NANOENGINEERED POLYMERIC CAPSULES

Nanoengineered polymeric capsules (NPCs) can be produced in the following way [1–3]. Particles of the desirable sizes and stable in one conditions and soluble in others (for example, in different pH ranges) are taken as templates. Then, a method of polyelectrolyte self-assembling (layer-by-layer method) is applied for the construction of the capsule shell on these template particles. The method is described in the appropriate section of our web-site. Thus, here we concentrate only on specific features, essential for working with particulate substrates. First, it is much difficult to transfer particles from solution of polyanion to the solution of polycation and vice versa.

 

Several methods were suggested to perform it [4].

First one is called a method of concentration matching. In this case, the number of the template particles and their total surface area must be precisely known. The amount of the polymers of each layer, added to the particle solution must correspond exactly to form a layer of about 1 nm on the surface of each particle. Thus, after the reaction there is no free polymers in the solution, and oppositely charged polymer molecules can be added to the solution. Their amount must again correspond well to that necessary for the second layer formation. The procedure must be repeated desirable number of times, giving necessary thickness of the shell. However, the method is not widely used, as it will need rather long time for all polymer molecules to be attached to the particles.

Second method is based on the centrifugation of the solutions after each layer formation. After the precipitation, the upper solution is removed from the vessel. It is useful to wash the particles several times in order to guarantee the complete removal of the excess polymer molecules. Thus, pure water must be added to the solution, carefully shacked and centrifuged again, and upper solution will be taken away. Only after this, the solution of oppositely charged polymer can be added and the procedure will be repeated. Even if the method implies the loss of some amount of particles during each washing procedure, it is the mostly frequently used one, as it is rather simple and reliable.

The other method is based on the electrophoretic removal of the excess polymer molecules after the layer formation. In this case, the template particle solution is limited with porous membrane with the hole size less than the particle diameter. Thus, after the layer formation, it is possible to remove the polymer molecules by applying appropriate electrical potential inducing their flox from the working area through the membrane.

When the shell of the capsule will reach the desirable thickness, the assembling process must be finished and the template particles must be dissolved. Usually, at can be done by varying the pH of the solution or by changing the solvent. After this, the solution of hollow polymeric capsules is realized. Capsule size and shape depends on the used templates. Currently, the usual sizes are in the 200 nm – several micron range. The capsule shell thickness can be formed with the resolution of about 1 micron (one layer thickness).

The capsule shell can contain not only usually used polyanions (PSS) and polycations (PAH), but also other charged molecules, such as proteins [5-6], DNA [7] and even inorganic particles, [8] providing programmed properties to the realized particles. In our case, for example, the presence of the oligonucleotites in the final layer of the capsule shell will allow specific recognition of the complimentary sequences in the single stranded DNA, immobilized on the solid surfaces.

Important feature of the NPCs is the possibility of opening and closing the pores in the capsule shell [9]. It can be done by the variation of the solvent properties (composition, pH, ionic strength). Thus, the capsules can be considered as a smart containers. For the pharmacology, for example, they can perform the intelligent drug release, when the capsule is in the zone where normal metabolism is interrupted.

AFM image of hollow PAH-PSS capsules.

1. G. B. Sukhorukov, E. Donath, H. Lichtenfeld, E. Knippel, M. Knippel, A. Budde, and H. Möhwald, Colloids and Surfaces A, 137, 253-266 (1998).

2. G.B. Sukhorukov, E. Donath, S.A. Davis, H. Lichtenfeld, F. Caruso, V.I. Popov, and H. Möhwald, Polymers for Adv. Technol., 9, 759-767 (1998).

3. A. Voigt, H. Lichtenfeld, H. Zastrow, G.B. Sukhorukov, E. Donath, and H. Möhwald, Ind. Engineer. Chem. Res., 38, 4037-4043 (1999).

4. G.B. Sukhorukov, Designed Nano-Engineered Polymer Films on Colloidal Particles and Capsules, in Novel Methods to Study Interfacial Layers (D. Möbius and R. Miller, eds.) Elsevier Science B.V., pp. 383-414 (2001).

5. N.G. Balabushevich, G.B. Sukhorukov, and N.I. Larionova, Macromol. Rapid Commun., 26, 1168-1172 (2005).

6. L. Pastorino, S. Disawal, C. Nicolini, Y.M. Lvov, and V. Erokhin, Biotechnol. Bioengineer., 84, 286-291 (2003).

7. D.G. Shchukin, A.A. Patel, G.B. Sukhorukov, and Y.M. Lvov, J. Am. Chem. Soc., 126, 3374-3375 (2004).

8. D.H. Turkenburg, A.A. Antipov, M.B. Thathagar, G. Rothenberg, G.B. Sukhorukov, and E. Eiser, Phys. Chem. Chem. Phys., 7, 2237-2240 (2005).

9. T. Mauser, C. Dejugnat, and G.B. Sukhorukov, Macromol. Rapid Commun., 25, 1781-1785 (2004).