Body Heat Drives New Drug-Delivery Micropump

When water is added and the patch is placed on the skin, the body heat and the added water causes the yeast and sugar to ferment, generating a small amount of carbon dioxide (CO2) gas, which pushes against a membrane, causing the pump to work continually pump for over two hours. According to the researchers, such miniature pumps could make possible drug-delivery patches that use arrays of microneedles to deliver a wider range of medications than is now possible using conventional patches.

The pump consists of stacked layers of polydimethylsiloxane (PDMS) and a silicon substrate that form a drug reservoir, and a yeast-solution-filled working chamber. The robustness of yeast allows for long shelf life under extreme environmental conditions. The generation of CO2 is a linear function of time for a given temperature, thus allowing for a controlled volume displacement. The researchers have developed a polymeric prototype with a slow flow rate of less than 0.23 μL per minute and a maximum backpressure of 5.86 kPa. The study describing the new pump was published online on August 24, 2012, in Lab on a Chip.

“Many drugs, including those for treating cancer and autoimmune disorders, cannot be delivered with patches because they are large molecules that won't go through the skin,” said lead author Babak Ziaie, PhD, a professor of electrical and computer engineering and biomedical engineering. “Although transdermal drug delivery via microneedle arrays has long been identified as a viable and promising method for delivering large hydrophilic molecules across the skin, a suitable pump has been hard to develop.”

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