Browsing by Subject "Extracellular matrix"

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Open Access
3D breast cancer model on silk fibroin–integrated microfluidic chips
(SPRINGER HEIDELBERG, 2024) Yılmaz, Eylül Gülşen; İnci, Fatih
To imitate in vivo environment of cells, microfluidics offer controllable fashions at micro-scale and enable regulate flow-related parameters precisely, leveraging the current state of 3D systems to 4D level through the inclusion of flow and shear stress. In particular, integrating silk fibroin as an adhering layer with microfluidic chips enables to form more comprehensive and biocompatible network between cells since silk fibroin holds outstanding mechanical and biological properties such as easy processability, biocompatibility, controllable biodegradation, and versatile functionalization. In this chapter, we describe design and fabrication of a microfluidic chip, with silk fibroin-covered microchannels for the formation of 3D structures, such as MCF-7 (human breast cancer) cell spheroids as a model system. All the steps performed here are characterized by surface-sensitive tools and standard tissue culture methods. Overall, this strategy can be easily integrated into various high-tech application areas such as drug delivery systems, regenerative medicine, and tissue engineering in near future.
Open Access
Affinity of glycopeptide nanofibers to growth factors and their effects on cells
(2017-09) Haştar, Nurcan
The development of scaffolds for growth factor delivery is a promising approach for tissue regeneration applications due to their crucial roles during regeneration. Growth factor secretion and interactions with glycosaminoglycans are essential steps for the regulation of cellular behavior. Therefore, glycosaminoglycan-mimetic scaffolds provide a great opportunity to modulate the effects of growth factor actions on cell fate. In this thesis, sugar-bearing peptide amphiphile molecules were characterized and tested for VEGF, FGF-2 and NGF affinity. ELISA-based affinity analyses revealed that glycopeptide nanofibers had high affinity to NGF; however, glycopeptides alone were not enough to interact efficiently with VEGF and FGF-2. Since VEGF and NGF contain heparin-binding domains, the addition of a sulfonated peptide amphiphile increased the affinity of the nanofiber network to these growth factors. Glycopeptide-sulfonate nanofibers were also found to promote in vitro tube formation through their VEGF and FGF-2 affinity. VEGF release profiles of HUVECs indicated that increasing concentration of VEGF may provide autocrine signaling and enhance tube formation without any exogenous pro-angiogenic factor addition. In addition, when NGF-responsive PC-12 cells were cultured on glycopeptide nanofibers, they extended their neurites to an extent comparable with a widely-used positive control molecule (poly-L-lysine). These results suggest that glycosaminoglycan-mimetic glycopeptide nanofiber networks can be used as efficient growth factor presentation platforms for tissue regeneration applications to induce angiogenesis or peripheral nerve regeneration.
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 peptide nanofibers for bone tissue regeneration
(2017-06) Tansık, Gülistan
Replacement and repair of bone tissue that is lost due to fractures, tumor resection, degenerative diseases and infections still remain major clinical challenges. Autografting, allografting and xenografting are the current strategies for the treatment of bone defects. However, these strategies cause problems such as immunological response and disease transmission in clinical applications. To overcome these limitations, regeneration of new bone can be induced by the use of synthetic bioactive materials. One of the most promising strategies is to develop synthetic scaffolds mimicking the functional components of the extracellular matrix (ECM). Biomineralization is mineralization carried out by living organisms. Glycosaminoglycans have crucial roles in biomineralization and enhance the functions of growth factors involved in biomineralization. Success in bone regeneration studies requires a thorough understanding of the necessary conditions for triggering biomineralization during the bone tissue formation process. In this study, the effect of bioactive and biocompatible peptide nanofibers on osteogenic differentiation, biomineralization and bone tissue regeneration are investigated under in vitro and in vivo conditions. In the first chapter, bone tissue composition, the clinical need for bone regeneration and general principles in bone tissue engineering are discussed. Bone tissue regeneration strategies are also highlighted in this part, with emphasis on peptide amphiphiles and self-assembly behavior. In the second chapter, a fully synthetic, extracellular matrix-mimetic peptide nanofiber system is described for enhancing the biomineralization and regeneration of bone tissue. This nanostructural environment forms artificial intracellular networks and supports biomineralization by providing cell-material and protein-material interactions. In the third chapter, effect of osteoinductive peptide nanofibers on osteogenic differentiation of rat mesenchymal stem cells (MSCs) were investigated. In the fourth chapter, the natural biomineralization process in bone tissue was mimicked on peptide nanofibers and the effect of this system on the osteogenic differentiation of osteoblast-like cells was investigated. In the fifth chapter, a dentin-mimetic peptide amphiphile (SpDSp-PA) molecule that is capable of emulating the structure and function of dentin phosphoprotein was designed and its capacity to support the deposition of hydroxyapatite and survival and biomineralization of osteoblast-like cells was evaluated.
