Drug-eluting non-vascular stents for localised drug targeting in obstructive gastrointestinal cancers

Coatings for Cardiovascular Stents-An Up-to-Date Review

Cardiovascular diseases (CVDs) increasingly burden health systems and patients worldwide, necessitating the improved awareness of current treatment possibilities and the development of more efficient therapeutic strategies. When plaque deposits narrow the arteries, the standard of care implies the insertion of a stent at the lesion site. The most promising development in cardiovascular stents has been the release of medications from these stents. However, the use of drug-eluting stents (DESs) is still challenged by in-stent restenosis occurrence. DESs' long-term clinical success depends on several parameters, including the degradability of the polymers, drug release profiles, stent platforms, coating polymers, and the metals and their alloys that are employed as metal frames in the stents. Thus, it is critical to investigate new approaches to optimize the most suitable DESs to solve problems with the inflammatory response, delayed endothelialization, and sub-acute stent thrombosis. As certain advancements have been reported in the literature, this review aims to present the latest updates in the coatings field for cardiovascular stents. Specifically, there are described various organic (e.g., synthetic and natural polymer-based coatings, stents coated directly with drugs, and coatings containing endothelial cells) and inorganic (e.g., metallic and nonmetallic materials) stent coating options, aiming to create an updated framework that would serve as an inception point for future research.

Biosynthetic Plastics as Tunable Elastic and Visible Stent with Shape-Memory to Treat Biliary Stricture

Common biliary tract is ≈4 mm in diameter to deliver bile from liver to small intestine to help digestion. The abnormal narrowing leads to severe symptoms such as pain and nausea. Stents are an effective treatment. Compared with non-degradable stents which require repeated removal, biodegradable stents have the advantage of reducing secondary injury related to endoscopic operation and patient burden. However, current biodegradable materials may cause tissue hyperplasia and the treatment method does not target etiology of stricture. So recurrence rates after biodegradable stent implantation are still high. Here, a biodegradable helical stent fabricated from biosynthetic P(3HB-co-4HB) is reported. Tunable properties can be acquired through altering culture substrates. Stent shows shape memory in various solvents. The stent has an optimized design with helical structure and outer track. The self-expanding of helical structure and double drainage realized by outer track greatly improve drainage of bile. Importantly, stent-loading triamcinolone acetonide can inhibit proliferation of fibroblasts and reduce incidence of restricture. Therapeutic effect is also demonstrated in minipigs with biliary stricture. The results of minipig experiments show that biliary duct in treatment group is unobstructed and tissue hyperplasia is effectively inhibited.

Cardiovascular Stents: Types and Future Landscape

One of the prominent reasons for mortality and morbidity worldwide is coronary artery disease (CAD), an ailment that manifests itself by the narrowing of the artery with the deposition of plaque. The definitive mode of action for dealing with this condition is using a medical device known as a stent at the affected location. This extremely important tubular equipment helps tremendously with vessel support. It also helps by keeping the path of blood flow clear for the heart muscle masses, its crucial nutrients, and oxygen supply. Several generations of stents have been continuously developed to improve patient outcomes and reduce side effects post-stent implantation. As we move from bare metal stents (BMSs) to drug-eluting stents (DESs) and, more recently, to bioabsorbable stents, the research area continues to develop. The use of this biomedical device has increased the standard of living in many cases; therefore, it is much needed to work on the possible growth areas in the cardiovascular stents and improve them to such an extent that the patients suffering from cardiovascular ailments get to live a comfortable life. Most articles deal with stents that are available for current use and their various types. They also cover the topic of stent optimization, as it is one of the key factors in enhancing stent usability and plays a prominent role in optimizing stent placement in the vessels of the body. To keep in touch with advances in stent technology over the past few decades, this article reviews advances in the devices, working on how available stents can be optimized to create new stents.

