Background Transdermal delivery has the advantage of bypassing the first-pass effect and allowing sustained release of the drug. However, the drug delivery is limited owing to the barrier created by the stratum corneum. Microneedles are a transdermal drug delivery system that is painless, less invasive, and easy to self-administer, with a high drug bioavailability. Area covered The dose, delivery rate, and efficacy of the drugs can be controlled by the microneedle design and drug formulations. This review introduces the types of microneedles and their design, materials used for fabrication, and manufacturing methods. Additionally, recent biological applications and clinical trials are introduced. Expert opinion With advancements made in formulation technologies, the drug-loading capability of microneedles can be improved. 3D printing and digital technology contribute to the improvement of microneedle fabrication technology. However, regulations regarding the manufacture of microneedle products should be established as soon as possible to promote commercialization.

Microneedles are transdermal drug delivery tools that can be fabricated simply, economically, and rapidly using SLA 3D printing. However, SLA 3D printing has a limitation in that the resolution is slightly lowered when the microneedle is precisely printed. To solve this issue, we optimized the SLA 3D printing conditions such as printing angle, needle height, aspect ratio, and spacing between the microneedles for high-resolution microneedle fabrication. The sharpest microneedle tip was obtained when the printing angle was adjusted to 60° in both the x and y axes. The aspect ratio and the spacing between the microneedles did not affect the output of the sharp tip. Under optimal conditions, the microneedles with 1180 ± 20 µm height, 490 ± 20 µm base, and 30.2 ± 3.4 µm tip diameter were obtained. The dissolving microneedle patch, prepared using the 3D printed microneedle as a mold, penetrated the porcine skin ex vivo. When the printing angle was 60° in the x and y axes, the area of the single stacking layer, including the microneedle tip, increased, and thus the sharp tip could be printed. A high-dimensional, side-notched arrowhead (SNA) microneedle was fabricated by applying the SLA 3D printing condition. Moreover, a letter-type microneedle patch was fabricated using the customized characteristics of 3D printing. Consequently, high-resolution and high-dimensional microneedles were successfully fabricated by adjusting the printing angle using a general SLA 3D printer, and this technology will be applied to the manufacture of drug delivery tools and various microstructures.

The purpose of this study was to investigate the efficacy of hydrophilic polymers in a solid dispersion formulation in improving the solubility and dissolution rate of rivaroxaban (RXB), a poorly soluble drug. The developed solid dispersion consisted of two components, a drug and a polymer, and the drug was dispersed as amorphous particles in a polymer matrix using the spray drying method. Polymeric solid dispersions were evaluated using solubility tests, in vitro dissolution tests, powder X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and particle size distribution analysis. To maximize physical stability against crystallization and improve the solubility and dissolution of RXB, it is important to select the appropriate polymer type and the optimal ratio of the polymer to the drug. The optimized polyvinyl alcohol (PVA)-based (1/0.5, w/w) and gelatin-based (1/5, w/w) solid dispersion formulations showed 6.3 and 3.6 times higher drug solubilities than pure RXB powder, respectively, and the final dissolution rate was improved by approximately 1.5 times. Scanning electron microscopy and particle size distribution analyses confirmed that the gelatin-based solid dispersion was smaller and more spherical than the PVA-based solid dispersion, suggesting that the gelatin-based solid dispersion had a faster initial dissolution rate. Differential scanning calorimetry and powder X-ray diffraction analyses confirmed that RXB had successfully changed from a crystalline form to an amorphous form, contributing to the improvement in its solubility and dissolution rate. This study provides a strategy for selecting suitable polymers for the development of amorphous polymer solid dispersions that can overcome precipitation during dissolution and stabilization of the amorphous state. In addition, the selected polymer solid dispersion improved the drug solubility and dissolution rate of RXB, a poorly soluble drug, and may be used as a promising drug delivery system.