order to obtain better insight into the changes in material properties of aortic valve tissue due to the treatment with glutaraldehyde, comparative tensile and relaxation experiments have been performed with strips taken from porcine aortic valve tissue in a fresh condition and after the treatment. To eliminate biological deviations between different strips, the comparative experiments were done on the same strip. The usual treatment for making a bioprosthesis, where an entire valve root is preserved under hydrostatic pressure of 13 kPa, was simulated by treating the strips under a uniaxial preload of 0.3 N. It was expected that the magnitude of the hydrostatic pressure over the valve during the treatment affects the material properties of the treated tissue. So, the treatments under hydrostatic pressures of 0 and 0.5 kPa were also simulated, by treating the tissue strips with uniaxial preloads of 0 and 0.01 N respectively. As a check leaflet strips of a Hancock bioprosthesis were also measured. To describe the elastic behaviour, two Youngs moduli are defined: one in the low strain region (E0) and one in the high strain region (E13). For describing the viscoelastic behaviour, use was made of the model of Fung (1972, Biomechanics, its Foundations and Objectives; Fung, Perrone and Anliker, Prentice Hall.) to fit the results. Here, the viscoelastic parameters to determine, were K, θ1 and θ2. Due to the treatment the stress-strain curve shifted to the stress-axis for the strips treated under 0.3 N and in the opposite direction for the strips treated under 0 and 0.01 N. For all strips after treatment the total amount of relaxation decreased, being the most pronounced (60%) for the strips treated under 0.3 N. For the tissue treated with preload of 0.3 N the changes in the elastic and viscoelastic parameters E0, E13 and K were the most pronounced: E0 changed from 0.18 × 106 to 1.7 × 106 N m−2, E13 from 6.6 × 106 to 23.0 × 106 N m−2, K from 0.085 to 0.024. On the contrary, the variation in the time constants θ1 and θ2 (from 0.0054 to 0.0034 s and from 71 to 37 s respectively) was hardly significant. The elastic behaviour of the Hancock leaflet strips confirms that of the tissue strips treated under 0.3 N, while the viscoelastic behaviour differs somewhat.

Aortic valve histology and its relation with mechanics—Preliminary report

Histological secitons of relaxed porcine aortic valves were studied from a mechanical point of view. The observations are combined into a tractable scheme of the tissue structure of the aortic valve. The valve leaflets can be regarded as an elastic meshwork, reinforced with stiff collagen bundles, showing an arrangement in one particular direction. The sinus walls consist of smooth muscle tissue, embedded in an elastic meshwork. The line of attachment of the leaflets to the sinus walls is constituted by the aortic ring, a crownlike fibrocartilaginous structure, containing large amounts of collagen fibres. This simple scheme of the tissue structure can be expected to provide important starting-points for both the interpretation of experimental results and the theoretical modelling of aortic valve mechanics and kinematics.

Model reduction tools for nonlinear structural dynamics

Abstract Three mode types are proposed for reducing nonlinear dynamical system equations, resulting from finite element discretizations: tangent modes, modal derivatives, and newly added static modes. Tangent modes are obtained from an eigenvalue problem with a momentary tangent stiffness matrix. Their derivatives with respect to modal coordinates contain much beneficial reduction information. Three approaches to obtain modal derivatives are presented, including a newly introduced numerical way. Direct and reduced integration results of truss examples show that tangent modes do not describe the nonlinear system sufficiently well, whereas combining tangent modes with modal derivatives and/or static modes provides much better reduction results.

Parameter estimation using the quasi-linear viscoelastic model proposed by Fung

Using the quasi-linear viscoelastic model proposed by Fung for the description of the viscoelastic properties of soft biological tissues, the parameters governing their time-dependent behavior are commonly estimated from relaxation experiments. Exact quantification is possible from the response to a step change in the strain. Since it is physically impossible to realize a true step change in the strain, in practice the response to a steplike strain change is used. In the present study the discrepancies between the exact and the estimated parameter values are investigated using a hypothetical quasi-linear viscoelastic material. The parameter tau 1, governing the fast viscous phenomena, is found to be subject to the largest errors. Methods for obtaining better estimates of tau 1 are outlined in a number of special cases.

A Global and a Detailed Mathematical Model for Head-Neck Dynamics

A detailed three-dimensional mathematical model describing the dynamic behavior of the human head and neck in automotive accidents is developed. The strategy is to proceed from a relatively simple model (the global model) for gaining insight into head-neck dynamics toward a complex model (the detailed model) providing the loads and deformations of the tissues of the neck. The models have been implemented in the integrated multibody/finite-element package MADYMO, version 5.1.1 of the TNO Crash Safety Research Centre. Language: en

A Note on the Reduced Creep Function Corresponding to the Quasi-Linear Visco-Elastic Model Proposed by Fung

For description of the visco-elastic behavior of soft biological tissues, Fung proposed a visco-elastic model formulated in terms of a relaxation function and corresponding relaxation spectrum. For the corresponding creep function, Fung proposed an expression which needs correction to obtain a consistent formulation. This creep function and the corresponding creep spectrum are derived in this note.

Multidisciplinary projects at the Eindhoven/Maastricht BME program

Integration and application of technical and (bio)medical knowledge in the complex area of biomedical engineering is a matter of teamwork. In our educational BME program special attention is focussed on this issue, by means of multidisciplinary projects (MDPs) for 3/sup rd/ and 4/sup th/ year students. The overall objective and learning targets of MDPs are presented. So far, evaluation of the projects has shown that students as well as staff are generally very enthusiastic about this special kind of Design Centred Learning.

Problem-based learning at the Eindhoven/Maastricht BME program

In the first two years of the 5-year Eindhoven/Maastricht biomedical education (BME) program problem based learning is used to develop engineering, problem solving and communicative skills. These skills are put into practice in the projects and internships during the remainder of the educational program.

A simplified quasi-static model of the human knee joint based on a general two-body-system theory

• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publishers website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.