Endoscopic Stenting for Malignant Dysphagia in Patients with Esophageal Cancer

Malignant dysphagia is a common problem in patients with esophageal cancer. Endoscopic stenting can resolve dysphagia caused by malignant stricture; however, controversy exists regarding the use of esophageal stenting for the treatment of malignant stricture, including whether stenting or radiotherapy is superior, whether stenting before or after radiotherapy is safe, whether stenting before or after chemotherapy is safe, and whether low-radial-force stents are safer than conventional stents. Among treatment options for malignant dysphagia, stenting may have some disadvantages in terms of pain relief and the risk of adverse events compared with radiotherapy and in terms of survival compared with gastrostomy. Additionally, the risk of stent-related adverse events is significantly associated with prior radiotherapy. The risk of perforation is especially high when a radiation dose of >40 Gy is delivered to the esophagus after stenting, whereas perforation is not associated with prior chemotherapy or additional chemotherapy after stenting. Nevertheless, stenting remains an important palliative option, especially for patients with a short life expectancy and a strong desire for oral intake, because stenting can facilitate a more rapid improvement in dysphagia than radiotherapy or gastrostomy. The application of a low-radial-force stent should be considered to reduce the risk of adverse events, especially in patients with prior radiotherapy.

Restoring endothelial function: shedding light on cardiovascular stent development

Complete endothelialization is highly important for maintaining long-term patency and avoiding subsequent complications in implanting cardiovascular stents. It not only refers to endothelial cells (ECs) fully covering the inserted stents, but also includes the newly formed endothelium, which could exert physiological functions, such as anti-thrombosis and anti-stenosis. Clinical outcomes have indicated that endothelial dysfunction, especially the insufficiency of antithrombotic and barrier functions, is responsible for stent failure. Learning from vascular pathophysiology, endothelial dysfunction on stents is closely linked to the microenvironment of ECs. Evidence points to inflammatory responses, oxidative stress, altered hemodynamic shear stress, and impaired endothelial barrier affecting the normal growth of ECs, which are the four major causes of endothelial dysfunction. The related molecular mechanisms and efforts dedicated to improving the endothelial function are emphasized in this review. From the perspective of endothelial function, the design principles, advantages, and disadvantages behind current stents are introduced to enlighten the development of new-generation stents, aiming to offer new alternatives for restoring endothelial function.

Utilizing 4D Printing to Design Smart Gastroretentive, Esophageal, and Intravesical Drug Delivery Systems

The breakthrough of 3D printing in biomedical research has paved the way for the next evolutionary step referred to as four dimensional (4D) printing. This new concept utilizes the time as the fourth dimension in addition to the x, y, and z axes with the idea to change the configuration of a printed construct with time usually in response to an external stimulus. This can be attained through the incorporation of smart materials or through a preset smart design. The 4D printed constructs may be designed to exhibit expandability, flexibility, self-folding, self-repair or deformability. This review focuses on 4D printed devices for gastroretentive, esophageal, and intravesical delivery. The currently unmet needs and challenges for these application sites are tried to be defined and reported on published solution concepts involving 4D printing. In addition, other promising application sites that may similarly benefit from 4D printing approaches such as tracheal and intrauterine drug delivery are proposed.

Intestinal stents: Structure, functionalization and advanced engineering innovation

Intestinal stents are a palliative treatment option that solves many shortcomings of traditional surgeries for cancer-induced intestinal obstructions. The present review provides an overview of the incidence, clinical manifestations and limitations in the treatment of intestinal cancers. The paper also discusses material property requirements, indications, complications and the future of stent-assisted therapy. The advantages and disadvantages of different materials and processing techniques for intestinal stents are reviewed along with new stent treatment combinations for colorectal cancer. Challenges that require further cooperative studies are also detailed. The future development of intestinal stents will depend on innovation in material designs as well as the utilization of multi-functional strategies and innovative engineering solutions.

