Determination of material models for arterial walls from uniaxial extension tests and histological structure

An approach is proposed that allows the determination of material models from uniaxial tests and histostructural data including fiber orientation of the tissue. A combination of neo-Hookean and Fung-type strain-energy functions is utilized, and inequality constraints imposed on the constitutive parameters are derived providing strict local convexity and preferred fiber orientations. It is shown how the Fung-type model gets a pseudo-structural aspect inherent in the phenomenological model; a correlation between the fiber structure and the parameters of the Fung-type model is explicitly provided. In order to apply the proposed approach, quasi-static uniaxial extension tests of preconditioned prepared strips from the intima, media and adventitia of a human aorta with non-atherosclerotic intimal thickening are acquired in axial and circumferential directions; structural information from histological analyses for each aortic tissue are documented. Data reveal a remarkable thickness, load-bearing capacity and stiffness of the intimal samples in comparison with the media and adventitia. Constitutive parameters for each aortic tissue layer are determined by solving the constrained problem using a penalty function method; a new approach for the estimation of appropriate start values is proposed. Finally, the predictivity and efficacy of the material models is shown by comparing model data with data from the uniaxial extension tests and histological image analyses.     

Haemodynamic effects of stent diameter and compaction ratio on flow-diversion treatment of intracranial aneurysms: A numerical study of a successful and an unsuccessful case

Background: Compacting a flow-diverting (FD) stent is an emerging technique to create a denser configuration of wires across the aneurysm ostium. However, quantitative analyses of post-stenting haemodynamics affected by the compaction level of different stent sizes remain inconclusive.Objective: To compare the aneurysmal haemodynamic alterations after virtual FD treatments with different device diameters at different compaction ratios.Methods: We virtually implanted three sizes of FD stent, with each size deployed at four compaction ratios, into two patient aneurysms previously treated with the Silk + FD—one successful case and the other unsuccessful. Wire configurations of the FD in the 24 treatment scenarios were examined, and aneurysmal haemodynamic alterations were resolved by computational fluid dynamics (CFD) simulations. We investigated the aneurysmal flow patterns, aneurysmal average velocity (AAV), mass flowrate (MF), and energy loss (EL) in each scenario.Results: Compactions of the stent in the successful case resulted in a greater metal coverage rate than that achieved in the unsuccessful one. A 25% increment in compaction ratio further decreased the AAV (12%), MF (11%), and EL (9%) in both cases (average values). The averaged maximum differences attributable to device size were 10% (AAV), 8% (MF), and 9% (EL).Conclusions: Both stent size and compaction level could markedly affect the FD treatment outcomes. It is therefore important to individualise the treatment plan by selecting the optimal stent size and deployment procedure. CFD simulation can be used to investigate the treatment outcomes, thereby assisting doctors in choosing a favourable treatment plan.     

Slow freezing versus vitrification technique for human ovarian tissue cryopreservation: An evaluation of histological changes,WNT signaling pathway and apoptotic genes expression

This study compared slow freezing and vitrification of ovarian tissue by evaluation of histological changes, WNT signaling pathway and apoptotic genes expression. Ovarian tissue was obtained from women aging 27–38 years old. Ovarian cortex from each patient was divided into three pieces and randomly grouped as slow freezing, vitrification and control groups for investigation of WNT signaling gene expression and β-CATENIN presence as well as histological studies. The stromal structure of all ovaries were preserved. The number of secondary follicles decreased in vitrified group (P < 0.05). WNT-3, β-CATENIN, FZD-2 and GSK-3β expressions were significantly higher in slow frozen and vitrified groups, compared to control group (P < 0.05). On the contrary, AXIN1 expression in slow frozen samples were significantly lower than that of the vitrified and control group. The expression of apoptotic genes, excluding CASP3, was significantly decreased in slow-frozen samples (P < 0.05). Conversely, BAX:BCL-2 percentage significantly increased in vitrification versus slow freezing and control(P < 0.05). Follicles in slow frozen samples displayed nuclear and cytoplasmic β-CATENIN staining, while control and vitrification groups only showed β-CATENIN protein in the cytoplasm. The presented data show that slow freezing results in a better preservation regardless of the type of follicle. Therefore, it is concluded that slow freezing is still an ideal method for ovary cryopreservation.     

Metabolism Comparative Cytotoxicity Assay (MCCA) and Cytotoxic Metabolic Pathway Identification Assay (CMPIA) with cryopreserved human hepatocytes for the evaluation of metabolism-based cytotoxicity in vitro: proof-of-concept study with aflatoxin B1

Recently, we have improved the cryopreservation procedures for human hepatocytes, leading to cells that can be cultured after thawing (“plateable” cryopreserved human hepatocytes). The ability to culture cryopreserved human hepatocytes allows application of the cells for prolonged incubations such as long-term (days) metabolism studies, enzyme induction studies, and cytotoxicity studies. We report here the application of the plateable cryopreserved human hepatocytes to evaluate the relationship between xenobiotic metabolism and toxicity. Two assays were developed: The Metabolism Comparative Cytotoxicity Assay (MCCA) and the Cytotoxic Metabolic Pathway Identification Assay (CMPIA). The MCCA was designed for the initial identification of the role of metabolism in cytotoxicity by comparing the cytotoxic potential of a toxicant in a metabolically competent (primary human hepatocytes) and a metabolically incompetent (Chinese hamster ovary (CHO)) cell type, as well as the evaluation of the role of P450 metabolism by comparing the cytotoxicity of the toxicant in question in human hepatocytes in the presence and absence of a nonspecific, irreversible P450 inhibitor, 1-aminobenzotriazole (ABT). The CMPIA was designed for the identification of the P450 isoforms involved in metabolic activation via the evaluation of the cytotoxicity of the toxicant in the presence and absence of isoform-selective P450 inhibitors. Results of a proof-of-concept study with the MCCA and CMPIA with a known hepatotoxicant, aflatoxin B1 (AFB1), are reported. AFB1 is known to require P450 metabolism for its toxicity. In the MCCA, AFB1 was found to have significantly higher cytotoxicity in human hepatocytes than CHO cells, therefore confirming its requirement for biotransformation to be toxic. ABT was found to effectively attenuate AFB1 cytotoxicity, confirming that P450 metabolism was involved in its metabolic activation. In the CMPIA, AFB1 cytotoxicity was found to be attenuated by ketoconazole and diethyldithiocarbamate, but not by furafylline, quinidine, and sulfaphenazole. Results with the isoform-selective inhibitors suggest that the isoforms inhibited by ketoconazole (mainly CYP3A4) and diethyldithiocarbamate (mainly CYP2A6, and CYP2E1), but not the isoforms inhibited by furafylline (mainly CYP1A2), sulfaphenazole (mainly CYP2C9) and quinidine (mainly CYP2D6) are involved in the metabolic activation of AFB1. This proof-of-concept study suggests that MCCA and CMPIA with cryopreserved human hepatocytes are potentially useful for the evaluation of the relationship between human xenobiotic metabolism and toxicity.