Protein-based polyelectrolyte multilayers

Crystallization-Assisted Asymmetric Synthesis of Enantiopure Amines Using Membrane-Immobilized Transaminase

The production of active pharmaceutical ingredients (APIs) requires enantiopure chiral amines, for which greener synthesis processes are needed. Transaminases (TAs) are enzymes that catalyze the enantioselective production of chiral amines from prochiral ketones through transamination under mild conditions. Yet, industrial applications of biocatalytic transamination remain currently hindered by the limited stability of soluble enzymes and by the unfavorable thermodynamic equilibrium of targeted asymmetric reactions. Enzyme immobilization can be applied to address stability, recoverability, and reusability issues. In the perspective of process intensification, we chose to immobilize TAs on polymeric (polypropylene) membranes. In the asymmetric synthesis of (R)-2-fluoro-α-methylbenzylamine ((R)-FMBA), such membrane-immobilized TAs exhibited superior specific activity and stability compared with soluble TAs; they also outperformed TAs immobilized on resins. The reaction yield remained, however, limited by thermodynamics. To further enhance the synthesis yield, the reaction was coupled with the in situ crystallization of (R)-FMBA with 3,3-diphenylpropionic acid (DPPA). By doing so, the theoretical equilibrium conversion was pushed from ∼44% to ∼83%. In fact, a 72% overall recovery yield of crystallized (R)-FMBA was demonstrated. The enantioselectivity of the reaction mixture was preserved. Importantly, purification was greatly facilitated since the target enantiopure amine was readily recovered as high-purity (R)-FMBA:DPPA crystals. The biocatalytic membranes were found to be fully reusable, performing successive high-yield asymmetric syntheses with only minor deactivation. Overall, the crystallization-assisted strategy proposed herein offers a greener path for the biocatalytic production of valuable chiral targets.

Zero-Order Kinetics Release of Lamivudine from Layer-by-Layer Coated Macromolecular Prodrug Particles

To reduce the risk of side effects and enhance therapeutic efficiency, drug delivery systems that offer precise control over active ingredient release while minimizing burst effects are considered advantageous. In this study, a novel approach for the controlled release of lamivudine (LV) was explored through the fabrication of polyelectrolyte-coated microparticles. LV was covalently attached to poly(ε-caprolactone) via ring-opening polymerization, resulting in a macromolecular prodrug (LV-PCL) with a hydrolytic release mechanism. The LV-PCL particles were subsequently coated using the layer-by-layer (LbL) technique, with polyelectrolyte multilayers assembled to potentially modify the carrier's properties. The LbL assembly process was comprehensively analyzed, including assessments of shell thickness, changes in ζ-potential, and thermodynamic properties, to provide insights into the multilayer structure and interactions. The sustained LV release over 7 weeks was observed, following zero-order kinetics (R2 > 0.99), indicating a controlled and predictable release mechanism. Carriers coated with polyethylene imine/heparin and chitosan/heparin tetralayers exhibited a distinct increase in the release rate after 6 weeks and 10 weeks, respectively, suggesting that this coating can facilitate the autocatalytic degradation of the polyester microparticles. These findings indicate the potential of this system for long-term, localized drug delivery applications, requiring sustained release with minimal burst effects.

Seriation of Enzyme-Functionalized Multilayers for the Design of Scalable Biomimetic Mineralized Structures

Biomimetic hydroxyapatites are widely explored for their potential applications in the repair of mineralized tissues, particularly dental enamel, which is acellular and, thus, not naturally reformed after damage. Enamel is formed with a highly-controlled hierarchical structure, which is difficult to replicate up to the macroscale. A biomimetic approach is thus warranted, based on the same principles that drive biomineralization in vivo. Herein, a strategy for the design of enamel-like architectures is described, utilizing enzymes embedded in polyelectrolyte multilayers to generate inorganic phosphate locally, and provide a favorable chemical environment for the nucleation and growth of minerals. Moreover, a method is proposed to build up seriated mineral layers with scalable thicknesses, continuous mineral growth, and tunable morphology. Results show the outstanding growth of cohesive mineral layers, yielding macroscopic standalone fluoride and/or carbonate-substituted hydroxyapatite materials with comparable crystal structure and composition to native human mineralized tissues. This strategy presents a promising path forward for the biomimetic design of biomineral materials, particularly relevant for restorative applications, with an exquisite level of synthetic control over multiple orders of magnitude.

