Browsing by Subject "Glycosaminoglycans"

Now showing 1 - 8 of 8

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
Biomimetic self-assembled peptide nanofibers for bone regeneration
(2012) Kocabey, Samet
Self-assembled peptide nanofibers are exploited in regenerative medicine applications due to their versatile, biofunctional and extracellular-matrixresembling structures. These properties provide peptide nanofibers with osteoinductive and osteoconductive behaviors for bone regeneration applications through several approaches. In this thesis, two different approaches were discussed, which were developed to induce bone regeneration and mineralization including extracellular matrix mimicking peptide nanofibers based 2-D gel formation and surface functionalization of titanium implants. For this purpose, we designed glycosaminoglycan-mimetic peptide nanofibers inspired by chemical structure of glycosaminoglycans present in the bone extracellular matrix. We demonstrated that glycosaminoglycan-mimetic peptide nanofibers interact with BMP-2, a critical growth factor for osteogenic activity. Glycosaminoglycan-mimicking ability of the peptide nanofibers and their interaction with BMP-2 promoted osteogenic activity of and mineralization by osteoblastic cells. ALP activity, Alizarin Red Staining and EDAX spectroscopy indicated efficacy of the peptide nanofibers for inducing mineralization. We also developed a hybrid osteoconductive system for titanium biomedical implants inspired by mussel adhesion mechanism in order to overcome bone tissue integration problems. For this purpose, Dopa conjugated peptide nanofiber coating was used along with bioactive peptide sequences for osteogenic activity to enhance osseointegration of titanium surface. Dopamediated immobilization of osteogenic peptide nanofibers on titanium surfaces created an osteoconductive interface between osteoblast-like cells and inhibited adhesion and viability of soft tissue forming fibroblasts compared to the uncoated titanium substrate. In summary, osteoinductive and osteoconductive self-assembled peptide nanofibers were developed to promote osteogenic activity and mineralization of osteogenic cells. These bioactive nanofibers provide a potent platform in clinical applications of bone tissue engineering.
Open Access
Development and characterization of peptide nanofibers for cartilage regeneration
(2015-09) Yaylacı, Seher
Articular cartilage is a tissue that is continuously exposed to cyclical compressive stresses, but exhibits no capacity for self-healing following trauma. Cartilage has a dense extracellular matrix that is sparsely populated with cells, and the whole tissue lacks blood and lymphatic vessels, which complicates the cell infiltration response that ordinarily occurs during inflammation. In addition, the only cell type capable of synthesizing new cartilage matrix lies deeper in the tissue, near the bone boundary, and due to the dense extracellular matrix, chondrocytes cannot migrate to the defect site following injury. Consequently, cartilage tissue cannot effectively respond to treatment options. Treatment options exist for the short-term reduction of pain in smaller defects, but larger injuries necessitate tissue donation, and there is a severe shortage of articular cartilage that can be donated for autografting. Microfracture and autologous chondrocyte implantation are the current treatment options that use cellular therapy for the repair of cartilage. However, the cartilage tissue that forms in the course of these treatments is not the functional hyaline cartilage, but rather fibrous cartilage, which is mechanically weaker and degenerates over time. Tissue engineering studies using biodegradable scaffolds and autologous cells are gaining importance as effective long-term treatment options for the postinjury production of hyaline cartilage. Such scaffold systems are designed to be biodegradable and bioactive, which allows them to induce new tissue formation in shorter periods of time. In this dissertation, peptide nanofibers mimicking glycosaminoglycan molecules, which are important constituents of cartilage extracellular matrix, are designed and the effectiveness of these materials in terms of chondrocyte differentation are tested under in vitro conditions. As a follow-up study to in vitro experiments, the capacity of bioactive peptide nanofibers to support cartilage regeneration is evaluated in the rabbit osteochondral defect model. Structural and mechanical properties of newly deposited cartilage are highly dependent on the quality and quantity of its extracellular matrix, which also has a major impact on the integration of replacement cartilage into the surrounding healthy tissue. Signals provided by bioactive peptide nanofibers to cells at the defect site can strongly alter the quality of the newly synthesized extracellular matrix. Consequently, we designed glycosaminoglycanmimetic peptide nanofibers that closely imitate the structure of the native cartilage extracellular matrix and demonstrated that these nanofiber networks are able to induce the synthesis of collagen II and aggrecan molecules, which are the main constituents of cartilage tissue, during chondrogenic differentiation.
Open Access
Diabetic wound regeneration using heparin-mimetic peptide amphiphile gel in db/db mice
(Royal Society of Chemistry, 2017) Senturk, Berna; Demircan, Burak M.; Ozkan, Alper D.; Tohumeken, Sehmus; Delibasi, T.; Güler, Mustafa O.; Tekinay, Ayse B.
