Zebrafish eggs have attracted considerable interest in developmental biology in recent years. Among the properties of these biological systems that require characterization, stiffness is a key mechanical parameter, as it provides an important indicator of the developmental stage of the egg and embryo. Highly localized stiffness measurements and the determination of the corresponding Young’s modulus require a force sensor with a tip radius comparable to that of an atomic force microscope (AFM). However, the length of a conventional AFM probe tip is typically less than a hundred micrometers, whereas zebrafish eggs have a diameter on the order of a millimeter. Consequently, standard AFM probes cannot access sufficient depths to mechanically characterize the outer membrane, inner medium, and embryo. This paper presents a proof of concept demonstrating the effectiveness of quartz tuning forks (QTFs) equipped with tungsten probes several millimeters in length and with tip radii of a few tens of nanometers for the mechanical characterization of zebrafish eggs. A model describing the relationship between QTF resonance-frequency shifts and egg stiffness is developed. Combined with experimental measurements, the model demonstrates that accounting for indentation depth is essential for accurate mechanical characterization. Comparison with existing approaches shows that the proposed indentation-depth-dependent formulation provides a more general framework for mechanical characterization than current state-of-the-art models. The work combines developments in robotics, modeling, and control with experimental characterization of zebrafish eggs. The results demonstrate that tungsten probes combined with QTF technology provide sufficient resolution to mechanically differentiate zebrafish eggs at different developmental stages, and that their length, rigidity, and strength enable efficient penetration into the eggs. To the best of our knowledge, this capability has not previously been demonstrated or systematically evaluated in the state of the art.
The electrode shape is a key design parameter in dielectrophoresis DEP-based devices, as it directly influences the electrical field distribution and the resulting DEP forces used for particles and cells manipulation. In our previous work, we developed a topology optimization framework that generates high performant electrode topologies for DEP trapping applications. The resulted electrodes were successfully validated numerically and experimentally. However, the influence of the optimization parameters on the resulting electrode topologies and their performances has not been studied. To further investigate this aspect, this study provides a numerical analysis of the impact of three key topology optimization parameters, namely volume fraction constraint, weighting factors and electric field constraint. A representative case study involving trapping within a convegence region inside a fluidic channel is considered to evaluate the influence of these parameters on the optimized electrodes and the resulting DEP forces distribution. The numerical results show that for each set of parameters, the methodology enables the generation of electrode topologies that effectively direct the DEP forces to trap the targeted particles. More importantly, the study demonstrates that imposing a volume constraint is not necessary for this class of problems as the optimization process naturally converges toward an appropriate conductive material distribution that provides the best compromise between electrode topology and DEP-force performance. Furthermore, the weighting factors are shown to strongly influence the balance of the DEP force components and, therefore, the topology of the optimized electrodes. Finally, introducing an electric field constraint limits the maximum electric field intensity while preserving trapping performance, making the optimized designs more suitable for biological applications where excessive electric fields may damage cells. These findings provide practical guidelines for selecting topology optimization parameters and contribute to design high performant DEP trapping electrodes.
This paper presents a scalable planar electromagnetic actuation platform for independent manipulation of micron-scale microrobots, addressing the limited field strength and scalability of conventional PCB-based electromagnetic systems. The proposed approach utilizes a helically wound copper-foil on a mild steel (MS) core to form a compact 3× 3 electromagnetic coil array, enabling high current operation, rapid prototyping, and flexible scaling while generating strong, spatially localized controllable magnetic field pockets. Finite element modeling analyzes the magnetic field distribution, field gradients, and inter-coil interference, providing quantitative design insight and guiding experimental validation. Magnetic characterization demonstrates peak flux densities of up to 23.73 mT and peak field gradients of approximately 16 T/m at sub-millimeter distances, exceeding typical earlier reported planar electromagnetic coils and enabling precise and repeatable actuation of spherical ferromagnetic microrobots with radii of 100–200 µm. Open-loop experiments in aqueous and viscous media demonstrate spatially selective trapping, translation, and parallel independent actuation of multiple microrobots within distinct workspace regions. The combination of high magnetic field strength, localized actuation, and scalable fabrication establishes the copper-foil electromagnetic coil array as a low-cost and high-performance alternative to existing planar actuation technologies, with direct applicability to high-throughput biological manipulation, micromanufacturing, and microassembly.
Micromanipulation of objects using a magnetic robot is critical for various applications, such as micro-assemblies. However, manipulation skills remain a significant challenge due to the nonlinear interaction between the robot and the object. The effects of pushing can vary from one object to another, depending on how intense the contact is, according to the contact point, surface properties, and so on. This paper presents a pushing controller for micromanipulation using Uncalibrated Visual Servo as robot control. The controller is based on a composite of specific motions or behaviours provided to the robot to maneuver an object. The main advantage of using the proposed controller is its independence from both the robot pusher and object configurations, making it adaptable. Experiments performed on a real system in different scenario show the effectiveness of the proposed controller. The mean absolute error (MAE) is 1.22
Mechanical properties of single cells offer insight into organismal development, disease progression, and mechanotransduction. Yet, estimating the complete mechanical state of single cells, involving multiple parameters, remains challenging due to limited deformation modes available in existing techniques and complex instrumentation. To address this gap, we are developing several compliant micromechanisms that together enable multiple modes of cell manipulation on a single chip. Building on an earlier uniaxial stretcher, here we demonstrate a biaxial stretching mechanism with vision-based force sensing. Because the mechanism uses elastic beams for actuation, stretching forces can be computed from optical displacement measurements using a closed-form analytical model derived from beam theory. This obviates the need for dedicated force sensors thereby simplifying device fabrication and operation. The force displacement relations were validated on macro- and microscale prototypes. The device is microfabricated out of SU-8 using a two-layer photolithography process, yielding an array of miniature stretchers that can be mounted on a coverslip for high-resolution imaging during manipulation. We stretch U87-MG human glioblastoma cells biaxially, compute bulk stiffness, stress and strain in orthogonal directions using microscopy and further fit 2D Fung’s model to investigate anisotropy. This biaxial stretcher can be combined with additional modules (e.g., for shear or twist) to realize a multimodal single-cell mechanophenotyping platform for comprehensive analysis of cellular mechanics. Such a versatile platform represents a new approach to single-cell mechanical characterization.
