Design And Performance Analysis Of Bionic Porous Scaffold For Bone Tissue Engineering

The application of bone tissue engineering technology in the treatment of bone defect is a research hotspot in life science and clinical medicine.With the development of technology,the cross integration of cytology,biomedicine,mechanics and computer digital aided design has become an important research means of bone tissue engineering.As one of the three core elements of bone tissue engineering,the structure design of porous scaffolds has always been a hot and difficult research topic in this field.However,the existing design methods of porous scaffolds are difficult to realize the bionic design of natural bone complex pore structure,and there are few design methods of porous scaffolds with bionic pore characteristics.Based on the above problems,from different design angles,two design methods of heterogeneous porous scaffolds with irregular pore shape,uneven pore distribution and biomimetic pore structure are proposed in this thesis.At the same time,the mechanical properties,internal flow field,permeability and degradation behavior of the two biomimetic scaffolds were studied in this thesis.The main research work of this thesis is as follows:The design and modeling method of heterogeneous porous scaffolds with bionic spatial pore structure were studied.According to the medical information of natural bone slice images and based on Voronoi and 3D spatial point set,the body-centered surface pore-forming method was proposed to construct heterogeneous porous scaffolds with bionic spatial pore structure(called type I scaffold).Applying the modeling method of "CAD+ Python",the efficient parametric modeling driven by program algorithm was realized.The relationship between the modeling parameters and the structural parameters of the scaffolds was studied,and the influences of the number of seed points,slice height,disturbance coefficient and "point-taking coefficient" on the porosity of the scaffold were obtained.The design and modeling method of heterogeneous porous scaffolds with bionic channel pore structure were studied.Combining random mathematics theory and NURBS curves,based on Voronoi and 2D point sets,the 2D pore slice model was designed using a cyclic algorithm.Based on the slice model,random path generation method was proposed to construct heterogeneous porous scaffolds(called type II scaffold)with bionic channel pore structure.Driven by the program algorithm,the efficient parametric modeling of the digital model of type II scaffold was realized,and the effects of modeling parameters such as the number of seed points,the "path" fluctuation and the ratio of pore area on the porosity of scaffold were analyzed.By introducing the concept of deformation gradient tensor,the pore structure of 2D pore slice model was compared and analyzed,and the morphological relationship between the pore structure of natural bone and 2D pore section model was analyzed.Based on mechanical tests and numerical simulation,the mechanical properties of two kinds of heterogeneous porous scaffolds were studied.Two kinds of heterogeneous porous scaffolds with different porosity were prepared by 3D printing technology.By means of quasi-static mechanical compression test and mechanical numerical simulation,the mechanical properties and damage locations of the two scaffolds were studied,and the ultimate strength and elastic modulus of the two scaffolds of the same material and size,as well as the influence of porosity on the mechanical properties of the scaffolds were obtained.The concept of equivalent elastic modulus was introduced to study the mechanical anisotropy of the two scaffolds.The damage forms and characteristics of uniform porous scaffolds and heterogeneous porous scaffolds were compared and analyzed.Based on numerical simulation experiments,the flow field characteristics and permeability of two heterogeneous porous scaffolds were studied.Through CFD numerical simulation,the fluid flow simulation of type Ⅰ and type Ⅱ scaffolds was carried out,and the velocity distribution and pressure distribution laws of the flow field in the two scaffolds with different porosity were obtained,and the relationship between the porosity and the distribution laws was analyzed.Combined with Darcy’s law,the permeability of two kinds of scaffolds with different porosity was calculated,and the influence of scaffold porosity on its permeability was studied.Based on the nonlinear fitting relationship curve between porosity and permeability,the prediction formula of scaffold permeability was obtained.Based on the degradation mechanism of degradable polymer materials,the degradation process of polymer materials scaffolds under different conditions was analyzed.The mathematical model of polymer scaffold degradation under stress excitation was analyzed and derived,and the degradation iterative subroutine(USDFLD)was developed.The degradation process of polymer scaffolds with different porosity,different stress excitation strength and different loading time was simulated numerically.The dynamic visualization of the degradation process of scaffold was realized,and the changes of shape,residual average molecular weight ratio and elastic modulus of scaffold were obtained.The degradation characteristics of uniform porous scaffolds and heterogeneous porous scaffolds were analyzed and compared.This study provides bionic design ideas of heterogeneous pores and efficient modeling techniques for the design of porous scaffolds,and provides a method reference for the performance analysis and evaluation of bionic pore structures,which has important technical basic significance for the clinical application and structural optimization of bionic porous scaffolds.