Biological Properties Of PEEK Implants Modified By Vascular Endothelial Growth Factor Mimetic Peptide In Vitro

Objective: In this study,we tried to improve biological activity of PEEK by modified the vascular endothelial growth factor(VEGF)mimetic peptide(QK)on its surface,concluding the hydrophilicity of PEEK and the adhesion,proliferation and functional activity of HUVECs.Our aim is to find an efficient and stable material modification method to improve the biological activity of PEEK,and promote the application of PEEK implants by 3D printing in bone repair.Methods: Experiment 1: Surface modification and characterization of PEEK: After immersed in weakly alkaline dopamine solution for 24 hours,the surface of PEEK had polydopamine(PDA)coat.Vascular endothelial growth factor(VEGF)mimetic peptide(QK)was grafted onto the surface of PEEK by PDA coat.The experiment was divided into three groups: The PEEK group,the PEEK-PDA group and the PEEK-PDA-QK group,and each group has six samples.The contact angle of samples in each group was measured by contact angle measuring instrument,and we could analyze the hydrophilicity of the samples.The main chemical elements of the samples were analyzed by X-ray photoelectron spectroscopy(XPS)to verify that QK was successfully modified on the surface of PEEK.Experiment 2: Cell experiment: Three groups of materials were co-cultured with HUVECs.At some stage of cell culture,the toxicity,adhesion,proliferation and functional activity HUVECs were analyzed.The experiment included lactate dehydrogenase(LDH)activity,CCK-8 test,nitric oxide(NO)content and ghost pencil ring peptide(GNP)cytoskeleton staining.Finally,quantitative data were analyzed by SPSS19.0 software and one-way analysis of variance.P values <0.05 means statistically significant.Results: Experiment 1: The contact angle of PEEK samples in three groups increased as follows: PEEK-PDA-QK group,PEEK-PDA group,PEEK group(P < 0.05).The hydrophilicity is inversely proportional to the contact angle.So,PEEK-PDA-QK group had the best hydrophilicity.The XPS showed that the main elements of PEEK group were C and O,but PEEK-PDA-QK group and PEEK-QK group were C,O and N.The PEEK-PDA-QK group had the highest content of N,and the N/C ratio were higher than PEEK-PDA group.XPS indicated that QK was successfully modified on the surface of PEEK.In addition,N was detected on the surface of PEEK-PDA group,which indicated that PDA coating had been loaded on the surface of PEEK.Experiments 2: After 1day,3 days of cell co-culturing,the LDH activity of HUVECs in three groups has no significant difference(P>0.05).After 12 hours,1day,3days and 5days of cell co-culturing,CCK-8 test examined the cell adhesion and proliferation of HUVECs.The OD value of three group were PEEK-PDA-QK group > PEEK-PDA group > PEEK group(P<0.05).After 1day,2days and 3days of cell co-culturing,the NO concentration in supernatant from large to small followed by PEEK-PDA-QK group,PEEK-PDA group,PEEK-PDA group(P<0.05).Cytoskeleton staining experiment showed that PEEK-PDA-QK group had the best cell attachment,and had regularly arranged microfilament cytoskeleton.Cells were fusiform flattening,and there were tight junctions between cells by lots of filamentous feet.PEEK-PDA group were worse than PEEK-PDA-QK group.There were more disordered filaments in cells,and a few filamentous feet between cells.But PEEK group were the worst.The cell attachment was the least,the junction between cells was bad,and the structure of intracellular microfilaments was blurred.Conclusion: QK was successfully grafted onto the surface of PEEK by PDA coating.The hydrophilicity of PEEK modified by QK was significantly improved.And the adhesion,proliferation and functional activity of HUVECs were significantly improved.So,the biological activity of PEEK was improved.At the same time,PDA coating could improve some biological activity of PEEK.In this study,it was concluded that t active polypeptide grafting by PDA coating was simple,effective and safe.PEEK with QK had a certain potential for angiogenesis.It could improve the properties of PEEK materials and provide a new idea for the research and application of PEEK materials.