Other additives such as oil and wax emulsions can modify the medium. These powders are often mixed with oil-water emulsions. In pharmaceutical formulations, MEA is used primarily for buffering or preparation of emulsions. Synthetic adhesives are based on elastomers, thermoplastics, emulsions, and thermosets. Examples of depot type adjuvants are oil emulsions. Early holograms used silver halide photographic emulsions as the recording medium. Transdermal estradiol is available in the forms of patches, gels, emulsions, and sprays. It can also improve the stability of foams and emulsions. Two liquids can form different types of emulsions. The agents are materials used to thicken and stabilize liquid solutions, emulsions, and suspensions. MCTs are an ingredient in some specialised parenteral nutritional emulsions in some countries. They are delivered as oils, water solutions, or water based emulsions. Polysorbate 20 is used as an excipient in pharmaceutical applications to stabilize emulsions and suspensions. Emulsions, being liquids, do not exhibit a static internal structure. Estradiol emulsions and sprays are administered daily.