## 3 Results and Discussion  
This section reports on an experiment which was performed to measure changes in fluid kinematic viscosity using the 3D polymeric suspended microfluidics. To modify kinematic viscosity of fluids in experiments, DI water with different concentrations of salt (NaCl), 0-15% as a solution, and milk with fat concentrations of 0-35% as a colloidal fluid were used. An optical laser deflection measurement system was used to detect microcantilever deflections against variations in fluid properties (Figure 4). The optical laser deflection measurement system works based on the reflection of a laser beam from the  
Figure 3: (a) Microchannel and nozzle models for PDMS microfabrication, (b) Fabricated 3D suspended polymeric microfluidic system (c) Detailed view of the SPMF\({}^{3}\). tip of the microcantilever. The light travel distance is read on a Photo Sensitive Detector (PSD), which can be calibrated with the cantilever tip deflection according to the measurement setup dimensions [37]. In this experiment, the salt-water and milk-fat solutions were injected into the SPMF\({}^{3}\) using a syringe pump at a flow rate of 50 \(\upmu\)L/min and the cantilever deflection was recorded. According to the salt-water solutions in Table 1, kinematic viscosity variations through the addition of salt could be detected by the SPMF\({}^{3}\) using tip deflection. However, both density and viscosity increased when salt was added to the DI water. As such, Table 1 summarizes the microcantilever deflections against changes with fat contents of milk. Milk viscosity increased with fat concentration while its density decreased [38]. The source of tip deflection variations among different solutions could have been due to changes in either density or dynamic viscosity, or both. To further investigate the source of this change, a finite element analysis (FEA) was done with different fluid densities while the viscosity was kept identical and vice versa, and then the results were compared with the experimental data of Table 1. In this FEA modeling, a microcantilever with length, width and thickness of 6000 \(\times\) 2000 \(\times\) 600 \(\upmu\)m, respectively,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Fluid**} & \multirow{2}{*}{**Concentration**} & **Density** & **Dynamic** & **Kinematic** & **Tip Deflection** \\  & & **(kg/m\({}^{3}\))** & **Viscosity (cP)** & **Viscosity (cSb)** & **(\(\upmu\)m)** \\ \hline \multirow{4}{*}{Water-Salt wt \%} & 0\% & 999 & 1.002 & 1.00 & 2.51 \\  & 10\% & 1070 & 1.193 & 1.11 & 2.75 \\  & 15\% & 1110 & 1.350 & 1.21 & 3.08 \\ \hline \multirow{4}{*}{Milk-Fat wt \%} & 0\% & 1033 & 3.594 & 3.48 & 10.48 \\  & 3.25\% & 1030 & 4.192 & 4.07 & 11.90 \\ \cline{1-1}  & 10\% & 1025 & 4.797 & 4.68 & 14.85 \\ \cline{1-1}  & 20\% & 1012 & 6.598 & 6.  
with an embedded microchannel of 200 \(\times\) 100 \(\upmu\)m was modeled. The flow rate was kept constant as 50 \(\upmu\)L/min, equal to the mass flow rate of \(\dot{m}\) = 8.33 \(\times\) 10\({}^{-7}\) kg/s at \(\rho\) = 10\({}^{3}\) kg/m\({}^{3}\), and the fluid was water. This analysis has been done using two ANSYS modules, namely CFX and Static (2017, ANSYS, Pittsburgh, PA, USA), to solve the Navier-Stockes equations of steady state fluid dynamics and structural behaviors in order to predict the resultant deflections due to applied flow forces on the microcantilever. As given in Figure 5a,b, the predicted variations of deflection show that the microcantilever deflection decreases when density is increased at a constant viscosity, while its deflection increases when viscosity is increased at constant density. Since the flow rate was kept constant during experiments and prediction, increasing of density decreased the pressure difference, which led to lower velocity difference and hence the deflection which is also seen in Equations (5) and (6). On the other hand, when viscosity was increased, pressure difference increased, which resulted in higher cantilever deflection.