Layer-by-layer films from hyaluronan and amine-modified hyaluronan

Hyaluronan is a polysaccharide that is increasingly investigated for its role in cellular adhesion and for the preparation of biomimetic matrices for tissue engineering. Hyaluronan gels are prepared for application as space fillers, whereas hyaluronan films are usually obtained by adsorbing or grafting a single hyaluronan layer onto a biomaterial surface. Here, we examine the possibility to employ the layer-by-layer technique to deposit thin films of cationic-modified hyaluronan (HA+) and hyaluronan (HA) of controlled thicknesses. The buildup conditions are investigated, and growth is compared to that of other polyelectrolyte multilayer films containing either HA as the polyanion or HA+ as the polycation. The films could be formed in a low ionic strength medium but are required to be cross-linked prior to contact with a physiological medium. NIH3T3 fibroblasts were perfectly viable on self-assembled hyaluronan films with, however, a preference for hyaluronan ending films. These findings point out the possibility to tune the thickness of thin hyaluronan films at the nanometer scale. Such architectures could be employed for investigating cell/substrate interactions or for functionalizing biomaterial surfaces.     

Nanocomposite silica/polyamine films prepared by a reactive layer-by-layer deposition

Composite material nanofilms of controlled thickness constituted by ceramics and polymers find more and more applications to improve the properties and functionalities of material surfaces. In this paper we present a new way to deposit such composite coatings by alternated contacts of a surface with a polyamine solution (either poly(allylamine), poly(ethyleneimine), poly-l-lysine, or poly(diallydimethylammonium)chloride and silicic acid. The experiments are mainly realized by spraying of solutions onto the surface. The polyamines deposited in the first spraying step catalyze silica formation upon further spraying of a silicic acid-containing solution. The film thickness increases linearly with the number of deposition steps, the thickness increment being of the order of a few nanometers per silicic acid/polyamine layer. Infrared spectroscopy in the total attenuated reflection mode reveals spectra that are close to those of pure silica particles. The film morphology is further investigated by means of atomic force microscopy and environmental scanning electron microscopy. This reactive layer-by-layer deposition constitutes a new way to build, in an easy way, nanocomposite coatings with precise control of their thickness.     

Anomalous thickness evolution of multilayer films made from poly-L-lysine and mixtures of hyaluronic acid and polystyrene sulfonate

Using a mixture of polyanions or polycations offers a new way to control the properties of polyelectrolyte multilayer (PEM) films. The central issue of PEM films made from blended polyelectrolyte solutions is the relation between the properties of the blended architecture and the properties of the films made from each pure component. Two situations are possible: either (i) the properties of the blended films are intermediate between those corresponding to the single components or (ii) new effects may emerge leading, for instance, to improved mechanical properties. Situation (i) is expected when the chemical natures of both polyelectrolytes from the blended mixture are close, whereas situation (ii) is more probable when the polyelectrolytes from the blend are very different. In this study, we focus on the buildup of PEM films made by the alternate spray deposition of a polyanion blend [a mixture of polystyrene-4-sulfonate (PSS) and hyaluronic acid (HA) in different mass fractions] and a polycation solution of poly-L-lysine (PLL). Whereas (HA-PLL) films exhibit a strong exponential growth with the number of deposition steps, the (PSS-PLL) system is only weakly exponential. We find that when the composition of the polyanion blend ranges from pure (HA-PLL) to pure (PSS-PLL), the films can always be constructed. However, the polyanion composition of the films is far from that of the polyanion solutions used for the buildup. One observes a strong preference for the incorporation of PSS over HA into the films. Moreover, the most striking feature is that the film thickness does not evolve monotonously with the polyanion solution composition but passes through a sharp minimum for a polyanion solution containing 90-95% HA. A possible mechanism for this peculiar finding is proposed.     

Bioactive Seed Layer for Surface‐Confined Self‐Assembly of Peptides

The design and control of molecular systems that self‐assemble spontaneously and exclusively at or near an interface represents a real scientific challenge. We present here a new concept, an active seed layer that allows to overcome this challenge. It is based on enzyme‐assisted self‐assembly. An enzyme, alkaline phosphatase, which transforms an original peptide, Fmoc‐FFY(PO₄^2?), into an efficient gelation agent by dephosphorylation, is embedded in a polyelectrolyte multilayer and constitutes the “reaction motor”. A seed layer composed of a polyelectrolyte covalently modified by anchoring hydrogelator peptides constitutes the top of the multilayer. This layer is the nucleation site for the Fmoc‐FFY peptide self‐assembly. When such a film is brought in contact with a Fmoc‐FFY(PO₄^2?) solution, a nanofiber network starts to form almost instantaneously which extents up to several micrometers into the solution after several hours. We demonstrate that the active seed layer allows convenient control over the self‐assembly kinetics and the geometric features of the fiber network simply by changing its peptide density.     

Structure and anisotropy of epitaxial fcc FePt films

Pulsed laser deposition (PLD) was used to deposit FePt films onto single crystalline MgO substrates. When deposited at room temperature, films grow epitaxial within the A1 phase. Structure and magnetic properties were examined by X-ray diffraction, Rutherford Backscattering Spectrometry (RBS), magneto-optic Kerr effect, Mössbauer spectroscopy, and Magnetic Orientation Mössbauer Spectroscopy (MOMS). These measurements allow to exclude local ordering and reveal the anisotropic intrinsic and extrinsic magnetic properties. These results are discussed with respect to the texture and microstructure of these films.     

Depth analysis by combination of conversion electron,conversion X-ray and γ-ray Mössbauer spectroscopy

Conversion electrons, conversion X-rays and transmitted γ-rays were used to determine magnetic structures. The penetration depths of these radiations allow the material to be scanned.     

Measurement of the parameter η̄ in the radiative decay of the muon as a test of the v-a structure of the weak interaction

The parameter η&#x0304; of muon decay has been measured in the radiative decay $\text{μ}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{ν}{}_{\mathrm{<mtext>e</mtext>}}\text{ν}\text{?}{}_{\mathrm{\mu }}\text{γ}$ of unpolarized positive muons. The result $\text{η}\text{?}\text{?0.083}$ (68% confidence) or $\text{η}\text{?}\text{= ?0.03±0.10}$ with ρ fixed at $\text{3}\text{4}$ yields an improvement of the previous value by more than a factor of two. An analysis of all data on muon decay that are presently available slightly improves the constraints on the weak coupling constants to: g_s?0.29g_v, g_p?0.27g_v, g_T?0.23g_v and 0.92g_v?g_A?1.2g_v