KULLANILAN FARKLI ÇÖZÜCÜLERİN İPEK FİBROİN-PVA KOMPOZİT SÜNGERLERİN YAPISINA OLAN ETKİSİ

İpek fibroini farklı formlarda elde edebilmek için (film, fiber, sünger vs. ), fibroinin uygun çözücüler içinde çözünmesi gerekmektedir. Bu işlem için farklı çözücüler kullanılmaktadır. Literatürde yer alan çalışmalardan çok azı, kullanılan çözücü sistemin, son ürünün yapısı üzerindeki etkilerini incelemiştir. Yapılan bu çalışma ile bu eksikliğin giderilmesi hedeflenmektedir. Bu nedenle, kullanılan farklı çözücülerin, elde edilen fibroin / Polivinilalkol (PVA) kompozit süngerlerin yapısı üzerine etkisinin araştırılması, bu çalışman ın temelini teşkil etmektedir. Elde edilen kompozit süngerlerin yara örtüsü olarak kullanılması hedeflendiğinden, yapılan bu çalışma, planlanan çalışmanın ilk aşaması olup, daha çok ön hazırlık aşamaların ı kapsamaktad ır. Bu çalışmada, fibroin/PVA kompozit yapılı süngerler, liyofilizasyon (dondurarak kurutma) yöntemi kullanılarak elde edilmiştir. Bu yöntem ile yüksek ve düzgün gözenekli ipek fibroin temelli süngerler üretilmiştir. Yapılan bu ön çalışmada, ilk olarak ipek fibroinin çözünmesinde kullanılan farklı çözücülerin, elde edilen malzemenin genel yapısını ve PVA ile oluşturduğu kompozit yapıya olan etkileri araştırılmıştır. Daha sonra, üretilen kompozit sünger yapılar; Taramalı Elektron Mikroskobu (SEM), Fourier Transform Infrared Spektroskopisi (FTIR), Termogravimetrik Analiz Cihazı (TGA) ve Diferansiyel Taramalı Kalorimetri (DSC) metotları kullanılarak karakterize edilmiştir. Kalsiyum Klorür (CaCl2)-Etanol-H2O den elde edilen kompozit sünger yapılar incelendiğinde ikincil yapın ın β sheet ağ ırlıklı olduğu görülmüştür. FTIR sonuçları, PVA ile karıştırıldıktan sonra Amid I ve Amid II bantlarının yerlerinde ve değerlerinde değişiklikler olduğunu göstermiştir. Bu sonuçlar, fibroin molekülleri ile PVA molekülleri arasındaki etkileşimin oldukça kuvvetli olduğunu göstermiştir. Lityum Bromür (LiBr) içerisinde çözünen ipek fibroin de ise, düzensiz (random coil) yapının ağırlıkta olduğu, kompozit oluşumu sırasında β tabakalarına (sheet) dönüşmediği görülmüştür ve bu da kristal yapının amorf yap ıya oranını ve termal kararlılığ ını etkilemektedir. Malzemelerin ısıl özellikleri TGA ve DSC kullanılarak analiz edilmiştir. Özet olarak, CaCl2-Etanol-H2O’dan oluşan sistem içinde çözülerek elde edilen fibroin çözeltisi, LiBr içinde çözülerek elde edilen fibroin çözeltileri ile karşılaştırıldığında, ikincil yapı konformasyonlarının ve morfolojilerinin farklılık gösterdiği ve ilk çözeltiden (CaCl2-Etanol-H2O) elde edilen fibroin yapıların PVA ile daha sağlam daha kararlı kompleks yapılar oluşturduğu gözlemlenmiştir.

THE EFFECT OF DIFFERENT SOLVENTS ON THE STRUCTURE OF SILK FIBROIN-PVA COMPOSITE FOAMS

To be able to obtain silk fibroin in different forms (film, fiber, sponge etc.), fibroin should be dissolved in suitable solvents. Different solvents are used for this process. Very few of the studies in the literature were investigated on the effects of the solvent system on the structure of the final product. This work aimed to fulfil this deficiency. For this reason, the main purpose of this work is to investigate the effect of different solvents on the obtained structure of fibroin / Polyvinyl Alcohol (PVA) composite sponges. Since this study’s final goal is to use the obtained composite sponges as a wound dressing, this presented work is the first part of the planned study that mainly consists of preliminary preparation steps. Fibroin / PVA composite sponges were obtained by using lyophilisation (freeze drying) method in this work. Silk fibroin based sponges with high porosity were produced by employing this technique. In this preliminary study, first the effects of different solvents that are used in the dissolution of silk fibroin on the general structure of the obtained material and the composite structures that are formed by mixing with PVA were investigated. Then, produced composite sponge structures were characterized by using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) methods. When the composite sponge structures, obtained in Calcium Chloride (CaCl2)-Ethanol-H2O, were examined, it was observed that the secondary structure was dominated mainly by β sheet. The FTIR results showed that the Amide I and Amide II bands had changes in their location and values after mixing with PVA. These results demonstrated that the interaction between fibroin molecules and PVA molecules is quite strong. The silk fibroin, dissolved in Lithium Bromide (LiBr), mainly consisted the random coil structures and the structure had not transformed into a β sheet conformation during the formation of the composites, which affected the ratio of the crystal structure to the amorphous structure and thermal stability of the composite sponges. The thermal properties of the material were analyzed using TGA and DSC. In summary, when the fibroin solution, obtained by dissolving fibroin in the solvent system of CaCl2-Ethanol-H2O, with the fibroin solutions, obtained by dissolving fibroin in the solvent system of LiBr are compared, it is found that their secondary structural conformation and morphologies were different and the fibroin structures that were obtained from CaCl2-Ethanol-H2O solvent system formed more stable and strong complexes with PVA.

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