{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,3]],"date-time":"2026-10-03T02:12:30Z","timestamp":1790993550072,"version":"4.1.0"},"reference-count":32,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2021,4,16]],"date-time":"2021-04-16T00:00:00Z","timestamp":1618531200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["51973144"],"award-info":[{"award-number":["51973144"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100010014","name":"Six Talent Peaks Project in Jiangsu Province","doi-asserted-by":"publisher","award":["SWYY-038"],"award-info":[{"award-number":["SWYY-038"]}],"id":[{"id":"10.13039\/501100010014","id-type":"DOI","asserted-by":"publisher"}]},{"name":"College Nature Science Research Project of Jiangsu Province","award":["20KJA540002"],"award-info":[{"award-number":["20KJA540002"]}]},{"name":"US Natural Science Foundation Biomaterials Program","award":["DMR-1809541"],"award-info":[{"award-number":["DMR-1809541"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>The crystalline structure of silk fibroin Silk I is generally considered to be a metastable structure; however, there is no definite conclusion under what circumstances this crystalline structure is stable or the crystal form will change. In this study, silk fibroin solution was prepared from B. Mori silkworm cocoons, and a combined method of freeze-crystallization and freeze-drying at different temperatures was used to obtain stable Silk I crystalline material and uncrystallized silk material, respectively. Different concentrations of methanol and ethanol were used to soak the two materials with different time periods to investigate the effect of immersion treatments on the crystalline structure of silk fibroin materials. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy (Raman), Scanning electron microscope (SEM), and Thermogravimetric analysis (TGA) were used to characterize the structure of silk fibroin before and after the treatments. The results showed that, after immersion treatments, uncrystallized silk fibroin material with random coil structure was transformed into Silk II crystal structure, while the silk material with dominated Silk I crystal structure showed good long-term stability without obvious transition to Silk II crystal structure. \u03b1-chymotrypsin biodegradation study showed that the crystalline structure of silk fibroin Silk I materials is enzymatically degradable with a much lower rate compared to uncrystallized silk materials. The crystalline structure of Silk I materials demonstrate a good long-term stability, endurance to alcohol sterilization without structural changes, and can be applied to many emerging fields, such as biomedical materials, sustainable materials, and biosensors.<\/jats:p>","DOI":"10.3390\/ijms22084136","type":"journal-article","created":{"date-parts":[[2021,4,16]],"date-time":"2021-04-16T10:20:11Z","timestamp":1618568411000},"page":"4136","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":122,"title":["Chemical, Thermal, Time, and Enzymatic Stability of Silk Materials with Silk I Structure"],"prefix":"10.3390","volume":"22","author":[{"given":"Meihui","family":"Zhao","sequence":"first","affiliation":[{"name":"National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhenzhen","family":"Qi","sequence":"additional","affiliation":[{"name":"National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiaosheng","family":"Tao","sequence":"additional","affiliation":[{"name":"National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chad","family":"Newkirk","sequence":"additional","affiliation":[{"name":"Department of Physics and Astronomy, Rowan University, Glassboro, NJ 08028, USA"},{"name":"Department of Molecular and Cellular Biosciences, Rowan University, Glassboro, NJ 08028, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2579-2820","authenticated-orcid":false,"given":"Xiao","family":"Hu","sequence":"additional","affiliation":[{"name":"Department of Physics and Astronomy, Rowan University, Glassboro, NJ 08028, USA"},{"name":"Department of Molecular and Cellular Biosciences, Rowan University, Glassboro, NJ 08028, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4188-2057","authenticated-orcid":false,"given":"Shenzhou","family":"Lu","sequence":"additional","affiliation":[{"name":"National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"991","DOI":"10.1016\/j.progpolymsci.2007.05.013","article-title":"Silk as a biomaterial","volume":"32","author":"Vepari","year":"2007","journal-title":"Prog. Polym. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"6856","DOI":"10.1021\/ma048988v","article-title":"Mechanical Properties of Electrospun Silk Fibers","volume":"37","author":"Wang","year":"2004","journal-title":"Macromolecules"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"145","DOI":"10.1016\/j.biomaterials.2015.08.039","article-title":"In vivo bioresponses to silk proteins","volume":"71","author":"Thurber","year":"2015","journal-title":"Biomaterials"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"119","DOI":"10.1002\/prot.1078","article-title":"Silk fibroin: Structural implications of a remarkable amino acid sequence","volume":"44","author":"Zhou","year":"2001","journal-title":"Proteins Struct. Funct. Bioinform."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"2413","DOI":"10.1093\/nar\/28.12.2413","article-title":"Fine organization of Bombyx mori fibroin heavy chain gene","volume":"28","author":"Fabrice","year":"2000","journal-title":"Nucleic Acids Res."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1612","DOI":"10.1038\/nprot.2011.379","article-title":"Materials fabrication from Bombyx mori silk fibroin","volume":"6","author":"Rockwood","year":"2011","journal-title":"Nat. Protoc."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"826","DOI":"10.1021\/bm201731e","article-title":"Silk Self-Assembly Mechanisms and Control-From Thermodynamics to Kinetics","volume":"13","author":"Lu","year":"2012","journal-title":"Biomacromolecules"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1937","DOI":"10.1002\/app.1992.070451108","article-title":"Improvements of the physical properties of fibroin membranes with sodium alginate","volume":"45","author":"Liang","year":"1992","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"319","DOI":"10.1038\/165319a0","article-title":"An Unstable Lattice in Silk Fibroin","volume":"165","author":"Kratky","year":"1950","journal-title":"Nature"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1686","DOI":"10.1021\/bm200062a","article-title":"Regulation of Silk Material Structure by Temperature-Controlled Water Vapor Annealing","volume":"12","author":"Hu","year":"2011","journal-title":"Biomacromolecules"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"323","DOI":"10.1016\/j.actbio.2017.04.001","article-title":"Silk I and Silk II studied by fast scanning calorimetry","volume":"55","author":"Cebe","year":"2017","journal-title":"Acta Biomater."