Adsorption of novel thermosensitive graft-copolymers: Core–shell particles prepared by polyelectrolyte multilayer self-assembly

Recent Advancements of Specific Functionalized Surfaces of Magnetic Nano- and Microparticles as a Theranostics Source in Biomedicine

Magnetic nano- and microparticles (MNMPs) belong to a highly versatile class of colloids with actuator and sensor properties that have been broadly studied for their application in theranostics such as molecular imaging and drug delivery. The use of advanced biocompatible, biodegradable polymers and polyelectrolytes as MNMP coating materials is essential to ensure the stability of MNMPs and enable efficient drug release while at the same time preventing cytotoxic effects. In the past years, huge progress has been made in terms of the design of MNMPs. Especially, the understanding of coating formation with respect to control of drug loading and release kinetics on the molecular level has significantly advanced. In this review, recent advancements in the field of MNMP surface engineering and the applicability of MNMPs in research fields of medical imaging, diagnosis, and nanotherapeutics are presented and discussed. Furthermore, in this review the main emphasis is put on the manipulation of biological specimens and cell trafficking, for which MNMPs represent a favorable tool enabling transport processes of drugs through cell membranes. Finally, challenges and future perspectives for applications of MNMPs as theranostic nanomaterials are discussed.

From polyelectrolyte complexes to polyelectrolyte multilayers: Electrostatic assembly, nanostructure, dynamics, and functional properties

Polyelectrolyte complexes (PECs) are three-dimensional macromolecular structures formed by association of oppositely charged polyelectrolytes in solution. Polyelectrolyte multilayers (PEMs) can be considered a special case of PECs prepared by layer-by-layer (LbL) assembly that involves sequential deposition of molecular-thick polyelectrolyte layers with nanoscale control over the size, shape, composition and internal organization. Although many functional PEMs with novel physical and chemical characteristics have been developed, the current practical applications of PEMs are limited to those that require only a few bilayers and are relatively easy to prepare. The viability of such engineered materials can be realized only after overcoming the scientific and engineering challenges of understanding the kinetics and transport phenomena involved in the multilayer growth and the factors governing their final structure, composition, and response to external stimuli. There is a great need to model PEMs and to connect PEM behavior with the characteristics of the PEC counterparts to allow for prediction of performance and better design of multilayered materials. This review focuses on the relationship between PEMs and PECs. The constitutive interactions, the thermodynamics and kinetics of polyelectrolyte complexation and PEM formation, PEC phase behavior, PEM growth, the internal structure and stability in PEMs and PECs, and their response to external stimuli are presented. Knowledge of such interactions and behavior can guide rapid fabrication of PEMs and can aid their applications as nanocomposites, coatings, nano-sized reactors, capsules, drug delivery systems, and in electrochemical and sensing devices. The challenges and opportunities in future research directions are also discussed.

pH-Triggered release from surface-modified poly(lactic-co-glycolic acid) nanoparticles

Nanoparticles (NP) of poly(lactic-co-glycolic acid) (PLGA) represent a promising biodegradable drug delivery system. We suggest here a two-step release system of PLGA nanoparticles with a pH-tunable polymeric shell, providing an initial pH-triggered step, releasing a membrane-toxic cationic compound. PLGA nanoparticles are coated by polyelectrolytes using the layer-by-layer self-assembly technique, employing poly(acrylic acid) (PAA) as a pH-sensitive component and poly(diallyldimethylammonium chloride) (PDADMAC) as the releasable polycation. The pH during multilayer deposition plays a major role and influences the titration curve of the layer system. The pH-tunability of PAA is intensively investigated with regard to the pH region, in which the particle system becomes uncharged. The isoelectric point can be shifted by employing suitable deposition pH values. The release is investigated by quantitative (1)H NMR, yielding a pH-dependent release curve. A release of PDADMAC is initiated by a decrease of the pH value. The released amount of polymer, as quantified by (1)H NMR analysis, clearly depends on the pH value and thus on the state of deprotonation of the pH-sensitive PAA layer. Subsequent incubation of the nanoparticles with high concentrations of sodium chloride shows no further release and thus demonstrates the pH-driven release to be quantitative.

