Blood compatibility and thrombogenicity are the two important host reactions that have to be evaluated before deploying any biomaterial into action. If the material is not tested for these two properties, there are chances that the developed material would trigger adverse host reactions like thrombosis, destruction of blood components, etc., decreasing the performance of the biomaterial.
BLOOD COMPATIBILITY
Blood compatibility is the property of the biomaterial that defines the compatibility or the ability to function in contact with blood without causing any adverse host reactions. This can be impacted by the biochemical properties of coagulation, blood materials interaction, and the device’s function, and design in the bloodstream. Adverse reactions are caused by materials that are not blood compatible in nature. This will lead to the formation of clot, thrombus, destruction of circulating blood components, hemolysis, emboli, and other adverse immunological processes.
EFFECT OF LEUKOCYTES:
Adhesion of leukocytes takes place onto an implanted biomaterial. Due to the interaction of the implant with the leukocytes present in the surrounding tissue, the activation of macrophages takes place. These are recruited to the implantation site leading to inflammation and further leading to thrombosis as the endothelium gets activated.
BLOOD COMPATIBILITY TEST
This test is done in order to evaluate whether the biomaterial is susceptible to inducing adsorption or adhesion of blood components, destruction of blood cells, coagulation of blood, formation of thrombus, etc. This can be done by selecting the appropriate evaluation tools, methods, and conditions with respect to the device’s clinical use. This test can be done in vivo, ex vivo, or in vitro conditions.
The assessment of blood compatibility is very essential while the biomaterial is being tested for surface and anti-corrosion properties. Hemolysis and blood coagulation assays are most widely used to test the property of hemocompatibility. A hemolytic ratio of <5% is required for excellent blood compatibility.
NANOSTRUCTURAL COATING TO PREVENT HOST REACTIONS
As discussed earlier, the adverse reactions caused by the biomaterial have led to the use of surface coatings in the implants. The most commonly used coatings are nanostructured ones which tend to express the property of excellent blood compatibility. In clinical practice, the heparin coating of medical devices has been widely used. Using bioactive nanostructured coatings helps in promoting endothelialization.
THROMBOGENECITY
Thrombogenicity is the tendency of the material in contact with the blood to induce blood clotting or thrombus. This is the main reason for the failure of blood-containing medical devices. A rapid thrombogenicity evaluation comprises the analysis of platelet adhesion and activation and spreading it on biomaterial surfaces. In dynamic test systems, this can also be analyzed using SEM. Time-resolved monitoring can also be done using video systems. All biomaterials are thrombogenic to a certain degree. Certain devices do appear to be less thrombogenic due to the high flow rate of blood. A thrombogenic implant is covered by a fibrous capsule to avoid thrombogenesis.
TESTING PROCESS
Using a hematology analyzer, the number of RBCs, WBCs, and platelets is measured before and after the incubation of the blood with biomaterial. This analyzer uses the property of measuring the electrical impedance. A decrease in the count of platelets indicates that the material under study is a thrombogenic material.
For short-term use devices, the 4-hour NAVI canine study is conducted. This is conducted when other large animal testing is not available for the same. This is done to test the thrombogenicity of guidewires, balloon, and stent delivery systems, etc. Long-term animal studies are required to test thrombogenicity for indwelling catheters like central venous catheters. Cardiopulmonary bypass oxygenators and arterial filters can be tested for thrombogenicity by using a 6-hour in vitro circulation of blood through these devices.
For long-term devices like hemodialysis catheters, large-scale animal testing is done to assess the thrombogenicity of the biomaterial.
Thus the development of highly compatible blood and non-thrombogenic materials is tested for the efficient performance of the biomaterial.
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