Bulk and micropatterned conjugation of extracellular matrix proteins to characterized polyacrylamide substrates for cell mechanotransduction assays

Increasing numbers of cell mechanotransduction studies art currently utilizing elastic substrates fabricated from polyacrylamide in the form of thin gels. Their versatility depends on the ability to ensure the appropriate gel stiffness and control the uniformity and geometry, of extracellular matrix protein coating of the gel. Beginning with a brief quantitative emphasis on the elastic properties of polyacrylamide gels, we present an inexpensive and highly reproducible method for uniform coating with a wide variety of extracellular matrix proteins. We used a reducing agent, hydrazine hydrate, to modify nonreactive amide groups in polyacrylamide to highly reactive hydrazide groups that can form covalent bonds with aldehyde or ketone groups in oxidized proteins. This simple conjugation method overcomes the limitations of previously used photoactivatable cross-linkers: nonuniform coating due to nonuniformity of irradiation and technically challenging procedures for micropatterning. As demonstrated in our study of cell polarity, during constrained migration, this conjugation method is especially effective in gel micropatterning by manual microcontact printing of protein patterns as small as 5 mu m and enables numerous studies of constrained cell attachment and migration that were previously unfeasible due to high cost or difficulty, in controlling the protein coating.