Internal Structure of Matrix-Type Multilayer Capsules Templated on Porous Vaterite CaCO3 Crystals as Probed by Staining with a Fluorescence Dye

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.

Layer-By-Layer Assemblies of Biopolymers: Build-Up, Mechanical Stability and Molecular Dynamics

“…Swelling or shrinkage of PEMs may also be induced via changes in the local microenvironment, such as changes in temperature, pH or ionic strength [ 152 ]. Controlled shrinkage and swelling upon these chemical [ 153 , 154 , 155 , 156 , 157 , 158 , 159 ] or physical stimuli (e.g., infra-red light [ 32 , 160 , 161 , 162 , 163 ], magnetic field [ 164 ]) has been mainly developed for polyelectrolyte capsules and biocoatings applied for drug delivery applications.…”

Encapsulation of Low-Molecular-Weight Drugs into Polymer Multilayer Capsules Templated on Vaterite CaCO3 Crystals

“…Such systems can effectively host proteins and other (bio)molecules of different nature, serving as high-level mimics of the extracellular matrix in 2D and 3D [12][13][14][15][16]. The utilization of this approach has assisted in the recent developments within the encapsulation of drug-loaded microparticles and in the reduction of release rate and the suppression of the initial burst release of these systems [17]. Popular drug delivery carriers developed as of recent are thin-walled PEMCs with a pre-designed geometry and size.…”

“…PEMCs are fabricated by the alternate deposition of oppositely charged polyelectrolytes onto decomposable core templates-resulting in a core-shell complex formation. This is followed by the elimination of the core template, leaving a free-standing polymeric shell or particle i.e., a PEMC [17][18][19]. Not only solid decomposable cores have been used for formation of advanced multilayer structures, but also soft particles such as protein aggregates [20,21] and biological cells [22].…”

Polyelectrolyte Multilayer Capsule (PEMC)-Based Scaffolds for Tissue Engineering

“…This is mainly driven by the binding of the drug molecule to free (uncompensated by permanent charges of oppositely charged polymer) charged groups of polymers in multilayers [ 187 ]. Based on this, the multilayer shell can be stained using fluorescent probes, which are typically small charged molecules [ 101 ] but can also host large proteins with molecular weight of a few hundreds of kDa [ 188 ]—providing large scope for scaffold-based applications.…”

“…Microencapsulation into PEMCs has been shown to be one of most promising techniques for the controlled delivery of bioactives [ 100 ] due to their many tunable properties and controlled modes of release [ 101 ]. Microencapsulation can be defined as the entrapment of molecules of interest into a particle within the particle size range typically from hundreds of nanometers [ 102 , 103 ] to tens of microns [ 104 , 105 ].…”