Semi-permeable vesicles composed of natural clay
The authors report a way to produce semi-permeable vesicles from montmorillonite, a natural plate-like clay mineral that occurs widely in the environment. Simple shearing forces can assemble an aqueous suspension of montmorillonite clay plates onto air bubbles producing clay-armoured bubbles. Replacing the water with organic liquids will displace the air pocket inside the clay-armour with the liquid forming vesicles. Clay vesicles are microporous, exhibit size-selective permeability. This is the first time that any group has demonstrated self-assembly of inorganic minerals into structured compartments.
Clay armoured bubbles are produced by sandwiching a suspension of clay plates and air bubbles between two glass slides, and sliding them. The trapped air bubble will gather sufficient clay plates to form clay-armoured bubbles. A schematic is shown in the figure below. The bubbles range from 5 to 100 microns in radius. The clay armoured bubbles can created by sliding this bubbly clay suspension between other hydrophilic suspensions such as aluminum, copper and stainless steel.
Thin-shell vesicles of clay can then be produced by exposing the clay-armoured bubbles to certain water-miscible organic liquids. The picture below shows a detailed image of the clay vesicles. Note that there are pores on the vesicles which allow for it to act as a semi-permeable membrane.
1. A.B. Subramaniam, J. Wan, A. Gopinath and H.A. Stone, "Semi-permeable vesicles composed of natural clay", Soft Matter, 2011, 7, 2600-2612
2. M.M. Hanczyc, S.M. Fujikawa and J.W. Szostak, "Experimental Models of Primitive Cellular Compartments: Encapsulation, Growth, and Division", Science, 2003, 302 5645, 618-622