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Aggregation and blood flow in health and disease
Published in Annie Viallat, Manouk Abkarian, Dynamics of Blood Cell Suspensions in Microflows, 2019
Viviana Clavería, Christian Wagner, Philippe Connes
The biggest vessels are connected to the heart, decreasing in size, bifurcating, and creating a network of vessels as they are spread out into the tissues. Capillaries are the smallest and most numerous blood vessels in the circulatory system, with diameters ranging from about 2 to 10 μm. The typical distance between bifurcations is hundreds of micrometers to a few millimeters [118]. Since the diameter of a RBC at rest is bigger than the diameter of many capillaries, RBCs are subjected to high deformation in order to pass through them. As previously mentioned, rouleaux structures are reversibly and continuously breaking down to single flowing discocytes for increasing shear rates above 10 s−1 (see Figure 6.6). This observation has been done in bulk flow and classical shear rheology using bulk viscometers (e.g., cone-plate rheometers). However, in a very confined capillaries, shear stresses cannot fully act on the breaking process due to the confinement of the cells.
Pulmonary Vascular Mechanobiology
Published in Jiro Nagatomi, Eno Essien Ebong, Mechanobiology Handbook, 2018
Diana M. Tabima Martinez, Naomi C. Chesler
Mean PAP can increase because of elevated left atrial pressures, increased CO or increased pulmonary vascular resistance (PVR=[mPAP-PCWP]/CO). Increased left atrial pressures are typically caused by left ventricular failure or mitral valve disease. Increases in CO can occur physiologically (e.g., with exercise) or pathologically (e.g., with atrial and ventricular septal defects). With exercise, the increase in mPAP is not as dramatic as one might expect given the increase in flow. This is because at rest many pulmonary capillaries and small arterioles are not required for adequate blood oxygenation and are thus not perfused. With exercise, these capillaries are recruited such that CO can increase without a dramatic increase in pressure. Once all capillaries are recruited, capillary and arteriolar dilation also occurs to permit further increases in blood flow without further increases in pressure.100 Increases in PVR are caused by arteriolar narrowing or obstructions to flow upstream of the capillaries. Hypoxia increases PVR via constriction of pulmonary arterioles. Emboli increase PVR by obstructing large or small arteries. Other diseases can also increase PVR and thereby increase mPAP to cause pulmonary hypertension.61
Cardiovascular System:
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
The capillaries are thin-walled and form the site of gas exchange within the tissues. The average size of the capillaries is 8–10 µm in diameter, which ensures that the blood cells travel through the vessel in single file. The resistance is highest in the capillaries, making blood flow slow and allowing for maximal gas and nutrient exchange. Tissues that have high metabolic demands (such as muscle) have a high density of capillaries, while tissues such as tendons and ligaments have very few capillaries. Continuous capillaries are found in abundance in the muscle and the skin and are the least permeable. The wall is one-cell thick and has enough gaps to allow the movement of fluids and small particles. Fenestrated capillaries have larger pores and greater permeability. These are found in the kidney and the small intestine, where active filtration or absorption occurs. The sinusoid capillaries are the most “leaky,” with pores large enough to allow blood cells to move through them. These are found in the liver and the spleen (where old red blood cells [RBCs] are removed from the circulation) and in the bone marrow (where new red cells are added to the circulation).
Synthesis, X-ray characterization and evaluation of potent anti-angiogenic activity of a novel copper(II)-imidazole-bipyridyl complex
Published in Inorganic and Nano-Metal Chemistry, 2022
Hakan Ünver, Gökhan Dıkmen, Hülya Tuba Kiyan
Angiogenesis or neovascularization which refers to new capillaries that occurs from preexisting ones plays a vital role in such pathologies as inflammation and cancer.[1,2] Neovascularization including the steps of vasodilation, increased endothelial permeability, dissolved basal membrane, proliferation of endothelial cells, processes of migration and tubule formation, replasticity, endothelial cell differentiation and maturation, has a complex mechanism needs the interaction between multiple cells, includes endothelial and wall cells, inflammatory and blood cells, and cytokines, the extra-cellular matrix and proteolytic enzymes.[3–5] Angiogenesis; besides involving processes of embryonic development, wound healing, tissue repair and organ regeneration, it is also a key process for pathologically metastasized invasive tumor growth and plays an important role in controlling cancer progression.[6] Under normal conditions, neovascularization is regulated by the local balance between proangiogenic and antiangiogenic factors such as growth factors, cytokines, proteolytic enzymes, integrins, and extracellular matrix components, and it is also known as the angiogenic switch.[7–9] In the pathological way, when the angiogenesis switched on, excessive or inadequate neovascularization may lead to several diseases including cancer, macular degeneration, retinopathy, rheumatoid arthritis and inflammation.
Polymeric biomaterials for wound healing applications: a comprehensive review
Published in Journal of Biomaterials Science, Polymer Edition, 2022
Ahmed Olanrewaju Ijaola, Damilola O. Akamo, Fouad Damiri, Cletus John Akisin, Emmanuel Anuoluwa Bamidele, Emmanuel Gboyega Ajiboye, Mohammed Berrada, Victor Onyebuchukwu Onyenokwe, Shang-You Yang, Eylem Asmatulu
The proliferation stage of the wound-healing process is the third phase when the wound is “rebuilt” through the proliferation of fibroblasts and collagen deposition to replace the tentative fibrin matrix. This stage commences about two to three days following the trauma and proceeds until the wound is closed [22]. This phase entails angiogenesis, re-epithelialization, tissue granulation, and wound contraction. Angiogenesis, a process where endothelial cells form new capillaries, takes place during the proliferation stage and is induced by some growth factors such as vascular endothelial growth factor A (VEGF-A), basic fibroblast growth factor (bFGF), TGF- and PDGF [42]. The newly generated capillaries convey oxygen and nutrients to the wound site and remove waste products. Angiogenesis is important for tissue granulation to occur during the proliferation stage, and these granulation tissues help starts the re-epithelialization. The formation of granulation tissue is triggered by inflammatory cytokines, which trigger fibroblasts to make growth factors which consequently cause keratinocytes to move to the wound bed [43]. Basal keratinocytes move from the wound edges and skin appendages to the injured site where they proliferate, differentiate, and immediately form a cover over the wound. On the other hand, fibroblasts could also move from bone marrow to the wound to activate and synthesize the extracellular matrix by releasing several extracellular matrix proteins such as fibronectin, hyaluronan or hyaluronic acid (HA), and collagens, as illustrated in Figure 4. Subsequently, wound contraction occurs, whereby the fibroblast, which is already in the wound bed, differentiates into myofibroblasts that close the wound area by pulling in the wound edges.
Preparation of gelatin nanoparticles by two step desolvation method for application in photodynamic therapy
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Janicy Arantes Carvalho, Alexandro Silva Abreu, Vitória Tonini Porto Ferreira, Erika Peterson Gonçalves, Antonio Claudio Tedesco, Juliana Guerra Pinto, Juliana Ferreira-Strixino, Milton Beltrame Junior, Andreza Ribeiro Simioni
Nanoparticles have a further advantage over large microparticles, they are better suited for intravenous delivery. The smallest capillaries in the body are of 5–6 μm in diameter. The size of particles in the bloodstream must be significantly smaller than 5 μm to ensure particles do not cause embolism [28]. Thus, it is important to measure particle size.