Browsing by Subject "nanofibers"

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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
Electrospinning of biocompatible polymeric nanofibers functionalized with cyclodextrin inclusion complex
(2012) Aytaç, Zeynep
Electrospinning is a simple, versatile and cost-effective method to produce nanofibers. Electrospun nanofibers have high surface area to volume ratio and nanoporous structure. Moreover, electrospun nanofibers could be functionalized with additives to extend their application areas. Cyclodextrins (CDs) are cyclic oligosaccharides and have truncated-cone shape structure. Due to their hydrophobic cavity, CDs have ability to form inclusion complex (IC) with a variety of molecule. In our study, we functionalized electrospun nanofibers with CDs and CD-ICs. In the first part, we successfully produced hydroxypropyl cellulose- (HPC), carboxymethyl cellulose- (CMC) and alginate-based nanofibers via electrospinning. Then we functionalized these nanofibers with CDs. The morphological characterizations of nanofibers were performed through scanning electron microscopy (SEM). Here, we have combined the properties of both electrospun nanofibers and CDs, and these nanofibers could be used in drug delivery, wound healing and tissue engineering applications. In the second part, we prepared IC of sulfisoxazole (SFS) (hydrophobic drug) with hydroxypropyl-beta-cyclodextrin (HPβCD) (SFS/HPβCD-IC). Then electrospinning of SFS/HPβCD-IC incorporating hydroxypropyl cellulose (HPC) nanofibers were performed (SFS/HPβCD-IC-HPC-NFs). In the third part of our study, we produced IC of α-tocopherol (α-TC) (antioxidant molecule) with beta-cyclodextrin (β-CD) (α-TC/β-CD-IC); and polycaprolactone (PCL) nanofibers incorporating α-TC/β-CD-IC was obtained via electrospinning (α- TC/β-CD-PCL-NFs). In the fourth part, IC of allyl isothiocyanate (AITC) (antibacterial compound) with β-CD (AITC/β-CD-IC) was produced. The electrospinning of AITC/β-CD-IC incorporating polyvinyl alcohol (PVA) nanofibers was carried out (AITC/β-CD-IC-PVA-NFs). In the fifth part, IC of quercetin (QU) (antioxidant molecule) with β-CD (QU/β-CD-IC) was prepared; and polyacrylic acid (PAA) nanofibers incorporating QU/β-CD-IC was obtained via electrospinning (QU/β-CD-IC-PAA-NFs). The structural and thermal characterizations of SFS/HPβCD-IC-HPC-NFs, α-TC/β-CD-PCL-NFs, AITC/β- CD-IC-PVA-NFs and QU/β-CD-IC-PAA-NFs were carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The amount of released molecules were determined via liquid chromatography-mass spectroscopy (LC-MS) for SFS/HPβCD-IC-HPC-NFs; high performance liquid chromatography (HPLC) for α-TC/β-CD-PCL-NFs and QU/β-CD-IC-PAA-NFs and gas chromatography-mass spectrometry (GC-MS) for AITC/β-CD-IC-PVANFs. The antioxidant activity of α-TC/β-CD-PCL-NFs and QU/β-CD-IC-PAANFs was investigated by using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Moreover, α-TC/β-CD-PCL-NFs released great proportion of α-TC after exposing UV light. Thus, α-TC/β-CD-PCL-NFs exhibited quite high photostability. The antibacterial activity of AITC/β-CD-IC-PVA-NFs was evaluated by colony counting method against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus). In brief, we concluded that SFS/HPβCD-ICHPC-NFs, α-TC/β-CD-PCL-NFs, AITC/β-CD-IC-PVA-NFs and QU/β-CD-ICPAA-NFs are promising materials for drug delivery and wound healing applications.
Open Access
Peptide nanofibers for engineering tissues and immune system
(2014) Mammadov, Rashad
Interdisciplinary work at the interface of biology and materials science is important for finding cures to complex diseases. Achievements in materials science allow us to control materials at nanoscale and design them according to specific therapeutic purposes. This includes incorporating biophysical and biochemical signals into materials to make them biologically functional. These signals are sensed by cells in normal or pathological cases and influence their decision-making process, which eventually alters cellular behavior. However, cellular environment is so complex in terms of these signals that recapitulating it with synthetic materials is unattainable considering our limited resources. Therefore, we need to distinguish those signals that are structurally simple, but at the same time biologically critical, that would drive cellular behavior to desired outcome. In this thesis, I will describe peptide nanofiber systems for tissue engineering and vaccinology applications. First system is inspired from heparan sulfate (HS) – a natural polymer in extracellular matrix – that bind to growth factors and regulate their functioning, therefore central for induction of various physiological processes. Peptide nanofibers with right composition of bioactive chemical functional groups from HS showed specific interaction with growth factors and induced endothelial cells to form blood vessels similar to natural matrices carrying HS. Considering mentioned features, these peptide nanofibers could be useful for effective regeneration of tissues. Secondly, the peptide nanofiber system carrying pathogenic DNA motives, which is an infection signal, was developed. While non-immunogenic by itself, these nanofibers shifted immune response against pathogenic DNA towards a context that is useful for fighting intracellular pathogens and cancer. Overall, this thesis demonstrates that structurally simple but appropriate biophysical and biochemical signals could be synergistic for inducing desired biological processes at the nanoscale.
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.