Tissue biocompatibility of new biodegradable drug-eluting stent materials

Antimicrobial and Antiproliferative Coatings for Stents in Veterinary Medicine-State of the Art and Perspectives

Microbial colonization in veterinary stents poses a significant and concerning issue in veterinary medicine. Over time, these pathogens, particularly bacteria, can colonize the stent surfaces, leading to various complications. Two weeks following the stent insertion procedure, the colonization becomes observable, with the aggressiveness of bacterial growth directly correlating with the duration of stent placement. Such microbial colonization can result in infections and inflammations, compromising the stent's efficacy and, subsequently, the animal patient's overall well-being. Managing and mitigating the impact of these pathogens on veterinary stents is a crucial challenge that veterinarians and researchers are actively addressing to ensure the successful treatment and recovery of their animal patients. In addition, irritation of the tissue in the form of an inserted stent can lead to overgrowth of granulation tissue, leading to the closure of the stent lumen, as is most often the case in the trachea. Such serious complications after stent placement require improvements in the procedures used to date. In this review, antibacterial or antibiofilm strategies for several stents used in veterinary medicine have been discussed based on the current literature and the perspectives have been drawn. Various coating strategies such as coating with hydrogel, antibiotic, or other antimicrobial agents have been reviewed.

Ureteral stent technology: Drug-eluting stents and stent coatings

Ureteral stents are commonly used following urological procedures to maintain ureteral patency. However, alongside the benefits of the device, indwelling stents frequently cause significant patient discomfort (pain, urgency, frequency) and can become encrusted and infected. The importance of these sequelae is that they are not only bothersome to the patient but can lead to significant morbidity, urinary retention, ureteral damage, recurrent infections, pyelonephritis and sepsis. When these problems occur, stent removal or replacement alongside antibiotic, analgesic and/or other symptom-modifying therapies are essential to successfully treat the patient. In an attempt to prevent such morbidity, numerous approaches have been investigated over the past several decades to modify the stent itself, thereby affecting changes locally within the urinary tract without significant systemic therapy. These strategies include changes to device design, polymeric composition, drug-elution and surface coatings. Of these, drug-elution and surface coatings are the most studied and display the most promise for advancing ureteral stent use and efficacy. This article reviews these two strategies in detail to determine their clinical potential and guide future research in the area.

Creation of a functional graded nanobiomembrane using a new electrospinning system for drug release control and an in vitro validation of drug release behavior of the coating membrane

Functional graded nanobiomembranes (FGMs) with multiple layers were created by a single process using a novel electrospinning system equipped with a generator and a PCI type motion board as a controller in order to control the drug release rate. By varying physical apparatus-related parameters such as nozzle-to-collector distance via a robot and the collector moving velocity the FGMs were formed. For the membrane base layer, poly-(ε-caprolactone) (PCL) with paclitaxel (PTX) was dissolved in a solvent (dichloromethane, N,N-dimethylformamide) and electrospun. For the top layers, the PCL solution was electrospun according to the distance and FGM system parameters, which can move the collector location at a constant ratio. It was observed that pore size, porosity, and permeability were higher when the membrane was spun at the far distance. The top surface of FGM is more porous, rougher, more permeable, and more hydrophilic so as to be active to the surrounding tissue cells. Meanwhile, the porous inside membrane was as low as the membrane spun at a close distance. Thus it induced a slow drug release due to the internal structure of FGM, which is considered to be very effective for slow drug release as well as bioactivity and bioconductivity.

A 5-fluorouracil-loaded polydioxanone weft-knitted stent for the treatment of colorectal cancer

In-stents restenosis caused by tumour ingrowth is a major problem for patients undergoing stent displacement because the conventional stents often lack a sustained anti-tumour capability. The aim of this paper was to develop a weft-knitted polydioxanone stent which can slow release 5-fluorouracil (5-FU). In order to determine the most suitable drug concentration, the 5-FU safe concentration in vivo and appropriate loading percentage in the membranes were investigated, and then 5-FU-loaded poly-l-lactide membranes at concentration of 3.2%, 6.4% and 12.8% were coated onto the stent using electro-spinning method, respectively. The morphology, chemical structure and in vitro drug release property of the coating membranes were subsequently examined. Their anti-tumour activity and mechanism were assessed in vitro and in vivo using a human colorectal cancer cell line HCT-116 and tumour-bearing BALB/c nude mice. The half maximal inhibitory concentration (IC50) and the median lethal dose (LD50) demonstrated that the 6.4% and 12.8% membranes had better anti-tumour effects than pure 5-FU due to the sustainable drug releasing property of the coated membranes on the stent. The membranes possessing appropriate drug loading doses, such as 6.4% or 12.8% also provided better anti-in-stents restenosis effects than other groups tested. Therefore, it is concluded that the drug-loaded stents have great potential for the use in the treatment of intestinal cancers in the future.

