# Self-Assembled Polymer Membrane Capsules Inflated by Osmotic Pressure

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Original entry: Alexander Lukin, AP 225, Fall 2012

## General information

"Authors:" Vernita D. Gordon, Xi Chen, John W. Hutchinson, Andreas R. Bausch, Manuel Marquez and David A. Weitz

"Publication:" http://www.ncbi.nlm.nih.gov/pubmed/15506776

"Key words:" Surfactants, Self-assembly, Polymer

## Summery

Fig.1 Scheme of fabrication pocess

Polymer membrane capsules are formed by colloidal particles that adsorb at the interface of an emulsion droplet and are stabilized by a network of polymer. Their properties are dominated by the adsorbed polymer, so that these capsules are much more resilient to mechanical deformation than sintered colloidosomes. This structures are very promising for holding sensitive contents and releasing them under certain environment conditions. Also the fabrication of such type of capsules uses simple few-step process so they are suitable for industrial manufacture.

## Fabrication process

1. Emulsification of an aqueous solution of poly-L-lysine (PLL) in a toluene suspension of 1.3 ${\mu}m$ diameter polystyrene beads with carboxyl surface groups (Fig. 1a)
2. The colloids self-assemble onto the emulsion interfaces, where PLL molecules adsorb to and lock together neighboring beads (Fig. 1b)
3. The coated emulsion droplets are gently washed into octanol, which has a lower interfacial tension with water than does toluene, and then centrifuged into an aqueous solution of nonionic surfactant (Fig. 1c)

These capsules are almost always spherical, since their size and shape are determined by the initial templating emulsion droplets; capsules keep their spherical shape for 2-4 days after fabrication. The sise of the capsule is determined by the size of emulsion droplet, thus can vary in large limits. For some applications, such as drug delivery capsules may be filled with contents from the templating emulsion; this two-step fabrication process with an intermediate emulsion ensures that the inner phase always remains separate from the outer phase, allowing high encapsulation efficiency.

## Properties

These capsules have polyelectrolyte membrane which is permeable for water and other "small" molecules but not for PPL, so due to the osmotic pressure they are inflated. The pressure inside is determined by the concentration of the PPL during fabrication process. Due to this properties capsules can be triggered do deflate under specific ambient conditions. In aqueous solutions, salt reduces polyelectrolyte osmotic pressure; the capsule membrane is permeable to small salt ions and aqueous countering. Capsules in 0.025 M NaCl solution become much softer to indentation, and in 1 M NaCl solution they are entirely deflated. These results suggest other possible release triggers, including pH, temperature, and solvent, upon which the charge and conformation of PLL are known to depend.

## Reference

Vernita D. Gordon, Xi Chen, John W. Hutchinson, Andreas R. Bausch, Manuel Marquez and David A. Weitz, "Self-Assembled Polymer Membrane Capsules Inflated by Osmotic Pressure" Journal of the American Chemical Society 126 (2004) 14117