Abstract
Multilayer capsules templated on decomposable vaterite CaCO3 crystals are widely used as vehicles for drug delivery. The capsule represents typically not a hollow but matrix-like structure due to polymer diffusion into the porous crystals during multilayer deposition. The capsule formation mechanism is not well-studied but its understanding is crucial to tune capsule structure for a proper drug release performance. This study proposes new approach to noninvasively probe and adjust internal capsule structure. Polymer capsules made of poly(styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDAD) have been stained with fluorescence dye rhodamine 6G. Physical-chemical aspects of intermolecular interactions required to validate the approach and adjust capsule structure are addressed. The capsules consist of a defined shell (typically 0.5–2 µm) and an internal matrix of PSS-PDAD complex (typically 10–40% of a total capsule volume). An increase of ionic strength and polymer deposition time leads to the thickening of the capsule shell and formation of a denser internal matrix, respectively. This is explained by effects of a polymer conformation and limitations in polymer diffusion through the crystal pores. We believe that the design of the capsules with desired internal structure will allow achieving effective encapsulation and controlled/programmed release of bioactives for advanced drug delivery applications.
Highlights
The layer-by-layer (LbL) assembly of oppositely charges polyelectrolytes is a simple but powerful method allowing the design of multilayer polymer architectures [1,2,3,4]
We present a new approach to identify the capsule structure that is based on the postloading of preformed capsules with the fluorescent dye, rhodamine 6G (R6G)
This study demonstrated development of novel approaches for the investigation of internal structure of polyelectrolyte capsules based on nondestructive postloading with fluorescent probes
Summary
The layer-by-layer (LbL) assembly of oppositely charges polyelectrolytes is a simple but powerful method allowing the design of multilayer polymer architectures [1,2,3,4]. Different release behavior for the capsules of identical composition but templated on the cores of different nature (MnCO3 and melamine formaldehyde) revealed that the capsules prepared using different core materials can be either hollow or filled with an internal polymer matrix present into the capsule lumen [10]. This depends on the porosity of the cores and ability of polymers to diffuse into the core
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