Iman Mansoor

Hollow Out-of-Plane Polymer Microneedles Made by Solvent Casting for Transdermal Drug Delivery

Although hollow microneedles have been proposed as an effective and convenient method for transdermal drug delivery, their expensive fabrication techniques to date have prevented their mass fabrication as a viable option. A novel method, based on solvent casting, is presented for inexpensive fabrication of hollow out-of-plane polymer microneedles. Microneedles are formed during a solvent evaporation process, which leaves a polymer layer around pillars in a prefabricated mold. The mold is fabricated using photolithography and can be used for consecutive solvent casting of microneedles. Arrays of microneedles with lengths up to 250 μm have been fabricated from clay-reinforced polyimide. Several mechanical tests were performed on solvent cast solid structures to find the optimum clay percentage in the polyimide that would lead to the highest compressive strength. The fabricated needles were tested for robustness, and it was observed that the needles were capable of withstanding on average compressive loads of up to 0.32 N. The suitability of the microneedles for skin penetration and drug delivery was demonstrated by injection of fluorescent beads into a skin sample.

A micromechanical comparison of human and porcine skin before and after preservation by freezing for medical device development.

Collecting human skin samples for medical research, including developing microneedle-based medical devices, is challenging and time-consuming. Researchers rely on human skin substitutes and skin preservation techniques, such as freezing, to overcome the lack of skin availability. Porcine skin is considered the best substitute to human skin, but their mechanical resemblance has not been fully validated. We provide a direct mechanical comparison between human and porcine skin samples using a conventional mechano-analytical technique (microindentation) and a medical application (microneedle insertion), at 35% and 100% relative humidity. Human and porcine skin samples were tested immediately after surgical excision from subjects, and after one freeze-thaw cycle at −80 °C to assess the impact of freezing on their mechanical properties. The mechanical properties of fresh human and porcine skin (especially of the stratum corneum) were found to be different for bulk measurements using microindentation; and both types of skin were mechanically affected by freezing. Localized in-plane mechanical properties of skin during microneedle insertion appeared to be more comparable between human and porcine skin samples than their bulk out-of-plane mechanical properties. The results from this study serve as a reference for future mechanical tests conducted with frozen human skin and/or porcine skin as a human skin substitute.

Arrays of solvent cast hollow out-of-plane polymer microneedles for drug delivery

Microneedles are tiny hollow structures that allow painless drug delivery into human skin. In this work, we present a novel fabrication method for microstructures based on solvent casting that allows rapid fabrication of inexpensive microneedles from polymer materials. The polymer microneedles are formed on a reusable mold made with a single photolithography step. The strength of the fabricated microneedles under compressive loading was investigated. The capability of the microneedles for drug delivery was also demonstrated by injection of fluorescent beads into rabbit ear skin and inspection of the penetration depth using confocal microscopy.

High Mechanical Bandwidth Polysilicon Micromirrors for Large Area / High Deflection Angle Micromirror Arrays

We demonstrate a new design for micromirror arrays that allow for high tilt angles (0.75deg) of mirror elements in arbitrary directions, large actuated areas (0.64 mm2), and high actuation bandwidth (measured resonant frequencies range from 100 to 450 kHz). This is achieved by subdividing each actuated mirror into several small submirrors that are addressed simultaneously, so that they behave as one large composite mirror. Submirrors increase the resonance frequency, surface area, and tilt angle of each composite mirror, at the expense of a slight reduction in fill factor. Different designs for the individual micromirrors were fabricated from polysilicon using standard surface micromachining technology (MUMPs) and characterized; a 5 x 5 array of composite mirrors was also fabricated and tested.