Composite material stent comprising metallic wire and polylactic acid fibers, and its mechanical strength and retrievability.

BACKGROUND: Although metallic stents are characterized by strong expanse of force, thin walls, and easy stent deployment, their removal from the body is usually difficult or impossible due to the difficulty of unraveling their mesh structure. A stent built of a composite material comprising a metallic wire and a polylactic acid (PLA) fiber, in which the metallic wire component could be unraveled after PLA fiber degradation in the body, should allow easy stent removal. PURPOSE: To evaluate the mechanical strength and retrievability of a composite material stent comprising a metallic wire and a PLA fiber. MATERIAL AND METHODS: We produced a composite material stent comprising a metallic wire and a biodegradable fiber (hybrid stent). As the metallic wire is not cross-linked with itself, but with the PLA fibers only, the hybrid stent can be easily unraveled after PLA fiber degradation. This stent was built with a 0.2-mm stainless-steel wire and a 0.23-mm PLA fiber knitted in the same textile as an Ultraflex stent. For comparison, an identical stent was built using PLA fiber only (PLA stent). The mechanical strength of these stents was tested by the radial expansive force response against circumferential shrinkage stress load. Change in radial force due to PLA fiber degradation was estimated by adding an artificial PLA degeneration process, by immersing each stent in a water bath at 80 degrees C for 48 hours. Retrievability of the hybrid stent after PLA degeneration was examined by hooking and pulling out the residual stainless-steel wire from a silicon tube. RESULTS: The hybrid stent exhibited a linear response in radial expansive force within the range of 15% diameter reduction. The PLA stent did not exhibit linear response at over 15% diameter reduction. Decrease of radial expansive force after PLA degradation was within 5% of the original force in the hybrid stent, but the PLA stent did not create effective radial expansive force. Hybrid stents, even after PLA degradation, exhibited a linear response in radial expansive force, within the range of 15% diameter reduction. The metallic component of the heat-processed hybrid stent was easily unraveled by pulling out the wire. CONCLUSION: The hybrid stent comprising a stainless-steel wire and a PLA fiber appears to provide effective radial expansive force and retrievability.

Study of the physical properties of expandable metallic stents.

The expansile force of self-expanding metallic stents is currently estimated only by wall-distending pressure (P). We estimated the expansile force of the stent not only by P but also by F, the degree of embedding into the vessel wall defined as force per unit length of wire. P and F were thought to be useful in selecting the best stent.

Gadolinium-enhanced magnetic resonance imaging after percutaneous vertebroplasty does not improve the short-term prediction of new compression fractures.

PURPOSE: To investigate the relationships between contrast-enhanced magnetic resonance imaging (MRI) findings and new compression fractures occurring after percutaneous vertebroplasty (PVP) in order to determine the necessity of contrast-enhanced MRI. MATERIAL AND METHODS: The material comprised 13 consecutive patients (27 vertebrae) with compression fractures who underwent vertebroplasty. Twenty-nine adjacent vertebrae were monitored for new compression fractures. We performed contrast-enhanced MRI within the 5 days following PVP. RESULTS: The 29 adjacent vertebrae displayed 10 enhanced lesions and 19 vertebral bodies without enhancement-unenhanced lesions on MRI within the 5 days after PVP. In 4 out of 10 vertebrae, enhanced lesions were seen within the 5 days after PVP, but no abnormalities were seen on preoperative MRI. In these 4 vertebrae, new compression fractures were seen within the 1 month following PVP. In the other 6 vertebrae, enhanced lesions were seen within the 5 days after PVP, and these signal changes were detected by preoperative MRI in the same area. In 3 of these 6 vertebrae, new compression fractures occurred at 4, 8, and 9 months after PVP, respectively. However, all of the enhanced lesions were detectable on unenhanced MRI, which was conducted at the same time as enhanced MRI. CONCLUSION: New compression fractures after PVP may be predicted with early postoperative MRI. Contrast-enhanced MRI does not improve detection of the new lesions.

Percutaneous vertebroplasty for compression fracture: analysis of vertebral body volume by CT volumetry.

PURPOSE: To evaluate the relationships between volume of vertebral bodies with compression fracture (measured by CT volumetry) before percutaneous vertebroplasty, the amount of bone cement injected, and the effect of treatment. MATERIAL AND METHODS: We examined 49 consecutive patients, with 104 vertebral body compression fractures, who underwent percutaneous injection of bone cement. Vertebral body volume was measured by CT volumetry. The patient's pain level was assessed using a visual analog scale (VAS) before and after the procedure. Improvement in VAS was defined as the decrease in VAS after the procedure. Relationships between vertebral body volume, the amount of bone cement, and the effect of treatment were evaluated using Pearson's correlation coefficient test. RESULTS: Average vertebral body volume was 26.3 +/- 8.1 cm3; average amount of bone cement was 3.2 +/- 1.1 ml; and average improvement in VAS was 4.9 +/- 2.7. The vertebral body volume was greater if a larger amount of bone cement was injected. There was a significant positive correlation between vertebral body volume and amount of bone cement (r = 0.44; P < 0.0001). However, there was no correlation between vertebral body volume and improvement in VAS, or between amount of bone cement and improvement in VAS. CONCLUSION: In percutaneous vertebroplasty for vertebral body compression fracture, there is a positive correlation between vertebral body volume and amount of bone cement, but improvement in VAS does not correlate with vertebral body volume or amount of bone cement.

