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Material extrusion AM , known commercially as Fused Filament Fabrication ( FFF ) technology , is a widely used polymer AM process , however , the effects of inherent porosity on mechanical strength continues to be researched to identify strength improvement solutions .
 Material extrusion AM, as, Filament, Fabrication, FFF, technology, polymer, AM process, porosity, mechanical strength, be, strength
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:
 Material extrusion AM, as, Filament, Fabrication, FFF, technology, polymer, AM process, porosity, mechanical strength, be, strength