Open Access
Bioactive peptide nanofibers for acceleration of burn wound healing
(2017-05) Yergöz, Fatih
Burn injuries are one of the most typical types of trauma worldwide, and the unique physiology of burn injuries requires the use of specialized therapeutic materials for treatment and makes the development of such materials especially challenging. Here, we report the use of synthetic, functional and biodegradable peptide nanofiber gels for improved healing of burn wounds to alleviate the progressive loss of tissue function at the post-burn wound site. These bioactive nanofiber gels form scaffolds which recapitulate the morphology and function of the natural extracellular matrix through peptide epitopes, which can trigger angiogenesis through significant affinity to basic growth factors. In this study, the angiogenesis-promoting properties of the bioactive scaffolds were utilized for the treatment of thermal burn model. Following the excision of necrotic tissue, bioactive gels and control solutions were applied topically onto the wound area. The wound healing process was evaluated at 7, 14 and 21 days following injury through histological observations, immunostaining and marker RNA / protein analysis. Bioactive peptide nanofiber treated burn wounds formed well-organized and collagen-rich granulation tissue layers, developed a greater density of newly formed blood vessels, and exhibited increased re-epithelialization and skin appendage formation with minimal crust formation. Overall, the heparin-mimetic peptide nanofiber gels increased the rate of repair of burn injuries and can be used as effective means of facilitating wound healing.
Open Access
Bioactive peptide nanofibers for tissue regeneration
(2016-01) Uzunallı, Gözde
Defects in the tissues or organs caused by trauma or diseases can have detrimental effects on all aspects of patients’ life quality. During the last three decades, considerable developments have been made in tissue engineering and regenerative medicine in order to find alternative treatment methods to recover tissue function after injury. These methods are based on the development of materials that are uniquely suited to the specific requirements of the tissue type and the repair process itself. Consequently, the implanted biomaterial must be compatible with biological systems and capable of delivering the signals necessary to facilitate tissue repair. In the present thesis, peptide amphiphile molecules were used to meet these requirements and develop next-generation biomaterials that are able to enhance the repair process while minimally affecting the integrity of surrounding tissues. Peptide amphiphiles are molecules that naturally self-assemble into nanofibrous hydrogel structures that closely emulate the composition of the extracellular matrix. As peptide amphiphiles contain amino acid sequences, bioactive signals can also be integrated into their structure to create a biocompatible environment and enhance the survival and proliferation of the resident cell population. In the scope of the present thesis, peptide amphiphile systems were utilized in three distinct applications. The first chapter covers the fundamentals of regenerative medicine and tissue engineering, the interactions between biomaterials and cells and extracellular materials, and the materials that are commonly used for these applications. The second chapter details the use of fibronectin- and laminin-derived peptide amphiphiles for the regeneration of corneal injuries. The third chapter investigates the ability of heparin-mimetic peptide hydrogels to facilitate the survival of pancreatic islets in vitro and demonstrates that islets transplanted in tandem with peptide gels trigger a local angiogenic response, decrease blood glucose levels and retain these functionalities even after 28 days of observation. The fourth chapter concerns the application of heparin-mimetic peptide amphiphile molecules for the recovery of acute wound injuries through the establishment of a well-ordered collagen matrix and the enhancement of the re-epithelialization process. Distinct peptide amphiphiles bearing bioactive signals conductive to tissue development were developed and utilized in all three studies, and the use of these materials has been demonstrated to serve as an adequate means of enhancing tissue repair.
