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Mechanical Effects of Cardiovascular Drugs and Devices
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Platelet activation is initiated by mechanical disruption of the vessel wall that exposes tissue factor, which leads to the production of small amounts of thrombin. Platelets also respond, by adhering at the injury site. This initial signal is amplified, as thrombin activates and recruits more platelets and coagulation factors, setting the stage for large-scale thrombin production, which occurs on the surface of activated platelets. More thrombin converts fibrinogen monomers to fibrin, leading to a clot formation. Thrombin bound to fibrin remains active, and thus, the clot becomes a reservoir of active thrombin, which continues to activate platelets and promote its own generation. The burst of thrombin further fuels thrombosis, by activating cells and proteins involved in inflammatory and thrombotic responses. A thrombus attached to a surface can obstruct passage of blood flow or interfere with device function. If the clot detaches and becomes an embolus and floats downstream, it can become lodged in a small artery, obstructing blood flow to tissues. If the blocked artery is in the brain, the tissue dies and a loss of neurological function, either motor or cognitive, may occur. This type of stroke is ischemic, but hemorrhage strokes may also occur due to vessels that burst and bleed.
Bioinks for 3D printing
Published in Ali Khademhosseini, Gulden Camci-Unal, 3D Bioprinting in Regenerative Engineering, 2018
Fibrin, the polymer that makes up blood clots, is formed through thrombin-mediated cleavage of fibrinogen. Following cleavage, fibrin monomers self-assemble into fibrils, which are stabilized by Factor XIII, transglutaminase, that links glutamine and lysine residues. Fibrin hydrogels can be fabricated, just as in nature, by mixing fibrinogen, thrombin, and calcium. Fibrinogen is easily isolated from blood, meaning that fibrinogen can be isolated from a patient’s own blood for autologous therapy, thereby reducing the risks of foreign body reactions (Buchta et al. 2005). Moreover, there is no added cost to using patient-derived fibrinogen compared to commercially available fibrinogen (Ahmed et al. 2008). Fibrin has an excellent bioactivity, with motifs for cell adhesion, heparin binding, ECM protein binding, and growth factor binding.
Extracorporeal devices
Published in Ronald L. Fournier, Basic Transport Phenomena in Biomedical Engineering, 2017
Another example of an immobilized enzyme reactor that we will look at in considerably more detail is that for the removal of heparin (Bernstein et al., 1987a,b; Ameer et al., 1999a,b). Recall that heparin is used as an anticoagulant in extracorporeal treatments such as hemodialysis and blood oxygenators. Heparin is a large negatively charged conjugated polysaccharide molecule that is produced by many types of cells in the body. By itself, heparin has little anticoagulant activity at the typical concentrations found in blood. However, in some regions of the body such as the liver and lungs, it is produced in greater amounts. Therefore, heparin has an important role in preventing blood clots in the slow-moving venous blood flow entering the capillaries of the lungs and liver. By combining with antithrombin III, it increases by several orders of magnitude the ability of antithrombin to remove thrombin. Thrombin is an enzyme that converts the plasma protein fibrinogen into fibrin, leading to the fibrous mesh-like structure characteristic of a blood clot. Therefore, this synergistic combination of heparin with antithrombin III results in a powerful anticoagulant.
The hemostatic effect and wound healing of novel collagen-containing polyester dressing
Published in Journal of Biomaterials Science, Polymer Edition, 2023
After activating the platelet to form the signal of the blood clot, integrin α2b1 promotes platelet adhesion to collagen and fibrin interactions to form a blood clot. Blood clots are generated and stably coordinated to activate the collagen pathway and TF (tissue factor) pathway, which can also be formed independently of collagen aggregation [21]. Thrombin is derived from soluble fibrin, which is produced by platelet aggregation and acts as an integrin α2b3 to stabilize the formation of blood clots. GPVI is a highly specific recognition of the GLY-PRO-HYP sequence in collagen and activated platelets. GPVI is the specificity of the Gly-Pro-Hyp sequence in collagen, the combination of the two activated platelets [22]. The interaction between collagen and glycoprotein GPVI is specific because GLY-PRO-HYP is a unique repetitive sequence in collagen [20].
Gelation-based visual detection of analytes
Published in Soft Materials, 2019
Wangkhem Paikhomba Singh, Rajkumar Sunil Singh
McNeil’s group took a distinctly different approach to elegantly design a generalized method for detection of different proteases (41). A modular sensor, 11, was designed containing the recognition sequence of a protease and a peptide-based gelator, 10 (Fig. 2). An oligo(ethylene glycol) unit and three hydrophilic amino acids were also attached to the N-terminal end to increase solubility and prevent unwanted gelation prior to the sensing event. In the presence of the target protease, this modular sensor is expected to be cleaved into two parts—the peptide-based gelator (10) and the recognition sequence along with the solubility-enhancing component. The peptide-based gelator identified was a p-aminobenzoic acid (PABA) derivative, PABA-(D-Phe)-(D-Phe)-NH2, 10. The proof of concept study was carried out with thrombin, an enzyme which helps in blood clotting. Addition of thrombin to the solution of 11 resulted in gelation within 10 min. The detection limit for thrombin was 400 pM which is within the range of the physiological concentration (0.1–3 nM). The generality of this approach was further confirmed by using two additional proteases (chymotrypsin and Glu-C). The same group extended this work further by applying a slightly modified method to two more proteins, MMP-9 and prostate-specific antigen (PSA) (42). This approach is general in nature and can be potentially applied for detection of any proteases by simply incorporating their respective recognition sequence into the structure of the modular sensor.
Review of pulmonary emboli and techniques for their mechanical removal to inform device design
Published in Journal of Medical Engineering & Technology, 2020
Jessica Brand, Roger McGowan, Amit Nimunkar
Blood clots are made via a complex cascade, as thrombin converts the fibrinogen to fibrin, creating protofibrils that combine into full-length fibres [12]. As protofibrils aggregate, exterior fibres straighten under tension. Fibres twist around one another and branch out at various points, creating networks that determine the structural behaviour of a blood clot [12,13]. Due to the large spaces between neighbouring protofibrils and fibres, blood clots are about 99.75% interstitial fluid [12].