Where Polyelectrolyte Multilayers and Polyelectrolyte Complexes Meet

Ion-Specific Effects on Ion and Polyelectrolyte Solvation

Ion-specific effects on aqueous solvation of monovalent counter ions, Na+ ${^+ }$ , K+ ${^+ }$ , Cl- ${^- }$ , and Br- ${^- }$ , and two model polyelectrolytes (PEs), poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA) were here studied with ab initio molecular dynamics (AIMD) and classical molecular dynamics (MD) simulations based on the OPLS-aa force-field which is an empirical fixed point-charge force-field. Ion-specific binding to the PE charge groups was also characterized. Both computational methods predict similar response for the solvation of the PEs but differ notably in description of ion solvation. Notably, AIMD captures the experimentally observed differences in Cl- ${^- }$ and Br- ${^- }$ anion solvation and binding with the PEs, while the classical MD simulations fail to differentiate the ion species response. Furthermore, the findings show that combining AIMD with the computationally less costly classical MD simulations allows benefiting from both the increased accuracy and statistics reach.

Polyelectrolyte complex formation of alginate and chito oligosaccharide is influenced by their proportion and alginate molecular weight

Sodium alginate (SA) and chito oligosaccharide (COS) are widely used food additives in the food industry, and exploring their interaction to form polyelectrolyte complexes (PECs) may provide insights into food development. In the present study, the effects of viscosity-average molecular weight (Mv) and relative amounts of SA on the formation of sodium alginate/chito oligosaccharide polyelectrolyte (SCP) complexes were investigated. The results showed that the electrostatic interaction between -COOH and -NH2 and the hydrogen bonding between OH, were attributed to the formation of the SCP complexes. Then the formation and properties of SCP complexes were greatly dependent on the Mv and the relative amount of SA. SA with Mv of ≥2.16 × 106 Da could form spherical SCP complexes, while the SA/COS ratio (w/w) ≥ 0.8 was not conducive to the formation of SCP complexes. Moreover, the SCP complexes were more stable in the gastric environment than in the intestinal condition. In addition, 1.73 × 107 Da was the optimal Mv of SA for SCP complexes formation. This study contributed to a comprehensive understanding of the interaction between SA and COS, and shed light on the potential application of SA and COS formulation to develop new food products.

Effect of polyacid architecture and polycation molecular weight on lateral diffusion within multilayer films

Despite the potential use of polyelectrolyte multilayers for biomedical, separation, and energy applications, their dynamic properties are not sufficiently understood. In this work, center-of-mass diffusion of a weak polyacid-poly(methacrylic acid) (PMAA) of linear and 8-arm architecture (L-PMAA and 8-PMAA, respectively) and matched molecular weight-was studied in layer-by-layer (LbL) assemblies with poly(diallyldimethylammonium) chloride (PDADMAC) of varied molecular weight. The film deposition at low-salt, acidic conditions when PMAA was only partially ionized yielded thicker, more diffused layers with shorter PDADMAC chains, and bilayer thickness decreased for multilayers constructed with longer PDADMAC. The molecular architecture of PMAA had a weak effect on film growth, with bilayer thickness being ∼20% larger for L-PMAA for the films constructed with the shortest PDADMAC (35 kDa) and identical film growth for L-PMAA and 8-PMAA with the longest PDADMAC (300 kDa). The exposure of the multilayer films to 0.2M NaCl triggered a reduction in PMAA ionization and significant lateral diffusivity of fluorescently labeled PMAA molecules (PMAA*), with diffusion coefficients D ranging from 10-13 to 10-12 cm2/s, as determined by the fluorescence recovery after photobleaching technique. For all the films, polymer mobility was higher for star polyacids as compared to their linear counterparts, and the dependence of PMAA diffusion coefficient D on PDADMAC molecular weight (D ∼ M-n) was relatively weak (n < 0.6). However, 8-PMAA demonstrated an approximately doubled power exponent compared to the L-PMAA chains, suggesting a stronger effect of the molecular connectivity of the partner polycation molecules on the diffusion of star polyelectrolytes.

Switching it Up: The Promise of Stimuli-Responsive Polymer Systems in Biomedical Science

Responsive polymer systems have the ability to change properties or behavior in response to external stimuli. The properties of responsive polymer systems can be fine-tuned by adjusting the stimuli, enabling tailored responses for specific applications. These systems have applications in drug delivery, biosensors, tissue engineering, and more, as their ability to adapt and respond to dynamic environments leads to improved performance. However, challenges such as synthesis complexity, sensitivity limitations, and manufacturing issues need to be addressed for successful implementation. In our review, we provide a comprehensive summary on stimuli-responsive polymer systems, delving into the intricacies of their mechanisms and actions. Future developments should focus on precision medicine, multifunctionality, reversibility, bioinspired designs, and integration with advanced technologies, driving the dynamic growth of sensitive polymer systems in biomedical applications.

