48 research outputs found
Mechanically induced collagen remodelling in the aortic valve : 3D FE analyses of fibre reorientation
No full textModeling and remodeling of the collagen architecture in cardiovascular tissues
No full textHeart valve replacement by a mechanical or biological prosthesis represents a common surgical therapy for end-stage valvular heart diseases. A critical drawback of these prostheses is the inability to grow, repair and remodel in response to changes in the tissue’s environment. Tissue engineering represents a promising alternative technology to overcome the disadvantages of the heart valve replacements currently used. The goal of tissue engineering is to create an autologous living tissue with properties that resemble those of the native tissue. The concept of tissue engineering is based on seeding autologous cells onto a biodegradable scaffold material and delivering the appropriate environmental cues to culture the construct. This technique is relatively successful and tissue-engineered heart valves have been placed at the pulmonary side in animal models. However, the mechanical properties of these tissue-engineered constructs are currently insufficient for implantation at the aortic side. In order to improve the mechanical properties of the constructs, tissue formation is stimulated via a conditioning protocol. The tissue is exposed to appropriate biochemical and biomechanical stimuli in a bioreactor system. As the mechanical properties of the engineered constructs are not yet optimal, the conditioning protocols should be improved and optimized. The load-bearing capacities of the aortic valve are mainly determined by a well organized network of collagen fibers which withstands the pressures during the cardiac cycle and transmits the forces into the aortic wall. For that reason, the conditioning protocol should focus on the deposition of sufficient amounts of properly organized collagen fibers. In these conditioning protocols mechanically induced tissue adaptation and remodeling play a crucial role. To optimize the protocols and to improve the mechanical properties of the tissue, it is desired to gain insight into these processes. However, the interaction between tissue remodeling and the mechanical loading condition is complex because these are highly coupled. Therefore, mathematical models are desired to study this interaction and to predict the tissue’s response to mechanical stimuli. The objective of this work is to gain insight into tissue remodeling due to mechanical stimuli. In this thesis, mathematical models are formulated that 1) describe the mechanical loading condition in the tissue, and 2) account for the effects of tissue remodeling on the mechanical behavior of the construct. The application of these models focuses on the aortic valve, but the models are also applied to arteries since these contain a specific architecture of collagen fibers as well. The starting point of this research is the formulation of remodeling laws which are based on the hyxi pothesis that the collagen fibers orient towards the strain field. The predicted fiber directions agree very well with experimental data from native aortic valves. However, the formulated hypothesis appears to be inadequate to describe the helical collagen orientation that is found in arterial walls. Subsequently, the hypothesis is successfully modified and the predicted fiber directions represent the architecture that is present in native arteries. The modified hypothesis is then applied to the aortic valve and this yields an improved prediction of the collagen architecture in the aortic valve. Next, a structurally-based constitutive model is presented to give an accurate description of the mechanical behavior of the tissues. This model contains structural parameters that describe the amount and orientation of collagen fibers and enables us to incorporate experimentally measured fiber distributions. Finally, the structural constitutive model is coupled with the hypotheses for collagen fiber remodeling. In this way, the evolution of the collagen fiber distribution and the mechanical properties of tissue-engineered cardiovascular tissues can be studied and predicted
Erratum to Remodelling of continuously distributed collagen fibres in soft connective tissues [Journal of biomechanics 36 ( 2003) 1151-1158]
No full textRefers to: Remodelling of continuously distributed collagen fibres in soft connective tissues
Journal of Biomechanics, Volume 36, Issue 8, August 2003, Pages 1151-1158
N. J. B. Driessen, G. W. M. Peters, J. M. Huyghe, C. V. C. Bouten, F. P. T. Baaijen
Modeling the mechanics of tissue-engineered human heart valve leaflets
No full textMathematical models can provide valuable information to assess and evaluate the mechanical behavior of tissue-engineered constructs. In this study, a structurally based model is applied to describe and analyze the mechanics of tissue-engineered human heart valve leaflets. The results from two orthogonal uniaxial tensile tests are used to determine the model parameters of the constructs after two, three and four weeks of culturing. Subsequently, finite element analyses are performed to simulate the mechanical response of the engineered leaflets to a pressure load. The stresses in the leaflets induced by the pressure load increase monotonically with culture time due to a decrease in the construct's thickness. The strains, on the other hand, eventually decrease as a result of an increase in the elastic modulus. Compared to native porcine leaflets, the mechanical response of the engineered tissues after four weeks of culturing is more linear, stiffer and less anisotropic. (c) 2006 Elsevier Ltd. All rights reserved
Real time, non-invasive assessment of leaflet deformation in heart valve tissue engineering
No full textIn heart valve tissue engineering, most bioreactors try to mimic physiological flow and operate with a preset transvalvular pressure applied to the tissue. The induced deformations are unknown and can vary during culturing as a consequence of changing mechanical properties of the engineered construct. Real-time measurement and control of local tissue strains are desired to systematically study the effects of mechanical loading on tissue development and, consequently, to design an optimal conditioning protocol. In this study, a method is presented to assess local tissue strains in heart valve leaflets during culturing. We hypothesize that local tissue strains can be determined from volumetric deformation. Volumetric deformation is defined as the amount of fluid displaced by the deformed heart valve leaflets in a stented configuration, and is measured, non-invasively, using a flow sensor. A numerical model is employed to relate volumetric deformation to local tissue strains in various regions of the leaflets (e.g. belly and commissures). The flow-based deformation measurement method was validated and its functionality was demonstrated in a tissue engineering experiment. Tri-leaflet, stented heart valves were cultured in vitro and during mechanical conditioning, realistic values for volumetric and local deformation were obtained. © 2008 The Author(s
