The Preparation、Biological And Mechanical Properties Of A Novel Graphene-based Composite Scaffold

The treatment of bone defect caused by trauma,severe infection,and tumor resection is a difficult problem in clinic.Bone grafts,especially for autologous bone grafts,are considered as the“gold standard”for repairing the bone defects in the clinic.However,bone grafts always encounter serious drawbacks,such as insufficient supply of graft,immune rejection,and thus impose a tremendous socioecological burden on patient’s family and whole community.These drawbacks greatly limit the practical application of bone graft in clinic.With the rapid development of bone tissue engineering,recently,artificial replacement materials,such as nano-hydroxyapatite and bone cement,can be synthesized and planted to repair the bone defects,and thus overcome the drawbacks of bone grafts.However,the obtained artificial replacement materials presented as small nanoparticles or micro-sized particles without opening pore size,and cannot completely mimic the morphology of natural bone with 3D macroporous structure,hindering the transportation of nutrients and excretion of metabolites.Moreover,the surface of these composites cannot be further modified by bioactive molecules,such as hydroxyapatite,protein,chitosan and so on.Three-dimensional(3D)graphene scaffold(foam)possesses many fascination properties,such as 3D macroporous structure(average pore diameter 200μm,similar to that of the natural bone),good biocompatibility,excellent mechanical properties,and bone osteo-conduction/induction.Besides,the pristine nature of graphene enables us to further modify the graphene foam as multi-functionalized 3D cross-linked scaffold in the field of bone tissue engineering.With these in mind,in present study,we prepared the two 3D macroporous graphene-based composite scaffolds,namely the 3D graphene/hydroxyapatite composite scaffold and casein phosphate peptide-modified 3D reduced graphene oxide/polypyrrole foam by using the synthesized 3D graphene foam as a template and explored their applications in bone tissue engineering.The results are listed as follows.(1)In present study,by using nickel foam as a template,combining with chemical vapor deposition method and electrodeposition technique,a novel 3D graphene/calcium phosphate complex scaffold was prepared for the first time.The influence of the electrodeposition parameters on the morphology of grown calcium phosphate composite was systematically investigated.The biocompatibility,cell adhesion,proliferation,and the osteogenic activity of MC3T3-E1 cells on3Dgraphene and 3D graphene/calcium phosphate complex scaffold were also evaluated.The results show that the surface of the 3D GF scaffold can be successfully mineralized in electrolyte containing calcium and phosphate species through electrochemical deposition strategy.By changing the electrodeposition parameters including deposition temperature and/or applied voltage,the size,morphology and crystal structure of the calcium phosphate complex can be altered.Especially,at higher deposition temperature of 60~oC,the calcium phosphate crystals with smaller size and higher crystallinity were homogenously distributed on the skeleton of 3D graphene foam.The biological experiments result shown that both the pristine 3D GF scaffold and 3D GF/calcium phosphate complex scaffold have non-cytotoxicity,and could promote the cell adhesion and proliferation of MC3T3-E1 cells,while The 3D GF/calcium phosphate complex scaffold has a better osteoblast performance.(2)Based on achieved results,a novel simple,low-cost and high-yield method for preparing the 3D graphene-based composite scaffold was further carried out and presented.Detailedly,3D reduced-graphene oxide(3D rGO)foam was fabricated through a simple but inexpensive electrostatic layer-by layer assembling strategy by using graphene oxide as a raw material and nickel foam as a template.The resultant3D rGO foam can be further consolidated and functionalized by polypyrrole(PPY)and casein phosphate peptide(CPP)molecules through an electrochemical deposition and electrostatic assembly strategy.The surface morphology,chemical composition,wettability,water absorption,water retention,osteogenic activity,osseointegration ability,biocompatibility,cell adhesion and proliferation of prepared 3D rGO/PPY and CPP-modified 3D rGO/PPY scaffolds were detected.Results show that we have successfully prepared the 3D rGO/PPY and CPP-modified 3D rGO/PPY by using the advanced LBL method.The wettability,water absorption,water retention,cell adhesion and proliferation of bone cell on the surface of CPP-modified 3D rGO/PPY scaffold could be greatly improved.Especially,the scaffold modified by high-concentration CPP molecules can effectively promote the differentiation of pre-osteoblasts toward mature osteoblasts.In addition,we modified the scaffold with chitosan molecules,and got a multi-functionalized composite scaffold.The morphology,chemical composition,and the wettability were analyzed.The antibacterial performance,biocompatibility,and osteogenic activity were evaluated by using colony counting and biological cell experiments,respectively.Results indicate that the modification of chitosan on 3D rGO scaffold could improve the wettability but does not affect the structure and good osteogenic ability of the scaffold.(3)The mechanical properties including Hardness and Young’s modulus of the prepared composite scaffolds were detected by nano-indentation technic.Results suggest that the young’s modulus value of the 3D rGO/PPY scaffold prepared in this thesis was similar to that of the cancellous mandible bone of our body in buccal-tongue direction.The young’s modulus value delivered by graphene-based scaffold in our thesis is tens to hundreds times higher than that of the scaffolds prepared by the traditional self-assembly method.Summarily,in this thesis,we present two simple but low-cost novel methods for mass-preparation of three-dimensional macroporous graphene-based scaffolds.The physicochemical,biological and mechanical properties of the prepared new scaffolds were characterized and evaluated by different experiments and technical tools.It is proved that the macroporous graphene-based scaffolds have excellent mechanical properties,good biocompatibility and antibacterial ability.The successful preparation and the good biological performance of these new scaffolds will bring light to the repairing of bone defect in clinic in the coming future.