Polymer vesicles, adhesion

The growth in size of polymer vesicles formed from PS- -PAA BCPs was attribnted to fnsion and fission mechanisms by Eisenberg. Fnsion occnrs by contact and adhesion between the two vesicles. Coalescence, followed by destabilization of the central wall, leads to the formation of a single large vesicle. The reverse fission process was also demonsffated. 

Adhesion of different immune cells to one another or to epithelial cells has also been studied using planar bilayer models. For example, lymphocyte function-associated protein-1 (LFA-1) promotes cell adhesion in inflammation [i.e., a reaction that can be mimicked by binding to purified ICAM-1 in supported membranes (70)]. Similarly, purified LFA-3 reconstituted into supported bilayers mediates efficient CD2-dependent adhesion and differentiation of lymphoblasts (71). This work was followed by a study in which transmembrane domain-anchored and GPl-anchored isoforms of LFA-3 were compared (72). Because this research occurred before the introduction of polymer cushions and because the bilayers were formed by the simple vesicle fusion technique, the transmembrane domain isoform was immobile, whereas the GPl isoform was partially mobile. By comparing results with these two isoforms at different protein densities in the supported bilayer, the authors showed that diffusible proteins at a sufficient minimal density in the supported membrane were required to form strong cell adhesion contacts in this system. 

Polymer films have been obtained by plasma polymerization of hexafluorobenzene, N-vinylpyrrolidine, and chloracrylonitrile (Munro). Higuchi et al. have shown that irradiation of an azobenzene-modified poly(Y-methyl-L-glutamate-CO-L-glutamic acid) in bilayer membrane vesicles of distearyldimethylammonium chloride leads to trans-cis isomerization of the polymer this leads to transfer of the polypeptide from the hydrophobic bilayer membrane interior to the hydrophilic surface. As a result, there was a decrease in the ion permeability through the bilayer membrane and the formation of intervesicular adhesion. Eisner and Ritter have prepared photosensitive membranes from an aromatic polyamide and a cinnamate that incorporates a liquid crystalline component. 

Clearly, our results for adhesion of lipid bilayers in fibrinogen and albumin solutions are consistent with the (non-adsorption) depletion type of assembly process. This deduction is based on (i) the null observation that no fiuorescently labelled material was detected in the gap between bilayers, (ii) the continuous increase of the free energy potential with concentration even for fairly large volume fractions, and (iii) the transfer of adherent vesicle pairs with subsequent separation which showed that adhesion energy depended only on the composition of the medium exterior to the gap but not the gap composition. Similar results have been obtained for adhesion of lipid oilayers in solutions of high molecular weight dextran polymers (Figure 4, J ). Hence, we have chosen to carefully examine (non-adsorption) depletion-based theories in conjunction with these experiments. 

With grafted polymers included in the lipid bilayer interfaces, the micropipet manipulation of giant vesicles has shown that adhesion is prevented [75]. However,... 

---