In Tuesday’s global health quiz, we asked what a phase-change material is and what it’s got to do with vaccines.
A phase change takes place when a solid, liquid, or gas changes from one state to another without a change in its chemical composition. Think water freezing to ice, then melting to liquid again. Phase-change materials, or PCMs, either absorb or give off heat as they move between solid and liquid states. As temperatures cool, for example, a PCM in its liquid state becomes solid and releases stored heat. When temperatures go up, a PCM in its solid state becomes liquid, absorbing heat and cooling whatever’s nearby.
What gives PCMs even more potential is that the temperature at which they change phases can be higher than 32° F (0° C). This is helpful if your goal is to keep items within a certain temperature range—say between 32° F and 46° F (0° C to 8° C), the temperature range at which many vaccines must be stored to prevent spoiling.
PATH is working on including phase-change materials in a plastic liner that could be used as a protective barrier in vaccine carriers to keep vaccines from freezing. The carriers could work with traditional ice packs to help protect vaccines from heat when the temperature goes up and—just as importantly—they could help protect vaccines from freezing that can occur when frozen ice packs make the container too cold.
We’re now expecting to begin testing PCMs in vaccine carriers in Vietnam. We’ll keep you posted as results become available. In the meantime, for a look at more of our work in tools for vaccines, see our technologies for vaccines slideshow.