title: Spider Silk-CBD-Cellulose Nanocrystal Composites: Mechanism of Assembly.
abstract: The fabrication of cellulose-spider silk bio-nanocomposites comprised of cellulose nanocrystals (CNCs) and recombinant spider silk protein fused to a cellulose binding domain (CBD) is described. Silk-CBD successfully binds cellulose, and unlike recombinant silk alone, silk-CBD self-assembles into microfibrils even in the absence of CNCs. Silk-CBD-CNC composite sponges and films show changes in internal structure and CNC alignment related to the addition of silk-CBD. The silk-CBD sponges exhibit improved thermal and structural characteristics in comparison to control recombinant spider silk sponges. The glass transition temperature (Tg) of the silk-CBD sponge was higher than the control silk sponge and similar to native dragline spider silk fibers. Gel filtration analysis, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and cryo-transmission electron microscopy (TEM) indicated that silk-CBD, but not the recombinant silk control, formed a nematic liquid crystalline phase similar to that observed in native spider silk during the silk spinning process. Silk-CBD microfibrils spontaneously formed in solution upon ultrasonication. We suggest a model for silk-CBD assembly that implicates CBD in the central role of driving the dimerization of spider silk monomers, a process essential to the molecular assembly of spider-silk nanofibers and silk-CNC composites.
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. sigal.meirovitch@mail.huji.ac.il.
authors.forename: Sigal
authors.initials: S
authors.lastname: Meirovitch
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. tsvika.shtein@gmail.com.
authors.forename: Zvi
authors.initials: Z
authors.lastname: Shtein
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. talbs87@gmail.com.
authors.forename: Tal
authors.initials: T
authors.lastname: Ben-Shalom
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. shaul@melodea.eu.
authors.forename: Shaul
authors.initials: S
authors.lastname: Lapidot
authors.affiliation: The Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel. carmen.tamburu@mail.huji.ac.il.
authors.forename: Carmen
authors.initials: C
authors.lastname: Tamburu
authors.affiliation: Department of Biomedical Engineering, 4 Colby Street, Tufts University, Medford, MA 02155, USA. hu@rowan.edu.|Department of Physics and Astronomy, Rowan University, Glassboro, NJ 08028, USA. hu@rowan.edu.
authors.forename: Xiao
authors.initials: X
authors.lastname: Hu
authors.affiliation: Department of Biomedical Engineering, 4 Colby Street, Tufts University, Medford, MA 02155, USA. jonathan.kluge@tufts.edu.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Kluge
authors.affiliation: The Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel. uri.raviv@mail.huji.ac.il.
authors.forename: Uri
authors.initials: U
authors.lastname: Raviv
authors.affiliation: Department of Biomedical Engineering, 4 Colby Street, Tufts University, Medford, MA 02155, USA. david.kaplan@tufts.edu.
authors.forename: David L
authors.initials: DL
authors.lastname: Kaplan
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel. oded.shoseyov@collplant.com.
authors.forename: Oded
authors.initials: O
authors.lastname: Shoseyov
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D002482:Cellulose / Q000737:chemistry*; D000067493:Dynamic Light Scattering; D008855:Microscopy, Electron, Scanning; D053758:Nanoparticles / Q000737:chemistry*; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D053838:Scattering, Small Angle; D047011:Silk / Q000737:chemistry*; D013112:Spiders; D044366:Transition Temperature; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D002135:Calcium-Binding Proteins; D011994:Recombinant Proteins; D047011:Silk; D002482:Cellulose
keywords: biomaterials; cellulose binding domain; cellulose nanocrystals; nanocomposite; spider silk