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It is shown that the optimal design can be fabricated by 3D printing and shows significant enhancement in natural frequency and reduction in weight .
 design, be, 3D printing, reduction, weight
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:
 design, be, 3D printing, reduction, weight