Regulation of Silk Material Structure by Temperature-Controlled Water Vapor Annealing

• Published in: Biomacromolecules Vol. 12; no. 5; pp. 1686 - 1696
• Main Authors: Hu, Xiao, Shmelev, Karen, Sun, Lin, Gil, Eun-Seok, Park, Sang-Hyug, Cebe, Peggy, Kaplan, David L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09.05.2011
• Subjects: Applied sciences; Biological and medical sciences; Calorimetry, Differential Scanning; Cell Proliferation; Exact sciences and technology; Humans; Medical sciences; Mesenchymal Stem Cells - cytology; Natural polymers; Physicochemistry of polymers; Proteins; Silk - chemistry; Spectroscopy, Fourier Transform Infrared; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Technology. Biomaterials. Equipments; Temperature; Tensile Strength; Water - chemistry; Cell proliferation; Biological properties; Annealing; Thermal transition; Enzyme; Biodegradability; Stem cell; Mechanical properties; Mesenchymal cell; Experimental study; Property processing relationship; Protein; Peptidases; Silk; Humidity effect; Cell adhesion; Enzymatic digestion; Hydrolases; Biomaterial; Fibroin; Kinetics; Mechanism of action; Isothermal crystallization
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm200062a

We present a simple and effective method to obtain refined control of the molecular structure of silk biomaterials through physical temperature-controlled water vapor annealing (TCWVA). The silk materials can be prepared with control of crystallinity, from a low content using conditions at 4 °C (α helix dominated silk I structure), to highest content of ∼60% crystallinity at 100 °C (β-sheet dominated silk II structure). This new physical approach covers the range of structures previously reported to govern crystallization during the fabrication of silk materials, yet offers a simpler, green chemistry, approach with tight control of reproducibility. The transition kinetics, thermal, mechanical, and biodegradation properties of the silk films prepared at different temperatures were investigated and compared by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), uniaxial tensile studies, and enzymatic degradation studies. The results revealed that this new physical processing method accurately controls structure, in turn providing control of mechanical properties, thermal stability, enzyme degradation rate, and human mesenchymal stem cell interactions. The mechanistic basis for the control is through the temperature-controlled regulation of water vapor to control crystallization. Control of silk structure via TCWVA represents a significant improvement in the fabrication of silk-based biomaterials, where control of structure−property relationships is key to regulating material properties. This new approach to control crystallization also provides an entirely new green approach, avoiding common methods that use organic solvents (methanol, ethanol) or organic acids. The method described here for silk proteins would also be universal for many other structural proteins (and likely other biopolymers), where water controls chain interactions related to material properties.