8951
METHODS : Millipore ultrafiltration membranes of three different pore sizes were used as model lenticule materials . The nominal membrane pore sizes were 0 . 1 microm , 0 . 45 microm , and 3 microm ; the surface roughness increased in the same order The membranes were coated with a thin layer of collagen I and implanted in a circular pocket of the anterior cornea of adult cats , and were clinically evaluated for the extent of epithelialization and the persistence of epithelial attachment .
 collagen I
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 collagen I