The structure of poly(L-lysine) (PLL)͞hyaluronan (HA) polyelectrolyte multilayers formed by electrostatic self-assembly is studied by using confocal laser scanning microscopy, quartz crystal microbalance, and optical waveguide lightmode spectroscopy. These films exhibit an exponential growth regime where the thickness increases exponentially with the number of deposited layers, leading to micrometer thick films. Previously such a growth regime was suggested to result from an ''in'' and ''out'' diffusion of the PLL chains through the film during buildup, but direct evidence was lacking. The use of dye-conjugated polyelectrolytes now allows a direct three-dimensional visualization of the film construction by introducing fluorescent polyelectrolytes at different steps during the film buildup. We find that, as postulated, PLL diffuses throughout the film down into the substrate after each new PLL injection and out of the film after each PLL rinsing and further after each HA injection. As PLL reaches the outer layer of the film it interacts with the incoming HA, forming the new HA͞PLL layer. The thickness of this new layer is thus proportional to the amount of PLL that diffuses out of the film during the buildup step, which explains the exponential growth regime. HA layers are also visualized but no diffusion is observed, leading to a stratified film structure. We believe that such a diffusion-based buildup mechanism explains most of the exponential-like growth processes of polyelectrolyte multilayers reported in the literature.hyaluronan ͉ poly(L-lysine) ͉ confocal laser scanning microscopy ͉ diffusion ͉ film structure

The formation ofpolysaccharide films based on the alternate deposition of chitosan (CHI) and hyaluronan (HA) was investigated by several techniques. The multilayer buildup takes place in two stages: during the first stage, the surface is covered by isolated islets that grow and coalesce as the construction goes on. After several deposition steps, a continuous film is formed and the second stage of the buildup process takes place. The whole process is characterized by an exponential increase of the mass and thickness of the film with the number of deposition steps. This exponential growth mechanism is related to the ability of the polycation to diffuse "in" and "out" of the whole film at each deposition step. Using confocal laser microscopy and fluorescently labeled CHI, we show that such a diffusion behavior, already observed with poly(L-lysine) as a polycation, is also found with CHI, a polycation presenting a large persistence length. We also analyze the effect of the molecular weight (MW) of the diffusing polyelectrolyte (CHI) on the buildup process and observe a faster growth for low MW chitosan. The influence of the salt concentration during buildup is also investigated. Whereas the CHI/HA films grow rapidly at high salt concentration (0.15 M NaCl) with the formation of a uniform film after only a few deposition steps, it is very difficult to build the film at 10(-4) M NaCl. In this latter case, the deposited mass increases linearly with the number of deposition steps and the first deposition stage, where the surface is covered by islets, lasts at least up to 50 bilayer deposition steps. However, even at these low salt concentrations and in the islet configuration, CHI chains seem to diffuse in and out of the CHI/HA complexes. The linear mass increase of the film with the number of deposition steps despite the CHI diffusion is explained by a partial redissolution of the CHI/HA complexes forming the film during different steps of the buildup process. Finally, the uniform films built at high salt concentrations were also found to be chondrocyte resistant and, more interestingly, bacterial resistant. Therefore, the (CHI/HA) films may be used as an antimicrobial coating.

Poly(L-lysine)/hyaluronan (PLL/HA) films were chemically cross-linked with a water soluble carbodiimide (EDC) in combination with a N-hydroxysulfo-succinimide (NHS) to induce amide formation. Fourier transform infrared spectroscopy confirms the conversion of carboxylate and ammonium groups into amide bonds. Quartz crystal microbalance-dissipation reveals that the cross linking reaction is accompanied by a change in the viscoelastic properties of the films leading to more rigid films. After the cross-linking reaction, both positively and negatively ending films exhibit a negative zeta potential. It is shown by fluorescence recovery after photobleaching measured by confocal laser scanning microscopy that cross-linking dramatically reduces the diffusion of the PLL chains in the network. Cross linking also renders the films highly resistant to hyaluronidase, an enzyme that naturally degrades hyaluronan. Finally, the adhesion of chondrosarcoma cells on the films terminating either with PLL or HA is also investigated. Whereas the non cross-linked films are highly resistant to cell adhesion, the cells adhere and spread well on the cross-linked films.

