Microfabricated Needles

McAllister D, et al. Microfabricated needles for transdermal delivery of macromolecules and nanoparticles fabrication methods and transport studies. Proc Natl Acad Sci USA 2003 24 13755-13760. 

Microfabricated needles Microhypodermic needles Microprojections Microscale needles Microtips and microspikes... 

The applications of microneedles are many and varied. In the fields of genetic engineering and molecular and cell biology, it is desired to develop a method to introduce peptides, proteins, oligonucleotides, DNA, and other probes into ceDs to alter their functions. For this purpose, microneedles can be applied for the delivery of molecules through impermeable membranes into cells. It has been demonstrated that microfabricated needle arrays could be used to deliver DNA into plant and mammalian cells, inducing cell transformation. 

In addition to these various chemical treatment methods, a number of physical methods of cell disruption can be used in a chip-based system. These physical methods include osmotic shock, which occurs when cells are suspended in a hypotonic solution shearing and fracturing of cells walls and membranes using microfabricated needles or spherical particles (beads) application of an electric field that causes electroporation ultrasonication of the cell sample and thermal lysis. 

FICU RE 21.30 SEM pictures of microfabricated needle-like (a) and hollow needle (b) probes, (c) Zoomed-in SEM image of a needle-like probe showing the submicrometer-sized Pt electrode located at the needle apex. Scale bars in (a through c) 10, 5, 1 pm, respectively. (Erom Fasching, R.J. et ah. Sens. Actual. B, 108, 964, 2011. With permission.)... 

These devices are similar to the microneedle devices produced by microfabrication technology. They include the use of needle-like structures or blades, which disrupt the skin barrier by creating holes and cuts as a result of a defined movement when in contact with the skin. Godshall and Anderson [101] described a method and apparatus for disruption of the epidermis in a reproducible manner. The apparatus consists of a plurality of microprotrusions of a length insufficient for penehation beyond the epidermis. The microprotrusions cut into the outer layers of the skin by movement of the device in a direction parallel to the skin surface. After disruption of the skin, passive (solution, patch, gel, ointment, etc.) or active (iontophoresis, electroporation, etc.) delivery methods can be used. Descriptions of other devices based on a similar mode of action have been described by Godshall [102], Kamen [103], Jang [104] and Lin et al. [105]. 

Pearton M, Allender C, Brain K, Anstey A, Gateley C, Wilke N, Morrissey A, Birchall J, Gene dehvery to the epidermal cells of human skin explants using microfabricated micro needles and hydrogel formulations. Pharm Res, 2007, 25, 407-16. 

Hollow microneedles work in a way similar to regular h3q)odermic microneedles. Fluids flow through the needle bore and into the tissue. The rate of fluid deUveiy is much faster than with solid microneedles, and the flow rate can be monitored and COTitroUed over time. Using microfabrication... 

As far as microfabrication is concerned, especially with silicon-based processes, microneedle design can be classified as out-of-plane or inplane depending on the orientation of the needle relative to that of the substrate material. Out-ofplane design refers to the microneedle configuration that protmdes perpendicularly from the plane of the substrate material (e.g., a silicon wafer), while in-plane refers to the design where the resulting needle lies lengthwise in the substrate plane. Examples of various microneedles (solid and hollow, out-of-plane and in-plane) are shown in Fig. la-d. 

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