Polyelectrolyte Multilayer Surfaces Research Articles

Highly penetrant organic solvent-resistant layer-by-layer assembled ultra-thin barrier coating for confined microchannel devices

Recently, there has been an increasing demand for developing high performance barrier films for effectively suppressing the penetration of organic solvent. Particularly, in microfluidic systems for lab-on-a-chip devices or inkjet printing, the predominantly faced challenges are swelling deformation and channel blockage by the penetrated solvents, which significantly deteriorates the device performance and lifetime. To address this issue, here we present a robust method for the deposition of barrier layers inside microchannels using a surface charge-regulated layer-by-layer assembly of polyelectrolyte multilayers (PEM). Owing to the highly negative surface charge and additionally employed crosslinking reaction using glutaraldehyde (GA), the Donnan repulsion at the barrier film surface and size-narrowing effect in internal pores can be simultaneously intensified, which rendered excellent barrier performance against highly penetrating organic solvents only with a 14-nm-thick coating layer. Further, we employed a wrinkling-based metrology for precisely evaluating the barrier property of the multilayered films. As a result, highly negatively charged PEM surface (−64.2 mV) with small inner pores (<0.5 nm) resulted in excellent barrier performance to the penetration of various conventional organic solvents used for microelectronic processing. Finally, the practical applicability of the PEM barrier films coated in complexly structured microchannels was demonstrated by fully securing the devices intact even under continuous exposure to organic solvent flowing for 4 h. As such, this study provides a general guideline for the internal deposition of barrier films regardless of the form factor of target surfaces toward next generation organic and wearable electronic devices, along with microfluidic chemical reactor systems.

Altered Proinflammatory Responses to Polyelectrolyte Multilayer Coatings Are Associated with Differences in Protein Adsorption and Wettability.

A full understanding of the relationship between surface properties, protein adsorption, and immune responses is lacking but is of great interest for the design of biomaterials with desired biological profiles. In this study, polyelectrolyte multilayer (PEM) coatings with gradient changes in surface wettability were developed to shed light on how this impacts protein adsorption and immune response in the context of material biocompatibility. The analysis of immune responses by peripheral blood mononuclear cells to PEM coatings revealed an increased expression of proinflammatory cytokines tumor necrosis factor (TNF)-α, macrophage inflammatory protein (MIP)-1β, monocyte chemoattractant protein (MCP)-1, and interleukin (IL)-6 and the surface marker CD86 in response to the most hydrophobic coating, whereas the most hydrophilic coating resulted in a comparatively mild immune response. These findings were subsequently confirmed in a cohort of 24 donors. Cytokines were produced predominantly by monocytes with a peak after 24 h. Experiments conducted in the absence of serum indicated a contributing role of the adsorbed protein layer in the observed immune response. Mass spectrometry analysis revealed distinct protein adsorption patterns, with more inflammation-related proteins (e.g., apolipoprotein A-II) present on the most hydrophobic PEM surface, while the most abundant protein on the hydrophilic PEM (apolipoprotein A-I) was related to anti-inflammatory roles. The pathway analysis revealed alterations in the mitogen-activated protein kinase (MAPK)-signaling pathway between the most hydrophilic and the most hydrophobic coating. The results show that the acute proinflammatory response to the more hydrophobic PEM surface is associated with the adsorption of inflammation-related proteins. Thus, this study provides insights into the interplay between material wettability, protein adsorption, and inflammatory response and may act as a basis for the rational design of biomaterials.

Improved stability of zeolitic imidazolate framework-8 photocatalytic coating on polyurethane foam via polyelectrolyte multilayer surface modification

Polycrystalline zeolitic imidazolate framework-8 (ZIF-8) layers have been coated on polyurethane (PU) foam substrate by a combined seed anchoring and secondary growth process. A polyelectrolyte multilayers (PEMs) primer was used to enhance the initial anchoring of the ZIF-8 seed crystals on the PU surface. X-Ray diffraction confirmed that the three-step process (PEM primer, MOF seed adsorption, secondary growth) produced a dense and homogeneous coating of ZIF-8 crystals on the PU foam substrate. The thickness of the ZIF-8 coating was observed by scanning electron microscopy (SEM) and was found to increased from 270 nm to 420 nm when the PEM primer was used when compared to the PU surface deposition. The PU/PEMs/ZIF-8/ foams were tested for their photocatalytic degradation of methylene blue (MB) under UV light and displayed a 4 folds increase in methylene blue (MB) adsorbtion over ZIF-8/PU foam. The photodegradation of MB was also increased from 31% in ZIF-8/PU to 51% in ZIF-8/PEMs/PU foams. Finally, The superior efficiency of the PEMs anchored seeds displayed outstanding photocatalytic efficiency with reusability up to 4 cycles when compared to the without PEMs modified one that lost their performance after only 1 cycle of the photodegradation test.

Enzymatic Degradation of Glycosaminoglycans and Proteoglycan-Mimetic Materials in Solution and on Polyelectrolyte Multilayer Surfaces

Proteoglycans (PGs) play many important roles in biology, contributing to the mechanical properties of tissues, helping to organize extracellular matrix components, and participating in signaling mechanisms related to mechanotransduction, cell differentiation, immune responses, and wound healing. Our lab has designed two different types of PG mimics: polyelectrolyte complex nanoparticles (PCNs) and PG-mimetic graft copolymers (GCs), both of which are prepared using naturally occurring glycosaminoglycans. This work evaluates the enzymatic stability of these PG mimics using hyaluronidases (I-S, IV-S, and II), chondroitinase ABC, and lysozyme, for PG mimics suspended in solution and adsorbed onto surfaces. Hyaluronan (HA)- and chondroitin sulfate (CS)-containing PG mimics are degraded by the hyaluronidases. PCNs prepared with CS and GCs prepared with heparin are the only CS- and HA-containing PG mimics protected from chondroitinase ABC. None of the materials are measurably degraded by lysozyme. Adsorption to polyelectrolyte multilayer surfaces protects PG mimics from degradation, compared to when PG mimics are combined with enzymes in solution; all surfaces are still intact after 21 days of enzyme exposure. This work reveals how the stability of PG mimics is controlled by both the composition and macromolecular assembly of the PG mimic and also by the size and specificity of the enzyme. Understanding and tuning these degradation susceptibilities are essential for advancing their applications in cardiovascular materials, orthopedic materials, and growth factor delivery applications.

Chitosan-miRNA functionalized microporous titanium oxide surfaces via a layer-by-layer approach with a sustained release profile for enhanced osteogenic activity

BackgroundThe biofunctionalization of titanium implants for high osteogenic ability is a promising approach for the development of advanced implants to promote osseointegration, especially in compromised bone conditions. In this study, polyelectrolyte multilayers (PEMs) were fabricated using the layer-by-layer approach with a chitosan-miRNA (CS-miRNA) complex and sodium hyaluronate (HA) as the positively and negatively charged polyelectrolytes on microarc-oxidized (MAO) Ti surfaces via silane-glutaraldehyde coupling.MethodsDynamic contact angle and scanning electron microscopy measurements were conducted to monitor the layer accumulation. RiboGreen was used to quantify the miRNA loading and release profile in phosphate-buffered saline. The in vitro transfection efficiency and the cytotoxicity were investigated after seeding mesenchymal stem cells (MSCs) on the CS-antimiR-138/HA PEM-functionalized microporous Ti surface. The in vitro osteogenic differentiation of the MSCs and the in vivo osseointegration were also evaluated.ResultsThe surface wettability alternately changed during the formation of PEMs. The CS-miRNA nanoparticles were distributed evenly across the MAO surface. The miRNA loading increased with increasing bilayer number. More importantly, a sustained miRNA release was obtained over a timeframe of approximately 2 weeks. In vitro transfection revealed that the CS-antimiR-138 nanoparticles were taken up efficiently by the cells and caused significant knockdown of miR-138 without showing significant cytotoxicity. The CS-antimiR-138/HA PEM surface enhanced the osteogenic differentiation of MSCs in terms of enhanced alkaline phosphatase, collagen production and extracellular matrix mineralization. Substantially enhanced in vivo osseointegration was observed in the rat model.ConclusionsThe findings demonstrated that the novel CS-antimiR-138/HA PEM-functionalized microporous Ti implant exhibited sustained release of CS-antimiR-138, and notably enhanced the in vitro osteogenic differentiation of MSCs and in vivo osseointegration. This novel miRNA-functionalized Ti implant may be used in the clinical setting to allow for more effective and robust osseointegration.

Impact of molecular weight on polyelectrolyte multilayer assembly and surface properties

Polyelectrolyte multilayers (PEMs) are a versatile category of materials due to their ability to modify surface properties for applications ranging from protective coatings to improved cell adhesion. Polyelectrolyte choice, including its structure and molecular weight (MW), is known to greatly influence PEM assembly and surface properties. In this work, poly(acrylic acid)/poly-l-lysine PEMs using three pairs of MWs (1.8k/15–30k, 100k/120k, and 250k/275k) were studied to determine the effects of their MWs on PEM assembly, topography and surface energy. PEMs assembly was monitored in a quartz crystal microbalance with dissipation, resulting in masses of 3.90 ± 0.87 µg/cm2, 10.80 ± 4.189 µg/cm2, and 30.04 ± 13.68 µg/cm2 for 10 bilayers of low, medium, and high MW pairs, respectively. The low MW PEM was more rigid. Low and high MW PEMs exhibited higher roughness than medium MW, caused by polyelectrolyte stripping. Surface energy remained constant with bilayer count in the low and high MW PEMs, but steadily increased in the medium MW PEM. Differences between medium MW PEMs from low and high MW systems indicate that, while PEM properties change with MW, they are not monotonically correlated and are instead related to changes in internal charge distributions and the resultant stripping that may occur.

Two types of polyelectrolyte multilayers hydrogel membrane based on chitosan and alginate with different self-assembled process for control L929 cell behavior

Controlling the adhesion of mammalian cells at the interface between materials and biological environments is a real challenge when designing materials for tissue engineering applications. The surface properties of implanted materials are known to have a significant impact on cell adhesion. Herein, two types of polyelectrolyte multilayers (PEMs) hydrogel membrane based on marine-derived polysaccharides of chitosan (CHI) and alginate (ALG) biopolymers were fabricated by the layer-by-layer (LbL) technique using simple approach involving the change in assemble sequence of chitosan with different degree of deacetylation (DD). The effect of PEMs formation on the surface properties and their effects on the adhesion of mouse fibroblast cell (L929) of the two membranes were studied. The results showed that the formations of ALG/CHI membranes were related to the rigidity and conformations of chitosan molecules. The adhesion of L929 cell was strongly depended on the surface roughness rather than stiffness. The surface of PEMs can be strongly cytophilic (cell adhesive, terminated with chitosan (C1)) or strongly cytophobic (cell resistant, terminated with chitosan (C2)). The results obtained indicate that ALG/CHI PEMs with different surface morphology and roughness could be used in vitro to manipulate cell behaviors to improve upon the design of tissue-engineered membranes.

Enhanced antiadhesive properties of chitosan/hyaluronic acid polyelectrolyte multilayers driven by thermal annealing: Low adherence for mammalian cells and selective decrease in adhesion for Gram-positive bacteria

The development of antifouling coatings with restricted cell and bacteria adherence is fundamental for many biomedical applications. A strategy for the fabrication of antifouling coatings based on the layer-by-layer assembly and thermal annealing is presented. Polyelectrolyte multilayers (PEMs) assembled from chitosan and hyaluronic acid were thermally annealed in an oven at 37°C for 72h. The effect of annealing on the PEM properties and topography was studied by atomic force microscopy, ζ-potential, circular dichroism and contact angle measurements. Cell adherence on PEMs before and after annealing was evaluated by measuring the cell spreading area and aspect ratio for the A549 epithelial, BHK kidney fibroblast, C2C12 myoblast and MC-3T3-E1 osteoblast cell lines. Chitosan/hyaluronic acid PEMs show a low cell adherence that decreases with the thermal annealing, as observed from the reduction in the average cell spreading area and more rounded cell morphology. The adhesion of S. aureus (Gram-positive) and E. coli (Gram-negative) bacteria strains was quantified by optical microscopy, counting the number of colony-forming units and measuring the light scattering of bacteria suspension after detachment from the PEM surface. A 20% decrease in bacteria adhesion was selectively observed in the S. aureus strain after annealing. The changes in mammalian cell and bacteria adhesion correlate with the changes in topography of the chitosan/hyaluronic PEMs from a rough fibrillar 3D structure to a smoother and planar surface after thermal annealing.

