Porous silicon microneedle patches for delivery of polymyxin-based antimicrobials

There is a global trend of increasing antibiotic resistance to Gram-negative bacteria and the medical research community is looking for alternative antibiotics. Antibiotics such as polymyxin B (PMB) show excellent efficacy and low resistance rates against Gram-negative bacteria. The topical administration of PMB, however, has clinical limitations such as minimal residence time, making it difficult for its use to treat skin infections. Here, we present porous silicon microneedle (pSi MN) patches to deliver PMB to the skin. pSi MN patches are fabricated by, first, generating the projections by dry Si etching techniques, followed by an electrochemical etching to create porous layers around the MNs. After loading PMB into the porous layer, the antibacterial activity of pSi MNs is determined by measuring the inhibition zone of Gram-negative Escherichia coli. Next, PMB is efficiently delivered into the epidermal layer of ex vivo skin models, as confirmed by chemical mapping using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). The results demonstrate that pSi MN patches are an efficient and versatile tool for the transdermal delivery of PMB with maintained bioactivity and antimicrobial efficacy, thus expanding the possibilities of current transdermal drug delivery systems.