| Bone tissue engineering implants were widely used in orthopaedics area as bone substitute.Ideal bone tissue engineering implants should have interconnected macroscopic porous structure to provide enough space for bone ingrowth and moderate mechanical properties.However,in tradition,lack of precise control of porous structure led to negligence of i MPact of topology design on mechanical properties and bone regeneration.Recently,Additive manufacturing has been greatly developed and allow the precise control of porous topology design of bone tissue engineering implants.Thus,based on selective laser melting(SLM),hydrothermal synthesis technique and with the help of computer aided design(CAD)and finite element analysis(FEA),we analyse the influence of bone tissue engineering implants porous topology design on morphology,mechanical properties and bone ingrowth in macro-,micro-and nanoscopic vision.We also designed a stress-balanced anterior cervical fusion cage with optimal osteointegration confirmed in goat cervical fusion cases.The research details are stated as followed:To overcome the low-efficiency of massive porous structure modelling,based the Thiessen polygon space subdivision method,we raised a pore-oriented modelling method.Three key parameters were established to control the porosity,pore size and mechanical properties of porous structure,including count and arrangement of random seeds and the strut size.The topology could be customized to fulfil specific need.Based on this design idea,this paper designed a controllable porous structure on the parametric design platform Grasshopper,which could achieve the controllable design with specific porosity,and meet the design requirements of the porous structure in terms of morphology and geometry.A series of diamond-like porous structure were established based on the pore-oriented modelling method and SLM,mimicking the crystal lattice of diamond.The unit size was fixed at 1500μm and the strut sizes were tuned from 200μm to 400μm,nominated P200-P400.Quasi-compressive test and FEA revealed the mechanical properties of porous structure had a negative correlation with porosity.As porosity increased from58.25% to 85.34%,the compressive yield strength decreased from 186.05 MPa to51.95 MPa and the stiffness decreased from 6.74 GPa to 0.98 GPa.Specimens with lower porosities had smoother surface curvature thus had better cyto-adhesion capability and proliferation.1 month after rabbit femur implantation,massive bone ingrowth identified at the co MPact bone defect area.Porous implants with lower porosity had less bone ingrowth for it had less space for bone regeneration.However,push-out results indicated higher osteointegration of porous implants with lower porosity.The pore sizes were tuned via scaling the unit.P400-0.5,P400 and P400-1.5 were designed based on P400 porous structure and had pore size of 330μm,660μm and990μm.the change of pore size led to no difference of mechanical properties in FEA.But the inaccuracy of SLM manufacturing led to the unmatch of printed specimens and CAD models and the error was significant when small pore size.P400-0.5 had tiny strut,pore and had great inaccuracy leading to the difference in mechanical properties and topology and the descend of bioco MPatibility.Besides,implants with invariant porosity and variant pore size have invariant mechanical properties and bioco MPatibility.Regular D structure,semi-stochastic SR structure and stochastic R structure were obtained via tuning random degree of seeds and the mechanical properties,CFD properties,in vitro cytoco MPatibility and in vivo osteointegration were evaluated.Results indicated that these structures had mechanical properties and permeability decreased from D,SR to R.The regular arrangement of strut of D structure balanced stress distribution and reduce the pressure loss of transport fluid.In vitro and in vivo results confirmed the randomness of porous structure helped cell adhesion and tissue ingrowth.However,the randomness might lead to local porosity decrease and difficulties of bone ingrowth.Co MPared with D structure and R structure,SR had semi-stochastic porous structure and had higher cytoco MPatibility and osteointegration.The laser power was modulated to obtain microscopic porous surface of titanium implants.The influence of decreased laser power to surface morphology,mechanical properties and hydrophilicity were analysed.The decrease of laser power might lead to the relative density and brings increasing rectangle pores and other defects.The mechanical properties decreased and the hydrophilicity climbed up and then declined.A titanium matrix via laser power of 40 W,scanning speed of 900mm/s had a porous surface and ideal cytoco MPatibility.However,it had relatively low mechanical properties and cannot be used into bone tissue engineering directly.The mechanical properties were reinforced via a modelling design.A core-shell porous structure was built with different manufacturing parameter.A high laser power and a low laser power were assigned to these two parts to build a porous implants than corereinforced and shell-porous.The mechanical properties were enhanced and the excellent cytoco MPatibility osteogenesis were confirmed via in vitro experiment.A novel hydrothermal synthesis method was introduced to fabricate a layer of nano hydroxyapatite coating on the surface of porous titanium implants to promote the bioco MPatibility and osteogenesis.EDTA-Ca Na2 and KH2PO4 were used as agent.The influence of hydrothermal time,temperature and concentration to coating were studied.Results indicated the titanium implants soaking in agent of 0.25 M EDTACa Na2 and 0.1M KH2PO4,hydrothermal treated 12 h at 180°C had well-distributed,abundant calcium hydroxyapatite.The phase were confirmed via EDX and TEM.In vitro data indicated hydroxyapatite coating promoted the cytoco MPatibility and osteogenesis.Goat cervical vertebra was analysed via reverse engineering and ex vivo biomechanics model were established.Intervertebral discs,from the perspective of structure,was divided into fibrous ring and nucleus pulposus and had different materials composition.In the mechanical environment of cervical vertebra,the nucleus bear more stress than fibrous ring.By mimicking the stress distribution,we design a stress-balanced anterior cervical fusion cage with exterior part and interior part.Assigning different materials into these two parts,the stress could be transformed into co MPact bone in vertebra and decrease the risk of cage sinking.FEA results indicated the ratio of reaction force of exterior part to interior part decreased three times co MPared with unoptimized cage.With interconnected porous structure and proper bioactive coating,excellent osteointegration was spotted 6 month after implantation and new bone tissue was found connecting C3 and C4 vertebra.However,cage carrying massive hydroxyapatite on their porous structure had bad osteointegration.A huge gap spotted between the cage and vertebra indicated the interconnected porous structure is the foundation of osteointegration. |
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