Due to the incapacity of many drugs to enter the skin at therapeutically useful rates, transdermal drug delivery with the advantages of controlled release, high safety and low degree of side effects is seriously hampered in efficiency and success. A microneedle approach can dramatically promote transdermal delivery, especially for macromolecules. In this paper, a fabrication process for hollow out-of-plane hafnium oxide microneedles on silicon wafer using only one mask has been developed. Photoresist is spun on a 4″ silicon (100) wafer and patterned by a mask. Deep reactive ion etching is used to form deep molds inside the wafer. A hafnium oxide film is deposited by atomic layer deposition to cover the top side of the wafer and the inside walls of the molds. Then the back side of silicon wafer is etched under the condition of 30 wt% KOH solution and a water-bath temperature of 81 °C until exposed hollow hafnium oxide microneedles are obtained. Compared to the processes that have been developed for silicon, silicon oxide, or polymer microneedles, the process presented here is simpler, and the strength and flexibility of hollow hafnium oxide microneedles can be easily adjusted by modifying the depositing time of hafnium oxide films. Hafnium oxide microneedles have potential applications in transdermal drug delivery.
Bibliographical noteFunding Information:
The authors would like to thank Tony Whipple, Mark Fisher, Paul Kimani and other members of the Minnesota Nano Center at the University of Minnesota for their advice and help. Funding was provided by State Scholarship Fund of China and the open research fund of Shanghai key Laboratory of Miltidimensional Information Processing, East China Normal University (Grant Nos. 201306145016 and 40500-542500-15202/007/002)
This work is supported by the State Scholarship Fund of China, and the open research fund of Shanghai Key Laboratory of Multidimensional Information Processing, East China Normal University, China.
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