The Regularity And Mechanism Of Interactions Between Small Biomolecules And Surfaces Of Magnesium Alloys For Vascular Stent

With good biodegradability,biocompatibility and mechanical compatibility,biomedical magnesium(Mg)alloys for biomedical applications are one of the promising biodegradable vascular stent materials,and have become a research hotspot of biomaterials in recent years.However,in the physiological environment,the slow endothelialization process and excessive corrosion rate of Mg alloys surfaces hinder the clinical application of Mg alloys vascular stents.In this paper,the regularity and mechanism of interactions between the surfaces of bio-magnesium alloys and biomolecular coatings with the rapid endothelialization were systematically investigated,which provide theoretical support for the selection of bio-coatings with the rapid endothelialization function.It is diff-icult to obtain the regularity and mechanism of interactions between coatings and surfaces only by means of experiments due to the complexity of the surface structure and the interaction between the surface and the biomolecular coating.In this paper,the first-principles calculation method based on the density functional theory is used to investigate the regularity and mechanism of interactions of small biomolecules(functional groups,amino acids,dipeptides and arginine-glycine-aspartic acid(RGD)tripeptide)on the surfaces of pure Mg and Mg alloys.It is of great theoretical significance for the selection of biomolecular coating,composition of magnesium alloys and the processing method of surface texture of Mg alloys.(l)Regularity and mechanism of interactions between Mg surfaces and small biomolecules at the atomic scale were studied by using the first-principles calculations.The adsorption energies of functional groups(amino,carboxyl and guanidine),amino acids(arginine,glycine and aspartic acid),dipeptides(arginine-glycine,glycine-aspartic acid and arginine-aspartic acid)and RGD tripeptide on the Mg(0001)surfaces were calculated,and the order of absolute values of adsorption energy of three functional groups is:guanidine(1.08 eV)>amino(0.71 eV)>carboxyl(0.64 eV);the order of absolute values of adsorption energy of three amino acids is:arginine(1.67 eV)>aspartic acid(1.23 eV)>glycine(1.16 eV);the order of absolute values of adsorption energy of three dipeptides is:arginine-aspartic acid(2.80 eV)>arginine-glycine(2.09 eV)>glycine-aspartic acid(1.73 eV);the absolute adsorption energy of RGD tripeptide is 3.24 eV.Before and after the adsorption process,the electronic structures of N and O atoms of small biomolecules on Mg(0001)surface were analyzed,revealing that pure Mg surfaces bind to small biomolecules in the form of coordinate covalent bond.(2)The effect of different alloying elements(Zn,Y and Nd)on the interaction regularity and mechanism of Mg alloys surfaces with functional groups,amino acids,dipeptides and RGD tripeptide were studied.It was found that Zn enhances the interactions between Mg alloys surfaces and small biomolecules,while Y and Nd weaken the interactions for the Mg alloys surfaces with l%Zn,1%Y and l%Nd;the adsorption energies of biomolecules gradually increase with the increase of Zn concentration for the surfaces of Mg alloys with l%Zn,2%Zn and 3%Zn.The charge distribution of Mg surface is changed by the addition of the alloying element,which affects the ability of N and O atoms of small biomolecules to form the coordinate covalent bond with Mg atoms,and thus influences the interactions between them.According to the quantitative experiments of amines of arginine on the Mg and Mg alloys surfaces(Mg-1Zn,Mg-2Zn,Mg-3Zn,Mg-1Y and Mg-INd),it is showed that the addition of Zn increased the amount of amines on the surface,and the amount of amines increased gradually with the increase of Zn concentration;the addition of rare earth element Y/Nd increased the concentration of amines on the Mg-1Y and Mg-1Nd surfaces;the absorption peaks of O-H,N-H,-C=O,-C-O and-NH2 groups were observed by infrared spectroscopy,indicating the existence of arginine on the surfaces of Mg and Mg alloys.(3)Studying the adsorption behavior of glycine on the Mg(0001)surface with different defect concentration and the Mg(0001)surface containing the hydroxyl group.The adsorption property of glycine on the Mg(0001)surfaces with defect concentration of 1/36,1/6,1/3 and 1/2 were investigated.The calculated results show that the adsorption configuration of glycine which adsorbs at the step edge in the form of coordinate covalent bond is the most stable.For the Mg(0001)surface adsorbed with hydroxyl group,some electrons are transferred from the surface to the adsorbed hydroxyl group,resulting in the changes of the electronic structure of the surface,and weakening the interaction between the surface and glycine.(4)The surface energy and work function of different Mg surfaces were studied.The results showed that the surface energy of the basal plane Mg(0001)is the lowest and the structure is the most stable;it is easy for the prismatic planes(1010),(1120),(2130)and pyramidal plane(1011)to interact with the small biomolecules as their higher surface energy compared with the basal plane;the reconstitution and relaxation of the surfaces were analyzed,and it was found that the layer spacing d12 of Mg(0001)is expanding,while the d12 of other surfaces are shrinking.The relaxation effect of the surface is an important factor which affect the stability of the Mg surface.(5)The regularity and mechanism of interactions of glycine and RGD tripeptide on the different surfaces of Mg and Mg alloys were studied.It was found that,similar to the adsorption behavior on Mg(0001)surface,Zn promotes the adsorption of glycine and RGD on the(1120)and(1011)surfaces,and the order of absolute values of the adsorption energy is AE(1120)>AE(1011)>AE(0001).The adsorption energies of glycine and RGD on the(0001),(1120)and(1011)surfaces increase gradually with the increase of Zn concentration.