Nucleobases modified azo-polysiloxanes, materials with potential application in biomolecules nanomanipulation

Direct observation of athermal photofluidisation in azo-polymer films

The surface relief gratings (SRGs) can be generated when azo-polymer films are exposed to laser beam interference as a result of mass migration. Despite considerable research effort over the past two decades this complex phenomenon remains incompletely understood. Here we show, for the first time, the athermal photofluidisation of azo-polysiloxane films exposed to 488 nm light, directly monitored by optical microscopy. A process of surface relief erasure occurring in parallel with its inscription was also observed during laser irradiation. We therefore propose a new mechanism of SRG formation, based on three different processes: (1) the polymer photo-fluidization in illuminated regions, (2) the mass displacement from illuminated to dark regions and (3) the inverse mass displacement, from dark to illuminated regions. The mechanical properties of the films during UV light irradiation were investigated by classical rheology and, for the first time, by using amplitude modulation-frequency modulation atomic force microscopy (AM-FM AFM).

Study of the nanostructuration capacity of some azopolymers with rigid or flexible chains

Azobenzene polymers have been the subject of intensive research due to their unique and unexpected properties that allow various applications triggered by light. One of their attractive features is the possibility of changing the orientation of azobenzene chain through trans-cis-trans photoisomerization cycles to photoinduce birefringerence and linear dichroism in thin polymer films. The photochromic behavior and surface structuring capacity of rigid or flexible polymers having side azobenzene units have been investigated. The polyimides with side azobenzene units have rigid structure, while polysiloxane chains modified with azobenzene groups and nucleobases are considered materials with flexible structure. During the photochromic studies of the investigated polymers, a mechanism concerning the possibility to generate a fluid phase under UV/VIS irradiation was proposed. The photoisomerisation kinetic by UV-Vis irradiation in the solid state compared with the solution and the cis-trans azobenzene relaxation phenomena were presented. The surface structuring capacity of these polymers was studied using a Nd:YAG laser at 355 nm, at different incident fluencies and pulse numbers.

Azo-polysiloxanes thermal stability study

This paper presents a thermogravimetric study of azo-polysiloxanic materials that may be used as supports for cells culture. This type of polymer may generate nanostructured surfaces when subjected to laser irradiation, yielding a cell response that depends on surface relief. Modification of cell growth supports using nanostructured synthetic materials improves general understanding of the complex mechanisms that control cell adhesion and migration in normal conditions, as well as in various pathologies. These polymers require good thermal stability, since they need to be able to withstand both the interaction with the laser source, as well as various sterilization processes, without noticeable alteration in structure and properties. Thermal stability analysis confirms that the azo-polysiloxanic materials under study here may be used up to 300 °C in dynamic temperature conditions and also for a period of 40 minutes in isothermal conditions at 180 °C.

Well-defined DNA-mimic brush polymers bearing adenine moieties: synthesis, layer-by-layer self-assembly, and biocompatibility

Two new DNA-mimicking brush polymers were synthesized: poly[oxy(11-(3-(9-adeninyl)propionato)-undecanyl-1-thiomethyl)ethylene] (PECH-AP) and poly[oxy(11-(5-(9-adenylethyloxy)-4-oxopentanoato)undecanyl-1-thiomethyl)ethylene] (PECH-AS). These polymers were found to be thermally stable up to 220 °C and could be applied easily by conventional coating processes to produce good quality films. Interestingly, both brush polymers formed molecular multibilayer structures to provide an adenine-rich surface. Despite the structural similarities, PECH-AS surprisingly exhibited higher hydrophilicity and better water sorption properties than PECH-AP. These differences were attributed to the chemical structures in the bristles of the polymers. The adenine-rich surfaces of the polymer films demonstrated selective protein adsorption, suppressed bacterial adherence, facilitated HEp-2 cell adhesion, and exhibited good biocompatibility in mice. However, the high hydrophilicity and good water sorption characteristics of the PECH-AS film suggest that this brush polymer is better suited to applications requiring good biocompatibility and reduced chance of bacterial infection compared with the PECH-AP film.

Azopolysiloxanes Modified with Nucleobases: 1. Thermal Characterization of some Nanostructurable Materials with Potential Application in Biology

New azopolysiloxanes modified with nucleobases with potential application in biology were synthesized and their thermal stability was evaluated. These types of materials can present two possible applications: obtaining of films with nanostructured surface that may be used in cell directional development control and in biomolecular binding and nanohandling. Both applications involve, however, material interaction with laser beams, which require a series of precautions with regard to polymer thermal stability. We considered it essential to perform very thorough thermal stability studies that would provide accurate information concerning the lowest temperature at which thermal degradation occurred. Some correlations between structure—thermal stability were derived.