Anti-coagulation and anti-hyperplasia coating for retrievable vena cava filters by electrospraying and their performance in vivo

A novel drug eluting retrievable vena cava filter (RVCF) with a heparin-modified poly(ε-caprolactone) (hPCL) coating containing rapamycin was prepared by electrospraying. The in vitro drug release pattern showed that the encapsulated rapamycin in the coating can be sustainably released within one month, whereas activated partial thromboplastin time (APTT) and in vitro cell culture showed that the drug eluting RVCF can effectively extend blood clotting time and inhibit smooth muscle cell (SMC) and endothelial cell (EC) proliferation, respectively. The as-prepared drug eluting RVCF and corresponding commercial RVCF were implanted into the vena cava of sheep. The retrieval operation at a predetermined time point showed that the drug eluting RVCF had a much higher retrieval rate than the commercial RVCF. Comprehensive investigations, including histological, immunohistological and immunofluorescence analyses, on explanted veins were carried out. The results demonstrated that the as-prepared RVCF possessed excellent antihyperplasia properties in vivo, significantly improving the retrieval rate and extending the in vivo dwelling time in sheep. Consequently, the drug eluting RVCF has promising potential for application in the clinic to improve RVCF retrieval rates.

Futuristic Developments and Applications in Endoluminal Stenting

Endoscopic stenting is a well-established option for the treatment of malignant obstruction, temporary management of benign strictures, and sealing transmural defects, as well as drainage of pancreatic fluid collections and biliary obstruction. In recent years, in addition to expansion in indications for endoscopic stenting, considerable strides have been made in stent technology, and several types of devices with advanced designs and materials are continuously being developed. In this review, we discuss the important developments in stent designs and novel indications for endoluminal and transluminal stenting. Our discussion specifically focuses on (i) biodegradable as well as (ii) irradiating and drug-eluting stents for esophageal, gastroduodenal, biliary, and colonic indications, (iii) endoscopic stenting in inflammatory bowel disease, and (iv) lumen-apposing metal stent.

Preparation, characterization and primary evaluation of trilayered biliary stent films for anti-cholangiocarcinoma and anti-biofilm formation

Excessive growth of tumor within biliary wall and formation of biofilm on inner surface of stent can cause restenosis or even obstruction after stent implantation. Therefore, it is important and valuable to develop a new biliary stent for anti-cholangiocarcinoma and anti-biofilm formation. Herein, we designed, prepared and primarily evaluated a new trilayered film for biliary stents consisting of one poly (lactic acid) (PLA) layer loaded with anti-tumor paclitaxel (PTX layer), one middle PLA isolation layer (isolation layer) and one PLA layer loaded with antimicrobial ofloxacin (OFLX layer). It is postulated that the PTX layer releases drug towards biliary wall with tumor, the OFLX layer releases drug towards lumen of bile duct and the isolation layer is used to separate from the PTX layer and the OFLX layer and facilitate drug release in unidirectional way. The prepared trilayered films were characterized in terms of morphology, microstructure, crystallinity and biodegradability. It was found that the films could effectively tune drug release by addition of different amounts of drug or PEG, release PTX and OFLX in opposite directions, effectively inhibit the proliferation of human cholangiocarcinoma RBE cells, the adherence of E. coli and S. aureus and the formation of biofilm in vitro. It is potential that the trilayered films can be used to fabricate a new biliary stent with a dual function of anti-cholangiocarcinoma and anti-biofilm formation.

Structural Design of Vascular Stents: A Review

Percutaneous Coronary Intervention (PCI) is currently the most conventional and effective method for clinically treating cardiovascular diseases such as atherosclerosis. Stent implantation, as one of the ways of PCI in the treatment of coronary artery diseases, has become a hot spot in scientific research with more and more patients suffering from cardiovascular diseases. However, vascular stent implanted into vessels of patients often causes complications such as In-Stent Restenosis (ISR). The vascular stent is one of the sophisticated medical devices, a reasonable structure of stent can effectively reduce the complications. In this paper, we introduce the evolution, performance evaluation standards, delivery and deployment, and manufacturing methods of vascular stents. Based on a large number of literature pieces, this paper focuses on designing structures of vascular stents in terms of “bridge (or link)” type, representative volume unit (RVE)/representative unit cell (RUC), and patient-specific stent. Finally, this paper gives an outlook on the future development of designing vascular stents.

