## 4 Discussion and Conclusions
These various strategies intended to reduce the twisting effect can be implemented together for a combined result. The onion architecture promises to have the ability to be enlarged in the radial direction with no predicted ill effects related to increasing the aspect ratio. This introduces the possibility of a concentric array containing a single onion fiber with many layers added. This concentric array could then be centered around a through hole fitted around a stiff member. This member would not contract with the fiber, instead remaining fixed in relation to the contractive motion. In this arrangement, the stiff member would add robustness to the overall muscle as well as provide a bone-like supporting structure to affix external loads or mechanical joints. One potentially important benefit of this scheme would be a different weighting of parameters for the tradeoff between force generation and force-transferring areas (capacitor plates and tendons) such that less tendon would be required. This can be thought of as similar in application to a pneumatic/hydraulic piston due to the constraint of movement along the axial direction. As with the other architectures, scaling significantly affects the onion design. If the onion is uniformly scaled down, the electrostatic force will disproportionately scale up in much the same way as with the potato spiral and serpentine architectures [36; 58]. In the same manner as the designs described earlier, there is a balance between the desired plate proximity for electrostatic reasons and the desired distance needed to prevent internal ruptures when pressure is applied. This distance is especially important with the onion due to the higher number of adjacent channels. If the axial direction is held constant and the lateral direction is scaled up (making the architecture \"wider \"), the result would be a structure somewhere between that of the potato spiral and onion. It may even be possible to obtain a hybrid formation that boasts the upsides of both. Channel sizes like those discussed for the serpentine architecture above would be feasible. The arraying techniques shown in Figure 4 are still subject to the tradeoff between the channels (shown in gray in Figure 4) needed to generate force for actuation and the tendon material (shown as whitespace in Figure 4) needed to transfer the generated force to the outside world. Hence, the utilization of heterogeneous arrays would require optimization through extensive parameter sweeps in FEA simulations. The complexity added through heterogeneity will have to be justified by concomitant, sizeable gains in output force density. One potential solution to find the best balance is to take an optimally nested array (an array with a minimized tendon area) and then enlarge the array uniformly while holding the fiber sizes constant. This should act to distribute the tendon more evenly throughout the array. Figure 4D illustrates that arrays can also be made of various sizes or orientations with the same architecture. In conclusion, recent advances in 3D-printed microfluidics have enabled the fabrication of artificial muscles based on the electrostatic actuation of large 3D arrays of microcapacitors, built from conductive microfluidic channels and the surrounding dielectric 3D-printed resin. This has necessitated the advent of respective microfluidic architectures that possess the necessary electrical and mechanical features. Herein, several such advanced architectures have been proposed, described, discussed and compared (see Table 3). Furthermore, the design choices have been checked against and backed with experimental results. The most important conclusion of this work is that its developments pave the way for the imminent implementation of practical and effective 3D-printed microfluidic, electrostatic artificial muscles. Experimental proof of principle through pyloned potato spirals appears to be only one or two tweaks away in terms of the scaling choices and clearing protocol, as demonstrated by the described devices.