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Fabricating needle arrays with a gray-scale x-ray mask
| Content Provider | Semantic Scholar |
|---|---|
| Author | Mekaru, Harutaka |
| Copyright Year | 2008 |
| Abstract | Microscopic needles long enough to penetrate skin but short enough to avoid touching nerves provide a method for painless injections. Research into a process for mass-producing microneedle arrays for drug delivery is leaping forward as the needles become a commodity. A painless needle can be less than 150μm long for injecting cosmetics, but for delivering medicine it must be 500μm–1mm, so that it can reach the subcutaneous tissue or even the underlying muscle. Short needles are easily created by silicon (Si) dry etching. Fabricating longer ones, however, is quite difficult. To solve this problem, we used x-ray lithography, which can handle a resist thicker than 1mm, combined with a gray-scale mask. A microstructure fabrication method called LIGA (from the German: ‘Lithographie,’ ‘Galvanik,’ and ‘Abformung’)1 already incorporates binary x-ray lithography. In a typical LIGA process, a resist master is produced by x-ray lithography, and a metallic mold is replicated from the master by electroforming. Then the pattern can be mass-produced using a molding technique. Because of its laserlike directional property, a synchrotron source is used to produce x-rays. LIGA has been successfully employed to make pillar structures with vertical sidewalls. However, because x-rays cannot be easily focused or reflected, it has not been successful in building 3D structures with sloped sidewalls. We proposed that the slopes needed to make pointed needles could be achieved by incorporating a gray-scale x-ray mask into the LIGA process. A conventional binary x-ray mask consists of a membrane with a pattern made of an x-ray-absorbing heavy element such as gold. The x-rays penetrate the membrane but are blocked completely by the absorber. Fabrication of the mask involves photolithography and electroplating to create 4μm-high vertical absorber sidewalls. We developed a gray-scale mask with inclined-sidewall absorber sections so that we could create a reFigure 1. (a) Photograph of x-ray gray-scale mask with silicon (Si) absorbers on an x-ray-transparent membrane. (b) Scanning electron microscope (SEM) image of Si cones before backside etching of the substrate. |
| File Format | PDF HTM / HTML |
| DOI | 10.1117/2.1200804.1113 |
| Alternate Webpage(s) | http://www.spie.org/documents/Newsroom/Imported/1113/1113-2008-04-18.pdf |
| Alternate Webpage(s) | https://doi.org/10.1117/2.1200804.1113 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