Cardiovascular Stents: A Review of Past, Current, and Emerging Devices

One of the leading causes of morbidity and mortality worldwide is coronary artery disease, a condition characterized by the narrowing of the artery due to plaque deposits. The standard of care for treating this disease is the introduction of a stent at the lesion site. This life-saving tubular device ensures vessel support, keeping the blood-flow path open so that the cardiac muscle receives its vital nutrients and oxygen supply. Several generations of stents have been iteratively developed towards improving patient outcomes and diminishing adverse side effects following the implanting procedure. Moving from bare-metal stents to drug-eluting stents, and recently reaching bioresorbable stents, this research field is under continuous development. To keep up with how stent technology has advanced in the past few decades, this paper reviews the evolution of these devices, focusing on how they can be further optimized towards creating an ideal vascular scaffold.

Pharmaceutical Development of 5-Fluorouracil-Eluting Stents for the Potential Treatment of Gastrointestinal Cancers and Related Obstructions

BACKGROUND

Drug-eluting gastrointestinal (GI) stents are emerging as promising platforms for the treatment of GI cancers and provide the combined advantages of mechanical support to prevent lumen occlusion and as a reservoir for localized drug delivery to tumors. Therefore, in this work we present a detailed quality assurance study of 5-fluorouracil (5FU) drug-eluting stents (DESs) as potential candidates for the treatment of obstructive GI cancers.

METHODS

The 5FU DESs were fabricated via a simple two-step sequential dip-coating process of commercial GI self-expanding nitinol stents with a 5FU-loaded polyurethane basecoat and a drug-free protective poly(ethylene-co-vinyl acetate) topcoat. The drug loading, content uniformity and drug stability were determined using a validated high-performance liquid chromatography (HPLC) method, which is also recommended in the United States Pharmacopeia. In vitro drug release studies were performed in phosphate buffered saline to determine the drug releasing properties of the two 5FU-loaded stents. Gas chromatography (GC) and HPLC were employed to determine total residual tetrahydrofuran and N,N-dimethylformamide in the stents remaining from the manufacturing process. Sterilization of the stents was performed using gamma radiation and stability testing was carried out for 3 months.

RESULTS

The drug loading analysis revealed excellent uniformity in the distribution of 5FU between and within individual stents. Determination of drug stability in the biorelevant release media confirmed that 5FU remains stable over 100 d. In vitro drug release studies from the stents revealed sustained release of 5FU across two different time scales (161 and 30 d), and mathematical modeling of drug release profiles revealed a diffusion-controlled mechanism for the sustained 5FU release. GC and HPLC analysis revealed that the daily residual solvent leached from the stents was below the United States (US) Food and Drug Administration (FDA) guidelines, and therefore, unlikely to cause localized/systemic toxicities. Sterilization of the stents with gamma radiation and accelerated stability tests over a period of 3 months revealed no significant effect on the stability or in vitro release of 5FU.

CONCLUSION

Our results demonstrate that the 5FU DESs meet relevant quality standards and display favourable drug release characteristics for the potential treatment of GI cancers and related obstructions.

Drug-Loaded, Polyurethane Coated Nitinol Stents for the Controlled Release of Docetaxel for the Treatment of Oesophageal Cancer

