w e have shown previously (Couvreur et a1 1977) that polyacrylamide nanocapsules are a new type of lysosomotropic carrier, but unfortunately they are unlikely to be digested by lysosomal enzymes. This article describes the preparation and the morphology of polyalkylcyanoacrylate nanocapsules since polyaanoacrylate may be biodegradable, as suggested by its us in surgery (Collins et al 1969;Heisterkamp et al 1969) and by its chemical properties (Cameron et al 1965; Leonard et a1 1966 a, b; Pani et al 1968).We also present results of the sorption of small molecules on these nanocapsules.f Correspondence. b. 1. Morphological appearance of polymethyl-VUoacrylate nanocapsules by scanning electron -0scopy.Polymethyl and polyethylcyanoacrylate nanocapsules were prepared by polymerization. To Tween 20 (0.25 g), HCI 0.1 M (5.0 ml) in distilled water (50.0 ml) was added 0.6 ml of either of the monomers (methyl-or-ethylcyanoacrylate). After mechanically stirring for 30 min the mixture was passed through a fritted glass filter (pore size 9-15 pm) and then distilled water added t o 200 ml. After preparation, nanocapsules form milky suspensions displaying a Tyndall effect. The particles pass through a Millipore filter with 0.45 pm pores. This method is rapid and easy and avoids the destructive y-irradiation used in the preparation of polyacrylamide nanocapsules (Couvreur et al 1977).Scanning electron microscopy shows spherical particles with a diameter of about 200nm (Fig. 1). Variation of the Tween 20 concentrations did not affect the morphological appearance and size. Particles obtained without surfactant seem to be more agglomerated and larger than those with surfactant.Suspension of nanocapsules prepared with Tween 20 (0.1%) were spray frozen (Bachmann & SchmittFumian 1973) and examined by the electron microscope after freeze fracture. The use of fixatives and cryoprotectants are avoided by this method, while surfactants do not appreciably interfere. Fig. 2 shows that the inner structure appears to be highly porous, de-FIG. 2. The appearance of the internal structure of polymethylcyanoacrylate nanocapsules by the electron microscopy after spray freezing and cryofracture (see (Bachmann et al 1973) for details).

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