Preventable infections kill millions of children in poor countries, partly because reliable refrigeration for vaccines isn't always available. Vaccines are refrigerated to slow the rate at which the biological molecules they contain gradually degrade, largely due to contact with water.

Fibroin, a protein in silk, forms stable sheets that contain tiny pockets lined with molecules that repel water. You can trap a biological molecule within these pockets by dissolving it with fibroin in water, then drying it to form a film. Tucked away in a pocket, the molecule is protected.

The Tufts University team made such films with the live measles, mumps and rubella viruses in the MMR vaccine. The films kept the viruses undamaged for six months, even powdered and at temperatures of 45 °C, when regular freeze-dried vaccines degraded rapidly.