Browsing by Subject "Peptide amphiphile"

Now showing 1 - 15 of 15

Open Access
Bioactive glycopeptide nanofibers for tissue regeneration applications
(2016-05) Çalışkan, Özüm Şehnaz.
Natural extracellular matrix (ECM) is rich in glycopeptides and glycosaminoglycans, which function in controlling cellular processes. In this thesis, glycopeptide molecules that mimic natural glycopeptides and glycosaminoglycans were designed and synthesized and it was demonstrated that they induce directed differentiation of mesenchymal stem cells into chondrogenic and adipogenic lineages. In the first part of the study, hyaluronic acid (HA)-mimicking glycopeptide amphiphile molecules were synthesized to induce chondrogenic differentiation of mesenchymal stem cells (MSC). HA is the most abundant glycosaminoglycan (GAG) found in hyaline cartilage ECM. Peptide amphiphiles were synthesized by solid phase peptide synthesis method and used to form self-assembled bioactive glycopeptide nanofibers which mimic fibrous morphology of the ECM. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and circular dichroism (CD) were used for morphology and secondary structure analyses of the obtained nanofibers. It was demonstrated that glycopeptide amphiphiles create fibrous structure formed by nanofibers. Morphological changes, GAG production (Safranin-O staining and DMMB analysis), and chondrogenic gene marker expressions (qRT-PCR) of MSCs cultured on HA-mimetic nanofibers were analyzed. It was shown that HA-mimetic glycopeptide nanofibers induce early differentiation of MSCs into hyaline like chondrocytes. In the second part of the study, it was demonstrated that minor changes on glycopeptide backbone can create specific glycopeptides which induce differentiation of MSCs into brown adipocytes. Brown fat adipocytes do not store chemical energy as fat but dissipates it as heat and so they have emerged as promising anti-obesity agents. Lipid droplet accumulation (Oil Red-O staining) and adipogenic gene marker expression analyses (qRT-PCR) showed that the new glycopeptide nanofiber scaffold is a specific inducer of differentiation of MSCs into brown fat adipocytes.
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
Biotinylated peptide nanofibers for modulating the immune response
(2016-06) Tohumeken, Şehmus
Despite the fact that vaccination eradicates many diseases, a broad variety of disorders cannot be treated using current vaccine development methods. In addition, it is difficult to rapidly develop new vaccines following the sudden onset of a new pandemic, as the production and transport of vaccines to impoverished areas is still a major issue. The lack of sufficient vaccine production, for example, enabled the spread of swine flu in 2009, while HIV, Zika and malaria viruses currently lack effective vaccinations. In addition, while cancer vaccines represent a promising area of research, their clinical implementation is also limited by the absence of rapid and effective vaccine development methods. The development of new and effective vaccines is therefore quite vital. Moreover, recently used vaccines promote either humoral or cellular immune responses, while effective treatment requires the induction of both systems. Consequently, there is an urgent need for effective and easy-to-prepare vaccines that are capable of eliciting immune action through multiple channels. Peptide amphiphiles are small molecules that are able to self-assemble into nanoscale fibrous networks. These nanofibers are biodegradable, biocompatible and do not generate toxic byproducts, making them ideal for designing biomaterials. As such, nanofibers are a promising class of materials for inducing an effective immune response and overcoming some of the problems faced by current vaccine development methods. In this thesis, I detail the use of biotinylated peptide nanofiber systems as immunomodulatory materials that are capable of incorporating a broad variety of antigens in a modular manner. Briefly, biotinylated and non-biotinylated peptide amphiphiles (PA) were first synthesized, purified and characterized to determine their material properties. PAs were then induced to self-assemble in the presence of CpG oligonucleotide (ODN) adjuvants, and ovalbumin was conjugated to self-assembled biotinylated-PA (B-PA) nanofibers by streptavidin linkers. Splenocytes were isolated from the mouse spleen and treated with bioactive nanofibers to investigate the effect of bioactive nanofibers on the immune response. Following the confirmation of an effective combined immune response, live mice were exposed to the nanofiber adjuvants as a proof-of-concept demonstration of in vivo PA-vaccine efficiency. Both in vivo and in vitro studies demonstrated that B-PA nanofibers are able to effectively modulate the immune response. Given these observations, I suggest that the B-PA nanofiber can be used as an immunomodulatory material for promoting effective immune response against extracellular and intracellular pathogens, and especially for the vaccine-based treatment of cancer. As the antigen presented by the PA system can be changed in a modular manner, B-PA nanofibers can also be employed to rapidly develop new vaccines against sudden outbreaks of new viral strains.
