## 1 Introduction
Echoing the motivation of these efforts, our aim was to find an alternative and sustainable solution by considering the following criteria: (i) trying to preserve the existing advantages of gravity drip which is easy to set up, electricity-free and highly affordable, (ii) placing priority on the stability of the infusion flow rate for treatment efficacy and patients' safety, and (iii) emphasizing compatibility with existing IV bags and  
Figure 1: Gravity versus atmospheric pressure as a driving force for drip infusion. (**a**) An IV drip bag hung from an IV pole at a constant height, \(\Delta h\), from a drip point on the arm maintains a constant infusion pressure to overcome the venous pressure. (**b**) Vacuum piston cylinder. A piston, with a cross-sectional area, \(a\), separating a sealed vacuum chamber and an open chamber under atmospheric pressure, \(p_{atm}\), moves towards the closed end of the cylinder. The larger the diameter, \(d\), of the piston (cross-sectional area \(a=\pi d^{2}/4\)), the larger the magnitude of the driving force, \(F=p_{atm}a\), on the piston. The length of the cylinder, \(L\), determines the moving stroke of the piston. infusion tube sets. With these criteria, we strove to achieve a concept of electricity-free and non-hanging IV drip therapy that will enhance resilience in medical treatments, especially at evacuation shelters in disaster-hit areas or refugee camps in war-stricken regions. In this work, we ventured into a novel approach in which we removed the IV pole but sustained the current design of the IV bag, and at the same time, sought a non-electric way to drive the infusion fluid. Our aim was to find an alternative driving force to gravity, design and test feasible pressurization mechanisms acting on an IV bag to transform the driving force into fluid pressure for fluid infusion, and find the best-performing pressurization mechanism for the infusion pump. As an alternative to gravitational force, for instance, a driving force can be derived from the pressure difference between a vacuum and the atmospheric pressure in a vacuum piston cylinder [39, 40, 41, 42, 43, 44]. Another feasible option could be an elastic force exerted by a spring [45, 46] or a bellows [47]. For the pressurization mechanism, viable approaches can generally be categorized into three options, namely, (a) pressing a rigid plate on a drip bag [43, 45, 46, 47], (b) squeezing a drip bag by one or multiple rollers [48], and (c) compressing a drip bag by an inflating air bag [49, 50, 51, 52]. However, it is unclear whether these mechanisms have been tested in terms of stability of infusion flow rate. First, we considered atmospheric pressure as a sustainable source of driving force on earth and, thus, an ideal alternative to gravity, leading us to employ the vacuum piston cylinder as the driving mechanism. Figure 1b presents a typical structure of a vacuum piston cylinder in which a piston separates a sealed vacuum chamber and an open atmospheric chamber. A driving force, derived from the pressure difference between the two chambers, acts towards the closed end of the cylinder. The magnitude and moving stroke of the resultant driving force are determined by the dimensions (i.e., diameter and length) of the cylinder. Second, we fabricated several novel and feasible prototypes combining one or multiple units of vacuum piston cylinder with each of the three pressurization mechanisms mentioned above. Third, to observe their potential in producing a stable infusion flow rate, we performed evaluation tests on the discharge flow rate from each prototype of infusion pump using a gravimetric test bench built for this purpose. Finally, a conclusion was drawn on the best pressurization mechanism, with prospects of future work.