4-Arm PEG-Dopamine has 4 dopamine molecules attached to the four arms through an amide bond. Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. On the chemical side, polydopamine is polymerized dopamine that is formed from a slightly basic dopamine solution in the presence of oxygen, and it is a bioinspired material from adhesive polyphenolic proteins in mussels.