Multi-level encapsulation strategy for brine gels: Enabling leakage-free thermal energy storage in portable vaccine preservation systems

The development of reliable, low leakage phase change gels is critical for ensuring vaccine cold chain safety and efficacy. This study presents a multi-stage network encapsulation strategy to fabricate leakage-resistant composite phase change materials (CPCMs), combining ionic cross linking and expanded graphite (EG) physical adsorption. The optimized composite retained 91.4 % latent heat (231.3 J/g), achieved high thermal conductivity (3.15 W/(m·K)), and exhibited minimal mass loss (<3.7 %). Accelerated thermal cycling tests (400 cycles, −40 °C to 25 °C) demonstrated robust cycling stability, with <13 % latent heat degradation. In addition, the aluminum plastic film encapsulation ensured zero leakage, aligning with stringent biomedical safety standards. Integration of composite cold storage modules at the box top extended the effective storage duration within the −25 °C to −15 °C range to 12.2 h (82.6 % improvement), addressing insufficient thermal buffering in conventional systems. This design enabled rapid thermal response and uniform temperature distribution within the transport box, providing a scalable solution for biomedical cold chain logistics.