No abstract

We report a direct method to amplify the exponential growth of multilayers significantly by the alternating deposition of polyethylenimine (PEI) at high pH and poly(acrylic acid) (PAA) at low pH. The alternating pH switches the degree of ionization of the polyelectrolytes in the multilayers, which enhances the diffusion of PEI into and out of the film and hence increases the deposited mass per cycle. The synergetic action of the pH-tunable charge density and diffusivity of the weak polyelectrolytes provides a new method for the enhanced growth of multilayers with hierarchal micro- and nanostructured surfaces.

Antibacterial multilayer films containing nanosilver were prepared via layer-by-layer fashion. PET film was aminolyzed with 1,6-hexanediamine to introduce amino groups on PET film surface; chitosan-silver nitrate complex and heparin were alternately deposited onto an aminolyzed PET film surface, and subsequently, the silver ions within the multilayer films were reduced with ascorbic acid to form silver nanoparticles. UV-visible spectroscopy and transmission electron microscopy confirmed the formation of well-dispersed nanosilver particles with sizes (10-40 nm) that depended on the initial concentration of silver ions in chitosan solution and the pH of ascorbic acid solution. The chitosan/heparin multilayer films were possessed of bactericidal effect on Escherichia coli (E. coli), and this antibacterial effect could be significantly enhanced by the incorporation of silver nanoparticles into the multilayer films. The multilayer films containing nanosilver were not only effective as antibacterial but also as anticoagulant coating. And cell toxicity evaluation suggested that the multilayer films containing nanosilver did not show any cytotoxicity. The multilayer films containing nanosilver may have good potentials for surface modification of medical devices, especially for cardiovascular implants.

Superhydrophobic surfaces have received much attention due to their novel aspects of surface physics and important applications ranging from self-cleaning materials to microfluidic devices. Taking their inspiration from the self-cleaning property of lotus leaves [1] and insects, [2] the biomimetic results reveal that the synergistic interaction of the hierarchical micro-and nanostructure can not only improve the surface hydrophobicity but also reduce the sliding angle (SA), which is crucial to the self-cleaning properties of these surfaces.[3] Many efforts, including electrodeposition, polymer-phase separation, sol-gel methods, and others have been carried out to develop hierarchical micro-and nanostructures to obtain superhydrophobic surfaces. [4][5][6] Layer-by-layer self-assembly (LbL), which is based on the alternating physisorption of oppositely charged building blocks, represents a method to immobilize polyelectrolytes, colloid nanoparticles, and biomacromolecules, such as enzymes, extracellular matrices (ECM), DNA, etc. [7][8] The sensitivity of the LbL multilayer towards its environment (pH, ionic strength, etc.) further provides new approaches to adjust the layered nanostructure with a tailored composition and architecture. Recently, the use of the LbL technique for constructing superhydrophobic coatings has been explored. [9][10][11][12] Shiratori and co-workers [9] first constructed multilayered films containing SiO 2 nanoparticles, which were further heated to 650°C to develop an inorganic nanostructure for superhydrophobic behavior. Zhang and co-workers [10] reported the use of polyelectrolyte multilayers as a matrix for electrochemical deposition to adjust the topography of gold and silver clusters, leading to superhydrophobic surfaces. Rubner and co-workers [11] mimicked the superhydrophobic behavior of the lotusleaf structure by creating a microporous polyelectrolyte multilayer surface over-coated with silica nanoparticles. Schlenoff and co-workers [12] created an ultrahydrophobic surface roughening on both the micrometer and nanometer scale using layer-by-layer deposition of clay and fluorinated polyelectrolytes. Most of these methods, however, developed hierarchical micro-and nanostructures by combining the multiple assembly steps and different self-assembling building blocks, such as polyelectrolytes, metals, and nanoparticles. Herein, we report the amplified exponential growth of a multilayer of polyelectrolytes as a facile method to construct hierarchical micro-and nanostructures simultaneously, which can be further transformed into superhydropobic surfaces. The 3-aminopropyltriethoxysilane-coated substrates were alternately immersed in an aqueous solution of poly(acrylic acid) (PAA, 3 mg mL -1

A superhydrophobic/hydrophilic asymmetric free-standing film has been created using layer-bylayer assembly technique. Poly(ethylene-imine)-Ag + complex (PEI-Ag + ) at pH 9.0 was assembled with poly(acrylic acid) (PAA) at pH 3.2 on a Teflon substrate to yield a micro-nanostructured surface that can be turned to be superhydrophobic after being coated with a low surface energy compound. Silver nanoparticle loaded free-standing film with one surface being superhydrophobic while the other surface is hydrophilic was then obtained after detachment from the substrate. The superhydrophobicity enabled the upper surface with anti adhesion and self-cleaning properties and the hydrophilic bottom surface can release silver ions as antibiotic agent. The broad-spectrum antimicrobial capability of silver ions released from the bottom surface coupled with superhydrophobic barrier protection of the upper surface may make the free-standing film a new therapy for open wound.