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Chronic otitis media is often connected to Eustachian tube dysfunction. As successful treatment cannot be guaranteed with the currently available options, the aim is to develop a stent for the Eustachian tube (ET). Over the course of this development, different prototypes were generated and tested in ex vivo experiments. Four different prototypes of an ET stent and one commercially available coronary stent were implanted in the ET of seven human donor bodies. The position of the stents was verified by cone beam CT. The implanted ETs were harvested, embedded in resin and ground at 200 µm steps. Resulting images of the single steps were used to generate 3D models. The 3D models were then evaluated regarding position of the stent in the ET, its diameters, amount of squeezing, orientation of the axes and other parameters. Virtual reconstruction of the implanted ET was successful in all cases and revealed one incorrect stent placement. The cross-section increased for all metal stents in direction from the isthmus towards the pharyngeal orifice of the ET. Depending on the individual design of the metal stents (open or closed design), the shape varied also between different positions along a single stent. In contrast, the cross-section area and shape remained constant along the polymeric prototype. With the current investigation, insight into the behavior of different prototypes of ET stents was gained, which can help in defining the specifications for the intended ET stent.

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Polylactic acid (PLA) has been widely used in the field of medical devices. However, few studies have been conducted on the extrusion molding of PLA micro tubes for the preparation of biodegradable vascular stents. In this paper, the extrusion die for PLA single-cavity micro tubes was designed and manufactured by micro-extrusion theory. Taking the outer diameter, wall thickness, wall thickness uniformity and ovality of micro tubes as the evaluation index, the influence of the main extrusion process parameters on the evaluation index was studied. The experimental results show that the outer diameter and wall thickness are significantly affected by screw speed, pulling speed and gas flow rate; extrusion process parameters have little influence on wall thickness uniformity and ovality within a certain range, which mainly depends on the processing accuracy and assembly accuracy of the extrusion die. However, excessively high screw speed and low gas flow rate have significant effects on ovality. Finally, according to the influence of extrusion process parameters on the evaluation index, a series of micro tubes that meet the design requirements are extruded and carved into vascular stent structures.

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Implantation of cardiovascular stents is an important therapeutic method to treat coronary artery diseases. Bare-metal and drug-eluting stents show promising clinical outcomes, however, their permanent presence may create complications. In recent years, numerous preclinical and clinical trials have evaluated the properties of bioresorbable stents, including polymer and magnesium-based stents. Three-dimensional (3D) printed-shape-memory polymeric materials enable the self-deployment of stents and provide a novel approach for individualized treatment. Novel bioresorbable metallic stents such as iron- and zinc-based stents have also been investigated and refined. However, the development of novel bioresorbable stents accompanied by clinical translation remains time-consuming and challenging. This review comprehensively summarizes the development of bioresorbable stents based on their preclinical/clinical trials and highlights translational research as well as novel technologies for stents (e.g., bioresorbable electronic stents integrated with biosensors). These findings are expected to inspire the design of novel stents and optimization approaches to improve the efficacy of treatments for cardiovascular diseases.

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Microinjection molding technology for degradable polymer stents has good development potential. However, there is a very complicated relationship between molding quality and process parameters of microinjection, and it is hard to determine the best combination of process parameters to optimize the molding quality of polymer stent. In this study, an adaptive optimization method based on the kriging surrogate model is proposed to reduce the residual stress and warpage of stent during its injection molding. Integrating design of experiment (DOE) methods with the kriging surrogate model can approximate the functional relationship between design goals and design variables, replacing the expensive reanalysis of the stent residual stress and warpage during the optimization process. In this proposed optimization algorithm, expected improvement (EI) is used to balance local and global search. The finite element method (FEM) is used to simulate the micro-injection molding process of polymer stent. As an example, a typical polymer vascular stent ART18Z was studied, where four key process parameters are selected to be the design variables. Numerical results demonstrate that the proposed adaptive optimization method can effectively decrease the residual stress and warpage during the stent injection molding process.

