Synthesis And Surface Modification Of Polyimide Hollow Fiber And Its Application In Biomaterials

Hollow fiber is able to remove small molecules from the blood leading to the increase of oxygen content and the decrease of carbone dioxide in the circulation system.As a result,hollow fibers are widely used in the application of membrane oxygenator,hemodialysis machine and other medical equipment as a medical separation membrane.Nowadays,microporous polypropylene（PP）or polysulfone（PSF）are widely used as the polymer matrix of medical hollow fiber separation membranes.Challenges still remain,such as the limited gas exchange capacity,the insufficient blood transmission efficiency,the insufficient service time,and the biocompatibility issues.Therefore,it is necessary to develop a new type of material for the hollow fiber with good gas transmission and blood compatibility,which is important practical significance for reducing medical costs and ensuring medical safety.Polyimide（PI）is a kind of polymer with imide ring in the main chain.It has high temperature resistance,excellent mechanical properties,low temperature resistance and chemical solvent resistance,and can be used for a long time under harsh medical operation conditions.PI hollow fiber membrane is a new type of membrane separation material,which has shown good gas separation selectivity in industrial applications,so it should also have potential application prospects in medical applications.However,the relationship between structure and properties and the related basic problems of biocompatibility are not clear,which need to be further studied.In this project,the application of PI hollow fiber in medical field was studied.Different morphologies of PI hollow fiber were obtained by changing the preparation process to adapt to different medical separation scenarios.The surface of PI hollow fiber was chemically modified by UV induced grafting enduing it excellent antibacterial properties and good biocompatibility.Combined with the actual application scenarios,the research on PI adhesive adaptability was further carried out to provide reference for its application.The main achievements are as follows:1.PI hollow fibers were prepared by two-step method using 3,3’,4,4’-biphenyltetracarboxylic dianhydride（BPDA）and 4,4’-diaminodiphenyl ether（ODA）monomers with good flexibility.The morphology,overall porosity,gas separation ability and mechanical properties of PI hollow fiber membrane were controlled by changing the spinning conditions（spinning liquid/core liquid flow rate ratio,core liquid composition,external coagulation bath temperature and air gap）.The results showed that with the increase of the flow rate of the core liquid,the pore diameter of the PI hollow fiber increased gradually,and the pipe wall became thinner.When the flow rate of the core liquid rised to 1.5 ml/min,the self-supporting force of the pipe wall was insufficient and collapsed.The porosity of the outer surface was adjusted by changing the length of the air gap.With the increase of the air gap from 1cm to 5cm,the porosity of the PI hollow fiber decreased,the gas permeability gradually decreased,and the oxygen permeability increased.The results showed that the content of DMAc in the core liquid was higher than that in the core liquid,and the coagulation ability of PAA primary fiber was poor,so it was easy to form large finger holes in the wall of hollow fiber.With the decrease of DMAc concentration,the finger like pores in the tube wall became smaller and less,the dense sponge structure increased,and the corresponding gas permeability decreased;reducing the temperature of external coagulation bath was also conducive to the reduction of finger like pores,and the overall porosity decreased and the mechanical properties were improved.When the external coagulation temperature reduced to 25℃,all sponge structure was then obtained,which had the potential application in the small molecule filtration of hemodialysis.It was presented that PI hollow fibers with different morphologies were prepared by adjusting the spinning process meeting the various medical separation needs.2.The modification is difficult to be established on the surface of PI surface due to the semi-crystal structure and the inertia chemical properties of PI.In this experiment,carbene free radicals were generated by UV excitation of bisacridine containing bromine which could insert to C-H bond on PI instantaneously and un-selectivity.PAMAM dendrimers were then induced onto the surface of PI hollow fibers reacting with the benzyl bromide groups.On the one hand,it provided active reaction groups for further heparin grafting;on the other hand,PI was endowed with certain bactericidal ability,so that it could be used in medical environment for a long time.After grafting PAMAM onto the surface of bpda/oda type PI film with the same structure,the structure of PAMAM was characterized by water contact angle（CA）,nano IR,XPS,AFM and orangeⅡstaining.The concentration of amine ions on the surface was calculated to be 1.5×10^-6 mmol/cm² with orange II staining solution.The height of the grafted dendrimer was about 5 nm,which indicated that the grafting had no effect on the separation performance of PI membrane.The results of the experiments of antibacterial adhesion and bacterial dying staining showed that the antibacterial property of PI was improved obviously after grafting PAMAM,which provided a new way for the antibacterial design of PI materials.3.In order to further improve the biocompatibility of PI in practical application,heparin was grafted onto the surface of PI modified by PAMAM by Schiff base reaction.Fourier transform infrared spectroscopy（FT-IR）and toluidine blue detection were used to qualitatively and quantitatively characterize the surface of heparin grafted PI.In vitro experiments showed that the hemolysis and platelet adhesion of the grafted PI decreased significantly,indicating that the modified PI had good blood compatibility.In vivo experiments,after embedding the material in mice for a period of time,compared with the PI fiber without heparin graft,the inflammatory infiltration rate around the material decreased significantly,and the local hemolysis decreased,indicating that the modified PI has good histocompatibility,which provides a good basis for the future application of PI in vivo materials.4.Reliable adhesion strength is required in the manufacture of medical devices.However,the semi-crystal structure and the chemical inertia leading to the low adhesion strength on the suface of PI.The surface of grafted PI hollow fiber was rich in amino groups.It was presented that the water contact angle significantly reduced and the wettability was improved.In this experiment,four types of commercial aviliable adhesives,poly(butyl a-cyanoacrylate,silicone,epoxy resin and polyurethane,were used to study the adhesive properties before and after the modification.The adhesive strength between the grafted PI and aluminum sheet was characterized by tensile shear test.Results indicated that the medical glue a-cyanoacrylate was able to generate tensile shear strength up to 9.6 MPa,which increased for 95%compared with that before the surface grafting.The microstructure of the bonded samples also proved its excellent interfacial force.This modification strategy to improve the bonding ability plays a good guiding role in the design and application of PI in practical medical devices.