Fully Collapsed (Kippah) Vesicles: Preparation and Characterization

Abstract

A study is presented of the formation of a kippah or hemispherical dome structure, a new morphology generated when a vesicle completely collapses to a hollow hemisphere. Justification for the new name is given in the Introduction. Relatively large vesicles of ca. approximately 500 nm in diameter were prepared from poly(acrylic acid)-block-polystyrene (PAA-b-PS) amphiphilic copolymer in the dioxane/water system. The vesicle specimens for transmission electron microscopy (TEM) were prepared using four different methods: drying under ambient conditions, freeze-drying, freeze-drying and subsequent resuspension in water, and drying under vacuum. The formation of the kippah was found to be strongly influenced by the method of preparation. When the vesicles were allowed to dry on the grid, either by drying under ambient conditions or by direct freeze-drying, "normal" vesicles (i.e., not kippah) with the classical indentation pattern were the only structures to be observed. Kippah vesicles, on the other hand, were obtained only by freeze-drying and subsequent rehydration in water or by direct drying under vacuum where no freezing is involved. The cause of the kippah vesicle formation is not yet completely understood for all methods of preparation; however, it was postulated to be strongly influenced by one or more of the following parameters: the relative flexibility of the vesicle wall, pressure gradient, and surface tension. Unlike "normal" vesicles, which exhibit, in TEM, a classical indentation pattern, kippah vesicles appear nearly round but with average wall thickness twice as large as in the "normal" vesicles. The study illustrates also the usefulness of specimen tilting in the analysis of the kippah. In addition, specimen tilting was found to allow the unambiguous determination of the orientation of the kippah on the surface (i.e., open-side-up or open-side-down).

Biomimetic block copolymer particles with gated nanopores and ultrahigh protein sorption capacity

“…2c). Collapsed vesicle structures similar to 'Kippah vesicles', described by Eisenberg 30 and van Hest 31 , are seen in this stage. The vesicles fuse to form lamellas, which are energetically favourable because the total interfacial energy between the aggregates and the solvent outside is reduced.…”

Cisplatin-Induced Formation of Biocompatible and Biodegradable Polypeptide-Based Vesicles for Targeted Anticancer Drug Delivery

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 Vesicles, unlike micelles, are prone to partial core collapse and membrane deformations due to their intrinsic hollow structure. [70][71][72] Drying of TEM samples cast onto copper grids by freezedrying or under direct vacuum has been reported to promote these deformations. 72 Using this method as an aid in further determining whether the self-assembly structures were indeed hollow structures suggestive of vesicles, TEM image of vacuum dried samples is presented in Figure 4C.…”

“…[70][71][72] Drying of TEM samples cast onto copper grids by freezedrying or under direct vacuum has been reported to promote these deformations. 72 Using this method as an aid in further determining whether the self-assembly structures were indeed hollow structures suggestive of vesicles, TEM image of vacuum dried samples is presented in Figure 4C.…”

Morphology control and 2D self-assembly of poly(styrene-co-divinylbenzene) capsules

“…Acetone was chosen as dispersant here based on its remarkable properties such as low density, low toxicity, difficult solubility for capsules, as well as better volatile performance than CCl 4 . During the follow-up evaporation process, since the diffusion rate of acetone through the PS-DVB wall toward the exterior is considerably faster than that of air toward the interior, a negative pressure is generated on the inside, thus leading to indentation [8,43]. By the time the pressure has equalized, the deformed PS-DVB wall would be rigid enough to withstand the pressure which, in turn, prevents the recovery and leads to the permanent setting of the indentation.…”

“…The concomitant micro-phase separation and symmetrical volume shrinkage of shell materials provided an approach to creating holes in polymer shell. Another significant approach was the deformation of hollow spheres [6][7][8][9], which is simple in mechanism. However, there is a little difficulty in morphology control of bowl-like particles in this approach.…”