Blood-implant interaction

A wide number and great variety of clinically important cardiovascular implants and devises exist. Some (e.g., catheters) may only contact the blood once, and for a relatively short time others (e.g., kidney dialyzers and blood oxygenators) may be exposed to blood for hours, while tissue implants (e.g., heart valves and vascular grafts) will hopefully last for years, or the lifetime of the patient. All of these implants nd devices contain materials that are recognized by blood as foreign the result is a process of thrombosis often followed by formation of thromboemboli. This process generally involves a sequence of protein adsorption steps followed by blood cell interactions (especially involving platelets). 

While studies of platelet and thrombus accumulation on surfaces have provided important information concerning blood-material interactions, that accumulation is not a direct index of the rate of microemboli generation [e.g., kidney embolism induced by implanted aortic rings often was most severe from rings that remained clean (26, 27)]. Thus, analytical tests that directly quantify microemboli are needed. 

In addition to blood-material interaction, fibrous encapsulation, and microbial infection, implantable prostheses are associated with a multitude of other interrelated biological phenomena including specific immunologic reactions, complement activation, systemic toxicity, hypersensitivity, and implant-associated tumor formation [9]. For more detailed discussion on these biological processes, the readers are referred to specialized textbooks [9,17] and reviews [12,30,40],... 

Blood-surface interactions are of great importance when medical polymers, such as those used in heart valves and artificial organs, are implanted into the body. When polymers come into contact with blood, complex reactions take place and can result in the formation of a blood clot. Infrared analysis has shown in ex vivo studies that during the early stages the proteins albnmin and glycoprotein are present, with fibronogen subsequently appearing. As the adsorption process continues, albumin is replaced by other proteins until a blood clot is formed. 

Table 6 shows that the surface of polycarbonate with adsorbed serum albumin is the most suitable one to be used in implant devices. The behavior of all lipids toward blood-polymer interaction is not similar and may change depending on the nature of lipid, net charge of the lipid-adsorbed surface and the lipid-protein/ lipid-platelet interaction at the interface. Under conditions of high cholesterol concentrations addition of vitamin C leads to suitable surface characteristics of polycarbonate. The question is how to garantee the preferential the albumin adsorption on an implant surface In works of Malmsten and Lassen [123] competitive adsorption at hydrophobic surfaces from binary protein solutions was... 

Inflammation is generally defined as the reaction of vascularized living tissue to local injury, that is, implantation of a biomaterial, prosthesis, medical device, or tissue-engineered device. Immediately following injury, blood-material interactions occur and a provisional matrix is formed that consists... 

Blood-biomaterial interactions, provisional matrix formation, acute and chronic inflammation, granulation tissue development, foreign body reaction, and fibrosis/ fibrous capsule development comprise the series of host reactions occurring after device implantation (Fig. 4.3b) [3]. 

Although red blood cells (erythrocytes) play only a minimal role in wound healing and blood-biomaterial interactions, the contact of red blood cells with the material can lead to hemolysis. Hemolysis is the breakage of the erythrocyte s membrane with the release of intracellular hemoglobin. Normally, red blood cells live for 110-120 days. After that, they naturally break down and are removed from the circulation by the spleen. Some diseases and medical devices cause red blood cells to break too soon requiring the bone marrow to accelerate the regeneration of red blood cells (erythropoesis). Medical devices for hemodialysis, heart-lung-bypass machines or mechanical heart valves induce more hemolysis than smaller implants like stents or catheters [201]. 

Interactions at surfaces and interfaces also play an essential role in the design and function of clinical implants and biomedical devices. With a few recent exceptions, implants do not attach well to tissue, and the resulting mobility of the tissue-implant interface encourages chroitic inflammation. The result can be a gathering of platelets at the site, leading to a blood clot or to the formation of a fibrous capsule, or scar, around the implant (Figure 3.3). 

For pH sensors used in in-vivo applications, especially those in continuous pH monitor or implantable applications, hemocompatibility is a key area of importance [150], The interaction of plasma proteins with sensor surface will affect sensor functions. Thrombus formation on the device surface due to accelerated coagulation, promoted by protein adsorption, provided platelet adhesion and activation. In addition, variation in the blood flow rate due to vasoconstriction (constriction of a blood vessel) and sensor attachment to vessel walls, known as wall effect , can cause significant errors during blood pH monitoring [50, 126],... 

Effects on blood pressure, heart rate, lead II ECG, core body temperature, and locomotor activity can be explored using DataSciences telemetry implanted devices in rats, guinea-pigs, dogs, or primates. Effects on behavior can be captured on video using CCTV for dog and primate studies. Repeated administration and interaction studies can be performed. 

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