21208
Self - assembling multidomain peptides have been shown to have desirable properties , such as the ability to form hydrogels that rapidly recover following shear - thinning and the potential to be tailored by amino acid selection to vary their elasticity and encapsulate and deliver proteins and cells .
 amino acid
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 amino acid