Complex Sequence-Defined Heteropolymers Enable Controlled Film Growth in Layer-By-Layer Assembly

Digitally-encoded poly(phosphodiesters) (d-PPDE) with highly complex primary structures are evaluated for layer-by-layer (LbL) assembly. To be easily decoded by mass spectrometry (MS), these digital polymers contain many different monomers: 2 coding units allowing binary encryption, 1 cleavable spacer allowing controlled MS fragmentation, and 3 mass tags allowing fragment identification. These complex heteropolymers are therefore composed of 6 different motifs. Despite this strong sequence heterogeneity, it is found that they enable a highly controlled LbL film formation. For instance, a regular growth is observed when alternating the deposition of negatively-charged d-PPDE and positively-charged poly(allyl amine hydrochloride) (PAH). Yet, in this approach, the interdistance between consecutive coded d-PPDE layers remains relatively small, which may be an issue for data storage applications, especially for the selective decoding of the stored information. Using poly(sodium 4-styrene sulfonate) (PSS) as an intermediate non-coded polyanion, it is shown that a controlled interdistance between d-PPDE layers can be easily achieved, while still maintaining a regular LbL growth. Last but not least, it is found in this work that d-PPDE of relatively small molecular weight (i.e., significantly smaller than those of PAH and PSS) still enables a controlled LbL assembly.

pH-response of protein-polysaccharide multilayers adsorbed on a flat gold surface: A surface plasmon resonance study

Polysaccharide-protein multilayers (PPMLs) consisting of bovine serum albumin (BSA) and chondroitin sulfate (CS) are assembled in acidic solution (pH 4.2) via layer-by-layer deposition method. The formation of PPMLs on gold surface and their responsiveness to pH change from 4.2 to 7 is investigated by Surface Plasmon Resonance Spectroscopy. The buildup of the multilayer at pH 4.2 exhibits non-linear growth while the formation of the first layers is strongly affected by the physicochemical properties of the gold surface. Neutral solution (pH 7) affects the interactions between the biopolymers and results in a partially disassemble (disintegration) of the multilayer film. On one hand, the single pair of layers, BSA-CS and the double pair of layers, (BSA-CS)2, assemblies are stable in neutral pH, a result that will be of interest for biomedical applications. On the other hand, multilayer films consisting of more than four layers that is (BSA-CS)2 Collapse

Key Words

• layer‐by‐layer
• multilayer
• pH‐responsiveness
• protein‐polysaccharide
• surface plasmon

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MESH Headings

• Gold/chemistry
• Surface Plasmon Resonance/methods
• Hydrogen-Ion Concentration
• Serum Albumin, Bovine/chemistry
• Adsorption
• Chondroitin Sulfates/chemistry
• Surface Properties
• Cattle
• Animals
• Polysaccharides/chemistry

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Affiliation(s)

Nikolitsa Katsenou Department of Physics, University of Patras, Patras, Greece
Nikolaos Spiliopoulos Department of Physics, University of Patras, Patras, Greece
Dimitrios L Anastassopoulos Department of Physics, University of Patras, Patras, Greece
Aristeidis Papagiannopoulos Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens, Greece
Chris Toprakcioglu Department of Physics, University of Patras, Patras, Greece

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Collaborators Collapse

Critical adsorption and charge reversal in polyelectrolyte solutions: Analytical mean-field theory

An analytical linearized mean-field theory is presented to describe the adsorption behavior of polyelectrolytes near charged colloidal surfaces with additional short-ranged non-electrostatic interactions. The coupling between the polyelectrolyte segment density and electrostatic potential is explicitly accounted for in a self-consistent manner. This coupling gives rise to highly non-linear behavior, such as oscillations of the electrostatic potential. We derive analytical expressions for the critical surface charge density σc, after which adsorption takes place, and recover the well-known σc∼ns3/2 scaling regime, where ns is the salt concentration. In addition, the theory yields a new ns1 scaling regime if the surface is hard and a unified ns1 scaling regime if the surface also possesses some short-ranged attraction with the polyelectrolyte. Furthermore, we derive an analytical expression to describe the critical polyelectrolyte concentration φc to achieve complete charge reversal, which is found to scale as φc ∼ σ2/(f2c2), where c is related to the magnitude of short-ranged interactions and f is the average charge per monomer of the polyelectrolyte. It is observed that within our theory, complete charge reversal can only take place if the short-ranged interactions are sufficiently strong to completely compensate for the entropy loss of adsorption.

