(REFEREED RESEARCH) EFFECTS OF DIFFERENT STERILIZATION METHODS ON POLYESTER SURFACES FARKLI STERİLİZASYON YÖNTEMLERİNİN POLİESTER YÜZEYLER ÜZERİNE ETKİLERİ Şebnem DÜZYER1, Serpil KORAL KOÇ1, Aslı HOCKENBERGER1, Elif EVKE2, Zeynep KAHVECİ2, Agah UĞUZ3 * 1 Uludağ University, Department of Textile Engineering, Bursa, Turkey 2 Uludağ University, Department of Histology & Embryology, Bursa, Turkey 3 Uludağ University, Department of Mechanical Engineering, Bursa, Turkey Received: 17.07.2013 Accepted: 03.10.2013 ABSTRACT The aim of this study is to investigate the effects of different sterilization methods on polyester surfaces. Therefore, ethylene oxide (EO), autoclave (AU) and ultraviolet (UV) sterilization methods were performed on two groups of polyester surfaces. In the first part, the effects of different sterilization methods on polyethylene terephthalate (PET) nanofibers produced by electrospinning with different concentrations were investigated. In the second part, the effects of different sterilization methods on PET fabrics were investigated. The effects of the different sterilization methods on surface properties of PET surfaces were examined by scanning electron microscope (SEM) studies and contact angle measurements. The changes in mechanical properties were investigated by Instron studies. It was seen that different sterilization methods affected the nanofibers significantly depending on the polymer concentration. This effect was less clear for the PET fabrics. It was concluded that UV sterilization gave less damage to the nanofibers. Key Words: Sterilization, Electrospinning, Nanofiber, Polyethylene terephthalate, Characterization. ÖZET Bu çalışmanın amacı farklı sterilizasyon yöntemlerinin polyester yüzeyler üzerine etkilerini incelemektir. Bu amaçla, iki grup polyester yüzey üzerine etilen oksit (EO), otoklav (AU) ve ultraviyole (UV) sterilizasyon yöntemleri uygulanmıştır. İlk kısımda, farklı konsantrasyonlarda elektro çekim (elektrospinning) yöntemi ile üretilen polietilen tereftalat (PET) nanolifler üzerine farklı sterilizasyon yöntemlerinin etkisi araştırılmıştır. İkinci kısımda, PET kumaş üzerine farklı sterilizasyon yöntemlerinin etkileri incelenmiştir. Farklı sterilizasyon yöntemlerinin yüzey özellikleri üzerine etkileri taramalı elektron mikroskobu (SEM) ve temas açısı ölçümleri ile incelenmiştir. Mekanik özelliklerdeki değişiklikler Instron çalışmaları ile incelenmiştir. Polimer konsantrasyonuna bağlı olarak, farklı sterilizasyon yöntemlerinin nanolifleri belirgin olarak etkilediği görülmüştür. Bu etki PET kumaşlar için daha azdır. UV sterilizasyon yönteminin nanoliflere en az hasarı verdiği sonucuna varılmıştır. Anahtar Kelimeler: Sterilizasyon, Elektrospinning, Nanolif, Polietilen tereftalat, Karakterizasyon. Corresponding Author: Aslı Hockenberger, sengonul@uludag.edu.tr, Tel: +90 224 294 20 44, Fax: +90 224 294 19 03 1. INTRODUCTION human body, such as scaffolds, fungi, bacteria (2,3). This process can implants and wound dressings. be either physical or chemical and Today’s one of the most important Therefore, sterilization and disinfection sometimes both, depending on the issue in health care is microorganisms of the equipment and materials used in type of the microorganisms and the which are spread from patient to surgery and hospitals play key role (1). type of the material used in surgery patient by many ways such as the and other materials used for patient equipment used in surgery, staff and In literature, sterilization is defined as care. other materials used for patient care. the destruction or removal process of There are many textile materials that all forms of microbial life present on Etyhlene oxide and autoclave can be used inside or outside of the the surface, such as microorganisms, sterilizations are the most commonly TEKSTİL ve KONFEKSİYON 23(4), 2013 319 used methods in hospitals. Ethylene the solution evaporates and leaves a Uludag University, Textile Engineering oxide can easily diffuse into the dry fiber on the collector surface (6-7). Department (Bursa, Turkey). material to be sterilized and is effective These nonwoven surfaces consist of at low temperatures. However, it nanofibers find many applications in The jet flows upward from the surface remains ethylene oxide residues and medical. Since these materials have to of a pendant drop of fluid toward a the unstable three-membered ring of be sterilized before application, most rotating drum (Figure 1). Table 1 the ethylene oxide can react with appropriate method has to be chosen shows the spinning parameters of the various functional groups including in order not to give any damage to the produced nanofibers. All the sulfhydryl, amino, carboxyl and material properties. experiments were carried out in air at hydroxyl groups of proteins and room conditions. nucleic acids (4). Considering these conditions, the aim of this study is to investigate the Autoclave sterilization can be used as effects of different sterilization an alternative method to the ethylene methods on electrospun polyester oxide sterilization. It involves high nanofibers and polyester fabrics. temperature, steam and pressure in Since, PET surfaces can be used in the process. Therefore, the the medical field as nanofiber mats or disadvantage of the process is the woven fabrics depending on the hydrolysis of the polymer during application area, the effect of ethylene sterilization (4). oxide (EO), autoclave (AU) and An alternative to those methods ultraviolet (UV) sterilization methods summed up below can be ultraviolet were investigated in both forms. From sterilization since it does not involve this point of view, this study consists of any heat or mechanical treatment and two parts. In the first part, the effects of is also eco-friendly. different sterilization methods on polyethylene terephthalate (PET) Polyethylene terephthalate (PET) is a nanofibers produced by linear polymer and is widely used in electrospinning with different Figure1. Electrospinning setup medical applications such surgery concentrations were investigated. In sutures, medical gowns, hospital the second part, the effects of different The surface morphologies of the sheets in the form of yarns and fabrics sterilization methods on PET fabrics fabrics and the nanofibers sterilized by because of its characteristics including were investigated. different methods were evaluated by a biostability, non-allergenic and non- Carl Zeiss Evo 40 (Uludag University, toxic properties (5). Bursa,TURKEY) and a JEOL 840JXA 2. MATERIALS AND METHODS model scanning electron microscopes With arising applications of nanofibers, (TUBITAK MAM, Gebze-TURKEY). PET nanofibers can also be used in 2.1. Materials medical applications such as scaffolds The contact angle of the fabrics and or drug delivery systems in the form of In this study commercially available electrospun nanofiber mats were nanofiber mats. Among various PET pellets and plain weave 100% measured using a KSV-The Modular methods, electrospinning is one the polyester (PET) fabric were used. PET CAM 200 contact angle measurement most commonly used method to solutions with different concentrations system (Uludag University, Bursa- produce nanofibers in recent years (10, 15 and 20 wt.%) were prepared by TURKEY). A distilled water drop was since it is simple and allows a wide the dissolution of PET pellets in dispersed on each sample using a range of polymers to electospun. The trifluoroacetic acid (TFA) (50 wt.%) micropipette; the image of each drop method involves using electrical and dichloromethane (DCM) (50 wt.%) was captured by the camera charges to produce nanofibers. In the solvents. All chemicals were connected with a computer based electrospinnnig process a high voltage commercially available from Sigma- image capture system. The images is applied to the polymer solution or Aldrich and used as received without were captured as quickly as possible melt held at the tip of a capillary. When any further purification. after water droplet was placed onto the the voltage overcomes the surface sample surface, and photographed in tension of the polymer solution, a 2.2. Methods less than 1 s. charged polymer jet ejects from the tip PET nanofibers were produced by an and moves towards to the charged electrospinning device (Inovenso collector. During the travel of the jet, NanoSpinner24) in the Laboratories of Table 1. Electrospinning parameters of nanofibers Concentration Voltage Distance (mm) Flow Rate (ml/h) Collector Speed (wt.