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ÖgeInvestigation of mechanical properties of small caliber fibrous vascular grafts(Graduate School, 2023)Cardiovascular diseases remain the most common cause of mortality worldwide, resulting in the deaths of 17.9 million people in 2019. Furthermore, previous cardiovascular diseases are a significant risk factor for COVID-19-related complications and deaths. According to the World Health Organization, the number of deaths would increase by 24.5% by 2030. The most frequent type of cardiovascular disease is coronary artery disease, which necessitates a surgical procedure called bypass grafting that involves arterial replacement. In bypass surgery, an autologous vein or synthetic graft is used to restore a diseased blood vessel that has become damaged or clogged. However, autologous grafts pose significant challenges due to scarcity and difficulties in graft harvesting operations. On the other hand, commercial synthetic ones are also problematic to be used as smaller diameter vascular grafts (< 6 mm) due to poor patency rates, thrombogenicity, and compliance mismatches, as well as neointimal hyperplasia in the peri-anastomotic regions. The compliance mismatch between the native vessel and the rigid synthetic graft at the anastomosis sites results in low blood flow rates and turbulent blood flow in small-diameter grafts. These mechanical issues lead to thrombosis and luminal narrowing due to intimal hyperplasia, which results in poor long-term patency, together with the thrombogenicity of the scaffold material and a lack of endothelialization. In order to address the demand for suitable scaffolds that can be utilized in bypass procedures by using new materials and production processes, researchers have concentrated on building an alternative tissue-engineered small-caliber vascular graft that can imitate the native artery in all ways. There is currently no small-caliber biodegradable vascular graft that has reached commercial success, despite the fact that significant breakthroughs have been made in the research that has intensified in recent years. The vascular graft is supposed to give structural support and promote cellular activity for the body to generate its vessels. The fundamental difficulty with vascular tissue engineering is still creating a perfect vascular graft that can replicate the structural, biological, and mechanical characteristics of the native blood vessels and be used in place of the disabled blood vessel. In this context, morphology and cellular analysis are typically given top priority, whereas mechanical aspects are only briefly discussed. To improve the clinical performance of vascular grafts, expose physiological stresses, and prevent graft failure brought on by intimal hyperplasia, thrombosis, aneurysm, blood leakage, and occlusion, it is essential to create grafts with good mechanical qualities comparable to native vessels. The mechanical characteristics of scaffolds, such as compliance, burst pressure, nonlinear elasticity, modulus, and suture retention strength, must match those of the native tissues because even a slight mechanical mismatch between the graft and the native vessel can cause graft failure. The mechanical properties of the vascular grafts are significantly influenced by the material and design. In this thesis, a detailed literature review was carried out to understand the native blood vessel structure and to provide a broad and comparative overview of recent studies on the mechanical properties of fibrous vascular grafts, with an emphasis on the effect of structural parameters on mechanical behavior in the experimental part. The purpose is to shed light on the design parameters needed to maintain the mechanical stability of vascular grafts that can be used as a temporary and biodegradable backbone, allowing an autologous vessel to take its place. An experimental study is carried out to produce fibrous vascular scaffolds made out of various biopolymers and their combinations with different fiber orientations and constructions and assess their physical, morphological, and mechanical properties. The first experimental part of the thesis is a preliminary study that includes the production of planar and tubular scaffolds made of neat PCL and PLA and their blends with the PCL/PLA blending ratios of 90/10, 80/20, 70/30, 60/40, and 50/50 by using an open system electrospinning unit. PCL is a flexible biopolymer with a long biodegradation time, whereas PLA is a strong polymer with high brittleness, higher biocompatibility, and a faster biodegradation time than PCL. The reason for utilizing these polymers together is to combine their mechanical and biological advantages and eliminate their inadequacies. The effect of the polymers and collector type on the fiber morphologies, diameters, and orientations, sample