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Etching of PVP from the PLLA - PVP composite fibers doped with increasing PVP concentrations yielded PLLA fibers with increasing nano - scale surface roughness and porosity , which increased the fiber hydrophilicity dramatically .
 PVP, PLLA, PVP, PVP, PLLA
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 PVP, PLLA, PVP, PVP, PLLA