Open Access
Chondrogenic differentiation of mesenchymal stem cells on glycosaminoglycan-mimetic peptide nanofibers
(American Chemical Society, 2016) Yaylaci, S .U.; Sen, M.; Bulut, O.; Arslan, E.; Güler, Mustafa O.; Tekinay, A. B.
Glycosaminoglycans (GAGs) are important extracellular matrix components of cartilage tissue and provide biological signals to stem cells and chondrocytes for development and functional regeneration of cartilage. Among their many functions, particularly sulfated glycosaminoglycans bind to growth factors and enhance their functionality through enabling growth factor-receptor interactions. Growth factor binding ability of the native sulfated glycosaminoglycans can be incorporated into the synthetic scaffold matrix through functionalization with specific chemical moieties. In this study, we used peptide amphiphile nanofibers functionalized with the chemical groups of native glycosaminoglycan molecules such as sulfonate, carboxylate and hydroxyl to induce the chondrogenic differentiation of rat mesenchymal stem cells (MSCs). The MSCs cultured on GAG-mimetic peptide nanofibers formed cartilage-like nodules and deposited cartilage-specific matrix components by day 7, suggesting that the GAG-mimetic peptide nanofibers effectively facilitated their commitment into the chondrogenic lineage. Interestingly, the chondrogenic differentiation degree was manipulated with the sulfonation degree of the nanofiber system. The GAG-mimetic peptide nanofibers network presented here serve as a tailorable bioactive and bioinductive platform for stem-cell-based cartilage regeneration studies.
Open Access
Design and development of ecm-inspired peptidebased nanostructures for bioengineering and biomedicine
(2017-08) Arslan, Elif
Advances in understanding of cell-matrix interactions and the regulation of cellular behaviors through nanobiotechnological tools have presented new perspectives for regenerative medicine. Peptide amphiphiles have been used as building blocks for development of bioactive synthetic nanofiber scaffolds for regenerative medicine applications. Biocompatibility, tailorable characteristics, and mechanical stability as well as bioactivitiy of these peptide nanostructures make them ideal candidates for biomedical applications. To guide natural cellular activities, biomaterials should provide a microenvironment similar to that experienced by cells under natural conditions. The native extracellular matrix (ECM) not only provides a suitable physical environment but also incorporates the necessary set of biochemical and mechanical signals to ensure the normal function of cells, as well as mediating their differentiation, morphogenesis and homeostasis by providing biological, physical, and chemical recognition signals that can trigger specific interactions with cell surface receptors. In this thesis, different ECM-mimetic peptide nanofiber formulations were designed and developed, which were shown to have superior chondrogenic and therapeutic effect on stem cell differentiation in vitro and cartilage regeneration in vivo. Hence, the synthetic peptide nanomaterials harbor great promise in mimicking specific ECM molecules as therapeutic agents and model systems.
