After experimenting with more than a dozen different formulations, drying them with custom-made machinery and heating them in ovens to test shelf life, Nektar hit upon a successful recipe that mixes insulin with glycine (an amino acid), citrate (the salt of an organic acid found in humans) and mannitol (a sugar used in intravenous products).
After drying and being treated with another solvent, the polymer settles into a regular hexagonal pattern--a kind of plastic-like screen--on the crystalline surface.