2 2 dimethoxy 2 phenylacetophenone

A resin blend was formulated containing 50:30:20 mass% bis-phenol A diglycidyl dimethacrylate, urethane dimethacrylate and triethylene glycol dimethacrylate (Esstech, Essington, PA, USA). 2,2-dimethoxy-2-phenylacetophenone at 0.1 mass%, and 2,6-di-tert-butyl-4-methylphenol at 0.5 mass% (SigmaAldrich, St. Louis, MO, USA), were used as the initiator and inhibitor, respectively. This formulation was similar to prior studies evaluating the addition of thiourethane to composite. ^{[5 (link)]} Ytterbium Fluoride fillers with average size of 0.11 μm (YBF100) and 0.05 μm (YBF402), and radiopaque Barium glass fillers with 0.80 μm were used in the study, and all fillers (Sukgyung AT. Co. Ltda, Ansa City, Korea) were almost spherical with a refractive index of 1.54. Fillers silanized using thiourethane or methacrylate were added at 40 mass% to the resin matrix.

PEGDA of molecular weights 1000, 4000, 8000, and 10 000 Da were purchased from Monomer-Polymer and Dajac Labs (an MPD Chemicals Company). MAETAC, 2,2-dimethoxy-2-phenylacetophenone, and 1-vinyl-2-pyrrolidinone were purchased from Sigma Aldrich. The photo-initiator solution of 300 mg/mL of 2,2-dimethoxy-2-phenylacetophenone in 1-vinyl-2-pyrrolidinone was prepared using a vortex mixer.
The hydrogels were formed by dissolving the PEGDA into deionized (DI) water using a vortex mixer. The MAETAC was then added and vortexed until sufficiently mixed. Various formulations were created to obtain a hydrogel with the best blend of actuation and biocompatibility. The formulations for each of the samples are listed in Table 1. The photo-initiator solution was added just prior to applying ultraviolet (UV) radiation at a concentration of 100 μL of photo-initiator solution per 1 mL of hydrogel solution. The hydrogel solution was then injected into a rectangular glass mold and cross-linked with UV radiation at a wavelength of 365 nm and intensity of 10 W for 2 minutes. The hydrogels were then placed in phosphate-buffered solution (PBS) overnight to achieve equilibrium swelling. For actuation testing, samples were cut into 20 × 5-mm shapes before actuation.