Allografts are produced in different formats. The temperature and method of storage is dependent on the type of tissue, its method of preservation, and its intended use. Methods of cold storage for tissue include refrigerated, frozen, or frozen-cryopreserved techniques, while simple ambient room temperature is appropriate for lyophilized, dehydrated, or desiccated tissues. 1
Standards have been set for cold storage of tissues which identify acceptable temperature ranges and their impact on shelf life. Tissues that can be kept refrigerated (above freezing, 0°C to 10°C) most commonly include placental tissues, cellular tissues, and osteoarticular or osteochondral grafts. The shelf life will vary based on the tissue and processing method. Placental tissue storage temperatures are currently established by the processing tissue bank. 1
Frozen and cryopreserved allografts must be stored at ultra-low temperatures to maintain their viability. Ultra-low freezer temperatures of -20°C to -39°C generally allow a shelf life of 6 months, whereas -40°C to -86°C allow longer terms up to 5 years. For example, tendons, skin, and osteoarticular grafts can be stored at -20°C to -39°C for 6 months or less, and at -40°C to -86°C (or colder) for up to 5 years. 1
Frozen and cryopreserved tissues are not the same. Cryopreserved tissues are specially preserved with a solution containing a cryoprotectant, such as glycerol or dimethylsulfoxide. 1 The purpose is to prevent cell death during freezing and thawing. Cryopreserved grafts are frozen slowly at a controlled rate and are used in procedures requiring viable cells such as chondrocytes.
Cardiac and vascular tissues are cryopreserved and can only be stored at -100°C or colder. 1 Reproductive tissues such as semen and ova must be stored in liquid nitrogen, in either the liquid or vapor phase. Cellular and birth tissues have no FDA-established standards, and as such the temperatures are established by the tissue bank. 1
Lyophilized tissue, commonly referred to as “freeze dried tissue,” is tissue that has been dehydrated for storage by converting the water to gas under a vacuum that extracts moisture. 1 Dehydrated and dessicated tissues are created by removing the water from the tissue, accomplished through chemical means such as alcohol soaks, critical/supercritical drying, simple air drying, or drying in a desiccator. 1 Lyophilized, dehydrated, and dessicated tissues can be stored at ambient room temperature. 1
A temperature monitoring system is required for both refrigerated and frozen systems, which must be utilized to document temperatures and to alert staff with audible and/or visual alarms when temperatures stray outside of set acceptable limits. 1 Many modern freezers and refrigerators also have alarms for power outages, low battery, door opening, filter blockages, or system failures.
Standards of procedure require operational protocols to be in place for reviewing temperature logs, and documenting the review. When storage methods utilize liquid nitrogen cooling, monitoring of either temperature or liquid nitrogen levels is necessary, and documentation is required at regular intervals. 1
1. American Association of Tissue Banks. (2016). Standards for Tissue Banking (14th ed.). J. C. Osborne, K. G. Norman, T. Maye, P. Malone, S. A. Brubaker, et al. (Eds.). Bethesda: Naval Medical Research and Development Command. Available from: