8511
The versatility of this hydrogel system was exemplified through variations in the degree of HPA substitution , polymer concentration , and the concentration of cross - linking reagents ( horseradish peroxidase and H ( 2 ) O ( 2 ) ) , which resulted in a range of mechanical properties and gelation kinetics for these gels .
 Chemical: HPA; Chemical: H ( 2 ) O ( 2 )
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: HPA; Chemical: H ( 2 ) O ( 2 )