Protein-based layer-by-layer films for biomedical applications

The surface engineering of biomaterials is crucial for their successful (bio)integration by the body, i.e. the colonization by the tissue-specific cell, and the prevention of fibrosis and/or bacterial colonization. Performed at room temperature in an aqueous medium, the layer-by-layer (LbL) coating method is based on the alternating deposition of macromolecules. Versatile and simple, this method allows the functionalization of surfaces with proteins, which play a crucial role in several biological mechanisms. Possessing intrinsic properties (cell adhesion, antibacterial, degradable, etc.), protein-based LbL films represent a powerful tool to control bacterial and mammalian cell fate. In this article, after a general introduction to the LbL technique, we will focus on protein-based LbL films addressing different biomedical issues/domains, such as bacterial infection, blood contacting surfaces, mammalian cell adhesion, drug and gene delivery, and bone and neural tissue engineering. We do not consider biosensing applications or electrochemical aspects using specific proteins such as enzymes.

Membrane-Free Lateral Flow Assay with the Active Control of Fluid Transport for Ultrasensitive Cardiac Biomarker Detection

Membrane-based lateral flow immunoassays (LFAs) have been employed as early point-of-care (POC) testing tools in clinical settings. However, the varying membrane properties, uncontrollable sample transport in LFAs, visual readout, and required large sample volumes have been major limiting factors in realizing needed sensitivity and desirable precise quantification. Addressing these challenges, we designed a membrane-free system in which the desirable three-dimensional (3D) structure of the detection zone is imitated and used a small pump for fluid flow and fluorescence as readout, all the while maintaining a one-step assay protocol. A hydrogel-like protein-polyelectrolyte complex (PPC) within a polyelectrolyte multilayer (PEM) was developed as the test line by complexing polystreptavidin (pSA) with poly(diallyldimethylammonium chloride) (PDDA), which in turn was layered with poly(acrylic acid) (PAA) resulting in a superior 3D streptavidin-rich test line. Since the remainder of the microchannel remains material-free, good flow control is achieved, and with the total volume of 20 μL, 7.5-fold smaller sample volumes can be used in comparison to conventional LFAs. High sensitivity with desirable reproducibility and a 20 min total assay time were achieved for the detection of NT-proBNP in plasma with a dynamic range of 60-9000 pg·mL-1 and a limit of detection of 56 pg·mL-1 using probe antibody-modified fluorescence nanoparticles. While instrument-free visual detection is no longer possible, the developed lateral flow channel platform has the potential to dramatically expand the LFA applicability, as it overcomes the limitations of membrane-based immunoassays, ultimately improving the accuracy and reducing the sample volume so that finger-prick analyses can easily be done in a one-step assay for analytes present at very low concentrations.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Harnessing Natural Polymers for Nano-Scaffolds in Bone Tissue Engineering: A Comprehensive Overview of Bone Disease Treatment

Numerous surgeries are carried out to replace tissues that have been harmed by an illness or an accident. Due to various surgical interventions and the requirement of bone substitutes, the emerging field of bone tissue engineering attempts to repair damaged tissues with the help of scaffolds. These scaffolds act as template for bone regeneration by controlling the development of new cells. For the creation of functional tissues and organs, there are three elements of bone tissue engineering that play very crucial role: cells, signals and scaffolds. For the achievement of these aims, various types of natural polymers, like chitosan, chitin, cellulose, albumin and silk fibroin, have been used for the preparation of scaffolds. Scaffolds produced from natural polymers have many advantages: they are less immunogenic as well as being biodegradable, biocompatible, non-toxic and cost effective. The hierarchal structure of bone, from microscale to nanoscale, is mostly made up of organic and inorganic components like nanohydroxyapatite and collagen components. This review paper summarizes the knowledge and updates the information about the use of natural polymers for the preparation of scaffolds, with their application in recent research trends and development in the area of bone tissue engineering (BTE). The article extensively explores the related research to analyze the advancement of nanotechnology for the treatment of bone-related diseases and bone repair.

Sprayable surface-adaptive biocompatible membranes for efficient hemostasis via assembly of chitosan and polyphosphate

This work describes a hemostatic membrane system (or surface coating) based on spray-assisted layer-by-layer electrostatic assemblies of oppositely charged polyphosphate (polyP) and chitosan (Cs). The as-prepared membrane formed a robust micro-stratified porous structure with high flexibility. Both blood clotting test and rodent hepatic severe hemorrhage model revealed the excellent hemostatic performance of the membrane system, benefitting from the robust assembly and synergistic effect of polyP/Cs as well as membrane surface chemistry. Compared to Cs-topped membrane surface, polyP-sprayed one exhibited further improved hemostatic effect via promoting fibrin formation. Besides, comprehensive in vitro and in vivo evaluations demonstrated good biocompatibility and biodegradability of the membrane. The present approach that integrated the hemostasis-stimulating capability of polyP/Cs with facile spraying method is highly scalable and flexible, which is envisioned to be adapted readily for other hemostatic polyelectrolytes and surface functionalization of diverse existing hemostatic products on demand.

Supramolecular Protein-Polyelectrolyte Assembly at Near Physiological Conditions-Water Proton NMR, ITC, and DLS Study

The in vivo potency of polyphosphazene immunoadjuvants is inherently linked to the ability of these ionic macromolecules to assemble with antigenic proteins in aqueous solutions and form physiologically stable supramolecular complexes. Therefore, in-depth knowledge of interactions in this biologically relevant system is a prerequisite for a better understanding of mechanism of immunoadjuvant activity. Present study explores a self-assembly of polyphosphazene immunoadjuvant-PCPP and a model antigen-lysozyme in a physiologically relevant environment-saline solution and neutral pH. Three analytical techniques were employed to characterize reaction thermodynamics, water-solute structural organization, and supramolecular dimensions: isothermal titration calorimetry (ITC), water proton nuclear magnetic resonance (wNMR), and dynamic light scattering (DLS). The formation of lysozyme-PCPP complexes at near physiological conditions was detected by all methods and the avidity was modulated by a physical state and dimensions of the assemblies. Thermodynamic analysis revealed the dissociation constant in micromolar range and the dominance of enthalpy factor in interactions, which is in line with previously suggested model of protein charge anisotropy and small persistence length of the polymer favoring the formation of high affinity complexes. The paper reports advantageous use of wNMR method for studying protein-polymer interactions, especially for low protein-load complexes.

Exploring the benefits of surface analysis techniques to develop double multilayer transfer printing of J-Aggregates cyanine dyes by integrating L-b-L and μCp processes

Layer-by-layer self-assembly (L-b-L assembly) makes possible to obtain polyelectrolyte multilayers (PEMs) and one of the polyelectrolytes could be replaced by a dye molecule to obtain multilayers which may exhibit optical properties of great interest. On the other hand, μCp has become a routine technique for the preparation of micro- and nanostructured surfaces. In our development in progress of a surface engineering strategy to transfer J-Agg cyanine dyes onto surfaces by integrating L-b-L process and μCp, this contribution highlights how surface analysis imaging techniques can bring valuable information for the development of the process involving a double Multilayers Transfer Printing (MTP) with a Moiré effect. Key parameters sustaining image interpretation are difference in deposit thickness (optical microscopy, atomic force microscopy, scanning electron microscopy), in roughness (atomic force microscopy and scanning electron microscopy), in charge effect (scanning electron microscopy) and the chemical contrast between unprinted and printed areas (time-of-flight secondary ion mass spectrometry).

Gas Cluster Ion Beams as a Versatile Soft-Landing Tool for the Controlled Construction of Thin (Bio)Films

Surface biofunctionalization with proteins is the key to many biomedical applications. In this study, a solvent-free method for the controlled construction of protein thin films is reported. Using large argon gas cluster ion beams, proteins are sputtered from a target (a pool of pure proteins), and collected on a chosen substrate, being nearly any solid material. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the presence of intact protein molecules on the collectors. Furthermore, lowering the energy per atom in the cluster projectiles down to 1 eV/atom allowed more than 60% of bradykinin molecules to be transferred intact. This protein deposition method offers a precise control of the film thickness as the transferred protein quantity is proportional to the argon clusters ion dose reached for the transfer. This major feature enables building protein films from (sub)mono- to multilayers, without upper limitation of the thickness. A procedure was developed to measure the film thickness in situ the ToF-SIMS instrument. The versatility and potential of this soft-landing alternative for further applications is demonstrated on the one hand by building a protein thin film at the surface of paper, a substrate hardly compatible with solution-based adsorption methods. On the other hand, the possibility to achieve alternated multilayer buildup is demonstrated with the construction of a bilayer composed of bradykinin and Irganox, with the two layers well separated. These results lay the first stone toward original and complex multilayers that could previously not be considered with solution-based adsorption methods, and this regardless of the substrate nature.

Facile Cellulase Immobilisation on Bioinspired Silica

Cellulases are enzymes with great potential for converting biomass to biofuels for sustainable energy. However, their commercial use is limited by their costs and low reusability. Therefore, the scientific and industrial sectors are focusing on finding better strategies to reuse enzymes and improve their performance. In this work, cellulase from Aspergillus niger was immobilised through in situ entrapment and adsorption on bio-inspired silica (BIS) supports. To the best of our knowledge, this green effect strategy has never been applied for cellulase into BIS. In situ entrapment was performed during support synthesis, applying a one-pot approach at mild conditions (room temperature, pH 7, and water solvent), while adsorption was performed after support formation. The loading efficiency was investigated on different immobilisation systems by Bradford assay and FTIR. Bovine serum albumin (BSA) was chosen as a control to optimize cellulase loading. The residual activity of cellulase was analysed by the dinitro salicylic acid (DNS) method. Activity of 90% was observed for the entrapped enzyme, while activity of ~55% was observed for the adsorbed enzyme. Moreover, the supported enzyme systems were recycled five times to evaluate their reuse potential. The thermal and pH stability tests suggested that both entrapment and adsorption strategies can increase enzyme activity. The results highlight that the entrapment in BIS is a potentially useful strategy to easily immobilise enzymes, while preserving their stability and recycle potential.

Layer-by-layer assembly methods and their biomedical applications

Various biomedical applications arising due to the development of different LbL assembly methods with unique process properties.

Enzymatic Approach in Calcium Phosphate Biomineralization: A Contribution to Reconcile the Physicochemical with the Physiological View

Biomineralization is the process by which organisms produce hard inorganic matter from soft tissues with outstanding control of mineral deposition in time and space. For this purpose, organisms deploy a sophisticated "toolkit" that has resulted in significant evolutionary innovations, for which calcium phosphate (CaP) is the biomineral selected for the skeleton of vertebrates. While CaP mineral formation in aqueous media can be investigated by studying thermodynamics and kinetics of phase transitions in supersaturated solutions, biogenic mineralization requires coping with the inherent complexity of biological systems. This mainly includes compartmentalization and homeostatic processes used by organisms to regulate key physiological factors, including temperature, pH and ion concentration. A detailed analysis of the literature shows the emergence of two main views describing the mechanism of CaP biomineralization. The first one, more dedicated to the study of in vivo systems and supported by researchers in physiology, often involves matrix vesicles (MVs). The second one, more investigated by the physicochemistry community, involves collagen intrafibrillar mineralization particularly through in vitro acellular models. Herein, we show that there is an obvious need in the biological systems to control both where and when the mineral forms through an in-depth survey of the mechanism of CaP mineralization. This necessity could gather both communities of physiologists and physicochemists under a common interest for an enzymatic approach to better describe CaP biomineralization. Both homogeneous and heterogeneous enzymatic catalyses are conceivable for these systems, and a few preliminary promising results on CaP mineralization for both types of enzymatic catalysis are reported in this work. Through them, we aim to describe the relevance of our point of view and the likely findings that could be obtained when adding an enzymatic approach to the already rich and creative research field dealing with CaP mineralization. This complementary approach could lead to a better understanding of the biomineralization mechanism and inspire the biomimetic design of new materials.

Protein Transport upon Advection at the Air/Water Interface: When Charge Matters

The formation of dense protein interfacial layers at a free air-water interface is known to result from both diffusion and advection. Furthermore, protein interactions in concentrated phases are strongly dependent on their overall positive or negative net charge, which is controlled by the solution pH. As a consequence, an interesting question is whether the presence of an advection flow of water toward the interface during protein adsorption produces different kinetics and interfacial structure of the adsorbed layer, depending on the net charge of the involved proteins and, possibly, on the sign of this charge. Here we test a combination of the following parameters using ovalbumin and lysozyme as model proteins: positive or negative net charge and the presence or absence of advection flow. The formation and the organization of the interfacial layers are studied by neutron reflectivity and null-ellipsometry measurements. We show that the combined effect of a positive charge of lysozyme and ovalbumin and the presence of advection flow does induce the formation of interfacial multilayers. Conversely, negatively charged ovalbumin forms monolayers, whether advection flow is present or not. We show that an advection/diffusion model cannot correctly describe the adsorption kinetics of multilayers, even in the hypothesis of a concentration-dependent diffusion coefficient as in colloidal filtration, for instance. Still, it is clear that advection is a necessary condition for making multilayers through a mechanism that remains to be determined, which paves the way for future research.

The role of the electrokinetic charge of neurotrophis-based nanocarriers: protein distribution, toxicity, and oxidative stress in in vitro setting

Background

The rational chemical design of nanoparticles can be readily controlled and optimized by quantitatively studying protein adsorption at variously charged polymer carriers, determining their fate in biological fluids. We manufactured brain-derived neurotrophic factor (BDNF) -based electrostatic nanocomplexes with a different type of dendrimer core (anionic or cationic), encapsulated or not in polyethylene glycol (PEG), and studied their physicochemical properties and behavior in a biological setting. We investigated whether the electrokinetic charge of dendrimer core influences BDNF loading and desorption from the nanoparticle and serves as a determinant of nanoparticles’ behavior in in vitro setting, influencing mitochondrial dysfunction, lipid peroxidation, and general nanoparticles’ cellular toxicity.

Results

We found that the electrokinetic charge of the dendrimer core influences nanoparticles in terms of BDNF release profile from their surfaces and their effect on cell viability, mitochondrial membrane potential, cell phenotype, and induction of oxidative stress. The electrostatic interaction of positively charged core of nanoparticles with cell membranes increases their cytotoxicity, as well as serious phenotype alterations compared to negatively charged nanoparticles core in neuron-like differentiated human neuroblastoma cells. Moreover, PEG adsorption at nanoparticles with negatively charged core presents a distinct decrease in metabolic cell activity. On the contrary, charge neutralization due to PEG adsorption on the surface of nanoparticles with positively charged core does not reduce their cytotoxicity, makes them less biocompatible with differentiated cells, and presumably shows non-specific toxicity.

Conclusions

The surface charge transformation after adsorption of protein or polyelectrolyte during nanocarriers formulation has an important role not only in designing nanomaterials with potent neuroprotective and neuroregenerative properties but also in applying them in a cellular environment.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00984-4.

EPR Spectroscopy as an Efficient Tool for Investigations of Polyelectrolyte Multilayer Growth and Local Chain Dynamics

The strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) and the weak polyanion poly(ethylene-alt-maleic acid) (P(E-alt-MA)) were used to build polyelectrolyte multilayers (PEMs) up to 31 layers. A spin-label (SL) was covalently attached to the polyanion for studying the rotational dynamics of the polyacid backbone in a swollen state of the PEMs using continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy. In the first step, the spin-labeled poly(ethylene-alt-maleic acid) (SL-P(E-alt-MA)) was used in every polyanion layer to monitor the PEMs growth by analyzing the integrated intensity of the spectra. The buildup was found to be pH-dependent resulting in PEM with different thicknesses. In the second step, SL-P(E-alt-MA) was selectively placed in a single polyanion layer to study the rotational dynamics of the polyacid backbone. The rotational diffusion coefficient of the polyacid backbone R_S and the internal rotational diffusion coefficient of the SL attached to the polymer backbone R_I were found to be higher at pH 5 than at pH 4, which is related to enhanced mobility.