There is an urgent need for more efficient treatment of chronic wounds in diabetic patients especially with a high risk of leg amputation. Biomaterials capable of presenting extracellular matrix-mimetic signals may assist in the recovery of diabetic wounds by creating a more conducive environment for blood vessel formation and modulating the immune system. In a previous study, we showed that glycosaminoglycan-mimetic peptide nanofibers are able to increase the rate of closure in STZ-induced diabetic rats by induction of angiogenesis. The present study investigates the effect of a heparin-mimetic peptide amphiphile (PA) nanofiber gel on full-thickness excisional wounds in a db/db diabetic mouse model, with emphasis on the ability of the PA nanofiber network to regulate angiogenesis and the expression of pro-inflammatory cytokines. Here, we showed that the heparin-mimetic PA gel can support tissue neovascularization, enhance the deposition of collagen and expression of alpha-smooth muscle actin (α-SMA), and eliminate the sustained presence of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in the diabetic wound site. As the absence of neovascularization and overexpression of pro-inflammatory markers are a hallmark of diabetes and interfere with wound recovery by preventing the healing process, the heparin-mimetic PA treatment is a promising candidate for acceleration of diabetic wound healing by modulating angiogenesis and local immune response. © 2017 The Royal Society of Chemistry.
Open Access
Effect of double growth factor release on cartilage tissue engineering
(2013) Ertan, A.B.; Yilgor P.; Bayyurt, B.; Çalikoǧlu, A.C.; Kaspar Ç.; Kök F.N.; Kose G.T.; Hasirci V.
The effects of double release of insulin-like growth factor I (IGF-I) and growth factor β1 (TGF-β1) from nanoparticles on the growth of bone marrow mesenchymal stem cells and their differentiation into cartilage cells were studied on PLGA scaffolds. The release was achieved by using nanoparticles of poly(lactic acid-co-glycolic acid) (PLGA) and poly(N-isopropylacrylamide) (PNIPAM) carrying IGF-I and TGF-β1, respectively. On tissue culture polystyrene (TCPS), TGF-β1 released from PNIPAM nanoparticles was found to have a significant effect on proliferation, while IGF-I encouraged differentiation, as shown by collagen type II deposition. The study was then conducted on macroporous (pore size 200-400μm) PLGA scaffolds. It was observed that the combination of IGF-I and TGF-β1 yielded better results in terms of collagen type II and aggrecan expression than GF-free and single GF-containing applications. It thus appears that gradual release of a combination of growth factors from nanoparticles could make a significant contribution to the quality of the engineered cartilage tissue. © 2011 John Wiley & Sons, Ltd.
Open Access
Sciatic nerve regeneration induced by glycosaminoglycan and laminin mimetic peptide nanofiber gels
(Royal Society of Chemistry, 2016) Mammadov, B.; Sever, M.; Gecer, M.; Zor, F.; Ozturk, S.; Akgun, H.; Ulas, U. H.; Orhan, Z.; Güler, Mustafa O.; Tekinay, A. B.
In the USA, 20 million patients suffer from neuropathy caused by peripheral nerve injuries, which costs approximately 150 billion annually. For longer nerve gaps and multiple injury sites, it is essential to use nerve guidance conduits for healthy pathfinding of regenerating axons. Here, extracellular matrix mimetic peptide nanofiber hydrogels were used for functionalizing guidance conduits to enhance neuronal regeneration in the distal stump of full transaction sciatic nerve injury in rats with functional repair. Conduits filled with heparan sulfate and laminin mimetic peptide nanofibers significantly improved electromyography response and promoted neuronal regeneration in a rat model of sciatic nerve defect. In addition, Schwann cells cultured on these nanofibers showed increased viability and significantly enhanced nerve growth factor (NGF) release. Overall, these results suggest that extracellular matrix mimetic peptide nanofibers present a promising treatment option for peripheral nerve injuries.
Open Access
Small functional groups presented on peptide nanofibers for determining fate of rat mesenchymal stem cells
(2014) Yaşa, Öncay
Glycosaminoglycans (GAGs) are negatively-charged, unbranched polysaccharides that play important roles in various biological processes and are vital for the regeneration of damaged tissues. Like other natural extracellular matrix components, glycosaminoglycans and proteoglycans show considerable variation in local concentration and chemical composition depending on tissue type. They are found in various connective tissues, including bone, cartilage and fat, and display strong water-binding capacity due to their negative charges. Mechanical characters of GAGs are heavily influenced by the degree and pattern of sulfation, which may greatly alter their viscoelasticity and physiological functions. Variations in GAG sulfation patterns are created principally through extracellular matrix modeling. Due to their extracellular matrix-organizing abilities, glycosaminoglycans are promising biomacromolecules for the design of new bioactive materials for tissue engineering and tissue reconstruction applications. In this study, we functionalized peptide amphiphile molecules with carboxylate and sulfonate groups to develop nanofibrous networks displaying a range of chemical patterns, and evaluated the effect of the chemical groups over the differentiation fate of rat mesenchymal stem cells. We demonstrate that higher sulfonate-to-glucose ratios are associated with adipogenesis, while higher carboxylate-to-glucose ratios resulted in chondrogenic and osteogenic differentiation of the rat mesenchymal stem cells.
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.