Open Access
Development of peptide based materials as a synthetic scaffold to mimic extracellular matrix
(2017-07) Sever, Melike
Biomaterials obtained through self-assembling process of peptide amphiphile (PA) molecules provide great potential to introduce new therapeutic approaches in regenerative medicine through mimicking the natural environments of different types of tissues. The ability of self-assembled PA nanofibers to mimic natural extracellular matrix (ECM) renders them attractive for regenerative medicine applications. The materials-cell interactions can be modulated through the surface modification of the materials such as introducing the bioactivity via short bioactive peptide sequences derived from natural ECM proteins, which regulate cell behavior through controlling of cellular activities such as proliferation and differentiation. Herein, I described my studies on the development of PA nanofibers in order to mimic natural ECM with differentiation and regeneration purposes. Heparan sulfate mimetic and laminin mimetic PA nanofibers were used as a potential therapeutic approach in Parkinson's disease (PD). These bioactive PA nanofibers were found to reduce the progressive cell loss in SH-SY5Y cells caused by 6-hydroxydopamine treatment in vitro, and improve neurochemical and behavioral consequences of Parkinsonism in rats and provide a promising new strategy for treatment of PD. These nanofibers also proved to be effective in enhancing the viability of Schwann cells and increase nerve growth factor (NGF) release from these cells in vitro. Since NGF has a crucial role in nerve injury repair and myelination in the regenerating nerve, the bioactive epitopes used in this study present also a promising approach as guidance cues for regenerating axons. Tenascin-C is another multifunctional ECM glycoprotein common in both nerve and bone tissue. By decorating peptide nanofibers with tenascin-C derived epitope and using in three-dimensional (3D) system, this tenascin-C mimetic 3D cell culture system was found to provide both the biochemical and physical aspects of the native environment of neural cells, thereby filling the gap between 2D cell culture models and in vivo environments and contributing to more tissue-like structure and more predictive approaches to organogenesis and tissue morphology. Within the scope of this thesis, tenascin-C mimetic nanofibers were also used for osteogenic differentiation of mesenchymal stem cells (MSCs). They were found to significantly enhance the attachment, proliferation, and osteogenic differentiation of MSCs even in the absence of any external bioactive factors and regardless of the suitable stiff mechanical properties normally required for osteogenic differentiation.
Open Access
Glycosaminoglycan-Mimetic Signals Direct the Osteo/Chondrogenic Differentiation of Mesenchymal Stem Cells in a Three-Dimensional Peptide Nanofiber Extracellular Matrix Mimetic Environment
(American Chemical Society, 2016-02) Arslan, E.; Güler, Mustafa O.; Tekinay, A. B.
Recent efforts in bioactive scaffold development focus strongly on the elucidation of complex cellular responses through the use of synthetic systems. Designing synthetic extracellular matrix (ECM) materials must be based on understanding of cellular behaviors upon interaction with natural and artificial scaffolds. Hence, due to their ability to mimic both the biochemical and mechanical properties of the native tissue environment, supramolecular assemblies of bioactive peptide nanostructures are especially promising for development of bioactive ECM-mimetic scaffolds. In this study, we used glycosaminoglycan (GAG) mimetic peptide nanofiber gel as a three-dimensional (3D) platform to investigate how cell lineage commitment is altered by external factors. We observed that amount of fetal bovine serum (FBS) presented in the cell media had synergistic effects on the ability of GAG-mimetic nanofiber gel to mediate the differentiation of mesenchymal stem cells into osteogenic and chondrogenic lineages. In particular, lower FBS concentration in the culture medium was observed to enhance osteogenic differentiation while higher amount FBS promotes chondrogenic differentiation in tandem with the effects of the GAG-mimetic 3D peptide nanofiber network, even in the absence of externally administered growth factors. We therefore demonstrate that mesenchymal stem cell differentiation can be specifically controlled by the combined influence of growth medium components and a 3D peptide nanofiber environment.
Open Access
In situ functionalization of poly(hydroxyethyl methacrylate) cryogels with oligopeptides via β-Cyclodextrin–adamantane complexation for studying cell-instructive peptide environment
(American Chemical Society, 2020) Luong, T. D.; Zoughaib, M.; Garifullin, Ruslan; Kuznetsova, S.; Güler, Mustafa O.; Abdullin, T. I.
