Advancements in biomaterial science and available cell sources have spurred the translation of tissue-engineering technology to the bedside, addressing the pressing clinical demands for replacement cardiovascular tissues. Here, the in vivo status of tissue-engineered blood vessels, heart valves, and myocardium is briefly reviewed, illustrating progress toward a tissue-engineered heart for clinical use.

Aim: Inflammatory myeloid lineage cells mediate neotissue formation in tissueengineered vascular grafts, but the molecular mechanism is not completely understood. We examined the role of vasculogenic PDGF-B in tissue-engineered vascular graft neotissue development. Materials & methods: Myeloid cell-specific PDGF-B knockout mice (PDGF-KO) were generated using bone marrow transplantation, and scaffolds were implanted as inferior vena cava interposition grafts in either PDGF-KO or wildtype mice. Results: After 2 weeks, grafts from PDGF-KO mice had more remaining scaffold polymer and less intimal neotissue development. Increased macrophage apoptosis, decreased smooth muscle cell proliferation and decreased collagen content was also observed. Conclusion: Myeloid cell-derived PDGF contributes to vascular neotissue formation by regulating macrophage apoptosis, smooth muscle cell proliferation and extracellular matrix deposition. Progress in tissue engineering continues to promise a solution to the lack of tissue available for reconstructive and replacement surgery. Our lab has worked over the past several years developing a tissue-engineered vascular graft (TEVG) for use in congenital heart and vascular surgery. Traditionally used prosthetic materials in the form of Dacron ® or Gore-Tex ® pose significant risk for thromboembolic and infectious complications and also lack growth capacity, making them less ideal for use in the pediatric population. Our ability to create a TEVG with growth capacity [1,2] has therefore been an important advancement in the field, but graft stenosis continues to be a major limitation to widespread clinical application. We have therefore concentrated our efforts on understanding the underlying processes of TEVG neotissue formation and stenosis development.We developed a murine model of TEVG stenosis [3] and found that seeding the grafts with bone marrow-derived mononuclear cells prior to implantation increases graft patency [4] in a dose responsive manner [5], but the seeded cells disappear shortly after implantation [6,7]. We thus hypothesized that a paracrine mechanism, rather than proliferation of seeded cells, was responsible for the remodeling of the TEVG and then demonstrated that host endothelial and smooth muscle cells from the adjacent vessel migrate to form the TEVG neotissue.Host monocytes and macrophages were identified as key mediators of graft remodeling. They infiltrate the graft in large numbers shortly after implantation, and excessive infiltration leads to graft stenosis [8].

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