Open Access
Characterization and corneal tissue engineering application of peptide amphiphiles
(2012) Dağdaş, Yavuz Selim
Molecular self-assembly is a powerful technique for developing novel nanostructures by using non-covalent interactions such as hydrogen bonding, hydrophobic, electrostatic, metal-ligand, π-π and van der Waals interactions. Hydrogen bonding, hydrophobic and electrostatic interactions promote self-assembly of peptide amphiphile molecules into nanofibers. Bundles of nanofibers form a three-dimensional network resulting in gel formation. Concentration and temperature dependent measurements of gel stiffness suggest that the mechanical properties of the gels are determined by a number of factors including the interfiber interactions and mechanical properties of individual nanofibers. Peptide amphiphile molecules provide a convenient model as extracellular matrix mimetic systems for regenerative medicine studies. Since the substrate stiffness is crucial for cellular behaviours such as proliferation, adhesion and differentiation, understanding the mechanisms behind the viscoelastic properties of the gels formed by self-assembling molecules can lead to development of new materials with controlled stiffness. In this study, regeneration of the corneal stroma was used as a model system for utilization of peptide amphiphile molecules in regenerative medicine studies. Corneal stroma is constituted by collagen fiber arrays that are closely packed forming a stiff environment for corneal fibroblasts. The tunability of mechanical properties of self-assembled peptide amphiphile nanostructures was aimed to be utilized in corneal stroma regeneration. Thinning of the corneal stroma is a debilitating problem that can be caused by diseases like keratoconus, infections or accidents. Since corneal stroma has a restricted regenerative capacity, thinning of stroma is usually treated with cornea transplantation, which is limited by the number of donors. In this thesis, I studied mechanical properties of self-assembled peptide amphiphile nanostructures in nanometer and micrometer scale. I found that the divergence in gel stiffness may arise from the difference of strength of interfiber bonds. An injectable, biocompatible, biodegradable and bioactive system that can be used for thickening the corneal stroma was developed. This system that is composed of nanofibers was observed to enhance viability and proliferation of keratocytes in vitro.
Open Access
Controlled enzymatic stability and release characteristics of supramolecular chiral peptide amphiphile nanofiber gels
(Elsevier B.V., 2017) Zengin, A.; Cinar, G.; Güler, Mustafa O.
Supramolecular bioarchitectures formed by assembly of achiral or chiral building blocks play important roles in various biochemical processes. Stereochemistry of amino acids is important for structural organization of peptide and protein assemblies and structure-microenvironment interactions. In this study, oppositely charged peptide amphiphile (PA) molecules with L-, D- and mixture of L- and D-amino acid conformations are coassembled into supramolecular nanofibers and formed self-supporting gels at pH 7.4 in water. The enzymatic stability of the PA nanofiber gels was studied in the presence of proteinase K enzyme, which digest a broad spectrum of proteins and peptides. The structural changes on the chiral PA nanofibers were also analyzed at different time periods in the presence of enzymatic activity. Controlled release of a model cargo molecule through the chiral PA nanofiber gels was monitored. The diffusivity parameters were measured for all gel systems. Release characteristics and the enzymatic stability of the peptide nanofiber gels were modulated depending on organization of the chiral PA molecules within the supramolecular assemblies.
Open Access
Dentin phosphoprotein mimetic peptide nanofibers promote biomineralization
(WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Gülseren, Gülcihan; Tansik, Gülistan; Garifullin, Ruslan; Tekinay, Ayse B.; Güler, Mustafa O.
Dentin phosphoprotein (DPP) is a major component of the dentin matrix playing crucial role in hydroxyapatite deposition during bone mineralization, making it a prime candidate for the design of novel materials for bone and tooth regeneration. The bioactivity of DPP‐derived proteins is controlled by the phosphorylation and dephosphorylation of the serine residues. Here an enzyme‐responsive peptide nanofiber system inducing biomineralization is demonstrated. It closely emulates the structural and functional properties of DPP and facilitates apatite‐like mineral deposition. The DPP‐mimetic peptide molecules self‐assemble through dephosphorylation by alkaline phosphatase (ALP), an enzyme participating in tooth and bone matrix mineralization. Nanofiber network formation is also induced through addition of calcium ions. The gelation process following nanofiber formation produces a mineralized extracellular matrix like material, where scaffold properties and phosphate groups promote mineralization. It is demonstrated that the DPP‐mimetic peptide nanofiber networks can be used for apatite‐like mineral deposition for bone regeneration.