Salt-Induced Diffusion of Star and Linear Polyelectrolytes within Multilayer Films

This study explores the effect of salt on the diffusivity of polyelectrolytes of varied molecular architecture in layer-by-layer (LbL) films in directions parallel and perpendicular to the substrate using fluorescence recovery after photobleaching (FRAP) and neutron reflectivity (NR) techniques, respectively. A family of linear, 4-arm, 6-arm, and 8-arm poly(methacrylic acids) (LPMAA, 4PMAA, 6PMAA, and 8PMAA, respectively) of matched molecular weights were synthesized using atom transfer radical polymerization and assembled with a linear polycation, poly[2-(trimethylammonium)ethyl methacrylate chloride] (QPC). NR studies involving deuterated QPC revealed ∼10-fold higher polycation mobility for the 8PMAA/QPC system compared to all-linear LbL films upon exposure to 0.25 M NaCl solutions at pH 6. FRAP experiments showed, however, that lateral diffusion of star PMAAs was lower than LPMAA at NaCl concentrations below ∼0.22 M NaCl, with a crossover to higher mobility of star polymers in more concentrated salt solutions. The stronger response of diffusion of star PMAA to salt is discussed in the context of several theories previously suggested for diffusivity of polyelectrolyte chains in multilayer films and coacervates.

A decade of developing applications exploiting the properties of polyelectrolyte multilayer capsules

Transferring the layer-by-layer (LbL) coating approach from planar surfaces to spherical templates and subsequently dissolving these templates leads to the fabrication of polyelectrolyte multilayer capsules. The versatility of the coatings of capsules and their flexibility upon bringing in virtually any material into the coatings has quickly drawn substantial attention. Here, we provide an overview of the main developments in this field, highlighting the trends in the last decade. In the beginning, various methods of encapsulation and release are discussed followed by a broad range of applications, which were developed and explored. We also outline the current trends, where the range of applications is continuing to grow, including addition of whole new and different application areas.

Nanoarchitectonics beyond perfect order - not quite perfect but quite useful

Nanoarchitectonics, like architectonics, allows the design and building of structures, but at the nanoscale. Unlike those in architectonics, and even macro-, micro-, and atomic-scale architectonics, the assembled structures at the nanoscale do not always follow the projected design. In fact, they do follow the projected design but only for self-assembly processes producing structures with perfect order. Here, we look at nanoarchitectonics allowing the building of nanostructures without a perfect arrangement of building blocks. Here, fabrication of structures from molecules, polymers, nanoparticles, and nanosheets to polymer brushes, layer-by-layer assembly structures, and hydrogels through self-assembly processes is discussed, where perfect order is not necessarily the aim to be achieved. Both planar substrate and spherical template-based assemblies are discussed, showing the challenging nature of research in this field and the usefulness of such structures for numerous applications, which are also discussed here.

Ecotoxicity of polyelectrolyte formulations in water and soil matrices

Interpolyelectrolyte complexes (IPECs) formed by the interaction of two oppositely charged polyelectrolytes have been proposed as soil structure stabilizers. However, little is known about the environmental safety of IPECs. The goal of this study was to investigate the toxicity of a positively charged IPEC formed by two commercial polymers, namely the cationic biopolymer poly(diallyldimethylammonium chloride) (PDDA) and the anionic biopolymer lignohumate (LH), a humic-based plant growth promoter. Toxicity was assessed using cultures of the bacteria Escherichia coli, the ciliate Paramecium caudatum, mammalian (Bos taurus) spermatozoa in vitro, and three plant species (Sinapis alba, Raphanus sativus, and Triticum durum). The responses of test organisms were evaluated in contact with (1) polymer and water and (2) polymer and soil. In water, PDDA and IPEC were highly toxic to bacteria and ciliates at all concentrations and less toxic to mammalian cells. Higher plants were less sensitive to the polymers, and the toxicity progressively decreased in the order PDDA > IPEC > LH. In soil matrices; the phytotoxicity of PDDA and IPEC was found to be quite low, and none of the polymers was toxic to plants at concentrations that allowed the formation of polymeric soil crusts against erosion. This is because the toxicity of cationic polymers decreases as they enter the soil matrix and bind to organic matter and minerals.

Role of PSS-based assemblies in stabilization of Eu and Sm luminescent complexes and their thermoresponsive luminescence

The present work introduces self-assembled polystyrenesulfonate (PSS) molecules as soft nanocapsules for incorporation of Eu³⁺-Sm³⁺ complexes by the solvent exchange procedure. The high levels of Eu³⁺- and Sm³⁺-luminescence of the complexes derives from the ligand-to-metal energy transfer, in turn, resulted from the complex formation of Eu³⁺and Sm³⁺ ions with the three recently synthesized cyclophanic 1,3-diketones. The structural features of the ligands are optimized for the high thermal sensitivity of Eu³⁺- luminescence in DMF solutions. The PSS-nanocapsules (∼100 nm) provide both colloid and chemical stabilization of the ultrasmall (3-5 nm) nanoprecipitates of the complexes, although their luminescence spectra patterns and excited state lifetimes differ from the values measured for the complexes in DMF solutions. The specific concentration ratio of the Eu³⁺-Sm³⁺ complexes in the DMF solutions allows to tune the intensity ratio of the luminescence bands at 612 and 650 nm in the heterometallic Eu³⁺-Sm³⁺ colloids. The thermal sensitivity of the Eu³⁺- and Sm³⁺-luminescence of the complexes derives from the static quenching both in PSS-colloids and in DMF solutions, while the thermo-induced dynamic quenching of the luminescence is significant only in DMF solutions. The reversibility of thermo-induced luminescence changes of the Eu³⁺-Sm³⁺ colloids is demonstrated by six heating-cooling cycles. The DLS measurements before and after the six cycles reveal the invariance of the PSS-based capsule as the prerequisite for the recyclability of the temperature monitoring through the ratio of Eu³⁺-to- Sm³⁺ luminescence.

