Figure 1

Coated microneedles. Microneedles were cut from stainless steel sheets using an infrared laser and electropolished as described before.¹⁰ (a) Photograph of a representative microneedle row held in a human hand. (b) Microneedle row with five microneedles uniformly coated with vitamin B₂ as a model compound. As plasmid coatings were difficult to visualize, the uniformity of coatings was assessed by coating microneedles with a model colored compound, vitamin B₂ (riboflavin-5′-phosphate sodium salt dihydrate) (Fisher Scientific, Fair Lawn, NJ, USA). The aqueous dip-coating solution contained 1% (w/v) carboxymethylcellulose sodium salt (CMC, low viscosity, USP grade, CarboMer, San Diego, CA, USA), 0.5% (w/v) Lutrol F-68 NF (BASF, Mt Olive, NJ, USA) and 20 mg ml⁻¹ vitamin B₂.¹⁸ Microneedles were coated using a custom dip-coating device and air dried for >24 h.¹⁰ For immunization, microneedles were coated using the same formulation, but by replacing vitamin B₂ with 5 mg ml⁻¹ codon-optimized NS3/4A plasmid DNA. To determine the amount of DNA coated on microneedles, DNA concentration was measured by a validated technique using ultraviolet (UV) absorbance at 260 nm in a solution prepared by vortexing coated microneedles for 1 min in 1 ml deionized water. (c) Histological section of porcine cadaver skin after inserting sulforhodamine-coated microneedle. To histologically characterize insertion of microneedles into the skin, microneedles were coated with 0.1% (w/v) sulforhodamine (Molecular Probes, Eugene, OR, USA) with CMC and Lutrol F-68 NF, as described above, and inserted into porcine cadaver skin for 1 min.