Fabrication Of Totally Biodegradable Cardiac Occluders From Biodegradable Copolyesters

A cardiac occluder is a medical device commonly used in the treatment of congenital heart disease.Currently used occluders are generally made of metal alloys.After implantation,the occluder will be permanently present in the heart,which may lead to endothelium-induced thrombosis,valve wear or perforation,nickel ion allergy or toxic reactions,and affect future open heart surgery of the left ventricular system.In this study,biodegradable polyesters were used to prepare a completely degradable cardiac occluder.High molecular weight poly(lactide-trimethylene carbonate)(PLT)binary copolymer and poly(lactide-trimethylene carbonate-glycolide)(PLTG)terpolymer were synthesized and characterized.The molecular weights,thermal properties,mechanical properties,degradation behavior and biocompatibility of the copolymers were determined.3D printing technology was used to design and fabricate a biodegradable cardiac occluder.The main research contents are as follows:(1)Binary copolymer PLT and terpolymer PLTG with different monomer ratio were synthesized by ring-opening polymerization with stannous octoate as catalyst.All the copolymers have a molecular weight of more than 80,000.The chemical structure,thermal properties and mechanical properties of the copolymers were characterized.The addition of TMC and GA monomer reduces the chain regularity,the crystallinity and the glass transition temperature of the copolymers are correspondingly reduced.Concerning the mechanical properties,the introduction of TMC monomer greatly improves the elongation at break of the copolymer,but the tensile strength and Young’s modulus are reduced.The addition of the GA component makes the tensile strength of the copolymer slightly decrease,but the elongation at break is greatly improved.(2)The degradation behavior of PLT95/5,PLT75/25,PLTG95/5/5,PLTG75/25/5 in phophate buffered saline(PBS)was studied.The degradation rate of PLT copolymers increases with increasing TMC content,and the degradation rate of terpolymers is faster than that of PLT copolymer.After 12 weeks of degradation,the molecular weight of the four groups was more than 50000,which should allow to conserve the mechanical strength,in accordance with the performance requirements of biodegradable materials.(3)The biocompatibility of PLT95/5,PLT75/25,PLTG95/5/5,PLTG75/25/5 was characterized.The results showed that the hemolysis rate of the material was less than 5%,the degree of damage to the red blood cells was very small.The time of plasma calcium recovery was more than 60% of the positive control.The dynamic coagulation test showed that the activation of the endogenous coagulation factor was low,indicating that the four groups of materials have good biocompatibility.(4)3D printing technology was used to fabricate a biodegradable occluder of PLT75/25 as a raw material.The molecular weight and elastic recovery ability of the occluder were characterized.The copolymer still has a high molecular weight after processing and maintains good mechanical strength.At the same time occluder samples also show good elastic recovery ability,and its mechanical properties should meet the static blocking environment.Therefore,the occluder produced from the copolymer has good strength and toughness,suitable degradation rate,excellent biocompatibility and processability,and has a good potential in the field of degradable occluders.