# Design and Analysis: Servo-Tube-Powered Liquid Jet Injector for Drug Delivery Applications
###### Abstract  
The current state of commercially available needle-free liquid jet injectors for drug delivery offers no way of controlling the output pressure of the device in real time, as the driving mechanism for these injectors provides a fixed delivery pressure profile. In order to improve the delivery efficiency as well as the precision of the targeted tissue depth, it is necessary to develop a power source that can accurately control the plunger velocity. The duration of a liquid jet injection can vary from 10 to 100 ms, and it generate acceleration greater than \(2\,g\) (where \(g\) is the gravity); thus, a platform for real-time control must exhibit a response time greater than 1 kHz and good accuracy. Improving the pioneering work by [PERSON] and others whereby a Lorentz force actuator based upon a voice coil is designed, this study presents a prototype injector system with greater controllability based on the use of a fully closed-loop control system and a classical three-phase linear motor consisting of three fixed coils and multiple permanent magnets. Apart from being capable of generating jets with a required stagnation pressure of 15-16 MPa for skin penetration and liquid injection, as well as reproducing typical injection dynamics using commercially available injectors, the novelty of this proposed platform is that it is proven to be capable of shaping the real-time jet injection pressure profile, including pulsed injection, so that it can later be tailored for more efficient drug delivery. needle-free injection technology; liquid jet injection; drug delivery; linear servo actuator 202220202202202202202202202202202202202202202202202202220220220220220222022022022202202220222022202220222022202220222022202220222022202220222022  
The production of needle-free liquid jet injections is accomplished by a high-speed jet created using a power source; the jet carries enough energy to puncture human skin and deliver a precise volume of medication within a specific target [2; 3]. In commercially available injectors, a power source compresses a piston, which in turn forces a column of fluid through a micro-orifice on the order of 50 to 250 \(\upmu\)m in diameter. The resulting compression of the fluid column creates a high-speed jet with speeds on the order of 100-200 m/s and Reynolds numbers in excess of 100,000. Typically, the pressure increase in the fluid column can peak at more than 30 MPa within 0.5 ms. These pressure values are well above the minimum threshold of 3-15 MPa for fracturing skin. In fact, commercially available injectors that are capable of producing such pressure peaks can routinely deliver 0.1 to 1 mL of fluid at depths greater than 10 mm. For summary, a number of recent review articles on this technology and its state-of-the-art can be found in the literature, e.g., [1; 2; 3; 4; 5; 6; 7; 8]. The power source driving an injection remains one of the most influential and researched aspects of liquid jet injectors. It is important to note that, although the compression of a fluid column to create a high-speed jet is common throughout various types of injectors, the power sources driving the injection vary greatly. Early needle-free injectors were spring-powered, e.g., [9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19]; driving the injection was accomplished by compressing a spring that is subsequently released to drive a plunger that forces fluid through an orifice. In these types of injectors, spring compression was achieved using screw mechanisms or bulky levers. Spring-powered injectors provide a very cost-effective means of delivering injection because the spring powering the injection can usually last for the life of the injector. Although spring-powered injectors are simple in construction and have an inexhaustible power source, they exhibit several problems. One of the major drawbacks deals with variable injection depth. Experimentation is often required in order to attain a target tissue region.