thickness, as well as the mechanical properties was assessed. It was observed from the results that all the samples were successfully produced, and they all have distinctive morphologies with smooth and continuous fibers. The tensile stress and elongation results revealed that polymer composition is highly effective on the tensile properties. Neat PCL samples had considerable elongation value with 390% whereas PLA showed good tensile strength with 2.73 MPa. When the blended samples were observed, it was seen that the blending affected the mechanical properties negatively based on the blending ratio that was used because of the immiscible characteristics of the polymers. The addition of PLA gradually improved the tensile properties, while using PCL in higher amounts caused better elongation values in blended samples, which shows the importance of the selection of a suitable blending ratio. According to the results of the planar samples, the PCLPLA90 and PCLPLA80 samples can be selected as they have moderate stress and strain values among the blended samples. Also, the use of tubular collectors enables the production of scaffolds with desired construction. On the second part, the monolayer tubular vascular prostheses were produced in a closed electrospinning system by using two rotational speeds to achieve scaffolds with randomly distributed or radially oriented fibers. In addition to the neat and blended samples made of PCL and PLA, two more polymers were added to the production stage, which are PLCL and PLGA. As PLCL is the copolymer of PCL and PLA and thought of as a better candidate to be used instead of physically blended scaffolds to eliminate the mechanical failure caused by blending, it was also used in the vascular graft fabrication process. On the other hand, PLGA has good biocompatibility and faster biocompatibility with good mechanical properties, which make it a good option to be used in vascular applications. When the physical and morphological results were investigated, it was seen that in a closed system, it is possible to produce vascular grafts with the desired thickness levels. Fiber orientation was also observed from SEM images in the radial direction within the tubular samples produced by using a high collector speed. The tensile test was performed on all the tubular samples in longitudinal and radial directions to see the effect of polymer composition, fiber orientation, and test direction on the tensile properties of the specimens. Results revealed that the neat PCL scaffolds showed more flexibility than the neat PLA samples, and the neat PLA samples show higher tensile strength than the neat PCL samples in general. Also in blended samples, tensile stress and elongation values were improved in some cases depending on the blending ratio, such as in PCLPLA90 and PCLPLA80 specimens. Also, neat PLCL samples had both higher elongation and strength values than all neat and blended scaffolds, with some exceptions. Generally, when the PLA ratio is increased, the tensile strength improves gradually, whereas the elongation values decrease. The maximum tensile strength belonged to PLCL100_O in the radial direction with 12.12 MPa, whereas it showed its highest elongation in the longitudinal test direction with 832%. In addition, PLGA100_R showed higher strength than the samples made of PCL and PLA, with very limited elongation. The strength values of PLGA samples were really promising, as it is a rigid polymer. On the other hand, radial fiber orientation greatly contributed to the tensile stress values in the radial direction and the elongation values in all directions compared to the samples with randomly oriented fibers. Higher stress values were obtained in the direction of the orientation whereas higher elongation values were achieved in the direction without fiber alignment. On the other hand, a custom-designed test device was specifically designed for vascular graft specimens to measure their burst strength and compliance. When the burst pressure values were assessed, the best results were obtained from the vascular grafts made of PLGA and then PCL/PLA blends with radial fiber orientations. The addition of PLA results in an increment in burst pressures up to a certain limit of PLA ratio. PLGA100_O showed the highest burst pressure at 2889 mmHg. According to the compliance measurements made using three different physiological blood pressure ranges, the scaffolds with higher flexibility possessed better compliance values. Thus, the samples with randomly distributed fibers had the highest compliance results when compared with the samples consisting of radially oriented fibers. PLCL100_R demonstrated the highest compliance with 4.924 mmHg %/100 mmHg at a 50–90 mmHg pressure range as the most flexible biopolymer among the others. Finally, considering the previously obtained