The evolving impact of microfabrication and nanotechnology on stent design

Laser machining methods. A, After the direct-write method, a pulsed laser is scanned over the workpiece using mirrors. B, The masked-projection method is used to process larger regions of the workpiece with a wide, patterned beam.

Drug-containing reservoirs permit more advanced drug-release strategies.

Left, A fabricated sample as cut from the metal foil with microelectrodischarge machining. Right, Angled and side views of an expanded stent.²⁴ (Reprinted with the permission of Journal of Microelectromechanical Systems ©2004.)

Production of silicon micro-needles, as described by Henry.²⁶ A silicon wafer is coated with chromium, and lithographic methods are used to pattern the chromium into dots, approximately the same diameter as the base of the desired micro-needles (steps 1-3). A reactive ion etching technique is used to erode the silicon. The chromium dot array protects regions of the silicon wafer, leaving a microneedle pattern (steps 4-5). Silicon microneedles arrays can subsequently serve as masters to form molds for the fabrication of metal and polymer micro-needles arrays.²⁷

Hollow microneedles fabricated out of silicon, metal, and glass imaged by optical and scanning electron microscopy. A, Straight-walled metal microneedle from a 100-needle array fabricated by electrodeposition onto a polymer mold (200 μm tall). B, Tip of a tapered, beveled, glass microneedle made by conventional micropipette puller (900 μm length shown). C, Tapered, metal microneedle (500 μm tall) from a 37-needle array made by electrodeposition onto a polymeric mold. D, Array of tapered metal micro-needles (500 μm height) shown next to the tip of a 26 gauge hypodermic needle. (Reprinted with permission of the National Academy of Sciences, USA ©2003.)²⁷