The Experimental Study Of Biodegradable Vena Cava Filter

Objective1. To investigate the feasibility of Biodegradable Vena Cava Filter (BVCF) withadvanced computer aided design (CAD) and laser engraving. To determine thedifferences in mechanical properties between the center-thread BVCF, nocenter-thread BVCF and stainless steel filter. To develop the release device ofthe center-thread BVCF.2. To evaluate the mechanical properties, deliver performance, the ability ofcapture thrombus and the degradation property in a vitro model.3. To investigate the biocompatibility of BVCF. To evaluate thehistopathological findings in different periods after implanting into a porcinevascular so as to determine the possibility of implanting it into vessels. Toinvestigate the feasibility of the inferior vena cava filter to preventingpulmonary embolism.Materials and Methods1. Three-dimensional design software was used to design the shape of BVCF.Finite element software was used to analyze and optimize the design of theBVCF. The Poly-L-Lacid (PLLA) thin films with polymer materials wereprepared with solution coating method and the BVCF was made by cutting,pasting, and heat setting.2. The mechanical properties, deliver performance, the ability of capturethrombus and the degradation property were tested in a vitro model.3. A total of twelve minipigs were used to test the feasibility of this BVCF. Theywere randomly divided into four groups. The BVCFs were placed into theinferior vena cava of pigs in the three experimental groups. The fourth group was used as a blank control group.2,5,8strips of thrombosis (2.5-3cm inlength,3-5mm in diameter) were implanted into pigs respectively. Theanimals’ breath, heartbeat and other vital signs were monitored. Contrastmediums were injected through catheters, and fluoroscopy examinations wereused to observe the abilities of the filter to capture thrombus. Enhanced CTexaminations were performed on the pigs1,6and12weeks later respectivelyto observe the BVCFs status and whether there is a pulmonary embolism. Theanimals were sacrificed according to a fixed time table for histopathologicalassessment. The pigs’ inferior vena cava segments placed BVCF wereremoved to observe the filter locations, shapes, intima-embedded and surfacethrombus attached. The lungs of experimental animals were removed forhistopathological assessment to evaluate the abilities of BVCF in preventingpulmonary embolism.Results1. The BVCF was successfully designed and produced. This kind of filter has5-8lateral branches which can expand by stretching the center-thread, and cancapture the thrombus through the filter.2. In vitro test results showed the radial force of two relatively collateral ofBVCF was approximately1.6N, BVCF can be implanted into the inferiorvena cava by minimally invasive method using catheter and can capturethrombus with a diameter larger than3mm, The vitro degradation test resultsshow that after soaked for1week, the catheter breaked and crumbled easily.3. The BVCFs were successfully implanted into the inferior vena cava of pigs. Inthrombus injection experiment, two of experimental pigs in the operationhad the symptoms of respiratory frequency and heartbeat accelerated slightly,and vital signs of other pigs in the three experimental groups were stable,without breathing difficulties, shortness of breath, cough and other symptomsof pulmonary embolism. Inferior vena cava angiography showed filling defectin front of the BVCF, which means the filter successfully capture the thrombosis. Two pigs with the symptoms confirmed to occur peripheralPulmonary Embolism by the CT examination, while other pigs had no clearsigns of Pulmonary Embolism. In control group, the symptoms such asaccelerate of respiratory rate, shortness of breath were observed in varyingdegree, the pig which was injected into8strips of thrombus dead in the sameday after surgery. There was large patch wedge deep redness area in bilaterallungs, which indicated bleeding infarction, and we could see the point flakebleeding in the Embolization lung areas on the section. Histological findingsshowed that the inner membrance partly covered the BVCF lateral branchafter one week, and covered thoroughly after six weeks, with the normalhaemal wall structure and no signs of the obvious inflammatory cellsinfiltration. Taking the the blood vessels of the specimen after12weeks, thehaemal wall structure was normal, and the lumen was unobstructed, and thecollateral of the filter partly degradated.Conclusions1. A new biodegradable vena cava filter was designed and producted.2. The radial force of this center-thread BVCF is close to metal filter, whichmade it deliver by catheter like metal filter and fix within the blood vessels.3. Animal experiments showed that the BVCF can effectively capture thethrombus injected into the inferior vena cava to prevent pulmonary embolism.But BVCF is not as convenient as metal filter in filter delivery aspects, and itsdegradation rate need to be accelerated.