Browsing by Author "Erkal, Turan S."

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Open Access
Amyloid inspired self-assembled peptide nanofibers
(American Chemical Society, 2012) Çınar, Göksu; Ceylan, Hakan; Urel, Mustafa; Erkal, Turan S.; Tekin, E. Deniz; Tekinay, Ayse B.; Dâna, Aykutlu; Güler, Mustafa O.
Amyloid peptides are important components in many degenerative diseases as well as in maintaining cellular metabolism. Their unique stable structure provides new insights in developing new materials. Designing bioinspired self-assembling peptides is essential to generate new forms of hierarchical nanostructures. Here we present oppositely charged amyloid inspired peptides (AIPs), which rapidly self-assemble into nanofibers at pH 7 upon mixing in water caused by noncovalent interactions. Mechanical properties of the gels formed by self-assembled AIP nanofibers were analyzed with oscillatory rheology. AIP gels exhibited strong mechanical characteristics superior to gels formed by self-assembly of previously reported synthetic short peptides. Rheological studies of gels composed of oppositely charged mixed AIP molecules (AIP-1 + 2) revealed superior mechanical stability compared to individual peptide networks (AIP-1 and AIP-2) formed by neutralization of net charges through pH change. Adhesion and elasticity properties of AIP mixed nanofibers and charge neutralized AIP-1, AIP-2 nanofibers were analyzed by high resolution force-distance mapping using atomic force microscopy (AFM). Nanomechanical characterization of self-assembled AIP-1 + 2, AIP-1, and AIP-2 nanofibers also confirmed macroscopic rheology results, and mechanical stability of AIP mixed nanofibers was higher compared to individual AIP-1 and AIP-2 nanofibers self-assembled at acidic and basic pH, respectively. Experimental results were supported with molecular dynamics simulations by considering potential noncovalent interactions between the amino acid residues and possible aggregate forms. In addition, HUVEC cells were cultured on AIP mixed nanofibers at pH 7 and biocompatibility and collagen mimetic scaffold properties of the nanofibrous system were observed. Encapsulation of a zwitterionic dye (rhodamine B) within AIP nanofiber network was accomplished at physiological conditions to demonstrate that this network can be utilized for inclusion of soluble factors as a scaffold for cell culture studies. © 2012 American Chemical Society.
Open Access
Bioactive self-assembled peptide nanofibers for corneal stroma regeneration
(Elsevier, 2014) Uzunallı, Gözde; Soran, Zeliha Soran; Erkal, Turan S.; Dagdas, Yavuz S; Dinc, E.; Hondur, A. M.; Bilgihan, K.; Aydin B.; Güler, Mustafa O.; Tekinay, Ayşe B.
Defects in the corneal stroma caused by trauma or diseases such as macular corneal dystrophy and keratoconus can be detrimental for vision. Development of therapeutic methods to enhance corneal regeneration is essential for treatment of these defects. This paper describes a bioactive peptide nanofiber scaffold system for corneal tissue regeneration. These nanofibers are formed by self-assembling peptide amphiphile molecules containing laminin and fibronectin inspired sequences. Human corneal keratocyte cells cultured on laminin-mimetic peptide nanofibers retained their characteristic morphology, and their proliferation was enhanced compared with cells cultured on fibronectin-mimetic nanofibers. When these nanofibers were used for damaged rabbit corneas, laminin-mimetic peptide nanofibers increased keratocyte migration and supported stroma regeneration. These results suggest that laminin-mimetic peptide nanofibers provide a promising injectable, synthetic scaffold system for cornea stroma regeneration.
Open Access
Mussel inspired dynamic cross-linking of self-healing peptide nanofiber network
(Wiley, 2013) Ceylan, Hakan; Urel, Mustafa; Erkal, Turan S.; Tekinay, Ayse B.; Dana, Aykutlu; Güler, Mustafa O.
