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Existing commercial three-dimensional ( 3D ) printing systems based on powder bed fusion approach can normally only print a single material in each component .
 three-dimensional, 3D, powder bed fusion, print, material, component
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:
 three-dimensional, 3D, powder bed fusion, print, material, component