Search

Tissue-engineered vascular grafts (TEVGs) require adequate extracellular matrix (ECM) to withstand arterial pressure. Tissue transglutaminase (TG2) and lysyl oxidase (LOX) are enzymes that cross-link ECM proteins and play a pivotal role in the development of vascular stiffness associated with aging. The purpose of this study is to investigate the expression of ECM cross-linking enzymes and mechanisms of scaffold degeneration leading to vascular stiffness in TEVG remodeling. Fast- and slow-degrading electrospun TEVGs were fabricated using polydioxanone (PDO) and poly(L-lactide-co-caprolactone) (PLCL) copolymer, with a PDO/PLCL ratio of 9:1 for fast-degrading and 1:1 for slow-degrading graft. These grafts were implanted in rats ( n  = 5/group) as abdominal aortic interposition conduits. The grafts were harvested at 1 month to evaluate patency, mechanical properties, vascular neotissue formation, and the expression of ECM cross-linking enzymes. All TEVGs were patent without any aneurysmal formation at 1 month. ECM area, TG2-positive area, and LOX-positive area were significantly greater in fast-degrading TEVGs compared to slow-degrading TEVGs, with significantly less remaining scaffold. The mechanical properties of fast-degrading TEVGs were similar to that of native aorta, as demonstrated by strain-stress curve. In conclusion, at 1 month, fast-degrading TEVGs had rapid and well-organized ECM with greater TG2 and LOX expression and native-like mechanical properties, compared to slow-degrading TEVGs. Impact statement Around 1.4 million patients in the United States require arterial prostheses each year due to cardiovascular diseases. Current synthetic vascular grafts suffer from increased risk of infection, thrombosis, a lack of endothelialization, and compliance mismatch to the native vasculature. Tissue-engineered vascular graft (TEVGs) presented in this study exhibited tunable biodegradation profiles by controlling the polymer ratio of polydioxanone/poly(L-lactide-co-caprolactone). One month after implantation, the fast-degrading TEVGs exhibited mechanical properties similar to that of native aorta, formation of endothelium, and well-organized extracellular matrix (ECM) with increased expression of tissue transglutaminase and lysyl oxidases, which are critical to the ECM remodeling process.

Impact Statement: We utilized innovative textile technology to create tissue-engineered vascular grafts (TEVGs) comprised exclusively of rapidly degrading material poly(glycolic acid). Our new technology led to robust neotissue formation in the TEVGs, especially extracellular matrix formation, such as elastin. In addition, the rapid degradation of the polymer significantly reduced complications, such as stenosis or calcification, as seen with the use of slow degrading polymers in the majority of previous studies for aortic small diameter TEVGs.

Most tissue-engineered arterial grafts are complicated by aneurysmal dilation secondary to insufficient neotissue formation after scaffold degradation. The optimal graft would form an organized multilayered structure with a robust extracellular matrix that could withstand arterial pressure. The purpose of the current study was to determine how oversizing a biodegradable arterial scaffold affects long-term neotissue formation. Size-matched (1.0 mm, n = 11) and oversized (1.6 mm, n = 9) electrospun polycaprolactone/chitosan scaffolds were implanted as abdominal aortic interposition grafts in Lewis rats. The mean lumen diameter of the 1.6 mm grafts was initially greater compared with the native vessel, but matched the native aorta by 6 months. In contrast, the 1.0 mm grafts experienced stenosis at 6 and 9 months. Total neotissue area and calponin-positive neotissue area were significantly greater in the 1.6 mm grafts by 6 months and similar to the native aorta. Late-term biomechanical testing was dominated by remaining polymer, but graft oversizing did not adversely affect the biomechanics of the adjacent vessel. Oversizing tissue-engineered arterial grafts may represent a strategy to increase the formation of organized neotissue without thrombosis or adverse remodeling of the adjacent native vessel by harnessing a previously undescribed process of adaptive vascular remodeling.