A general drawback of supramolecular peptide networks is their weak mechanical properties. In order to overcome a similar challenge, mussels have adapted to a pH-dependent iron complexation strategy for adhesion and curing. This strategy also provides successful stiffening and self-healing properties. The present study is inspired by the mussel curing strategy to establish iron cross-link points in self-assembled peptide networks. The impact of peptide-iron complexation on the morphology and secondary structure of the supramolecular nanofibers is characterized by scanning electron microscopy, circular dichroism and Fourier transform infrared spectroscopy. Mechanical properties of the cross-linked network are probed by small angle oscillatory rheology and nanoindentation by atomic force microscopy. It is shown that iron complexation has no influence on self-assembly and β-sheet-driven elongation of the nanofibers. On the other hand, the organic-inorganic hybrid network of iron cross-linked nanofibers demonstrates strong mechanical properties comparable to that of covalently cross-linked network. Strikingly, iron cross-linking does not inhibit intrinsic reversibility of supramolecular peptide polymers into disassembled building blocks and the self-healing ability upon high shear load. The strategy described here could be extended to improve mechanical properties of a wide range of supramolecular polymer networks. A simple and versatile method for improving mechanical performance of supramolecular polymers is described. Inspired by a mussel curing mechanism, reversible iron cross-linking into a self-assembled peptide network significantly enhances the mechanical properties while having no impact on the β-sheet-driven self-assembly. The network retains its pH-dependent reversibility and self-healing properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Size-controlled conformal nanofabrication of biotemplated three-dimensional TiO2 and ZnO nanonetworks
(Nature, 2013) Ceylan, Hakan; Ozgit-Akgun, Çağla; Erkal, Turan S.; Donmez, İnci; Garifullin, Ruslan; Tekinay, Ayse B.; Usta H.; Biyikli, Necmi; Güler, Mustafa O.
A solvent-free fabrication of TiO2 and ZnO nanonetworks is demonstrated by using supramolecular nanotemplates with high coating conformity, uniformity, and atomic scale size control. Deposition of TiO2 and ZnO on three-dimensional nanofibrous network template is accomplished. Ultrafine control over nanotube diameter allows robust and systematic evaluation of the electrochemical properties of TiO2 and ZnO nanonetworks in terms of size-function relationship. We observe hypsochromic shift in UV absorbance maxima correlated with decrease in wall thickness of the nanotubes. Photocatalytic activities of anatase TiO2 and hexagonal wurtzite ZnO nanonetworks are found to be dependent on both the wall thickness and total surface area per unit of mass. Wall thickness has effect on photoexcitation properties of both TiO2 and ZnO due to band gap energies and total surface area per unit of mass. The present work is a successful example that concentrates on nanofabrication of intact three-dimensional semiconductor nanonetworks with controlled band gap energies.
Open Access
Slow release and delivery of antisense oligonucleotide drug by self-assembled peptide amphiphile nanofibers
(American Chemical Society, 2011) Bulut, Selma; Erkal, Turan S.; Toksoz, Sıla; Tekinay, Ayse B.; Tekinay, Turgay; Güler, Mustafa O.
Antisense oligonucleotides provide a promising therapeutic approach for several disorders including cancer. Chemical stability, controlled release, and intracellular delivery are crucial factors determining their efficacy. Gels composed of nanofibrous peptide network have been previously suggested as carriers for controlled delivery of drugs to improve stability and to provide controlled release, but have not been used for oligonucleotide delivery. In this work, a self-assembled peptide nanofibrous system is formed by mixing a cationic peptide amphiphile (PA) with Bcl-2 antisense oligodeoxynucleotide (ODN), G3139, through electrostatic interactions. The self-assembly of PA-ODN gel was characterized by circular dichroism, rheology, atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM images revealed establishment of the nanofibrous PA-ODN network. Due to the electrostatic interactions between PA and ODN, ODN release can be controlled by changing PA and ODN concentrations in the PA-ODN gel. Cellular delivery of the ODN by PA-ODN nanofiber complex was observed by using fluorescently labeled ODN molecule. Cells incubated with PA-ODN complex had enhanced cellular uptake compared to cells incubated with naked ODN. Furthermore, Bcl-2 mRNA amounts were lower in MCF-7 human breast cancer cells in the presence of PA-ODN complex compared to naked ODN and mismatch ODN evidenced by quantitative RT-PCR studies. These results suggest that PA molecules can control ODN release, enhance cellular uptake and present a novel efficient approach for gene therapy studies and oligonucleotide based drug delivery. © 2011 American Chemical Society.