Abstract
The objective of this research is to fabricate a poly(lactic acid) hydrophobic microneedle (MN) patch and also to assess the feasibility of drug loading process with dropping and dip coating techniques. This research is divided into two stages: fabrication of MN patches and the study of the drug loading process. The first stage includes three parts, i.e., formulation, experimental process and microneedle property test. We fabricated two different kinds of MN patches. The first one was based on PLA solution. The development included coating, vacuuming and drying under room temperature (RT). The other one is the melting type MN patches. We could either employ the high temperature melting process, or directly melt the PLA particles to obtain the patches. As soon as the fabrication process was completed, we then used digital camera to visualize the structure and configuration of the needles. Needle fracture force test and porcine skin penetration test were also applied to make sure the needle achieve the designated strength. When obtaining the acceptable MN patches, we then moved to the second stage - using the fluorescent drug test solution to study the drug loading process on the MNs. The results indicate that we can successfully fabricate a high quality MN patch. As for drug loading, when dropping a designated volume of drug solution, we found the solution could form a meniscus shape between the needles, and there also existed a “pin point”, where the curvature would start to change dramatically. In this drying process, although higher viscosities would lead to higher curvature and pin point positions, liquid surface tension would mitigate the effect of viscosity, which was actually the dominant factor on the curvature of the meniscus. As for the study of dip coating, we established a dip coating system with a flow visualization apparatus. The preliminary results show that the drug loading amount is proportional to the capillary number (=μV/σ) where μ,V and σ represent liquid viscosity, coating velocity and fluid surface tension, respectively. During the drying process, gravity would pull the liquid flow downward and thus formed a thin film on the needle surface. However, due to the capillary effect, the prediction of the dipping length could be difficult.