Construction And Properties Investigation Of 3D Printed Porous Polyetherimide Bone Implants For Promoting Osteogenesis And Anti-tumor Functionalization

Bone implants can be used to fill the huge bone defect that the human body can not repair by itself.It can not only fill the defect,but also bear a certain mechanical load.The most commonly used clinical titanium alloy implant modulus is higher than the elastic modulus of bone,which may lead to stress shielding effect,osteolysis and even implant loosening.High-performance polymers are a new type of materials that can be used in the field of bone implants.They have high mechanical strength and modulus closer to human bones,which could avoid stress shielding to a certain extent,such as polyetherimide(PEI).PEI is an amorphous high-performance polymer with excellent mechanical strength,Young's modulus close to human bone,good biocompatibility and thermal stability,so it is suitable for the field of bone implants.At the same time,PEI is a candidate material of bone implants with broad application prospect because of its low synthesis cost,less difficulty in processing and molding,ease of combination with other materials,and easier to popularize and transform.The shape of bone defect is usually irregular.3D printing technology can customize the shape of the implant to match the irregular bone defect and make the implant match well with the bone defect.At the same time,the pore structure of 3D printing implant scaffold can provide larger cell adhesion area and space for new bone,blood vessel growth and nutrient exchange.3D printing PEI porous scaffold can be used in the field of bone implants.When dealing with conventional huge bone defects,PEI can improve the therapeutic effect by enhancing biological activity and promoting osteogenic differentiation.Arginine-glycine-aspartic acid(RGD)peptide can bind to integrin receptors,promote cell adhesion and osteogenic differentiation,and other cellular behaviors conducive to bone repair.Through the introduction of bioactive small molecule RGD peptide on the surface of PEI,it is helpful to bone tissue regeneration at the defect site.When dealing with huge bone defects caused by bone tumors,PEI needs to have both osteogenic and anti-tumor functions.Because the tumor tissue will invade the bone tissue and plunder nutrition,affecting bone regeneration,and tumor metastasis will seriously endanger the lives of patients.Reduced graphene oxide(r GO)and gold nanoparticles(Au NP)can achieve triggered bone tumor therapy through synergistic enhanced photothermal therapy(PTT)the tumor area under the excitation of nearinfrared light(NIR).?-tricalcium phosphate(?-TCP,briefly referred to as TCP in the later text)is a commonly used bone repair material,which can achieve a continuous and stable osteogenic effect without interfering with the therapeutic effect of PTT.Therefore,the combination of TCP inside PEI and external loading of r GO-Au NP can effectively achieve the dual functions of promoting osteogenesis and anti-tumor.In this study,porous PEI bone implant scaffolds were developed by fused deposition modeling(FDM)3D printing technology,and the ability to treat conventional bone defects was further improved by loading RGD on the surface of PEI.Finally,the ability to treat neoplastic bone defects was improved by compounding TCP inside PEI and loading r GO-Au NP externally.The research content mainly includes the following three parts:1.Study on the fabrication of 3D printed porous PEI scaffoldThis part of the work is reflected in Chapter 2.In order to achieve appropriate mechanical properties,customizable implant shape and reasonable pore structure,we designed a complete preparation process of FDM 3D printing PEI porous bone implant scaffold from raw material to the final product.Firstly,the crushed PEI raw material was used to prepare the PEI or composite of PEI and TCP(10wt.% TCP)into special consumables for FDM 3D printer at high temperature by a twin-screw extruder.Then,according to the different needs of the experiment,modeling and slicing were carried out,the stable 3D printing code was repeatedly debugged and generated,and the code was imported into the 3D printer.3D printing porous PEI scaffolds and PEI-TCP composite(P-TCP)scaffolds were successfully prepared by using PEI consumables and composite consumables of PEI and TCP.According to the optical images and Micro-CT,the 3D printed porous PEI scaffolds and P-TCP scaffolds prepared by this process have customizable shapes and pore structures.2.3D printed porous PEI scaffold loaded with RGD peptide to deal with conventional bone defectsThis part of the work is reflected in Chapter 3.In this part of the work,polydopamine(PDA)coating was deposited on the surface of 3D printed porous PEI scaffold employing dopamine