Simulation Study On The Effect Of Bone Scaffold Morphology On Cell Differentiation

Bone tissue engineering,as a new method to repair bone defects,has been applied to repair bone defects due to its good clinical adaptability.The process is as follows: the seed cells are implanted on the artificial bone scaffold through the bioreactor,and then the bone scaffold attached with differentiated cells will be transplanted to the bone defect site to achieve the purpose of repair.When cells are cultured in a bioreactor,the main structural factors that stimulated the differentiation of seed cells are the permeability determined by geometry and porosity,and the two important mechanical factors are fluid-induced wall shear stress and strain distribution.The effects of scaffold geometry,porosity,WSS and structural strain on the degree of differentiation of bone and cartilage were studied by using control variables.In this paper,an artificial bone scaffold model with eight kinds of structures and three kinds of porosity was established by using Solid Works software based on the lattice model and the system of TPMS-Triply Periodic Minimal Surface.Fluent software was used to simulate CFD fluid dynamics based on the properties of Newtonian fluid and non-Newtonian fluid.The permeability was calculated by using Darcy's formula and the improved Darcy's formula respectively.Meanwhile,the effective elastic modulus of bone scaffold was calculated.In addition,the unidirectional fluid-structure coupling simulation was carried out.Considering the influence of fluid domain pressure on the solid model,the strain distribution of the model was obtained.Combined with the WSS distribution,the influence of structural strain and WSS on the differentiation degree of bone and cartilage was analyzed according to the mechanical regulation theory.CFD simulations based on both Newtonian and non-Newtonian fluids show that the model pressure and WSS calculated based on non-Newtonian fluids are higher than those of Newtonian fluids,and the permeability of the former is lower than that of the latter.Compared with the lattice model and TPMS model,the pressure drop and WSS of the lattice based scaffold were lower than those observed in TPMS model,and the permeability of the former was higher than that of the latter.The accuracy of permeability calculation based on Newtonian fluid was verified,and two optimal models were selected according to WSS distribution: optimized lattice and diamond bone scaffold.The effect of compressive strain or inlet flow rate on cell differentiation was considered separately.With the increase of strain or inlet flow rate,bones differentiation first appeared on the surface of bone scaffold,and then cartilages gradually replaced bones,and then fiber cell differentiation appeared.Therefore,the degree of differentiation of bones and cartilages increased at first and then decreased.Considering the effects of compressive strain and inlet fluidity,the differentiation rate of bones in the eight models showed a downward trend with the increase of inlet flow rate and strain rate.The combination of lower flow rate and lower strain rate can further promote cell differentiation.However,when the strain rate and inlet flow velocity exceed a certain degree,the combination of the two mechanical stimuli does not promote the differentiation of bone and chondrocyte,and even inhibits it.The increase of porosity will decrease the elastic modulus of the model structure.At the same time,the pressure drop and WSS in the fluid domain show a decreasing trend.In addition,the higher the porosity,the higher the permeability;Considering the effect of compressive strain and inlet flow rate on cell differentiation,bone differentiation is easier in the structure with greater porosity.