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Recent advances in additive manufacturing promise extending the presented grading strategy for polymeric , composite , and metallic 3D printed cellular materials to fabricate high performance lightweight structural elements at a relatively low cost .
 additive manufacturing, composite, metallic, 3D printed, materials, fabricate, performance lightweight, elements
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:
 additive manufacturing, composite, metallic, 3D printed, materials, fabricate, performance lightweight, elements