The fabrication of polyelectrolyte multilayer films (PEMs) using the Layer-by-Layer (LbL) method is one of the most versatile approaches for manufacturing functional surfaces. This is the result of ...the possibility to control the assembly process of the LbL films almost at will, by changing the nature of the assembled materials (building blocks), the assembly conditions (pH, ionic strength, temperature, etc.) or even by changing some other operational parameters which may impact in the structure and physico-chemical properties of the obtained multi-layered films. Therefore, the understanding of the impact of the above mentioned parameters on the assembly process of LbL materials plays a critical role in the potential use of the LbL method for the fabrication of new functional materials with technological interest. This review tries to provide a broad physico-chemical perspective to the study of the fabrication process of PEMs by the LbL method, which allows one to take advantage of the many possibilities offered for this approach on the fabrication of new functional nanomaterials.
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•Layer-by-layer (LbL) method is a powerful tool for the assembly of supramolecular materials.•Absence of any theoretical limitations to the assembled compounds and the geometry of the final material•Assembly of LbL multilayers is governed by an intricate balance of interactions.•Study of physico-chemical properties and structure of the LbL films is critical for their potential applications.
The bulk and interfacial properties of solutions formed by a polycation (i.e., poly(diallyl-dimethylammonium chloride), PDADMAC) and two different zwitterionic surfactants (i.e., coco-betaine (CB) ...and cocoamidopropyl-betaine (CAPB)) have been studied. The bulk aggregation of the polyelectrolyte and the two surfactants was analyzed by turbidity and electrophoretic mobility measurements, and the adsorption of the solutions at the fluid interface was studied by surface tension and interfacial dilational rheology measurements. Evidence of polymer-surfactant complex formation in bulk was only found when the number of surfactant molecules was closer to the number of charged monomers in solutions, which suggests that the electrostatic repulsion associated with the presence of a positively charged group in the surfactant hinders the association between PDADMAC and the zwitterionic surfactant for concentrations in which there are no micelles in solution. This lack of interaction in bulk is reflected in the absence of an influence of the polyelectrolyte in the interfacial properties of the mixtures, with the behavior being controlled by the presence of surfactant. This work has evidenced the significant importance of the different interactions involved in the system for controlling the interaction and complexation mechanisms of in polyelectrolyte-surfactant mixtures.
The interaction of particles with fluid interfaces is ubiquitous in synthetic and natural work, involving two types of interactions: particle–interface interactions (trapping energy) and ...interparticle interactions. Therefore, it is urgent to gain a deep understanding of the main forces controlling the trapping of particles at fluid interfaces, and their assembly to generate a broad range of structures characterized by different degrees of order. This Perspective tries to provide an overview of the main contributions to the energetic landscape controlling the assembly of particles at fluid interfaces, which is essential for exploiting this type of interfacial systems as platforms for the fabrication of interface-based soft materials with technological interest.
Soft assemblies obtained following the Layer-by-Layer (LbL) approach are accounted among the most interesting systems for designing biomaterials and drug delivery platforms. This is due to the ...extraordinary versatility and flexibility offered by the LbL method, allowing for the fabrication of supramolecular multifunctional materials using a wide range of building blocks through different types of interactions (electrostatic, hydrogen bonds, acid-base or coordination interactions, or even covalent bonds). This provides the bases for the building of materials with different sizes, shapes, compositions and morphologies, gathering important possibilities for tuning and controlling the physico-chemical properties of the assembled materials with precision in the nanometer scale, and consequently creating important perspective for the application of these multifunctional materials as cargo systems in many areas of technological interest. This review studies different physico – chemical aspects associated with the assembly of supramolecular materials by the LbL method, paying special attention to the description of these aspects playing a central role in the application of these materials as cargo platforms for encapsulation and release of active compounds.
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•Layer-by-Layer (LbL) films present many potential applications for encapsulating active ingredients.•The versatility of the LbL methods allows tuning the properties of the encapsulation platforms.•Real applications of LbL materials are in the initial steps.•Many questions are open about LbL materials yet.
