Sonication-induced gelation of silk fibroin for cell encapsulation

Abstract

Purified native silk fibroin forms beta-sheet-rich, physically cross-linked, hydrogels from aqueous solution, in a process influenced by environmental parameters. Previously we reported gelation times of days to weeks for aqueous native silk protein solutions, with high ionic strength and temperature and low pH responsible for increasing gelation kinetics. Here we report a novel method to accelerate the process and control silk fibroin gelation through ultrasonication. Depending on the sonication parameters, including power output and time, along with silk fibroin concentration, gelation could be controlled from minutes to hours, allowing the post-sonication addition of cells prior to final gel setting. Mechanistically, ultrasonication initiated the formation of beta-sheets by alteration in hydrophobic hydration, thus accelerating the formation of physical cross-links responsible for gel stabilization. K(+) at physiological concentrations and low pH promoted gelation, which was not observed in the presence of Ca(2+). The hydrogels were assessed for mechanical properties and proteolytic degradation; reported values matched or exceeded other cell-encapsulating gel material systems. Human bone marrow derived mesenchymal stem cells (hMSCs) were successfully incorporated into these silk fibroin hydrogels after sonication, followed by rapid gelation and sustained cell function. Sonicated silk fibroin solutions at 4%, 8%, and 12% (w/v), followed by mixing in hMSCs, gelled within 0.5-2 h. The cells grew and proliferated in the 4% gels over 21 days, while survival was lower in the gels with higher protein content. Thus, sonication provides a useful new tool with which to initiate rapid sol-gel transitions, such as for cell encapsulation.

Comparison of Gelation Time and Polyalcohol Effect on Hydrogels from Domestic and Wild Silk Fibroins

“…Therefore, the transition to β-sheets in both the pure A. pernyi SF aqueous solution and the solutions blended 103 0 0 8.12 5.9 9 9 9 9 9 9 9 9 9 9 9 99 9 9 9 9 9 9 9 9 9 9 9 9 with PEG would be more rapid and much easier. Gelation of B. mori SF is both time-and energy-consuming, which has also been proven in other research [6,7,24]. In the present study, the gelation time of A. pernyi SF was proven to be much shorter than that of B. mori SF, even when nonauxiliary materials were added.…”

“…Silkworm silk fibroin is excreted by domestic (B. mori) and wild (A. pernyi) silkworms. Domestic SF hydrogels are of interest for use as bonefilling biomaterials, wound dressing, and so on and have proved to be promising for healing efficacy [5][6][7][8][9][10]. Compared with B. mori SF, A. pernyi SF, the most familiar wild SF, has more advantages in terms of chemical activity and highaffinity interactions with mammalian cells [11].…”

“…Through reviewing research articles about B. mori SF hydrogels, we found that the gelation time of SF hydrogels is excessively long unless nonphysiological treatments (such as low pH, high temperature, or additives) are considered [6,[13][14][15][16][17]. The question we want to answer is do the A. pernyi SF hydrogels have a similar problem?…”

Chemically cross-linked silk fibroin hydrogel with enhanced elastic properties, biodegradability, and biocompatibility

“…The control sample SF C-gels incubated in PBS solution without protease showed a slow degradation throughout the incubation period. 29 The fast degradation of SF C-gel due to proteolytic processes may be suitable for various applications, such as in tissue engineering or rapid drug delivery systems. The structural changes in the degradation process were further investigated using SEM.…”

Structural and thermal characteristics of photocrosslinked silk fibroin - PEG hydrogel

“…concentration, temperature, mechanical strength, chemical treatment, ultrasound sonication, and composition (Kim et al, 2015;Samal et al, 2013;Wang et al, 2008;Kweon et al, 2000;Kang et al, 2000;Ayub et al, 1994). Among them, sonication induced rapid gelation by reduction of molecular weight and β-sheet conformation (Samal et al, 2013).…”