biological analysis results, bilayer vascular grafts were fabricated by combining monolayer scaffolds with the best mechanical properties to obtain a prosthesis that could mimic the topography of the natural artery. The inner layer was constructed from randomly distributed fibers, whereas the radially oriented fibers were included in the outer layer. PCL100_R and PCLPLA80_R monolayers were selected as the inner layers while PLCL_O was used in the outer layers of the bilayered grafts due to their appropriate mechanical advantages. Results indicated that although the samples had a delamination problem in some cases, they had improved mechanical advantages in the tensile and bursting testing processes. On the other hand, the compliance results were still sufficient and comparable with the native blood vessels. All the results that have been achieved in this thesis shed light on the examination of the mechanical properties of vascular grafts and contain significant information for vascular prostheses to be produced in further research. The bilayered grafts that will be constructed in the future studies will be designed by considering the results of the mechanical assessments of the samples that have been optimized by using PCL, PLA, PLCL, and PLGA within the scope of this thesis and the biological examinations. In the following process, it is aimed to switch to in-vivo studies with the most appropriate bilayer scaffold designs to be obtained and to study the biological process in an interdisciplinary manner.
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ÖgeDevelopment of textile-based resistive pressure sensing socks in diabetes mellitus for early detection of DFU(Graduate School, 2024-06-28)Today, millions of people suffer from diabetes that will last a lifetime. The energy necessary for people to continue their daily life activities is obtained from protein, carbonhydrates and fats. These basic nutrients need to be broken down into the smallest pieces in order to be absorbed. The most important of these nutrients are simple sugars called glucose. Cells contain glucose, which the human body needs, It makes it usable with the help of the hormone secreted by the organ called the pancreas. The name of this hormone is insulin. If this hormone does not work properly, the food taken cannot be used as energy. Diseases that occur as a result of a deficiency of the insulin hormone or not working properly are called diabetes. This disease can occur in people during childhood, or it can occur after the age of 20s and 25th depending on genetic reasons. The disease shows itself as Type 1 and Type 2 Diabetes. Since it is a disease that progresses in a very insidious and painless way, the disease may not be diagnosed for many years. Since Type 1 diabetes mostly occurs in childhood and youth, this disease is called juvenile diabetes in the literature. These patients have to take insulin hormone externally as a lifelong supplement. In our society, 10% of diabetes patients are Type 1. Type 1 diabetes is a disease that is included in the group of diseases called autoimmune diseases and continues throughout life. The immune system, which acts for an unknown reason, damages beta cells in the pancreas, which are responsible for insulin production. When this damage exceeds 80%, disease specifications emerge. The only rule in the treatment of type 1 diabetes patients is insulin therapy. In this type of diabetes, insulin injection is essential and plays a role in saving the patients' life. In addition to insulin injection, a healthy and regular diet, sports and education should be an invariable part of patients' life. In order to maintain these principles and personal care, they should pay maximum attention to these principles. It is essential for patients to keep blood sugar between acceptable levels, to prevent very serious complications such as hyperglycemia and hypoglycemia that may put the person's life at risk, and to provide and maintain ideal body weight and protein consumption, consumption of various foods, excess fiber in foods, consumption of simple sugars under the control of a dietitian and regular doctor appointments should not be interrupted. Exercise should be done regularly every day. In order for patients not to be exposed to advanced complications, they should first take all precautions for their own health. The other disease seen in diabetes patients is type 2 diabetes. Genetic and environmental factors play a role in type 2 diabetes patients. These patients have insulin resistance and insulin secretion abnormality. There are abnormalities in insulin secretion due to genetic factors. Inactivity and desk life trigger this disease as environmental factors. In addition, obesity, one of today's diseases, causes insulin resistance and as a result, diabetes is inevitable. As in Type 1 diabetes