%) (kV) (rpm) 10 10 10 1 250 15 10 10 1 250 20 10 10 1 250 320 TEKSTİL ve KONFEKSİYON 23(4), 2013 Mechanical characteristics of the PET III (4 min.)- Sterilization (15 min.)- section became more uniform. fabrics and nanofiber mats were Drying (10 min.)- Vacuum IV (4 min.) Although thicker fibers were produced evaluated by Instron Universal Testing from 20% wt. solution, fiber diameters Machine (Model No. 4301) in the 3. UV sterilization; The samples were were mostly uniform along the fiber Laboratories of Uludag University, first rinsed with ethylene alcohol and length. Textile Engineering Department then with phosphate buffered saline (Bursa, Turkey). (PBS) solution 3 times. Afterwards, the Different sterilization methods made samples were sterilized in a laminar significant changes on the surfaces of Sterilization Methods: Before cell flow sterile cabinet (Thermo, Hera the nanofibers. Among all sterilization culture studies, fabrics and nanofibers guard, model HPH) under UV light for methods, UV method gave less should be sterilized. Although there 1 hour. The procedure was repeated damage to the surfaces for all are many researches about for both sides of the samples. concentrations and EO sterilization sterilization of fabrics, there isn’t affected the surfaces the most. This enough information about sterilization may be attributed to the unstable of nanofiber mats. Therefore, most 3. RESULTS AND DISCUSSION three-membered ring of ethylene oxide common sterilization methods namely; as it was reported in literature [4]. For ethylene oxide (EO), autoclave (AU) 3.1 PET Nanofiber Mats the nanofibers produced from 10% wt. and ultraviolet (UV) sterilizations were The morphology of the nanofiber mats solution, agglomeration of the fiber applied to the nanofiber mats were investigated by SEM studies bundles was observed with EO produced from different concentrations (Figures 2-4). Nanofibers formed sterilization. For the nanofibers of PET. All the sterilizations were nonwoven surfaces with different produced from 15% wt. solution, the carried out according to the standard diameters and were placed randomly effect of ethylene oxide sterilization procedures used in the sterilization in the nanofiber mat depending on the was quite decreased; fiber uniformity unit of the Medical Faculty of Uludag polymer concentration. With the was disturbed along the length. For the University. increasing polymer concentration, nanofibers produced from 20% wt. 1. Ethylene oxide sterilization: PET nanofibers with larger diameters and solution, effect of EO sterilization was fabric and nanofiber mats were treated fewer beads were produced because less intense compared to the by ethylene oxide for 4 hours at 55°C. of the increasing viscosity of the nanofibers produced from 10% wt. After treatment, samples were left at polymer solutions. Table 2 shows the solution. For autoclave sterilization room conditions for 4 hours. diameter distribution and coefficient of which includes high temperature and variation (CV) of the nanofibers. SEM pressure, diameter along the fiber 2. Autoclave sterilization: The samples images also showed that PET length was not uniform in lower were sterilized in a Class B type nanofibers were not exactly aligned in concentrations (10% wt. and 15%wt.). autoclave (Dentsan) The procude was the mat and PET nanofibers As a result, stiffer handle was as follows: electrospun from 10% wt. solution had obtained. Moreover, as the fiber diameter decreased, the effect of 121°C – 1.1 bar (65 min.) - Vacuum I a non-uniform cross-section along the (4 min.)- Vacuum II (4 min.)