Coupled FEA Model with Continuum Damage Mechanics for the Degradation of Polymer-based coatings on Drug-Eluting Stents.

Drug-Eluting Stents (DES) are commonly used in Coronary angioplasty procedures to reduce the phenomenon of restenosis. Numerical simulations are proven to be a useful tool to the Bioengineering community in computing the mechanical performance of stents. BioCoStent is a research project aiming to develop a DES with retinoic acid (RA) coating, in the frame of which FEAC is responsible for the in silico numerical simulation of the coating's degradation in terms of Finite Element Analysis (FEA). The coatings under study are poly(lactic-co-glycolic acid) (PLGA) and polylactide (PLA). The FEA is based on the Continuum Damage Mechanics (CDM) theory and considers a mechanistic model for polymer bulk degradation of the coatings. The degradation algorithm is implemented on the NX Nastran solver through a user-defined material UMAT subroutine. This paper describes the developed numerical model to compute the degradation of biodegradable coatings on DES. The transient numerical model provides useful insight into the critical areas with regards to the scalar damage of the coatings. The FEA results present a complete degradation of polymers after several weeks.

FEA of Drug-Eluting Stents and Sensitivity Analysis of a Continuum Damage Model for the Degradation of PLGA Coating.

Drug-Eluting Stents (DES) are commonly used in coronary angioplasty operations as a solution against artery stenosis and restenosis. Computational Bioengineering allows for the in-silico analysis of their performance. The scope of this work is to develop a DES Digital Twin, focusing on the mechanical integrity of its biodegradable coating throughout the operational lifecycle. The implementation leverages the Finite Element Method (FEM) to compute the developed mechanical stress field on the DES during the inflation/deflation stage, followed by the degradation of the polymer-based coating. The simulation of the degradation process is based on a Continuum Damage Mechanics (CDM) model that considers bulk degradation. The CDM algorithm is implemented on the NX Nastran solver through a user-defined material (UMAT) subroutine. For benchmarking purposes and to compare with the baseline design of the BioCoStent project, this conceptual study implements an alternative stent design, to study the effect of the geometry on the developed stresses. Additionally, the effect of the degradation rate on the polymer-based coating's lifecycle is studied via sensitivity analysis.

Retinol Binding Protein-4 and Adiponectin Levels in Thyroid Overt and Subclinical Dysfunction.

Thyroid dysfunction is accompanied by numerous changes in intermediary metabolism. Retinol binding protein-4 (RBP-4) and adiponectin are 2 adipocytokines that have multiple metabolic functions. The aim of our study was to examine serum RBP4 and adiponectin levels in clinical (before and after therapy) and subclinical hyperthyroid and hypothyroid subjects as compared to controls.150 patients with thyroid dysfunction were recruited (65 hyperthyroid and 85 hypothyroid) while 28 euthyroid subjects served as a control group. We measured anthropometric, biochemical and hormonal (free T4, free T3, TSH, insulin) parameters in all participants. RBP-4 and adiponectin were measured using commercial ELISA kits.Mean baseline levels of RBP-4 were higher in patients with clinical hypothyroidism (29.0±10.2 ng/ml, 25.1±12.6 ng/ml, 38.8±16.5 ng/ml, 31.9±13.2 ng/ml, 20.4±8.2 ng/ml in patients with hyperthyroidism, subclinical hyperthryrodism, hypothyroidism, subclinical hypothyroidism and controls respectively, F=4.86, P<0.001) and decreased significantly in patients with clinical hyperthyroidism and hypothyroidism after normalization of thyroid hormones' levels (from 29.0±10.2 to 24.9±8.4 ng/ml, p=0.003 and from 38.8±16.5 to 29.0±10.8 ng/ml, p=0.001 respectively). We did not observe analogous changes in adiponectin levels in any of the studied groups.RBP-4 levels are higher in patients with clinical hypothyroidism and exhibit a marked decrease after normalization of thyroid function in both hyper and hypothyroid patients. We suggest that RBP-4 may play a role in the metabolic disturbances which accompany thyroid dysfunction.