patients, Type 2 diabetes patients have to pay close attention to their nutrition, daily physical activity and blood sugar. The person should eat healthy and regularly, and avoid foods and drinks that will cause sudden rise and fall in blood sugar. The patient should also regularly measure blood sugar 6 times on an empty stomach and note the averages and not neglect the doctor's appointments. In both Type 1 and Type 2 diabetes diseases, diabetic coma, irreversible damage to vital organs, especially (silent and latent period of diabetes) and in cases where the patient does not receive adequate treatment or neglects the kidneys insidiously and without pain, in the more normal-high stages of diabetes. Bleeding due to intraocular vascular structure can lead the patient to blindness in a very short time. As a result of the deterioration of kidney functions, the patient may be sentenced to dialysis for life. Depending on the damage to the cardiovascular system, permanent damage may occur in the feet and hand limbs of the patients, and accordingly, these limbs must be cut off suddenly. Since the blood cannot go to all organs and limbs in the body in an equal and balanced way in diabetic patients, over time, excess pressure and numbness occur in areas with less blood flow, and accordingly the areas where numbness occurs should be surgically cut. The best example for this is the foot part of diabetic patients. Depending on the disease, the blood cannot reach every region equally on the soles and fingers of the foot and over time, numbness and pressure increasement occur in certain parts of the foot. If the person does not realize this situation in time the damaged tissue is removed by incision method in order to prevent the decay from progressing to other areas comes into play at this point. In the thesis study, it is aimed to carry out a study in order to make early diagnosis in diabetes patients by integrating switch mechanism that is pressure sensitive sensors under socks. The working principle of switch sensors is based on short-cut under pressure. The usage area of switch sensors is gradually expanding due to their advantages such as flexibility, accuracy of data, low energy use and sensor design. In terms of sustainability and ease, the use of switch sensors with parallel conductive layers seems more logical. In this thesis, 3 conductive layers were manufactured and they were separated with mesh fabrics. In the case of abnormal external pressure bottom conductive layers become active and short-cut occurs and in the case of lower external pressure top conductive layers touch each other and short-cut occurs. The data is transferred whereby conductive channels which is TPU coated in order to thwart short-cut during transmitting data from soft sensors to central unit. The resistive sensing mechanism has been adopted due to it is simple to manufacture and doesn't require any kind of dexterity or knowledge of making patterns. It is also overt that there will not be any defect which is derived from sock knitting machine and the budget to set up this system is pretty much lower when it is compared to sock knitting machines. When it is gathered up all these advantages, we can absurb that switch resistive sensing is also workable and effective approach in order to predict DFU before any possible amputation.
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ÖgeTekstilde ERP (enterprise resource planning) kullanımı ve var olan bir ERP yazılımının geliştirilmesi(Lisansüstü Eğitim Enstitüsü, 2024-07-01)Kurumsal kaynak planlama (ERP), işletmenin tüm kaynaklarını verimli/etkin şekilde kullanması için tasarlanmış bir sistemdir. ERP sistemleri, şirketlerin hedeflerine ulaşmasındaki temel süreçleri ve fonksiyonları birleştirir, iş uygulamalarının çoğunun entegre olarak yürütülmesini sağlar. Bu sistemler sayesinde işletmedeki bölümler arasında bilgi akışı olmakta ve iletişim sağlanmaktadır. Bununla birlikte tekstil sektörü birçok sektörden farklı bir ürün yapısına sahiptir. Örnek olarak konfeksiyon firmalarında sipariş mantığı ile çalışılmaktadır. Varyantlar, sezonlar, aksesuarlar, prosesler gibi standardize edilemeyen özellikleri bulunmaktadır. Bu nedenle sektörden bir firmanın ERP sistemi seçerken özelliklerine uygun bir yazılım seçmesi gerekmektedir. Bu çalışma denim üretiminde kullanılan bir ERP sisteminin sektörün gerekliliklerini karşılaması adına ERP modüllerindeki eksikliklerin iyileştirilmesi üzerine yapılmış ilk akademik çalışmadır. İstanbul merkezli, denim ve non-denim hazır giyim üretimi gerçekleştiren, sektörün önde gelen anonim bir firmasında çalışmalar yapılmıştır. Microsoft SQL veri tabanı kullanılmış olup, arayüz tasarım geliştiricide Delphi dili ve C# dili kullanılmıştır. Tespit edilen sorunlar sırasıyla, numunelerin fiziki olarak takibinin yapılamaması, kumaş toplarının farklı LOT ve özelliklerde