The adsorption of concentrated poly(diallyldimethylammonium chloride) (PDADMAC)–sodium lauryl ether sulfate (SLES) mixtures at the water/vapor interface has been studied by different surface ...tension techniques and dilational viscoelasticity measurements. This work tries to shed light on the way in which the formation of polyelectrolyte–surfactant complexes in the bulk affects the interfacial properties of mixtures formed by a polycation and an oppositely charged surfactant. The results are discussed in terms of a two-step adsorption–equilibration of PDADMAC–SLES complexes at the interface, with the initial stages involving the diffusion of kinetically trapped aggregates formed in the bulk to the interface followed by the dissociation and spreading of such aggregates at the interface. This latter process becomes the main contribution to the surface tension decrease. This work aids our understanding of the most fundamental basis of the physicochemical behavior of concentrated polyelectrolyte–surfactant mixtures which present complex bulk and interfacial interactions with interest in both basic and applied sciences.
The contact angle of particles attached to fluid interfaces plays a key role in many scientific and technological aspects of particle-laden layers. In spite of the recognized importance, the laws ...that govern this property are still poorly understood. The main problem associated with the study of this property is that multiple variables are involved in the wetting process of particles by fluid interfaces. Such variables are associated with the chemical nature of both the particles and the fluid phases, and with the particle’s size. Understanding of the different aspects controlling the contact angle of particles is a physico-chemical challenge, and is very important because of the many technological aspects in which particle laden interfaces are involved. This review discusses the current status and the aspects to be dealt with in the near future in the study of the contact angle of particles attached to fluid interfaces.
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The adsorption of mixtures formed by chitosan and sodium lauryl ether sulfate (SLES) at the water/vapor interface has been studied on the basis of their impact on the equilibrium surface tension of ...the interface, and the response of such an interface to mechanical deformations. The analysis of the surfactant binding to the chitosan chains evidenced that the chitosan-SLES solutions were mixtures of polyelectrolyte-surfactant complexes and a non-negligible amount of free surfactant molecules. The interfacial properties showed two well-differentiated regions for interfacial adsorption as a function of the SLES concentration: (i) at a low surfactant concentration, co-adsorption of chitosan and SLES occurs, and (ii) at high concentrations, the surface is mostly occupied by SLES molecules. This behavior may be interpreted in terms of a complex equilibration mechanism of the interfacial layers, where different coupled dynamic processes may be involved. Furthermore, the use of the time-concentration superposition principle has confirmed the different dynamic behaviors of the chitosan-SLES adsorption as a function of the SLES concentration. This work sheds light on some of the most fundamental bases governing the physico-chemical behavior of mixtures formed by a biopolymer and a surfactant, where their complex behavior is governed by an intricate balance of bulk and interfacial interactions.
Adsorption of chitosan-sodium laureth sulfate mixtures at the water/vapor interface appears very different to that of other oppositely charged polyelectrolyte-surfactant mixtures.
The interest of polymer–surfactant systems has undergone a spectacular development in the last thirty years due to their complex behavior and their importance in different industrial sectors. The ...importance can be mainly associated with the rich phase behavior of these mixtures that confers a wide range of physico-chemical properties to the complexes formed by polymers and surfactants, both in bulk and at the interfaces. This latter aspect is especially relevant because of the use of their mixture for the stabilization of dispersed systems such as foams and emulsions, with an increasing interest in several fields such as cosmetic, food science or fabrication of controlled drug delivery structures. This review presents a comprehensive analysis of different aspects related to the phase behavior of these mixtures and their intriguing behavior after adsorption at the liquid/air interface. A discussion of some physical properties of the bulk is also included. The discussion clearly points out that much more work is needed for obtaining the necessary insights for designing polymer–surfactant mixtures for specific applications.
