Zinc is proposed as an exciting new biomaterial for use in bioabsorbable cardiac stents. Not only is zinc a physiologically relevant metal with behavior that promotes healthy vessels, but it combines the best behaviors of both current bioabsorbable stent materials: iron and magnesium. Shown here is a composite image of zinc degradation in a murine (rat) artery.
Metallic stents are commonly used to promote revascularization and maintain patency of plaqued or damaged arteries following balloon angioplasty. To mitigate the long-term side effects associated with corrosion-resistant stents (i.e. chronic inflammation and late stage thrombosis), a new generation of so-called “bioabsorbable” stents is currently being developed. The bioabsorbable coronary stents will corrode and be absorbed by the artery after completing their task as vascular scaffolding. Research spanning the last two decades has focused on biodegradable polymeric, iron-based, and magnesium-based stent materials. The inherent mechanical and surface properties of metals make them more attractive stent material candidates than their polymeric counterparts. Unfortunately, iron produces a voluminous, retained oxide product in the arterial wall, whereas magnesium and its alloys corrode too rapidly. A third class of metallic bioabsorbable materials that are based on zinc has been introduced in the last few years. As summarized in this contribution, this new zinc-based class of materials demonstrates the potential for an absorbable metallic stent with the mechanical and biodegradation characteristics required for optimal stent performance. They appear to be free of flaws that limit the application of iron- and magnesium-based alloys, and polymers. This review compares bioabsorbable materials and summarizes progress towards bioabsorbable stents. It emphasizes on current understanding of physiological and biological benefits of zinc and its biocompatibility. Finally, the review provides an outlook on challenges in designing zinc-based stents of optimal mechanical properties and biodegradation rate.
Disturbances in the microcirculation can lead to secondary lymphedema, a common pathological condition that, despite its frequency, still lacks a cure. Lymphedema is clinically well described, but while the genetic underpinnings that cause lymphatic malformations and primary lymphedema are being discovered, the pathophysiology and pathobiology of secondary lymphedema remain poorly understood, partly due to the lack of well-described experimental models. Here, we provide a detailed characterization of secondary lymphedema in the mouse tail and correlate the evolution of tissue swelling to changes in tissue architecture, infiltration of immune cells, deposition of lipids, and proliferation and morphology of the lymphatic vessels. We show that sustained swelling leads to lymphatic hyperplasia and upregulation of vascular endothelial growth factor (VEGF)-C, which may exacerbate the edema because the hyperplastic vessels are poorly functional. The onset of lymphatic hyperplasia occurred prior to the onset of lipid accumulation and peak VEGF-C expression. Langerhans dendritic cells were seen in the dermis migrating from the epidermis to the lymphatic capillaries in edematous tissue. Furthermore, these results were consistent between two different normal mouse strains, but swelling was significantly greater in a matrix metalloproteinase (MMP)-9 null strain. Thus, by characterizing this highly reproducible model of secondary lymphedema, we conclude that VEGF-C upregulation and lymphatic hyperplasia resulting from dermal lymphatic ligation and lymphedema leads to decreased drainage function and that MMP-9 may be important in counteracting tissue swelling.
Blocking VEGFR-3 completely and specifically prevented both physiologically normal and tumor VEGF-C-enhanced lymphangiogenesis in the adult mouse but had no effect on either blood angiogenesis or the survival or function of existing lymphatic vessels. Thus, targeting VEGFR-3 with specific inhibitors may block new lymphatic growth exclusively.
Tissue engineered vascular grafts (TEVGs) are beginning to achieve clinical success and hold promise as a source of grafting material when donor grafts are unsuitable or unavailable. Significant technological advances have generated small-diameter TEVGs that are mechanically stable and promote functional remodeling by regenerating host cells. However, developing a biocompatible blood-contacting surface remains a major challenge. The TEVG luminal surface must avoid negative inflammatory responses and thrombogenesis immediately upon implantation and promote endothelialization. The surface has therefore become a primary focus for research and development efforts. The current state of TEVGs is herein reviewed with an emphasis on the blood-contacting surface. General vascular physiology and developmental challenges and strategies are briefly described, followed by an overview of the materials currently employed in TEVGs. The use of biodegradable materials and stem cells requires careful control of graft composition, degradation behavior, and cell recruitment ability to ensure that a physiologically relevant vessel structure is ultimately achieved. The establishment of a stable monolayer of endothelial cells and the quiescence of smooth muscle cells are critical to the maintenance of patency. Several strategies to modify blood-contacting surfaces to resist thrombosis and control cellular recruitment are reviewed, including coatings of biomimetic peptides and heparin.
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