autopolymerization,and P-PDA scaffold was constructed.Based on it,RGD peptide was loaded and P-PDA-RGD scaffold was constructed.Through the characterization of physical and chemical properties,it was proved that PDA and RGD were successfully introduced into the surface of the scaffold,and did not affect the excellent mechanical properties of the scaffold.P-PDA-RGD scaffolds have good pore structure,rough surface and excellent hydrophilicity.In the study of cell viability,cell adhesion and cell proliferation,it was found that P-PDA-RGD group showed the best biocompatibility.In the osteogenesis experiment in vitro,P-PDA-RGD group promoted alkaline phosphatase(ALP)secretion and calcium deposition.P-PDARGD can significantly up-regulate the expression of Runt-related transcription factor 2(RUNX-2),Bone morphogenetic protein 2(BMP-2),Osteocalcin(OCN),Osteopontin(OPN),type 1 collagen(COL-1)and ALP,especially the expression of COL-1.The results of 4 and 12 weeks after implantation of femoral condyle defects in rabbits showed that the P-PDA-RGD group had the highest new bone volume / total volume,showing a more direct combination of bone and implants.The excellent performance of P-PDA-RGD scaffold shows that 3D printed PEI scaffold loaded with RGD peptide is a potential filling therapy for clinical transformation when dealing with the clinical scene of conventional bone defect.3.3D printing porous PEI scaffold combined with TCP and loading r GOAu NP through PTT for neoplastic bone defect therapy.This part of the work is reflected in Chapter 4.In this part of the work,r GO and r GO-Au NP were loaded on the surface of P-TCP scaffolds respectively utilizing dopamine autopolymerization,and P-TCP-r G scaffolds and P-TCP-r G-Au scaffolds were constructed.Both PEI and P-TCP scaffolds were used as comparison.The results of chemical detection showed that r GO-Au NP was successfully loaded on the surface of the scaffold.SEM showed that P-TCP-r G-Au scaffolds have good pore structure,rough surfaces and hydrophilic properties.The mechanical properties test showed that the mechanical properties of PEI scaffolds were improved by adding TCP.The cells in P-TCP-r G-Au group showed good vitality,adhesion and growth,and P-TCP-r G-Au scaffolds had good biocompatibility.In the study of osteogenesis in vitro,P-TCP-r GAu scaffolds showed good ability of ALP secretion and mineralization.OPN,RUNX-2,OCN and COL-1 genes were up-regulated in P-TCP-r G-Au group.The results of 4and 12 weeks after implantation of femoral condyle defect in rabbits showed that PTCP-r G-Au group had the highest ratio of new bone volume to total bone volume,and the new bone was closely combined with the implant.In the aspect of photothermal anti-tumor,firstly,the power density of NIR was screened,and the photothermal performance of each group was characterized.P-TCP-r G-Au group has the strongest photothermal performance.Under the excitation of NIR,P-TCP-r G-Au can effectively reduce the activity and survival rate of tumor cells,induce apoptosis of tumor cells,destroy the morphology of tumor cells and damage the nucleus of tumor cells after PTT.Furthermore,the tumor-bearing model of mice was used to evaluate the anti-tumor ability of PTT in vivo.P-TCP-r G-Au group had the strongest photothermal effect in vivo.During the treatment,compared with other groups and self-control without NIR irradiation,P-TCP-r G-Au group had the smallest tumor volume and the best therapeutic effect.Tumor tissue slice of P-TCP-r G-Au group showed that morphological destruction and nuclear fragmentation occurred in the tumor cells treated with PTT.In addition,the results of tissue slices of heart,liver,spleen,lung and kidney and the blood biochemical tests showed that the samples of each group had no obvious toxicity to important organs.Furthermore,the possible anti-tumor mechanism of P-TCP-r G-Au group was analyzed by transcriptome sequencing,and it was found that MAPK and other pathways were related to its anti-tumor function,and the biological processes of transcription and translation of tumor cells changed.The above results show that with the internal added TCP and externally loaded r GO-Au NP,P-TCP-r G-Au scaffolds have good osteogenic and anti-tumor ability by PTT.P-TCP-r G-Au scaffold is a new treatment strategy in the clinical scene of neoplastic bone defect,and it has the potential to be used in the clinical transformation of neoplastic bone defect.In summary,this study reflects the application potential of 3D printed porous PEI scaffolds in clinical scenarios such as conventional bone defects and neoplastic bone defects.This study makes a beneficial exploration on the multi-function of 3D printed porous PEI scaffold for bone implant,and provides a new reference for the future application of 3D printed porous PEI scaffold in orthopedics.