A-199 Development and evaluation of low-cost reusable subzero phase change material systems for frozen specimen shipment

Abstract Background Numerous clinical analytes are sensitive to thermal degradation and require specimens to be transported in a frozen state to maintain stability. Cold chain transport for frozen specimens typically uses dry ice. While effective, dry ice is not suitable for use in most collection sites due to the cost of constant replenishment and the required hazardous good training for site staff. Furthermore, dry ice is bulky, embodies significant CO2 emissions, and is subject to a 5.5lb commercial air-shipping limit which restricts endurance time. Here we introduce a set of sub-zero phase change materials (PCMs) based on low-cost salt-in-water formulations. These inexpensive PCMs were packaged in commercial heat-seal jugs and bottles to facilitate rapid prototyping and deployment. Methods Three low-cost, non-toxic PCM formulations were developed from a mixture of tap water and the following commodity salts near the eutectic concentration: (1) KCl (2) a mixture of KCl and NaCl, (3) a mixture of KCl, NH4Cl, and NaCl. The melting temperatures were measured by exposing test packages to an environmental chamber while logging internal temperature. Two packing configurations were developed for frozen specimens using these PCMs: (1) a large EPS insulated shipper to provide multi-day subzero shipping (2) vacuum insulated containers for rapid freezing and short-term lockbox maintenance To evaluate the first configuration, 4x 32oz jugs containing a solution of KCl in water were pre-frozen in a conventional -20C freezer and placed in a standard EPS shipper. An identical EPS shipper was filled with the commercial air shipment limit (5.5lb/2.5kg) dry ice as a control, and both shippers were exposed to simulated summer conditions for 72hrs with internal temperature logging. To evaluate the second test configuration, 6oz bottles containing each of the 3 saltwater PCMs were pre-frozen and placed in 18oz vacuum flasks along with a 4mL specimen tube containing water. The internal temperature of each specimen tube was measured by a temperature logger over the course of 36hrs under varying external temperature. The initial freezing rate was compared to a matched 4mL specimen tube placed in a conventional -20C freezer. Results The following phase change temperatures were assessed for the 3 salt-in water PCMs: -10.8C (KCl), -23.4C (NaCl + KCl), -25.8C (NaCl+KCl+NH4Cl). In the first package test set, the KCl-based PCM outperformed dry ice, maintaining sub-zero temperature within the EPS shipper for 48hrs compared to 40hrs for the dry ice control. In the second package test, specimens placed in a vacuum flask with frozen KCl/NaCl and KCl/NaCl/NH4Cl PCMs froze and reached -10C in 28 minutes and 32 minutes respectively compared to 86 minutes for conventional freezing. Both PCMs maintained specimen temperature below the freezer temperature (-20C) for more than 32hrs. In a 6 month pilot test of a KCl-based vacuum flask system in lockboxes across 5 sites in Florida, no instances of thawed specimens were observed during pickup. Conclusion Salt-in-water based PCMs stored in plastic bottles or jugs are a cost-effective and reusable alternative to dry ice for fast freezing, short-term maintenance, or multi-day shipping of frozen specimens.