Adsorption and interlayer diffusion controlled growth and unique surface patterned growth of polyelectrolyte multilayers

In this work, extremely high molecular weight (Mw) poly(allylamine hydrochloride) (PAH, 900K g/mol) and poly(acrylic acid) (PAA, 225 K g/mol) were selected to amplify the difference in the growth of multilayers in comparison with low Mw PAA (15K g/mol) and PAH (15K g/mol). By varying the pH conditions, the PAH/PAA multilayers were fabricated via the layer-by-layer (LbL) assembly in both linear and exponential growth regimes. In the linear growth regime with interlayer diffusion suppressed, high Mw polyelectrolytes with low charge density could slow down the adsorption step, leading to the decrease of thickness compared to low Mw polyelectrolytes when the deposition time was limited. However, the effect of Mw could be reversed by increasing the deposition time, for the adsorption of low Mw polyelectrolyte reached equilibrium, while the adsorption of high Mw polyelectrolyte continued. The larger coil size of high Mw polyelectrolyte could enable the surpassing of multilayer thickness compared with low Mw polyelectrolyte. In the exponential growth regime, besides the slow adsorption, the application of high Mw polyelectrolytes further suppressed the interlayer diffusion, leading to the decrease of multilayer thickness regardless of deposition time. We further studied the effects of deposition time, Mw of polyelectrolytes, and the number of bilayers on the surface morphology in the exponential growth regime. Surface roughness significantly increased with the application of high Mw PAA and the increase in deposition time. For the first time, the unique LbL film growth patterns of islet, ring and cantaloupe skin-like structures that consecutively formed on the surface of polyelectrolyte multilayers were reported by tuning the above parameters.

Effect of Assembly pH on Polyelectrolyte Multilayer Surface Properties and BMP-2 Release.

The effect of solution pH during layer-by-layer assembly of polyelectrolyte multilayer (PEM) coatings on properties relevant to orthopedic implant success was investigated. Bone morphogenetic protein 2 (BMP-2), a potent osteoconductive growth factor, was adsorbed onto the surface of anodized titanium, and PEM coatings prepared from solutions of poly-l-histidine and poly(methacrylic acid) were built on top of the BMP-2. High levels of BMP-2 released over several months were achieved. Approximately 2 μg/cm(2) of BMP-2 were initially adsorbed on the anodized titanium and a pH-dependent release behavior was observed, with more stable coatings assembled at pH = 6-7. Three different diffusion regimes could be determined from the release profiles: an initial burst release, a sustained release regime, and a depletion regime. BMP-2 was shown to maintain bioactivity after release from a PEM and the presence of a PEM was shown to preserve BMP-2 structure. No visible change was observed in surface roughness as the assembly pH was varied, whereas the surface energy decreased for samples prepared at more basic pH. These results indicate that the initial BMP-2 layer affects PEM surface structure, but not the functional groups exposed on the surface.

The design of antimicrobial LL37-modified collagen-hyaluronic acid detachable multilayers

The design of antimicrobial membranes and thin films are critical for the design of biomaterials that can combat bacterial contamination. Since the long-term use of conventional antibiotics can result in bacterial resistance, there is a critical need to incorporate natural antimicrobial peptides (AMPs) that not only prevent a wide range of pathogens from causing infections but can also promote many beneficial outcomes in wounded tissues. We report the design and antimicrobial properties of detachable collagen (COL)/hyaluronic acid (HA) polyelectrolyte multilayers (PEMs) modified with LL-37, a naturally occurring human AMP. LL-37 was physically adsorbed and chemically immobilized on the surface of PEMs. The antimicrobial and cytotoxic properties of PEMs were tested with Gram-negative Escherichia coli (E. coli, strain DH10B) and primary rat hepatocytes, respectively. The ability to prevent bacterial adhesion and to neutralize an E. coli layer was investigated as a function of LL-37 concentration. An interesting trend was that even unmodified PEMs exhibited a 40% reduction in bacterial adhesion. When LL-37 was physically adsorbed on PEMs, bacterial adhesion was significantly lower on the surface of the films as well as in the surrounding broth. Immobilizing LL-37 resulted in less than 3% bacterial adhesion on the surface due to the presence of the peptide. LL-37 modified PEMs did not result in any cytotoxicity up to input concentrations of 16μM. More importantly, urea and albumin secretion by hepatocytes were unaffected even at high LL-37 concentrations. The COL/HA PEMs can serve as antimicrobial coatings, biological membranes and as in vitro platforms to investigate pathogen-tissue interactions. Statement of SignificanceAntimicrobial peptides (AMPs) are emerging as an alternative to conventional antibiotics. We report the antimicrobial properties of detachable collagen (COL)/hyaluronic acid (HA) polyelectrolyte multilayers (PEMs) modified with LL-37, a human AMP. The antimicrobial and cytotoxic properties were tested with gram-negative Escherichia coli (E. coli, strain DH10B) and primary rat hepatocytes, respectively. Unmodified PEMs exhibited a 40% reduction in bacterial adhesion. When LL-37 was physically adsorbed on PEMs, the sustained release of the active peptide killed planktonic bacteria. Immobilizing LL-37 resulted in less than 3% bacterial adhesion. LL-37 modified PEMs did not result in cytotoxicity up to input concentrations of 16μM. The COL/HA PEMs can serve as antimicrobial coatings and to investigate pathogen-cell interactions.

