Development of 3D Printed Biodegradable, Entirely X-ray Visible Stents for Rabbit Carotid Artery Implantation

Biodegradable stents are considered a promising strategy for the endovascular treatment of cerebrovascular diseases. The visualization of biodegradable stents is of significance during the implantation and long-term follow-up. Endowing biodegradable stents with X-ray radiopacity can overcome the weakness of intrinsic radioparency of polymers. Hence, this work focuses on the development of an entirely X-ray visible biodegradable stent (PCL-KIO3 ) composed of polycaprolactone (PCL) and potassium iodate via physical blending and 3D printing. The in vitro results show that the introduction of potassium iodate makes the 3D-printed PCL stents visualizable under X-ray. So far, there is inadequate study about polymeric stent visualization in vivo. Therefore, PCL-KIO3 stents are implanted into the rabbit carotid artery to evaluate the biosafety and visibility performance. During stent deployment, the visualization of the PCL-KIO3 stent effectively helps to understand the position and dilation status of stents. At 6-month follow-up, the PCL-KIO3 stent could still be observed under X-ray and maintains excellent vessel patency. To sum up, this study demonstrates that PCL-KIO3 stent may provide a robust strategy for biodegradable stent visualization.

Research on the Current Application Status of Magnesium Metal Stents in Human Luminal Cavities

The human body comprises various tubular structures that have essential functions in different bodily systems. These structures are responsible for transporting food, liquids, waste, and other substances throughout the body. However, factors such as inflammation, tumors, stones, infections, or the accumulation of substances can lead to the narrowing or blockage of these tubular structures, which can impair the normal function of the corresponding organs or tissues. To address luminal obstructions, stenting is a commonly used treatment. However, to minimize complications associated with the long-term implantation of permanent stents, there is an increasing demand for biodegradable stents (BDS). Magnesium (Mg) metal is an exceptional choice for creating BDS due to its degradability, good mechanical properties, and biocompatibility. Currently, the Magmaris® coronary stents and UNITY-BTM biliary stent have obtained Conformité Européene (CE) certification. Moreover, there are several other types of stents undergoing research and development as well as clinical trials. In this review, we discuss the required degradation cycle and the specific properties (anti-inflammatory effect, antibacterial effect, etc.) of BDS in different lumen areas based on the biocompatibility and degradability of currently available magnesium-based scaffolds. We also offer potential insights into the future development of BDS.

A Battery Method to Enhance the Degradation of Iron Stent and Regulating the Effect on Living Cells

Iron is a promising material for cardiovascular stent applications, however, the low biodegradation rate presents a challenge. Here, a dynamic method to improve the degradation rate of iron and simultaneously deliver electrical energy that could potentially inhibit cell proliferation on the device is reported. It is realized by pairing iron with a biocompatible hydrogel cathode in a cell culture media-based electrolyte forming an iron-air battery. This system does not show cytotoxicity to human adipose-stem cells over a period of 21 days but inhibits cell proliferation. The combination of enhanced iron degradation and inhibited cell proliferation by this dynamic method suggests it might be an approach for restenosis inhibition of biodegradable stents.

Bio-Degradable Stents: Primary Experience in a Tertiary Hepatopancreaticobiliary Center in the United Kingdom

BACKGROUND

Management of benign biliary strictures (BBS) post bilioenteric anastomoses requires a multidisciplinary approach including surgical, radiological, and/or endoscopic input. Patients often need multiple hospital visits for treatment with the long-term possibility of restenosis. Conventionally BBS have been treated with serial percutaneous transhepatic biliary dilatations necessitating repeat procedures for drain exchange or removal. Surgery may become necessary in refractory strictures. In the last decade, there have been increasing reports of the use of biodegradable stents (BDS) in treating biliary strictures mainly to address the need for repeated procedures for drain exchange.

AIM

 This study aimed to report the early outcomes in patients with BBS treated with BDS.

METHODS

Retrospective analysis of prospectively collected data was performed in patients who had a bilioenteric anastomosis presenting with an anastomotic stricture and were intended to be treated with BDS. The primary endpoints reported were technical success (defined as a successful resolution of stricture on repeat cholangiogram) and clinical success (defined as the absence of repeated cholangitis). Clavien-Dindo (CD) grade of complication was reported.

