4847
In current literature , the environmental sustainability for 4D printing has not yet been evaluated , leading to unknown environmental impacts that could be caused by 4D printing processes and/or materials .
 sustainability, 4D printing, be, 4D printing, materials
Please list all entity words in the text that fit the category. Output format is "word1, 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:
 sustainability, 4D printing, be, 4D printing, materials