Stents are implantable devices designed as endoluminal scaffolds to maintain patency following recanalization of occluded or structurally compromised vascular (and non-vascular) circulatory conduits that enable energy supply and metabolic exchange in various organs and tissues of the human body. Palliative stenting has been routinely used for decades in the management of acute and chronic obstructions of gastro-intestinal, pulmonary and urinary tracts secondary to benign or malignant neoplasms or other cite-specific or systemic pathologies. However, a real explosion in utilization of stents was triggered in the early 1990s by the advent of vascular stenting devices, which allowed radically improved clinical outcomes of balloon angioplasty and supported its emergence as the first choice treatment modality for occlusive peripheral and coronary artery disease (PAD and CAD). By the end of 2014, more than three quarters of patients with acute and chronic arterial occlusions warranting intervention were referred for angioplasty-based therapy, which entailed placement of stenting devices in over 80% of commonly performed peripheral revascularization procedures.
To be accepted in clinical practices, stenting implants should satisfy a number of general and application-specific requirements relating to device biocompatibility, functional performance, and end-user and patient friendliness which are summarized in the exhibit below. In very general terms, stenting device biocompatibility refers to minimization of hostile immune responses (and other local and systemic adverse reactions) that are inevitably triggered by a direct contact of any implantable medical device with living tissues and bodily fluids in situ. For understandable reasons, biocompatibility depends primarily on the implant surface material, including such characteristics as chemical inertness and stability, corrosion resistance, etc. The stenting device biocompatibility can also be effected somewhat by the duration of its presence in situ and specifics of the deployment site and occlusion causing pathology.
The stent’s functional performance (or ability to maintain adequate scaffolding support and lumen patency for a desired period of time) represents a complex function of the device design/architecture and the relative static and dynamic strength of its base material. The chosen stenting device’s architecture and structural material predetermine it radial strength, longitudinal flexibility, conformability and foreshortening, as well as relative lesion coverage, fatigue and kinking resistance, circulatory flow obstruction, etc.
Finally, the stent’s end-user and patient friendliness are predicated both by the design concept of the delivery system and stenting device and refers to procedural convenience, predictability, safety, morbidity, availability of bail-out options, etc. The commonly acknowledged stenting system characteristics relating to the end-user/patient friendliness include low profile, flexibility, traceability, high radiopacity, compatibility with established transcatheter tools and techniques, ease of use and short learning curve, simplicity of retrieval in case of procedural failure, possibility of emergent /elective conversion to surgery, etc.
Selected Biomedical, Clinical and Technical Requirements
for Stenting Implants
Source: MedMarket Diligence, LLC; Report #V201.