The invention provides a method of preventing or reducing the growth of crystals in a substance which is susceptible to crystal growth in which colloidal particles having an amphiphilic structure, e.g. Janus particles, are contacted with the substance. Colloidal particles suitable for use in the invention include cross-linked, colloidal materials formed from hydrophobic monomers such as acrylates or methacrylates and hydrophilic monomers such as those derived from acrylic and/or methacrylic acid. The colloidal particles find particular use in methods of cryopreservation of biological samples (e.g. cells, tissues or organs), as a texture modifier in frozen food products, in the inhibition of gas hydrate formation, and as scale inhibitors.
