Photonic crystals in biology - NanoTR-VI

T PeptideTPP,PP,PP andTT2429TTTTTT TTPoster Session, Thursday, June 17Theme F686 - N1123TNano and Micro Mechanical Study of Self-Assembled Peptide Amphiphile Nanofibers1111Yavuz Selim DadaPPAye Begüm TekinayPPAykutlu DanaPUMustafa Özgür GülerUP P*1PUNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800, TurkeyAbstract-Peptide amphiphile nanostructures have been used for various tissue engineering applications. Peptide amphiphile molecules selfassembleinto nanofibers due to hydrogen bonding, hydrophobic interactions and electrostatic interactions. Three-dimensional network of thesenanostructures form hydrogels that are used to culture cells for tissue engineering applications. In this study, we investigate the relationshipbetween nanostructure and hydrogel mechanical properties. A direct relation between gel stiffness and -sheet forming tendency has beenobserved and it led us to measure the stiffness of individual nanofibers by AFM. Our results indicate that nano and micro mechanical propertiescan differ through self-assembly mechanism. This result is important in terms of characterization of peptide amphiphile materials and theirapplications in tissue engineering studies.amphiphiles are a group of molecules that containboth hydrophobic alkyl tail and bioactive peptide sequencewhich enables these molecules to form differentnanostructures when they come together. The amphiphiliccharacter of these molecules enables these molecules toassemble nanofibers and hydrophilic bioactive peptidesequences are presented on the periphery of the nanostructures[1]. These molecules can be easily programmed to selfassemble into nanofibers by changing pH, and electrolyteaddition [2,3]. These nanofibers assemble to form 3-Dnetworks that can mimic extracellular matrix. Structure andbioactivity of the nanostructures make these materialspromising for tissue engineering applications. Extracellularmatrix (ECM) differs in terms of structural features andbioactivity in each tissue. The rigidity of the ECM has beenshown to affect cell behavior; the cell motility [4], growth [5]and focal adhesion [6]. In addition, it has been shown that themechanical properties of the ECM environment affect stemcell differentiation [7]. In a recent study, it has been shownthat stiffness of these gels differs with regard to self assemblymechanism (pH and salt concentration) [8].the pH and the electrolyte addition on self-assemblymechanism was studied. It has been observed that thesemolecules form gel at low pH and with addition of CaClR2 Ratneutral pH. We studied the effect of the differences in pH andelectrolyte assembly with circular dichroism, FT-IR andrheology.We performed SEM in order to observe the nanofibernetwork. The stiffness of the hydrogels was measured by2+rheology and it has been observed that CaPPgels are stifferthan low pH gels. We also studied the secondary structureformation which is the main mechanism of self-assemblythrough these formulations by using circular dichroism andFT-IR. We observed elevated levels of -sheet structure incalcium formulations than the low pH formulation.We are currently measuring stiffness of individualnanofibers by AFM. The mechanical properties of thenanofibers formed are compared through differentformulations. The stiffness of the gels and individual fiberswill be studied to understand the relationship between them.*Corresponding author: HTmoguler@unam.bilkent.edu.trT[1] TM. O. Guler et al., TTBiomacromoleculesTT TT2006T,T TT7T, 1855-1863.T[2]T J. D. Hartgerink et al., Proc. Natl. Acad. Sci. U.S.A. 2002, 99,(8), 5133-5138.T[3]T J. C. Stendahl et al., Adv. Funct. Mater. 2006, 16, (4), 499-508.[4] TR. J. Pelham et al., MolTT. Biol. CellTT TT1996TT,TT TT7TT,TT TT2429 TT.[5] P. C. Georges et al., TJ. Appl. Physiol.TT TT2005T,T TT98T,(T4T),T TT1547TT TT1553T.[6] R. J Pelham et al., TProc. Natl. Acad. Sci. U.S.A. 1997T,T TT94T,(T25T),T TT13661TT TT13665T.[7] A. J. Engler et al., TCell TT2006T,T TT126T, (T4T),T TT677TT TT689T.[8] M. A. Greenfield et al.,T TTLangmuirTT TT26(5)T, (2010) 3641-3647.TFigure 1. Hydrogels formed by the 3-D network of peptideamphiphile nanofibers.In this study, we analyzed nano and micro mechanicalproperties of peptide amphiphile materials since cell-matrixinteraction occurs through individual nanofibers and comparedthese mechanical properties with the stiffness of hydrogel.There is a direct relation between nanofiber stiffness and gelstiffness. TWe first synthesized a negatively charged peptideamphiphile molecule at physiologic conditions containingbioactive amino acid sequence; arginine-glycine-aspartic acid“RGD”. The synthesis and purity of the molecule is verifiedby liquid chromatography-mass spectrometry. The effect of6th Nanoscience and Nanotechnology Conference, zmir, 2010 670