Do-It-Yourself Device for Recovery of Cryopreserved Samples Accidentally Dropped into Cryogenic Storage Tanks

Summary

Here we present a low cost, durable cryotolerant device for sample retrieval from Dewar tanks filled with liquid nitrogen. The ease of construction and modular design of the device makes the process of sample retrieval from cryogenic tanks safe and easy.

Abstract

Liquid nitrogen is colorless, odorless, extremely cold (-196 °C) liquid kept under pressure. It is commonly used as a cryogenic fluid for long term storage of biological materials such as blood, cells and tissues ^1,2. The cryogenic nature of liquid nitrogen, while ideal for sample preservation, can cause rapid freezing of live tissues on contact - known as 'cryogenic burn'², which may lead to severe frostbite in persons closely involved in storage and retrieval of samples from Dewars. Additionally, as liquid nitrogen evaporates it reduces the oxygen concentration in the air and might cause asphyxia, especially in confined spaces².

In laboratories, biological samples are often stored in cryovials or cryoboxes stacked in stainless steel racks within the Dewar tanks¹. These storage racks are provided with a long shaft to prevent boxes from slipping out from the racks and into the bottom of Dewars during routine handling. All too often, however, boxes or vials with precious samples slip out and sink to the bottom of liquid nitrogen filled tank. In such cases, samples could be tediously retrieved after transferring the liquid nitrogen into a spare container or discarding it. The boxes and vials can then be relatively safely recovered from emptied Dewar. However, the cryogenic nature of liquid nitrogen and its expansion rate makes sunken sample retrieval hazardous. It is commonly recommended by Safety Offices that sample retrieval be never carried out by a single person. Another alternative is to use commercially available cool grabbers or tongs to pull out the vials³. However, limited visibility within the dark liquid filled Dewars poses a major limitation in their use.

In this article, we describe the construction of a Cryotolerant DIY retrieval device, which makes sample retrieval from Dewar containing cryogenic fluids both safe and easy.

Protocol

1. Assembly of Cryotolerant Device for Retrieval of Cryoboxes

1. Using pliers, straighten out one side of 3 sided strong-tie (Figure 1A) to make an L shaped strong-tie shown in Figure 1B. Note: The dimensions of strong-tie can be selected depending on the diameter of the neck of Dewar.
2. Secure two such strong-ties with a strong-tie T strap (Figure 2) using Crown bolt nut, washer and screw to form the Cryoscoop base as shown in Figure 3(A-B). Note: Two strong ties are used to allow retrieval of 5 ½ in. X 5 ½ in. cryoboxes.
3. Using a slotted pl....

Discussion

One of the most common methods of retrieving cryoboxes and cryovials from the bottom of the Dewar tank is to decant liquid nitrogen into a spare container and pull out the samples remaining in the flask or floating in the decanted liquid nitrogen. This is, however, an unsafe practice that may cause cryogenic burns or asphyxiation due to prolonged exposure to liquid nitrogen vapors². Other common way of retrieval of fallen cryovials involves use of cryovial tongs³. However, the limited visibility wit.......