Structure biocompatibility related

Design considerations for vascular access devices include ease of handling, insertion, and use minimal thrombotic and other biocompatibility-related complications stmctural and operational reliability over time and optimization for application-specific performance issues (Canaud et al., 2000). Three different catheter tips are shown in Fig. 20.10 to illustrate these variations in design and structure. Because of the distinct characteristics of the different treatments and agents deployed through catheters, it is not practical to provide specific values for flow rates, pressure drops, viscosities, and other important transport properties. 

Adsorbents are used in medicine mainly for the treatment of acute poisoning, whereas other extracorporeal techniques based on physico-chemical principles, such as dialysis and ultrafiltration, currently have much wider clinical applications [1]. Nevertheless, there are medical conditions, such as acute inflammation, hepatic and multi-organ failure and sepsis, for which mortality rates have not improved in the last forty years. These conditions are usually associated with the presence of endotoxin - lipopolysaccharide (LPS) or inflammatory cytokines - molecules of peptide/protein nature [2]. Advantages of adsorption over other extracorporeal techniques include ability to adsorb high molecular mass (HMM) metabolites and toxins. Conventional adsorbents, however, have poor biocompatibility. They are used coated with a semipermeable membrane of a more biocompatible material to allow for a direct contact with blood. Respectively, ability of coated adsorbents to remove HMM solutes is dramatically reduced. In this paper, preliminary results on adsorption of LPS and one of the most common inflammatory cytokines, TNF-a, on uncoated porous polymers and activated carbons, are presented. The aim of this work is to estimate the potential of extracorporeal adsorption technique to remove these substances and to relate it to the porous structure of adsorbents. 

Dendrimers such as poly(amidoamine) (PAMAM) and poly(propylenimine) (PPI) have also been studied for gene delivery in vitro and in vivo due to their high transfection efficiency. However, the toxicity of the dendrimers is of major concern for their medical use. Generally, in vivo toxicity of dendrimers is related to various factors, including their chemical structure, surface charge, generation and the dose of dendrimer used. Surface modification with PEG or replacement with low generation dendrimers have been reported to be able to improve the biocompatibility of these biomaterials. ... 

The surfactant properties of macromolecules (and hence their ability to self-assemble into functionally interesting motifs) can be controlled with high sensitivity by manipulating molecular architecture without changing the chemical identity of the amphiphilic moieties. In addition to differences in surfactant properties between macromolecules in different architectural classes, subtle variations in an architectural class also lead to significant effects. This is due to the importance of conformational entropy for self-assembly processes of polymers. This notion of choosing the nature of the connections between the amphiphilic moieties to control surfactant properties may prove useful in applications where the choice of chemical structure is restricted (e.g., for concerns related to biocompatibility or toxicity). 

Another type of carbon layer useful for the preparation of biocompatible surfaces includes chemical and physical vapor deposition. The preparation of the carbon layers on pol3rtetrafluoroethylene (PTFE) by photoinduced CVD from acetylene and their physical properties and chemical structure have been studied. These properties related to the adhesion and proliferation of human umbilical endothelial cells (HUVEC) seeded thereon were characterized [39]. 

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