Preparation And Shape Memory Properties Of Biodegradable Poly(Ether-Ester-Urethane)/Poly(Ester-Urethane)

The application of shape memory polymer(SMPs)in medical implants is limited due to their non-degradability and low biocompatibility.Biodegradable shape memory polyurethane(SMPUs),which possesses the advantages of high recovery strain,low density and simple processing,has been proposed to be used in many medical devices.In this paper,the feasibility of polyurethane in medical field is improved by designing the components,controlling the properties and changing the critical deformation conditions.Thepaper is mainly divided into three parts:I.Shape-memory poly(ether-ester-urethane)(SMPEEU):The prepolymers of triblock poly(ether-ester)(poly(?-caprolactone)-ploy(ethyleneglycol)-poly(?-caprolactone),PECL)was synthesizedvia ring-opening polymerization with poly(ethylene glycol)(PEG)as initiator and?-caprolactone(?-CL)as monomer.By chain extension of PECL with uniform-size aliphatic diurethane diisocyanate(HBH),the biodegradable SMPEEU with varying PEG content were prepared.The chemical structures of PECL and SMPEEU were characterized by ~1H NMR,FT-IR and GPC,and the influence of PEG content on the physicochemical properties of SMPEEU,including thermal properties,crystallization behavior,mechanical properties,surface and bulk hydrophilicity and in vitro degradability,was extensively researched.The results demonstrated that the introduction of PEG segments could lead to low transition temperature and decreasethe crystallinity of the polymers.With the PEG content increasing from 9.25 to 47.5 wt%,the strain at break increased from 483 to 956%,and the ultimate stress decreased from 23.1 to 9.0 MPa.In vitro hydrolytic degradation studies indicated that the time of the SMPEEU films becoming fragments was 4-12 weeks and the degradation rate increased with the increase of PEG content.The shape memory properties were evaluated by fold-deploy test,and the results manifested that the SMPEEU-III films with PEG content of 23.4 wt%displayed excellent recovery properties with recovery ratio of 99.8%and recovery time of 3.9 s at body temperature.And after four fold-deploy cycles,the film could almost recover its original shape rapidly.The cytotoxicity test of film extracts indicated good cytocompatibility in vitro.The SMPEEU,which possess not only satisfied tensile properties,biodegradability,non-toxic degradation products and good cytocompatibility but also excellent shape recovery properties at body temperature,were promised to be an excellent candidate for medical device application.II.Shape-memory chitooligosaccharide-based poly(ester-urethane)(SMCPU):A new kind of SMCPU with various chitooligosaccharide(COS)content were prepared according to the conventional two-step method.First,prepolymer was synthesized from PCL and HBH.Then,the prepolymer was chain-extended by COS to obtain the weak-crosslinked SMCPU.The chemical structure of SMCPU was characterized by FT-IR and the effect of COS content on the physicochemical properties of the material was studied.With the increase of COS content,the tensile strength,initial modulus and surface hydrophilicity increase,while the elongation at break and swelling rate decrease.In vitro degradation test showed that the degradation rate increased with the increase of COS content,indicating that the degradation rate could be adjusted by adjusting the amount of COS.Fold-deploy test shows that SMPCU has good shape memory performance at body temperature.With the increase of COS content(cross-linking degree),the fixity ratio and recovery ratio increased and the recovery time decreased.After 10 fold-deploy cycles,the film could still quickly return to its initial shape.In addition,the blood compatibility of the membrane material was studied by protein adsorption and platelet adhesion.The results showed that the introduction of COS greatly enhanced the ability to resist protein adsorption and platelet adhesion,showing good hemocompatibility.Excellent mechanical properties,controllable degradation rate,good hemocompatibility and excellent shape recovery properties at body temperaturmanifest that SMPCU has a wider range of applications in the medical field,and also provides new ideas for the design and preparation of SMPUs materials.The material still contains many active hydroxyl groups and unreacted amino groups,which can be further modified as a modified material to broaden its application in the field of biomedical materials.III.pH-sensitive shape-memory poly(ether-ester-urethane)(SMPEEU-Py):Dihydroxy-terminated pyridine compounds(PyDH)were first synthesized from 1-thioglycerol and4-vinylpyridine by Michael addition.Then,a serie of pH-sensitive SMPEEU-Py with pyridine groups on the side chains were prepared by chain extension of the mixture of PECL and PyDH with diphenylmethane diisocyanate.The chemical structures of PyDH and SPMEEU-Py were characterized by ~1H NMR,FT-IR and GPC.And the influence of PyDH content and/or pH value on the thermal properties,crystallinity,water absorption,tensile properties and in vitro degradation properties of SMPEEU-Py films was studied.The water absorption test at medium with different pH values showed that the material had better pH sensitivity.The higher the PyDH content,the better the pH sensitivity.The results of hydrolysis degradation in vitro showed that the degradation rate of film in alkaline and acidic medium was significantly higher than that in neutral medium.The pH-sensitive shape memory performance studies showed that the recovery rate of SMPEEU-Py-1/8 film with 21.19 wt%PyDH content was 91.7%at pH=1.5,but the recovery time was about 25 minutes.SMPEEU-Py,which possesses good physicochemical properties and pH-sensitive shape memory performance,has a high application potential in pH-sensitive drug carrier material.Three kinds of SMPUs including linear-chain,low-cross linking and pH-sensitive materials were prepared and researched in the paper.The research can provide new design ideas for new medical multifunctional SMPUs,and broaden the medical application field of PU materials.