Fabrication of Robust Capsules by Sequential Assembly of Polyelectrolytes onto Charged Liposomes

Abstract

This work presents a simple methodology for coating small unilamellar liposomes bearing different degrees of positive charge with polyelectrolyte multilayers using the sequential layer-by-layer deposition method. The liposomes were made of mixtures of 1,2-dioleyl-sn-glycero-3-phosphocoline and dimethyl dioctadecyl ammonium bromide (DODAB) and coated by alternated layers of the sodium salt of poly­(4-styrenesulfonate) (PSS) and poly­(allylamine) (PAH) as polyanions and polycations, respectively. The results show that the zeta potential of the liposomes was not very sensitive to the mole fraction of DODAB in the membrane, X D, in the range 0.3 ≤ X D ≤ 0.8. We were able to coat the liposomes with up to four polymer bilayers. The growth of the capsule size was followed by dynamic light scattering, and in some cases, by cryo-transmission electron microscopy, with good agreement between both techniques. The thickness of the layers, measured from the hydrodynamic radius of the coated liposome, depends on the polyelectrolyte used, so that the PSS layers adopt a much more packaged conformation than the PAH layers. An interesting finding is that the PSS amount needed to reach the isoelectric point of the capsules increases linearly with the charge density of the bare liposomes, whereas the amount of PAH does not depend on it. As expected, the preparation of the multilayers has to be done in such a way that when the system is close to the isoelectric point, the capsules do not aggregate. For this, we dropped the polyelectrolyte solution quickly, stirred it fast, and used dilute liposome suspensions. The method is very flexible and not limited to liposomes or polyelectrolyte multilayers; also, coatings containing charged nanoparticles can be easily made. Once the liposomes have been coated, lipids can be easily eliminated, giving rise to polyelectrolyte nanocapsules (polyelectrosomes) with potential applications as drug delivery platforms.

Essential Oils and Their Individual Components in Cosmetic Products

“…It was stated above that the use of EOs and EOCs in the formulation of products present several drawbacks, which make difficult their manipulation and handling due to their volatility, limited solubility in water, and thermal and chemical lability (most of these substances undergo fast oxidation process upon exposure to the environment). These problems may be partially overcome by solubilizing, encapsulating and/or protecting the active molecules by using different type of nanocarriers, e.g., soft nanoparticles (polymeric or solid lipid), hard nanomaterials, cyclodextrins, liposomes or emulsions [175][176][177][178][179][180][181][182][183][184][185][186]. The use of nanocarriers may help on preparing formulations containing the active compounds (EOs and EOCs) within a well-controlled container, which can contribute to the enhancement of their stability and availability.…”

Polyelectrolyte Multilayered Capsules as Biomedical Tools

“…Thus, the lower density of the emulsion droplets in relation to the aqueous continuous phase facilitates their recovery by flotation in the layering solutions [65,66], and the use of centrifugation can be exploited to obtain an enhanced creaming yield [67][68][69]. Conversely, the separation of the excess unbound material when vesicles or liposomes are used as templates for the LbL assembly becomes even more complex, involving in some cases up to three different steps for each pair of deposited bilayers [70,71]: (i) The first layering solution is added to a diluted suspension containing vesicles/liposomes to form the first layer; (ii) the second layering solution is added to the dispersion containing the polyelectrolyte-decorated vesicles/liposomes, and the excess unbound material resulting after the deposition of the first layer, leading to the formation of the second layer and interpolyelectrolyte complexes; and (iii) the interpolyelectrolyte complexes are settled by centrifugation, and a dispersion containing the polyelectrolyte-decorated vesicles/liposomes is obtained. It should be noted that after the deposition of the first bilayer, the deposition of the subsequent bilayers can be obtained following a similar sequence.…”

Probing the effect of the capping polyelectrolyte on the internal structure of Layer-by-Layer decorated nanoliposomes

“…Moreover, the necessity of supporting the samples for its visualization in the above mentioned microscopy techniques can also contribute to obtain structural information about the capsules that is not provides a true representation of the system under preparation, storage or application conditions. Furthermore, SANS and SAXS provide information even on the wall thickness which is not easily accessible by other techniques, such as dynamic light scattering (DLS) or cryogenic transmission electronic microscopy (cryo-TEM) [27]. SANS and SAXS provide important information on the density profiles along with the multilayer structure, which can be used for deepening on the characterization of the organization of the polyelectrolyte layers in relation to the template.…”

“…SANS and SAXS provide important information on the density profiles along with the multilayer structure, which can be used for deepening on the characterization of the organization of the polyelectrolyte layers in relation to the template. The combination of scattering results with data obtained by using other techniques, e.g., Electron Spin Resonance (ESR), can contribute obtaining a realistic picture of the internal structure of polyelectrolyte films deposited on soft colloidal templates [27].…”