Open Access
Electrostatic effects on nanofiber formation of self-assembling peptide amphiphiles
(Elsevier, 2011) Toksoz, S.; Mammadov R.; Tekinay, A. B.; Güler, Mustafa O.
Self-assembling peptide amphiphile molecules have been of interest to various tissue engineering studies. These molecules self-assemble into nanofibers which organize into three-dimensional networks to form hydrocolloid systems mimicking the extracellular matrix. The formation of nanofibers is affected by the electrostatic interactions among the peptides. In this work, we studied the effect of charged groups on the peptides on nanofiber formation. The self-assembly process was studied by pH and zeta potential measurements, FT-IR, circular dichroism, rheology, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The aggregation of the peptides was triggered upon neutralization of the charged residues by pH change or addition of electrolyte or biomacromolecules. Understanding the controlled formation of the hydrocolloid gels composed of peptide amphiphile nanofibers can lead us to develop in situ gel forming bioactive collagen mimetic nanofibers for various tissue engineering studies including bioactive surface coatings. © 2010 Elsevier Inc.
Open Access
Enzymatic degradation of self-assembled peptide nanofiber gels
(2016-02) Zengin, Aygül
The self-assembled peptide nano ber gels have received enormous attention because of their inherent biocompatible, biodegradable and functional properties. They provide a smart platform for a range of applications such as tissue engineering, drug delivery and wound healing. These gels are formed through noncovalent interactions such as hydrogen bonding, hydrophobic interactions and electrostatic interactions among the peptide amphiphile molecules at physiological conditions. In order to understand the stability of these gels in the presence of proteases in natural conditions, we studied degradation behavior of the gels with proteinase K, which is a non-speci c protease cleaving the peptide bonds. Degradation process was studied by measuring weight measurement and TEM imaging. In addition, sustained release of Rhodamine B from these gels was also studied in the presence of proteases. The results clearly demonstrated that presence of D- amino acids in the peptide nano ber network signi cantly improves their stability against enzymatic degradation and change the release pro le of the encapsulated molecules in the gels. These ndings are interesting for biomedical applications of these materials due to their tunable degradation and controlled release behavior.
Open Access
Force and time-dependent self-assembly, disruption and recovery of supramolecular peptide amphiphile nanofibers
(Institute of Physics Publishing, 2018) Dikecoglu, F. B.; Topal, A. E.; Ozkan A.D.; Tekin, E. D.; Tekinay, A. B.; Güler, Mustafa O.; Dana, A.
Biological feedback mechanisms exert precise control over the initiation and termination of molecular self-assembly in response to environmental stimuli, while minimizing the formation and propagation of defects through self-repair processes. Peptide amphiphile (PA) molecules can self-assemble at physiological conditions to form supramolecular nanostructures that structurally and functionally resemble the nanofibrous proteins of the extracellular matrix, and their ability to reconfigure themselves in response to external stimuli is crucial for the design of intelligent biomaterials systems. Here, we investigated real-time self-assembly, deformation, and recovery of PA nanofibers in aqueous solution by using a force-stabilizing double-pass scanning atomic force microscopy imaging method to disrupt the self-assembled peptide nanofibers in a force-dependent manner. We demonstrate that nanofiber damage occurs at tip-sample interaction forces exceeding 1 nN, and the damaged fibers subsequently recover when the tip pressure is reduced. Nanofiber ends occasionally fail to reconnect following breakage and continue to grow as two individual nanofibers. Energy minimization calculations of nanofibers with increasing cross-sectional ellipticity (corresponding to varying levels of tip-induced fiber deformation) support our observations, with high-ellipticity nanofibers exhibiting lower stability compared to their non-deformed counterparts. Consequently, tip-mediated mechanical forces can provide an effective means of altering nanofiber integrity and visualizing the self-recovery of PA assemblies.
Open Access
A hybrid nanofiber matrix to control the survival and maturation of brain neurons
(Elsevier BV, 2012) Sur, S.; Pashuck, E. T.; Güler, Mustafa O.; Ito, M.; Stupp, S. I.; Launey, T.