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"237","DOI":"10.1016\/S0141-8130(99)00002-1","article-title":"Orientation of silk III at the air-water interface","volume":"24","author":"Valluzzi","year":"1999","journal-title":"Int. J. Biol. Macromol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2599","DOI":"10.1039\/C4TB01873G","article-title":"The influence of the hydrophilic\u2013lipophilic environment on the structure of silk fibroin protein","volume":"3","author":"Lu","year":"2015","journal-title":"J. Mater. Chem. B"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1380","DOI":"10.1016\/j.actbio.2009.10.041","article-title":"Water-insoluble silk films with silk I structure","volume":"6","author":"Lu","year":"2010","journal-title":"Acta Biomater."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"751","DOI":"10.1021\/bm0343693","article-title":"Phase Behavior and Hydration of Silk Fibroin","volume":"5","author":"Sohn","year":"2004","journal-title":"Biomacromolecules"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"233","DOI":"10.4028\/www.scientific.net\/KEM.342-343.233","article-title":"Study on Silk I Porous 3-D Scaffolds","volume":"342-343","author":"Lu","year":"2007","journal-title":"Key Eng. Mater."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1241","DOI":"10.1002\/adfm.200400405","article-title":"Water\u2014Stable Silk Films with Reduced \u03b2\u2014Sheet Content","volume":"15","author":"Jin","year":"2005","journal-title":"Adv. Funct. Mater."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"3422","DOI":"10.1021\/acsbiomaterials.0c00273","article-title":"Combined Silk Fibroin Microneedles for Insulin Delivery","volume":"6","author":"Zhu","year":"2020","journal-title":"ACS Biomater. Sci. Eng."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Riekel, C., Burghammer, M., and Rosenthal, M. (2019). Nanoscale X-Ray Diffraction of Silk Fibers. Front. Mater., 6.","DOI":"10.3389\/fmats.2019.00315"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2185","DOI":"10.1002\/1097-4628(20010321)79:12<2185::AID-APP1026>3.0.CO;2-3","article-title":"Study on porous silk fibroin materials. I. Fine structure of freeze dried silk fibroin","volume":"79","author":"Li","year":"2001","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"7","DOI":"10.1016\/S0301-4622(99)00060-5","article-title":"Identification of \u03b2-turn and random coil amide III infrared bands for secondary structure estimation of proteins","volume":"80","author":"Cai","year":"1999","journal-title":"Biophys. Chem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"382","DOI":"10.1038\/nprot.2015.024","article-title":"Obtaining information about protein secondary structures in aqueous solution using Fourier transform IR spectroscopy","volume":"10","author":"Yang","year":"2015","journal-title":"Nat. Protoc."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"103","DOI":"10.1002\/jrs.675","article-title":"Raman spectroscopic characterization of Bombyx mori silk fibroin: Raman spectrum of Silk I","volume":"32","author":"Monti","year":"2001","journal-title":"J. Raman Spectrosc."},{"key":"ref_24","unstructured":"Tu, A.T. (1982). Raman Spectroscopie in Biology. Principles and Applications, A Wiley-Interscience Publication, John Wiley and Sons."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"11302","DOI":"10.1021\/bi049344i","article-title":"Effects of pH and Calcium Ions on the Conformational Transitions in Silk Fibroin Using 2D Raman Correlation Spectroscopy and 13C Solid-State NMR","volume":"43","author":"Zhou","year":"2004","journal-title":"Biochemistry"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"137","DOI":"10.1016\/j.tca.2006.12.011","article-title":"Effect of water on the thermal properties of silk fibroin","volume":"461","author":"Hu","year":"2007","journal-title":"Thermochim. Acta"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"719","DOI":"10.1021\/bm3018033","article-title":"Macroporous Silk Fibroin Cryogels","volume":"14","author":"Ak","year":"2013","journal-title":"Biomacromolecules"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1021\/bm900993n","article-title":"Insoluble and Flexible Silk Films Containing Glycerol","volume":"11","author":"Lu","year":"2010","journal-title":"Biomacromolecules"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1080","DOI":"10.1021\/bm101422j","article-title":"Degradation Mechanism and Control of Silk Fibroin","volume":"12","author":"Lu","year":"2011","journal-title":"Biomacromolecules"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"841","DOI":"10.1002\/(SICI)1099-0488(19970415)35:5<841::AID-POLB13>3.0.CO;2-A","article-title":"Structure and molecular conformation of tussah silk fibroin films: Effect of heat treatment","volume":"35","author":"Freddi","year":"1997","journal-title":"J. Polym. Sci. Part B Polym. Phys."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/s42452-019-1486-0","article-title":"Influence of ethanol post-treatments on the properties of silk protein materials","volume":"1","author":"Puerta","year":"2019","journal-title":"SN Appl. Sci."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"2926","DOI":"10.1016\/j.biomaterials.2009.12.026","article-title":"Mechanism of enzymatic degradation of beta-sheet crystals","volume":"31","author":"Numata","year":"2010","journal-title":"Biomaterials"}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/22\/8\/4136\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:48:53Z","timestamp":1760161733000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/22\/8\/4136"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,4,16]]},"references-count":32,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2021,4]]}},"alternative-id":["ijms22084136"],"URL":"https:\/\/doi.org\/10.3390\/ijms22084136","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,4,16]]}}}