For several decades, self-expanding metal stents (SEMSs) have shown significant clinical success in the palliation of obstructive metastatic oesophageal cancer. However, these conventional oesophageal stents can suffer from stent blockage caused by malignant tumour cell growth. To overcome this challenge, there is growing interest in drug-releasing stents that, in addition to palliation, provide a sustained and localized release of anticancer drugs to minimise tumour growth. Therefore, in this study we prepared and evaluated an oesophageal stent-based drug delivery platform to provide the sustained release of docetaxel (DTX) for the treatment of oesophageal cancer-related obstructions. The DTX-loaded oesophageal stents were fabricated via dip-coating of bare nitinol stents with DTX-polyurethane (PU) solutions to provide PU coated stents with DTX loadings of 1.92 and 2.79% w/w. Mechanical testing of the DTX-PU coated stents revealed that an increase in the drug loading resulted in a reduction in the ultimate tensile strength, toughness and Young’s modulus. In vitro release studies showed a sustained release of DTX, with ~80–90% released over a period of 33 days. While the DTX-loaded stents exhibited good stability to gamma radiation sterilisation, UV sterilisation or accelerated storage at elevated temperatures (40 °C) resulted in significant DTX degradation. Cell proliferation, apoptosis and Western blotting assays revealed that the DTX released from the stents had comparable anticancer activity to pure DTX against oesophageal cancer cells (KYSE-30). This research demonstrates that the dip-coating technique can be considered as a promising approach for the fabrication of drug-eluting stents (DESs) for oesophageal cancer treatment.

Development and In Vitro Evaluation of 5-Fluorouracil-Eluting Stents for the Treatment of Colorectal Cancer and Cancer-Related Obstruction

Self-expanding metal stents (SEMSs) are currently the gold standard for the localised management of malignant gastrointestinal (GI) stenosis and/or obstructions. Despite encouraging clinical success, in-stent restenosis caused by tumour growth is a significant challenge. Incorporating chemotherapeutic drugs into GI stents is an emerging strategy to provide localised and sustained release of drugs to intestinal malignant tissues to prevent tumour growth. Therefore, the aim of this work was to develop and evaluate a local GI stent-based delivery system that provides a controlled release of 5-fluorouracil (5FU) over a course of several weeks to months, for the treatment of colorectal cancer and cancer-related stenosis/obstructions. The 5FU-loaded GI stents were fabricated via sequential dip-coating of commercial GI stents with a drug-loaded polyurethane (PU) basecoat and a drug-free poly(ethylene-co-vinyl acetate) (PEVA) topcoat. For comparison, two types of commercial stents were investigated, including bare and silicone (Si) membrane-covered stents. The physicochemical properties of the 5FU-loaded stents were evaluated using photoacoustic Fourier-transform infrared (PA-FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermal analysis. In vitro release studies in biological medium revealed that the 5FU-loaded stents provided a sustained release of drug over the period studied (18 d), and cell viability, cell cycle distribution and apoptosis assays showed that the released 5FU had comparable anticancer activity against human colon cancer cells (HCT-116) to pure 5FU. This study demonstrates that dip-coating is a facile and reliable approach for fabricating drug-eluting stents (DESs) that are promising candidates for the treatment of GI obstructions and/or restenosis.

Expanded Poly(tetrafluoroethylene) Blood Vessel Grafts with Embedded Reactive Oxygen Species (ROS)-Responsive Antithrombogenic Drug for Elimination of Thrombosis

Treatment of cardiovascular diseases suffers from the lack of transplantable small-diameter blood vessel (SDBV) grafts that can prohibit/eliminate thrombosis. Although expanded poly(tetrafluoroethylene) (ePTFE) has the potential to be used for SDBV grafts, recurrence of thrombus remains the biggest challenge. In this study, a reactive oxygen species (ROS)-responsive antithrombogenic drug synthesis and a bulk coating process were employed to fabricate functional ePTFE grafts capable of prohibiting/eliminating blood clots. The synthesized drug that would release antiplatelet ethyl salicylate (ESA), in responding to ROS, was dissolved in a polycaprolactone (PCL) solution, followed by a bulk coating of the as-fabricated ePTFE grafts with the PCL/drug solution. Nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were employed to investigate and confirm the synthesis and presence of the ROS-responsive drug in the ePTFE grafts. The ESA release functions were demonstrated via the drug-release profile and dynamic anticoagulation tests. The biocompatibility of the ROS-responsive ePTFE grafts was demonstrated via lactate dehydrogenase (LDH) cytotoxicity assays, live and dead cell assays, cell morphology, and cell-graft interactions. The ROS-responsive, antithrombogenic ePTFE grafts provide a feasible way for maintaining long-term patency, potentially solving a critical challenge in SDBV applications.

