The role of dialysis and freezing on structural conformation, thermal properties and morphology of silk fibroin hydrogels

Abstract

Silk fibroin has been widely explored for many biomedical applications, due to its biocompatibility and biodegradability. The aim of this work was to study the role of dialysis and freezing on structural conformation, thermal properties and morphology of silk fibroin hydrogels. Hydrogels were prepared after 3 and 7 days of dialysis and the effect of freezing was analyzed. For that purpose, a part of the fibroin hydrogels underwent freezing at -20 °C for 24 h, followed by lyophilization and the rest of the hydrogels were kept at 8 °C for 24 h, with further lyophilization. The fibroin hydrogels were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Measurements by XRD and FTIR indicated that silk I and silk II structures were present in the fibroin hydrogels and that the secondary structure of fibroin is transformed mostly to β-sheet during the gelation process. Thermal analysis indicated that fibroin hydrogels are thermally stable with the degradation peak at around 330–340 °C. SEM micrographs showed porous structures and the fibroin hydrogels subjected to freezing presented a much larger pore size. Results indicate that the dialysis time and freezing did not alter the material crystallinity, conformation or thermal behavior; however, hydrogel microstructure was strongly affected by dialysis time and freezing, showing controlled pores size. This study provides fundamental knowledge on silk fibroin hydrogels preparation and properties and the studied hydrogels are promising to be used in the biomaterial field.

Silk fibroin hydrogels for potential applications in photodynamic therapy

“…The fibroin gelation is a natural process that can be accelerated by factors such as pH, temperature, salt concentration, and addition of alcohol, which attenuate hydrophobic interactions amongst protein chains. The addition of ethanol to SF solutions dehydrates the protein molecules, increasing the intra‐ and intermolecular interactions leading to the formation of silk II structures that stabilize the hydrogel . The lower dielectric constant of ethanol (24.3 ε 0 at 20°C) relative to water (80 ε 0 at 20°C) causes the ethanol to gradually replace water molecules solvating the hydrophobic groups of fibroin .…”

Potential of biocompatible regenerated silk fibroin/sodium N-lauroyl sarcosinate hydrogels

“…The plates were transferred in a 37°C/5% CO 2 incubator in 95% humidity for seven days, and the medium was changed every second day. [40][41][42][43][44][45] The proliferation activity was assessed through the use of Alamar Blue. The staining solution was added to the culture wells at concentration of 10% and incubated for 6 h, according to manufacturer's procedure.…”

Estudo do equilí­brio de fases em sistemas contendo polímeros naturais: fibroí­na de seda e alginato de sódio.

“…Primeiramente os casulos foram lavados com água. Em seguida foram imersos em solução de NaCO3 1 g/L pelo período de 30 min a 85 °C, para cada 50 g de casulos foi utilizado 600 mL de solução de NaCO3 (Ribeiro, 2014). Este processo foi repetido por três vezes.…”

“…A fibroína purificada foi dissolvida em solvente ternário de CaCl2, etanol e água (proporção molar 1:2:8). Uma vez preparado o solvente ternário, este foi aquecido em banho termostático até 85 °C, em seguida a fibroína foi adicionada e a solução mantida no banho até sua total dissolução pelo período máximo de 1h 30 (Ribeiro, 2014). O volume de solvente e massa de fibroína utilizados foram calculados de forma que a solução final obtida tivesse 5 % em massa de fibroína (Ajisawa, 1997).…”

“…A solução de fibroína em solvente ternário foi submetida ao processo de diálise para a obtenção de uma solução aquosa. No processo, 10 mL de solução de fibroína em solvente ternário foram colocados em uma membrana de diálise Viscofan 22 EU -20 USA com corte de massa molecular de 3,5 kDa, e esta foi colocada em um béquer com água ultrapura na proporção volumétrica entre a solução de fibroína e água de 1:15 (Ribeiro, 2014). A água de diálise foi trocada a cada 24h pelo período de 3 dias.…”