Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:5% gelatin coated chamber slides in RPMI-B27 medium supplemented with 10% FBS, 10 uM Y-27632 (Sigma), Polybrene (Millipore) and 5000 particles per cell of a lentivirus expressing Cre under the striated muscle-specific CK7 regulatory cassette, based on the muscle creatine kinase promoter (MCK) [9–11].
Category: