Dextran Coatings for Aggregation Control of Layer-by-Layer Assembled Polyelectrolyte Microcapsules

Abstract

We propose dextran and dextran polyaldehyde (DPA) coatings for modification of layer-by-layer (LbL) assembled polyelectrolyte microcapsules which provide stability against aggregation in 0.75 M aqueous solutions of mono- and bivalent ions (Na(+), Cl(-), Ca(2+), HPO(4)(2-)). The microcapsules were prepared of three bilayers of poly(4-styrenesulfonate) (PSS) and poly(allylamine) (PAH). Dextran and its derivatives were attached to amino-terminated surface of the microcapsules via three types of chemical bonds of subsequently increasing strength: (1) hydrogen bonds, (2) hydrolyzable covalent cross-links resulting from aldehydes and primary amines coupling, and (3) nonhydrolyzable covalent C-N single bonds of secondary amines. Attachment of the DPA materials via the latter two types of bonds resulted in strengthening the capsules' walls which preserved a fraction of the microcapsules from disintegration upon electrostatic swelling in 0.1 M NaOH. The non-disintegrated fraction of the DPA-coated microcapsules restored their initial size after pH was decreased back to neutral. The microcapsules coated with the original dextran immobilized via hydrogen bonds and the bare microcapsules were fully dissolved under the alkaline conditions. The preserved fraction of the microcapsules was higher for the DPA materials with higher contents of the aldehyde groups and after conversion of the hydrolyzable covalent cross-links to the nonhydrolyzable secondary amines via reduction with NaBH(4). The higher contents of the aldehyde groups and the reduction led to the lower limiting swelling degree of the DPA-coated microcapsules at alkaline pH. The proposed coatings can be used for colloid stabilization of polyelectrolyte microcapsules in aqueous medium, encapsulation of pH-insensitive macromolecules at the postpreparation stage, and pH-triggered release of encapsulated material.

Intracellularly Biodegradable Polyelectrolyte/Silica Composite Microcapsules as Carriers for Small Molecules

“…The red fluorescent signal was observed with a main distribution around the inner shell of the composite capsules, Figure 3B, due to the attachment of dextran to the amino-terminated inner surface of the microcapsules. 47 Actually this type of attachment can be facilitated by both hydrogen bonds and hydrolyzable covalent cross-links resulting from aldehydes and primary amines coupling. 47 In order to investigate whether it is possible to encapsulate small drugs, Rh-B was used as a model molecule.…”

Supramolecular hydrogel microcapsules via cucurbit[8]uril host–guest interactions with triggered and UV-controlled molecular permeability

“…Although powerful, the requirement for multiple immersion-centrifugation/filtration-washing steps render the preparation process both time and material intensive. 20–22 …”

Layer‐by‐Layer Assembly Through Weak Interactions and Their Biomedical Applications

“…At the beginning, only electrostatic interactions were utilized for LbL assembly. Subsequently, other interactions such as covalent bond,38–44 hydrogen bonding,45–51 charge transfer,52, 53 hydrophobic,54–56 host–gest,57–60 and coordination bond61–67 interactions have been investigated to facilitate polymer association for ultrathin film deposition. The most important concept for LbL assembly is how to use the interactions between the polymeric materials.…”