Objective: Electrospinning is a promising technology that provides biodegradable nanofiber scaffolds for cardiovascular tissue engineering. However, success with these materials has been limited, and the optimal combination of scaffold parameters for a tissue-engineered vascular graft (TEVG) remains elusive. The purpose of the present study is to evaluate the effect of bone marrow mononuclear cell (BM-MNC) seeding in electrospun scaffolds to support the rational design of optimized TEVGs., Methods: Nanofiber scaffolds were fabricated from co-electrospinning a solution of polyglycolic acid and a solution of poly(ι-lactide-co-ɛ-caprolactone) and characterized with scanning electron microscopy. Platelet activation and cell seeding efficiency were assessed by ATP secretion and DNA assays, respectively. Cell-free and BM-MNC seeded scaffolds were implanted in C57BL/6 mice (n = 15/group) as infrarenal inferior vena cava (IVC) interposition conduits. Animals were followed with serial ultrasonography for 6 months, after which grafts were harvested for evaluation of patency and neotissue formation by histology and immunohistochemistry (n = 10/group) and PCR (n = 5/group) analyses., Results: BM-MNC seeding of electrospun scaffolds prevented stenosis compared with unseeded scaffolds (seeded: 9/10 patent vs. unseeded: 1/10 patent, p = 0.0003). Seeded vascular grafts demonstrated concentric laminated smooth muscle cells, a confluent endothelial monolayer, and a collagen-rich extracellular matrix. Platelet-derived ATP, a marker of platelet activation, was significantly reduced after incubating thrombin-activated platelets in the presence of seeded scaffolds compared with unseeded scaffolds (p < 0.0001). In addition, reduced macrophage infiltration and a higher M2 macrophage percentage were observed in seeded grafts., Conclusions: The beneficial effects of BM-MNC seeding apply to electrospun TEVG scaffolds by attenuating stenosis through the regulation of platelet activation and inflammatory macrophage function, leading to well-organized neotissue formation. BM-MNC seeding is a valuable technique that can be used in the rational design of optimal TEVG scaffolds.

The development of a tissue-engineered vascular graft (TEVG) holds great promise for advancing the field of cardiac surgery. Despite the successful translation of this technology, previous reports identify the primary mode of graft failure as stenosis secondary to intimal hyperplasia. MicroRNAs (miRNAs) regulate gene expression by interfering with mRNA function and recent research has suggested miRNA as a potential therapeutic target. The role of miRNAs in TEVGs during neotissue formation is currently unknown. In this study, we investigated if miRNAs regulate the inhibition of graft stenosis. Biodegradable PGA-P(LA/CL) scaffolds were implanted as inferior vena cava interposition grafts in a murine model (n = 14). Mice were sacrificed 14 days following implantation and TEVGs were harvested for histological analysis and miRNA profiling using Affymetrix miRNA arrays. Graft diameters were measured histologically, and the largest grafts (patent group) and smallest grafts (stenosed group) were profiled (n = 4 for each group). Cell population in each graft was analyzed with immunohistochemistry using antismooth muscle actin (SMA) and antimacrophage (F4/80) antibodies. The graft diameter was significantly greater in the patent group (0.63 ± 0.06 mm) than in the stenosed group (0.17 ± 0.06 mm) (p < 0.01). Cell proliferation was significantly greater in the stenosed grafts than in patent grafts (p < 0.01: SMA [187 ± 11 vs. 77 ± 8 cells] vs. p = 0.025: F4/80 [245 ± 23 vs. 187 ± 11 cells]). MiRNA array of 1416 genes showed that in stenosed grafts, mir-451, mir-338, and mir-466 were downregulated and mir-154 was upregulated. Mir-451 exhibited the greatest difference in expression between stenosed and patent grafts by -3.1-fold. Significant negative correlation was found between the expression of mir-451 and cell proliferation (SMA: r = -0.86, p = 0.003; F4/80: r = -0.89, p = 0.001). Our data, along with previous evidence that mir-451 regulates tumor suppressor genes, suggest that downregulation of mir-451 promotes acute proliferation of macrophages and smooth muscle cells, thereby inducing TEVG stenosis. Adequate expression of mir-451 may be critical for improving TEVG patency.

Pericardium-based cardiovascular devices are currently bound by a 10-year maximum lifetime due to detrimental calcification and degradation. The goal of this work is to develop a novel synthetic material to create a lasting replacement for malfunctioning or diseased tissue in the cardiovascular system. This study couples poly(propylene fumarate) (PPF) and a natural biomaterial together in an unprecedented hybrid composite and evaluates the composite versus the standard glutaraldehyde-treated tissue. The polymer reinforcement is hypothesized to provide initial physical protection from proteolytic enzymes and degradation, but leave the original collagen and elastin matrix unaltered. The calcification rate and durability of the hybrid material are evaluated in vitro and in an in vivo subdermal animal model. Results demonstrate that PPF is an effective support and leads to significantly less calcium deposition, important metrics when evaluating cardiovascular material. By avoiding chemical crosslinking of the tissue and associated side effects, PPF-reinforced pericardium as a biohybrid material offers a promising potential direction for further development in cardiovascular material alternatives. Eliminating the basis for the majority of cardiovascular prosthetic failures could revolutionize expectations for extent of cardiovascular repair.