Abstract
Polyelectrolyte multilayer capsules (PEMCs) templated onto biocompatible and easily degradable vaterite CaCO3 crystals via the layer-by-layer (LbL) polymer deposition process have served as multifunctional and tailor-made vehicles for advanced drug delivery. Since the last two decades, the PEMCs were utilized for effective encapsulation and controlled release of bioactive macromolecules (proteins, nucleic acids, etc.). However, their capacity to host low-molecular-weight (LMW) drugs (<1–2 kDa) has been demonstrated rather recently due to a limited retention ability of multilayers to small molecules. The safe and controlled delivery of LMW drugs plays a vital role for the treatment of cancers and other diseases, and, due to their tunable and inherent properties, PEMCs have shown to be good candidates for smart drug delivery. Herein, we summarize recent progress on the encapsulation of LMW drugs into PEMCs templated onto vaterite CaCO3 crystals. The drug loading and release mechanisms, advantages and limitations of the PEMCs as LMW drug carriers, as well as bio-applications of drug-laden capsules are discussed based upon the recent literature findings.
Highlights
The recent development of drug delivery systems such as liposomes, micelles and polymeric micro-/nanoparticles and containers plays a vital role in the confrontation of several diseases and for use in vaccinations
This is followed by the elimination of the core template, leaving a free-standing polymeric shell or particle i.e., a Polyelectrolyte multilayer capsules (PEMCs) [17,18,19]
The PEMCs formed onto the vaterite crystals may be of either hollow or matrix type depending upon diffusion of polymers during the LbL deposition that is governed by polymer interactions and properties [17,43]
Summary
For the loading of small positively charged and water-soluble drugs, two strategies have recently attracted awareness; these are the “spontaneous” and the “charge-controlled attraction and repulsion” processes [66,67,68,69,70,71,72]. The pre-loading step includes pre-encapsulation of the matrix material (typically a polyelectrolyte); in which case, this material must have a high affinity to the core (i.e., lentinan [73] or heparin [74]), as well hold some affinity to the drug of interest This is followed by the elimination of the core, where the pre-loaded polyelectrolyte remains inside the formed capsule (this step is crucial for both methods). In some cases during this matrix-loading, after the pre-loading of a negatively charged polyelectrolyte and the removal of the core, a part of the negatively charged polyelectrolyte is entangled within the multilayers; some of which is paired up with the excess adsorbed polycation This is the ‘charge-controlled attraction repulsion’ effect. Tnshtiistumenetshodf hamsuslhtiolwaynertsofdoramminagticPaElMlyCresd[u88c]e. capsule permeability and enhance retention after shrinkage
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