Two types of polyelectrolyte multilayer films have been reported in the literature. These are (i) films whose mass and thickness increase linearly as the number of deposited bilayers increases and (ii) films that grow exponentially. We present a model for the buildup of exponentially growing films that allows a discussion of the behavior of them in a unified manner. This model is based on the diffusion both in and out the whole film of part of the chains of at least one of the polyelectrolytes constituting the multilayer. In short, the film is brought into contact with the solution of polyelectrolytes that are able to diffuse into the film. Inside of the film, chains of this polyelectrolyte constitute the “free” chains. At the subsequent rinsing step, some of them diffuse outward from the film. The remaining chains leave the film as it is brought into contact further with the polyelectrolyte solution of opposite charge. As the “free” chains reach the film/solution interface, they are complexed by the polyelectrolytes of opposite charge. These complexes, which are composed of both types of polyelectrolytes, contribute to the formation of the additional mass of the multilayer. The model relies on the evaluation of the electrostatic potential in the film within the framework of the Debye−Hückel approximation and takes into consideration the Donnan effect, which is due to noncompensated fixed charges in the film. It also includes the situation where none of the polyelectrolytes diffuse within the multilayer, in which case the film grows linearly. The model predicts the existence of a free-energy barrier that prevents total diffusion of any “free” polyelectrolyte outward from the film during a rinsing step, following contact with a polyelectrolyte solution. It also predicts that usually only one of the two polyelectrolytes that comprise the film diffuses readily into it. Both polyelectrolytes that comprise the film can diffuse “into” and “out of” the multilayer only when the concentration of noncompensated fixed charges within the film is very small. Several predictions of the model are discussed in the light of experimental results that have already been published or are new.

There exist two types of polyelectrolyte multilayers: those whose thickness increases linearly with the number of deposition steps, which are nicely structured, and those whose thickness increases exponentially, which resembles hydrogels. This simple picture has recently slightly evolved with the finding that some exponentially growing films enter into a linear growth phase after a certain number of deposition steps. In this study, we investigate the buildup process of hyaluronic acid/poly(L-lysine) (HA/PLL) multilayers that constitute one of the best known exponentially growing systems. The films are built by using two deposition methods: the well-known dipping method and the more recent spraying method where the polyelectrolyte solutions are sprayed alternately onto a vertical substrate. The goal of this study is twofold. First, we investigate the influence of the main parameters (i.e., spraying rate and spraying time) of the spraying method on the film growth process. We find that, as for the dipping method, the film thickness first evolves exponentially with the number of deposition steps, and after a given number of deposition steps, it follows a linear evolution. We find that similar behavior is observed with the dipping method. Second, because the spraying method allows the very fine variation of the different parameters of the buildup, we use this method to investigate the exponential-to-linear transition. We find that this transition always takes place after about 12 deposition steps whatever the values of the parameters controlling the deposition process. We discuss our results in light of a model proposed by Hübsch et al. (Hübsch, E.; Ball, V.; Senger, B.; Decher, G.; Voegel, J. C.; Schaaf, P. Langmuir 2004, 20, 1980-1985) and later by Salomäki et al. (Salomäki, M.; Vinokurov, I. A.; Kankare, J. Langmuir 2005, 21, 11232-11240) in which it is assumed that the exponential-to-linear transition is due to a film restructuring that progressively forbids the diffusion of one of the polyelectrolytes constituting the film over part of the film. This "forbidden" zone then grows with the number of deposition steps so that the outer zone of the film that is still concerned with diffusion keeps a constant thickness and moves upward as the total film thickness increases.

