7399
Pores generated by fused-filament fabrication ( FFF ) are characterized , charged , and the resultant piezoelectret activity measured .
 Pores, fused-filament fabrication, FFF, piezoelectret
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:
 Pores, fused-filament fabrication, FFF, piezoelectret