Nanoparticles with projection coronas were prepared by the one-step dispersion terpolymerization of styrene, acrylonitrile, and poly(ethylene glycol) monomethacrylate in ethanol−water solution, and their morphologies were controlled. When the mole composition of acrylonitrile to the total monomers C AN was 0.49−0.66, electron microscopy showed that the nanoparticles were spherical and had a number of projections on the surface. A C AN of more than 0.66 yielded no nanospheres, and a C AN smaller than 0.49 yielded projection-free nanospheres. The morphology of the nanospheres could be controlled by changing the reaction conditions, and some conditions yielded a regular arrangement of uniform projections on the surface similar to that seen in some coronaviruses. X-ray and spectroscopic studies suggested that the projections might be formed as a result of the nonequilibrated swelling of acrylonitrile and poly(ethylene glycol) domains on the surface.

The self-assembly of organic [1,2] and inorganic [3±6] particles can lead to various constructs with unique morphologies. Velev et al. reported the dielectrophoretic assembly of gold nanoparticle wires, [3] and Caruso et al. produced thin films of gold nanoparticles and hierarchically ordered monoliths of zeolite nanoparticles. [4,5] On the other hand, the three-dimensional (3D) assembly of organic particles can be manipulated by various organochemical modifications and can be controlled to give a wide-range of sizes. These features are important in the study of biomedical materials that use nanoparticles with immobilizing bioactive molecules on their surfaces, as well as in photonic devices prepared by colloidal crystallization [7] of nanoparticles, comparable in size to the wavelength of visible light (about 200±800 nm). Three-dimensional microconstructs with spherical morphology have been formed by the organization of nanoparticles on a spherical solid template, i.e., hetero-assembly, [8,9] which creates constructs based on nanoparticle±template interactions, and the construct morphology is controlled by the template shape. The organization of only one species of nanoparticles (homoassembly) can also lead to 3D microconstructs, some of which have been prepared by interparticle accumulation on a droplet template in a liquid±liquid [10±12] or an air±liquid system. [13] As the morphology is determined by the droplet shape, the constructs were always spherical or hemispherical. Homoassembly may represent a simple bottom±up technique using interparticle interactions and may be a basic step leading to the development of more complex organization methods, such as hetero-assembly. However, to the best of our knowledge, there have been no studies on 3D-microconstruct formation using simple polymeric-particle homo-assembly without a solid or liquid-droplet template. We have demonstrated an efficient one-step method for controlling the shape of a nanoparticle. [14,15] Here we report that freeze-drying results in the successful formation of 3D microconstructs by the simple homo-assembly of shape-controlled polymeric nanoparticles, by using physical interactions such as the exclusion force from freezing water.We recently prepared uniform nanoparticles of poly(styrene-co-acrylonitrile-co-poly(ethylene glycol) monomethoxy methacrylate, poly(St-co-AN-co-PEGm)s, with projection coronas (Fig. 1a) by the dispersion radical polymerization of monomers in an ethanol±water mixture. [14,15] The projection size increased with increasing polymerization period, whereas the polymer composition did not change.[15] Polymerization for 1 h yielded nanospheres without projections (Fig. 1c). The projections began to appear at 2 h, and after 3 h the projections gradually began to grow (transmission electron microscopy (TEM) images inset in Figs. 1d,e). However, we previously showed that the number of projections per nanosphere remained at 26 ± 2, regardless of the polymerization period after 2 h.[15]Figures 1c±e show scanning electron microsc...

We prepared irregularly shaped nanoparticles with carboxyl groups on the surface of nanoparticles in a "confetti"-like arrangement by dispersion copolymerization in the presence of the functional macromonomers methacryloyl-endcapped poly(methacrylic acid) (PMAA), poly(ethylene glycol) monomethoxymonomethacrylate (PEGm) with styrene (St), and acrylonitrile (AN), in the presence of 2,2′-azobis(isobutyronitrile) (AIBN) in a polar solvent. Concanavalin A (Con A) can be immobilized on the surface of these confetti nanoparticles, which showed a higher efficiency of Con A immobilization than the corresponding spherical nanoparticles (PMAA-PEGm-St nanoparticles and PMAA-St nanoparticles). Moreover, these Con A-immobilized confetti nanoparticles were able to capture HIV-1 virions (100 nm), even in the presence of erythrocytes (10 µm). This size-selective material adsorption property of the confetti nanoparticles is expected to be useful for various separation materials by changing the projection morphologies.