Hierarchically Structured, All-Aqueous-Coated Hydrophobic Surfaces with pH-Selective Droplet Transfer Capability

Often inspired by nature, techniques for precise droplet manipulation have found applications in microfluidics, microreactors, and water harvesting. However, a widely applicable strategy for surface modification combining simultaneous hydrophobicity and pH-sensitivity has not yet been achieved by employing environmentally friendly assembly conditions. The introduction of pH-responsive groups to an otherwise fluorinated polyphosphazene (PPZ) unlocks pH-selective droplet capture and transfer. Here, an all-aqueous layer-by-layer (LbL) deposition of polyelectrolytes is used to create unique hydrophobic coatings, endowing surfaces with the ability to sense environmental pH. The high hydrophobicity of these coatings (ultimately reaching a contact angle >120° on flat surfaces) is enabled by the formation of hydrophobic nanoscale domains and controllable by the degree of fluorination of PPZs, polyamine-binding partners, deposition pH, and coating thickness. Inspired by the hierarchical structure of rose petals, these versatile coatings reach a contact angle >150° when deposited on structured surfaces while introducing a tunable adhesivity that enables precise droplet manipulation. The films exhibited a strongly pronounced parahydrophobic rose petal behavior characterized through the contact angle hysteresis. Depositing as few as five bilayers (∼25 nm) on microstructured rather than smooth substrates resulted in superhydrophobicity with water contact angles >150° and the attenuation of the contact angle hysteresis, enabling highly controlled transfer of aqueous droplets. The pH-selective droplet transfer was achieved between surfaces with either the same microstructure and LbL film building blocks, which were assembled at different pH, or between surfaces with different microstructures coated with identical films. The demonstrated capability of these hydrophobic LbL films to endow surfaces with controlled hydrophobicity through adsorption from aqueous solutions and control the adhesion and transfer of water droplets between surfaces can be used in droplet-based microfluidics applications and water collection/harvesting.

Layer-by-Layer Nanoarchitectonics Using Protein-Polyelectrolyte Complexes toward a Generalizable Tool for Protein Surface Immobilization

Layer-by-layer (LbL) self-assembly is an attractive method for the immobilization of macromolecules at interfaces. Integrating proteins in LbL thin films is however challenging due to their polyampholyte nature. Recently, we developed a method to integrate lysozyme into multilayers using protein-polyelectrolytes complexes (PPCs). In this work, we extended this method to a wide range of protein-polyelectrolyte combinations. We demonstrated the robustness and versatility of PPCs as building blocks. LL-37, insulin, lysozyme, and glucose oxidase were complexed with alginate, poly(styrenesulfonate), heparin, and poly(allylamine hydrochloride). The resulting PPCs were then LbL self-assembled with chitosan, PAH, and heparin. We demonstrated that multilayers built with PPCs are thicker compared to the LbL self-assembly of bare protein molecules. This is attributed to the higher mass of protein in the multilayers and/or the more hydrated state of the assemblies. PPCs enabled the self-assembly of proteins that could otherwise not be LbL assembled with a PE or with another protein. Furthermore, the results also show that LbL with PPCs enabled the construction of multilayers combining different proteins, highlighting the formation of multifunctional films. Importantly, we show that the adsorption behavior and thus the multilayer growth strongly depend on the nature of the protein and polyelectrolyte used. In this work, we elaborated a rationale to help and guide the use of PPCs for protein LbL assembly. It will therefore be beneficial to the many scientific communities willing to modify interfaces with hard-to-immobilize proteins and peptides.

Effect of Ethanol and Urea as Solvent Additives on PSS–PDADMA Polyelectrolyte Complexation

The effect of urea and ethanol additives on aqueous solutions of poly(styrenesulfonate) (PSS), poly(diallyldimethylammonium) (PDADMA), and their complexation interactions are examined here via molecular dynamics simulations, interconnected laser Doppler velocimetry, and quartz crystal microbalance with dissipation. It is found that urea and ethanol have significant, yet opposite influences on PSS and PDADMA solvation and interactions. Notably, ethanol is systematically depleted from solvating the charge groups but condenses at the hydrophobic backbone of PSS. As a consequence of the poorer solvation environment for the ionic groups, ethanol significantly increases the extent of counterion condensation. On the other hand, urea readily solvates both polyelectrolytes and replaces water in solvation. For PSS, urea causes disruption of the hydrogen bonding of the PSS headgroup with water. In PSS–PDADMA complexation, these differences influence changes in the binding configurations relative to the case of pure water. Specifically, added ethanol leads to loosening of the complex caused by the enhancement of counterion condensation; added urea pushes polyelectrolyte chains further apart because of the formation of a persistent solvation shell. In total, we find that the effects of urea and ethanol rise from changes in the microscopic-level solvation environment and conformation resulting from solvating water being replaced by the additive. The differences cannot be explained purely via considering relative permittivity and continuum level electrostatic screening. Taken together, the findings could bear significance in tuning polyelectrolyte materials’ mechanical and swelling characteristics via solution additives.