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•Polymer–surfactant systems are one of the most studied systems in colloidal science.•Interest for both scientific and technological purposes•Rich phase behavior that determines their physico-chemical properties and applications•Important correlations between bulk behavior and adsorption to fluid interfaces
Synthetic insecticides have been used for a long time as one of the most effective tools for insect pest control. However, the re-emergence of insect pests and their fast development of resistance, ...as has occurred for pyrethroid-resistant bed bugs
L., make it necessary to develop new and safe strategies for effective pest control. This has fostered the research on new eco-sustainable formulations based on essential oils, which allows reducing the impact associated with the intensive use of synthetic insecticides on the environment and their effects on human health. This research explores the stability of water/eugenol/ethanol surfactantless emulsions loaded with imidacloprid (0.003 wt%), and their toxicity against a resistant bed bug strain. The results have shown that these emulsions enable the solubilization of a poorly water-soluble drug, such as the imidacloprid, without any significant modification of their stability. Furthermore, the application of the obtained formulations against the pyrethroid-resistant bed bug results in mortality in the 50-85% range upon topical and spray applications, with the increase of the eugenol content enhancing the effectiveness of the formulations. It may be expected that the ternary water/eugenol/ethanol mixtures could be further developed in the preparation of ready to use formulations, enabling the dispersion of insecticides for pest control.
To evaluate the 12-month efficacy and safety of intravitreal ranibizumab 0.5 mg and 2.0 mg administered monthly and on an as-needed (PRN) basis in treatment-naïve patients with subfoveal neovascular ...age-related macular degeneration (wet AMD).
A 24-month, phase III, randomized, multicenter, double-masked, dose-response study.
Patients aged ≥50 years with subfoveal wet AMD.
Patients (n = 1098) were randomized to receive ranibizumab 0.5 mg or 2.0 mg intravitreal injections administered monthly or on a PRN basis after 3 monthly loading doses.
The primary efficacy end point was the mean change from baseline in best-corrected visual acuity (BCVA) at month 12. Key secondary end points included the mean number of ranibizumab injections, the mean change from baseline in central foveal thickness (CFT) over time, and the proportion of patients who gained ≥15 letters of BCVA. Unless otherwise specified, end point analyses were performed using the last-observation-carried-forward method to impute missing data.
At month 12, the mean change from baseline in BCVA for the 4 groups was +10.1 letters (0.5 mg monthly), +8.2 letters (0.5 mg PRN), +9.2 letters (2.0 mg monthly), and +8.6 letters (2.0 mg PRN). The proportion of patients who gained ≥15 letters from baseline at month 12 in the 4 groups was 34.5%, 30.2%, 36.1%, and 33.0%, respectively. The mean change from baseline in CFT at month 12 in the 4 groups was −172.0 μm, −161.2 μm, −163.3 μm, and −172.4 μm, respectively. The mean number of injections was 7.7 and 6.9 for the 0.5-mg PRN and 2.0-mg PRN groups, respectively. Ocular and systemic safety profiles were consistent with previous ranibizumab trials in AMD and comparable between groups.
At month 12, the ranibizumab 2.0 mg monthly group did not meet the prespecified superiority comparison and the ranibizumab 0.5 mg and 2.0 mg PRN groups did not meet the prespecified noninferiority (NI) comparison. However, all treatment groups demonstrated clinically meaningful visual improvement (+8.2 to +10.1 letters) and improved anatomic outcomes, with the PRN groups requiring approximately 4 fewer injections (6.9–7.7) than the monthly groups (11.2–11.3). No new safety events were observed despite a 4-fold dose escalation in the study. The pHase III, double-masked, multicenter, randomized, Active treatment-controlled study of the efficacy and safety of 0.5 mg and 2.0 mg Ranibizumab administered monthly or on an as-needed Basis (PRN) in patients with subfoveal neOvasculaR age-related macular degeneration (HARBOR) study confirmed that ranibizumab 0.5 mg dosed monthly provides optimum results in patients with wet AMD.
Proprietary or commercial disclosure may be found after the references.
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