Investigation of viscoelastic properties of peptide gels with passive mşkrorheology method

Among all organic structures, peptides have an importance due to their biocompatibility, chemical diversity, similarity to proteins and self-assembly characteristics. Peptide amphiphile, which consist of peptide-based molecules are used in a variety of fields such as pharmaceutical industry, tissue engineering, imaging devices and energy storage. Therefore knowing the mechanical properties of the nanofiber structures plays an important role in investigating the feasibility of their use in various fields. The typical rheometer which is used to examine the structural characteristics of the materials, measures the response of the material by applying an external force on it and displays an average value of the response. The lack of local measurement and a minimum volume requirement of 5-10 ml to perform the measurement makes it difficult to examine the systems that are inhomogeneous and difficult to synthesise. Moreover, the fragile nanofiber structure formed by the spontaneous configuration of the peptide amphiphile molecules is damaged by the presence of an external force. In this study, the characteristic features of the nanofiber structure formed by the combination of two different peptide amphiphiles which are synthesised in a controlled manner in Bilkent UNAM were analyzed with using passive microrheology method. In passive microrheology method, a sample volume of 5-10 microliter is sufficient for the measurement. The external force required for the measurement is provided by Brownian motion, which is originated from the colloid particles added to the material, and it did not cause any damage to the reticular structure in the course of the measurement. In addition, contrary to the conventional methods, this technique enables to determine the characteristic features of inhomogeneous materials by making it possible to perform local measurements. In this method, Brownian motion of the colloid particles in the peptide gel which have different surface chemistries (amine and carboxil group) and different radius (0,5-1 micrometer) is imaged by a fluorescence microscope, and the images were recorded. By using the image analyzing software IDL (Interactive Data Language), the viscoelastic properties of the peptide gels were determined and their structures that have local heterogeneities were investigated. The effects of differences in surface chemistry and radius of the colloid particles embedded in the same gel structure are investigated.