Alcohol-triggered silk fibroin hydrogels having random coil and β-turn structures enhanced for cytocompatible cell response Kanyaluk Kaewprasit, 1 Takaomi Kobayashi, 2 Siriporn Damrongsakkul 1,3 1 Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Phayathai Road, Bangkok 10330, Thailand 2 Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan 3 Biomaterial Engineering for Medical and Health Research Unit, Chulalongkorn University, Phayathai Road, Bangkok 10330, Thailand Correspondence to: S. Damrongsakkul (E-mail: siriporn.d@chula.ac.th) ABSTRACT: Alcohol additive is one of the stimulants that induces the fast gelation of silk fibroin solution. Based on our previous report, different alcohol types influence the gelation kinetic and the properties of resulting silk fibroin hydrogels. Here, the effects of alcohol concentrations on the silk fibroin gelation and cell response were reported. All fibroin hydrogels prepared with various alcohol additives showed cell biocompatibility, especially the fibroin hydrogel prepared with 10 wt % n-butanol. Results on the mechanical properties of hydrogels, n-butanol additive enhanced a higher compressive modulus up to ~ 22 times in comparison to non-alcoholic fibroin hydro- gel. Fourier transform infrared analysis and peak deconvolution showed a possible formation of more β-turn linkage and random coil structure of fibroin segments in alcoholic fibroin hydrogel. So, the micro-segmental structure of fibroin hydrogel caused the higher com- pressive modulus, prolonged deformation of the hydrogels, and efficient cell growth on the fibroin hydrogel. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48731. KEYWORDS: biocompatibility; biomaterials; gels Received 14 June 2019; accepted 23 October 2019 DOI: 10.1002/app.48731 INTRODUCTION Hydrogels containing three-dimensional hydrophilic polymer net- works are well known to retain large amounts of water and have promising potential for many biomedical applications because of their biocompatible nature. 1,2 Among hydrogels fabricated from synthetic 3–5 and natural polymers, 6–8 silk fibroin is one of the nat- ural polymers having many advantages such as nontoxicity, high dissolved-oxygen and water vapor permeability, good mechanical properties, and controllable degradation. 9–11 It is known that Bombyx mori silk cocoon contains two major silk fibroin fibers and both are joined via silk sericin coating. In case of silk fibroin, three polypeptide segments are composed of heavy chain (H), light chain (L), and P25 at a molar ratio of 6:6:1. 12 The H segment is a repetitive hydrophobic domain which is a building domain of β-sheet structure. 13 The L segment is a non-repetitive and more hydrophilic sequence which is linked with heavy chain by disulfide bond, while the P25 is associated with the H-L complex by hydro- phobic interactions. 12 For the β-turn structure in silk fibroin, it is a tetrapeptide which consists of four consecutive amino acids (GAAS). 13,14 This structure leads silk fibroin chain to fold back on itself by nearly 180  of the direction of the chain. 15,16 It has been known that the gelation of silk fibroin solution is quite slow, so this has been the challenged issue for the process of hydrogel fabrication. The gelation of silk fibroin-based hydro- gel could be triggered by physical 17,18 and chemical cro- sslinking. 19,20 These stimulants induced the conformational transition of silk fibroin from random coil to β-sheet structure. 21 Because of lacking mechanical properties of the self-assembled silk fibroin hydrogel, many researchers attempted to induce the silk fibroin gelation and improve the mechanical properties. For example, the addition of other natural polymers and surfactants, 22–24 and the increase of enzymatic crosslinking con- centration. 25 In our previous work, 26 the effects of monohydric or polyhydric alcohol additives were studied on the gelation pro- cess of Thai silk fibroin solution. Due to the shorter gelation time, the monohydric alcohol with longer alkyl carbon chain induced the gelation process faster than the polyhydric alcohol. As a result, silk fibroin hydrogels induced with longer alkyl chain alcohol had a good mechanical property. However, the previous work reported only alcohol type effect on the gelation. Therefore, in the present work, the gelation effects of alcohol additive were interesting topics on one of the biomedical applications in © 2019 Wiley Periodicals, Inc. 48731 (1 of 10) J. APPL. POLYM. SCI. 2019, DOI: 10.1002/APP.48731