Oligopeptides are versatile cell modulators resembling pleiotropic activities of ECM proteins and growth factors. Studying the role of cellinstructive peptide signals within 3D scaffolds, yet poorly known, requires effective approaches to introducing bioactive sequences into appropriate materials. We synthesized RGD and GHK motif based peptides 1 and 2 linked to the terminal adamantyl group (Ad) and their fluorescent derivatives 3 and 4. Poly(hydroxyethyl methacrylate) (pHEMA) cryogels with additional PEG/β- cyclodextrin (CD) units were prepared as an inert macroporous scaffold capable to bind the adamantylated peptides via affinity CD-Ad complexation. According to toluidine blue staining, the CD moieties were effectively and stably incorporated in the pHEMA cryogels at nanomolar amounts per milligram of material. The CD component gradually increased the thickness and swelling ability of the polymer walls of cryogels, resulting in a noticeable decrease in macropore size and modulation of viscoelastic properties. The labeled peptides exhibited fast kinetics of specific binding to the CD-modified cryogels and were simultaneously immobilized by coincubation. The peptide loading approached ca. 0.31 mg per cm2 of cryogel sheet. A well-defined mitogenic effect of the immobilized peptides (2 < 1≪ 1 + 2) was revealed toward 3T3 and PC-12 cells. The synergistic action of RGD and GHK peptides induced a profound change in cell behavior/morphology attributed to a growth-factor-like activity of the composition. Altogether, our results provide an effective procedure for the preparation of CDmodified pHEMA cryogels and their uniform in situ functionalization with bioactive peptide(s) of interest and an informative study of cellular responses in the functionalized scaffolds
Open Access
Microfluidic chip-based systems for monitoring cancer therapy
(2022-12) Yılmaz, Eylül Gülşen
In tumor microenvironment, cancer cells are exposed to a range of fluid shear stresses (FSS); yet, current in vitro three-dimensional (3D) models have limitations to investigate the impact of biophysical stimuli on cancer mechanism and chemoresistance in a dynamic manner. In the past few decades, vital demand for exploring biological significance of mechanical forces has led to the development of several innovative approaches. One of these approaches is the integration of microfluidic systems into cancer studies. The use of microfluidic chips has garnered increasing attention since they offer ease-of-manipulation, high-throughput, less material/reagent consumption, and low-cost. On the other hand, the researches have stated explicitly that tumor-derived extracellular vesicles (EVs) regulate local and systemic milieu to drive the development and spread of cancer through nano- and micron-sized vesicles they carry. In this thesis, breast cancer cells (MCF-7) have been utilized as a model cancer system, and accordingly, they are cultivated through SF-coated microfluidic systems in order to mimic tumor microenvironment, exhibiting a more dynamic condition. Simultaneously, traditional static culture of MCF-7 cells is also performed as a control group in order to understand the impact of flow conditions. The effects of FSS on gene expression—in particular, EpCAM and CK-18 genes, which are highly expressed in MCF-7 cells— have been examined at the end of cell culturing process. In addition, cancer cells developing any resistance to anti-cancer drugs on the course of FSS have been investigated. In this regard, the cells are treated with either doxorubicin or docetaxel (anti-cancer drugs) in the cases of dynamic (microfluidic system) and static (tissue culture flask) culture conditions. Multi-Drug Resistance 1 (MDR-1) and Breast Cancer Resistance Protein (BCRP) gene expression levels have been assessed once anti-cancer treatment has been finalized. The final step of this study relies on the isolation and analysis of EVs from both static and dynamic conditions with the presence and absence of anti-cancer drug treatment. The utility of EVs has been evaluated deliberately as biomarkers for real-time monitoring of treatment efficacy.
Open Access
Nanomaterials for neural regeneration
(John Wiley & Sons, 2016-03-11) Sever, Melike; Mammadov, Büşra; Geçer, Mevhibe; Güler, Mustafa O.; Tekinay, Ayşe B.; Güler, Mustafa O.; Tekinay, Ayşe B.