Water jet angioplasty--an experimental study.

The usefulness and safety of water jet angioplasty was studied in vitro, using agar phantom and autopsied aorta, and in vivo in acute and chronic arterial occlusions in mongrel dogs. At an injection rate of 1.0 ml/s, the water jet produced erosion of the agar surface when the distance between the catheter and the agar was 1 mm. With an injection rate of 1.5 ml/s, erosion was produced at a distance of 15 mm from the catheter tip. When the water jet was directed at an arterial wall, intimal ablation and ruptured elastic fibers were found histopathologically. A smaller angle between the vascular wall and the catheter was associated with less vascular damage. In vivo, water jet angioplasty was effective against acute obstructions, but not against chronic obstructions. These results suggest that water jet angioplasty may be effective against arterial obstruction due to acute thrombus.

Symptomatic improvement in dyspnea following tracheobronchial metallic stenting for malignant airway obstruction.

PURPOSE: To investigate the value and limitation of Gianturco expandable metallic stenting for patients with dyspnea due to stenotic tracheobronchial lesions associated with malignancies. MATERIAL AND METHODS: We treated 55 lesions of 44 patients with obstructing stenotic tracheobronchial lesions related to end-stage malignancies by Gianturco expandable metallic stents (EMSs). RESULTS: In 42 of 44 patients, the dyspnea subjectively improved after the procedure (95.5%). An improvement over one grade of the Hugh-Jones classification was shown in 79.5% (35/44); in 80% (20 of 25 patients) with intraluminal tumor and in 78.9% (15 of 19 patients) with extrinsic compression. Seven of the 44 patients developed dyspnea related to re-stenosis of 10 lesions and 1 of these patients developed dyspnea related to re-re-stenosis during follow-up. The mean duration of survival was 4.3 months in patients who underwent stenting. No significant differences in survival rates and primary patency rates were seen in patients with extrinsic compression compared to patients with intraluminal tumors. CONCLUSION: Gianturco EMS therapy was valuable in patients who suffered from dyspnea due to airway stenosis causing obstruction.

A new liquid embolic material for liver tumors.

PURPOSE: To evaluate the feasibility of a new liquid embolic material, Onyx, for treating liver tumors. MATERIAL AND METHODS: Onyx is a mixture of 6% (w/v) ethylene-vinyl-alcohol copolymer dissolved in anhydrous dimethyl sulfoxide (DMSO) with 28% (w/v) tantalum powder. In addition to 6% Onyx, we also tried 4%, 2% and 1% solutions, prepared by adjusting the amount of DMSO. We used 15 white rabbits with liver tumors created by percutaneous injection of VX2 tumor cells. In 4 groups with 3 rabbits in each, the liver arteries were embolized with 6%, 4%, 2% and 1% Onyx, respectively, and in 3 rabbits DMSO alone was injected. The injections were performed just proximal to the bifurcation of the proper hepatic artery, followed by celiac arteriography. Post mortem, the livers were examined by soft-tissue radiography, and liver-tissue section microscopy. RESULTS: The maximum number of arterial branching points passed by embolic material in either the right or left hepatic arteries was 11, 15 and 16, for 6%, 4% and 2% Onyx, respectively, but was non-measurable for 1% Onyx. Minimum diameters of arteries reached by 6%, 4%, 2% and 1% Onyx in tumorous areas were 40 microm, 35 microm, 20 microm and 10 microm, respectively, and in non-tumorous areas 35 microm, 5 microm, 5 microm and 5 microm, respectively. CONCLUSION: This study suggests that Onyx may be feasible for treatment of hepatic tumors.

[An animal experiment on arterial wall reaction to stents coated with gold, silver and copper].

Expandable metallic stents coated with gold, silver, and copper, and bare stainless steel stents were implanted into the abdominal aorta of eight dogs to determine their effect on the vessel wall. The animals were observed for two weeks. Abdominal angiograms were taken every week. The dogs were then killed for macroscopic and histopathological examination. The results were as follows. (1) The stents coated with gold and the noncoated stainless steel stents showed less histopathologic change than the other stents. (2) The stents coated with copper were associated with severe erosion of the vessel wall and marked thrombus formation.

[Percutaneous placement of intraluminal stent-graft for aortic dissection: experimental study].

Highly porous fabric vascular grafts fabricated of ultrafine polyester fibers (UFPF-graft; porosity, 7,000 ml, 9,000 ml, 11,000 ml at 120 mmHg) were attached between two Gianturco stents connected with two stainless steel struts. UFPF-grafts with two Gianturco stents were placed into the aortas of six adult mongrel dogs without firm contact with the luminal surface. From two days to four months after placement, all the UFPF-grafts were completely sealed with fresh thrombus or neointima. Within two months, complete endothelialization was observed on both surfaces of the neointima. In three dogs, aortic dissections were created experimentally. Then an UFPF-graft (porosity, 9,000 ml) with two Gianturco stents was placed at the site of entry of the dissection, followed by additional Gianturco stents to expand the UFPF-graft. X-ray angiography showed that the entries were closed immediately after placement, and false lumens disappeared within one hour after placement. These results indicated that the method has the possibility of treating aortic dissection with complete sealing of the fabric by the neointima.