üretime çıkışının yapılması, stok takibinin ve depo düzeninin sağlanamaması, fiziksel kimyasal test laboratuvarındaki testlerin sistemsel olarak bir kaydının tutulmamasıdır. Numune takibini sağlamak için süreçteki her aşamaya bir üretim hareketi tanımlanmıştır ve her aşamada bu hareketler okutularak sistemde tutulmuştur. Yanlış kumaş topu çıkışını engellemek için top rezervasyonu arayüzü tanımlanıp, topun siparişe rezervasyonu yapılmadan çıkışı engellenmiştir. Depolarda fiziki düzenin sağlanması ve stok takibinin yapılması için el terminali cihazı veri tabanına bağlanmıştır. Test verilerinin kaydı için iki arayüz oluşturulup müşterilerin isteklerine göre test seçimi sağlanmış ve sonuçlarının girilip otomatik geçti-kaldı sonucunun gösterildiği bir geliştirme yapılmıştır.
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ÖgeDesign and development of pva/hydrocortisone loaded xerogel nanofibrous mat for topical drug delivery(Graduate School, 2023)Textile materials have always been utilized in the medical field. The unique properties they offer, biocompatibility and versatility are the major reasons behind that. They can be found in applications ranging from a simple bandage to full on blood vessels. Nanofiber-based textile materials are textile materials known for their high surface area and interconnected porosity. Nanofiber- based textile materials can be fabricated with a variety of methods yet; the most dominant method is electrospinning. Furthermore, in the recent years there has been a rise of interest in different materials as well such as; aerogels. Aerogels are porous materials that have unique properties that make them good candidates for drug careering and releasing. Aerogels can be made of different materials such as polymers, biopolymers and metal oxides but the most common types of aerogels are silica, carbon and metal oxide aerogels. The process of synthesizing aerogel consists mainly of three stages; gelation, aging and drying. The process of drying aerogels affects the synthesized aerogel greatly as you can have three different types of aerogels by just using a different drying technique. Xerogel is one of the types of aerogels and it is achieved by drying aerogels at ambient pressure. This study aimed to design and develop a PVA/hydrocortisone loaded xerogel electrospun mat for topical drug delivery. The silica xerogel was synthesized using TMOS as a silica precursor, Ammonium hydroxide as a catalyst and Methanol as a co-solvent. The xerogel was ball-milled into fine powder and had its surface area, pore size and volume analyzed. In addition to that, hydrocortisone was loaded into three different samples; one consisting of only xerogel, the second of only PVA nanofibrous mat and the third consisting of both xerogel and PVA nanofibrous mat. In vitro drug release analysis was carried out for all of these samples. PVA was chosen for its biocompatible properties and stability. SEM and EDAX analyses were carried out to investigate the surface of the fibers and elements existing in the samples respectively. In addition to that, FTIR analysis was performed to identify the different materials making up the nanofibrous mats. The synthesized silica xerogel had a surface area of around 505 m²/g, pore size of around 3.8 nm and a pore volume of 0.48 cm³/g. SEM images showed the hydrocortisone loaded xerogel inside the PVA nanofibrous mat and the EDAX analysis confirmed the existence of silicone in the samples due to the existence of silica xerogel as well as a high concentration of Carbon due to hydrocortisone. The hydrocortisone loaded xerogel showed a slow sustained drug delivery release behavior and around 69.3% of the loaded hydrocortisone was released in 25 days. The PVA/xerogel/hydrocortisone nanofibrous mat showed a similar drug release behavior with a release of around 79.2% of the hydrocortisone initially loaded with PVA was released in just 30 minutes. Demonstrating a conventional or retarded drug release behavior. Meanwhile, the PVA/hydrocortisone electrospun mat showed a completely different drug release behavior. Around 98.55% of the hydrocortisone initially loaded into the PVA. In conclusion, Silica xerogel as a drug carrier was successfully synthesized. It was loaded with hydrocortisone. Hydrocortisone loaded silica xerogel drug release was investigated as well as PVA/xerogel/hydrocortisone and PVA/hydrocortisone. The result of these three different sample types were collected and compared. Both hydrocortisones loaded xerogel and PVA/xerogel/hydrocortisone showed a slow sustained drug release behavior. Meanwhile PVA/hydrocortisone showed a retarded drug release behavior. These results suggest the capability of PVA/hydrocortisone load xerogel mat to work as a sustained/controlled topical drug delivery carrier.
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ÖgeDevelopment of a novel drying algorithm for reducing dimensional change on cotton textiles during tumble drying(Graduate School, 2023-01-20)With the development of technology, the need for drying machines, which entered our lives, is increasing day by day as people are more involved in working life. People who want to save time and space and want to spend less effort for washing-drying processes are more attracted to this machine. Although the dryer appears to be a useful product in theory, it is a product that people use hesitantly. The main reason for this feeling is that drying machines shrink certain types of textiles, especially cotton-containing textiles. Within the scope of this study, a survey was conducted in order to determine the main source of the problem and to get to know the laundry habits of the users in daily life. According to the results of the survey, the shrinkage problem was determined and a phased experiment plan was designed by procuring fabric samples to simulate the textile products that the users most frequently observed shrinkage in daily life. Drying machines of different brands and models specified in the questionnaire were purchased and detailed algorithm analysis and shrinkage tests were applied. This study was carried out as a preliminary study and as a result, it was seen that there was no obvious difference between the shrinkage rates of the dryers available in the market, and all of them caused shrinkage at similar rates. It has been determined that slow drum rotation and high drum inlet temperature are the parameters that partially affect the shrinkage positively. Then, the test plan was designed considering the user conditions and the ½ Fractional Factorial Design of Experiment (DOE) study was planned. All data obtained as a result of experimental design tests and preliminary study were collected to form a mathematical model. The mathematical model was developed using the R program. By feeding 111 test data directly to the model, it is aimed to predict the shrinkage regardless of the dryer brand and model. The created model can make predictions with an accuracy rate of 97.5%. While creating the mathematical model, the importance and degree of influence of the parameters added to the model were determined and it was determined that the most important parameter affecting the shrinkage was the drum speed and drying time. Before the algorithm was designed, the shrinkage rates of the test samples were measured at different capacities periodically every 20 minutes in order to understand the development of shrinkage in the dryer and its relationship with humidity. By graphing the obtained data, it has been determined that there is a point where shrinkage gives the best results from the beginning of drying. This point is called the "Critical Moisture Point". In the periodic follow-up tests, it was determined that cotton textiles were not affected by any mechanical action and did not show shrinkage until the critical moisture point. On the contrary, it has been determined that when the textile, which comes from the washing machine with a certain amount of shrinkage, is put into the dryer, it releases itself and expands in size until it reaches the critical moisture point. It has been observed that when drying is continued after the critical moisture point, the textile starts to shrink and shrinks until the drying is complete. By combining the findings obtained as a result of all the experiments, an algorithm was designed to reduce the shrinkage rate during tumble drying of cotton textiles. Since the most important criterion in the algorithm design is the drum rotation, various iterations have been made by constructing drum stop and rotation durations at low speed and high speed. The purpose of the design is providing minimum mechanical drum movement. After drying in the 2800 RPM configuration until the critical humidity level, the configuration where the drum is slowed down to 1800 RPM and rotated for 2,5 minutes, then stopped for 7,5 minutes gives the lowest shrinkage rate among all trials. In order to ensure homogeneity and faster drying in the determined algorithm design, the system was supported with an additional heater. In the preliminary studies and as a result of the DOE tests, since the drying time directly affects the shrinkage, the shrinkage rate is further improved with the addition of an additional heater. While the lengthwise shrinkage rate of the reference Cotton Economic program was 9,2% in the knitted test sample and 2,1% in the woven test sample, the lengthwise shrinkage rate was measured as 6,6% in the knitted test sample and 1.6% in the woven test sample after the innovative algorithm design was developed. As a result of the new algorithm design, the lengthwise shrinkage rate has been improved by 28% in knitted textiles and 24% in woven textiles.