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PURPOSE: To compare treatment outcomes, more specifically patency rate, of polymeric and metallic stents for malignant ureteral obstruction. PATIENTS AND METHODS: Between August 2007 and September 2017, we retrospectively analyzed the data of 92 patients (126 ureters) having a diagnosis of malignant extrinsic ureteral obstruction treated with indwelling ureteral stents (polymeric and full-length metallic stents). Of these patients, 35 (54 ureters) were treated with polymeric stents and 57 (72 ureters) with a Resonance® metallic stent. The observation period was censored to 1 year. Survival rate in cases of malignant ureteral obstruction was calculated, and the relationship between the causes of ureteral obstruction, the stent type, and the patency rate was evaluated. RESULTS: The median observation period was 145 days, with a median survival time of 258 days. The stent patency rate was 70.9% at 1 year, regardless of stent type. Stent occlusion was observed in 20 patients (33 ureters). According to stent type, occlusion of the polymeric and metallic stents was identified in 12 (22%) and 8 (11%) cases, respectively. The clinical features associated with stent failure were assessed. In univariate analysis, the patency rate was significantly better for the metallic stent than for the polymeric stent (1-year patency rate; 78.4%, 61.1%, respectively, HR, 2.15; 95% CI, 1.07-4.33; p=0.031). However, the patency rate among patients with abdominal dissemination, lymph node metastasis, and direct compression by tumor was not significantly different. CONCLUSION: Indwelling ureteral stents, particularly metallic stents, are effective for the treatment of malignant ureteral obstruction.

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OBJECTIVES: To report the treatment outcomes of patients with extrinsic ureteral obstruction treated with metallic stents and to identify the factors predicting stent failure. METHODS: A total of 52 patients with extrinsic ureteral obstruction as a result of malignancy (66 ureters) were treated with metallic stents (Resonance® ) and included in the study. The median observation period was 118 days. RESULTS: The median survival time of these patients was 210 days, and the stent patency rate was 86.0% at 6 months and 60.0% at 1 year. Eight (15.4%) patients underwent nephrostomy as a result of stent failure. The occlusion rate of bilateral ureteral obstructed cases was significantly higher than that of unilateral cases. There was no correlation between the preoperative serum creatinine level, causes of ureteral occlusions (compression by tumor, lymph node metastasis, peritoneal dissemination), obstructed site (upper, middle, lower ureter) and stent failure. CONCLUSIONS: Metallic stents are excellent in maintaining patency compared with the conventional stents. Therefore, they can be used as first-line treatment of malignant ureteral obstructions.

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OBJECTIVES: The aim of this fractal bifurcation bench study was to compare provisional bifurcation stenting with a "re-POT" sequence, comprising a proximal optimizing technique (POT), side branch inflation, and final POT, between a bioresorbable vascular scaffold (BVS) and a metallic stent. BACKGROUND: Re-POT proved significantly better than kissing balloon inflation in maintaining circular geometry without overstretch in metal stents, while significantly reducing side branch ostium strut obstruction and global strut malapposition. This should be useful for BVSs, which are more easily breakable. METHODS: Twenty left main-like and 20 left anterior descending-like fractal coronary bifurcation bench models used 10 each 2.5 × 24 mm and 3.5 × 24 mm Absorb (Ab) BVSs and 10 each 2.5 × 24 mm and 3.5 × 24 mm XIENCE Xpedition (XX) metal stents, implanted by re-POT, with optical coherence tomographic analysis at each step and micro-computed tomographic analysis of Ab devices to detect strut fracture. RESULTS: With Ab devices, re-POT reduced percentage strut malapposition close to XX rates (0.8 ± 0.7% vs. 0.0 ± 0.0%, p < 0.05; 3.5 ± 1.7% vs. 0.3 ± 0.6%, p < 0.05), conserving proximal circularity (elliptical ratio, 1.04 vs. 1.03 and 1.04 vs. 1.04; p = NS). Mean post-re-POT proximal expansion was 0.6 ± 0.1 mm (+21.6 ± 2.1%) for 2.5-mm and 1.0 ± 0.1 mm (+23.6 ± 2.2%) for 3.5-mm Ab devices, with only 1 strut fracture (left anterior descending-like bench). Side branch ostium strut obstruction was greater with Ab scaffolds than XX stents: 41.1 ± 9.4% versus 16.4 ± 8.1% (p < 0.05) and 31.8 ± 3.2% versus 10.0 ± 5.3% (p < 0.05), respectively, for 2.5- and 3.5-mm scaffolds and stents. Ab scaffolds showed 2 ± 1% moderate but significant late recoil as of 1 h, reaching 4 ± 2% by 24 h (p < 0.05). CONCLUSIONS: Re-POT optimized most Ab provisional bifurcation treatments, without fracture, respecting fractal geometry, and without exceeding 1.0-mm proximal differential diameter.

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