Scaffold design plays a crucial role in developing graft-based regenerative strategies, especially when intended to be used in a highly ordered nerve tissue. Here we describe a hybrid matrix approach, which combines the structural properties of collagen (type I) with the epitope-presenting ability of peptide amphiphile (PA) nanofibers. Self-assembly of PA and collagen molecules results in a nanofibrous scaffold with homogeneous fiber diameter of 20-30 nm, where the number of laminin epitopes IKVAV and YIGSR can be varied by changing the PA concentrations over a broad range of 0.125-2 mg/ml. Granule cells (GC) and Purkinje cells (PC), two major neuronal subtypes of cerebellar cortex, demonstrate distinct response to this change of epitope concentration. On IKVAV hybrid constructs, GC density increases three-fold compared with the control collagen substrate at a PA concentration of ≥0.25 mg/ml, while PC density reaches a maximum (five-fold vs. control) at 0.25 mg/ml of PA and rapidly decreases at higher PA concentrations. In addition, adjustment of the epitope number allowed us to achieve fine control over PC dendrite and axon growth. Due to the ability to modulate neuron survival and maturation by easy manipulation of epitope density, our design offers a versatile test bed to study the extracellular matrix (ECM) contribution in neuron development and the design of optimal neuronal scaffold biomaterials. © 2011 Elsevier Ltd.
Open Access
Nanomechanical characterization of osteogenic differentiation of mesenchymal stem cells on bioactive peptide nanofiber hydrogels
(Wiley-VCH Verlag, 2017-08) Topal, A. E.; Tansik, G.; Ozkan A.D.; Güler, Mustafa O.; Dana, A.; Tekinay, A. B.
Stem cell differentiation is known to be influenced by the mechanical properties of the surrounding extracellular matrix (ECM); however, little is known about the mechanical phenotypes of differentiating stem cells within the ECM. Here, this study uses osteoinductive, ECM-mimetic peptide nanofibers to investigate the changes in the mechanical properties of rat mesenchymal stem cells (rMSCs) during osteogenic differentiation. In addition, octafluorocyclobutane (C4F8)-coated atomic force microscopy (AFM) cantilevers are developed to minimize tip–sample adhesion during the nanomechanical characterization of rMSCs, and osteogenic differentiation is monitored through molecular analysis in conjunction with AFM measurements. rMSCs cultured on osteoinductive peptide nanofibers differentiate at substantially higher rates, form osteogenic cell clusters, deposit calcium to the surrounding matrix, and strikingly increase their Young's moduli throughout the osteogenic differentiation process compared to controls. These results show that the elasticity profiles of differentiating rMSCs may change significantly depending on environmental factors and especially the degree of biomineralization, and that the natural elasticity responses of cells cultured on scaffolds may be considerably different from those observed on non-bioactive surfaces. This is important for the identification of cell elasticity as a biophysical marker of osteogenic differentiation of MSCs, and indicates that biomineralization might have a predominant role on cell mechanics.
Open Access
One-dimensional peptide nanostructure templated growth of iron phosphate nanostructures for lithium-ion battery cathodes
(American Chemical Society, 2016-06) Susapto, H. H.; Kudu, O. U.; Garifullin, R.; Yllmaz, E.; Güler, Mustafa O.
Template-directed synthesis of nanomaterials can provide benefits such as small crystalline size, high surface area, large surface-to-volume ratio, and structural stability. These properties are important for shorter distance in ion/electron movement and better electrode surface/electrolyte contact for energy storage applications. Here nanostructured FePO4 cathode materials were synthesized by using peptide nanostructures as a template inspired by biomineralization process. The amorphous, high surface area FePO4 nanostructures were utilized as a cathode for lithium-ion batteries. Discharge capacity of 155 mAh/g was achieved at C/20 current rate. The superior properties of biotemplated and nanostructured amorphous FePO4 are shown compared to template-free crystalline FePO4.
