Unpowered Microfluidic Long Lifetime Time-Temperature Indicator

Reference#: P02937

Many perishable products have a limited lifetime that can be dependent, at least in part, on the temperatures to which the products are exposed. Moreover, in some cases, the length of time of such exposure may further impact the rate of degradation of the product. For example, some foods and pharmaceuticals may have a nominal expiration date at a certain temperature but may expire more quickly if they are exposed to other temperatures for a given time period.

Because products are often shipped and may change hands and experience different conditions during their shipment process, it cannot be assumed that a product that was initially shipped at a particular temperature, and arrives at its destination at the same temperature, has been maintained at that temperature throughout the shipping process. Moreover, the simple fact that a temperature fluctuation occurred, even a fluctuation above a certain amount, may not necessarily mean that the product is compromised. Thus, an indication that a certain temperature was reached (for which there are existing commercial devices), without a corresponding indication of the length of time that the exposure to that temperature lasted, may lead to unnecessary destruction of products.

To address the issues described above, time-temperature indicators of various types have been developed. Many such time-temperature indicators rely on powered monitoring devices, chemical reactions, or diffusion of controlled dyes. However, the properties of the chemicals or dyes may change over time, and the power is only available for a limited time. Thus, such devices may have a limited life span and may not be very robust.

Researchers at APL have developed a rugged, non-powered time-temperature indication device. The output of the device is simply the distance that a fluid migrates in a capillary tube. With the right choice of fluid, fluid reservoir, and capillary, the fluid always moves in one direction, and the distance moved tracks the cumulative time-temperature exposure over target lifetimes longer than 10 years. Capacitive readout offers potential for stand-off radio-frequency identification applications.

Mr. K. Chao
Phone: (443) 778-7927