pH-Dependent Loading and Release Behavior of Small Hydrophilic Molecules in Weak Polyelectrolyte Multilayer Films

Abstract

The pH-dependent loading and release behavior of small hydrophilic molecular probes in polyallylamine and hyaluronic acid multilayer films was investigated. These studies were carried out using the water-soluble dyes Indoine Blue and Chromotrope 2R, and their loading and release profiles were followed with UV-vis spectroscopy. The results of these studies suggest that the incorporation and release of material from such films depend on the degree of film swelling, the ability of the dye molecules to aggregate in the film, as well as the attractive and repulsive interactions occurring between the probe molecules and the acid-base functional groups in the films. Both the degree of dissociation of the acidbase functional groups and the extent of film swelling are pH-sensitive. As a result, the amount of each dye incorporated in the film also depends on the pH conditions, with a maximum loading capacity of 3.8 × 10 -3 mg/cm 3 of Chromotrope 2R and 5.7 × 10 -2 mg/cm -3 of Indoine Blue. In turn, we found that by manipulating the pH of the release solution it is possible not only to control the rate of the release of the molecular probes but also to regulate the amount of probe material released. In fact, completely trapping the incorporated probes in the multilayer films was also successfully demonstrated. These findings can be rationalized by examining the interactions of the dye molecules with the polyelectrolytes, the ability of molecules to form J-aggregates, and pH-dependent physicochemical properties of the multilayer system, such as the acid-base equilibria of the polyelectrolytes and the swelling behavior of the films. It is believed that this information is fundamentally important to understanding of how to effectively manipulate the films for potential controlled release applications.

pH‐Switchable Bioelectrocatalysis Based on Weak Polyelectrolyte Multilayers

“…Similar results were reported previously [30], in which the dramatic change in thickness of {PAH/PAA} n films could be induced by changing the pH of assembly solutions. For the films assembled at PAH/PAA pH 4/8, for example, PAH is almost completely protonated at pH 4.0 and takes the extended conformation with its pK a at about 8.5 in solution [24,33,40], while PAA is nearly totally ionized at pH 8.0 with its pK a at around 5.0 [28,33] and also takes the stretched and rodlike conformation in solution. Under this condition, fully ionized and oppositely charged PAH and PAA tend to form a very flat and thin film in their LBL assembly with many ionic cross-links [28,30].…”

Multilayered drug delivery coatings composed of daidzein-loaded PHBV microspheres embedded in a biodegradable polymer matrix by electrophoretic deposition

“…1,2 In particular, polymer based coatings can serve as drug delivery platforms, releasing biomolecules (antibiotics, growth factors, proteins, peptides, genes) preloaded into the coating matrix, to convert conventional implants into biologically active components. 3,4 In comparison with conventional oral or injectable therapies usually associated with side effects, such coating systems should be able to release drug molecules locally and in a controlled manner for prolonged periods. 3,5 Local drug release provides the possibility of an efficient dosage at the defect site while avoiding undesired systemic effects.…”

“…3,4 In comparison with conventional oral or injectable therapies usually associated with side effects, such coating systems should be able to release drug molecules locally and in a controlled manner for prolonged periods. 3,5 Local drug release provides the possibility of an efficient dosage at the defect site while avoiding undesired systemic effects. Furthermore, the coating materials, mainly constituted of watersoluble or biodegradable polymers, could be degraded gradually under physiological conditions.…”

Temperature-induced molecular transport through polymer multilayers coated with PNIPAM microgels

“…Nowadays these multilayer films are extensively used as reservoirs to host bioactive molecules aiming at biological applications. [6][7][8][9][10] A variety of molecules can be embedded into the films; they include small drugs and dyes, [11][12][13][14][15][16][17] proteins and peptides, [18][19][20][21] or nucleic acids. 22,23 Extensive reviews on the reservoir properties of the multilayers can be found elsewhere.…”