Cellular material

Cellular materials have large use in many components acting as impact energy absorbers. These components have to be designed on the basis of the kind of impact, of the involved energy amount and of the maximum admissible load. The choice of the most suitable density for the selected type of foam is based on stress-strain behaviour, obtained by means of experimental tests and/or models. Only a few micro-mechanical models, as the Gibson model, take into account the density effects. These models could result quite complex to manage because of the need of, at least, a rough analysis of the actual foam structure. Conversely, most of the models used for numerical simulations are phenomenological models and have simple parameter identification based on fitting of experimental data, but they do not account for density effect.

Bovine pericardium is a collagenous tissue commonly used as a natural biomaterial in the fabrication of cardiovascular devices. For tissue engineering purposes, this xenogeneic biomaterial must be decellularized to remove cellular antigens. With this in mind, three decellularization protocols were compared in terms of their effectiveness to extract cellular materials, their effect on glycosaminoglycan (GAG) content and, finally, their effect on tensile biomechanical behavior. The tissue decellularization was achieved by treatment with t-octyl phenoxy polyethoxy ethanol (Triton X-100), tridecyl polyethoxy ethanol (ATE) and alkaline treatment and subsequent treatment with nucleases (DNase/RNase). The quantified residual DNA content (3.0 ± 0.4%, 4.4 ± 0.6% and 5.6 ± 0.7% for Triton X-100, ATE and alkaline treatment, respectively) and the absence of nuclear structures (hematoxylin and eosin staining) were indicators of effective cell removal. In the same way, it was found that the native tissue GAG content decreased to 61.6 ± 0.6%, 62.7 ± 1.1% and 88.6 ± 0.2% for Triton X-100, ATE and alkaline treatment, respectively. In addition, an alteration in the tissue stress relaxation characteristics was observed after alkaline treatment. We can conclude that the three decellularization agents preserved the collagen structural network, anisotropy and the tensile modulus, tensile strength and maximum strain at failure of native tissue.

Clinical medicine and biotechnology increasingly utilise and transform human bodily tissues in novel ways. Today more and more tissues-blood, whole organs, ova, embryos, sperm, skin, bone, heart valves, cellular material, bone marrow and corneas-can be transferred between donors and recipients. Hence more and more people in developed nations have the experience of giving a fragment of their body to another, or receiving such a fragment as part of some kind of therapy. These systems for the circulation of tissues raise the question of what we have termed 'bioidentity'. Bioidentity describes our common-sense understanding of our bodies as 'ours', as both supporting and being included in our social and subjective identities. Within this framework, how are we to understand the status of detachable bodily fragments like blood, ova or organs? As parts of our bodies do they retain a trace of our identity after donation, or are they detachable things? What is our relationship, if any, to the patient who receives our tissues as part of their treatment? This paper investigates the specific case of blood transfusion and donation. It draws upon in depth interviews with 55 people who have specific experience with blood. They either have hepatitis C (are HCV+) acquired by transfusion or intravenous drug use, or have donated blood or received a blood transfusion but are free of hepatitis C (are HCVÀ). We analyse this material according to the themes-Donated Blood as 'Self', Blood as Alienable, Blood as Communal Substance, and Contaminated Gifts and the Blood of Strangers. We find that, generally speaking the HCV+ and HCVÀ groups share very similar ideas about blood donation and transfusion. For a minority of both groups, blood was understood as a decisive site of self irrespective of location, but for the remainder donated blood was either ambiguous with regard to identity, a shared substance, or not considered to have any lingering relationship to the self once given. However both groups regarded blood as strongly imbued with 'risk identity'. In particular the HCV+ interviewees regarded their blood as a dangerous personal attribute, one that they must be careful to withhold from circulation, whereas the blood donors felt obliged to donate their blood precisely because they considered it clean and risk free. r (C. Waldby).

In this paper, the effective stress-strain behaviours of four typical low-density 2D structures are comparatively studied by means of finite element analysis using the representative volume element approach. The relation between the relative density and cell wall thickness-to-length ratio for the structures are determined based on geometry analysis and periodic boundary conditions are employed in models of comparable densities. The dependence of the Young's moduli and the collapse strength on cell parameters have been established and compared with analytical solutions. The effect of defects in the form of broken cell walls on deformational behaviour is studied systematically and correlated to the connectivity of the foam based on percolation analysis.