Seung-Joon Paik

Hollow polymer microneedle array fabricated by photolithography process combined with micromolding technique

Transdermal drug delivery through microneedles is a minimally invasive procedure causing little or no pain, and is a potentially attractive alternative to intramuscular and subdermal drug delivery methods. This paper demonstrates the fabrication of a hollow microneedle array using a polymer-based process combining UV photolithography and replica molding techniques. The key characteristic of the proposed fabrication process is to define a hollow lumen for microfluidic access via photopatterning, allowing a batch process as well as high throughput. A hollow SU-8 microneedle array, consisting of 825μm tall and 400 μm wide microneedles with 15-25 μm tip diameters and 120 μm diameter hollow lumens was designed, fabricated and characterized.

Fabrication and Characterization of Polymer Hollow Microneedle Array Using UV Lithography Into Micromolds

Drug delivery through micromachined needles is an attractive alternative to intramuscular and subdermal injection by hypodermic needles, due to the potential for reduced pain caused by the micro-sized needles. In this paper, a polymer-based fabrication process using UV lithography into micromolds is developed, allowing the fabrication of microneedle (MN) shafts, tips, lumens, and substrate baseplate using lithography. Using UV lithography into micromolds allows complex three-dimensional structures to be defined, since both mask patterns and mold topography are available to define the structures. A hollow MN array and baseplate, in which the needle lumens extend through the thickness of the baseplate, are demonstrated. Fabricated SU-8 MNs are 825 μm in height and 400 μm in width, with a pyramidal tip; the needle lumen, 120 μm in diameter, intersects with one of the faces of the pyramidal tip. Mechanical characterization of the fabricated MNs shows that the fracture force of a single needle against a rigid surface is 12.0 N. The insertion force of a single needle into porcine skin is empirically determined to be 2.4 N. The fracture force of the needle against porcine skin is observed to be in excess of 90 N.

Hypodermic-Needle-Like Hollow Polymer Microneedle Array: Fabrication and Characterization

A hollow polymer microneedle array with tips and lumens that mimic conventional hypodermic needles, fabricated using UV lithography, and a single-step micromolding technique, is presented for drug delivery into skin. This 6 × 6 needle array consists of 1-mm tall high-aspect ratio hollow microneedles with sharp beveled tips and 150-μm diameter side-opened lumens. A 2-D lithographic mask pattern and the topography of the micromold are utilized simultaneously to define the geometry of the beveled tip and the position of the lumen. Mechanical insertion and fluidic injection characterization of these hypodermic-needle-like (HNL) microneedles (MNs) were performed using excised porcine skin as a substrate. The required insertion force of an HNL MN is 0.275 N, which is comparable with that of a 26-gauge hypodermic needle, 0.284 N. These results are an order of magnitude reduction in insertion force over pyramidal-tip MNs of comparable diameter previously reported by us. This insertion force reduction confirms that the tip geometry is an important factor in utilization of MNs in these applications. No needle fracture was observed under an optical microscope following the pressing of an HNL MN against excised porcine skin with application force of 50 N. Preliminary manual injection of dye through an HNL MN from a syringe into excised porcine skin verified the injection functionality of HNL MNs. [2013-0219].

Hypodermic-needle-like hollow polymer microneedle array using UV lithography into micromolds

This paper presents a polymer hollow microneedle array for transdermal drug delivery that is fabricated using UV photolithography and a single-step micromolding technique. This fabrication process patterns a 6×6 array of 1mm tall high-aspect-ratio hollow microneedles with sharp beveled tips and 150µm diameter side-opened lumens. The geometry of the beveled tip and the position of the lumen are defined simultaneously by a two-dimensional lithography mask pattern and the topography of the micromold. This three-dimensional geometry improves insertion performance and potentially the drug delivery efficiency without additional fabrication processes. These hypodermic-needle-like microneedles have been successfully constructed, packaged, and tested for fluidic functionality and skin penetrability.

Dissolvable-tipped, drug-reservoir integrated microneedle array for transdermal drug delivery

This paper presents a dissolvable-tipped, drug-reservoir integrated microneedle array for transdermal drug delivery. The hydrogel-based dissolvable tips are formed in a reusable polydimethylsiloxane (PDMS) mold, and then contact-transferred onto a microtube array with drug-surrogate pre-filled reservoirs incorporated into each microneedle. The microtube array is fabricated by a single photolithography process using a gray-tone mask. After insertion into an agarose gel, the water-soluble tips effectively dissolve within a minute to expose each reservoir, and the pre-filled drug-surrogate successfully diffuses. A preliminary tissue penetration test shows mechanical stability of the dissolvable tipped microneedle and feasibility of drug delivery as well as safe prevention of the proposed microneedle from possible reuse.

A non-enzymatic micro-needle patch sensor for freecholesterol continuous monitoring

A patch type non-enzymatic free-cholesterol sensor was newly developed for continuous monitoring by using stainless steel based micro-needle patch and nanoporous platinum (NPt) sensing electrodes. The formed micro-needle patch was coated with parylene/gold/parylene film and selectively dry-etched to form the gold electrodes at the tips of micro-needles. The bare gold tips were finally electroplated with nanoporous platinum. The sensor was then characterized and analyzed by using cyclic voltammetry and chronoamperometry measurement techniques. The fabricated sensor exhibited high sensitivity of 305nA/mM·cm2 and correlation coefficient of 0.964 in 0.1M PBS (pH 7.4). In the recovery test, recovery rate was more than 89%.

Maskless fabrication of high aspect ratio structures by combination of micromolding and direct drawing

This paper presents a fabrication process combining micromolding and direct drawing, and its application to the development of high aspect ratio microneedles. Without using photolithography or etching, the proposed process creates microneedles with: 1) higher aspect ratios than that of the original mold, 2) controllable needle diameter for optimized mechanical strength, and 3) arrowhead-shaped tips for potentially increased capacity and effective payload delivery. The needles presented are formed with biocompatible, water-soluble polymers, but the fabrication process inherently allows many kinds of polymers to be exploited. Various high aspect ratio 3D structures were fabricated and characterized, and the fabrication result was compared with theoretical prediction. Water-soluble microneedle arrays have been fabricated and successfully penetrated into porcine skin, fully releasing the drug-surrogate into the dermis layer within a minute.