RESULTS

Twelve patients presented with BBS and nine patients had BDS. Three patients were not considered suitable for BDS due to a non-traversable stricture and had surgery. The male-female ratio was 1:2. There was 100% technical and clinical success with one patient having stent migration not needing intervention. The procedure took an average of 45 min. In seven (77.7%) patients, it was safely performed under local anesthesia with sedation. Two patients preferred general anesthesia. There was no restenosis noted at a median follow-up of 11 months.

CONCLUSION

The use of BDS in the treatment of BBS is a safe and effective procedure. Longer-term follow-up with multi-institutional reporting on a national database is needed to assess its long-term benefits.

The differences between surface degradation and bulk degradation of FEM on the prediction of the degradation time for poly (lactic-co-glycolic acid) stent

The degradation time is a crucial factor in evaluating the performance of poly (lactic-co-glycolic acid) (PLGA) stents. Bulk degradation mode was commonly used to analyze the stent degradation behavior by finite element approach. However, the PLGA stents may present surface degradation more than bulk degradation under certain conditions, which will greatly affect the degradation time after implantation. In this study, the degradation processes of the poly (lactic-co-glycolic acid) stent were reproduced utilizing finite element analysis. Both bulk degradation and surface degradation modes were considered. The correlation between tensile stress and degradation rate was investigated. The degradation time was analyzed selectively. The stress distribution, fracture, and mass loss were also compared between bulk degradation mode and surface degradation mode. The simulation results showed that, in both evolution modes, the degradation began at the 'peak-valley' region and fracture occurred at the cross of links and rings. Additionally, high levels of Von-Mises stress were observed in these two regions. Compared with bulk degradation, the fracture time of the stent was delayed by 63% in the surface degradation mode. In conclusion, the mass loss rate and scaffolding period showed great differences between surface degradation and bulk degradation. Based on this study, it is suggested that bulk degradation mode is not applicable to the case of inadequate water uptake mode, such as the tracheal stent degradation process. More experimental research should be carried out to accurately predict the scaffolding period after implantation. The mechanical properties of the fracture zone should be strengthened.

Tracheobronchial stent sizing and deployment practices airway stenting practices around the world: a survey study

Background

Tracheobronchial stents types, uses, techniques for deployment and extraction have practice variations around the world.

Methods

We collected responses by sending an online survey of 8 questions to world interventional bronchology member societies and social media groups.

Results

There were 269 respondents from 47 countries. Europe had 97 respondents from 22 countries. There were 8 respondents from Australia, 7 from Africa (3 countries) and 7 from 4 countries in South America (SA). North America (NA) had 72 respondents from 3 countries. Asia had 78 respondents from 14 countries. For stent placements 15% [41] used fiberoptic bronchoscope (FB) only. Rigid bronchoscopy (RB) was solely utilized by 38% [102]. Forty-six percent [123] used a combination of RB and FB (P value <0.00001). For stent extraction 13% [19] used FB alone, 57% [85] used RB, and 36% [54] used a combination of RB and FB (P value <0.00001). Placement of stents were 50.5% [135] only by direct visualization. Twenty-three percent [61] always used fluoroscopic guidance. Twenty-six-point-five percent [71] used fluoroscopy in certain cases (P value <0.00001). Sixty percent [162] decided stent sizing by measurements of stenotic and non-stenotic areas on radiology. Twelve percent [32] respondents used sizing devices. Sixty-five percent [177] used a ruler and bronchoscope to measure stenotic areas. Thirty-eight percent [104] used visual estimation and experience. Seven percent [19] used serial balloon dilatation size. To prevent clogging of stents, 22% [59] prescribed mucolytics. Seventy-three percent [195] nebulized saline, 26% [70] had Mucomyst Nebulization, 24% [65] Nebulized bronchodilators and other methods 11% [30] were advised. Covered self-expandable metal stents (SEMS) 44% was the commonest type of stent used around the world. Silicone stents 37%, Y stents 15%, uncovered SEMS 12%, Montgomery T tube 5% followed. Polyflex stents 3% and custom-made stents 3% were least used. Biodegradable stents were used by 7.5%, and not used by 92.5%.

