Collagen-based compositions useful in the attachment of tissues, or the attachment of tissues to synthetic implant materials, are disclosed. The compositions comprise collagen crosslinked using a multifunctionally activated synthetic hydrophilic polymer. A particularly preferred composition comprises fibrillar collagen, a fiber disassembly agent, and a multifunctionally activated synthetic hydrophilic polymer. Methods are disclosed for using the compositions to effect the attachment of a native tissue to the surface of another native tissue, a non-native tissue, or a synthetic implant. Also disclosed are methods of using the compositions to prevent the formation of surgical adhesions.