The Challenges of Vascular Implants: Regulatory Strategies and Biological Responses

Figures

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  Figure 1. Clinical impact and translational challenges of implantable vascular devices for HF. FDA; ESC; ISO.

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  Figure 2. Medical device life cycle. The diagram outlines the main stages of developing a medical device life cycle, from initial concept and design, through prototyping and preclinical testing, to clinical evaluation, regulatory approval, and postapproval monitoring.

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  Figure 3. Schematic representation of the thrombo‐inflammatory response to device implantation. The device surface adsorbs plasma proteins, triggering the activation of immune cells (neutrophils and macrophages) and initiating the FBR, an acute and chronic inflammatory response triggered by the surface device, often resulting in the fibrosis and encapsulation of the implant. Activated endothelial cells promote platelet and leukocyte adhesion and transmigration by upregulation of adhesion molecules, cytokine release, and area of denudations expose subendothelial matrix components such as TF, promoting platelet adhesion, thrombus formation, and immune cell recruitment. In parallel, activation of abluminal fibroblasts and VSMCs promotes ECM deposition and the formation of a dense fibrotic capsule around the implant, impairing its function. VSMCs further contribute to neointimal hyperplasia and luminal narrowing, ultimately resulting in restenosis.

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  Figure 4. The stages of the FBR. FBR begins with acute inflammation involving neutrophils and macrophages, followed by chronic inflammation driven by persistent macrophage activity and fibroblast recruitment. This culminates in fibrotic encapsulation, where collagen and FBGCs isolate the implant. The timeline represents the typical progression of FBR following biomaterial implantation, including acute inflammation (1–7 days), chronic inflammation (>7 days), and fibrotic encapsulation (2–4 weeks).

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  Figure 5. Virchow's triad in medical device‐related thrombosis. A modified version of Virchow's triad explains the mechanisms underlying device‐related thrombosis through three main factors: hypercoagulability, blood‐contacting surfaces (device surface, endothelial injury), and abnormal flows. CV.

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  Figure 6. Schematic representation of thrombus formation on a medical device surface. Protein adsorption, including fibrinogen, vWF, complement components and factor XII (FXII), triggers a cascade of events: platelet adhesion and activation, with release of agonists that enhance aggregation; activation of the complement system, which amplifies platelet and leukocyte activation and promotes inflammation; and FXII initiating the intrinsic coagulation pathway, leading to fibrin clot formation and thrombus development. Plasmin, generated from plasminogen by tissue plasminogen activator (tPA), degrades fibrin (fibrinolysis), and restores normal blood flow.