29677
Hollow hybrid nanogels were prepared first by co - assembly of the citric acid - coated superparamagnetic iron oxide nanoparticles ( SPIONs ) ( 44 wt % ) with the graft copolymer ( 56 wt % ) comprising acrylic acid and 2 - methacryloylethyl acrylate units as the backbone and poly ( ethylene glycol ) and poly ( N - isopropylacrylamide ) as the grafts in aqueous phase of pH 3 . 0 into the hybrid vesicle structure , followed by in situ covalent stabilization via the photo - initiated polymerization of MEA residues within vesicles .
 citric acid, iron oxide, acrylic acid, 2 - methacryloylethyl acrylate, poly ( ethylene glycol ), poly ( N - isopropylacrylamide ), MEA
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 citric acid, iron oxide, acrylic acid, 2 - methacryloylethyl acrylate, poly ( ethylene glycol ), poly ( N - isopropylacrylamide ), MEA