# Light-Controlled Microbots in Biomedical Application: A Review
## 2 Prospective Applications
### Micro Manipulation  
Light manipulation brings up new possibilities for micro assemblies. Assembly on the microscale becomes challenging due to the negligible gravity force of the weak forces (capillary, van der walls, etc) acting on the light-weighted object. Optical tweezers, which use light to manipulate micro-objects, can play an important role in actuating these microtools. There has previously been research on using different types of microbots in micromachines [72]. The feasibility of using light in micro actuation has already been demonstrated [73; 74; 75]. The researchers were able to put together a screw through a nut with optical handlers. This mechanism might be useful to analyze and study microscopic organisms such as bacteria or cells because many times, it is required to attach them on top of a coverslip without using any harmful adhesives, and this micro screw mechanism system will provide this physical fixation without using any chemicals in an aqueous medium. Moreover, this can be applied to microfluidic systems for micro pumping or mixing of microfluidics. Micro assembly is very important in terms of improving device integration, miniaturization, and pushing the limits of the minuscule world of technologies. This approach can also be used to enhance micromechanics and microbotics where biological cells are involved as it complies with a less invasive control modality to perform the  
Figure 2: Targeted drug delivery: (**a**) Bacteria, such as _Clostridia_, and higher eukaryotic immune cells exhibiting intrinsic tumourtaxis, (**b**) FDA-approved pipeline for producing CAR-T cells as a tailored cancer therapy (left). CAR-T cells target cancer cells by identifying tumor antigens on their surface, resulting in downstream TCR signaling such as cytotoxic perforin and granzyme responses (**c**) Direct surface coupling or combining microbots with nanoparticles as showed for nanoliposomes, (**d**) Magnetic and light assisted external guidance for the microbots to reach the targeted region, (**e**) Biohybrid microbots such as sperm coated with nanoparticles to target the cancer cells in the female reproductive system for easy access, and (**f**) The acidic environment inside the stomach lumen is neutralized using chemically activated microbots. Notes—RBCs: red blood cells, aq: aqueous, and g: gaseous [71]. Reproduced under the terms of the CC-BY license.  
operation. Figure 3 illustrates micro manipulation using an optoelectronic tweezers (OET) system and an optic tweezers system.  
Figure 3: Micro manipulation using light actuation (**i**) (**A–G**) Fabrication of micro tools, (**H–J**) Different light patterns to manipulate the micro tools, (**K–M**) Performance curves for various shapes of micro tools, (**N**) Three-dimensional simulation of an OET device with a purple light pattern projected onto an a-Si:H surface. XY plots at \(Z=1.1\) m of simulated, (**O**) Electric potential distribution and (**P**) Electric field distribution for a device driven at 20 Vpp (25 kHz), with heat maps indicating the simulated electric potential and field (blue = low, red = high). The (**N–P**) axis dimensions are in micrometers. Copyright (2019) National Academy of Sciences (76), and (**ii**) (**a–d**) An optical screw-wrench system for micro-assembly using optical tweezers (73). Reproduced under the terms of the CC-BY license.