In this communication, anti-streptavidin M13 viruses were used to self-assemble various nanosized materials. We believe the anti-streptavidin M13 viruses provide a convenient method to organize a variety of nanosized materials into self-assembled ordered structures. Because the modification of the DNA insert allows controlled modification of the virus length, the spacing in the smectic layer can be genetically controlled.[12] By conjugating other nanosized materials (magnetic nanoparticles, II±VI semiconductor nanoparticles, functional chemicals, etc.) with streptavidin, we believe that this anti-streptavidin method can be used to align various nanosized materials at the desired length scale, which is defined by the smectic layers. ExperimentalThe anti-streptavidin virus was selected by a phage display method using a M13 bacteriophage library (New England Biolab). The virus was amplified in a large volume (400 mL scale, 7 10 7 pfu/lL). The virus suspension was precipitated into a pellet. 20 mg of the virus pellet was suspended with 1.0 mL of 10 nm gold nanoparticles (Abs: 2.5 at 520 nm), conjugated with a streptavidin colloidal suspension (Sigma Co.), and agitated using a rocker for 1 day. The viruses conjugated with gold nanoparticles (Au±virus) were centrifuged after adding 167 lL of poly(ethylene glycol) solution. The red colored pellet was suspended using~20 lL of Tris-buffered saline solution (pH 7.5) to form a Au± virus liquid-crystalline suspension (virus concentration: 83.2 mg mL ±1 ). In order to fabricate the Au±virus film, the Au±virus suspension was diluted tõ 6 mg mL ±1 (400 lL) and kept dry in a dessicator for two weeks. Fluorescein-Virus Cast Film Fabrication: 20 lL of virus suspension (1.9 10 ±7 M in Tris±HCl saline buffered solution (pH 7.5)) was mixed with 20 lL of 0.01 mg mL ±1 (1.9 10 ±7 M, MW: 53 200) fluorescent-streptavidin suspension. 1 lL of suspension was cast and dried on the glass substrate. The molarity of virus suspension was measured using a UV-vis spectrophotometer (extinction coefficient: 1.2 10 8 M ±1 cm ±1 at 268 nm) [13]. Phycoerythrin-Virus and Cast Film Fabrication: 20 lL of the virus suspension (~6 mg mL ±1 , 1.9 10 ±7 M, MW: 292 800 Tris±HCl saline buffered solution (pH 7.5)) was mixed with 20 lL of 0.05 mg mL ±1 (1.7 10 ±7 M in Tris±HCl saline-buffered solution (pH 7.5) with 5 % sucrose) of R-phycoerythrin-streptavidin. 1 lL of suspension was cast and dried on the glass substrate.Microscopy: POM images were obtained using an Olympus polarized optical microscope. Images were taken using a SPOT Digital camera (Diagnostic Inc.). Scanning laser microscopy images was obtained using a Leica TCS 4D and SEM images were obtained using LEO1530, operating at an accelerating voltage of 1 kV. TEM images were obtained using a Philips 208 at an accelerating voltage of 80 kV and a JEOL 2010F at 200 kV. The AFM images (Digital Instruments) were taken in air using tapping mode. The AFM probes were etched silicon with 125 lm cantilevers and spring constants of 20±100 N m ±1 driven near their...

The basic premise of gene therapy is that genes can be used to produce in situ therapeutic proteins. The controlled delivery of DNA complexes from biomaterials offers the potential to enhance gene transfer by maintaining an elevated concentration of DNA within the cellular microenvironment. Immobilization of the DNA to the substrate to which cells adhere maintains the DNA in the cell microenvironment for subsequent cellular internalization. Here, layer-by-layer (LBL) films made from poly(L-glutamic acid) (PLGA) and poly(L-lysine) (PLL) containing DNA were built in the presence of charged cyclodextrins. The biological activities of these polyelectrolyte films were tested by means of induced production of a specific protein in the nucleus or in the cytoplasm by cells in contact with the films. This type of coating offers the possibility for either simultaneous or sequential interfacial delivery of different DNA molecules aimed at cell transfection. These results open the route to numerous potential applications in patch vaccination, for example.gene delivery ͉ layer-by-layer films ͉ transfection T he basic premise of somatic gene therapy is that genes can be used to cause in vivo production of therapeutic proteins. Controlled and efficient gene delivery has implications in many fields ranging from basic science to clinical medicine. Current strategies to enhance gene delivery involve the complexation of DNA with cationic polymers or lipids delivery. Cationic polymers or lipids can self-assemble with DNA to form particles that are capable of being endocytosed by cells (1). These complexes reduce effective size and cellular degradation of DNA (2) and are often delivered as a bolus, added to culture wells in vitro. Bolus delivery of these complexes can be hindered by mass transport limitations or deactivation processes, such as degradation or aggregation. For example, in vitro studies have estimated that bolus addition of complexes to the culture media results in internalization of only 20% of the DNA added (3). These limitations motivated the development of alternative delivery strategies.The controlled delivery of DNA complexes from biomaterials offers the potential to enhance gene transfer by maintaining an elevated concentration of DNA within the cellular microenvironment (4). DNA delivery systems from biomaterials are designed to maintain elevated concentrations locally by supplying DNA to balance the loss by degradation. The continued presence of the DNA during cell division seems to facilitate entry into the nucleus (5). In recent years, considerable effort has been devoted to the design and the controlled fabrication of structured materials with functional properties (6). The layer-by-layer (LBL) buildup of polyelectrolyte films from oppositely charged polyelectrolytes (7) offers opportunities for the preparation of functionalized biomaterial coatings. This technique allows the preparation of supramolecular nano-architectures (8-13) exhibiting specific properties in terms of control of cell activation (8-11) ...

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