Preparation Of Biodegradable Poly(ester-urethane)s With High Mechanical Properties And The Studies On Film Surface Modification

Polyurethane?PU?is a block copolymer in which a flexible soft segment and a rigid hard segment are alternately connected.The hard segment and the soft segment are thermodynamically incompatible,and each of them aggregates to form a microphase separation.It has excellent mechanical properties and is widely used in plastics,adhesives,rubber and the like.In biomedical science,due to its excellent mechanical properties and relatively good biocompatibility,PU is widely used as a long-term implantable material in blood vessels,artificial heart,cardiac assist devices,nerve conduits,ureters,etc.Modern medicine has increasingly strict requirements for adverse biological reactions caused by long-term implantable medical PUmaterials applied to living tissues,and how to improve the blood compatibility of PU without impairing its excellent mechanical properties has become the focus in this field at present.In this paper,poly?ester-urethane?s?PEUs?were prepared by chain extension of poly??-caprolactone??PCL?with unform-sizealiphaticdiurethanediisocyanate,and the corresponding films were obtainedvia solvent evaporation method.Monomethoxyl PEG?MPEG?and2-methacryloyloxyethyl phosphorylcholine?MPC??MPC?were chemically grafted onto the film surface by aminolysisreactionandallophanate reaction,respectively.The physico chemical properties and blood compatibilityof the materials before and after the modification were studied.The relevant research contents and results are as follows:?1?PCLs with different molecular weight?M_n=600?1000?2000?3000?were prepared under vacuum via ring-opening polymerizationswith1,4-butanediol?BDO?as initiator,?-caprolactone??-CL?as monomer and stannous octoate as catalyst.Subsequently,the PCL was chain-extended with diurethanediisocyanate?1,6-hexamethylene diisocyanate-1,4-butanediol-1,6-hexamethylene diisocyanate,HBH?to obtainPEUswith different soft segment molecular weights,and the corresponding films were prepared by solvent evaporation.The chemical structures of PCLs and PEUs were characterized by ¹HNMR,FT-IR and gel permeation chromatography?GPC?,and the results showed that the PEUshad high molecular weight?M_n>1.0×10⁵ g/mol?and low polydispersity?<1.5?.The physicochemical propertiesof the films,including thermal properties,crystallization behavior,tensile properties,and in vitro degradability,were reaearched by differential scanning calorimetry?DSC?,The results of thermogravimetric analysis?TGA?showed that PEUs possessed better thermal stability than that of PCL,which was probably ascribedto the high molecular weight of PEU.Two glass transition temperatures were observed in the differentialscanningcalorimetry?DSC?curvesofPEUs,demonstratinga microphase-separated structure.The PEU films exhibited excellent tensile properties with an ultimate stress of 34-519 MPa and an elongation at breakof 900-1480%,which should be attributed to the more compact network structure formed by uniform-sized hard segments and denser hydrogen bonds among the hard segments.In vitro degradation tests indicated that the PEU films had slow degradation rate and could maintain the mechanical properties for more than six months?even 12 months?,which meets the requirements of long-term implant materials.?2?Free amino groups were introducedonto the surface of PEU film?adopting PEU1000 as a test sample,PEU?via aminolysisreactionwith hexamethylenediamine,and then the NH₂-grafted PEU surfaces?PEU-NH₂?were reacted with isocyanate-terminated monomethoxyl PEG?MPEG-NCO?to obtain the PEG-grafted PEUsurfaces?PEU-PEG?.The results of FT-IR and ¹H NMR indicated that MPEG was successfully grafted onto the surface of the PEU film.The influence of aminolysis on the physical-mechanical properties of PEU films was investigated.The PEU-PEG film exhibited excellent tensile properties,which was slightly lower than that of PEU,indicating that the aminolysis has little influence on the tensileproperties.The blood compatibility tests of the films indicated that the PEG-grafted surface had improved resistance to protein adsorption and excellentresistance to platelet adhesion.In vitro degradation tests showed that the PEU-PEG film could maintain its mechanicalproperties for more than six months and only lost 25%weight after 18 months.?3?MPC was immobilized onto the PEU film surface(?adopting PEU2000 as a test sample,H-PEU?with high grafting efficiency by three-step chemical treatments under mild reaction conditions.The PEU film was firstly treated with 1,6-hexanediisocyanate to introduce-NCO groups on the surface?H-PEU-NCO?through an allophanate reaction;the-NCO groups were then coupled via a condensation reaction with one of-NH₂ groups of tris?2-aminoethyl?amine to immobilize-NH₂ on the surface?H-PEU-NH₂?;finally,the double bond of MPC reacted with-NH₂ by Michael addition toobtain MPC-grafted PEU?H-PEU-MPC?.The modified surfaces were characterized by FT-IR and X-ray photoelectron spectroscopy?XPS?,andthe results verified that MPC was successfully grafted onto H-PEU surface with high grafting density.The blank and modified films showed similar crystallization behaviors,thermal stabilities and mechanical properties,indicating that the chemical treatments had minimum influence on the physicochemical properties of the substrate.The H-PEU-MPC displaying a much lower water contact anglethanH-PEU meant that the hydrophilic phosphorylcholinefunctional groups improved the surface hydrophilicity significantly.The tests of surface blood compatibility revealed that H-PEU-MPC had improved resistance to protein adsorption and anti-platelet adhesion capacity.The surface hydrophilically modified PUmaterials,which possess excellent mechanical tensile properties,slow biodegradability,non-toxic absorption of degradation products and good surface blood compatibility,hold significant promise forlong-term implant biomaterials and blood contact materials.