Bone Scaffold Structures Modeling With Controlling Surface Morphology And Proe Size Distribution

With the development of tissue engineering and rapid prototyping technology,bone scaffolds for tissue engineering can be constructed based on seed cells,scaffold and growth factors,providing an effective way to solve problems of large bone defects.It is required that the estabilished bionic scaffold satisfying the function of organization.However,there are still many challenges in designing and manufacturing bionic scafffold with complex microstructures and surface topography,suitable pore size and distribution at present.In this paper,triply periodic minimal surface(TPMS)and fractal geometry are combined and extended to construct fractal pore-making element that can be controlled in terms of both morphology and structure.On this basis,a serial pore size distribution approches are developed by taking advantages of hexahderal meshing,all-hexahedral meshe reinement,and optimal algorithm technologies,so that the desired pore size distribution can be mapped into scaffold models.Together,these studies form a microstructure modeling method focusing on the description of surface morphology and size distribution for scaffolds' design.(1)Pore-making element with controllable morphology and structure is constructed based on the combination and extension of TPMS and fractal geometry.Fractal parameters and porosity are obtained by analyzing and measuring the bio-derived bone scaffolds.The fractal feature is attached to TPMS to establish fractal pore-making element.Then,the association relationships between the mathemtical parameters and structures characteristic of TPMS are also investigated,so that the TPMS-based pore making element can be modeled.(2)Pore size distribution with random distribution is achieved by extending the shape function and hexahedral meshing method for scaffold design.Firstly,the bone scaffold is subdivided into all hexahedrons by Dual Contouring algorithm and octree-based algorithm.Secondly,the TPMS-based pore-making element is mapped into hexahedron based on the shape function,so that whe whole micro porous structure of scaffold can be modeled.Thirdly,the domain where the pore size distribution that needs to be adjusted is determined,and allhexahedral mesh refinement algorithm is used to change the hexahedral size,or vertexes random moving method is used to change the position of hexahedral vertexs,thus the random pore size distribution can be mapped into scafffold models.(3)Pore size distribution based the extension of optimal algorithm is fulfilled for scafffold design.Firstly,the explicit relationship between TPMS-based pore size and hexahedral mesh is established.Secondly,the hexahedral meshing method is extended to incorporate the structure characteristic into the hexahedral mesh of scaffold models.Thirdly,to further optimize the pore size distribution of the bone scaffold,the genetic algorithm is extended by customizing genetic operations such as the real number coding,selection,crossover,mutation and etc.Especially,the moving range of the highly coupled hexahedral mesh vertices is dynamically determined during the optimization.(4)The prototype system for porous bone scaffold modeling is developed based on the platform of OpenCASCADE,VTK and Visual Studio.The proposed approaches are evaluated based on the system.Then the porous structure is simulated by Fluent,and the tissue engineering scaffolds are manufactured by additive manufacturing.By doing so,the preliminary application of the scaffold models is discussed.