Adsorption natural materials, advantages

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. 

Traditional (i.e., non-MIP) SPE sorbents are similar to HPLC stationary phases. The advantages of many of these materials are that they are widely available, well characterized, have high binding capacity, and show linear adsorption behavior. One may observe that just a few types are used in the majority of sample preparations, i.e., these materials are quite generic, and it is the wash and elution step which is varied according to the application. The generic nature of these materials is also a drawback because it reflects their limited selectivity. 

An enzyme can be immobilized on/in a resin carrier either by adsorption (by hydrophobic, electrostatic or other forces) or it can be covalently linked to the resin. Carrier materials used for immobilization in biocatalysis include natural, synthetic, organic, inorganic, porous and non-porous materials. The main advantage compared to immobilization without a carrier is in general a better defined immobilized enzyme, as particle size, pore size, porosity, hydrophobicity and so on is pre-determined from the choice of carrier. However, the carrier cost is often significant. 

The crystalline nature of zeolites and MOFs allows structures to be designed with very narrow pore size distributions. This opens up another potential application for such materials as porous membranes for the separation, and/ or purification of hydrogen supplies. Size separation could be augmented by selective adsorption of impurities, taking advantage of the inherently low enthalpy of adsorption for hydrogen on these surfaces. 

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