Polyelectrolyte Multilayers: A Versatile Tool for Preparing Antimicrobial Coatings.

The prevention of pathogen colonization of medical implants represents a major medical and financial issue. The development of antimicrobial coatings aimed at protecting against such infections has thus become a major field of scientific and technological research. Three main strategies are developed to design such coatings: (i) the prevention of microorganisms adhesion and the killing of microorganisms (ii) by contact and (iii) by the release of active compounds in the vicinity of the implant. Polyelectrolyte multilayer (PEM) technology alone covers the entire widespread spectrum of functionalization possibilities. PEMs are obtained through the alternating deposition of polyanions and polycations on a substrate, and the great advantages of PEMs are that (i) they can be applied to almost any type of substrate whatever its shape and composition; (ii) various chemical, physicochemical, and mechanical properties of the coatings can be obtained; and (iii) active compounds can be embedded and released in a controlled manner. In this article we will give an overview of the field of PEMs applied to the design of antimicrobial coatings, illustrating the large versatility of the PEM technology.

Influence of the interaction strength between supramolecular complexes on the topography of neutral polymer multilayer films.

Step-by-step polymer film buildup processes lead to polymer coatings, e.g., polyelectrolyte multilayers, of various structures ranging from continuous smooth films to droplet like discontinuous coatings. Yet, the origin of these different behaviors depending upon the system is not yet known. This study is a first attempt to rationalize the evolution of the coating structure as a function of the strength of the interactions between the polymers constituting the film. We investigated the influence of the strength of noncovalent host-guest interactions between cyclodextrin (CD) and pyrene (Py), ferrocene (Fc) or adamantane (Ad) on the structure of neutral poly(N-hydroxypropylmethacrylamide) (PHPMA) multilayers films formed in a step-by-step manner. In solution, the strength of the inclusion complex (measured by log K where K is the complex association constant) is increasing in the order Py/ß-CD < Fc/ß-CD < Ad/ß-CD and can be further varied in the presence of different sodium salts at different ionic strengths. Depending upon this strength, the buildup process is limited to the formation of isolated aggregates for PHPMA-CD/PHPMA-Py, leading to smooth continuous films for PHPMA-CD/PHPMA-Fc and to droplet-like films, not entirely covering the substrate, for PHPMA-CD/PHPMA-Ad. To study the influence of the strength of the host-guest interactions on the film topography, PHPMA-CD/PHPMA-Fc films were built in the presence of different sodium salts at different ionic strengths. For low host-guest interactions, only isolated aggregates are formed on the substrate. As the strength of the host-guest interactions increases (increase of log K), the formed films go through a droplet-like structure, before becoming continuous but rough for stronger interactions. When the interaction strength is further increased, the roughness of the films decreases, leading to a smooth continuous film before becoming rough again at still higher interaction strength. Smooth continuous multilayers seem thus to be obtained for an optimal range of the interaction strength.