Dexamethasone-eluting vascular stents

Percutaneous transluminal angioplasty (PTA) with stenting is widely used in the treatment of vascular disorders, but restenosis remains a significant problem. Drug-eluting stents (DES) have been developed as an attempt to reduce the intimal response leading to restenosis. Drugs used in DES include mainly immunosuppressive and anti-proliferative compounds. Glucocorticoids are also an interesting possibility for those purposes because they have anti-proliferative effects in vascular smooth muscle cells and down-regulate the production of cytokines and growth factors driving inflammation and fibrosis. In this MiniReview, feasibility and safety of drug-eluting metal and biodegradable vascular stents are discussed with special emphasis on dexamethasone-eluting stents.

Development and characterization of a coronary polylactic acid stent prototype generated by selective laser melting

In-stent restenosis is still an important issue and stent thrombosis is an unresolved risk after coronary intervention. Biodegradable stents would provide initial scaffolding of the stenosed segment and disappear subsequently. The additive manufacturing technology Selective Laser Melting (SLM) enables rapid, parallel, and raw material saving generation of complex 3- dimensional structures with extensive geometric freedom and is currently in use in orthopedic or dental applications. Here, SLM process parameters were adapted for poly-L-lactid acid (PLLA) and PLLA-co-poly-ε-caprolactone (PCL) powders to generate degradable coronary stent prototypes. Biocompatibility of both polymers was evidenced by assessment of cell morphology and of metabolic and adhesive activity at direct and indirect contact with human coronary artery smooth muscle cells, umbilical vein endothelial cells, and endothelial progenitor cells. γ-sterilization was demonstrated to guarantee safety of SLM-processed parts. From PLLA and PCL, stent prototypes were successfully generated and post-processing by spray- and dip-coating proved to thoroughly smoothen stent surfaces. In conclusion, for the first time, biodegradable polymers and the SLM technique were combined for the manufacturing of customized biodegradable coronary artery stent prototypes. SLM is advocated for the development of biodegradable coronary PLLA and PCL stents, potentially optimized for future bifurcation applications.

Mediation of the migration of endothelial cells and fibroblasts on polyurethane nanocomposites by the activation of integrin-focal adhesion kinase signaling

Model surfaces of polyurethane-gold nanocomposites (PU-Au) were used to examine cell behavior on nanophase-segregated materials. Previously we showed that endothelial cell (EC) migration on these materials was modulated by the PI3K/Akt/eNOS pathway. The present study, investigated the expressions of alpha5/beta3 (α5β3) integrin, focal adhesion kinase (FAK), and other downstream signal molecules such as the Rho family and matrix metalloproteinases 2 (MMP-2) induced by the materials in two different cells, that is bovine arterial endothelial cells (BAEC) and human skin fibroblasts (HSF). Both cells proliferated better on the more phase-separated PU-Au 43.5 ppm than on the less phase-separated controls (PU and PU-Au 174 ppm). On PU-Au 43.5 ppm, BAEC compared to HSF had denser actin fibers and were more extended. BAEC became rounded with Y-27632 treatment and shrunk with LY294002 treatment. Treatment by inhibitors only caused slight changes in HSF. The migration distance of BAEC on PU-Au 43.5 ppm was greater than that of HSF, and was significantly reduced by LY294002 or Y-27632 but not SU-1498. The expressions of p-FAK, p-RhoA, p-Rac/Cdc42, MMP2, and α5β3 integrin induced by PU-Au 43.5 ppm were more pronounced in BAEC versus HSF. Further enhancement in MMP2 and α5β3 integrin expressions by FAK-GFP transfection was more remarkable for cells on PU-Au 43.5 ppm. Our findings suggested that the integrin α5β3/FAK pathway may be induced by nanophase-separated materials in both ECs and fibroblasts to promote their proliferation/migration, while the crosstalk between the PI3K/Akt/eNOS pathway and FAK/Rho-GTPase activation may account for the greater effect in ECs than in fibroblasts.