Predicting the outcomes of interpolyelectrolyte neutralization at surfaces on the basis of complexation experiments and vice versa

This study was carried out with the aim of establishing how the outcomes of polyelectrolyte multilayer formation can be predicted on the basis of the results of complexation studies in solution and vice versa. For this purpose, the correlation between the processes of complex and multilayer formation involving three pairs of vinylic polyions in solutions of binary 1 : 1 sodium salts (NaX; X = F, Cl, Br, I, NO₃, ClO₄) was explored by means of dynamic and electrophoretic light scattering, potentiometry, microcalorimetry, spectrophotometry and quartz crystal microbalance. The gradual reactant mixing in solution at lower salt concentrations resulted in a Fuoss-Sadek sequence of events (primary complexes → secondary complexes → 1 : 1 flocculate), whereby the obtained nano-complexes could be successively overcharged. At high salt concentration and with excess polycation present, metastable nano-complexes and precipitates containing surplus of positively charged monomers were formed. The amount of extrinsically compensated charge was in accord with the polycation affinities toward counteranions, established by monitoring the electrolyte-induced aggregation of positively charged nano-complexes. Perfect analogy with respect to counteranion influence on the amount of adsorbed polycation was noticed for corresponding multilayers. Aside from providing a deeper understanding of interpolyelectrolyte neutralization, the gained insights can also be used to steer the polyelectrolyte multilayer composition and properties.

Silica-Supported Assemblage of CuII Ions with Carbon Dots for Self-Boosting and Glutathione-Induced ROS Generation

The present work introduces coordinative binding of CuII ions with both amino-functionalized silica nanoparticles (SNs) and green-emitting carbon dots (CDs) as the pregrequisite for the CuII-assisted self-assembly of the CDs at the surface of the SNs. The produced composite SNs exhibit stable in time stimuli-responsive green fluorescence derived from the CuII-assisted assemblage of CDs. The fluorescence response of the composite SNs is sensitive to the complex formation with glutathione (GSH), enabling them to detect it with the lower limit of detection of 0.15 μM. The spin-trap-facilitated electron spin resonance technique indicated that the composite SNs are capable of self-boosting generation of ROS due to CuII→CuI reduction by carbon in low oxidation states as a part of the CDs. The intensity of the ESR signals is enhanced under the heating to 38 °C. The intensity is suppressed at the GSH concentration of 0.35 mM but is enhanced at 1.0 mM of glutathione, while it is suppressed once more at the highest intracellular concentration level of GSH (10 mM). These tendencies reveal the concentrations optimal for the scavenger or reductive potential of GSH. Flow cytometry and fluorescence and confocal microscopy methods revealed efficient cell internalization of SNs-NH2-CuII-CDs comparable with that of “free” CDs.

Swelling Effects on the Conductivity of Graphene/PSS/PAH Composites

Graphene/poly-(sodium-4-styrene sulfonate)(PSS)/poly-(allylamine hydrochloride) (PAH) composite is a frequently adopted system for fabricating polyelectrolyte multilayer films. Swelling is the bottleneck limiting its applications, and its effects on the conductivity is still controversial. Herein, we report successful swelling of a graphene/PSS/PAH composite in a vapor atmosphere, and the relation with the mass fraction of water is uncovered. The composite was prepared via a layer-by-layer assembly technique and systematically characterized. The results indicated that the average thickness for each bilayer was about 0.95 nm. The hardness and modulus were 2.5 ± 0.2 and 68 ± 5 GPa, respectively, and both were independent of thickness. The sheet resistance decreased slightly with the prolongation of immersion time, but was distinct from that of the water mass fraction. It reduced from 2.44 × 105 to 2.34 × 105 ohm/sq, and the change accelerated as the water mass fraction rose, especially when it was larger than 5%. This could be attributing to the lubrication effect of the water molecules, which sped up the migration of charged groups in the polyelectrolytes. Moreover, molecular dynamics simulations confirmed that a microphase separation occurred when the fraction reached an extreme value owing to the dominated interaction between PSS and PAH. These results provide support for the structural stability of this composite material and its applications in devices.

