Synthesis And Structure-Properties Of Polycarbonate Based Polyurethane Elastomers For Artificial Blood Vessel

Cardiovascular disease is still the major burden facing the aging society in China in the next 10 years.Artificial replacement implants(such as artificial blood vessels and valves)are important high-value products in surgery.Thermoplastic polyurethane(TPU)elastomer is widely used in the manufacture of blood vessel patches,pacemaker wires,artificial blood vessels and ventricular assistant devices due to its good biocompatibility and mechanical properties,saving the lives of substantial cardiovascular patients.However,at present,the medical TPU elastomers for long-term blood contacting only rely on the import from foreign chemical enterprises,and the domestic market in China lacks the independent capacity for producing long-term implantable medical TPU elastomers in industrial scale.In order to research and develop domestic medical TPU elastomers with domestic independent patents,we investigated the previous literature,patents and the experience of the current polyurethane industrial production in this study,and through nuclear magnetic resonance,infrared spectroscopy,scanning electron microscopy(SEM),we studied the market medical TPU elastomers in terms of its chain structure,and morphology.Dynamic mechanical analysis(DMA),in situ small-angle X-ray scattering/wide-angle X-ray diffraction(in situ SAXS/WAXD)and engineering stress-strain tensile tests were carried out to compare the changes in chain structure,aggregation state structure and mechanical properties of polyurethane artificial blood vessels and their biodegradation resistance during the acute phase after 24 weeks of implantation in sheep.Its molecular chain was not broken after the implantation.No obvious crack under SEM scopes was found on the surface,and the mechanical properties of the bulk were not significantly changed before and after implantation,which demonstrated the excellent anti-biodegradation ability of imported TPU products in the acute stage of the implantation.Through the retro-analysis of the structure of the imported products,the synthetic formula of medical TPU elastomer in this study was independently explored aimed at the domestic functional substitute.Four TPU samples with different chain extenders(Series I)and four samples with different hard segment contents(Series II)were synthesized by the one-step polymerization.Fourier transform infrared spectroscopy(FT-IR),hydrogen magnetic resonance spectroscopy(1H NMR),gel permeation chromatography(GPC),thermogravimetric analysis(TGA),differential scanning calorimetry(DSC),dynamic mechanical analysis(DMA),engineering stress-strain tensile test,scanning electron microscopy(SEM),atomic force microscopy(AFM),small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD),in vitro cytotoxicity tests and hemolysis tests were carried out respectively to characterize the chemical structure,mechanical properties and biocompatibility of these two series of samples.Among the Series 1 samples,the FT-IR results of PCU-EO showed the most proportion of the ordered crystal phase of the carbonyl hydrogen bonding stretching vibration signals,while PCU-PDO with the most disordered/amorphous phase,and PCU-MEA with the most weight of free carbonyl stretching vibration peak area.PCU-BDO had the best thermal stability through TGA tests.DMA analysis showed that PCU-MEA and PCU-BDO had higher storage modulus at 37℃,the glass transition temperature of the soft segment of PCU-MEA was-13.1℃.In situ WAXD/SAXS results indicated that PCU-EO demonstrated the highest degree of microphase separation,while PCU-PDO showed no phase separation signal,and the four samples remained amorphous in the 500%strain process.PCU-MEA had the highest tensile strength(57.8±4.0 MPa)among the series I samples.PCU-BDO had the highest elongation at break.BDO and MEA showed better improvement in mechanical properties among the four chain extenders.The samples in series 2 showed their amorphous state by DSC.The thermal stability of PCU-36 was the best at 100-280℃.the Tg of the soft segment was-5.82℃,and the strength modulus of PCU-36 in the Series II was the highest(54.2±6.7 MPa).The comprehensive function was optimal when the hard segment content was 32-36%.The cytotoxicity tests of the two series of samples indicated cytotoxicity,while the samples synthesized with low dose catalyst showed no cytotoxicity.It was preliminarily considered that the toxicity of the samples’ extraction was most likely due to the high dosage of catalyst.The next step is to explore the synthesis method with low dose catalyst and the re-characterization of the mechanical properties of the samples obtained by this way.In the second series of samples,PCU-32 and PCU-36 have passed hemolysis tests in vitro and preliminatively proved their good blood compatibility.Through the analysis of the imported samples and the comparison of these two series samples,we concluded that the PCU with the two chain extenders,BDO and MEA had optimal mechanical properties and biocompatibility,which is equivalent to the imported samples and similar chain structure.And this type of TPU has a application prospect in the manufacturing of high-tech cardiovascular implantation products for long-term blood contact.