Anastomotic Engineering

We are studying biomechanical forces and the relationship with arteriosclerosis, intimal thickening (IT) and restenosis. Certain haemodynamic features e.g. low mean wall shear stress (WSS), oscillating WSS, abnormal temporal and spatial shear stress gradients, and high particle residence times, are found in the locations where IT preferentially develops. This suggests a possible link between these features and cellular responses and failure of the endovascular device or surgical bypasses.

It is evident from our work that geometrical features play an influential role in controlling the flow features and therefore there is clinical relevance and benefits for anastomotic engineering, a process of modifying the geometry of the graft or anastomosis to improve their haemodynamic performance.

Graphs showing shear stress in arteries.

Thus far, we have developed a computational model, validated by particle imaging velocimetry (left upper panel, comparing the variation of wall shear stress at different locations on the hood of graft and floor of artery), to quantify haemodynamic parameters in distal coronary anastomoses and it was confirmed that geometric factors like diameter ratio and angle between the graft and host artery (right upper panel, variation of spatial WSS gradient on the floor), and smooth graft–artery transition play similar roles in distal coronary anastomoses as in the peripheral region.

The impact of geometric alteration on haemodynamics has been further demonstrated in infragenicular supplementary vein cuffs which configuration, specifically the length-to-height ratio, is critical in controlling local haemodynamics. However, it is still not entirely clear which and to what extent, these flow parameters actually trigger the undesired cellular response and the true mechanisms involved.

We are currently developing a flow system capable of exposing viable cells cultured/co-cultured in well-defined geometries to precisely-controlled flow parameters to systematically understand and establish the quantitative correlations (employing both experimental and computational approaches) and, hopefully obtain more insights on the true mechanisms (e.g. biochemical cascade) involved. The information is expected to be useful in developing anastomotically-engineered vascular tissue graft, acknowledging that anastomosis is inevitable.

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CK Chong

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