Surface Modification Of The Blood-Contacting Polymers For Improvement Of Antithrombogenic And Antimicrobial Properties

In recent years, synthetic polymers are widely used in biomedical materials for artificial organs including cardiovascular artificial organs. However, when the blood-contacting polymers contact with blood, complicated interaction will happen on the interface so as to form coagulating reaction and thrombus. The patient's life is threatened by Biomaterial Centered Infection (BCI) and the bacteria adhesion is the first step of this infection, so inhibition of the bacteria adhesion and growth onto the surface of biomaterials is very important. Therefore, blood-contacting polymers need to be modified to improve their antithrombogenic and antibacterial properties, which have been focused in research.Polyethylene terephthalate (PET) and polyvinyl chloride (PVC) are chosen as the materials in our reseach. These materials are pre-treated by oxygen radio frequency plasma method or ozone method. Then polyacrylic acid molecules are grafted by ultraviolet (UV) irradiation. Furthermore, the chitosan molecules are immobilized through chitosans' amino groups reacting with carboxyl group of polyacrylic acid. Finally, the immobilized chitosan can act as the bridge and react with the heparin molecules.According to the result of X-ray photoelectron spectroscopy (XPS), polyacrylic acid, chitosan and heparin have been effectively grafted and immobilized by two modified methods on the PET and PVC surfaces. The concentration of the immobilized heparin is 7.2μg/cm² and 4.5μg/cm² respectively on the PET surface pre-treated by oxygen plasma and ozone. The results of static contact angle indicate the hydrophilicity of the modified PET surface is more remarkably improved than that of the unmodified PET surface. The results of platelet adhesion show that the numbers of adhered platelet decrease and platelets don't aggregate and distort on the PET and PVC surfaces immoilized with heparin. The results of coagulant factor tests reveal that the activated partially thromboplastion time (APTT) of PET and PVC immobilized with heparin by oxygen plasma pre-treated method is 23.1s and 57.4s which is longer than that of the virgin plasma. The APTT of PET and PVC immobilized with the heparin by plasma pre-treated method is 60.5s and 100s respectively. While APTT of PET immobilized the heparin by ozone pre-treated method is 15.8s which is longer than that of virgin plasma. The change of APTT indicates that the modified PET and PVC films can suppress intrinsic coagulant system.Silver beam ion implantation (BII) and silver plasma immersion ion implantation-deposition (PIII-D) techniques have been used to treat PET in order to improve its antibacterial activity. The results of the X-Ray diffraction ( XRD ) and XPS analysis indicate that silver has been successfully implanted into the surface of PET modified by silver BII, and silver coating is deposited on the surface of PET modified by silver PIII-D. The atomic absorption spectrometry (AAS) analyzes the silver ions releasing under the water medium. The result indicates that the releasing concentration of silver ions of the PET modified by the silver BII is higher than that of the PET modified by silver PIII-D. The capacities of Staphylococcus epidermidis (SE) adhered on PET are suppressed by silver BII and PIII-D. The adhered concentration of SE surface is 2.23×10⁷CFU/ml on the control PET surface but that is 5.3×10⁶CFU/ml and 1.12×10⁷ CFU/ml on the PET surfaces modified by silver BII and PIII-D respectively with incubation time of 24h. The concentration of antibacterial silver ion is higher which may make less SE adhere to the PET surfacemodified by silver BUThe results of static contact angle show the hydrophilic property of the modified PET is improved. The free energy of adhesion (â–³F_Adh) predicts whethermicrobial adhesion is energetically favorable (â–³F_Adh<0) or not (â–³F_Adh>0). Thecalculated results show that bacterial adhesion is energetically unfavorable on the modified PET surface. The results of lactate dehydrogenase (LDH) show that the PET surface modified by silver BII and PIII-D do not have acute toxicity on the endothelium cell (EC). Alamar Blue evaluation indicates that the modified PET surface can inhibit the growth and proliferation of EC, and especially the higher inhition on the adhesion and proliferation of EC on the PET surface modified by silver PIII-D can be observed.