Growth and motility of human skin fibroblasts on multilayer strong polyelectrolyte films

Polyelectrolyte multilayers (PEMs) have found application in modifying material surfaces to make them adhesive or non-adhesive for animal cells. However, PEMs made of strong polyelectrolytes are not fully recognized in the literature. This study focuses on the interplay between the properties of PEM assembled from strong polyelectrolytes and cell adhesion and motility. Strong polycations (with quaternary ammonium groups) and a polyanion (with sulfonate groups) were obtained by modification of poly(allylamine hydrochloride) (PAH). Two types of multilayer films were assembled from these PAH derivatives and used to investigate the behavior of human skin fibroblasts (HSFs). The effect of surface charge, hydrophobicity, and film thickness on adhesion of HSFs in a serum-containing medium was studied with immunofluorescence microscopy. The results showed that adhesion of HSFs was strongly depended on the chemical functions of the terminal layer, whereas the wettability was not important. The surface of PEM can be strongly cytophobic (the quaternary ammonium terminal groups) or strongly cytophilic (the sulfonate terminal groups). Finally, the motile activity of HSFs seeded on glass coated with a varying number of polymer layers was investigated. It was demonstrated using an in vitro model that coating the substrate with only two polymer layers can considerably increase the average speed of HSFs movement and stimulate cell migration into the wound.

Breast Cancer/Stromal Cells Coculture on Polyelectrolyte Films Emulates Tumor Stages and miRNA Profiles of Clinical Samples.

In this study, we demonstrate a method for controlling breast cancer cells adhesion on polyelectrolyte multilayer (PEM) films without the aid of adhesive proteins/ligands to study the role of tumor and stromal cell interaction on cancer biology. Numerous studies have explored engineering coculture of tumor and stromal cells predominantly using transwell coculture of stromal cells cultured onto coverslips that were subsequently added to tumor cell cultures. However, these systems imposed an artificial boundary that precluded cell-cell interactions. To our knowledge, this is the first demonstration of patterned coculture of tumor cells and stromal cells that captures the temporal changes in the miRNA signature as the breast tumor develops through various stages. In our study we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated poly(styrene) (SPS), as the polycation and polyanion, respectively, to build PEMs. Breast cancer cells attached and spread preferentially on SPS surfaces while stromal cells attached to both SPS and PDAC surfaces. SPS patterns were formed on PEM surfaces, by either capillary force lithography (CFL) of SPS onto PDAC surfaces or vice versa, to obtain patterns of breast cancer cells and patterned cocultures of breast cancer and stromal cells. In this study, we utilized cancer cells derived from two different tumor stages and two different stromal cells to effectively model a heterogeneous tumor microenvironment and emulate various tumor stages. The coculture model mimics the proliferative index (Ki67 expression) and tumor aggressiveness (HER-2 expression) akin to those observed in clinical tumor samples. We also demonstrated that our patterned coculture model captures the temporal changes in the miRNA-21 and miRNA-34 signature as the breast tumor develops through various stages. The engineered coculture platform lays groundwork toward precision medicine wherein patient-derived tumor cells can be incorporated within our in vitro models to identify potential pathways and drug treatment regimens for individual patients.

Sustainable polyelectrolyte multilayer surfaces: possible matrix for salt/dye separation.

