## 4 Results and Discussions
### Experimental Verification  
After analyzing the T-channel's trapping ability by simulation, five microchips were fabricated with a trap channel size appropriate to trap a cell aggregate with a diameter of 25-35 \(\upmu\)m. The trap channel's size was designed to be \(W_{\text{Trap}}\) 25 \(\upmu\)m, \(W_{\text{Hole}}\) 15 \(\upmu\)m, \(L_{\text{Trap}}\) 25 \(\upmu\)m, and \(H_{\text{Channel}}\) 15 \(\upmu\)m with an \(Rh_{\text{Main}}/Rh_{\text{Trap}}\) ratio of 3. The computational prediction for - channel trapping was further validated experimentally using fabricated microfluidic devices and HUVEC cell aggregates. A single HUVEC cell aggregate was found to be directed by the fluid flow to enter the trap channel and trapped. Consistent results were obtained using all five fabricated microchips. Figure 14A-F demonstrate the movement of cell aggregates inside the T-channel from the channel's inlet (right side) before and after trapping, sequentially. The single-cell aggregate moved from the inlet into the main channel (Figure 14A), reached the junction between the trap and main path (Figure 14B), entered the trap channel (Figure 14C), and was captured in the trap channel (Figure 14D). Results show that the fluid stream produced inside the T-channel was able to direct and lead the cell aggregate to enter the trap channel. In addition, the subsequent cell aggregate moved to bypass the trap channel (Figure 14E) and passed through the main channel (Figure 14F). This finding demonstrated that a change of hydrodynamic resistance between the channels occurred after the cell aggregate was trapped. This caused the increase of \(Rh_{\text{Trap}}\) and prevented subsequent cell aggregates from entering the trap channel. This result was in agreement with the simulation data and hydrodynamic trapping concept. This T-channel trapping could be applied to trapping other cell types and sizes. For example, for the purpose of trapping a smaller single cell, \(W_{\text{Trap}}\), \(W_{\text{Hole}}\), \(L_{\text{Trap}}\), and \(H_{\text{Channel}}\) dimensions should be reduced, while for single spheroid capture, the dimension should be increased appropriately for the target cell.  
The proposed T-channel trapping is an approach to trap a single cell with a platform for single-cell analysis plus access for further manipulation through the \(W_{\text{Hole}}\) and its outlet. This T-channel could be upgraded by increasing its throughput ability through applying more parallel trapping channels in a single microfluidic chip. Therefore, many single cells/3D cells could be cultured and applied with treatments at a time. The treated cells/3D cells could be further analyzed by applying mechanical or electrical characterization (e.g., stiffness, adhesion, or electrical measurements) in the manipulation platform and can be harvested from the microfluidic chip for further analysis.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \(W_{\text{Hole}}\)/\(Rh_{\text{Main}}\)/ & & & & & & & & & \\ \(Rh_{\text{Trap}}\) Ratio & & & & & & & & & \\ \hline
**0.5** & no & no & no & no & no & no & no & no & no \\
**1.0** & no & no & no & no & no & no & no & no & no \\
**1.5** & no & no & no & no & yes & yes & yes & yes & yes \\
**2.0** & no & no & no & yes & yes & yes & yes & yes & yes \\
**2.5** & no & no & no & no & yes & yes & yes & yes & yes \\
**3.0** & no & no & no & yes & yes & yes & yes & yes \\
**3.5** & no & no & no & no & yes & yes & yes & yes & yes \\
**4.0** & no & no & no & yes & yes & yes & yes & yes \\
**4.5** & no & no & no & no & yes & yes & yes & yes & yes \\
**5.0** & no & no & no & yes & yes & yes & yes & yes & yes \\
**5.5** & no & no & no & no & yes & yes & yes & yes & yes \\
**6.0** & no & no & no & yes & yes & yes & yes & yes & yes \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the simulation results for a single-cell trapping model’s ability for different values of \(W_{\text{Hole}}\) and various \(Rh_{\text{Main}}/Rh_{\text{Trap}}\) ratios.