The layer-by-layer (LbL) method has proved to be a simple but versatile technique for the construction of self-assembled films with controlled thickness and composition since it was first introduced by Decher et al. [1] Using this method, biopolymers, electroactive polymers, and photoactive polymers can be easily introduced into thin films. The resulting films can be bio-, electro-, or photoactive. [2] One advantage of the LbL method is that there is no restriction on the size and morphology of the substrate on which the film is constructed, which implies that the LbL method can be extended from twodimensional (2D) systems (i.e., planar substrates) to threedimensional (3D) systems (for example, spherical or other non-planar substrates). Consequently, a large variety of core± shell particles with finely tuned polymer layer thickness and compositions have been synthesized, [3] and a series of novel hollow microcapsules fabricated by subsequent removal of the sacrificial core of the resulting core±shell particles.[4] Since these supramolecular assemblies offer exciting prospects for the encapsulation of drugs, enzymes, proteins, and other active materials, they are attracting more and more attention.Up to now almost all papers in this area have employed the electrostatic self-assembly method, which is based on the sequential adsorption of oppositely charged polyelectrolytes, except for several cases with some minor modifications.[5] On the other hand, LbL strategies employing other driving forces, such as the hydrogen bond, have been developed.[6] Hydrogen-bonding self-assembly (HSA) was first introduced by Stockton and Rubner in 1997.[6a] Since then, several pairs of polymers have been successfully used in the self-assembly processes.[6b±f] However, no success has been reported in extending the HSA method from 2D to 3D systems and preparing hollow capsules by further removing the sacrificial core. One reason for the increased difficulty of this hydrogen-bonding process is the fact that hydrogen bonding is much weaker than the electrostatic interaction; consequently, rupture may occur when the sacrificial core is being removed. Since the formation and destruction of hydrogen bonds can be controlled easily by external stimuli, such as pH, [6d±f] capsules based on hydrogen bonding may have great merit when being used in controlled drug-release systems. In this report, we demonstrate that it is possible to extend the HSA method from 2D to 3D systems and further to prepare hollow capsules with successful procedures in removing the sacrificial core without rupturing the multilayer shell. Poly(vinylpyrrolidone), PVP, and m-methylphenol-formaldehyde resin (MPR) are employed as hydrogen acceptor and donor, respectively, in this method. Self-assembled films were first fabricated on planar substrates, i.e., quartz and silica slides, to examine the feasibility for HSA. The self-assembly process on quartz is followed by UV-vis spectroscopy (data not shown here). The absorbance of the film increases regularly with increasing bi...
