## 1 Introduction  
Motion is an essential element in maintaining the life of living organisms, and life has evolved to induce efficient movement for a long time. Scientists have been steadily making efforts to develop microscale actuators inspired by the mechanisms of the movement organs of life forms. Micro-actuators are small in size and capable of non-contact/non-invasive manipulation, and they can be used in various applications such as targeted drug delivery [1, 2], non-invasive surgery, and cell manipulation [3] with additional functionalization. Moreover, unlike conventional macroscale actuators, interest is increasing in micro-actuators that can precisely operate in harsh conditions such as narrow passages, enclosed conditions, and high viscosity environments. In particular, research into bio/medical technology advancement has been accelerated due to the promise of control under in vivo-like conditions.  
Conventional microscale actuators have been fabricated using various techniques such as photolithography [4], 3D printing [5], shape memory [6], and soft lithography [7]. A fabricated micro-actuator can be manipulated by various energy sources. A commonly used propulsion mechanism is a chemical-based actuation mechanism that is based on the conversion of chemical energy into propulsion [8, 9]. In this process, the actuator's driving force can be obtained from the concentration gradient of molecules or the microbubble generation during chemical decomposition. Actuation through direct chemical decomposition is easy to fabricate and induce, but biocompatibility issues can arise when chemical substances remain due to incomplete chemical degradation [10]. To overcome these limitations, actuation can be induced using biocompatible chemicals such as enzymes [11] and urea [12]. Moreover, several types of methods such as magnetic [13, 14], optical [15], and acoustic [16] can be used to create a microscale actuator's remote control. The advantages of a long lifespan, on-demand motion control, and excellent biocompatibility have shown great potential for in vivo research. Nonetheless, most work remains in the early stages, and related technologies are being developed through the efforts of many researchers. As the demand for three-dimensional (3D) complexes with high-precision micro-actuators increases, new fabrication methods are being required. As a solution to this, two-photon polymerization (TPP) based on the two-photon absorption (TPA) principle was devised to fabricate precise 3D micro-structures without the use of photomasks or iterative processes [17; 18; 19; 20]. However, due to the lack of mechanical strength, electrical conductivity, and magnetic and optical properties of structures fabricated by TPP [21], additional processes are required for the remote manipulation or driving of actuators by magnetic, optical, and acoustic control.  
In this review, we explore the driving/control methods of micro-actuators fabricated based on the TPP technique. We summarize the progress of the remote control of 3D micro-actuators/robots concerning the fabrication processes, actuation mechanisms, limitations, and reviews of the potential applications and challenges to be solved.