Inflation of elastomeric circular membranes using network constitutive equations

International audienceThe present paper deals with the use of network-based hyperelastic constitutive equations in the context of thin membranes inflation. The study focus on the inflation of plane circular membranes and the materials are assumed to obey Gaussian and non-Gaussian statistical chains network models. The governing equations of the inflation of axisymmetric thin rubber-like membranes are briefly recalled. The material models are implemented in a numerical tool that incorporates an efficient B-spline interpolation method and a coupled Newton-Raphson/arc-length solving algorithm. Two numerical examples are studied: the homogeneous inflation of spherical balloons and the inflation of initially plane circular membranes. In the second example, the inflation profiles and the distributions of extension ratios along the membrane are extensively analysed during the inflation process. Both examples highlight the need of an accurate modelling of the strain-hardening phenomenon in elastomers

Efficiency of hyperelastic models for rubber-like materials

International audienceThis paper focuses on the modeling of rubber-like material behaviour under several modes of deformation using hyperelastic constitutive equations. A procedure based on genetic algorithms coupled to classical optimisation methods is proposed to identify the parameters of the models upon experimental data given in the literature. This leads to the classification of nineteen models with respect to criteria related to their capability to predict material behaviour

Re-focusing the ethical discourse on personalized medicine: a qualitative interview study with stakeholders in the German healthcare system

Background: In recent years, personalized medicine (PM) has become a highly regarded line of development in medicine. Yet, it is still a relatively new field. As a consequence, the discussion of its future developments, in particular of its ethical implications, in most cases can only be anticipative. Such anticipative discussions, however, pose several challenges. Nevertheless, they play a crucial role for shaping PM's further developments. Therefore, it is vital to understand how the ethical discourse on PM is conducted, i.e. on what - empirical and normative - assumptions ethical arguments are based regarding PM's current and future developments. Methods: To gather this information, we conducted a qualitative interview study with stakeholders in the German health care system. Our purposive sample included 17 representatives of basic research, clinical research, health economics, regulatory authorities, reimbursement institutions, pharmaceutical industry, patient organizations, as well as clinicians and legal experts involved in PM developments or policy making. We used an interview guide with open-ended questions and analyzed transcriptions of the interviews by means of qualitative content analysis. Results: The respondents addressed a multitude of concerns in the context of research on as well as application of personalized preventive and therapeutic measures both on the individual and on the societal level. Interestingly, regarding future developments of PM the ethical evaluation seemed to follow the rule: the less likely its application, the more problematic a PM measure is assessed. The more likely its application, on the other hand, the less problematic it is evaluated. Conclusions: The results of our study suggest re-focusing the ethical discourse on PM in Germany towards a constructive ethical monitoring which ensures to include only, nevertheless all of the actual and/or potential concerns that are ethically relevant in order to allow balancing them against the actual and potential ethically relevant benefits of PM measures. To render this possible, we propose a strategy for evaluating ethical concerns in the context of PM

A comparison of the Hart-Smith model with the Arruda-Boyce and Gent formulations for rubber elasticity

International audienceThe present paper demonstrates that the Hart-Smith constitutive model and the more recent Arruda and Boyce eight chains and Gent constitutive models are closely related. The ability of these three models to predict both small and large strain responses of rubbers is highlighted and equations that relate their material parameters are established

Dynamic inflation of non-linear elastic and viscoelastic rubberlike membranes

International audienceThe present paper deals with the dynamic inflation of rubber-like membranes. The material is assumed to obey the hyperelastic Mooney's model or the non-linear viscoelastic Christensen's model. The governing equations of free inflation are solved by a total Lagrangian finite element method for the spatial discretization and an explicit finite-difference algorithm for the time-integration scheme. The numerical implementation of constitutive equations is highlighted and the special case of integral viscoelastic models is examined in detail. The external force consists in a gas flow rate, which is more realistic than a pressure time history. Then, an original method is used to calculate the pressure evolution inside the bubble depending on the deformation state. Our numerical procedure is illustrated through different examples and compared with both analytical and experimental results. These comparisons yield good agreement and show the ability of our approach to simulate both stable and unstable large strain inflations of rubber-like membranes

Evaluating a patient's request for life-prolonging treatment: an ethical framework