The development of a sustainable membrane surface based on chitosan/poly(acrylic acid) (CHI/PAA) multilayers suitable for applications in analytical separations is reported here. Bilayers are constructed on polyamide microfiltration membranes at a pH combination of 3/3 (CHI pH/PAA pH) through a layer by layer approach. A 12.5 bilayer yielded a thickness of 400 nm. Low pressure (10 psi) filtrations through a 5.5 bilayered membrane exhibited high flux (7 m(3) m(-2) day(-1)) and selectivity (NaCl/reactive black 5 (RB5) selectivity >8000). The selectivity and flux observed here are the highest reported to date for low pressure filtrations through membranes. The increase in flux with increasing feed salt concentration is correlated with morphological transformations. Salt content above 7500 ppm causes some perturbation of surface layers. The presence of RB5, a model dye in the feed, restores the surface to maintain sustainability. A skin layer as thin as 50 nm imparts a large separation window. An RB5 feed concentration of 500 ppm results in 98.64% rejection with a flux of 25.79 m(3) m(-2) day(-1). The increase in flux with feed dye concentration supports the plasticizing action of RB5. The transport studies with large feed dye concentrations indicate that at a dye concentration of 500 ppm, the linear growing region (pre-exponential, 5.5 bilayer) itself provides a separation window similar to that of 100 ppm. At the same time, 1000 ppm requires a 9.5 bilayer that falls in the nonlinear growing region. Scanning electron microscopy images show the increase in porosity with respect to feed dye. Interesting morphologies that show the sustainable nature of the membrane surfaces along with the transport data of RB5 are presented.

Tuning liquid absorption and ink spreading by polyelectrolyte multilayering on substrates with different levels of internal sizing

The effect of base paper hydrophobicity and polyelectrolyte multilayer surface treatment on the subsequent liquid absorption and ink&#x2013;substrate interaction was studied. It was found that the internal sizing degree affects the inkjet print quality, but that it is dependent on deposited polyelectrolyte layer chemistry and composition. A rather different ink absorption and spreading behavior was seen with dyes than with pigment-based inks.

Hyaluronan-based pericellular matrix: substrate electrostatic charges and early cell adhesion events

Cells are surrounded by a hyaluronan-rich coat called 'pericellular matrix' (PCM), mainly constituted by hyaluronan, a long-chain linear polysaccharide which is secreted and resorbed by the cell, depending on its activity. Cell attachment to a surface is mediated by PCM before integrins and focal adhesions are involved. As hyaluronan is known to bear a negative charge at physiological pH, the relevance of its electrical properties in driving the early cell adhesion steps has been studied, exploring how PCM mediates cell adhesion to charged surfaces, such as polyelectrolyte multilayer (PEM) films. Poly(ethylene imine) (PEI) and poly(sodium 4-styrene sulphonate) (PSS), assembled as PEI/PSS and PEI/PSS/PEI layers, were used. The nanoscale morphology of such layers was analysed by atomic force microscopy, and the detailed surface structure was analysed by X-ray photoemission spectroscopy. PCM-coated and PCM-depleted MG63 osteoblast-like cells were used, and cell density, morphology and adhesive structures were analysed during early steps of cell attachment to the PEM surfaces (1-6h). The present study demonstrates that the pericellular matrix is involved in cell adhesion to material surfaces, and its arrangement depends on the cell interaction with the surface. Moreover, the PCM/surface interaction is not simply driven by electrostatic effects, as the cell response may be affected by specific chemical groups at the material surface. In the development of biomimetic surfaces promoting cell adhesion and function, the role of this unrecognised outer cell structure has to be taken into account.

Role of interfacial interactions in ordering of two-dimensional colloidal self-assemblies on polyelectrolyte multilayer surfaces

In this study, we examined the ordering of 2D colloidal particle monolayer structures formed atop polyelectrolyte multilayers (PEM) constructed by layer-by-layer deposition. We focused on the interactions between the particles and the substrate surface by changing the top layer of PEMs, along with the fabrication procedure for the PEMs. For PEMs prepared by rinsing with pure water in the fabrication process, the 2D assembly of negatively charged colloidal spheres exhibited a disordered state for positively charged PEM surfaces, whereas a well-ordered structure was formed on a negatively charged surface. Investigations with a colloid-probe atomic force microscope technique revealed that the friction force between the colloid and substrate at a zero load condition strongly affects the ordering state of the particle monolayers for relatively rigid surfaces. However, swollen PEM surfaces that were prepared by rinsing the layers with a salt solution rendered disordering of the colloidal monolayer for both positively and negatively charged surfaces and shifted to a less ordered state as the number of polyelectrolyte layers increased. For the salt-rinsed PEMs, we found that the range of the steric force of the PEMs rather than the friction force appears to be critical for the ordering of the 2D colloidal assemblies. For such swollen PEMs, we consider that the entanglement of the polymers to the colloidal particles invokes the hindrance of the particle ordering in the 2D colloidal assembly formation even though electrostatic repulsion between the colloids and the polymer layer takes place.

