Modelling of the dielectric properties of trabecular bone samples at microwave frequency

In this paper the dielectric properties of human trabecular bone are evaluated under physiological condition in the microwave range. Assuming a two components medium, simulation and experimental data are presented and discussed. A special experimental setup is developed in order to deal with inhomogeneous samples. Simulation data are obtained using finite difference time domain from a realistic sample. The bone mineral density of the samples are also measured. The simulation and experimental results of the present study suggest that there is a negative relation between bone volume fraction (BV/TV) and permittivity (conductivity): the higher the BV/TV the lower the permittivity (conductivity). This is in agreement with the recently published in vivo data. Keywords: Bone dielectric properties, Microwave tomography, Finite difference time domain.Comment: 10 pages, 5 figures, 4 table

Mathematical modeling of uniaxial mechanical properties of collagen gel scaffolds for vascular tissue engineering

Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model.Facultad de Ciencias ExactasInstituto de Física de Líquidos y Sistemas Biológico

Mathematical Modeling of Uniaxial Mechanical Properties of Collagen Gel Scaffolds for Vascular Tissue Engineering

Article ID 859416Small diameter tissue - engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and-or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control systemtheory. Second,models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed:Mooney - Rivlin inspired and Hammerstein models. Theresults suggest that Mooney - Rivlin andHammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3 per cent and .75.8 per cent, resp.). When Akaike criterion is used, the best is the Mooney - Rivlin inspired model

Modelling of the dielectric properties of trabecular bone samples at microwave frequency

In this paper the dielectric properties of human trabecular bone are evaluated under physiological condition in the microwave range. Assuming a two components medium, simulation and experimental data are presented and discussed. A special experimental setup is developed in order to deal with inhomogeneous samples. Simulation data are obtained using finite difference time domain from a realistic sample. The bone mineral density of the samples are also measured. The simulation and experimental results of the present study suggest that there is a negative relation between bone volume fraction (BV/TV) and permittivity (conductivity): the higher the BV/TV the lower the permittivity (conductivity). This is in agreement with the recently published in vivo data.Instituto de Física de Líquidos y Sistemas BiológicosGrupo de Aplicaciones Matemáticas y Estadísticas de la Facultad de Ingenierí

Técnicas de ultrasonido : Una herramienta potencial para la ingeniería de tejidos

El objetivo de este trabajo es desarrollar dos montajes experimentales para la evaluación de las propiedades acústicas de hidrogeles de colágeno y para estudiar su correlación con las propiedades mecánicas. El primero permite estimar la velocidad del sonido, atenuación e impedancia acústica de las muestras manejando la temperatura. En el segundo, la configuración anterior se combina con un ensayo mecánico de compresión, lo que permite interrogar al mismo tiempo, tanto propiedades acústicas como mecánicas de la muestra. Se observan las propiedades acústicas y mecánicas de los geles de colágeno preparados de acuerdo a diferentes condiciones experimentales: pH y la concentración de colágeno. La variación de estos parámetros permite modificar las condiciones mecánicas de la matriz.Facultad de Ingenierí

The effect of mechanical constraints on gelatin samples under pulsatile flux

It is of great interest in tissue engineering the role of collagen gel-based structures (scaffolds, grafts and -by cell seeded and maturation- tissue equivalents (TEs) for several purposes). It is expected the appropriate biological compatibility when the extracellular matrix (ECM) is collagen-based. Regarding the mechanical properties (MP), great efforts in tissue engineering are focused in tailoring TE properties by controlling ECM composition and organization. When cells are seeded, the collagen network is remodeled by cell-driven compaction and consolidation, produced mainly through the mechanical stimuli that can be directed selecting the geometry and the surfaces exposed to the cells. Collagen gels have different (chemical and mechanical) properties depending on their origin and preparation conditions. The MP of the collagen network are derived from the degree of cross-linking (CLD) which can be modified by different treatments. One of the techniques to evaluate MP in the network is by ultrasound (US). In this work we analyse the effect of several mechanical constraints (similar to that imposed to promote cell growth on certain sample surfaces, when seeded) on samples of gelatin with a specific geometry (thick walls cylinders) under loading conditions of pulsatile flow. We checked US parameters and estimates evolution of the network structure for different restrictions in the sample mobility. It was implemented by adapting devices specially built to measure elastic properties of biological tissues by US. The material (origin and purity) and the preparation conditions for the gelatin were selected in order to compare the results with those of literature.Fil: BLANGINO, Eugenia.Fil: CAGNOLI, Martín A..Fil: IRASTORZA, Ramiro M..Fil: Vericat, Fernando