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.

Drug-delivering devices in the urinary tract: A systematic review

Objective

: To systematically review the use of drug-eluting stents (DES) and drug-coated balloons (DCB) in urology.

Materials and Methods

The systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. PubMed, Scopus, Web of science and Cochrane Library online databases were searched in February 2019. Experimental and clinical studies, which included the placement of a DES or dilatation with DCB for investigating their potential use in the urinary tract for the management of ureteric or urethral pathologies, were included. The primary endpoint was to evaluate the current use of DES and DCB in urology.

Results

A total of 29 articles were included in the systematic review. A total of 10 studies tested DES or DCB containing anti-proliferative agents (paclitaxel, zotarolimus, sirolimus, halofugione). Antibiotic agent-containing DES were tested in nine studies (triclosan, quinolones, teicoplanin, nitrofurantoin, silver sulfadiazine). A total of eight studies investigated the release of anti-inflammatory agents by DES (ketorolac, indomethacin, EW-7197). Another group studied heparin-eluting stents.

Conclusion

Despite the inconclusive outcomes of the three randomised controlled trials, drug-coated/eluting devices constitute a promising field in urology for the prevention of complications associated with conventional stents including pain and encrustation. Pre-clinical in vitro and in vivo studies have shown their ability to mitigate inflammation, inhibit re-stenosis and improve pain as indicated by declined use of anti-inflammatory drugs.

Abbreviations: DES: drug-eluting stents; DCB: drug-coated balloons; DCS: drug-coated stents; HF: halofungione; MCP-1: monocyte chemoattractant protein 1; PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses; PTCA: percutaneous transluminal coronary angioplasty; RANTES: regulated on activation, normal T-cell expressed and secreted; RCT: randomised controlled trial; USSQ, Ureteric Stent Symptoms Questionaire.

Biodegradable drug-eluting urethral stent in limiting urethral stricture formation after urethral injury: An experimental study in rabbit

In this study, a reproducible urethral injury animal model was developed and the role of the biodegradable drug-eluting urethral stent in limiting urethral stricture formation after urethral injury was evaluated. A total of 22 rabbits were used, and 20 rabbits were randomly chosen to develop urethral injury animal model. Bulbar urethral injury was made by a self-designed explosion device in the 20 rabbits. The urethral injury animal model was then randomly assigned to 2 groups of 10 each, which received a treatment of biodegradable paclitaxel-eluting urethral stent or only end-to-end anastomosis. Other two rabbits served as normal control group. Stents were surgically implanted into the injured urethras of rabbits under direct vision. Reparative effects, including stent degradation, were evaluated by urethroscopy, retrograde urethrography, and histology at different intervals at weeks 4, 8, and 12. In stent-free group, 8 of 10 rabbits developed obvious urethral stricture which was demonstrated by urethroscopy and retrograde urethrography, while in biodegradable paclitaxel-eluting stent group, urethral stricture was absent in all animals (p < 0.05). Histological follow-up indicated that the drug-eluting stents can also minimize the inflammatory reactions and fibrosis formation compared with the stent-free groups. Scanning electron microscope demonstrated that the biodegradable drug-eluting stent can gradually degrade in 12 weeks. The biodegradable paclitaxel-eluting urethral stent is effective in limiting urethral stricture formation after urethral injury.

Crack prevention of biodegradable polymer coating on metal facilitated by a nano-coupled interlayer

Crack prevention of biodegradable polymer coatings on drug-eluting stents was investigated by introducing a nano-coupled layer at the interface between the metal surface and the polymer coating layer using surface-initiated ring-opening polymerization of ε-caprolactone. Poly(d,l-lactide-co-glycolide) coating on cobalt-chromium control and ricinoleic acid-poly(caprolactone)–grafted cobalt-chromium was carried out using electrospraying. The cracking of the biodegradable polymer coating on drug-eluting stents during ballooning was addressed by introducing a nano-coupled interlayer on the cobalt-chromium surface. The ricinoleic acid-poly(caprolactone) nano-coupled interlayer and poly(d,l-lactide-co-glycolide)-coated top layer were characterized using attenuated total reflection Fourier transform infrared, contact angle, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy. Based on scratch tests, the nano-coupled samples had stronger interfacial adhesion compared to the control sample without the nano-coupled layer. Scanning electron microscope images indicated that the cracking on the poly(d,l-lactide-co-glycolide) coating was addressed. Introducing a nano-coupling interlayer may be an important strategy to preventing polymer coating cracking on drug-eluting stents.

Bioactive coatings for coronary stents: Modulation of cell proliferation by controlled release of anti-proliferative drugs

Drug eluting coronary stents coated with a bioactive and biostable polymer system (THBA70), based on acrylate copolymers bearing a salicylic acid derivative as side substituent, were evaluated. The microstructural architecture of the copolymer THBA70 comprises a random copolymer of a methacrylate derivative from triflusal (4-trifluoromethyl salicylic acid) with 45 mol% of THEMA (2-methacryloyloxyethyl [2-(acetyloxy)-4-(trifluoromethyl)] benzoate), which makes the system anti-thrombogenic with good adhesion to the surface of metallic stents. The bioactive coating prevented thrombosis, an adverse effect associated with the implantation of drug-eluting stents. The in vitro drug delivery of drug-eluting stents under dynamic conditions indicated excellent controlled drug release. The THBA70 films loaded with relatively low concentrations of taxol or simvastatin in contact with fibroblasts produced inhibition of cell proliferation with a dose-dependent bioactivity.

Biodegradable tocopherol acetate as a drug carrier to prevent ureteral stent-associated infection

Biomaterial-centred bacterial infections present common and challenging complications with medical implants like ureteral stent which provide substratum for the biofilm formation. Hence the purpose of this study is to make antibacterial stent surface with biodegradable polymer (tocopherol acetate) and anti-infective agents (norfloxacin and metronidazole) using a modified dip-coating procedure. This is done by impregnating the stent pieces in the anti-infective solution (a mixture of norfloxacin-metronidazole and polymer) for uniform surface coating (drug-carrier-coated stents). After coating, agar diffusion test was performed as qualitative test to find out the sensitivity of coated stents against the clinical isolates, Staphylococcus epidermidis and Escherichia coli. Quantitative test was measured by calculating the numbers of adhered bacteria on coated and uncoated stents by incubating the stent pieces in artificial urine. Difference in the number of viable bacteria adhered on the surface of coated and uncoated stents were statistically calculated using chi square test with p < 0.05 considered significant. The stent colonising ability of Staphylococcus epidermidis and Escherichia coli in a controlled environment chamber was determined using two-challenge dose of the isolates by in vitro challenge test. In qualitative test, the zone of inhibition around the coated stents showed sensitivity against the clinical isolates. In quantitative test, the number of adhered bacteria on the surface of coated stents was reduced to a significant level (p < 0.05). The polymer, tocopherol acetate is highly biodegradable in nature. Due to its degrading ability in body tissues, it releases the anti-infective drugs at a constant and sustained rate.