Determination of an implantation area for interstitial fluid extraction in cows and feasibility of adapted microneedles

Abstract

We present a preliminary study of a wearable system to monitor biomarkers for dairy and suckling cattle. Finding the optimal location on the cow body (ears) and designing the adapted microneedles to reach the interstitial fluids underneath the cow skin are the two points addressed here. For the selection of the location, 4 breeds of suckling cows (Aubrac, Charolaise, Limousine, Salers) and 3 breeds of dairy cows (Abondance, Montbéliarde, Holstein) were chosen. Measurements of the thickness of the ear tissues were conducted on three areas of the ear (top, apex and base of the pinna), on the external and internal sides. Results show that the apex of the pinna, external side, is the best area for microneedle implantation with an implantation window of 1403 ± 589 μm (DeepDe), considering all breeds. To reach this implantation window located between the stratum corneum and the cartilage, the microneedle has to pass through 1323 ± 404 μm of tissues (SupDe), considering all breeds. From these results, a microneedle design was made on SolidWorks. With a conical shape 2.89 mm in height and a conical channel 300 μm in diameter (at the tip of the microneedle), the model was made using 3D printing. The resulting microneedles respect the SolidWorks design with fair accuracy. They were connected to a microfluidic channel for sampling or releasing fluids. • Structure of the cow ear tissues depends on side/area of the pinna and cow breed. • The apex of the pinna is the most convenient location for microneedle implantation. • Microneedles are a promising tool for the extraction of interstitial fluids. • 3D printing is a fast and inexpensive way to prototype microneedles.