Conclusions

Tracheobronchial stent practice norms have slowly evolved, but its practice variations lack uniformity, and have sparse evidence-based studies for its direction.

[The study of effectiveness of polyhydroxyalkanoates based biodegradable stents in ureteropelvic segment pyeloplasty]

INTRODUCTION

Among urologic diseases, ureteropelvic segment stenosis with hydronephrosis is a common indication for instrumental or surgical correction. The restriction of urine flow with dilatation proximal to obstruction develops in 6.5-37% of cases at different times after the ureteral reconstruction. All this urges to develop and improve stents and search for effective ways to place stents and control their function.

AIM

To investigate the effectiveness of polyhydroxyalkanoates based biodegradable stent compared with a commercial analogue in upper urinary tract drainage after ureteropelvic segment pyeloplasty.

MATERIALS AND METHODS

Morphological and functional changes in the stented ureter were investigated in 45 male rabbits of "Soviet chinchilla" breed weighing 4550-5200 g that underwent stenting of ureteropelvic segment (UPS). The study used polymeric stents based on poly-3-hydroxybutyrate, poly-4-gidroksibutirotom P (3GB/4GB) and a mixture of poly-3-hydroxybutyrate with polycaprolactone II (3GB)/PCL with the inclusion of PCL 75%; the control material was polyurethane stents. Morphologic evaluation was conducted on ureteral fragments and UPSs in the area of the stent placement at 7, 14 and 28 days after operation.

RESULTS

Throughout the experiment, excretory urography and spiral tomography in experimental groups showed no changes in the pelvicalyceal system after placing polymeric stents. The morphologic examination in the experimental group at day 28 after surgery revealed preserved longitudinal folding of ureteral mucosa and absence of muscle hypertrophy. Transitional epithelium had no signs of atrophy and desquamation, its mean thickness was 112.4+/-8.5 mm, whereas in the control group a productive inflammation resulting in sclerosis was found to develop.

CONCLUSIONS

We conducted a comparative study of morphologic and functional changes in rabbit ureters after stenting using polyurethane stents (control group) and polymeric stents made of poly-3-hydroxybutyrate, poly-4-hydroxybutyrate II (3GB /4GB) and a mixture of poly-3-hydroxybutyrate with polycaprolactone II (3Gb)/PCL (experimental group). Despite the difference in physical and mechanical properties of biodegradable PGA-based stents, the tissue response to both types of stent was comparable. Ureteral wall preserved longitudinal folds, there was no muscle layer hypertrophy, and mucous membrane had smooth contours with a uniform thickness of the transitional epithelium, whereas in the control group a productive inflammation resulting in sclerosis was found to develop.

Polymeric Biodegradable Stent Insertion in the Esophagus

Esophageal stent insertion has been used as a well-accepted and effective alternative to manage and improve the quality of life for patients diagnosed with esophageal diseases and disorders. Current stents are either permanent or temporary and are fabricated from either metal or plastic. The partially covered self-expanding metal stent (SEMS) has a firm anchoring effect and prevent stent migration, however, the hyperplastic tissue reaction cause stent restenosis and make it difficult to remove. A fully covered SEMS and self-expanding plastic stent (SEPS) reduced reactive hyperplasia but has a high migration rate. The main advantage that polymeric biodegradable stents (BDSs) have over metal or plastic stents is that removal is not require and reduce the need for repeated stent insertion. But the slightly lower radial force of BDS may be its main shortcoming and a post-implant problem. Thus, strengthening support of BDS is a content of the research in the future. BDSs are often temporarily effective in esophageal stricture to relieve dysphagia. In the future, it can be expect that biodegradable drug-eluting stents (DES) will be available to treat benign esophageal stricture, perforations or leaks with additional use as palliative modalities for treating malignant esophageal stricture, as the bridge to surgery or to maintain luminal patency during neoadjuvant chemoradiation.