- Vacuum fiber length. With the increasing sterilization method on the fiber polymer concentration, the fiber cross- surface was more pronounced. Figure 2. SEM micrographs nanofibers produced from 10% wt. PET solution, a) non-sterilized, b) EO, c) AU, d) UV sterilized, respectively Figure 3. SEM micrographs of nanofibers from 15% wt. PET solution a) non-sterilized, b) EO, c) AU, d) UV sterilized, respectively TEKSTİL ve KONFEKSİYON 23(4), 2013 321 Figure 4. SEM micrographs of nanofibers produced from 20% wt. PET solution, a) non-sterilized, b) EO, c) AU, d) UV sterilized, respectively. Table 2. Diameters of the nanofibers Material (PET) Diameter (µm) CV (%) 10% wt.(non-sterilized) 0.66 46.97 10% wt.(EO sterilized) 0.91 20.88 10% wt. (AU sterilized) 0.94 34.47 10% wt. (UV sterilized) 0.66 45.76 15% wt. (non-sterilized) 0.87 27.59 15% wt. (EO sterilized) 1.88 42.55 15% wt. (AU sterilized) 1.46 21.37 15% wt. (UV sterilized) 1.34 25.37 20% wt. (non-sterilized) 2.36 27.80 20% wt. (EO sterilized) 2.92 77.81 20% wt. (AU sterilized) 2.33 37.39 20% wt. (UV sterilized) 2.48 16.61 Contact angle of the surfaces are one of the most important properties in order to understand the surface characteristics of the fibers like adhesion, wettability and absorption. Table 3 shows the contact angles of the nanofiber mats. Table 3. Contact angles of the nanofiber mats Material (PET) Contact Angle (°) 10% wt.(non-sterilized) 132.71 10% wt.(EO sterilized) 122.90 10% wt. (AU sterilized) 127.41 10% wt. (UV sterilized) 97.05 15% wt. (non-sterilized) 140.02 15% wt. (EO sterilized) 122.67 15% wt. (AU sterilized) 124.12 15% wt. (UV sterilized) 115.21 20% wt. (non-sterilized) 141.71 20% wt. (EO sterilized) 109.02 20% wt. (AU sterilized) 136.12 20% wt. (UV sterilized) 112.53 For nanofiber mats, the results show sterilization. A decrease in contact PET solutions gave the highest that contact angle values change angles after UV sterilization was modulus and lowest elongation at depending on the polymer recorded. This decrease did not follow a break. Young modulus and the concentration. As the fiber diameter regular regime with the increasing elongation values of the nanofiber decreases, the nanofiber mats become polymer concentration and it was not a mats were changed with different super hydrophobic. Different significant change. sterilization methods. This change was sterilization methods also affect the more significant especially with surface properties of the nanofibers. In order to understand the mechanical autoclave sterilization. AU sterilization The contact angle values were behavior of the PET nanofiber mats, resulted in a decrease in both modulus decreased with the different sterilization tensile tests were performed. The and elongation at break values. The methods. It was seen that there was a results are given in Table 4. decrease in modulus was attributed to decrease in contact angles with UV Nanofibers produced from 20% wt. the stiffer structure of the surfaces. 322 TEKSTİL ve KONFEKSİYON 23(4), 2013 Table 4. Tensile results of nanofiber mats Material Young Modulus (MPa) Elongation at Break (%) 10% wt.(non-sterilized) 137.4 104.68 10% wt.(EO sterilized) 218.1 99.12 10% wt. (AU sterilized) 125.7 36.83 10% wt. (UV sterilized) 132.8 121.72 15% wt. (non-sterilized) 154.7 99.35 15% wt. (EO sterilized) 148.7 62.86 15% wt. (AU sterilized) 79.68 32.08 15% wt. (UV sterilized) 124.8 84.87 20% wt. (non-sterilized) 224.1 55.95 20% wt. (EO sterilized) 222.5 53.37 20% wt. (AU sterilized) 85.3 23.12 20% wt. (UV sterilized) 219.6 78.52 3.2 PET Fabrics The structure of the PET fabrics sterilized by different methods was investigated by SEM studies. Figure 5 shows the micrographs of the single fibers and Figure 6 shows the SEM micrographs of the fabrics. SEM images show that, different sterilization methods didn’t make any significant change on the surface of the PET fabrics. Figure 5. SEM micrographs of single fiber of PET fabric sterilized by different methods, a) non-sterilized, b) EO, c) AU, d) UV sterilized, respectively Figure 6. SEM