Customized fast-separable microneedles prepared with the aid of 3D printing for nanoparticle delivery

3D printing of master molds for soft lithography-based fabrication of microneedles (MNs) is a cost effective, easy and fast method for producing MNs with variable designs. Deviating from the classical geometries of MNs, 'tanto blade'-inspired MNs showed effective skin penetration, acting as sharp structures with low insertion force of 10.6 N, which is sufficient for manual insertion. Additionally, hydrophilic, fluorescent noble metal nanocluster-modified gelatin nanocarriers were loaded in polyvinyl alcohol/sucrose MNs to act as a novel potential theranostic system emitting light in the near-infrared (λ_em = ~700 nm). Nanoparticles (NPs) distribution within the MNs and release have been monitored using confocal laser scanning microscopy by means of spectral analysis and linear unmixing. Furthermore, the MNs patch was modified by carving a channel at each of the four corners of the patch. This facilitated the separation process of MNs from the patch base into skin, when 15 µL phosphate buffered saline was applied through each channel post-skin insertion of the MNs. Then, the patch base can be removed easily leaving the implanted MNs inside the skin for further release of the NP cargo. This successfully reduced the application time to 1 min for enhanced patient compliance.