Study on synthesized azopolymer brushes as novel photoresponsive biomaterials
Creators: name: Kollarigowda, Ravichandran Honnavally
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2015

description: The present work describes the design and synthesis of new azopolymer brushes able to generate SRG patterns. Fluorescence correlation spectroscopy (FCS) technique allowed us to investigate the dynamics of azobenzene-grafted polymer brushes upon photo-induced isomerization process in order to clarify how such a single molecular event can lead to the macroscopic phenomenon of mass-migration and aggregation yielding SRGs. Moreover, Lloyd's mirror method imprinted SRG of 60 nm on these azopolymer brushes. Furthermore, modification of their topography using mild conditions close to physiological environment were tested as well as their biocompatibility in order to confirm them as new light-responsive materials for biological applications in the field of tissue engineering. Smart polymer brushes (SPBs) with azo-chromophores have a photo-responsive nature and act as superior materials that can alter their properties by light. The work reported in this thesis described the design and synthesis of new azopolymer brushes for the formation and erasure of micro-scale surface relief gratings (SRGs). An interesting and promising application of azopolymer is in the fabrication and modification of topographical feature using mild conditions for cell engineering in order to provide useful substrates for controlling cellular orientation and migration. In Chapter 2, we describe the synthesis of all azopolymer brushes via RAFT technique by "grafting from" approach. RAFT polymerization is one of the finest synthetic methodologies to achieve polymers having narrow polydispersity index and high graft density. The thickness of the polymer brushes was controlled by tuning concentration of the RAFT agent immobilized on glass surface as well as polymerization time. Polymer brushes of polymethacrylic acid (pMAb) were firstly prepared and then post modified with a derivative of a well-known azobenzene (Disperse Red 1) on the side chains and a cyanine 5 dye (Cy5) on top of the polymer brush. A comprehensive characterization of each synthesized sample is also presented. In Chapter 3 the influence of the azobenzene molecules on the polymer brush dynamics was investigated for the first time by Fluorescence Correlation Spectroscopy (FCS). For this purpose three type of azopolymer brushes were used. Two dynamics were observed, a short one coming from the fluctuation of azobenzene and a long one related to the main chain of the polymer brush, where Cy5 was linked. Furthermore, dynamics was reversible. Thanks to FCS data, we could propose a mechanism of azobenzene dynamics that led to obtain a pattern of micrometric widths, resembling to SRG. In Chapter 4, we discuss mainly on the synthesis of a new type of azopolymer brushes, based on acrylamide derivative of Disperse red 1 as monomer, by RAFT approach. Using Lloyd's mirror method SRGs were created and the reversibility of the pattern was obtained by sonication using water at room temperature. These azopolymer brushes were conducted and biocompatibility test with NIH-3T3 and HUVEC cells. These primary results foresee the possibility to use these azopolymer brushes as novel cell instructive biomaterials.