Single Excited Dual Band Luminescent Hybrid Carbon Dots-Terbium Chelate Nanothermometer

The report introduces hybrid polyelectrolyte-stabilized colloids combining blue and green-emitting building blocks, which are citrate carbon dots (CDs) and [TbL]+ chelate complexes with 1,3-diketonate derivatives of calix[4]arene. The joint incorporation of green and blue-emitting blocks into the polysodium polystyrenesulfonate (PSS) aggregates is carried out through the solvent-exchange synthetic technique. The coordinative binding between Tb3+ centers and CD surface groups in initial DMF solutions both facilitates joint incorporation of [TbL]+ complexes and the CDs into the PSS-based nanobeads and affects fluorescence properties of [TbL]+ complexes and CDs, as well as their ability for temperature sensing. The variation of the synthetic conditions is represented herein as a tool for tuning the fluorescent response of the blue and green-emitting blocks upon heating and cooling. The revealed regularities enable developing either dual-band luminescent colloids for monitoring temperature changes within 25-50 °C through double color emission or transforming the colloids into ratiometric temperature sensors via simple concentration variation of [TbL]+ and CDs in the initial DMF solution. Novel hybrid carbon dots-terbium chelate PSS-based nanoplatform opens an avenue for a new generation of sensitive and customizable single excited dual-band nanothermometers.

Structure impact on photodynamic therapy and cellular contrasting functions of colloids constructed from dimeric Au(I) complex and hexamolybdenum clusters

Electrostatically driven self-assembly of [Au₂L₂]²⁺ (L is cyclic PNNP ligand) with [{Mo₆I₈}(L')₆]^2- (L' = I^-, CH₃COO^-) in aqueous solutions is introduced as facile route for combination of therapeutic and cellular contrasting functions within heterometallic colloids (Mo₆-Au₂). The nature of L' affects the size and aggregation behavior of crystalline Mo₆-Au₂ aggregates, which in turn affect the luminescence of the cluster units incorporated into Mo₆-Au₂ colloids. The spin trap facilitated electron spin resonance spectroscopy technique indicates that the level of ROS generated by Mo₆-Au₂ colloids is also affected by their size. Both (L' = I^-, CH₃COO^-) Mo₆-Au₂ colloids undergo cell internalization, which is enhanced by their assembly with poly-DL-lysine (PL) for L' = CH₃COO^-, but remains unchanged for L' = I^-. The colloids PL-Mo₆-Au₂ (L' = CH₃COO^-) are visualized as huge crystalline aggregates both outside and inside the cell cytoplasm by confocal microscopy imaging of the incubated cells, while the smaller sized (30-50 nm) PL-Mo₆-Au₂ (L' = I^-) efficiently stain the cell nuclei. Quantitative colocalization analysis of PL-Mo₆-Au₂ (L' = CH₃COO^-) in lysosomal compartments points to the fast endo-lysosomal escape of the colloids followed by their intracellular aggregation. The cytotoxicity of PL-Mo₆-Au₂ differs from that of Mo₆ and Au₂ blocks, predominantly acting through apoptotic pathway. The photodynamic therapeutic effect of the PL-Mo₆-Au₂ colloids on the cancer cells correlates with their intracellular trafficking and aggregation.

Study on polysaccharide polyelectrolyte complex and fabrication of alginate/chitosan derivative composite fibers

Sodium alginate (SA) blending with quaternary ammonium chitosan (QAC) polysaccharide polyelectrolyte complex (PEC) system was chosen to research the binary blending of anionic and cationic polyelectrolytes in detail and to fabricate SA/QAC composite fibers. The potential charge and the rheology of the PEC solution were characterized through Zeta Laser Particle Size Analyzer and DV-C Rotary Rheometer, the structure and properties of the composite fiber were examined by FT-IR, XRD, SEM, EDS, and YG004 single fiber strength meter. The results showed that as the mass ratio of SA to QAC increased from 0/1 to 10/1, the state of the binary solution in water changed from transparent uniform solution to turbid solution with flocculent precipitate, then back to uniform solution, accompanied by the electrical potential change. Moreover, the electrical potential also depended on salt in solution. By using this uniform PEC solution with the mass ratio of SA to QAC 10/1 and concentration 5.5 wt% in water, SA/QAC composite fibers with excellent performances of breaking strength 2.37 cN·dtex^-1 and breaking elongation 14.11%, good antibacterial and hydrophobic properties were fabricated via green wet-spinning process. The FT-IR and EDS determination indicated there formed egg-box between SA and Ca²⁺, cross-linked network between glutaraldehyde(GA) and SA, QAC, respectively. Depending on its mechanical, natural, and antibacterial properties, the SA/QAC composite fiber has advantages in wound dressing, medical gauze, medical absorbable suture, and tissue engineering.

Half-life modeling of basic fibroblast growth factor released from growth factor-eluting polyelectrolyte multilayers

Growth factor-eluting polymer systems have been widely reported to improve cell and tissue outcomes; however, measurements of actual growth factor concentration in cell culture conditions are limited. The problem is compounded by a lack of knowledge of growth factor half-lives, which impedes efforts to determine real-time growth factor concentrations. In this work, the half-life of basic fibroblast growth factor (FGF2) was determined using enzyme linked immunosorbent assay (ELISA). FGF2 release from polyelectrolyte multilayers (PEMs) was measured and the data was fit to a simple degradation model, allowing for the determination of FGF2 concentrations between 2 and 4 days of culture time. After the first hour, the FGF2 concentration for PEMs assembled at pH = 4 ranged from 2.67 ng/mL to 5.76 ng/mL, while for PEMs assembled at pH = 5, the concentration ranged from 0.62 ng/mL to 2.12 ng/mL. CRL-2352 fibroblasts were cultured on PEMs assembled at pH = 4 and pH = 5. After 2 days, the FGF2-eluting PEM conditions showed improved cell count and spreading. After 4 days, only the pH = 4 assembly condition had higher cells counts, while the PEM assembled at pH = 5 and PEM with no FGF2 showed increased spreading. Overall, the half-life model and cell culture study provide optimal concentration ranges for fibroblast proliferation and a framework for understanding how temporal FGF2 concentration may affect other cell types.

