Bioinspired by Nature, Designed for Flow: Engineering Functional Interfaces for Small-Caliber Vascular Grafts

This thesis investigates the use of marine sulfated polysaccharides (MSPs) and other natural bioactive molecules for the design of next-generation small-caliber vascular grafts. Specifically: Chapter 2 provides a comprehensive review of MSPs as biofunctional agents for enhancing hemocompatibility and endothelialization in tissue-engineered vascular grafts. MSPs, including fucoidans, carrageenans, and fucosylated chondroitin sulfates (FCS), have attracted increasing attention due to their structural resemblance to glycosaminoglycans such as heparin, which endows them with anticoagulant, anti-inflammatory, and pro-endothelial properties. Sourced from marine organisms such as sea cucumbers (Holothuria tubulosa) and sponges (Sarcotragus spinosulus), these molecules can interfere with multiple steps of the coagulation cascade, reduce platelet adhesion, and mimic the endothelial glycocalyx. Importantly, they can be sustainably sourced from marine environments, offering a viable alternative to other bioactive sulfated polysaccharides. Chapter 3 reports the purification and structural characterization of anticoagulant MSPs from Holothuria tubulosa and Sarcotragus spinosulus, and evaluates their anticoagulant activity. Using anion exchange chromatography, different fractions of sulfated polysaccharides were isolated, and their molecular structure, anticoagulant activity, and preliminary cytotoxicity on human dermal fibroblasts were assessed. Two fractions demonstrated strong anticoagulant activity comparable to unfractionated heparin and were selected for further functional studies in Chapter 4. Chapter 4 describes the functionalization of electrospun poly(ε-caprolactone) (PCL) scaffolds with the selected MSP fractions. Functionalized scaffolds exhibited enhanced hemocompatibility, as shown by reduced platelet adhesion, and improved endothelialization, achieving complete endothelial cell coverage within 2–4 days. Importantly, the anticoagulant activity observed in solution was preserved after scaffold functionalization, as confirmed by aPTT and PT assays. These results demonstrate that MSPs can be used to design an engineered surface that improves both hemocompatibility and endothelialization of electrospun PCL scaffolds, establishing a foundation for vascular scaffold fabrication. Chapter 5 presents the development of multilayer bioresorbable vascular grafts with MSP-functionalized PCL. By combining electrospinning with 4-axis printing, scaffolds with tunable mechanical properties, high burst strength, and structural integrity suitable for arterial applications were produced. The study also examined smooth muscle cells, as well as endothelial cells, behavior on these grafts. While heparin-functionalized scaffolds inhibited SMC proliferation and induced disorganized morphology, MSP-functionalized scaffolds supported SMC spreading, alignment, and contractile phenotype, with abundant α-SMA fibers. These findings indicate that MSP-functionalized grafts not only promote rapid endothelialization, but also support stable medial integration, addressing two critical requirements for long-term graft patency and function. Chapter 6 explores an additional strategy for enhancing hemocompatibility and biocompatibility by embedding Notoginsenoside Fc (NgFc), a natural saponin, into electrospun PCL scaffolds for controlled release. This chapter provides proof of concept for NgFc as a bioactive agent to improve anti-thrombogenicity. Future work will focus on optimizing NgFc release through polymer blending and combining it with established agents such as heparin or fucosylated chondroitin sulfate to further enhance graft performance. Chapter 7 places the main findings of this thesis in the context of the current state of the art, discussing their significance and highlighting the remaining challenges for clinical translation of these vascular constructs. Finally, Chapter 8 outlines the scientific and societal impact of the work presented.