In situ microscopic studies on the structures and phase behaviors of SF/PEG films using solid-state NMR and Raman imaging

Abstract

In order to overcome the drawbacks of silk fibroin (SF)-based materials, SF has been blended with some polymers. Before using the blend material, understanding of the structures and phase behaviors of the blend is thought to be essential. In this study, solid-state (13)C CP-MAS NMR and Raman imaging techniques were used to study the structures and phase behaviors of blends of SF with polyethylene glycol (PEG) at a molecular weight that varied from 2 to 20 kDa and a blend ratio of SF/PEG from 95/5 to 70/30 (w/w%) at the molecular and microscopic levels. It is found that the conformational transition of SF to the β-sheet increased as the PEG content increased, while the amount of the formed β-sheet conformers was decreased as the PEG molecular weight increased for a given content. It is also observed that SF was incompatible with PEG to some extent. The phase separation into "sea" and "island" domains took place in the SF/PEG blend films. SF was dominantly present in the "sea" domain, while PEG in the "island" domains. The conformation of SF in the interface between SF and PEG was changed to the β-sheet, while that in the protein-rich domain remained in the random coil and/or helix conformation. These observations suggest that the specifically expected materials, for example, the silk-based microspheres or scaffold materials can be manufactured by controlling the molecular weight and content of PEG in the blend system.

Silk Sericin Semi-interpenetrating Network Hydrogels Based on PEG-Diacrylate for Wound Healing Treatment

“…Such reduced water molecules around the peptide chains would allow the molecules of SS to hydrophobically intertwine, agglomerate, and eventually undergo an α-to-β phase transition. The ability of the poly(ethylene glycol) derivatives to act as an inducer of silk phase transition has already been reported earlier [14,29,30]. A slightly shift of the Amide I signal observed in Figure 4 also reconfirms the formation of such silk crystallization.…”

Poly(isophthalic acid)(ethylene oxide) as a Macromolecular Modulator for Metal–Organic Polyhedra

“…With the low refractive index of porous materials, this technique can analyze the surface of crystals with ∼0.2 μm depth resolution . PEG polymers have been characterized by Raman spectroscopy, and several characteristic spectral features of the ethylene oxide chains have been reported . However, polymer 1 showed evidence of fluorescence (Figure ) upon excitation in the Raman experiments, perhaps due to the close proximity of isophthalic acid groups in the polymer backbone.…”

Degradation Behavior of Silk Nanoparticles—Enzyme Responsiveness

“…The typical wavenumbers in Raman spectroscopy for protein secondary structure are 1662–1655, 1272–1264, and 1104 cm –1 for random coils/α-helixes and 1674–1672, 1242–1227, and 1084 cm –1 for β-sheets. , The Raman spectra of native and PEGylated silk nanoparticles showed signal intensities at 1665, 1229, and 1084 cm –1 , which indicated a β-sheet conformation for silk (Figure ). No changes were evident in the amide I spectra of the enzyme-treated nanoparticles due to the lower sensitivity of the Raman versus the FTIR spectra . However, the band at 1104 and 1084 cm –1 was used to analyze secondary structure changes of silk nanoparticles.…”

“…No changes were evident in the amide I spectra of the enzymetreated nanoparticles due to the lower sensitivity of the Raman versus the FTIR spectra. 38 However, the band at 1104 and 1084 cm −1 was used to analyze secondary structure changes of silk nanoparticles. The bandwidth in this region became progressively broader for silk nanoparticles exposed to protease XIV and papain, from 5 days onward, indicating that these enzymes digested β-sheet sequences.…”