Millimeter-scale macrocapsules with cold energy storage and temperature indication for vaccine storage

This study aims to prepare millimeter-scale macrocapsules with cold energy storage and temperature indication suitable for the requirement of vaccine storage (−25 °C ∼ -15 °C). In these macrocapsules, reversible thermochromic microencapsulated phase change materials (TC-MPCMs) are used as dispersions, and flexible calcium alginate is served as the polymer matrix. Macrocapsules exhibit a particle size distribution from 0.5 mm to 3.0 mm, with a melting temperature of −18.4 °C, a melting enthalpy of 86.0 J/g and an encapsulation efficiency of 45.5 %. After melting of the PCMs (Phase change materials), these macrocapsules can undergo a reversible discoloration, with a color difference of 27.54. Additionally, the volatilization of internal PCMs can also trigger the discoloration reaction. After 100 thermal cycles, the latent heat loss of the macrocapsules is less than 5 %, and the calcium alginate shell material delays the thermal decomposition of internal PCMs. Finally, the storage-release cold energy test shows that at 25 °C, the macrocapsules can maintain the ideal temperature range (−25 °C ∼ -15 °C) for 10.34 min. The millimeter-scale macrocapsules successfully address the issues of ultrafine powder contamination, difficulty in reuse and recycling of micron-scale TC-MPCMs, and show excellent potential for vaccine frozen storage.