Silk Fibroin-Based Shape-Memory Organohydrogels with Semicrystalline Microinclusions

Abstract

Inspired by nature, we designed organohydrogels (OHGs) consisting of a silk fibroin (SF) hydrogel as the continuous phase and the hydrophobic microinclusions based on semicrystalline poly(n-octadecyl acrylate) (PC18A) as the dispersed phase. SF acts as a self-emulsifier to obtain oil-in-water emulsions, and hence, it is a versatile and green alternative to chemical emulsifiers. We first prepared a stable oil-in-water emulsion without an external emulsifier by dispersing the noctadecyl acrylate (C18A) monomer in an aqueous SF solution.To stabilize the emulsions for longer times, gelation in the continuous SF phase was induced by the addition of ethanol, which is known to trigger the conformational transition in SF from random coil to β-sheet structures. In the second step, in situ polymerization of C18A droplets in the emulsion system was conducted under UV light in the presence of a photoinitiator to obtain high-strength OHGs with shape-memory function, and good cytocompatibility. The incorporation of hydrophilic N,Ndimethylacrylamide and noncrystallizable hydrophobic lauryl methacrylate units in the hydrogel and organogel phases of OHGs, respectively, further improved their mechanical and shape-memory properties. The shape-memory OHGs presented here exhibit switchable viscoelasticity and mechanics, a high Young's modulus (up to 4.3 ± 0.1 MPa), compressive strength (up to 2.5 ± 0.1 MPa), and toughness (up to 0.68 MPa).

Cryogelation reactions and cryogels: principles and challenges

“…OHGs attract great interest for various application areas such as freeze-tolerant materials, signal transmission, sensors, soft robotics, and optical devices [ 55 – 58 ]. Dispersing a discontinuous organic (lyophilic) phase in a continuous aqueous phase to create an oil-in-water emulsion followed by polymerization is a commonly used technique to prepare an OHG [ 59 ]. A series of OHGs with freeze-tolerant properties were also prepared by adding a lyophilic phase to a freeze-dried poly(DMAA) hydrogel [ 60 ].…”

Mechanically Robust Shape‐Memory Organohydrogels Based on Silk Fibroin with Organogel Microinclusions of Various Sizes

“…[5][6][7][8][9] A commonly used technique to synthesize OHGs is to disperse a hydrophobic phase in an aqueous solution to form an oil-in-water emulsion followed by gelation of the aqueous phase. [10,11] Alternatively, lyophilic or hydrophobic components are introduced into a preformed hydrophilic network. For instance, freeze-inhibiting compounds such as sorbitol, glycol, and glycerol were incorporated into a previously prepared alginatebased hydrogel to produce freeze-tolerant materials.…”