Overcharging of polyelectrolyte complexes: an entropic phenomenon

Overcharging in complex coacervation, in which a polyelectrolyte complex coacervate (PEC) initially containing equal moles of the cationic and anionic monomers absorbs a large excess of one type of polyelectrolyte species, is predicted using a recently developed thermodynamic model describing complexation through a combination of reversible ion binding on the chains and long-range electrostatic correlations. We show that overcharging is favored roughly equally by the translational entropy of released counterions and the binding entropy of polyelectrolytes in the polyelectrolyte complex, thus helping resolve competing explanations for overcharging in the literature. We find that the extent of overcharging is non-monotonic in the concentration of added salt and increases with both strength of ion-pairing between polyions and chain hydrophobicity. The predicted extent of overcharging of the PEC is directly compared with that of multilayers made of poly(diallyldimethylammonium), PDADMA, and poly(styrene-sulfonate), PSS, overcompensated by the polycation in two different salts: KBr and NaCl. Accounting for the specificity of salt ion interactions with the polyelectrolytes, we find good qualitative agreement between theory and experiment.

Cr(VI) visualization via transmittance of electrorheological display medium with core/shell polystyrene/polyvinyltetrazole microspheres

In the course of time, significant amounts of heavy-ion pollutants have been dispersed into the environment. Rapid on-site detection of heavy metal ions is crucial to monitor their dispersion in the nascent stages. In this study, 2.2-μm-diameter polystyrene microspheres (PSM) were synthesized via emulsifier-free polymerization to coat polyacrylonitrile (PSM@PAN) and form core/shell-structured microspheres. Core/shell polystyrene/polyvinyltetrazole (PSM@PVT) microspheres were obtained after a cyano-to-tetrazole conversion reaction, loaded in an electrorheological device (ERD) display constructed using two indium tin oxide glasses with a spacer seal. The ERD loading dispersed the microsphere solution by scattering light through the ERD, resulting in a low transmittance in the absence of an alternating electric field (AEF). Particles in the fluid medium were polarized to induce negative and positive charges at each end of the particles under the AEF, and the resultant particle chains enhanced transmittance. The optimal frequency to generate the highest degree of particle chaining in the presence of an AEF is defined as its characteristic frequency (Fc), which also serves as an indicator to identify the shell materials. The Fc of PSM@PVT shifted from 350 kHz to 30 kHz after adsorbing Cr(VI) from the PVT coating. Transmittance of the ERD loading of PSM@PVT with Cr(VI) increased linearly with the concentration of Cr(VI). Approximately 40 ng mL^-1 of the limit of detection was calculated in the linear range of 10-540 ng mL^-1. The Fc of the PSM@PVT adsorbing the Cr(VI) was not influenced by Na(I), K(I), Ca(II), Mg(II), Fe(III), and Zn(II) coexisting in the ERD.

A closer physico-chemical look to the Layer-by-Layer electrostatic self-assembly of polyelectrolyte multilayers

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.

Electrorheological Sensor Encapsulating Microsphere Media for Plague Diagnosis with Rapid Visualization

Plague is a disease infected by an etiological agent, which is transmitted from fleas to a variety of wildlife rodents. Therefore, rapid diagnosis of plague on-site in the field is important. Polystyrene microspheres (SMs) of 2.2 μm diameter were synthesized by emulsion polymerization to adsorb magnetic nanoparticles (FNs), resulting in core-/shell-structured microspheres that generate a significant contrast in relative permittivities between SMs and FNs. Electrorheological displays (EDs) consisting of two indium tin oxide glasses with spacers were constructed to contain core-/shell-structured SM/FN (SM@FN) solutions for observing their transmittance change. The ED encapsulating dispersed SM@FN solution exhibited an opaque state because light was scattered significantly without the application of an alternating electric field (AEF). In the presence of an AEF, the particle chaining behavior results in enhancement of the transmittance of ED. At a specific frequency, the so-called characteristic frequency (F_c), the transmittance reaches a maximum. F_c could be used as an indicator to mark the shell materials. The antibody of Yersinia pestis (ab-Yp) was coated onto the SM@FN as a biosensing medium. The F_c of ab-Yp-modified microspheres shifted from 200 to 750 kHz with antigen coupling of Y. pestis antigen (ag-Yp). In the absence of fluorescence labeling, the large change in ED transmittance could be visualized during the Y. pestis detection. The limit of detection and the limit of quantification were ∼30 and ∼40 ng/μL, respectively, obtained within 30 s according to the highest transmittance of ED under the AEF at 750 kHz. Y. pestis detection was not affected by Escherichia coli and Staphylococcus aureus significantly. Compared with other common immunoassays, including the secondary immunochemical or enzyme-linked steps, this simple electrorheological sensor with high sensitivity and selectivity could be a candidate for on-site plague diagnosis.

