Influence of grafting with acrylate compounds on the conformational rearrangements of silk fibroin upon electrospinning and treatment with aqueous methanol

Abstract

Silk fabrics from Bombyx mori silkworm were grafted with 2‐hydroxyethyl methacrylate (HEMA) as well as a binary system of HEMA and 4‐hydroxybutyl acrylate (HBA) and then analysed by Raman and infrared (IR) spectroscopy to elucidate the interactions between the components and their possible conformational changes. The samples were then dissolved in trifluoroacetic acid and electrospun; the influence of the grafted polymers on the silk fibroin rearrangements upon these treatments was investigated by vibrational spectroscopy. Upon grafting, the fabrics underwent conformational rearrangements towards a more unordered state, although they kept their prevailing β‐sheet conformation; also the polymeric component underwent hydrogen bonding and backbone rearrangements upon interaction with silk fibroin and the occurrence of strong covalent bonds cannot be excluded. By immersing the as‐electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β‐sheet content observed in the corresponding starting fabrics; the percentage of recovery decreased along the series: pure silk > HEMA‐grafted silk > HEMA and HBA‐grafted silk. This trend suggests that the presence of the polyHEMA grafted component hinders the silk fibroin recrystallization into β‐sheet upon aqueous methanol treatment; moreover, the addition of the more sterically hindered HBA monomer in the grafting system further prevented this process. Copyright © 2016 John Wiley & Sons, Ltd.

Vibrational Study on Structure and Bioactivity of Protein Fibers Grafted with Phosphorylated Methacrylates

“…As mentioned in the Introduction, crystalline regions of silk fibroin have a prevailing β-sheet conformation and are rich in simple amino acids (Ala, Gly, Ser), while amorphous regions are rich in bulky and polar amino acids [40]. In agreement with previous studies [33], the A 1226 /A 1261 ratio was found to decrease upon grafting, suggesting that the grafted polymer introduced a certain disorder into the fiber; as shown in Figure 7, the ratio well correlates to weight gain for both phosmers. However, it must be observed that A 1226 /A 1261 may also change because of the contribution of the band at about 1255 cm −1 , which is assignable to P=O stretching of the phosphate group [17,43].…”

“…Other bands were found to strengthen upon grafting, such as the CH 2 bending mode at about 1450 cm −1 , which also showed an increase of its full-width at half-maximum (FWHM) from 25 cm −1 (control) to 28 cm −1 (grafted samples). Moreover, a new component was detected at 1485 cm −1 , in agreement with the trend observed upon grafting with HEMA [33].…”

“…In the CC stretching range [31,32], slight enhancements were detected for the bands at about 1125 and 1035 cm −1 ; these bands were observed to strengthen also upon grafting with HEMA [33], being characteristic of poly HEMA (i.e., they appeared as distinct spectral features upon polymerization of HEMA). Their strengthening suggests that phosmers polymerize onto silk fibroin; actually, both phosmers show broad and weak bands in this spectral region.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Upon grafting, the fabrics underwent conformational rearrangements towards a more unordered state, although they kept their prevailing β‐sheet conformation. By immersing the as‐electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β‐sheet content observed in the corresponding starting fabrics …”

“…By immersing the as-electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β-sheet content observed in the corresponding starting fabrics. [151] 15.5 | Glasses, ceramics, powders, and disordered materials Magyari and co-workers studied the effect of titania on the bioactivity of silicate bioactive glasses. Their investigation demonstrates that the FWHM of the Raman band combined with the FT-IR data recorded in reflection mode can be used as key spectral indicators for elucidating the evolution of apatite-like structures developed on the bioactive material surface.…”