The central nervous system (CNS) consists of a dense network of cells leaving a smaller volume for the extracellular matrix (ECM) components (10‐20% for the brain unlike most other tissues (Cragg, 1979)). The reaction of the nervous tissue to any injury leading to scar tissue formation acts as a barrier for regeneration in the CNS, while it supports regeneration in the peripheral nervous system (PNS). By mimicking several unique characteristics of the natural environment of cells, synthetic materials for neural regeneration can be improved chemically and biologically. Especially bioactivation of materials can be achieved by addition of small chemical moieties to the scaffold particularly found in specific tissues or addition of biologically active molecules derived from natural ECM. The ECM‐derived short peptides are promising candidates to be presented as functional domains on the scaffold surface for use in neural regeneration.
Open Access
Neural ECM mimetics
(Elsevier, 2014) Estrada, V.; Tekinay, Ayşe B.; Müller, H. W.
The consequence of numerous neurological disorders is the significant loss of neural cells, which further results in multilevel dysfunction or severe functional deficits. The extracellular matrix (ECM) is of tremendous importance for neural regeneration mediating ambivalent functions: ECM serves as a growth-promoting substrate for neurons but, on the other hand, is a major constituent of the inhibitory scar, which results from traumatic injuries of the central nervous system. Therefore, cell and tissue replacement strategies on the basis of ECM mimetics are very promising therapeutic interventions. Numerous synthetic and natural materials have proven effective both in vitro and in vivo. The closer a material's physicochemical and molecular properties are to the original extracellular matrix, the more promising its effectiveness may be. Relevant factors that need to be taken into account when designing such materials for neural repair relate to receptor-mediated cell-matrix interactions, which are dependent on chemical and mechanical sensing. This chapter outlines important characteristics of natural and synthetic ECM materials (scaffolds) and provides an overview of recent advances in design and application of ECM materials for neural regeneration, both in therapeutic applications and in basic biological research. © 2014 Elsevier B.V.
Open Access
Peripheral nerve regeneration by synthetic peptide nanofibers
(2016-09) Geçer, Mevhibe
The peripheral nervous system (PNS) has a complex structure that consists of high numbers of nerve cells and communication networks between the central nervous system and the body parts. Unlike the central nervous system, the PNS exhibits a considerable capacity for regeneration; however, peripheral nerve injuries can nevertheless cause lifelong disability. Various methods are currently available for the treatment of nerve injuries, but autologous nerve grafting is considered as ‘the gold standard’. Donor site morbidity, neuroma formation and failure of functional recovery are some limitations of this technique, especially when used for the repair of long nerve gaps. Polymeric nerve conduits are clinically available alternatives to nerve grafting, and function by guiding the axonal growth and isolating the regenerating axon from the inhibitory environment present in the post-injury neuroma. In this thesis, we used peptide amphiphile molecules (PAs) that can self-assemble into the nanofibers and mimic both the structure and function of healthy ECM of nerve cells for sciatic nerve regeneration. Two bioactive PAs, LN-PA (derived from laminin) and GAG-PA (derived from glycosaminoglycan), were tested for their ability to induce neural regeneration in a rat sciatic nerve model. Hollow nerve conduits were filled with peptide nanofiber gels, and electrophysiology and histology results were compared with autologous graft treated groups. Our results show that bioactive peptide nanofibers are able to boost regeneration and functional motor and sensory recovery. Electromyography results demonstrated that better signal transmission was observed in peptide nanofiber treated groups compared with empty conduits and autograft treated groups. Histological assessments also confirmed that bioactive peptide nanofiber treated groups exhibited better axonal regeneration. These results suggest that these biologically active PA nanofiber gels may be used as a biomaterial for peripheral nerve regeneration in clinical practice.
