Surface Properties of Artificial Cell Membranes

As discussed under the section on blood substitutes, the surface property of artificial cell membranes is important in terms of their biocompatibility and retention in the circulation, as it is in terms of blood compatibility in hemoperfusion systems. Artificial cells for delivery systems also need to have different types of surface properties. Cellulose nitrate membrane artificial cells (Chang, 1957, 1964) contain negative charges due to the carboxyl groups in the polymer. Polyamide nylon membrane artificial cells (Chang et al., 1963, 1966; Chang, 1964) contain both carboxyl and amino groups. With the proper selection of polymer materials, membranes with the desired fixed charges can be obtained. For example, artificial cell membranes with strong negative charge groups have been prepared by using different amounts of sulfonated diamine such as 4,4'-diamine-2,2'-diphenyldisulfonic acid when preparing polyamide

Perspectives on the Future of Artificial Cells as Suggested by Past Research 313 VARIATIONS IN SURFACE PROPERTIES OF ARTIFICIAL CELLS

Other polyethylene glycol (PEG)

Perspectives on the Future of Artificial Cells as Suggested by Past Research 313 VARIATIONS IN SURFACE PROPERTIES OF ARTIFICIAL CELLS

Other polyethylene glycol (PEG)

Fig. 11.8. Surface properties of artificial cell membranes can be varied by 1) incorporation of negative or positive charge; 2) incorporation of albumin to increase blood compatibility; 3) incorporation of antigens to bind antibodies or antibodies to bind antigen; 4) incorporation of polysaccharide like heparin or polyethylene glycol (PEG) to increase compatibility or retention time in circulation.

Fig. 11.8. Surface properties of artificial cell membranes can be varied by 1) incorporation of negative or positive charge; 2) incorporation of albumin to increase blood compatibility; 3) incorporation of antigens to bind antibodies or antibodies to bind antigen; 4) incorporation of polysaccharide like heparin or polyethylene glycol (PEG) to increase compatibility or retention time in circulation.

membrane artificial cells (Chang, 1964, 1965, 1972a). The principle of incorporation of surface charges has also been used the preparation of lipid membrane artificial cells, lipid vesicles, drug delivery systems (Gregoriadis, 1976; Torchilin, 2005).

Albumin can bind tightly to the ultrathin collodion membrane of adsorbent artificial cells. This is initially used to increase the blood compatibility of the adsorbent artificial cells for hemoperfusion (Chang, 1969a). This albumin coating has also been applied to synthetic immunosorbents, resulting in blood compatible synthetic blood group immunosorbents (Chang, 1980d). In addition, Terman etal. (1977) showed in animal studies that albumin-coated collodion activated charcoal (ACAC) can remove antibodies to albumin. This has become a basis of one line of his research in which other types of antigens or antibodies are applied to the collodion coating of the artificial cells to form immunosorbents. Other immunosorbents based on this principle have also been developed for the treatment of human systemic lupus erythematosus; removal of antiHLA antibodies in transplant candidates; treatment of familial hypercholesterolemia with monoclonal antibodies to low-density lipoproteins (Terman, 1980;

Terman et al., 1979a, 1979b; Hakim et al., 1990; Wingard et al., 1991; Yang etal., 2004). Antibodies have also been incorporated in the surface of lipid liposomes to allow for drug targeting to cells bearing the corresponding antigen (Torchilin, 2005).

Mucopolysaccharides are important components of the surface of cell membranes. Incorporating a polyscharide, heparin to the artificial cell membrane, increases the biocompatibility and circulation time of artificial cells (Chang etal., 1967, 1968). Incorporation of a synthetic polymer, polyethylene glycol (PEG) into the membrane of artificial cells, nanocapsules and lipid vesicles, is even more effective for increasing biocompatibility and circulation time (Chang et al., 2003; LaVan etal., 2002; Torchilin 2005).

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