Effects of two droplet-based dissolving microneedle manufacturing methods on the activity of encapsulated epidermal growth factor and ascorbic acid

Dissolving microneedle (DMN) is an attractive, minimally invasive transdermal drug delivery technology. The drugs encapsulated in the DMNs are exposed to a series of thermal, chemical, and physical stresses during the fabrication process, decreasing their therapeutic activity. Current DMN fabrication methods, such as micro-molding, drawing lithography, droplet-born air blowing, and centrifugal lithography, undergo different manufacturing processes involving differing stress conditions. Among the methods, we compared the effects of two droplet-based methods, droplet-born air blowing and centrifugal lithography, on the activity of encapsulated drugs using epidermal growth factor and ascorbic acid as model drugs. Although the appearance and physical properties of DMNs fabricated by the two methods were similar, the immunoreactivity of encapsulated epidermal growth factor in centrifugal lithography and droplet-born air blowing was 92.08 ± 2.86% and 80.67 ± 8.00%, respectively, at baseline, and decreased to 75.32 ± 19.40% and 41.75 ± 16.17%, respectively, 24 h after drug-loading. The free-radical scavenging activity of ascorbic acid was maintained at 88.24 ± 0.78% in DMNs fabricated by centrifugal lithography, but decreased over time to 67.02 ± 1.11% in DMNs fabricated by droplet-born air blowing. These findings indicate that the manufacturing conditions of centrifugal lithography exert less stress on the drug-loaded DMNs, minimizing activity loss over time, and therefore that centrifugal lithography is suitable for fabricating DMNs loaded with fragile biological drugs.