Biochemical Modification of Titanium Oral Implants: Evidence from In Vivo Studies

The discovery of osseointegration of titanium implants revolutionized the dental prosthesis field. Traditionally, implants have a surface that is processed by additive or subtractive techniques, which have positive effects on the osseointegration process by altering the topography. In the last decade, innovative implant surfaces have been developed, on which biologically active molecules have been immobilized with the aim of increasing stimulation at the implant-biological tissue interface, thus favoring the quality of osseointegration. Among these molecules, some are normally present in the human body, and the techniques for the immobilization of these molecules on the implant surface have been called Biochemical Modification of Titanium Surfaces (BMTiS). Different techniques have been described in order to immobilize those biomolecules on titanium implant surfaces. The aim of the present paper is to present evidence, available from in vivo studies, about the effects of biochemical modification of titanium oral implants on osseointegration.

Layer-by-layer assembly in nanochannels: assembly mechanism and applications

Layer-by-layer (LbL) assembly is a versatile technology to construct multifunctional nanomaterials using various supporting substrates, enabled by the large selection freedom of building materials and diversity of possible driving forces. The fine regulation over the film thickness and structure provides an elegant way to tune the physical/chemical properties by mild assembly conditions (e.g. pH, ion strength). In this review, we focus on LbL in nanochannels, which exhibit a different growth mechanism compared to "open", convex substrates. The assembly mechanism in nanochannels is discussed in detail, followed by the summary of applications of LbL assemblies liberated from nanochannel templates which can be used as nanoreactors, drug carriers and transporting channels across cell membranes. For fluidic applications, robust membrane substrates are required to keep in place nanotube arrays for membrane-based separation, purification, biosensing and energy harvesting, which are also discussed. The good compatibility of LbL with crossover technologies from other fields allows researchers to further extend this technology to a broader range of research fields, which is expected to result in an increased number of applications of LbL technology in the future.

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

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.

Deposition of Intact and Active Proteins In Vacuo Using Large Argon Cluster Ion Beams

Providing inert materials with a biochemical function, for example using proteins, is a cornerstone technology underlying many applications. However, the controlled construction of protein thin films remains a major challenge. Here, an innovative solvent-free approach for protein deposition is reported, using lysozyme as a model. By diverting a time-of-flight secondary ion mass spectrometer (ToF-SIMS) from its standard analytical function, large argon clusters were used to achieve protein transfer. A target consisting of a pool of proteins was bombarded with 10 keV Ar₅₀₀₀⁺ ions, and the ejected proteins were collected on a silicon wafer. The ellipsoidal deposition pattern was evidenced by ToF-SIMS analysis, while SDS-PAGE electrophoresis confirmed the presence of intact lysozyme on the collector. Finally, enzymatic activity assays demonstrated the preservation of the three-dimensional structure of the transferred proteins. These results pave the way to well-controlled protein deposition using ion beams and to the investigation of more complex multilayer architectures.

Adsorption and Release of Rose Bengal on Layer-by-Layer Films of Poly(Vinyl Alcohol) and Poly(Amidoamine) Dendrimers Bearing 4-Carboxyphenylboronic Acid

Phenylboronic acid-bearing polyamidoamine dendrimer (PBA-PAMAM)/poly(vinyl alcohol) (PVA) multilayer films were prepared through the layer-by-layer (LbL) deposition of PBA-PAMAM solution and PVA solution. PBA-PAMAM/PVA films were constructed successfully through the formation of boronate ester bonds between the boronic acid moiety in PBA and 1,3-diol units in PVA. When the (PBA-PAMAM/PVA)₅ films were immersed in rose bengal (RB) solution, RB was adsorbed onto the LbL films. The amount of RB adsorbed was higher in the LbL films immersed in acidic solution than in basic solution. The release of RB from the LbL films was also promoted in the basic solution, while it was suppressed in the acidic solution. The boronic acid ester is oxidized to phenol by hydrogen peroxide (H₂O₂) and the carbon-boron bond is cleaved, so that the (PBA-PAMAM/PVA)₅ films can be decomposed by immersion in H₂O₂ solution. Therefore, when RB-adsorbed (PBA-PAMAM/PVA)₅ films were immersed in H₂O₂ solution, the release of RB was moderately promoted when the solution was weakly acidic.

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.