Assembly of poly(dopamine)/poly(N-isopropylacrylamide) mixed films and their temperature-dependent interaction with proteins, liposomes, and cells

Many biomedical applications benefit from responsive polymer coatings. The properties of poly(dopamine) (PDA) films can be affected by codepositing dopamine (DA) with the temperature-responsive polymer poly(N-isopropylacrylamide) (pNiPAAm). We characterize the film assembly at 24 and 39 °C using DA and aminated or carboxylated pNiPAAm by a quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray photoelectron spectroscopy, UV-vis, ellipsometry, and atomic force microscopy. It was found that pNiPAAm with both types of end groups are incorporated into the films. We then identified a temperature-dependent adsorption behavior of proteins and liposomes to these PDA and pNiPAAm containing coatings by QCM-D and optical microscopy. Finally, a difference in myoblast cell response was found when these cells were allowed to adhere to these coatings. Taken together, these fundamental findings considerably broaden the potential biomedical applications of PDA films due to the added temperature responsiveness.

Microstructures and growth characteristics of polyelectrolytes on silicon using layer-by-layer assembly

Growth processes of nanocomposite layers obtained by polyelectrolytes, poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC), self-assembled on silicon surface using layer-by-layer (LbL) technique were investigated, and theoretical and experimental data are herein reported. Complementary microstructural and compositional analyses techniques (scanning electron microscopy, ellipsometry, X-ray reflectivity, zeta (ξ) potential measurements and attenuated total reflection infrared spectroscopy) were used for deep characterization of the multilayer structure formation. Electrophoretic zeta (ξ) potential measurements indicated that the surface charge was either positive or negative, depending on the polyelectrolyte used (PDADMAC or PSS). ATR-IR spectra confirmed the successfully silanization process and then, the building up of the nanocomposite layer. Morphological investigation and X-ray reflectivity demonstrated the growth process and cross-section size of the bilayers. Ellipsometric measurements were in very good agreement with SEM and XRR, showing once again the successful deposition of polyelectrolyte multilayers.

Dynamic aspects of films prepared by a sequential deposition of species: perspectives for smart and responsive materials

The deposition of surface coatings using a step-by-step approach from mutually interacting species allows the fabrication of so called "multilayered films". These coatings are very versatile and easy to produce in environmentally friendly conditions, mostly from aqueous solution. They find more and more applications in many hot topic areas, such as in biomaterials and nanoelectronics but also in stimuli-responsive films. We aim to review the most recent developments in such stimuli-responsive coatings based on layer-by-layer (LBL) depositions in relationship to the properties of these coatings. The most investigated stimuli are based on changes in ionic strength, temperature, exposure to light, and mechanical forces. The possibility to induce a transition from linear to exponential growth in thickness and to change the charge compensation from "intrinsic" to "extrinsic" by controlling parameters such as temperature, pH, and ionic strength are the ways to confer their responsiveness to the films. Chemical post-modifications also allow to significantly modify the film properties.

Mechanism of surface molecular imprinting in polyelectrolyte multilayers

The combination of Layer-by-Layer (LbL) self-assembly of oppositely charged polymers with the concept of molecular imprinting in polymers promises faster loading/unloading as compared to bulk systems. Here, we monitor the construction of LbL self-assembled polyelectrolyte multilayers (PEM) including template molecules and the binding and release dynamics of the guest molecules in the imprinted sites employing a quartz crystal microbalance with dissipation measurement (QCM-D). It is found that pH-dependent removal and rebinding of the template leads to a simultaneous swelling of the film. Separating the swelling from the template kinetics is a task which can be carried out by careful interpretation of the obtained QCM-D data. Considering correlated frequency and dissipation changes, evidence is found that the film features binding sites that can be loaded with the template such that the major part of template uptake is due to selective binding into imprinted sites. Template uptake is causing an enhanced cross-linking, as monitored by a reduced dissipation. The mechanism of reversible template uptake and release is shown to be based on the charge equilibrium in the film, which is manipulated by pH variation.

Internal structure of polyelectrolyte multilayer assemblies

The paper deals with the correlation between the internal structure and dynamics of polyelectrolyte multilayers on one hand and their functional properties on the other hand. It considers different concepts of multilayer formation like driving forces, adsorption kinetics, mode of growth and stability aspects. A further focus is the control of internal structure and dynamics which is of high impact with respect to the design of stimuli-responsive material.