4D Printed Drug-loaded Shape Memory Porous Polylactic Acid Composite Scaffold For Bone Tissue Repair

Bone defect is a common difficult problem in clinical work,which is mainly caused by trauma,infection,tumor and various congenital diseases.Bone graft as a mainstream method was widely used in clinical treatment,whereas traditional bone grafts have limited sources and often accompanied by disease transmission and immune respond.The emergence of bone tissue engineering provided a new method for the treatment of bone defects,which used biomaterials to replace the traditional transplants.Nowadays polymer-based scaffolds were widely used in repairing bone tissue due to their good biocompatibility,non-toxicity and degradability.In addition,Polymers with a shape memory effect（SME）may be better used in self-fitting scaffolds for bone tissue engineering.Compared with traditional materials,shape memory polymers have the advantages of low price,light weight,adjustable glass transition temperature.3D printing technology based on smart materials is called 4D printing technology.4D printing combines smart materials and additive manufacturing technologies to provide a new method for precise treatment of bone tissue engineering.Though heating is the most common driving method for SMP,direct heating also has limited to application in some special case.Therefore,SMP are often mixed with some functional nanoparticles such as magnet particles,carbon nanofibers,silicon carbide to achieve remote driving and satisfy different requirements when stimulated by electricity and an alternant magnetic fields.In this paper,a bionic bone repair scaffold was designed based on the natural bone tissue structure,and a 3D modeling technique was used to successfully construct a bone repair scaffold model.Based on shape memory polylactic acid（PLA）material,4D printing technology was successfully prepared PLA/Fe₃O₄ and PLA/Fe₃O₄/HA shape memory porous scaffolds and PLA/Fe₃O₄/HA/Aln and PLA/Fe₃O₄/HA/Aln-Col/Dex drug-loaded shape memory porous scaffolds.Fourier transform infrared spectroscopy（FITR）,Differential scanning calorimetry（DSC）,Thermogravimetric analysis（TGA）,Dynamic thermo-mechanical analysis（DMA）and static mechanical analysis were used to characterize the thermodynamic properties of porous scaffolds.The Aln and Dex drug release behavior and shape memory performance of the porous scaffolds were tested.The results showed that the porous scaffolds had good thermodynamic performance,drug release behavior and shape memory performance,and the fixation rate and recovery rate were above 98%,which could realize large size deformation.L929 mouse fibroblasts were used as test cells,and the cytotoxicity of PLA/Fe₃O₄,PLA/Fe₃O₄/HA,PLA/Fe₃O₄/HA/Aln and PLA/Fe₃O₄/HA/Aln-Col/Dex porous scaffolds was detected by MTT.The results showed that the scaffold extracts of different concentrations had no cytotoxicity and the porous scaffolds had good biocompatibility.To verify the proliferation of PLA/Fe₃O₄,PLA/Fe₃O₄/HA,PLA/Fe₃O₄/HA/Aln and PLA/Fe₃O₄/HA/Aln-Col/Dex porous scaffolds on bone marrow mesenchymal stem cells:MTT and Hoechst 33342 fluorescence Staining were used to detect the proliferation of bone marrow mesenchymal stem cells（BMSCs）,Quantitative Real-time PCR（q RT-PCR）was used to study the expression level of osteogenic genes（ALP,OPN,OCN,RUNX2）.The results of MTT experiment showed that the shape memory porous scaffold prepared by 4D printing technology had good proliferation performance and could significantly promote the proliferation of BMSCs cells.Hoechst 33342 fluorescent staining showed that the porous scaffolds could increase the proliferation of BMSCs.The results of q RT-PCR indicated that the porous scaffold prepared in this study can promote the expression level of osteogenic genes（ALP,OPN,OCN,RUNX2）to different degrees.In order to investigate the repair ability of PLA/Fe₃O₄,PLA/Fe₃O₄/HA,PLA/Fe₃O₄/HA/Aln and PLA/Fe₃O₄/HA/Aln-Col/Dex porous scaffolds to rabbit leg defects,a rabbit leg bone defect model was constructed.One and three months after implantation of the porous scaffolds,Micro-CT was used to observed the bone repair.The results of Micro-CT showed that after scaffolds implantation,the scaffolds could completely fill the bone defect adaptively under the external alternating magnetic field drive,realizing personalized treatment.And after three months implantation of rabbit leg bones,the porous scaffolds achieved different degrees of bone repair,of which the PLA/Fe₃O₄/HA/Aln-Col/Dex scaffold had repaired most of the bones at the third month.These results proved that the porous scaffold prepared in this paper has good bone repair performance and provides a new method for clinical treatment.In this paper,a new drug-loaded shape-memory porous scaffold prepared by 4D printing technology combines the drug controlled-release and rapid-release system with a biological scaffold.It provides a research basis for the combined application of new polymer drug delivery system and 4D printing technology to treat bone defects.This method can realize personalized repair according to different conditions of patients,and provides new ideas for precise treatment and new polymer-controlled drug release system.