Thermally Induced Increase in Energy Transport Capacity of Silkworm Silks Guoqing Liu, 1 Shen Xu, 1 Ting-Ting Cao, 2 Huan Lin, 1 Xiaoduan Tang, 1 Yu-Qing Zhang, 2 Xinwei Wang 1 1 Department of Mechanical Engineering, Iowa State University, Ames 50011, Iowa 2 Silk Biotechnology Key Laboratory of Suzhou City, School of Biology and Basic Medical Sciences, Soochow University, Suzhou 215123, People’s Republic of China Received 28 October 2013; revised 7 April 2014; accepted 8 April 2014 Published online 11 April 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/bip.22496 ABSTRACT: This work reports on the first study of thermally induced effect on energy transport in single filaments of silkworm (Bombyx mori) fibroin degummed mild (type 1), mod- erate (type 2), to strong (type 3). After heat treatment from 140 to 220  C, the thermal diffusivity of silk fibroin type 1, 2, and 3 increases up to 37.9, 20.9, and 21.5%, respectively. Our detailed scanning electron microscopy study confirms that the sample diameter change is almost negligible before and after heat treatment. Raman analysis is performed on the original and heat- treated (at 147  C) samples. After heat treatment at 147  C, the Raman peaks at 1081, 1230, and 1665 cm 21 become stronger and narrower, indicating structural transformation from amorphous to crystalline. A struc- ture model composed of amorphous, crystalline, and lat- erally ordered regions is proposed to explain the structural change by heat treatment. Owing to the close packing of more adjacent laterally ordered regions, the number and size of the crystalline regions of Bombyx mori silk fibroin increase by heat treatment. This struc- ture change gives the observed significant thermal diffu- sivity increase by heat treatment. V C 2014 Wiley Periodicals, Inc. Biopolymers 101: 1029–1037, 2014. Keywords: silkworm silk; thermal treatment; thermal diffusivity; Raman spectroscopy This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by email- ing the Biopolymers editorial office at biopolymers@wiley.com INTRODUCTION S ilkworm silk from Bombyx mori has many advan- tages, such as comfort, high mechanical strength and elasticity, 1 and has been widely used in textile indus- try for thousands of years. 2 In the past century, this material also provided important clinical repair options for many applications, such as suture material. 3 With the development of biomedical and biotechnological engineering, it finds more and more applications in biosen- sors, drug delivery, etc. 2–5 It is well known that silkworm silk is a fibrous protein composed of two strands of fibroin coated with a layer of sericin. The sericin layer is usually removed for making regenerated silk-based devices. The properties of degummed silk (fibroin) fibers need to be fully characterized and recognized, and the thermal property is one of the most important properties. In past studies, some works studied the changes of silkworm silk proteins’ structures and mechanical properties by using thermal treatment, 6–8 and other thermal analysis of silk fibroins is focused on reconstituted silk fibroin (RSF) films, 2,9– 11 not the native silks naturally produced by silkworms. For RSF films, there are various ways to induce structural changes (from amorphous to crystalline). For temperature-controlled water vapor annealing, the b-sheets crystallinity can increase Correspondence to: Xinwei Wang; e-mail: xwang3@iastate.edu V C 2014 Wiley Periodicals, Inc. Biopolymers Volume 101 / Number 10 1029