The influence of thermal treatments on the secondary structure of silk fibroin scaffolds and their interaction with fibroblasts

Abstract

Background Recently, silk fibroin-based biomaterials have received attention for application in tissue engineering and drug delivery systems. The usefulness of heat sterilization methods for silk fibroin-based biomaterials was investigated in this study as all biomaterials are required to undergo a sterilization process when they are used in medical devices. Methods The influence of wet and dry heating on the properties of fibroin molecules in silk fibroin sponges was investigated by measurements of solid-state 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analyses, strength tests, and cell proliferation/migration assays. Results 13C CP/MAS NMR spectra of wet-heated sponges revealed no changes in the molecular structure below 50 °C. However, above 60 °C, the crystalline structure of the silk proteins transitioned from silk I to silk II; the silk II:silk I ratio increased with temperature. In contrast, dry heating (below 190 °C for up to 180 min) induced no structural changes in the fibroin molecules. These results indicate that, although autoclave sterilization (121 °C for 20 min) induces structural changes in silk fibroin sponges, no such changes are observed with the dry-heat sterilization (180 °C for 30 min). Sterilized sponges with a silk I structure can be obtained using dry-heat method during sterilization. Moreover, the structural differences between the wet- and dry-heated silk fibroin sponges did not influence their interaction with fibroblasts. Discussion This study indicates that both autoclaving and dry heating are acceptable sterilization methods for silk fibroin-based sponges as the scaffold. In particular, dry heating maintains the stability of the secondary structure of the sterilized silk fibroin-based biomaterials.

Evaluation of the Modification Effects of Heparin/Dalteparin on Silk Fibroin Structure and Physical Properties for Skin Wound Healing

“…In other words, it was qualitatively confirmed that the BSF component in the HSF underwent reformation of the crystalline structure. To evaluate the crystalline structure of BSF further quantitatively, it is possible to separate the peak components derived from each secondary structure and compare the transitions in their respective proportions [38,51]. However, when using the polysaccharide heparin, the spectrum overlaps with the protein BSF.…”

Bioresorbable Insertion Aids for Brain Implantable Flexible Probes: A Comparative Study on Silk Fibroin, Alginate, and Disaccharides

“…[48] The amide groups-which are involved in the hydrogen bonds between the chains of the coils-are associated with two distinct vibrations in literature infrared (IR) data which appear at 1600-1700 cm À1 (Amide I) and 1500-1600 cm À1 (Amide II). [49,50] After the silk fibroin has been extracted-in its "untreated" form-it is mostly composed of random coils, which result in the Amide I vibration peak at 1645 cm À1 and a pair of faintly distinguishable overlapping peaks at 1515 and 1530 cm À1 in the Amide II region. Previous FTIR measurements of silk fibroin which had been treated by these methods show a strong emergent peak in the Amide I region between 1620 and 1630 cm À1 which has been attributed to the presence of crystalline β-sheet structures, also referred to as Silk II.…”

“…Our FTIR measurements of the four samples (untreated, dry heat, water annealed, and methanol vapor) are presented in [48][49][50] but some show the disparity between treatment methods. The untreated sample and the dry heat-treated sample show a peak at approximately 1635 cm À1 in the Amide I region, with a new peak emerging at 1620 cm À1 as well for the methanol and water annealed samples.…”