Biomimetic multilayer coatings deliver gentamicin and reduce implant-related osteomyelitis in rats

Implant-related infections like periprosthetic joint infections (PJI) are still a challenging issue in orthopedic surgery. In this study, we present a prophylactic anti-infective approach based on a local delivery of the antibiotic gentamicin. The local delivery is achieved via a nanoscale polyelectrolyte multilayer (PEM) coating that leaves the bulk material properties of the implant unaffected while tuning the surface properties. The main components of the coating, i.e. polypeptides and sulfated glycosaminoglycans (sGAG) render this coating both biomimetic (matrix mimetic) and biodegradable. We show how adaptions in the conditions of the multilayer assembly process and the antibiotic loading process affect the amount of delivered gentamicin. The highest concentration of gentamicin could be loaded into films composed of polypeptide poly-glutamic acid when the pH of the loading solution was acidic. The concentration of gentamicin on the surface could be tailored with the number of deposited PEM layers. The resulting coatings reveal a bacteriotoxic effect on Staphylococcus cells but show no signs of cytotoxic effects on MC3T3-E1 osteoblasts. Moreover, when multilayer-coated titanium rods were implanted into contaminated medullae of rat tibiae, a reduction in the development of implant-related osteomyelitis was observed. This reduction was more pronounced for the multifunctional, matrix-mimetic heparin-based coatings that only deliver lower amounts of gentamicin.

Ionic conductivity of solid polyelectrolyte complexes with varying water content: application of the dynamic structure model

We present a systematic study of the dc conductivity of solid polyelectrolyte complexes (PEC) of type x_PSS PSS·(1 − x_PSS) PDADMA as a function of temperature, and of PSS and water content, respectively. The data are discussed in the framework of the dynamic structure model.

Polyelectrolyte-coated ultra-small nanoparticles with Tb(III)-centered luminescence as cell labels with unusual charge effect on their cell internalization

The present work reports ultra-small polyelectrolyte-coated water insoluble Tb(III) complex species with bright Tb(III)-centered luminescence resulted from efficient ligand-to-metal energy transfer as efficient labels for Hep-2 cells. The flow cytometry data revealed the enhanced cellular uptake of negatively charged nanoparticles coated by the polystyrenesulfonate (PSS)-monolayer versus the positively charged nanoparticles. The latter are obtained by layer-by-layer deposition of polyethyleneimine (PEI) onto PSS-coated ones. Confocal and TEM images of Hep-2 cells exposed by the colloids confirm favorable cell internalization of the PSS- compared to PEI-PSS-coated colloids illustrating unusual charge-effect. Dynamic light scattering data indicate significant effect of the biological background exemplified by serum bovine albumin and phosphatidylcholine-based bilayers on the exterior charge and aggregation behavior of the colloids. The obtained results reveal the PSS-coated nanoparticles based on water insoluble Tb(III) complex as promising cell labels.

Formation of core/corona nanoparticles with interpolyelectrolyte complex cores in aqueous solution: insight into chain dynamics in the complex from fluorescence quenching

Formation of interpolyelectrolyte complexes (IPECs) of poly(methacrylic acid) (PMAA) bearing a fluorescent label (umbelliferone) at the chain end and poly[3,5-bis(trimethyl ammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) acting as a fluorescence quencher, was followed using a combination of scattering, calorimetry, microscopy and fluorescence spectroscopy techniques. While scattering and microscopy measurements indicated formation of spherical core/corona nanoparticles with the core of the QNPHOS/PMAA complex and the PEO corona, fluorescence measurements showed that both static and dynamic quenching efficiency were increased in the nanoparticle stability region. As the dynamic quenching rate constant remained unchanged, the quenching enhancement was caused by the increase in the local concentration of QNPHOS segments in the microenvironment of the label. This finding implies that the local dynamics of PMAA end chains affecting the interaction of the label with QNPHOS segments was independent of both PMAA and QNPHOS chain conformations.

Multilayer Assembly of Tannic Acid and an Amphiphilic Copolymer Poloxamer 188 on Planar Substrates toward Multifunctional Surfaces with Discrete Microdome-Shaped Features

Tannic acid (TA) is a natural polyphenol compound with a broad spectrum of biological activities, the most notable of which being antioxidation. Poloxamer 188 (P188), a synthetic triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), is amphiphilic in nature and best known for its ability to seal structurally damaged cellular membranes. The integration of both substances onto planar substrates could bring a new option for multifunctional coatings that are advantageous for implantable biomedical devices. Here, we demonstrate the feasibility of multilayer assembly of TA/P188 toward such a coating based on hydrogen bonding between phenolic hydroxyls of TA and ether groups of P188, and the unique surface feature it generates. The interactions between these two compounds were studied both in solution and in substrate-supported layer-by-layer assembly. The multilayer assembly process exhibits an exponential growth pattern as characterized by UV-vis spectrophotometry and quartz crystal microbalance with dissipation. Morphologically unique, microdome-shaped surface features emerge and evolve with the number of layers assembled. Such features bring a reservoir function to this coating, as demonstrated by the loading of hydrophobic nile red dye. Furthermore, the presence of TA in the multilayers was revealed by silver nitrate staining, and its antioxidation activity was demonstrated through a 2,2-diphenyl-1-picryl-hydrazyl free-radical scavenging assay.