Influence of Polymer Composition on the Controlled Release of Docetaxel: A Comparison of Non-Degradable Polymer Films for Oesophageal Drug-Eluting Stents

Following the huge clinical success of drug-eluting vascular stents, there is a significant interest in the development of drug-eluting stents for other applications, such as the treatment of gastrointestinal (GI) cancers. Central to this process is understanding how particular drugs are released from stent coatings, which to a large extent is controlled by drug-polymer interactions. Therefore, in this study we investigated the release of docetaxel (DTX) from a selection of non-degradable polymer films. DTX-polymer films were prepared at various loadings (1, 5 and 10% w/w) using three commercially available polymers including poly(dimethylsiloxane) (PSi), poly (ethylene-co-vinyl acetate) (PEVA) and Chronosil polyurethane (PU). The formulations were characterised using different techniques such as photoacoustic Fourier-transform infrared (PA-FTIR) spectrophotometry, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The effect of DTX on the mechanical properties of the films, in-vitro release, and degradation tests were also assessed. For all polymers and DTX loadings, the drug was found to disperse homogenously without crystallisation within the polymer matrix. While no specific interactions were observed between DTX and PSi or PEVA, hydrogen-bonding appeared to be present between DTX and PU, which resulted in a concentration-dependent decrease in the Young’s moduli of the films due to disruption of inter-polymeric molecular interactions. In addition, the DTX-PU interactions were found to modulate drug release, providing near-linear release over 30 days, which was accompanied by a significant reduction in degradation products. The results indicate that DTX-loaded PU films are excellent candidates for drug-eluting stents for the treatment of oesophageal cancer.

Occurrence and predictive factors of restenosis in coronary heart disease patients underwent sirolimus-eluting stent implantation

BACKGROUND

This study aimed to investigate the occurrence and predictive factors of restenosis in coronary heart disease (CHD) patients underwent percutaneous coronary intervention (PCI) with sirolimus-eluting stent (SES).

METHODS

Demographic data, clinical features, and laboratory tests of 398 CHD patients underwent PCI with SES were retrospectively reviewed. Coronary angiography was performed to evaluate coronary stenosis before PCI and in-stent restenosis at 1-year follow-up.

RESULTS

There were 37 (9.3%) patients suffered restenosis, but 361 (90.7%) patients did not develop restenosis at 1-year follow-up. Demographic characteristic (age), cardiovascular risk factors (hypertension and hyperuricemia), biochemical indexes (fasting blood-glucose, total cholesterol, low density lipoprotein cholesterol (LDL-C) and high-sensitivity C-reactive protein (HsCRP)), cardiac function index (cardiac troponin I), lesion features (multivessel artery lesions, target lesion at left circumflex artery (LCX), two target lesions and length of target lesion), and operation procedure (length of stent) were correlated with higher restenosis risk. Moreover, age, hypertension, diabetes mellitus, LDL-C, HsCRP, and target lesion at LCX were independent predictive factors for raised restenosis risk. Based on these independent predictive factors, we established a restenosis risk prediction model, and receiver-operating characteristic curves displayed that this model exhibited an excellent predictive value for higher restenosis risk (areas under the curve 0.953 (95% CI 0.926-0.981)).

CONCLUSION

Our findings provide a new insight into the prediction for restenosis in CHD patients underwent PCI with SES.

Three-dimensional printed 5-fluorouracil eluting polyurethane stents for the treatment of oesophageal cancers

3D printing is introduced as rapid and facile approach to prepare personalized drug-eluting stents for the treatment of oesophageal cancers.