The Experimental Research Of Insertion Of Microneedle And Microneedle Array Into Silicon Membrane

Microneedles and microneedle array can be used for transdermal drug delivery (TDD) and biochemical sampling in a painless, minimally invasive and controllable manner. Therefore, they have received increasing attention. These advantages are mainly attributed to the micro-size of microneedles. However, micro-size also makes microneedles be in a risk of failure due to mechanical fracture or buckling when they are pressed against skin. This has strongly hindered the applications of microneedles in clinical therapies. Up to now, there have been few studies to discuss the mechanical problem of microneedles. Moreover, among these few studies, people mainly pay their attentions to the simple mechanical analysis and structure optimization design of the microneedle. This is not good enough to overcome the safety problems that microneedles faced. Considering the fact that low insertion force and insertion displacement is helpful to prevent the microneedles from failure, experiments were carried out to determine the factors that can reduce the insertion force and insertion displacement of microneedles in this thesis. In our experiments, the skin is deliberately replaced by silicon membrane due to its homogenous properties and single microneedle, single row of microneedles and complex microneedles are investigated in detail.Firstly, the influences of microneedle size, microneedle shape, inserting velocity and pre-stretching of silicone membrane on the insertion force and insertion displacement of single micrneedle are studied. And then, a row of microneedles were studied for determining the effects of microneedle number, interspace and height distribution on the insertion force and insertion displacement. Finally, similar experiments were carried out on the microneedle array.The results show that both the tip shape (sharp tip and truncated tip) and tip sizes (radius of tip, tip area and tip angle) can significantly influence the insertion force and insertion displacement. When the tip is sharp, the insertion force and insertion displacement will increase with the radius of tip and tip angle in an approximate linearly manner. However, when the tip is truncated, the insertion force and insertion displacement will increase with the tip area in an approximate linearly manner. Moreover, a pre-stretching of the silicon membrane is useful to reduce the insertion force and insertion displacement, but increasing the inserting velocity (from 30mm/min to 500mm/min) is not helpful to reduce them. Finally, it is found that the outside microneedles of a microneedle array usually pierce the silicone membrane prior to these inside microneedles, i.e., displaying a’boundary effect’. This means that the microneedles of an array will not be inserted into the skin simultaneously and insertion depth will not be same. This is much harmful to painlessness and controlling release of drugs. Therefore, an idea of eliminating this phenomenon by optimizing the height distribution of microneedles is proposed and it is also be tested by experiments.It is believed that these findings discovered in this thesis are useful to improve the microneedle design and can help the microneedle technique be widely used in clinical therapies.