Open Access
Peptide nanostructure templated growth of iron phosphate nanostrustures for energy storage applications
(2015-12) Susapto, Hepi Hari
The use of primary cells has been replaced with rechargeable batteries due to environmental concerns. Li-ion batteries are examples of the rechargeable batteries that have replaced other types of rechargeable batteries from market due to high capacity, high electrochemical potential, superior energy density, durability, as well as the flexibility in design. Compared to other cathode materials used in Li-ion batteries, the iron oxide (FePO4) is less toxic, environmentally friendly, and less expensive. Inorganic materials can be fabricated by template-directed mineralization to enable control over size and morphology. One-Dimensional (1-D) nanostructures can be used for template directed mineralization method. The nanostructures are particularly interesting as electrode materials due to their high surface area, large surface-to-volume ratio, and favorable structural stability. They provide fast ion/electron transfer by sufficient contact between the active materials and electrolyte. In this thesis, 1-D nanostructures of FePO4 materials with high surface area were synthesized to enhance the efficiency of Li-ion batteries. The synthesis of iron phosphate nanostructures was performed by using peptide amphiphile nanostructures. Iron (III) chloride (FeCl3) was used to trigger the self-assembly of the peptide amphiphile molecules forming nanostructures, which can nucleate FePO4 formation. The electrochemical performance of these nanostructures for Li-ion battery was analyzed. In conclusion, the template directed electrode materials revealed fast ion/electron transfer and sufficient contact between materials and electrolyte. They also exhibited enhanced flexibility leading to higher capacity than the electrode material synthesized without the template.
Open Access
A self assembled nanofibrous structure as a novel vaccine adjuvant
(2017-01) Demircan, Muhammed Burak
Vaccination is the most effective and cost-efficient way of protection against the major infectious diseases but ideal vaccine formulation has not been found. Recent vaccine systems are mainly composed of two major substitutes that are antigen and adjuvant. Recently it was demonstrated that widely used adjuvants exhibit some safety problems that affect the neural system such as neurotoxicity and autoimmune diseases. Therefore, there are increased concerns about side effects of the adjuvants and many researchers focus on developing new adjuvants that are effective and safe. Peptide amphiphiles are chemically defined molecules that are able to self-assemble into nanofibrous structures. The nanofibrous structures are biocompatible, biodegradable, and biosafe and thereby they are ideal for vaccine systems. Also, nanofibrous structures don’t contain any substance that are potentially dangerous for neural system such as metals. Thus, nanofibrous structures are promising candidates to be alternative novel vaccine adjuvants. In this thesis, I investigated the potential of a biotinylated nanofibrous structure as a novel vaccine adjuvant that is potentially safe. Briefly, biotinylated peptide amphiphiles were synthesized, purified and characterized to analyze the features of the novel material. The peptide amphiphiles were induced to form nanofibrous structures by self-assembly and antigens (ovalbumin) were bound to the biotinylated nanofibrous structures through streptavidin linkers. Splenocytes were treated with the nanofibrous structures to demonstrate the effects of the nanofibrous structures on the immune response. After the confirmation of efficient immune response that are induced by the nanofibrous structure in vitro, as enhancing release of stimulatory cytokines, inducing dendritic cell maturation and triggering the cross-presentation of the antigen, mice were immunized with the nanofibrous structure in the presence of antigen for further analysis of the nanofibrous structure efficiency as adjuvant in vivo. Both in vivo and in vitro results showed that the nanofibrous structure is able to effectively trigger the antigen specific immune response and thereby exhibit adjuvant properties. Overall, I suggest that the nanofibrous structure is able to be used as a new vaccine adjuvant that induces effective antigen specific adoptive immune response and thereby it could be a good alternative of recently used adjuvants that are suspected to contribute some impairments in neural system.
Open Access
Synthesis and characterization of metallopeptide nanostructures
(2013) Ustahüseyin, Oya
Organic-inorganic hybrid structures play a number of distinguished roles in the living milieu. For instance, metal ions function as cofactors of enzymes and apatite mineralization in bone is driven by collagen nanofibers serve as both physical and chemical templates. These unique interactions in natural systems are examples for development of synthetic materials for many applications such as catalysts, artificial enzymes or materials for regenerative medicine etc. Manufacturing a catalyst at the nanoscale is important due to increased specific surface area and reduced diffusion path length. In this thesis, we demonstrated peptide based bioinspired nanomaterials. The self-assembled peptide nanofibers were utilized as templates for palladium nanoparticle formation. Functionalization of insoluble electrospun nanofibers with a heavy metal binding peptide sequence was utilized to remove toxic metal ions from water. In addition, peptide amphiphile nanofibers complexed with ZnII were used as enzyme mimics. The resulting nanostructures resemble natural bone alkaline phosphatase activity, which is a major enzyme for natural bone apatite formation.