Integrating Proteins in Layer-by-Layer Assemblies Independently of their Electrical Charge

Layer-by-layer (LbL) assembly is an attractive method for protein immobilization at interfaces, a much wanted step for biotechnologies and biomedicine. Integrating proteins in LbL thin films is however very challenging due to their low conformational entropy, heterogeneous spatial distribution of charges, and polyampholyte nature. Protein-polyelectrolyte complexes (PPCs) are promising building blocks for LbL construction owing to their standardized charge and polyelectrolyte (PE) corona. In this work, lysozyme was complexed with poly(styrenesulfonate) (PSS) at different ionic strengths and pH values. The PPCs size and electrical properties were investigated, and the forces driving complexation were elucidated, in the light of computations of polyelectrolyte conformation, with a view to further unravel LbL construction mechanisms. Quartz crystal microbalance and atomic force microscopy were used to monitor the integration of PPCs compared to the one of bare protein molecules in LbL assemblies, and colorimetric assays were performed to determine the protein amount in the thin films. Layers built with PPCs show higher protein contents and hydration levels. Very importantly, the results also show that LbL construction with PPCs mainly relies on standard PE-PE interactions, independent of the charge state of the protein, in contrast to classical bare protein assembly with PEs. This considerably simplifies the incorporation of proteins in multilayers, which will be beneficial for biosensing, heterogeneous biocatalysis, biotechnologies, and medical applications that require active proteins at interfaces.

Biorelated Polyelectrolyte Coatings Studied by in Situ Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy: Deposition Concepts, Wet Adhesiveness, and Biomedical Applications

In this conceptual contribution, thin functional coatings consisting of either pure polyelectrolytes (PELs) or complexes between oppositely charged PELs at model and applied substrates are outlined. Latter PEL/PEL complexes were deposited by two concepts. In a first well-known concept, PEL multilayers (PEM) were consecutively deposited according to the layer-by-layer (LbL) technique. In a second less known concept, PEL complex (PEC) nanoparticles (NPs) preformed by mixing polycation (PC) and polyanion (PA) solutions were deposited in one step. Both concepts based on binary oppositely charged PELs are compared to one based on a single polycation system. Examples shall be given on adhesiveness, nanostructure, and biomedical applications of PEM and PEC NP coatings. In situ attenuated total reflection (ATR) infrared (IR) spectroscopy, circular dichroism (CD), and scanning force microscopy (SFM) were used for molecular, optical, and microscopic characterization. At first, results on the adsorbed amount and wet adhesiveness of pure (single-component) PEL coatings as a function of charge density are given to motivate coatings of mixed oppositely charged PELs. Second, the wet adhesiveness of PEM and PEC NP coatings of identical PEL compounds in aqueous media varying the molar charge ratio ( n-/ n+) and the deposition step z, respectively, is compared. Upon comparing the three PEL deposition concepts, it is suggested that the lack or absence of excess charge at the PEL/surface interface is one of the main factors for the wet adhesiveness of all pure PEL, PEM, and PEC NP coatings. Finally, the potential of PEM and PEC NP coatings for biomedical applications is outlined. Concerning biopassivation, PEM coatings excessed or terminated by PA repel proteins with low isoelectric points. Concerning bioactivation, PEM coatings loaded with antibiotics as well as PEC NP coatings loaded with therapeutic bisphosphonates showed retarded, optionally temperature responsive drug release for applications in acute surgery and bone healing, and immunoglobulin/PEL complex coatings might open theranostic applications.

Theory of polyelectrolyte complexation-Complex coacervates are self-coacervates

The complexation of mixtures of cationic and anionic polymers to produce complex-coacervate phases is a subject of fundamental importance to colloid and polymer science as well as to applications including drug delivery, sensing technologies, and bio-inspired adhesives. Unfortunately the theoretical underpinnings of complex coacervation are widely misunderstood and conceptual mistakes have propagated in the literature. Here, a simple symmetric polyelectrolyte mixture model in the absence of salt is used to discuss the salient features of the phase diagram, including the location of the critical point, binodals, and spinodals. It is argued that charge compensation by dimerization in the dilute region renders the phase diagram of an oppositely charged polyelectrolyte mixture qualitatively and quantitatively similar to that of a single-component symmetric diblock polyampholyte solution, a system capable of "self-coacervation." The theoretical predictions are verified using fully fluctuating field-theoretic simulations for corresponding polyelectrolyte and diblock polyampholyte models. These represent the first comprehensive, approximation-free phase diagrams for coacervate and self-coacervate systems to appear in the literature.