Biocompatibility improvement

In addition to laboratory blood analyzers and portable point-of-care devices, which require blood collection, continuous monitoring of ion activities in a blood stream via implanted ion-selective electrodes is of great interest. The term biocompatibility refers to the abihty of a sensor not to cause toxic or injurious effects while being in contact with living tissue. As dealing with any foreign object introduced into the human body, bio-compatibihty and hemocompatibility particularly are the most important requirements. 

The first aspect of biocompatibility is a natural immune response. When a foreign object enters the blood stream, it can be attacked by the body s defense system. The first step is protein adsorption on an object surface. It is believed that the amount and type of protein adsorption is one of the most important steps determining whether the object is tolerated or rejected by the body. The next step is cell adhesion, which may cause aggregation and activation of platelets and triggering of the blood coagulation system with resulting thrombus formation. It may not only lead to sensor failure via surface blocking but directly threatens the patient s health. 

In order to improve the biocompatibility of ISEs and reduce adsorption of cells and polypeptides several approaches have been used. Among them are immobilization of 

Electrochemical Sensors, Biosensors and Their Biomedical Apphcations 

The second aspect of biocompatibility is a leaching problem. Ion-selective electrode materials, especially components of solvent polymeric membranes, are subject to leaching upon prolonged contact with physiological media. Membrane components such as plasticizers, ion exchangers and ionophores may activate the clotting cascade or stimulate an immune response. Moreover, they can be potentially toxic when released to the blood stream in significant concentrations. 

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Looking beyond ceramic materials to elec-trets, polymer and elastomeric piezoelectric materials, and so-caUed electroactive materials, a wide-open field of research in high-strain piezoelectric materials is appearing. Using the same technology to manipulate the chemical and physical stractures of complex ionic or nanotube-imbibed polymers, strains of well over 50 % have been obtained in this new class of material, many examples of which are biocompatible. Improvements in reliability, tolerance of extreme ambient conditions, and modeling are important areas that remain to be considered. 

This example of vascular grafts devices points out the evolution of fibrous implantable medical devices and highlights the great potential offered by each scale level of fibrous structures for biocompatibility improvements. Fibers as well as whole fibrous stmctures should be considered as implantable devices that have inherent abilities to interact with the biological environment at each of the three predetermined scale levels. Study of characteristics and specificities of fibers, fibrous siuface, and fibrous volume should then provide a more forward-looking approach in the textile substitute s area for design and achievement of smart medical implantable textile devices. 

Negative results of protein adsorption, such as membrane fouling, thromboembolitic effects of implants, deffects of contact lens and others have been considered and some ways to reduce undesirable processes are given. To remove these difficulties it is useful to use low energetic surfaces of optimal surface energy with well water saturated surfaces, to avoid essential contributions of electrostatic interactions between the surfaces of protein and adsorbent, as well as conditions inducing denaturation of proteins in a solution. Materials with pre-adsorbed HSA, or a mixture of HSA and vitamin C are useful especially for biocompatibility improving. 

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