Highly water-absorbing silk yarn with interpenetrating network via in situ polymerization
Introduction
Silk is a well-known natural protein fiber that has been used in textile industry for thousands of years. It is mainly consisted of sericin and fibroin. The sericin acts like a glue to cement two fibroin fibers together during cocoon formation so as to protect the growing worm [1]. The fibroin contains mainly four types of amino acids: alanine, glycine, serine, and tyrosine, forming the anti-parallel β–sheet structure (silk II) predominantly in the fiber core [2], [3]. Silk has many desirable biological properties such as biodegradability, good oxygen and water vapor permeability, and minimal inflammatory reaction [4], [5], [6]. Thus, it has been widely studied as artificial ligament [7], [8], bone tissue scaffolds [9], and wound healing materials [10], [11]. However, silk also has several drawbacks such as wrinkling, photo-yellowing, and especially low water retention [12], [13]. Although silk has a smooth surface with many hydroxyl groups to adsorb water rapidly, it cannot retain water that highly affects its comfort and limits its end uses. Therefore, modification of silk with added features is advantageous to widen its applications.
To impart desirable properties to silk fibers without damaging them and deteriorating their fundamental properties, an alternative approach is to modify their surface [14], [15]. S. Periyasamy et al. applied the physical technique vacuum ultraviolet irradiation on fiber surface to increase its surface roughness and hence enhance its wettability and wickability [16], [17]. A more permanent approach is to utilize the active sites on the main peptide chains and the side chains of silk fibroins through chemical reactions. Graft polymerization on the silk fiber surface was extensively studied. For example, grafting methyl methacrylate onto silk enhanced several properties of silk, including mechanical properties, crease recovery, resistance to chemical, and dyeability [18], [19], while grafting acrylamide onto silk mainly improved its tensile strength. Even though numerous polymers were grafted on silk, their water retention values remained lower than that of the raw silk [14], [17], [18].
Currently, silk fibroin fibers are dissolved in various solutions, such as highly concentrated or mixed salts (e.g., LiSCN, LiBr, and CaCl2–EtOH
H2O) and ionic liquid (e.g., 1–butyl–3–methylimidazolium) [20], [21], and then fabricated into films, sponges, fibers, and hydrogels [22]. In order to further enhance the silk fibroin hydrogel gelation process and its properties, it has been blended with synthetic polymers like poloxamer 407 and poly(ethylene oxide) [23], [24], as well as natural polymers like elastin and alginate [25], [26]. However, these blended silk fibroin hydrogels still have poor swelling property and weak mechanical strength that hinder their applications.
Inspired by the above dissolution process, a LiBr solution, which is a good and common dissolution system [27], with low concentration is used to swell the silk fiber for additional functionalization. In this study, the natural silk yarn was modified by in situ free radical polymerization of acrylamide or sodium acrylate after it was swollen in 4.65 M LiBr solution. Swelling of silk in 4.65 M LiBr was observed under optical microscope. The structural change was characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The morphologies, water absorption properties, mechanical properties, and cytotoxicity of the modified silks were evaluated. These novel modified silks are ready to be woven or knitted into textiles, having potentials in biomedical textiles such as wound dressings and wound sutures. This suggested method offers a new approach to modify the silks with interpenetrating network and hence enhance their properties and performance for various applications.
Section snippets
Materials
Silk yarn of 20/22D was composed of 14 silk fibroin filaments and was purchased from Huasheng Industrial Co., Ltd. (Hangzhou, China). Its sericin content was measured as 25 wt% by infrared (IR) degumming method. All silk yarns for modification were degummed by IR heating with DI water (1:40 liquor ratio) at 110 °C for 60 min. Lithium bromide (LiBr), acrylamide (Am), sodium acrylate (NaA), ammonium persulfate (APS), and N,N’-methylene bisacrylamide (MBAm) were purchased from Sigma Aldrich and used
Effect of LiBr solutions on silk
Swelling of silk yarns in 9.3 M and 4.65 M LiBr solutions at room temperature (T = 23 °C) was observed under optical microscope with plane-polarized and cross-polarized lights as shown in Fig. 1. When the silk was immersed in 9.3 M LiBr, its diameter increased dramatically and became more than double after 120 min. Meanwhile, its crystallinity lost after 120 min as the bright-field disappeared under cross-polarized light. It was completely dissolved within 180 min since 9.3 M LiBr is an effective
Conclusions
The silk yarns have been successfully modified through in situ polymerization of Am and NaA after swelling in 4.65 M LiBr. The optical microscopic images revealed the swelling of silk in 4.65 M LiBr without destroying their fiber integrity. XRD and FTIR suggested that the conformational changes in 4.65 M LiBr allowed the penetration of monomers into the silk. Dissolution tests and FTIR spectra of these modified silks confirmed the interpenetrating network of polyacrylamide and poly(sodium
Acknowledgements
This study was supported by the Hong Kong Polytechnic University fund (G-UC30) and the General Research Fund (B-Q41H).
References (37)
- et al.
Biomaterials
(2003) - et al.
Polymer
(1990) - et al.
Biomaterials
(2002) - et al.
Biomaterials
(2014) - et al.
Biomaterials
(2006) - et al.
Acta Biomater.
(2009) - et al.
Int. J. Pharm.
(2015) - et al.
Polym. Degrad. Stab.
(1998) - et al.
Mat. Sci. Eng. C Biomim.
(2012) - et al.
Acta Biomater.
(2012)
Int. J. Biol. Macromol.
Acta Biomater.
Biomaterials
Acta Biomater.
Carbohydr. Polym.
J. Biochem.
Nucleic Acids Res.
Biomacromolecules
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