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Material extrusion additive manufacturing is widely used for porous scaffolds in which polymer filaments are extruded in the form of log-pile structures .
 Material extrusion additive manufacturing, porous scaffolds, polymer filaments, extruded
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 additive manufacturing, porous scaffolds, polymer filaments, extruded