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:Recent years have seen growing interest in the automated design and synthesis of microfluidic biochips [39], [44], [47]–[51], [53]–[56], [59]–[61], [63]–[67], [69].
Category: