Research On Additive Manufacturing Process And Structure Design For PEEK/TiO₂ Assembled Implant

The highly customized features of additive manufacturing have promoted the development of matching and personalized prosthesis manufacturing technology,which brings a new hope for precision treatment in orthopedic.Currently,the additive manufacturing prosthesis mainly made of titanium or tantalum metals has disadvantages such as artifacts and stress shielding.Non-metallic prostheses,such as poly-ether-ether-ketone（PEEK）,have good levels of biological properties and modulus,which is the key areas of additive manufacturing prosthesis technology.However,non-metallic additive manufacturing is prone to defects such as warpage and cracks,and the multi-functional balance control of prosthesis pore structure is difficult.It is an important factor limiting its development.Therefore,this thesis takes the interbody cage as an example to carry out the technical research on the additive manufacturing technology and porous design method of the PEEK/TiO₂ assembled prosthesis.Mainly facing the following problems:（1）the high melting point and high viscosity of PEEK materials cause the problem of difficult molding and low strength;（2）sintering defects and low strength in porous TiO₂ photocuring molding;（3）the high cost design of multifunctional pore structure of prosthesis parts.In response to the above problems,the main works of the thesis are as follows:（1）The fused deposition modeling platform with a heat collection mechanism was constructed,which achieved the effect of stabilizing the temperature gradient in the forming domain and alleviated the warpage problem of structural layering.The average warpage rate was reduced from 20.4%to 5.0%.Through the characterization and analysis of the strength and crystallinity of the samples,it was found that the effect of the heat collection mechanism to the temperature gradient acts on the cooling and crystallization process of the PEEK samples,reaching the crystalline state after heat treatment and improving the strength of the parts.Further,through the study of key parameters such as molding temperature,nozzle diameter and filling angle,the effect mechanism of the process parameters on the micro-morphology and macro-strength of the part was found.The rapid prototyping of PEEK and its short carbon fiber composites was finally realized.And the strength was nearly doubled compared with that before the improvement.（2）The TiO₂ ceramic additive manufacturing method with MgO as a multi-effect additive was developed.By introducing MgO and composite initiator into the ceramic slurry,the solidification and degreasing process of the slurry was improved.Further,based on the solid-state reaction between MgO and TiO₂,the reactive sintering process was introduced and combined with the bulk heat source advantage of the microwave sintering process,the rapid densification of ceramics and the reduction of the sintering temperature were achieved.And the sintering temperature was effectively reduced by about 200°C.The new phase Mg Ti₂O₅ formed by the solid-state reaction filling up for the defects such as the gap and viods between the microscopic grains of the structure during the formation process.It realizes the macroscopic performance improvement of the final overall porous product,which is nearly an order of magnitude higher than the strength of the reported TiO₂ porous ceramics.（3）The rapid design method based on Bayesian theory combined with finite element simulation has been proposed,which realizes the multi-objective rapid design of the three-period minimal surface structure on the mass transfer and strength performance.Through the parametric modeling method via implicit function and the finite element model verified by experiments,the independent action mechanism of main parameters（thickness P_t,array number P_a,constant number P_c）on performance was explored.And using Bayesian theory to speed up the design process,the Pareto front was obtained after only 9 iterations.The modulus and permeability of the optimal structural combination（P_t=0.28,P_c=-0.49,P_a=3.5）respectively reached 1.21 GPa and 4.03×10^-9 m^-2 meet the design requirements.Further,combined with the advantages of the two materials,a PEEK/TiO₂ assembled prosthesis with embedded porous ceramics was designed,and the key compressive properties of the prosthesis were tested by compressive strength.At the same time,the cytotoxicity experiment proved that it has no toxic and side effects on bone tissue.