The Construction Of Nano-functionalized 3D Printed Polylactic Acid Bone Tissue Engineering Scaffold And Its Mechanical And Osteogenic Properties

Polylactic acid(PLA),a type of polyester material with good processability,biodegradability,and biocompatibility,has been widely used to prepare bone tissue engineering scaffold with the help of efficient and designable 3D printing technology.However,there are still many issues in the application of PLA-based scaffold as bone tissue engineering scaffold.For example,the mechanical properties of PLA scaffold are not ideal for matching the natural bone.Meanwhile,PLA also owns the poor cell affinity as well as osteogenic activity.In this study,on one hand,the strategies of structure and material optimization were employed to improve the mechanical properties of 3D printing PLA-based bone tissue engineering scaffold.On the other hand,the cell affinity,osteogenic ability and vascularization ability of PLA-based bone tissue engineering scaffolds were also enhanced by surface fabricating liquid crystal structure and loading bioactive natural medicines.Focusing on the above research purposes,the following works were carried out:1.Due to the excellent mechanical properties,specific structure,large aspect ratio,good cell affinity and osteogenic activity of magnesium oxide whiskers(Mg Os)and halloysite nanotubes(HNTs),both surface grafted Mg Os(g Mg Os)and HNTs(g HNTs)with PLA segments were introduced into poly(L-lactide)(PLLA)matrix to prepare composite 3D printing wires.Then,the g Mg Os/g HNTs/PLLA composite porous scaffolds were constructed by FDM method.The results showed that the dispersion of the two kinds of fillers in the matrix was highly improved and the interfacial adhesion between the fillers and PLA matrix was enhanced by surface grafting with PLA segments of the fillers.More importantly,g Mg Os and g HNTs play different roles in improving the performances of the composite scaffolds.The g HNTs can effectively improve the mechanical properties of the scaffolds,while the g Mg Os were more beneficial to the adhesion,proliferation and migration behaviors,as well as promoting the secretion of alkaline phosphatase(ALP)and formation of calcium nodules of mouse embryo osteoblast precursor(MC3T3-E1)cells on the scaffolds.In conclusion,a kind of PLLA-based bone tissue engineering scaffold with high porosity,good mechanical properties,excellent cell affinity and osteogenic activity was obtained.2.Inspired by the superior mechanical properties,cell affinity and osteogenic activity of chitin whiskers(CHW),herein,positively charged CHW(HCHW)and negatively charged maleation CHW(m CHW)were prepared,respectively.Meanwhile,poly(D,L-lactide)(PDLLA)membrane was prepared by solution casting method,and polydopamine(PDA)-modified PDLLA membrane(PPDA)was also obtained for further modification.At a p H value of 4.3,the process of LBL electrostatic self-assembly between the HCHW and m CHW on the PPDA membranes was successfully performed,which can be directly proved by the cross-sectional morphology,light transmittance,surface composition and topography of the membranes.Especially,polydopamine,as an intermediate layer,can greatly enhance the stability and adhesion of the first HCHW layer on PDLLA membrane.Compared with the PDLLA membrane,the mechanical properties of selfassembly membranes are highly enhanced and showed the corresponding increment with the number of self-assembly whisker layers increased.In vitro biological evaluation showed that the HCHW and m CHW modified PDLLA membranes own the better cell proliferation and adhesion properties than PDLLA membrane,while the HCHW-assembled surface owns a higher cell affinity than that of the m CHW-assembled one,which may be attributed to different protein adsorption.Moreover,the interesting directional cell migration behavior was observed on the HCHWassembled surface,which was explained by the guiding effect of surface ordered topology structure and collective cell migration.3.Inspired by the fact that LBL self-assembly of CHW can significantly enhance the mechanical properties of PDLLA membrane in the previous chapter,we try to further enhance 3D printing PLLA scaffold by LBL self-assembly of CHW.Moreover,in order to further improve the biofunctionality of the scaffolds,the drug-loaded HCHW-CS liquid crystal gel was introduced into the scaffolds.In detail,HCHW and m CHW were modified to the surface of the PLLA scaffold via LBL method,and then the morphology,microstructure,surface composition and mechanical propertiesof the as-prepared self-assembly scaffolds were further investigated.The results showed that the compressive properties of the scaffolds can be obviously enhanced by the introduction of CHW layers and also own the controllability by adjusting the number of CHW layers.Meanwhile,the HCHW-CS liquid crystal suspension with deferoxamine(DFO)and genipin was prepared to obtain the drug-loaded gel precursor suspension,which was then injected into the self-assembly PLLA scaffold and further continued to cross link.Finally,the liquid crystal gel-PLLA scaffold(P@CG)and DFO-loaded P@CG(P@CG-D)were obtained.The HCHW-CS liquid crystal gel not only own the liquid crystal texture and good viscoelasticity,but also the loaded DFO in liquid crystal gel can be released slowly and steadily.Through in vitro cytotoxicity evaluation,we found that the scaffolds which were modified by CHW layers and liquid crystal gel showed the enhanced cell affinity and proliferation compared to the PLLA scaffold,especially for the P@CG-D scaffold,it owned the best cell affinity and proliferation performance.The ALP and calcium deposition tests showed that P@CG-D can promote the differentiation of mouse mesenchymal stem cells(BMSCs)into osteoblasts in early,middle and late stages,and the synergistic effect of HCHW-CS liquid gel and DFO on promoting osteogenesis was also proved.Finally,the tube formation and chicken embryo chorioallantoic membrane(CAM)tests were employed to demonstrate the angiogenic ability of P@CG-D.The tube formation test verified the synergistic effect of liquid crystal gel and DFO on promoting tube formation on P@CG-D scaffolds.And according to the changes of the length and area of the blood vessel in CAM,compared to the P@CG scaffold,the P@CG-D seems to be more effective in promoting angiogenesis due to the existence of DFO.These results indicated that a kind of PLA-based bone tissue engineering scaffolds with good mechanical properties,cell affinity,excellent osteogenic activity as well as vascularization properties have been successfully prepared.