micrographs PET fabric sterilized by different methods, a) non-sterilized, b) EO, c) AU, d) UV sterilized, respectively Results of the contact angle measurements are given in Table 5. The highest contact angle was observed with UV sterilization. Table 5. Contact angles of the PET fabric sterilized by different methods Material Contact Angle (°) non-sterilized fabric 54.71 EO sterilized fabric 69.23 AU sterilized fabric 77.28 UV sterilized fabric 115.19 Instron tests were also performed on PET fabrics sterilized with different sterilization methods. Table 6 shows the Young modulus and elongation at break values of the fabrics. Young modulus increased and the elongation at break decreased with different sterilization methods. TEKSTİL ve KONFEKSİYON 23(4), 2013 323 Table 6. Tensile results of PET fabrics sterilized by different methods Material (PET) Young modulus (MPa) Elongation at Break (%) non-sterilized fabric 358.34 31.97 EO sterilized fabric 429.14 23.59 AU sterilized fabric 428.64 26.45 UV sterilized fabric 422.38 27.13 4. CONCLUSION became more uniform and thicker For PET fabrics, Young modulus Conventional PET fabrics and fibers were obtained. Among all increased and the elongation at break nanofibers are widely used in many sterilization methods, UV method gave decreased with different sterilization medical applications. PET fabrics are less damage to the surfaces for all methods. mostly used as hospital sheets and concentrations and EO sterilization It is crucial to choose the most surgical gowns, while PET nanofibers affected the surfaces the most. For can be used as implants, scaffolds or PET fabrics, it was concluded that appropriate method as they affect both mechanical and surface properties. In drug delivery systems. In order to use sterilization methods did not have a this study, UV sterilization method is these materials in medical significant effect on surface properties. suggested since it is a suitable applications, all must be sterilized The contact angle values of both sterilization for nanofiber surfaces. otherwise microorganisms may cause nanofiber mats and fabrics changed deleterious effects. Understanding the with the different sterilization methods. ACKNOWLEDGEMENTS effects of sterilization is very beneficial For nanofiber mats, it was seen that to choose the most appropriate there was a decrease in contact This study is a part of the PhD thesis method. Therefore SEM studies, angles with UV sterilization which did of the first author. The study is contact angle measurements and not follow a regular regime with the supported by The Scientific and mechanical analysis were performed increasing polymer concentration. For Technological Research Council of on nanofiber mats and fabrics the sterilized fabrics, the highest Turkey (Project number: 110M793) sterilized by EO, AU and UV methods. contact angle was observed with UV within the COST ACTION MP 1206 sterilization. "Electrospun Nano-fibres for Bio For nanofiber mats, SEM images Inspired Composite Materials and showed that PET nanofibers were not Nanofibers produced from 20% wt. Innovative Industrial Applications". exactly aligned in the mat and had a PET solutions gave the highest non-uniform cross section along the modulus and the lowest elongation at fiber length at lower concentrations. break. It was also seen that the With the increasing polymer modulus and the elongation at break concentration, the fiber cross-section decreased with the AU sterilization. REFERENCES 1. Nagaraja, N. A., 2011, ”Introduction to Central Sterile Supply Department”, Hospital Sterilization, Prem Anand Nagaraja, Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India, pp. 1-8 2. Block, S. S., 2001, “Definition of Terms”, Disinfection, Sterilization and Preservation, Seymour S. Block, Lippincott Williams & Wilkins, Philadelphia, USA, pp. 19-28 3. Sykes, G., 1965, “Introduction: Historical, terminology”, Disinfection and Sterilization, G. Skykes, Pitman Press, Britain, pp. 3-9 4. Nair, P. 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