Fabrication of microporous inorganic microneedles by centrifugal casting method for transdermal extraction and delivery.

Microneedle patches have been widely used as transdermal transport systems because of their painless and easy application. Marked rigidity, strength, biocompatibility, and physiological stability are unique features of microneedles fabricated from ceramic materials to be used as microneedle patches. However, the conventional ceramic microneedles are typically dense structures with limited free space for biomolecule loading. A facile method is required for fabrication of biocompatible ceramic microneedles with interconnected porosity. Herein, the simple method of centrifugal casting was developed for fabrication of microporous microneedles from alumina suspensions. The slurry or resin-based alumina suspensions were casted into micromolds under centrifugal force, followed by sintering at high temperatures. The effects of particle size, solvent type, binder amount, resin content and sintering temperature on the microstructure and mechanical properties of microneedles were investigated. By optimizing the process parameters, highly porous (up to 60%) microneedles with interconnected micropores (of diameter ∼1-1.5 μm) were produced. The microporous microneedles were biocompatible and mechanically strong for skin penetration. The potential use of the microneedles for transdermal transportation of biomolecules was shown by fast and accurate extraction of glucose from a skin model and efficient loading and fast release of insulin under physiological conditions. The results suggested that the microporous alumina microneedles may serve as molecular transport systems in transdermal biosensing and drug delivery.