Ion Dispositions in Polyelectrolyte Multilayer Films

Polyelectrolyte multilayers (PEMs) fabricated through layer-by-layer.(LbL) assembly from sodium chloride containing solutions of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrene sulfonate) (PSS) were examined by quartz crystal microbalance (QCM), QCM with dissipation (QCM-D), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) to determine the dispositions of polyelectrolytes and counterions across the PEM thickness. The key experiment was dry film QCM, which by quantifying the incremental mass depositions during LbL assembly uncovered :excess polyelectrolyte charge and excess polyelectrolyte charge density as functions of deposition number. Counterion dispositions depended strongly on salt concentration, and trends in the two PEM charge parameters established three salt concentration regimes: zero to near zero salt ([NaCl] less than or similar to 0.1 M), low salt (0.1 M less than or similar to [NaCl] less than or similar to 0.75 M), and high salt ([NaCl] greater than or similar to 1.5 M]). The first two are associated with linear LbL growth while the latter is associated with exponential LbL growth. At zero salt, no counterions are present in the PEM bulk (middle), while at low salt, an excess of PDDA charge across the bulk coincides with an excess of counteranions. Differently, at high salt, deposited PSS permeates the PEM bulk, conveying an excess of countercations. At all salt concentrations, the PEM surface charge alternates according to the capping polyelectrolyte's identity. Accumulations of small ions in the PEM bulk can be ascribed to property asymmetries between the two deposited polyelectrolytes, but the roles played by different chain properties remain incompletely understood.

Quantification of antibiotic in biofilm-inhibiting multilayers by 7.87 eV laser desorption postionization MS imaging.

The potential of laser desorption postionization mass spectrometry (LDPI-MS) imaging for small molecule quantification is demonstrated here. The N-methylpiperazine acetamide (MPA) of ampicillin was adsorbed into polyelectrolyte multilayer surface coatings composed of chitosan and alginate, both high molecular weight biopolymers. These MPA-ampicillin spiked multilayers were then shown to inhibit the growth of Enterococcus faecalis biofilms that play a role in early stage infection of implanted medical devices. Finally, LDPI-MS imaging using 7.87 eV single-photon ionization was found to detect MPA-ampicillin within the multilayers before and after biofilm growth with limits of quantification and detection of 0.6 and 0.3 nmol, respectively. The capabilities of LDPI-MS imaging for small molecule quantification are compared to those of MALDI-MS. Furthermore, these results indicate that 7.87 eV LDPI-MS imaging should be applicable to quantification of a range of small molecular species on a variety of complex organic and biological surfaces. Finally, while MS imaging for quantification was demonstrated here using LDPI, it is a generally useful strategy that can be applied to other methods.

Surface modification of poly(propylene carbonate) by aminolysis and layer-by-layer assembly for enhanced cytocompatibility

Poly(propylene carbonate) (PPC) is a biodegradable polymer with desirable mechanical properties for bone and cartilage repair. However, the poor biocompatibility impedes its applications in tissue engineering. The aim of this study was to evaluate the effect of surface modification of PPC on the improvement of its cytocompatibility. The combination of aminolysis and layer-by-layer (LBL) assembly techniques was used to modify the PPC surface. The results of ATR–FTIR measurement demonstrated that PPC was aminolyzed by polyethylenimine (PEI) at specific reaction conditions and the degree of aminolyzation was quantitatively determined by ninhydrin method. Positively charged PEI and negatively charged gelatin were alternatively deposited on the aminolyzed PPC membranes at pH 7.4, which formed polyelectrolyte multilayers surface with gelatin as the outermost layer. The presence of amino groups on the aminolyzed PPC and gelatin on the multilayers had significant impact on enhancing the hydrophilicity of PPC. Fibroblast and primary human osteoblasts (HOBs) were used to assess the cytocompatibility of PPC. The deposition of PEI and gelatin bilayers on PPC remarkably promoted both fibroblast and HOBs cell attachment, spreading and growth. In particular, the osteogenic gene expression of HOBs cultured on the multilayers modified PPC was substantially increased. The aminolysis followed by LBL assembly is a convenient and cost effective technique for enhancing cell attachment and proliferation. The product has high potential for musculoskeletal tissue engineering applications due to its desirable mechanical strength and tunable cytocompatibility.