Cellulose nanofiber-reinforced dissolving microneedles for transdermal delivery of a water-soluble compound

Cellulose nanofibers (CNFs) were included in dissolving microneedle (MN) arrays to increase needle stiffness and control the dissolving rate and transdermal delivery rate. A metallic MN master was fabricated to build pyramidal needles in a 15 × 15 array using a pre-fabricated silicone mold as a template. The dissolving MNs with different CNF contents were replicated by casting the polymeric mixtures on the molds. X-ray diffraction study revealed that CNFs were included in the MN arrays with maintaining its crystalline structure. The compressive strength test showed that the addition of CNFs increased the stiffness of the needles, and the needles underwent the elastic deformation, the failure of the tip, and the elastic deformation of stem. The skin-piercing capability of the MNs was enhanced by including CNFs in the MN arrays. Once the needles penetrated into the skin, the depth was almost the same, regardless of CNF content. As CNF content increased, the release rate of a water-soluble cargo loaded in the MNs, the dissolution rate of the MNs, and the in vitro transdermal delivery rate of the cargo decreased, possibly because CNFs would form networks within the MNs through physical entanglement and/or hydrogen bonding.