New Structure Design And Evaluation Of Mechanical Properties Of Porous Bone Scaffold Based On SLM

Bone defects could be caused by sport injuries,accidents,bone tumour treatments,and so on.It is usually occurred in tibia,ilium,femur etc.,and repaired by implanting bone scaffolds.However,the metallic scaffolds fabricated by traditional methods are limited by the mismatch between its shape and the defected bone,stress shielding due to high elastic modulus,disabling in individualized design corresponding to patients.To address these issues,the technique selective laser melting(SLM)emerges,which allows us to tackle above problems.SLM fabricates metallic scaffolds consisting of triply periodic minimal surface(TPMS)structures by its layer-by-layer melting method.As SLM-built TPMS scaffolds enable shape match and elastic modulus reduction etc.,they receive wide attentions in personalized bone repair area.Unfortunately,current research on TPMS scaffolds remains challenge,which are illustrated as follows:(1)whether the porous bone scaffolds can meet the multi requirements in mechanical properties and mass-transporting in bone repair process is still unknown;(2)the differences between strut-based and sheet-based structures which designed by the same TPMS primitive surface are unclear;(3)the stress matching flexibility of current porous structures needs to be improved.(4)the prediction methods of mechanical properties of porous structures had poor generality and time-consuming,which hinders the effective design of porous scaffoldsTo address the above problems,this paper firstly studied the capabilities of SLM-built TPMS bone scaffolds in mechanical properties,mass-transporting and biological activity during the bone repair process.Then the mechanical behaviour between strut-based and sheet-based structures were compared.Based on above studied,a new strut-based and sheet-based fusion structure was proposed.Finally,a new method on the basis of machine learning was proposed to predict the mechanical property of porous structures.The key points of this dissertation are illustrated as below:(1)To investigate the feasibility of SLM-built bone scaffolds consisting of TPMS structures in bone repair,this paper studied gyroid scaffolds with different design parameters by considering the requirements for porous scaffolds in mechanics,nutrient transport,fabrication accuracy,and biocompatibility.The samples were characterized by relative density,as-built porosities,thickness,roughness,and manufactured defects.Furthermore,the mechanical properties and failure modes were studied by compressive tests and finite element analysis;and mass-transporting performance was investigated through permeability test and computational fluid dynamics simulation;the biocompatibility of bone scaffolds are studied by in-vitro experiments.The systematic study on the properties of bone scaffolds proved that the TPMS bone scaffolds has meet the multiple needs of the bone repair process.(2)To further expand the application of TPMS structures in bone scaffolds,this paper studied the difference between the strut-based and sheet-based Schwarz-P structures.This paper designed five kinds of strut-based and sheet-based scaffolds with different geometric parameters and compared their precision and manufactured defects.The mechanical properties and energy absorption were studied by compressive tests,and the failure modes and fracture modes were then studied.Next,the bone repair effects of these two kinds of structures were investigated by the in-vivo experiment.The experimental results provide rich opportunities for selecting suitable porous structures for bone scaffolds.(3)On the basis of the study on strut and sheet-based structures,this paper proposed a new fusion structure.Samples with different proportion,distribution of strut and sheet-based structures were designed.The effect of proportion and distribution of strut and sheet-based structures on mechanical properties were studied.Then,failure modes of new designed structures were analysed by the observation of compressive processes.The energy absorption and bear capability were studied through stress-strain curves.This study effectively enhances the design flexibility and are benefit for stress matching of porous bone scaffolds.(4)This paper proposed a predicted model based on machine learning,which reduces the time and costs.This method is suitable for various structures rather than limited by specific materials.The predicted model extracted the entropy vector to represent the geomatical feature of porous structures,and predict the elastic modulus and yield strength by referring to geometric and material-based parameters of other structures and materials.This method has achieved a fast prediction in the mechanical properties of porous structures and thus enhance the design efficiency.