Abstract
An experimental study was carried out to investigate the amount of drugs loaded on microneedles. The microneedles were made with poly (lactic acid). Aqueous poly (vinyl alcohol) solutions were prepared as drug solutions. Two drug loading approaches, i.e., dropping and dipping, were examined. It was found that capillary number is the only relevant dimensionless group for the two methods. For the dropping approach, dried drugs will spread near the bottom of a microneedle patch provided the surface tension is low. As for the dipping approach, both a single microneedle and an array of nine microneedles were examined. For a single microneedle, high capillary rises before pulling and pulling speed are two key factors to increase the drug loading volume. For an array of microneedles, the effect of capillary rise owing to the interaction between microneedles would increase the drug loading volume several times higher than a single microneedle of the same dimension.
Highlights
Microneedles (MNs) were first developed by Henry et al [1] as a new and effective drug delivery system to transport drugs into human bodies in a painless way, since MNs can penetrate human skin but are short enough not to affect the nerve system
Vaccines such as enterovirus 71 [9], influenza [10] [11], hepatitis B [12], bacillus Calmette-Guérin (BCG) [13], human immunodeficiency virus (HIV) [14], human papillomavirus (HPV) [15], recombinant adenovirus [16], diphtheria [17], and drugs such as insulin [18] [19], human growth hormone [20], lidocaine [21] have been considered as drugs suitable for the combination with MNs, just to name a few here
For a solution with high viscosity and surface tension, the solution will retain on the upper part of the microneedle surface after drying
Summary
Microneedles (MNs) were first developed by Henry et al [1] as a new and effective drug delivery system to transport drugs into human bodies in a painless way, since MNs can penetrate human skin but are short enough not to affect the nerve system. The existing works have been focusing heavily on the materials that can be used to make MNs [4], the shapes and geometries of MNs for better insertion into human bodies [5] [6] [7] [8], but most importantly the selection of a suitable drug that can be combined with MNs to effectively deliver drugs into human body. Interested readers may refer to several review articles for more details [2] [3] [22]
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