Effects of polyvinylpyrrolidone on in vitro melamine-cyanurate crystal formation: an electron microscopy study

Melamine-cyanurate (M-C) crystals, formed by melamine and cyanuric acid, are water-insoluble urolites that can cause renal tubule occlusion, leading to kidney failure. The morphology of the crystals in vivo differs from that in vitro, being rounded in the former case but needle-like in the latter. The reason for this difference remains unknown, but we have previously found that serum proteins, such as bovine serum albumin (BSA), can contribute to in vitro formation of rounded M-C crystals. In the present study, using scanning electron microscopy, we confirmed that, like BSA, polyvinylpyrrolidone (PVP), a synthetic macromolecule, can alter the crystal morphology to a spherical form. The size and surface structure differed between BSA- and PVP-induced M-C crystals.