Yüksek şişme kapasitesine sahip hidrojel ve nanolif yara örtülerinin geliştirilmesi = Development of hydrogel and nanofiber wound dressings with high swelling capacity

Abstract

The skin, which makes up approximately 20% of the body's total mass and protects the organism from the external environment by covering it, is the organ responsible for maintaining the body's homeostasis. The skin consists of stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum basal; dermis, and hypodermis layers from the outside to the inside. Wounds and burns may occur on the skin for reasons such as accidents, surgical operations, traumas, electricity, chemicals, and radiation. If the wound heals within the first three months from the formation of the wound, the wound is considered acute, while if it lasts longer, it is called a chronic wound. Wound healing physiology consists of four intertwined stages. These stages are hemostasis, inflammation, proliferation, and remodeling. During the hemostasis phase, platelets migrate to the injured tissue and stop bleeding. In the inflammation stage, neutrophils protect the injured tissue against microorganisms. In the proliferation and remodeling stages, growth factors are effective and the extracellular matrix regains its integrity. There are customized wound dressings depending on the cause and type of wound. Alginate wound dressings absorb exudate with their high absorption capacity and comfort the patient. Hydrocolloid wound dressings have biodegradable properties suitable for wounds and burns. Hydrogel wound dressings allow gas inflow and outflow thanks to their porous structure. Foam wound dressings easily grasp the wounded tissue with their flexible structure. Nanofiber wound dressings accelerate tissue repair by acting as an extracellular matrix. In addition, cell scaffolds that accelerate three-dimensional tissue repair, which is one of the tissue engineering applications, support the healing of wounded tissue by accelerating cell proliferation with the combined use of natural and synthetic materials. Hydrogels are cross-linked three-dimensional polymeric network structures and various methods can form cross-bonds in hydrogels. These generally include chemical bonding techniques based on the Schiff base formation technique. Chemical cross-linking is preferred when designing a polymeric matrix structure with high mechanical strength. However, most chemical cross-linking materials exhibit toxicity. In addition to chemical cross-linking techniques in biomedical applications, physical cross-linking methods come to the fore for hydrogels. Physical cross-linking for hydrogels is directly related to the molecular structure of the hydrogel polymer, while physical cross-linking can be supported by the crystallization method. The crystallization method involves the freezing and thawing cycles of the hydrogel and the ice crystals that form bring the polymer chains closer together. Various techniques are used in nanofiber production, including drawing techniques, template synthesis methods, phase separation techniques, self-assembly, and electrospinning. Drawing techniques are usually used in laboratory settings, while electrospinning is generally preferred because it allows continuous production and is compatible with a wider range of polymer types. Electrospinning has various methods, such as mixture electrospinning (also known as conventional electrospinning), co-electrospinning, gas jet electrospinning, and centrifugal electrospinning. In general, the electrospinning setup consists of three main components: a power source, a syringe pump, and a collector. Approximately two kilovolts of power per centimeter are required for the distance between the syringe needle tip and the collector. The applied power transforms the polymer solution at the needle tip from a droplet to a triangular form, where surface charges are effective. The changed droplet form is called the Taylor cone. The formation of the Taylor cone is followed by the formation of a liquid jet and the transition to the spinning zone (Whipping instability region). The spinning movement is the process of removing the solvent from the polymer solution and the accumulation of dry homogeneous fibers in the collector. The methodology used in this thesis involved blend electrospinning, resulting in the generation of fibers with a random configuration. The resulting irregular pore structure is considered suitable for various biomedical applications. In this thesis, polyvinyl alcohol and carboxymethyl cellulose-based hydrogels were combined with different cross-linking ratios. These hydrogels, in which synthetic polymer and polysaccharide groups are used together, are designed to be equivalent to the epidermis and dermis layers of the skin. The hydrogel selected as the epidermis equivalent was prepared with polyvinyl alcohol: carboxymethyl cellulose 1:1 ratio and citric acid, a natural crosslinker, was added as 20% of the total polymer weight. The density of the crosslinks resulted in a tight polymeric network and the porosity ratio of the hydrogel was determined as 42.529%. In addition, the gelation ratio was determined as 45.33%. The water retention capacity of the epidermis equivalent hydrogel is higher than the other hydrogels prepared, due to the increase in cellulose. The dermis equivalent hydrogel was prepared with polyvinyl alcohol: carboxymethyl cellulose 4:3 ratio and the porosity ratio was 63.722%. The dermis equivalent hydrogel has pore sizes ranging from 2.244 to 73.539 μm. This hydrogel exhibited a swelling capacity of approximately 15 times its dry weight. Nanofiber mats consisting of various combinations of polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, polyethyleneimine, and polymethyl methacrylate polymers were produced by electrospinning technique. The production process of these polymers was optimized by the electrospinning technique. In the optimization process, attention was paid to parameters such as molecular weight of polymers, viscosity of polymer solution, solvent volatility; syringe diameter, applied voltage, and distance between syringe tip and collector. The minimum nanofiber diameter of the polyvinyl alcohol mat was recorded as 43 nm and the maximum nanofiber diameter was 318 nm, and these are beaded nanofibers. The standard deviation of the nanofiber diameters of the polyvinyl alcohol mat was calculated as 53 nm. The nanofiber diameters of the polyvinyl alcohol/carboxymethyl cellulose composite mat were in the range of 93 nm and 249 nm. The nanofiber diameters of the polyvinylpyrrolidone mat were in the range of 499 nm and 2.447 μm. The addition of polyethyleneimine to the polyvinylpyrrolidone polymer solution resulted in wet nanofibers, similar to the literature. The polymethylmethacrylate nanofiber mat contained nanofibers with a minimum diameter of 1.777 μm and a maximum diameter of 3.107 μm, and the fibers had a porous structure. In further studies, polyvinyl pyrrolidone nanofiber mat was cut to 1 cmx1 cm and added to the hydrogel solution. The cell scaffold was frozen at -58°C for 48 hours and then freeze-dried. The internal structure of the cell scaffold prepared by the freeze-drying technique attributes a rough structure suitable for the attachment of mammalian cells. The chemical structure of the cell scaffold was examined by FT-IR characterization and it was concluded that the nanofiber mat was integrated into the cell scaffold. This thesis presents the development of hydrogels characterized by varying porosity rates, employing both chemical and physical cross-linking techniques. Additionally, nanofiber dressings derived from biopolymers and a composite cell scaffold integrating these two elements have been created. The products developed in this study exhibit considerable potential to enhance patient comfort throughout the processes of wound healing and tissue repair.