Polyelectrolyte Multilayers on Soft Colloidal Nanosurfaces: A New Life for the Layer-By-Layer Method

Abstract

The Layer-by-Layer (LbL) method is a well-established method for the assembly of nanomaterials with controlled structure and functionality through the alternate deposition onto a template of two mutual interacting molecules, e.g., polyelectrolytes bearing opposite charge. The current development of this methodology has allowed the fabrication of a broad range of systems by assembling different types of molecules onto substrates with different chemical nature, size, or shape, resulting in numerous applications for LbL systems. In particular, the use of soft colloidal nanosurfaces, including nanogels, vesicles, liposomes, micelles, and emulsion droplets as a template for the assembly of LbL materials has undergone a significant growth in recent years due to their potential impact on the design of platforms for the encapsulation and controlled release of active molecules. This review proposes an analysis of some of the current trends on the fabrication of LbL materials using soft colloidal nanosurfaces, including liposomes, emulsion droplets, or even cells, as templates. Furthermore, some fundamental aspects related to deposition methodologies commonly used for fabricating LbL materials on colloidal templates together with the most fundamental physicochemical aspects involved in the assembly of LbL materials will also be discussed.

Keywords: electrostatic self-assembly; layer by layer; multilayers; nanosurfaces; polyelectrolytes; soft colloids.

Figure 1

Sketch showing an idealization of the linear and non-linear trends of polyelectrolyte multilayers as the dependence of the adsorbed amount on the number of bilayers, N.

Figure 2

Change of the ξ potential (blue symbols) and multilayer thickness (red symbols) with the alternate deposition of poly(diallyldimethylammonium chloride (PDADMAC) and poly(4-styrenesulfonate of sodium) (PSS) layers onto silicon wafers from polyelectrolyte solutions with concentration 10 mM, and ionic strength fixed in 100 mM. Reprinted from reference [139], Copyright (2014), with permission from the American Chemical Society.

Figure 3

Scheme of the expected configuration of polyelectrolyte layers and counterions in intrinsically and extrinsically compensated polyelectrolyte multilayers.

Figure 4

(a) Compensation ratio R_c in (PDADMAC-PSS)_n multilayers as a function of the ionic strengths. Data adapted from reference [89], Copyright (2009), with permission from The Royal Society of Chemistry. (b) Sketch displaying the general internal charge balance in polyelectrolyte multilayers. Reprinted from reference [140]. Copyright (2013), with permission from American Chemical Society. (c) Representation of the asymmetrical compensation in polyelectrolyte multilayers as a function of the nature of the last deposited layer. Reprinted with permission from reference [149]. Copyright (2012) American Chemical Society.

Figure 5

Sketch of the common methodology used for the fabrication of Layer-by-Layer (LbL) multilayers on a flat substrate by deposition for immersion.

Figure 6

Sketch of the most frequent approach for the deposition of LbL multilayers onto colloidal particles. Reprinted from reference [184], Copyright (2014), with permission from the American Chemical Society.

Figure 7

Sketch of the LbL approach for the fabrication of different LbL decorated liposomes. Reprinted with permission from reference [238]. Copyright (2020), with permission from the American Chemical Society.

Figure 8

Release profiles for ellagic acid from bare liposomes (L) and biopolymer-coated liposomes with two and four bilayers (CHT: chitosan and DXS: dextran sulfate). Data adapted from reference [254], Copyright (2010), with permission from Elsevier.

Figure 9

(a) Temporal evolution of the gene silencing effect of liposomes loaded with a 21-base-pair locked nucleic acid siRNA analogue on the human ovarian cancer cell line OVCAR8 depending on their preparation protocol: untreated (black symbols), assembled in deuterated water (red symbols) and assembled in HEPES and NaCl (blue symbols9 (b) Gene silencing effect of liposomes loaded with 21-base-pair locked nucleic acid siRNA analogue on the human ovarian cancer cell line OVCAR8 depending on their preparation protocol after two days of their injection. Reprinted with permission from reference [260]. Copyright (2019), with permission from American Chemical Society.

Figure 10

Sketch of the LbL approach for the fabrication of different nanocarriers using multilayers. Reprinted with permission from reference [284]. Copyright (2015), with permission from Elsevier.

Figure 11

Cyanine IR-786 (a) dispersed in water, (b) solubilized in bare nanoemulsion, and (c) encapsulated in nanoemulsion coated by (PSS-PDADMAC)_4.5. Reprinted with permission from reference [297]. Copyright (2012), with permission from Elsevier.

Figure 12

Time evolution of the creaming index for emulsions coated with different numbers of PSS and poly(allylamine hydrochloride) (PAH) layers. Reprinted with permission from reference [290]. Copyright (2011) with permission from PCCP Owner Societies.

Figure 13

Schematic representation of the positive effect of LbL films on the stability of cells against physical stresses: (a) effect of physical stresses on a nude cell and (b) effect of physical stresses on a LbL coated cell. Reprinted with permission from reference [315]. Copyright (2013), with permission from American Chemical Society.

Figure 14

Cell viability after centrifugation for human hepatocyte carcinoma cells with (○) and without (Δ) fibronectin–gelatin containing nine layers. Reprinted with permission from reference [315]. Copyright (2013), with permission from American Chemical Society.