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One biological structure that is of particular interest to biomimetic studies , and which has been studied extensively using microCT , is the lightweight structure of bird feathers and bones .
 engineering feature: biological structure; concept or principle: biomimetic studies; process characterization: microCT; machine or equipment: lightweight structure; material: bird feathers
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 engineering feature: biological structure; concept or principle: biomimetic studies; process characterization: microCT; machine or equipment: lightweight structure; material: bird feathers