Biofluid Mechanics / Biofluids
Pooya Abdi; Bahman Vahidi
Volume 17, Issue 1 , May 2023, , Pages 41-50
Abstract
Topography of extracellular matrix plays a major role in many biological events including tissue healing, morphogenesis and growth. It is known that matrix constitution and mechanical properties are deciding factors in governing the fate of its inhabitant cells. Besides the direct mechanical cues, matrices ...
Read More
Topography of extracellular matrix plays a major role in many biological events including tissue healing, morphogenesis and growth. It is known that matrix constitution and mechanical properties are deciding factors in governing the fate of its inhabitant cells. Besides the direct mechanical cues, matrices also facilitate the release and uptake of certain chemicals and participate in cell-cell and cell-ECM crosstalk. Mechanical strains in the matrix are proved to direct endothelial cell migration and elongation leading to angiogenesis, and there is a consensus that matrix stiffness, fiber density and fiber orientation can enhance angiogenesis in the preferred direction of stiffness gradient. In this study, we specifically investigated the role of topography in guidance of endothelial self-reorganization prompted by the effect of fluid flow hindrance and facilitation in certain directions. We adopted our previous model of fluid flow guided angiogenesis for cellular responses. Lattice Boltzmann model of fluid flow was adopted and modified to study the effect of unidirectional and randomly oriented fibers. To study the effect of fiber orientation, we customized a previously proposed model of porosity in lattice Boltzmann to suit this purpose. This model could reproduce the effects of fiber orientations in matrix on endothelial migration and vasculogenesis. Simulations showed better confluency of formed lumens when prescribed flow is in the direction of fiber orientation. These results can have further implications in understanding endothelial complications in certain diseases as well as in tumor angiogenesis and metastasis.
Biofluid Mechanics / Biofluids
Milad Mahdinezhad Asiyabi; Bahman Vahidi
Volume 14, Issue 4 , February 2021, , Pages 345-355
Abstract
It is possible to replace or repair damaged tissue with regenerative medicine. Most tissues in the body rely on blood vessels to supply oxygen and nutrients to individual cells. New blood vessels are essential to grow tissue longer than 100-200 mm due to limited oxygen delivery; This restriction also ...
Read More
It is possible to replace or repair damaged tissue with regenerative medicine. Most tissues in the body rely on blood vessels to supply oxygen and nutrients to individual cells. New blood vessels are essential to grow tissue longer than 100-200 mm due to limited oxygen delivery; This restriction also applies to engineered tissues. Therefore, one of the prerequisites for tissue survival and growth is the presence of vasculature. One way to overcome this limitation is to use microfluidic channels that are created by planting a layer of endothelial cells on the channel wall and applying in vitro flow. In this study, the channels were placed inside a type 1 collagen scaffold with 81% porosity, and a drainage channel was considered for the scaffold with lymphatic function. The geometry of the perfusion channel was based on Murray’s law. The effect of parameters such as drainage channel radius, perfusion channel pressure difference, scaffold hydraulic conductivity, and vascular hydraulic conductivity on transmural pressure and shear stress was investigated. The effect of the bifurcation angle on shear stress was also studied. The finite element method was used to solve the problem. In the simulation on a vessel with a diameter of 100 mm, the maximum interstitial velocity was 50E-9 m/s, the maximum interstitial pressure was 1.34E+3 Pa, and the minimum transmural pressure was 1.49E+3 Pa. The average shear stress on the vessel walls was 10 dyn/cm2. It was noted that reducing the pressure at the drainage channel outlet, the internal insulation of the scaffold from the pressure difference within the perfusion channel, reducing the vascular hydraulic conductivity, increasing the scaffold hydraulic conductivity, and increasing the radius of the drainage channel will create and maintain positive transmural pressure. The results of this study can be used in creating implantable tissue consisting of vascular network and drainage.
Biofluid Mechanics / Biofluids
Mohammad Ahmadi Alashti; Bahman Vahidi; Mahtab Ebad
Volume 13, Issue 1 , April 2019, , Pages 1-15
Abstract
The large surface area of the lung with its thin air-blood barrier is exposed to particles in the inhaled air. In this condition, if the inhaled pollutant aerosols are toxic, the particle-lung interaction may cause serious hazards and injuries on human’s health. On the otherhand, these interactions ...
Read More
The large surface area of the lung with its thin air-blood barrier is exposed to particles in the inhaled air. In this condition, if the inhaled pollutant aerosols are toxic, the particle-lung interaction may cause serious hazards and injuries on human’s health. On the otherhand, these interactions are also used for drug delivery to human’s body. In either case, an accurate estimation of dose and sites of deposition in the respiratory tract is fundamental for understanding mechanobiology of these deseases. Obtaining in vivo data of particle transportation in the human lung experimentally is often difficult. But, computational fluid-particle dynamics (CFPD) has provided the possibility to gain aerosol transportion data in realistic airway geometries. Aerosols deposition in the human lung mainly occurs due to combination of inertial impaction, gravitational sedimentation and diffusion. For particles with aerodynamic size of 0.5 to 5 micron and in inhalation state of lung, the main mechanisms of particle deposition in distal parts of human’s respiratory system are sedimentation, due to gravity and convective transfer due to wall movement. In this study, deposition of particles in distal part of human respiratory system, specifically 18th generation, has been modeled for two gravity conditions, normal and absent gravity, by assuming isotropic displacements on the walls and with the rate of 1 (mg/sec) for particle input. By analyzing the results, it was determined that the amount of particle deposition in distal airways reduces a great amount by omitting the effect of gravitational force because, particles smaller than 5 micron can penetrate into that airways. Particles with the diameter of 5 micron deposit under the effect of inertial impact, whereas this mechanism occurs mostly in airways with large and medium diameters and also, by sedimentation which occurs in the distal lung.
