## 1 Introduction
The effect of microchannel geometry on cell adhesion has been investigated by designing channels with sharp and curved turns and performing fluid dynamic simulations showing the uniform distribution of velocity and stress within curved-turn microchannels [26; 27; 28]. The effect of shear stress within the channels of different widths on the function of aortic valvular interstitial cells was studied, indicating that the magnitude of shear stress regulates cell morphology, phenotype transformation, and the formation of focal adhesion while the cells align in the direction of the flow [29; 30]. On the other hand, OOC devices still have some limitations, such as the difficulty of modelling the organs on micrometric scales, creating vascularised tissues, and the difficulty of reproducing adequate levels of oxygen and nutrients [31]. The controlled environment of microfluidic devices offers the ability to change the fluidic parameters, making it possible to study cell interactions and fluid behaviour. For example, the changes in flow rate and pressure at varied geometric dimensions have led to the understanding of the role of various factors responsible for cell adhesion, gene expression, remodelling of the cytoskeleton and cell death [27; 32; 33]. Computational tools have played an important role in complementing experimental studies, as they allow parameters to be defined that are difficult to measure with experimental methods, such as velocity, shear stress and pressure [34; 35; 36]. [PERSON] et al. [37] simulated the flow behavior and glucose concentration profiles to study the geometry of two microfluidic channels that were separated by a porous membrane. They demonstrated that the rate of glucose diffusion increases with membrane porosity and decreases with a flow rate of 50 uL/h. [PERSON] et al. studied fluid flow velocity (0.01-0.05 m/s) and heat transfer using a COMSOL Multiphysics simulation to evaluate the temperature profile at different locations of a microfluidic device consisting of three layers, in which the cell suspension flows across the fluidic layers in the chip with a width-to-height ratio of 5:1. They demonstrated an actual temperature control and manipulation of the developed microfluidic cooling/heating system offering the capability of manipulating on-chip localised temperature (2 \({}^{\circ}\)C to 37 \({}^{\circ}\)C) due to typical cytotoxic issues with additive cryoprotective agents [38]. Other researchers examined metastatic behaviour within a 3D-bioprinted vasculature to validate a 3D computational flow model showing the contribution of hydrodynamics in determining sites of circulating tumor cell vascular colonization. They demonstrated that the bioprinted analog was readily capable of evaluating the accuracy and integrated complexity of a computational flow model and the discrete contribution of hydrodynamics in vascular colonization [39]. In addition to normal planar microfluidic channels, we have designed and simulated four different 3D microfluidic channel geometries incorporating micropillars compared to previous studies. Given that geometrical (i.e., width and height) and fluid dynamic parameters (i.e., wall shear stress, pressure, flow rate, velocity) have significant effects on cell morphology, proliferation, alignment, migration, and cell adhesion, various flow velocities within different design geometries were studied for the effects of their geometrical and fluid dynamic parameters in order to predict and control the effects of these forces and their potential as an alternative to conventional cell culture as well as for cell survivability and to recapitulate the cell- and organ-specific microenvironment.