The demand in the biomedical field for fast and precise devices for in vitro applications has increased in recent years. Mobile microrobots are significantly suitable for such applications and are developing rapidly. These microrobots offer untethered actuation toward a contamination-free environment while allowing for fast and precise handling of biological entities for applications such as positioning, sensing, delivery, and cell surgery that are highly effective for new drug discoveries and improving our understanding of cells’ behavior on the single-cell level. Here, we present a review of the recent state of the art in the actuation and implementation of mobile microrobots for in vitro applications. We first explore the widely used methods of wireless actuation. Next, we address the challenge of implementing an on-board interaction technique to handle the target biological entity without affecting the actuation of the microrobot. Finally, we discuss the future directions that would draw the basic outline for the next generation of mobile microrobots for in vitro applications.

In this article, we propose laser actuated microjoints which can be remotely actuated in both air and water. Their actuation relies on the optothermal response of a spiral bimaterial. The microjoints are fabricated using two-photon polymerization technology that offers the ability to tune the thermal and mechanical properties of the material by controlling the laser printing power. Modeling is first conducted to verify the parameters of the spiral that affect the rotational displacement and generated torque of the microjoint. Then, microjoints having a diameter of less than 200 $\mu$ m are characterized. The microjoints can realize a maximum deflection of approximately 8.5 $^{\circ }$ , a force in the $\mu$ N-order using a 265- $\mu$ m long arm, an actuation repeatability of more than 100 times, and a time response of approximately 34 ms. Finally, the microjoints are implemented in a microgripper and an xy serial microarm. Successful micromanipulation of 40 $\mu$ m microbeads using the microgripper, and the simultaneous actuation of multiple microjoints of the xy serial microarm with two degrees of freedom are shown. This kind of rotational, compact, selective, and remotely actuated microjoints would allow the deployment of individually controlled mobile microrobots with several degrees of freedom for complex applications such as cell manipulation and microassembly.

In this paper, we propose a laser actuated microgripper that can be activated remotely for micromanipulation applications. The gripper is based on an optothermally actuated polymeric chevron-shaped structure coated with optimized metallic layers to enhance its optical absorbance. Gold is used as a metallic layer due to its good absorption of visible light. The thermal deformation of the chevron-shaped actuator with metallic layers is first modeled to identify the parameters affecting its behavior. Then, an optimal thickness of the metallic layers that allows the largest possible deformation is obtained and compared with simulation results. Next, microgrippers are fabricated using conventional photolithography and metal deposition techniques for further characterization. The experiments show that the microgripper can realize an opening of 40 µm, a response time of 60 ms, and a generated force in the order of hundreds of µN. Finally, a pick-and-place experiment of 120 µm microbeads is conducted to confirm the performance of the microgripper. The remote actuation and the simple fabrication and actuation of the proposed microgripper makes it a highly promising candidate to be utilized as a mobile microrobot for lab-on-chip applications.

In this letter, we propose a mobile microgripper actuated using laser optothermal and magnetic actuation in liquid environments. This hybrid actuation scheme allows the full decoupling between the in-plane positioning of the mobile microgripper and the actuation of its gripping mechanism, which reduces the control complexity of such microgrippers. The developed mobile microgripper with the dimensions of 1500 $\times 700\times$ 250 μ $\mathrm{m^{3}}$ can realize an open and close gripping motion of 35 μm, a magnetic positioning accuracy of 6 μm for translation over an area of 1 × 1 mm and 2 $^{\circ }$ for rotation, and a laser steering accuracy of 25 μm. Finally, the mobile microgripper is used to control the position of a microbead inside a liquid environment. Our work provides a proof of concept of laser optothermal-magnetic hybrid actuation, which has the potential to enhance the deployment of microtools in biomedical applications including cell manipulation and lab-on-chip devices.

We propose a method to measure the six degrees of freedom (DoFs) of an object moving in space with nanometric resolutions over millimetric ranges. Similar to conventional motion capture systems, a marker is attached to the object and tracked using an imaging system. However, the proposed method relies on digital holography rather than conventional refractive microscopy and involves two complementary measurement principles, i.e., interferometry and phase-based motion estimation, applied simultaneously to the hologram of a micro-structured pattern. Interferometry addresses out-of-plane motions, while phase-based motion estimation addresses complementary inplane displacements to address the six DoFs. Performance metrics, namely, resolution, linearity, range, and repeatability, are evaluated experimentally. Finally, the proposed measurement method is applied to capture the motion of a precision hexapod to demonstrate its potential for 3D metrology applications at the nanometer scale.

Microgrippers have emerged in minimally invasive surgery and biomedical applications, enabling tasks such as gripping, micro-assembly, and cell manipulation. Realizing microgrippers with multiple degrees-of-freedom (DoFs) enables higher dexterity and multi-functionality. However, due to their small size and limited working space, the development of microgrippers with multi-DoF faces great challenges, requiring complex fabrication technologies and actuation mechanisms. Here we report a novel optothermally-actuated multi-DoF microgripper with multiple functionalities for micromanipulation. For this, three types of optothermal microactuators, namely bimaterial microjoints, chevron-shaped microactuators, and hot-cold arm microactuators are considered. The suitability of the chevron-shaped and hot-cold arm microactuators for mechanical pushing tasks is evaluated through modeling and simulation. Then, a 3-DoF microgripper incorporating two spiral bimaterial microjoints and one chevron-shaped microactuator is designed and fabricated. The selective and individual actuation of these microactuators is facilitated using a fiber bundle and a digital micromirror device. Finally, the performance and multi-functionality of the microgripper are demonstrated by performing multiple micromanipulation tasks of mechanical pushing and pick-and-release of microbeads. This work provides a proof of concept of an optothermal multi-DoF microgripper with multiple functionalities, opening the way for advanced dexterity at the microscale that is difficult to achieve using the current technology.