A multiscale computational fluid dynamics approach to simulate the micro-fluidic environment within a tissue engineering scaffold with highly irregular pore geometry

\u3cp\u3eMechanical stimulation can regulate cellular behavior, e.g., differentiation, proliferation, matrix production and mineralization. To apply fluid-induced wall shear stress (WSS) on cells, perfusion bioreactors have been commonly used in tissue engineering experiments. The WSS on cells depends on the nature of the micro-fluidic environment within scaffolds under medium perfusion. Simulating the fluidic environment within scaffolds will be important for gaining a better insight into the actual mechanical stimulation on cells in a tissue engineering experiment. However, biomaterial scaffolds used in tissue engineering experiments typically have highly irregular pore geometries. This complexity in scaffold geometry implies high computational costs for simulating the precise fluidic environment within the scaffolds. In this study, we propose a low-computational cost and feasible technique for quantifying the micro-fluidic environment within the scaffolds, which have highly irregular pore geometries. This technique is based on a multiscale computational fluid dynamics approach. It is demonstrated that this approach can capture the WSS distribution in most regions within the scaffold. Importantly, the central process unit time needed to run the model is considerably low.\u3c/p\u3

Localisation of mineralised tissue in a complex spinner flask environment correlates with predicted wall shear stress level localisation

\u3cp\u3eSpinner flask bioreactors have often been employed for bone tissue engineering. However, the reasons for their success in facilitating bone growth remain inconclusive. It was hypothesised that engineered bone tissue formation can be attributed to mechanical stimuli, which can be predicted in the tissue engineered construct. To test the hypothesis and draw conclusions as to how mechanical stimulation affects cell behaviour, a multi- disciplinary approach using cell culture experiments and computational fluid dynamics (CFD) to simulate the complex flow within the spinner flask and scaffold was employed. Micro-computed tomography and histology showed that statically cultured human bone marrow derived stromal cells on silk fibroin scaffolds did not form extracellular matrix (ECM) or deposit minerals. However, constructs cultured at 60 rpm resulted in ECM formation and mineralisation, mainly at the bottom of the scaffold (bottom: 78 ± 7 %, middle: 17 ± 5 %, top: 5 ± 2 % of total mineralised volume). Culturing at 300 rpm led to a more homogeneously distributed ECM (bottom: 40 ± 14 %, middle: 33 ± 1 %, top: 27 ± 14 % of total mineralised volume). These observations were in agreement (Pearson correlation coefficient: 97 %) with the computational simulations that predicted maximal scaffold mineralisation, based on wall shear stress stimulation, in the bottom at 60 rpm and in the main body at 300 rpm. Such combinations of CFD modelling and experimentation could advance our knowledge of the mechanical stimuli that cells experience in vitro and link them to biological responses.\u3c/p\u3

Microvascular networks from endothelial cells and mesenchymal stromal cells from adipose tissue and bone marrow:A comparison

\u3cp\u3eA promising approach to overcome hypoxic conditions in tissue engineered constructs is to use the potential of endothelial cells (EC) to form networks in vitro when co-cultured with a supporting cell type in a 3D environment. Adipose tissue-derived stromal cells (ASC) as well as bone marrow-derived stromal cells (BMSC) have been shown to support vessel formation of EC in vitro, but only very few studies compared the angiogenic potential of both cell types using the same model. Here, we aimed at investigating the ability of ASC and BMSC to induce network formation of EC in a co-culture model in fibrin. While vascular structures of BMSC and EC remained stable over the course of 3 weeks, ASC-EC co-cultures developed more junctions and higher network density within the same time frame. Both co-cultures showed positive staining for neural glial antigen 2 (NG2) and basal lamina proteins. This indicates that vessels matured and were surrounded by perivascular cells as well as matrix molecules involved in stabilization. Gene expression analysis revealed a significant increase of vascular endothelial growth factor (VEGF) expression in ASC-EC co-culture compared to BMSC-EC co-culture. These observations were donor-independent and highlight the importance of organotypic cell sources for vascular tissue engineering.\u3c/p\u3