The effect of the preparation process on the swelling behavior of silk fibroin-polyurethane composite hydrogels using a full factorial experimental design

Polyurethane prepolymer (PUP) was synthesized by polyethylene glycol (PEG) and polypropylene glycol (PPG) as the soft segments, isophorone diisocyanate (IPDI) as the hard segment and dimethylol propionic acid (DMPA) and diethylene glycol (DEG) as chain extenders. Silk fibroin (SF)-PU composite hydrogels were prepared by SF and PUP through chemical crosslinking and physical crosslinking interactions. A full factorial experimental design with four factors and four levels was applied to optimize the craft of preparing SF-PU composite hydrogels. The molecular weight of PEG, IPDI/(PEG+PPG) (molar ratio), PEG/(PEG+PPG) (molar ratio) and SF/(SF+PU) (mass ratio) were the factors. The swelling behavior of hydrogels was tested in deionized water at 30 degrees C. The results showed that the equilibrium swelling ratio (ESR) was the largest by tuning the molecular weight of PEG to 4000, IPDI/(PEG+PPG)(molar ratio) to 3, PEG/(PEG+PPG) (molar ratio) to 40% and SF/(SF+PU) (mass ratio) to 2%. Fickian diffusion played a dominant role in the initial stage of swelling. For the whole process, the results fitted well into the Schott second-order kinetic equation.