# Light-Controlled Microbots in Biomedical Application: A Review
## 1 Introduction  
The evolution of robotics over the past few decades has opened the ground for new ways of thinking about robotics' potential activities [1]. Recent breakthroughs in micro and nanoscale robotics have influenced biomedical applications [2; 3; 4; 5]. Microbots are tiny robots with features that are less than \(1\) mm in any dimension. The ability to operate in confined spaces and delicate environments, such as cell manipulation, Lab on Chip (LOC) development, etc., is one of many benefits of microbots' smaller size. Because of how easily and inexpensively they can be produced in large numbers given their small size, they are often referred to as \"swarms of robots\". The other benefit is that they are low-powered and sometimes can be powered from distance without the need for an onboard active power source, e.g., light-powered microbots, magnetically actuated microbots, etc. Despite the existing technological challenges, untethered microbots have already shown tremendous potential for a wide range of applications, particularly in the biomedical field [6; 7]. The developments in micro and nanofabrication have aided the evolution of miniature robotics with a variety of designs, control systems, and functions [8; 9; 10; 11; 12]. Microbot motion control has evolved in a number of ways over time. When working on a macro scale, using complicated electronics to regulate the robot's maneuverability can be highly effective. However, integrating complex circuits for proper control at the micron and submicron scales is extremely difficult. Rather, microbots are frequently designed by mimicking nature, which serves as a major source of inspiration in modern scientific studies. Biohybrid systems, in which a living organism is used to act as a microbot, have been used in some unique studies. From the aid of a microorganism [13; 14; 15] to different physical propulsion such as magnetic [16; 17], thermal [18; 19], electrostatic [20; 21],optical [22; 23], etc., and chemical strategies such as enzyme gradient propulsion [24], self-electrophotesis [25], etc., or acoustic actuation [26] are originated to control the microbots. Sometimes, multiple control modalities are combined to achieve more accurate and precise control of the microbot [27; 28]. Although many control modalities are now being employed to demonstrate the potential applications of microbots, they all have their own set of trade-offs [29; 30]. For example, the chemical mode of control requires the use of harmful fuels such as Hydrogen Peroxides in high concentrations, which are incompatible with real-world biomedical applications and limit their use [31; 32; 33]. Unless there is a safety guarantee, magnetic control is also limited by the US Food and Drug Administration (FDA) field strength limitation for clinical procedure applications [34]. Magnetic fields have also been reported to have an impact on an organism's physiology by increasing blood circulation and metabolism [35]. However, to date, there is a gap between proof-of-concept laboratory trials and real-world implementations of these technologies. Although most studies are conducted in vitro in settings significantly different from those seen in the human body [30], the field is very promising, and medical robotics potentials are plentiful [36; 37; 38; 39]. In the near future, microscale robots will be used to perform least invasive diagnostic and therapeutic activities within the human body [40]. The use of light to control microbots has gained popularity in recent years due to its noncontact and noninvasive properties [41; 42]. Thousands of studies are being done to determine how to make the best use of this mechanism [43; 44; 45; 46; 47]. [PERSON], who worked at Bell Laboratories, was the first to employ concentrated laser beams to introduce optical trapping in 1970 [48]. This breakthrough paved the way for today's optical tweezers and the development of light-powered microbots.