Atherosclerosis, a chronic inflammatory condition, occurs due to the accumulated fatty deposits within coronary arteries, which in turn, causes arterial narrowing, thereby hampering blood flow. Coronary intervention procedures and intravascular stenting has aided coronary artery disease. Bare-metal stents (BMS) and drug-eluting stents (DES) are the pioneers in this interventional cardiology field.
Advancing in technology novel stent material/surface that can promote re-endothelialisation and concurrently inhibit restenosis, without altering the hemocompatibility or stent characteristics are being developed in lab-scale and clinically testing. Later research shift toward nanoengineered technology comprising stent coatings to improve stent efficacy, which involves polymer-less techniques of stent modification, drug-free Nano topographical approaches, and nanoparticle (NP)-eluting/nanofiber-coated stents. Even with these technological advances, a suitable clinical translation of stents using this technology in the biomedical device industry is still a long way to go. This helps us to think about versatile nano surface modification strategies that are largely opted for developing advanced stents and their associated cellular responses.
Nanostructured surfaces and nano-thin-film coatings
Changing the stent surface at the nano-level maybe an advantage. As nano surface topography mimics the real extracellular matrix and can retain vascular cell adherence and proliferation. Cells when interacting with these nanostructured surfaces respond to the type of material and also to their surface topology. Protein and cell adhesion are influenced by surface properties such as topography roughness and wettability. Moreover, the creation of reservoirs and pores at the nanoscale provides a platform to load drugs efficiently.
Nanotubular structures such as Titanium dioxide nanotubes (titania nanotubes or TNT) can be modified using various methods including sol-gel, hydrothermal processes, template-assisted synthesis and electrochemical anodization. Out of this electrochemical anodization is widely used, because it provides a relatively simple, effective, and cost-effective process which offers the feasibility to tune the size and shape of nanotubular arrays to the required dimensions. As another option to anodization, researchers have developed chemical/thermochemical processing or lithography to develop uniform and homogeneous nanostructures on metallic surfaces called nano topographies.
Stent coatings were designed to mask the underlying stent surface, to stop ion leaching from the bare-metal stent surface into the bloodstream as these were observed in a lot of cases. Coating can reduce this critical corrosion. Out of which Titanium-oxide and titanium-oxy-nitride nano-thin-film coatings on stents are the viable for cardiovascular stent applications among all inorganic materials, offering good blood compatibility.
Apart from inorganic coatings on stents, polymeric coatings of nano thickness have also been widely investigated. Such as polyzene-F (PzF) surface coating has been top due to its multifarious characteristics which include its biocompatibility, anti-inflammatory, and inherent thromboresistance.
These systems have nanoscale diameter, tunable surface morphology, flexibility, porosity, and higher length/diameter ratio as unique feature The large surface area to volume ratio of NFs allow them to be a great design for incorporation of drugs/biologics with high drug loading. Alternative to drug-loaded stents, biological molecules have also been used for preparing stents.
These have significant benefits and can be readily capitalized in the Cardiovascular field. Nanoparticles loaded with drugs, when diffused into stent platforms, shows improved release kinetics and also promote a spatiotemporal delivery at the site of intervention They may also allow higher arterial wall concentrations than traditional drugs, which is crucial for the prevention of restenosis.
A leap forward to advance the clinical drug-eluting stents is to legally utilize the concept of nanotechnology in the field of coronary stenting. Due to promising future, extensive research has been performed in this area using diverse nanomaterials/surfaces that have displayed effective re-endothelialization and simultaneous inhibition of in-stent restenosis. Nano thin coatings, nanotextured surfaces, and nanofibrous and nanoparticulate coatings on stents, with or without the use of active pharmaceutical ingredients, are widely explored. Specifically, those stents devoid of polymers or drugs can be a facile and cost-effective alternative to DES.
In vitro and preclinical evaluations in small and large animal models have confirmed the utility of such nanotechnology-based stents in providing enhanced therapeutic benefits, with very few in clinical trials. The possible reasons include the risks with nanosized coatings, its flaking, and thereby integrity, which needs to be confirmed before a clinical translation. Scaling up and regulatory approvals are also possible deterrents. To advance more of these stent candidates to the clinic's demands surpassing the regulatory standards of functionality (especially the long-term stability and durability of nanocoatings) and toxicology as well. The promising benefits of nanomaterials science and technology would certainly help to evolve and translate these stents possessing surface modifications at the nanoscale into reality in the immediate future. In summary, nanotechnology can shape the foundation of next-generation coronary stent coatings by addressing the challenges of present-day stents.