Design And Performance Study Of Personalized Porous Femur Combined Scaffold

Femur is one of the main weight-bearing bones of human body,and it is also one of the most common sites of bone tumors.At present,the femoral tumor prostheses used in clinical practice have some problems,such as low biological activity,poor match with the anatomical shape of the bone defect site and stress shielding,which may lead to loosening or even failure of the femoral scaffold.Therefore,how to quickly design a personalized scaffold with good mechanical and biological properties and matching with the anatomical shape of the patient has become the key to femoral reconstruction.In this paper,a personalized design method of porous femoral combined scaffold was proposed by using modular design method combined with 3D printing technology.The modular design of femoral combined scaffold,the design and selection of the porous structure of the scaffold,the surface modification of the scaffold,the selection of the repair materials for different modules of the scaffold and the fixation methods of the scaffold were studied.The main research contents and results of this thesis are as follows:(1)The traditional compact titanium alloy scaffold for femoral repair has some problems such as low biological activity and stress shielding effect.A 3D printed porous titanium alloy scaffold was proposed to repair the femoral defect.The porous structure reduces the elastic modulus of the material and allows bone tissue to grow into the scaffold.Using the bone reconstruction theory,the mechanical stimulation and bone reconstruction of the surrounding bone tissue by traditional femoral scaffolds and3 D printed porous titanium alloy scaffolds were analyzed.The results showed that 3D printed porous titanium alloy scaffolds had good bone reconstruction function.Combined with the structure of human femur and the mechanical and biological properties of existing bone repair materials,the design idea of modular combined scaffold for femur was proposed.Modular design adopts matched scaffold materials and porous structure according to different functional modules of the scaffold,which can realize rapid personalized customization and lay a solid foundation for the subsequent design of high strength,high biological activity and high stability of the femoral repair scaffold.(2)An important requirement of bone scaffolds is to make bone cells grow better.However,it is still unclear how to improve the cellular activity of scaffolds under a certain elastic modulus.A method for deriving the mathematical relationships among design parameters,porosity and mechanical properties of homogeneous structures in the design of porous functionally graded scaffolds(PFGS)is presented.PFGS is designed to combine different uniform structures by matching design parameters.The microstructure of 10 × 10 × 12 mm titanium alloy scaffolds was manufactured by selective laser melting(SLM)method.The mechanical properties and cell proliferation of these structures were investigated.The results show that the mathematical models of elastic modulus,yield strength and porosity can accurately predict the mechanical properties of structures.For PFGS,the cell proliferation rate from 4 to 7 days was 140%,whereas for homogeneous structures it was only 90%.This suggests that PFGS is more suitable for bone tissue implantation.(3)The geometrical structure of the porous scaffold plays an important role in bone growth,but there is still a lack of in-depth research on this aspect.The porous scaffolds with curved structure and strut structure with porosity of 65% and pore size of 650 ?m were established.The bone ingrowth in vivo was studied by distal femur implantation in rabbits.The internal hydrodynamic properties and fluid flow trajectory of the scaffold structure were calculated by computer fluid dynamics.The results showed that curved scaffolds had better bone ingrowth performance than strut scaffolds in vivo,but their mechanical properties were inferior to those of strut scaffolds.Both fluid flow and velocity difference within the scaffold structure have a great influence on bone ingrowth.Under the same circumstances,the smaller the fluid velocity difference within the scaffold structure,the larger the area the fluid flows through,the better the bone ingrowth will be.The results showed that the geometrical structure of the scaffold could be optimized according to different implantation sites to meet the needs of different implantation sites.(4)The surface state of the porous scaffold has a great influence on the proliferation and adhesion of cells.The surface of 3D-printed titanium alloy was modified by femtosecond laser,and the surface with high roughness,more trough than peak and antibacterial properties was obtained.The results of in vitro experiments show that the modified surface has better wettability than the surface before modification,and the surface structure is more conducive to the deposition of hydroxyapatite.The bone ingrowth in vivo was studied by the tibia implantation in rabbits,results showed that the surface of the modified scaffold had better adhesion and diffusion ability.The results show that the surface modification of 3D-printed titanium alloy by femtosecond laser can improve the physical properties of the surface,such as wettability,roughness,kurtosis and slanting,so that the surface has a higher ability of bone integration.(5)The mechanical properties and biological properties of human femoral cortical bone and cancellous bone are very different,so it is obviously unrealistic to match the mechanical properties and biological properties of host bone tissue with one material and one structure.Compared with the titanium alloy scaffold,the biodegradable calcium silicate bioceramic scaffold has better biological activity,and its mechanical properties are better matched with the femoral cancellous bone.Therefore,the bioceramic scaffold was selected to repair the femoral cancellous bone.Firstly,the titanium alloy and Mg-doped calcium silicate bioceramic scaffolds with the same porosity and pore size were established.Then,the differences of bone ingrowth performance and compressive strength between two kinds of scaffolds were studied by using rabbit skull implantation.Finally,the biological properties were modified by adding strontium ions to Mg-doped calcium silicate by chemical precipitation method.The results showed that the bone ingrowth performance of Mg-doped calcium silicate bioceramic scaffolds was higher than that of titanium alloy scaffolds,but the compressive strength of the scaffolds decreased rapidly with the prolongation of implantation time,and it was not suitable for bone defect repair in the weight-bearing zone.The addition of strontium ions increased the bioactivity and degradation rate of Mg-doped calcium silicate bioceramic scaffolds,but decreased the compressive strength of the scaffolds.The results showed that the effect of bioceramic scaffolds in the non-weight-bearing area of bone repair was significantly better than that of titanium alloy scaffolds,and titanium alloy scaffolds could maintain good compressive strength in vivo and could be used for weight-bearing bone repair.(6)Taking a patient with malignant femoral tumor as an example,a personalized titanium alloy and bioceramic combined scaffold for femoral repair was designed through the processes of magnetic resonance imaging,CT three-dimensional reconstruction,simulated osteotomy and the modular design of personalized combined scaffold.Finite element method was used to analyze the stability of different fixation modes of the scaffold.The results show that the integrated fixation mode has stronger stability than the traditional fixation mode of steel plate and fixation screw.Taking clinical practice as an example,the great potential of modular design in personalized femoral prosthesis was demonstrated through design and analysis,which laid a foundation for subsequent clinical customization of femoral prosthesis scaffold that both mechanical property and anatomical shape can meet the personalized needs of different patients.