A stent is a small, tube-like device used in medicine to open and widen arteries that have become narrowed or blocked, often due to plaque buildup. These devices are typically made of metal mesh and are placed during a procedure called angioplasty to restore blood flow. A newer development in this field is the bioabsorbable stent, also known as a bioresorbable scaffold, which is designed to dissolve or be absorbed by the body over time. This innovative approach aims to provide temporary support to the vessel and then disappear, leaving no permanent implant behind.
Understanding Bioabsorbable Stents: Design and Function
Bioabsorbable stents are constructed from materials that the body can safely break down and absorb. Common materials include biodegradable polymers, such as poly-L-lactic acid (PLLA), or magnesium alloys. For example, the Absorb stent had a PLLA backbone, and magnesium-based scaffolds have also been developed, with approximately 95% of the magnesium alloy resorbing within one year of implantation.
The absorption process for these stents involves hydrolysis, where the material breaks down into smaller components. For PLLA, this process produces lactic acid, which the body then metabolizes into carbon dioxide and water. The stent provides mechanical support to the vessel during the initial healing period, within the first three to nine months after placement. This temporary scaffolding helps restore blood flow and prevents the artery from narrowing again. The complete absorption of these stents takes several months to a few years, with some devices fully dissolving between two and three years after implantation.
Distinguishing Features from Permanent Stents
A primary distinction between bioabsorbable and permanent metal stents lies in their long-term presence. While traditional metal stents remain indefinitely, bioabsorbable stents disappear, leaving no foreign material behind. This absence of a permanent implant can prevent chronic inflammation that occurs with metal stents. The continuous presence of a metal stent can also hinder the natural movement and function of the artery, affecting its ability to expand and contract.
The temporary nature of bioabsorbable stents offers advantages for future medical interventions. If further treatment, such as repeat stenting or bypass surgery, becomes necessary, the absence of a permanent metal scaffold can simplify these procedures. Without a metal implant, future imaging techniques like CT scans of the treated vessel yield clearer results, avoiding artifacts that metal stents can create. This “leave nothing behind” strategy allows the vessel to return to a more natural state.
Clinical Applications and Outcomes
Bioabsorbable stents are used to address narrowed or blocked coronary arteries. They are considered for patients with coronary artery disease, where plaque buildup restricts blood flow to the heart. First-generation bioresorbable vascular scaffolds (BVS) were found to have comparable outcomes to metallic drug-eluting stents when properly implanted.
Patient suitability for bioabsorbable stents may involve considerations such as younger age or specific lesion characteristics where restoring the vessel’s natural state is desirable. The immediate goal of implanting these stents is to re-establish blood flow through the narrowed artery. Over the longer term, these devices support the vessel during its healing phase and then dissolve, allowing the artery to regain its natural function.
The Vessel’s Journey After Stent Absorption
Once a bioabsorbable stent has fully dissolved, the treated artery can regain its natural characteristics and function. The vessel recovers its ability to expand and contract normally, a process known as vasomotion. This restoration of vascular function is a long-term benefit of this technology, as it leaves behind only healed, native vessel tissue.
The vessel remains open and healthy without a foreign body, reducing the risk of late complications associated with permanent implants. Patients are monitored after the procedure to ensure the vessel remains open and functions well. The disappearance of the scaffold eliminates the stimulus for chronic inflammation and promotes healing within the artery.