Mosquitos and Painless Blood Drawing
My research at NCSU was in the area of structural mechanics. My work, combined with my advisor and one other MS student, eventually led to the following paper, which was published in the Institute of Physics Journal Bioinspiration and Biomimetics in 2008. Please continue to read below for a simplified overview of what we were trying to accomplish.
http://www.iop.org/EJ/abstract/1748-3190/3/4/046001
Mosquito footage published with paper.
Basic Concept
Mosquitos are equipped by mother nature to draw blood through the use of their fascicle, a long, slender, flexible, needle-like tube. It is so small in diameter (roughly 0.000030m) that humans cannot actually feel it when it is inserted into the skin (you may have noticed a mosquito on yourself that is busy drawing blood, although you did not feel him prick you, and swatted him away, only to see a raised bump appear later), and the common reaction of a bump on the skin is due to the interaction of the mosquito's saliva, which contains a blood-thinning agent, and the blood. Below you can see a scanning electron microscope picture of a female mosquito (scale in upper left is 500 micro-meters) (both males and females feed primarily on plant nectars; females use nutrients found in human blood to help in developing eggs).
If needles on this scale could be designed and manufactured artificially, painful blood drawing and drug delivery could be a thing of the past. Diabetics, young infants and anyone that dislikes needles would no longer feel the pain now associated with them. In the schematic below, it is shown that theoretically such needles could reach the blood supply without contacting nerve endings.
Can we presently manufacture needles on this scale?
Yes, needles have been produced using various chemical "growing" processes, but unfortunately generating the right combination of mechanical properties has been difficult. Penetrating the various layers of the skin without exceeding these properties has been challenging. If a needle were to break off inside the skin, and piece(s) could travel through the circulatory system, it could have disastrous consequences for the patient, so this must be avoided at all cost.
Research
Research started with an attempt to understand how the mosquito penetrates tough human skin with its small, flexible "straw" without breaking/buckling it. Mosquitos were dissected and the mechanical properties of the biological material chitin were recorded. Additionally, the outer sheath or covering (the labium) was thought to play a role in the insertion of the needle, as a literature search showed that when researchers stripped the labium from female mosquitos, they were no longer able to penetrate skin.
A mathematical model was created to describe the principles at play, which took into account 3 main factors acting on the fascicle: A conservative "Euler" load, a non-conservative "Beck" load, and the foundation stiffness along the length of the fascicle (representing the effect of the labium). The schematic below shows the difference between the Euler and Beck loads (Pe & Pb, respectively) as a "fixed-free" supported column is loaded - Beck loads are also referred to as "follower load" due to the fact they remain tangent to the bending column at the point of application.
The schematic above shows the force applied by the mosquito at every axial thrust, which can be resolved into the two components previously discussed. The fascicle is supported laterally by the labium, which is modeled as an elastic foundation that opposes the lateral motion of the fascicle. q is the distributed force per unit length, and β is the foundation modulus (force per unit deflection per unit length).
Results
The equations were mathematically modeled (using the computer code Matlab), and the effects of varying Beck load and labium support were examined. It was determined that labium support has a much greater affect on critical buckling load (how much force you can apply to the needle before it breaks or bends so that it cannot be inserted into the skin) compared to the Beck load.
This information could potentially help future research in the area by showing the potential of engineering support structures for these small needles to help them penetrate the skin's tough outermost layer.