Open Access
Three dimensional glycosaminoglycan mimetic peptide amphiphile hydrogels for regenerative medicine applications
(2015-05) Tümtaş, Yasin
Defects and impairments of tissues or organs affect millions of people, resulting in considerable losses in workforce and life quality. The treatment of major tissue injuries requires the development of advanced medical techniques that enhance the natural repair processes of the human body. Novel biomaterials can modulate the repair of organs and tissues by providing a suitable environment for the recruitment, proliferation and differentiation of stem and progenitor cells, allowing the recovery of degenerated or otherwise nonfunctional tissues. Peptide amphiphiles (PAs) serve as model biomaterials due to their capacity for self-assembly, which allows peptide monomers to form complex networks that approximate the structure and function of the natural extracellular matrix. Peptide networks can be further modified by the attachment of various epitopes and functional groups, allowing these materials to present bioactive signals to surrounding cells. Glycosaminoglycans (GAGs) are negatively charged, unbranched polysaccharides that constitute a substantial part of the ECM in various tissues and play an important role in maintaining tissue integrity. Therefore, mimicking GAGs presents a suitable means for modulating cell behavior and especially lineage commitment in stem cells. In this work, I describe the design and synthesis of several bioactive, three dimensional (3D) GAG-mimetic peptide amphiphile hydrogels for in vitro stem cell differentiation and in vivo pancreatic islet transplantation. In Chapter 1, I detail the extracellular environment of tissues and the importance of GAGs in maintaining cell and tissue function. In Chapter 2, I describe the in vitro experiments involving the effects of sulfonation and the presence of glucose units on the differentiation of mesenchymal stem cells. In Chapter 3, I utilize a heparin-mimetic PA to increase the survival of pancreatic islets transplanted into the rat omentum, and demonstrate that increased angiogenesis results in enhanced survival. Lastly, in Chapter 4, I summarize my results and describe the course of future experiments for the artificial regeneration of tissues through peptide amphiphile networks.
Open Access
Three-Dimensional Laminin Mimetic Peptide Nanofiber Gels for In Vitro Neural Differentiation
(Wiley-VCH Verlag, 2017) Gunay, Gokhan; Sever, Melike; Tekinay, Ayse B.; Güler, Mustafa O.
The extracellular matrix (ECM) provides biochemical signals and structural support for cells, and its functional imitation is a fundamental aspect of biomaterial design for regenerative medicine applications. The stimulation of neural differentiation by a laminin protein-derived epitope in two-dimensional (2D) and three-dimensional (3D) environments is investigated. The 3D gel system is found to be superior to its 2D counterpart for the induction of neural differentiation, even in the absence of a crucial biological inducer in nerve growth factor (NGF). In addition, cells cultured in 3D gels exhibits a spherical morphology that is consistent with their form under in vivo conditions. Overall, the present study underlines the impact of bioactivity, dimension, and NGF addition, as well as the cooperative effects thereof, on the neural differentiation of PC-12 cells. These results underline the significance of 3D culture systems in the development of scaffolds that closely replicate in vivo environments for the formation of cellular organoid models in vitro. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Open Access
Toxicity of internalized laser generated pure silver nanoparticles to the isolated rat hippocampus cells
(SAGE, 2017-02) Kursungoz, C.; Taş, S. T.; Sargon, M. F.; Sara, Y.; Ortaç, B.
Silver nanoparticles (AgNPs) are the most commonly used nanoparticles (NPs) in medicine, industry and cosmetics. They are generally considered as biocompatible. However, contradictory reports on their biosafety render them difficult to accept as 'safe'. In this study, we evaluated the neurotoxicity of direct AgNP treatment in rat hippocampal slices. We produced pure uncoated AgNPs by a pulsed laser ablation method. NP characterization was performed by Ultraviolet (UV) visible spectrophotometer, scanning electron microscope, transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy. Rat hippocampal slices were treated with AgNPs for an hour. AgNP exposure of hippocampal tissue resulted in a significant decrease in cell survival in a dose-dependent manner. Our TEM results showed that AgNPs were distributed in the extracellular matrix and were taken into the cytoplasm of the neurons. Moreover, we found that only larger AgNPs were taken into the neurons via phagocytosis. This study showed that the pure AgNPs produced by laser ablation are toxic to the neural tissue. We also found that neurons internalized only the large NPs by phagocytosis which seems to be the major mechanism in AgNP neurotoxicity.