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In this study , an innovative method , electrically-assisted ultrasonic nanocrystal surface modification ( EA-UNSM ) was introduced to process 3D-printed Ti-6Al-4V samples .
 surface modification, process, 3D-printed, samples
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:
 surface modification, process, 3D-printed, samples