1917
Even though it is hard to totally avoid the use of support structures , researchers in still tried to obtain optimal 3D TO structures without supports for several relative simple demonstration cases .
 engineering feature: support structures; concept or principle: 3D; application: supports; manufacturing process: simple
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: support structures; concept or principle: 3D; application: supports; manufacturing process: simple