Research On Shape Memory Polymer Heart Occluder Structure And Its Performance

Congenital heart disease（CHD）is one of the most common congenital malformations.Interventional therapy is often used in clinical diagnosis and treatment of CHD.Heart occluder is one of the important types of these implanted devices.At present,most mainstream occluders are made of non-degradable alloy materials,which have excellent clamping and supporting effects but severely corrode tissues.And the device remains permanently in the body after the defect is healed,which poses a relatively serious risk of long-term complications.In response to this drawback,researchers have used degradable materials to fabricate heart occluders.These degradable materials are mainly biodegradable polymers or bio-derived materials.These materials are less harmful to the human body and will not remain for a long time,resulting in an avoidance of the risk of complications.But on the other hand,there are general problems of poor elasticity and weak clamping effects of these bio-degradable occluders.This work focuses on the advantages and disadvantages of the two kinds of occluders,and proposes the use of shape memory polymers to fabricate heart occluders,replaces the traditional elastic deformation mechanism with shape memory effects,and aims to improve the shape memory properties of the occluder under the premise of ensuring safety and degradability,achieving a more ideal clamping and occluding effect.The main research contents of the work are the design and preparation of shape memory cardiac occluder and its materials.Using polylactic acid（PLA）as the matrix,firstly mix polyethylene glycol（PEG）with Mn of 400 and 800,tributyl citrate（TBC）and acetyl tributyl citrate（ATBC）with PLA by a solution blending method to prepare a series of plasticized PLA for the purpose of toughening and lowering the glass transition temperature,performance of plasticized PLA was characterized and the most suitable plasticizer type and proportion were selected.Subsequently,the plasticized PLA and barium sulfate were physically mixed to prepare a composite material with X-ray developability,and the most suitable composite ratio was obtained through a series of analysis and tests.Afterwards,based on the oxidative self-polymerization reaction of dopamine hydrochloride under the action of alkaline environment and oxygen,a layer of polydopamine,a material with photothermal effect,was adhered to the developable composite material to prepare a shape memory polymer composite（SMPC）with photothermal-active shape memory effect.Finally,the shape memory occluder was prepared by a three-step process of spinning-weaving-setting.The shape memory performance,biocompatibility and degradation performance of the occluder were investigated to verify whether it had practical value.The research results showed that among several alternative plasticizers,the glass transition temperature of PLA/TBC was effectively reduced,the toughening and plasticizing effect was significant,the shape memory performance was excellent,and the plasticizer was not easy to migrate,which proved it suitable for this work.When the plasticizing ratio of TBC was 14wt.%,the glass transition temperature of PLA/TBC dropped to 42.1℃,and the shape recovery ratio reached 96%,which can meet the requirement of close body temperature activation of the occluder.In the plasticized PLA/Ba SO4 system,the content of barium sulfate had a greater impact on the mechanical properties of the composite,and the tensile performance was rather ideal when Ba SO₄content was 10wt.%,and the composite had good radiopacity at this concentration and the contrast is obvious.The addition of barium sulfate had no adverse effect on the thermal stability of the material,but the decomposition temperature of the material after the plasticization of TBC dropped to 220.8°C,which corresponded to the boiling point of TBC.After adhering to the polydopamine（PDA）coating,the composite material was endowed with near-infrared photothermal driving ability,and the conversion efficiency is proportional to the coating processing time.The specimen processed for three days rose from room temperature to 62.3°C within 60 seconds.The photomicrograph showed that after the specimen was treated in the PDA reaction system for three days,a continuous and uniform PDA coating is formed on the surface.Finally,the shape memory occluder with photothermal-active shape memory effect was successfully prepared using the above-mentioned SMPC as raw material,which achieved a shape recovery ratio of 91.6%within 50 seconds under 800nm near-infrared light,and could maintain a shape fixation ratio of 98.7%at body temperature.The cytotoxicity test and blood compatibility test of the occluder material showed that the specimens had good biocompatibility and met expectations.In vitro degradation experiments showed that the degradation performance of the PLA/TBC matrix was similar to that of pure PLA.The specimen disintegrated after160 days of experimentation,which could meet the requirements of cardiac endothelialization for the material degradation cycle.The shape memory occluder developed in this subject solved the shortcomings of both alloy occluder and degradable occluder to a certain extent,which could be seen as a successful attempt to combine smart materials with biomedicine.