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This great achievement is mainly ascribed to the unique characteristics of IF-WS2 nanoparticles , acting as both reinforcing and lubricating agents , indicated by a reduction in coefficient of friction .
 nanoparticles, as, reduction, coefficient of friction
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:
 nanoparticles, as, reduction, coefficient of friction