Mass transport and fluid flow-induced wall shear stress in auxetic bone scaffolds during deformation process: a numerical study

Auxetic structures exhibit an extraordinary response to mechanical forces by expanding or contracting in the transverse direction during stretching or compression, making them highly suitable for porous biomedical implants. However, their biological functions, including nutrient transport, metabolic waste removal, and cell proliferation and differentiation, remain unexplored. This study employs computational fluid dynamics (CFD) to analyze how the auxetic deformation of a scaffold influences its biological performance. An auxetic scaffold (A-scaffold) was designed alongside a non-auxetic scaffold (N-scaffold) with identical porosity (80 ​%) for comparison. Deformations at compressive strains of 0 ​%, 5 ​%, and 10 ​% were analyzed and utilized in CFD simulations to evaluate the fluid dynamics within the scaffolds. The interaction of water flow with the scaffolds was simulated, leading to predictions of mass transport and fluid flow-induced wall shear stress (WSS). Results indicated that both the fluid flow direction and scaffold architecture significantly influenced mass transport characteristics. The deformation response also impacted scaffold biological performance; specifically, the A-scaffold's concave struts hindered fluid flow in the X direction, reducing permeability but potentially promoting uniform internal fluid distribution. Although the auxetic deformation of the A-scaffold decreased its permeability, it resulted in a more irregular WSS distribution, suggesting enhanced dynamic cellular stimulation under mechanical loading. The WSS_AVG of the A-scaffold and its variation during deformation were larger in the X direction than that of the Z direction. As a result, the A-scaffold exhibited better ability to transmit mechanical stimulation in the X direction. These preliminary studies numerically characterized the mass transport properties of scaffolds under auxetic deformation for the first time, provided guidance for the design and application of an auxetic scaffold.