| Bone tissue engineering provides a promising strategy for the regeneration of segmental bone defects caused by fracture,trauma and disease.Tissue engineering scaffold could structurally and functionally simulate the host tissue,and provide three-dimensional space for the regeneration process,which is the key start of the treatment.Mg exhibited comparable mechanical properties to bone tissue and good biocompatibility,and recent study indicated that Mg implants could stimulate the healing process of bone fracture.Thus,Mg could be a unique alternative material for tissue engineering scaffold.However,the most appllied replication method still has some drawbacks such as incomplete removal of the template,inevitable degradation of Mg during leaching process and insufficient control of the pare characteristics.In this work,a novel template replication method was designed,and open porous Mg scaffolds with precisely tailored pore characteristics were fabricated with no defects in the structure.The relationship between the space holder particles and the pore characteristics was evaluated.Static and dynamic degradation environments were designed to investigate the evolution of structural interconnectivity and degradation rates.Direct cell culture on Mg scaffold with different pore characteristics were carried out to study the cell behavior in 3D environment.The compressive mechanical properties of Mg scaffolds were also tested.The main conclusions are listed as follows.1.Hot press sintering was applied on Na Cl particles to achieve a defectless template.Open porous Mg scaffolds were received after replication and leaching process.Spherical Na Cl particles exhibited higher sintering efficiency than that of irregular particles,and consequently Mg scaffold replicated from spherical particles shows higher porosity than that of Mg scaffolds replicated from irregular ones.Both scaffolds exhibited hierarchical porous structures,which consist of main pores and interconnected pores.The interconnected pore size of S-scaffold intensively distributed in the range of 200-350 ?m,while the interconnected pore size of I-scaffold was equably in the range of 50-250 ?m.The uniform distribution and orientation of the interconnected pores in S-scaffold indicated a superior interconnectivity.I-scaffold showed higher compressive strength,but a stress decrease was found beyond 40% strain with severe cracks in the pore strut.2.Static and dynamic immersion tests were separately designed to evaluate the evolution of interconnectivity and degradation behavior of S-scaffold and I-scaffold.Under static state,deposition layer quickly formed on the surface of Mg scaffolds and got thicker along with immersion time.The external pores were clogged after 14 days,while the thickness of the deposition on the internal porous structure did not increase during the tests.Under dynamic state,no deposition products were observed on the surface pores within 28 days for both groups,but partial internal porous structures of I-scaffold were clogged.Obvious degradation layer was found after 42 days,but the entire porous structure of S-scaffold,especially the interconnectivity was not affected by the degradation products.Mg scaffolds lost about 30-40 vol.% after 14 days under static degradation,but the volume loss was reduced to 10-15% under dynamic state.The degradation rates under static state were much higher than that under dynamic state,and S-scaffold degraded faster than I-scaffold.3.S-scaffold and I-scaffold were coated by DCPD calcium phosphate coating.SEM observation showed that DCPD coating tightly distributed on the pore wall and no defects was found at the interface.The porosity of S-scaffold and I-scaffold was reduced by 10% and 14%,respectively,but the mechanical properties and degradation resistance were significantly enhanced.Osteoblasts and endothelial cells were well adhered on the two scaffolds,but cell proliferation ability could be greatly affected by the pore architecture.Better cell distribution and viability were showed on S-DCPD,which possessed smooth pore wall and intensively distributed larger interconnected pores.4.Spherical Ti beads were used as new space holder particles,and spark plasma sintering technique was carried out to tailor the architecture of Ti templates.A protective Mg F2 coating formed during leaching process.The grain refinement of Mg scaffolds was achieved through recrystallization process by adopting compressive deformation on Ti&Mg composite followed by annealing technique.Five Mg scaffolds with different pore characteristics was prepared.Immersion tests showed that lower porosity led to higher ion concentration in extracts due to the higher specific surface area.However,no difference of degradation rate was found among the five Mg scaffolds due to the same pore strut.With the same porosity,smaller pore strut showed higher compressive strength.Direct cell culture experiment showed that higher porosity and larger pore size were favourable to cell proliferation as well as infiltrability. |
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