Contrary to the widespread concern about over-treatment at the end of life, today, patient preferences for palliative care at the end of life are frequently respected. However, ethically challenging situations in the current healthcare climate are, instead, situations in which a competent patient requests active treatment with the goal of life-prolongation while the physician suggests best supportive care only. The argument of futility has often been used to justify unilateral decisions made by physicians to withhold or withdraw life-sustaining treatment. However, we argue that neither the concept of futility nor that of patient autonomy alone is apt for resolving situations in which physicians are confronted with patients' requests for active treatment. Instead, we integrate the relevant arguments that have been put forward in the academic discussion about 'futile' treatment into an ethical algorithm with five guiding questions: (1) Is there a chance that medical intervention will be effective in achieving the patient's treatment goal? (2) How does the physician evaluate the expected benefit and the potential harm of the treatment? (3) Does the patient understand his or her medical situation? (4) Does the patient prefer receiving treatment after evaluating the benefit-harm ratio and the costs? (5) Does the treatment require many resources? This algorithm shall facilitate approaching patients' requests for treatments deemed futile by the physician in a systematic way, and responding to these requests in an ethically appropriate manner. It thereby adds substantive considerations to the current procedural approaches of conflict resolution in order to improve decision making among physicians, patients and families

Unified model for Mullins effect and high cycle fatigue life prediction of rubber materials

Proceedings of the 8th European Conference on constitutive models for rubbers (ECCMR VIII), San Sebastian, Spain, 25-28 June 2013International audienceThe study describes the basic principles of a general damage model (GDMF) for Mullins effect and high cycle fatigue loadings of rubber materials and demonstrates its prediction possibilities for simulating the complete fatigue failure phenomenon. The present paper focuses on stiffness modelling of rubber materials for uniaxial and multiaxial static and fatigue loadings with a minimal number of material parameters in order to ensure robustness of the identification. The proposed hyperplastic model is expressed in terms of classical independent strain invariants. Mullins effect and high cycle fatigue loadings are both modelled according to a continuum damage mechanics approach

Transformative medical ethics: a framework for changing practice according to normative–ethical requirements

We propose a step-by-step methodological framework of translational bioethics that aims at changing medical practice according to normative–ethical requirements, which we will thus call “transformative medical ethics.” The framework becomes especially important when there is a gap between widely acknowledged, ethically justified normative claims and their realization in the practice of biomedicine and technology (ought–is gap). Building on prior work on translational bioethics, the framework maps a process with six different phases and 12 distinct translational steps. The steps involve various research activities including conceptual philosophical inquiry and (socio-)empirical research. On the one hand, the framework can be used as a heuristic tool to identify barriers to the transformation process. On the other hand, it can provide guidance for researchers and practitioners to develop appropriate (conceptual action and practice) models, which are then implemented and evaluated in specific practice contexts. We use the example of realizing the norm of respect for autonomy in the practice of medical decision-making to illustrate the framework. Further research is required, for example, to theoretically underpin the framework, to apply it to other ought–is gaps, and to evaluate its feasibility and effectiveness in various practice areas. Overall, the framework of transformative medical ethics suggests a strategic process to investigate and promote practice change that is ethically informed in all phases

Transformative medical ethics: A framework for changing practice according to normative–ethical requirements

We propose a step-by-step methodological framework of translational bioethics that aims at changing medical practice according to normative–ethical requirements, which we will thus call “transformative medical ethics.” The framework becomes especially important when there is a gap between widely acknowledged, ethically justified normative claims and their realization in the practice of biomedicine and technology (ought–is gap). Building on prior work on translational bioethics, the framework maps a process with six different phases and 12 distinct translational steps. The steps involve various research activities including conceptual philosophical inquiry and (socio-)empirical research. On the one hand, the framework can be used as a heuristic tool to identify barriers to the transformation process. On the other hand, it can provide guidance for researchers and practitioners to develop appropriate (conceptual action and practice) models, which are then implemented and evaluated in specific practice contexts. We use the example of realizing the norm of respect for autonomy in the practice of medical decision-making to illustrate the framework. Further research is required, for example, to theoretically underpin the framework, to apply it to other ought–is gaps, and to evaluate its feasibility and effectiveness in various practice areas. Overall, the framework of transformative medical ethics suggests a strategic process to investigate and promote practice change that is ethically informed in all phases