## 1 Introduction  
From treating acute stroke patients or patients with acute pain in emergency cases [1; 2; 3], to providing medical care for terminally ill and critical pediatric patients [4; 5; 6; 7], to administering therapeutic treatment for home care patients [8; 9], as well as managing nutritional support to enhance health recovery [10], intravenous (IV) fluid therapy is a common medical practice at all levels of urgency, with 80-90% of all patients receiving IV therapy during a hospital stay [11]. IV therapy allows the parenteral administration of a fluid substance (solution) directly into a patient's vein, mainly for three purposes: to provide fluids, to give drugs, or to transfuse blood products [11]. The first attempts at IV therapy can be dated back to the 17 th century in which experiments were performed on animals using a device comprising a quill and a bladder [12]. It was not until the early 19 th century, that practices on humans were first documented as curative treatments for hemorrhage during delivery [13] and for dehydration during the cholera epidemic [14; 15]. While previous IV infusions were performed at a rapid pace, the slow and continuous drip method was first reported in the early 20 th century [16]. IV therapy has since become established in modern healthcare and today is not limited to hospital settings, but is also implemented at home, in nursing centers and practitioners' clinics. The devices have evolved from a quill and bladder, to a disposable catheter and plastic bag. Advances in modern technologiessuch as microelectromechanical systems (MEMS) and the Internet of Things (IoT) have also prompted many studies applying sensing and wireless communication technologies to IV drip devices for the detection of IV fluid level [17; 18; 19], sensing of dosing flow rate [20; 21; 22] and remote monitoring of IV therapy [23; 24; 25; 26]. Yet, the fundamental method of gravity drip infusion in which an IV bag is suspended (typically on an IV pole) at a constant height from a drip point (usually the antecubital vein of an elbow) to maintain an infusion pressure (derived from the gravitational potential) as shown in Figure 1a, has remained largely unchanged, mainly due to its unrivaled simplicity, practicality and cost-effectiveness. However, the gravity-driven method is imperfect: it confines a patient's movement, causing stress, especially for patients routinely undergoing long hours of slow drip such as IV chemotherapy for oncology patients [27]. For hospitalized athletes, limiting their mobility may also affect their physical and mental rehabilitation [28]. On the other hand, elderly patients who move with a wheeled IV pole, for instance, to attend toileting needs, may risk an accidental fall, resulting in unintentional injuries [29]. These problems of gravity drip have motivated much effort to produce inventive and innovative drip devices such as shoulder-mounted drip poles [30; 31; 32; 33], a neck-mountable IV bag design such as a U-shaped pillow [34], wearables for carrying battery-powered infusion pumps [35; 36; 37], and even an autonomous IV stand that can monitor a patient's movement and move concurrently with the patient [38]. These studies provide solutions from different perspectives. Efforts in [30; 31; 32; 33; 38] focused on the IV pole, modifying it to become body-mountable [30; 31; 32] with automatic pole-balancing control [33], or sustaining the pole structure but causing it to move and follow the patient on its own [38]. The approach taken in [34; 35; 36; 37] was to remove the IV pole and re-design the IV bag to make it attachable to the neck to gain gravity potential [34], or to maintain the current IV bag design but resort to battery-driven actuators for fluid delivery [35; 36; 37].