# Finger-Actuated Microneedle Array for Sampling Body Fluids
## 1 Introduction  
Since their inception in 1976 as a drug delivery device [1] until 2020 where they were regarded as one of the top 10 emerging technologies [2], microneedles (MNs) have presented many advantages in injection processes, including minimizing insertion pain and reducing tissue damage and controlled drug delivery as compared to the conventional needle technologies. With different geometries and designs [3, 4], such as solid, hollow, coated, or biodegradable [5] needle types in the scale of micrometers and nanometers [6], microneedle arrays (MNAs) can be fabricated with numerous methods such as 3D printing [7, 8]. MNAs can be inserted into a target area, even within the depth of skin epidermis and thus they have emerging biomedical applications in drug delivery systems [9, 10, 11, 12] with the capability of programmed deliveries of drug doses for multiple-injection therapies such as vaccination [13], sampling interstitial fluid (ISF) [14, 15] biomarker detection [16], enhanced wound healing [17], fertility control [18], point-of-care (POC) setups and diagnostic tests [19, 20], DNA extraction [21, 22], cancer therapy [23], and force sensing [24].  
Computational methods that allow for simulation of the experiment or setup conditions for prognosticating their behaviors with conceivable problems or using artificial intelligence techniques for post analysis of data [25] have also emerged in MNs. Finite element analysis was used for simulating the transdermal drug delivery process of MNs into the skin in order to study the effect of penetration depth and number of MNs on each patch, demonstrating increasing proportionality of delivered drugs with both factors [26]. To study the Von Mises stress, an index of yield or fracture in materials, in a design ofMNAs with triangular-shaped bases, researchers demonstrated that the MNs in the middle part of the array were under more stress and displacement [27]. In addition, in a microfluidic system with MNs including a drug reservoir, displacement of MNs was modeled and simulated [28]. Structural analysis of MNs was also reported [29]. In another study using finite element analysis (FEM), the bending procedure and the distribution of the loaded stress on the MNs during their insertion into the skin were simulated [30]. A circular flange was introduced to the base of each MN as the results of the simulation demonstrated that MNs were most likely to fail in the area between the needle body and the supporting array because of stress concentration in this spot. Furthermore, finite element analysis was used to study modeling the surface concentration profiles of the delivered drug in a MN design with hemispherical convexities on the needle for the aim of increasing drug delivery flux [31].  
In this study, a microneedle array (MNA) integrated with a microfluidic channel chip was designed to extract and sample body fluids powered by finger press, featuring an easy procedure that can be applied by the user without need for the presence of healthcare workers. This design contains an array of 100 MNs with co-centric circular holes for fluid transport. The target fluid, for example blood or interstitial fluid (ISF), can be extracted by the power created by pressing with fingers followed by flowing in the microfluidics and finally being collected in a reservoir. The process of fluid flow and its transport across the device and its collection was modeled and simulated with a finite element model. The amount of the extracted fluid was studied with the simulation along with the generation of the curves for mass flow rate at the reservoir.