The effect of treatment temperature on corrosion resistance and hydrophilicity of an ionic liquid coating for Mg-based stents

Mg alloys are attractive candidate materials for biodegradable stents. However, there are few commercially available Mg-based stents in clinical use because Mg alloys generally undergo rapid localized corrosion in the body. In this study, we report a new surface coating for Mg alloy AZ31 based on a low-toxicity ionic liquid (IL), tributyl(methyl)phosphonium diphenyl phosphate (P1,4,4,4 dpp), to control its corrosion rate. Emphasis is placed on the effect of treatment temperature. We showed that enhancing the treatment temperature provided remarkable improvements in the performances of both corrosion resistance and biocompatibility. Increasing treatment temperature resulted in a thicker (although still nanometer scale) and more homogeneous IL film on the surface. Scanning electron microscopy and optical profilometry observations showed that there were many large, deep pits formed on the surface of bare AZ31 after 2 h of immersion in simulated body fluid (SBF). The IL coating (particularly when formed at 100 °C for 1 h) significantly suppressed the formation of these pits on the surface, making corrosion occur more uniformly. The P1,4,4,4 dpp IL film formed at 100 °C was more hydrophilic than the bare AZ31 surface, which was believed to be beneficial for avoiding the deposition of the proteins and cells on the surface and therefore improving the biocompatibility of AZ31 in blood. The interaction mechanism between this IL and AZ31 was also investigated using ATR-FTIR, which showed that both anion and cation of this IL were present in the film, and there was a chemical interaction between dpp(-) anion and the surface of AZ31 during the film formation.

A novel design biodegradable stent for use in congenital heart disease: mid-term results in rabbit descending aorta

OBJECTIVES

This study evaluates the feasibility of delivery and deployment of low and medium molecular weight (LMW and MMW, respectively) double-opposing helical (DH) poly-l-lactic acid biodegradable stent (BDS) in rabbit descending aorta (DAO). Secondary objectives were to assess patency and inflammation of stented vessels at 9 months and to investigate safety following intentional embolization of stent fragments in DAO.

BACKGROUND

A BDS that will relieve aortic obstruction and disappears as the child grows older allowing for preservation of aortic wall elasticity and natural growth of aorta will be ideal to treat Coarctation (CoA). BDS have never been evaluated in the DAO.

METHODS

Seven New Zealand white rabbits underwent implantation of DH-LMW (n = 7), DH-MMW (n = 3), and metal stents (n = 7) in DAO. BDS fragments were intentionally embolized into DAO in two rabbits.

RESULTS

All stents were deployed via a 6-French sheath. Five BDS covered the origin of major DAO side branches. Angiography and intravascular ultrasound showed good stent apposition to the wall of DAO with minimal luminal loss at 9 months follow-up. All stents had minimal neointimal hyperplasia on histopathology. Adverse events included 1 death, 1 aortic aneurysm, and lower extremity ulceration due to self-mutilation in an embolization rabbit.

CONCLUSIONS

Pilot study confirms the feasibility of delivery and deployment of up to 6-millimeter diameter DH BDS in rabbit DAO. Stent integrity with DH design was maintained at 9 months with minimal vessel inflammation. Potential morbidity due to embolized BD fragments cannot be ruled out and needs further evaluation.

Biodegradable metals for cardiovascular stent application: interests and new opportunities

During the last decade, biodegradable metallic stents have been developed and investigated as alternatives for the currently-used permanent cardiovascular stents. Degradable metallic materials could potentially replace corrosion-resistant metals currently used for stent application as it has been shown that the role of stenting is temporary and limited to a period of 6-12 months after implantation during which arterial remodeling and healing occur. Although corrosion is generally considered as a failure in metallurgy, the corrodibility of certain metals can be an advantage for their application as degradable implants. The candidate materials for such application should have mechanical properties ideally close to those of 316L stainless steel which is the gold standard material for stent application in order to provide mechanical support to diseased arteries. Non-toxicity of the metal itself and its degradation products is another requirement as the material is absorbed by blood and cells. Based on the mentioned requirements, iron-based and magnesium-based alloys have been the investigated candidates for biodegradable stents. This article reviews the recent developments in the design and evaluation of metallic materials for biodegradable stents. It also introduces the new metallurgical processes which could be applied for the production of metallic biodegradable stents and their effect on the properties of the produced metals.