Fabrication microneedles

Henry S, McAllister D, Allen MG, Prausnitz MR (1998) Micro-fabricated microneedles a novel method to increase transdermal drug delivery. J Pharm Sci 87(8) 922-925... 

The proposed fabrication process of microneedles and reservoir involves isotropic and anisotropic etching processes using standard silicon wafers. The desired shape of microneedle structures is controlled is achieved by controlling the etching timings at various processing steps. Three set of chrome masks were fabricated. Microneedle Mask MNl has been used to fabricate microneedle outside shape. Microneedle mask MN2 has been used to fabricate inner hole called lumen while the third microneedle Mask has been used for backside reservoir etching. 

Microneedles with high aspect ratio have been fabricated using a series of combined isotropic and anisotropic etching processes in ICP etching machine. The SEM images of the fabricated microneedles are shown in Fig. 7 and 8 respectively. 

Park, J.-H., Allen, M.G. and Prausnitz, M.R. (2005) Biodegradable polymer microneedles fabrication, mechanics and transdermal drug delivery. Journal of Controlled Release, 104, 51-66. 

FIGURE 18.2 Scanning electron micrographs of silicon microneedles, (a) Silicon microneedles micro-fabricated using a modified form of the BOSCH deep reactive ion etching process. The microfabrication process was accomplished at CCLRC Rutherford Appleton Laboratory (Chilton, Didcot, Oxon, UK). The wafer was prepared at the Cardiff School of Engineering, Cardiff University, UK. Bar = 100 pm (b-d) platinum-coated silicon microneedles prepared using a wet-etch microfabrication process performed at the Tyndall National Institute, Cork, Ireland. Bar = 1 mm (b), 100 pm (c,d). 

Wilke, N., et al. 2004. Fabrication and characterization of microneedle electrode arrays using wet etch technologies. Abstract presented at EMN04, Paris. 

Tan, P.Y.J., et al. 2002. Novel low cost fabrication of microneedle arrays for drug delivery applications. Proc SPIE 4936 113. 

A Si microneedle has been fabricated, though the application was not in making the ESI tip, but in transdermal drug or vaccine delivery. Figure 7.40 shows how the microneedle penetrates a 10-pm-thick A1 foil. This needle has the openings in the shaft, rather than in an orifice at the tip [791]. 

The microneedle concept was first proposed as a technique for transdermal drug delivery in the 1970s [1], and the recent advances in the microelectronics industry have provided the technical capability to make microneedles into reality. The first microneedle experiments were reported in 1998 [2], Since then, there has been a rapid increase of interest in the field. Much of this effort concerns the development of novel needle fabrication technologies by adopting various needle designs and materials for use in biological and pharmaceutical applications. 

The fabrication of microneedles, in and of itself, is the main challenge in microneedle development. The task involves finding fabrication techniques that are capable of defining materials precisely in three dimensions at the microscale and are amenable to mass production. Additionally, the material used to produce the microneedles must be compatible with the fabrication tools and offer sufficient resistance to buckling, bending, and shear forces. 

Transdermal drug delivery with Si pSi is fabricated on top of Si microneedle arrays microneedles by electrochemical etch (the rest of the microneedles being protected) Biodegradability useful in case top of microneedles breaks off and remains in the skin. Enhanced drug loading capability Ji et al. 2006... 

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