21724
Rapid self - healable and biocompatible hydrogels were prepared using the selective formation of metal - ligand interactions between selected metal ions and phosphate end groups of poly ( ethylene glycol ) ( PEG ) .
 Chemical: phosphate; Chemical: poly ( ethylene glycol ); Chemical: PEG
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: phosphate; Chemical: poly ( ethylene glycol ); Chemical: PEG