Icy microneedles deliver cells across skin

A new microneedle patch offers a cool way to deliver therapeutic cells across skin. Microneedles made of ice with suspended cells frozen in the tips penetrate skin before melting instantly and releasing the cells.

Microneedles have been successfully used to deliver a variety of drugs, often with their payloads dissolved in liquid that seeps through the skin penetrations made by the needles. Delivering cells with microneedles has required drying and then reconstituting cells, which doesn’t work well for mammalian cells, or has involved hollow microneedles, which are more complicated to make and sacrifice some of the advantages of other types of microneedles, says Mark R. Prausnitz, an expert on microneedle drug delivery at the Georgia Institute of Technology. To address these problem, Chenjie Xu of the City University of Hong Kong and coworkers made microneedles of ice to preserve cells and deliver them through skin (Nat. Biomed. Eng. 2021 DOI: 10.1038/s41551-021-00720-1). Such devices could be used to deliver cell-based cancer vaccines or stem cell therapies.

The researchers make the microneedles of an aqueous solution of saline, dimethylsulfoxide (DMSO), and sucrose. The DMSO and sucrose protect cells from damage at cryogenic temperatures. The researchers add cells to the solution, transfer the solution to polymeric microneedle molds, allow the cells to settle into the tips, and freeze the mixture at successively colder temperatures.

The microneedles, which are about 900 µm long, are strong enough to penetrate skin. They begin melting within 30 s of being removed from liquid nitrogen (−196 °C) in a 24 °C room.

Xu and coworkers used the microneedle patches to deliver cancer vaccines to mice with melanoma tumors. Cells delivered in this way elicited higher antigen responses and slower tumor growth than cells delivered via other types of injections.

Prausnitz calls the device “an exciting new microneedle technology that can enable delivery of mammalian cells to the skin.” He notes that the need to keep the patches frozen until use will require specific storage conditions and training to make sure health professional can use them correctly.

Xu agrees that the need for such low temperatures limits the practicality for remote areas and developing countries. He and his colleagues are working on new formulations that will allow the patches to be transported and stored using −20 °C freezers rather than −80 °C freezers, he adds.