As technology around us enters unconventional areas, such as rings and glasses, it is nothing but the marvels of miniaturization and microassembly redefining the rules. Miniaturization refers to the trend of making products and devices smaller, particularly in electronics, mechanics, and optics. Microassembly, on the other hand, is the precise manipulation, orientation, and assembly of microscale components, often smaller than 1000 micrometers, into complex, functional hybrid microsystems, such as those found in Microelectromechanical Systems (MEMS).
The two concepts, miniaturization and microassembly, are the most interconnected themes of the electronics industry, powering the next generation of technology revolution from homes to appliances and roads to vehicles. This vast application compels us to track and see what’s latest with the technology while also considering the challenges and opportunities the sector has to offer. Recent studies in the field of medical electronics have unveiled certain challenges that have led to the development of new micro-systems. The following article intends to unravel those very latest observations and developments.
What’s the problem with heterogeneous integration?
As the macroscopic devices are converted into their micro/nano-scale counterparts, integration of components like electronic devices, micro-electromechanical structures (MEMS), and optoelectronic devices on the same substrate is a debated issue. It is because of the different physical forces manifesting themselves in varying proportions owing to scaling effects.
For instance, adhesion forces that originate primarily from surface tension, van der Waals forces, and electrostatic forces are fundamental limitations of micromanipulation. In particular, the adhesion forces between objects are significant compared with the gravitational forces when the sizes of the components are less than 1 mm. This means that as the components, the target objects, become smaller, the surface-area-to-volume ratio increases, leading to a more pronounced scaling effect, hence originating difficulties in the fabrication of miniature devices.
All this is because the physical considerations change as we move from the macro- to the microscale. Earlier conducted studies have considerably shown that micro/nano-robots are sensitive to environmental parameters and that the dominant forces in different media are distinct (only van der Waals forces are ubiquitous).
As the scale decreases, objects invisible to the naked eye must be studied using light or electron microscopes. While the ability to control each object diminishes, their collective properties become more significant. These scale-dependent physical principles demand different strategies for designing devices at the micro- and nano-levels. Naturally, challenges that are straightforward at the macroscopic scale become far more complex in this domain.
As we move into exploring various domains using this technology, the design of microassembly/micromanipulation processes must consider these factors to isolate undesired interference, which is a challenging task in practice.
What is the solution?
According to a paper published in Elsevier’s Engineering Monthly, it discusses this very problem to reach a solution. The paper discusses various solutions, one of which is a multimer design by Yu et al., where the researcher combines several small pieces of different materials into a connected group. This makes sure that the nanoparticles that were earlier prone to sticking due to higher forces are prevented from tumbling end-over-end, which keeps changing the contact points. This dynamic motion reduces the time and area of contact, so sticking is weaker.
This logically translates into building components with different microscale components with different geometries and materials. Assembled devices, which are usually manipulated through non-covalent interactions, are responsive to environmental stimuli such as temperature, pressure, and flow. Eventually, the paper suggests using magnetic, optical, and acoustic fields and mechanical methods to generate actuation power at the micro/nano-scale.Additionally, owing to their rapid response and ability to be remotely controlled, magnetic field-based methods offer a pathway for one-dimensional (1D) to 3D microassembly.
While there are various ways, we’ll focus on electromagnetic principles only, for now. Magnetic field-induced assembly (MFIA) of nanoparticles allows for the 1D, two-dimensional (2D), or 3D organization of magnetic particles under the influence of a magnetic field. This refers to the automatic and spontaneous arrangement of particles within a magnetic field rather than an assembly induced by artificially moving targets. Experiments also show that under a uniform intensity of magnetic field, the nanoparticles arrange themselves in a linear, chain-like, or hexagonal pattern even in in vivo applications.
Hence, using an external magnetic field, programmed devices can be made, turning them into magnetically actuated microrobots. Using the same principle, magnetically controlled microrobots have been used for several different microassembly tasks. The assembled block, spherical, and flake-like magnetic doping devices can be used to assist robots in pushing different units for the assembly of micro components.
How does this improve grip & control?
Electromagnetic fields allow magnetic micro-units to be precisely controlled. By programming their magnetic response, these units can move in a directed way and assemble into desired structures or swarms. Temporary anchoring methods (like hydrogels or mechanical locks) prevent accidental movement, ensuring stability until assembly is complete. Advanced designs, such as quadrupole modules, also minimize interference between neighboring units. Together, these techniques improve both the precision of positioning and the grip or stability of micro-components during assembly.
Another approach to microassembly uses magnetic microgrippers that can hold and transport individual units. Unlike magnetic microrobots that mainly push components into place, microgrippers can grasp them directly, allowing for more precise and complex 3D assembly.
In conclusion, assembled magnetic microrobots demonstrate versatile and controllable propulsion under rotating magnetic fields, enabling functions such as transport, stirring, and targeted delivery. While artificial designs like magnetic microcubes showcase structured assembly for cell transport, biohybrid microrobots expand these possibilities by integrating magnetic materials with living cells. Such innovations, including macrophage-based robots capable of 3D navigation and drug delivery, highlight the growing potential of magnetic microrobots in advanced biomedical applications.
Applications
These microcomponents can form diverse geometries and can easily be decoupled as the magnetic field gradually dissipates. This flexibility in structural reorganization allows them to adapt to and overcome different environmental constraints. Expanding programmed magnetic assemblies to biological materials with programmed orientations and structures, the paramagnetism of radicals to biological materials has been used in order to endow magnetic assemblies of different arbitrariness with programmed orientations and structures.
Eventually, the use of magnetic devices provides the basis for the development of microbiotics. When these units become functional with closed-loop control, for instance, in drug delivery, they can be classified as microrobots rather than merely micro-patterned components.
Micro-assemblies with magnetic Microrobots: The application of an external magnetic field can both convert different components into programmed devices and turn them into magnetically actuated microrobots. This section summarizes the magnetic actuation and navigation of assembled micro-robots. These microrobots can be divided into two main types: magnetically actuated microrobots for robot-assisted assembly and assembled swimming magnetic microrobots as carriers or deliverers.
- Bio-inspired microrobots: Magnetically controlled bio-inspired microrobots have shown great potential in microassembly tasks. Different geometries—such as blocks, spheres, flakes, and cubes—enable them to push, grasp, or transport components in both fluid and solid environments.
- Magnetic Micro-Grippers: These are microassembly tools capable of grabbing and transporting units, enabling more sophisticated 3D assembly than pushing-based microrobots. Fabricated using techniques like digital light-processing 3D printing with magnetic and nonmagnetic resins, they can be remotely guided by magnetic fields to operate in confined spaces.
Assembled Swimming Magnetic Microrobots as Carriers or Deliverers: Assembled magnetic microrobots, driven by a rotating magnetic field, can achieve controllable propulsion in diverse fluidic environments. They can be configured into chain-like structures for transporting cells or act as microstirrers. Beyond artificial designs, biohybrid microrobots—such as macrophage-based systems or magnetotactic bacteria—enable precise drug delivery and cancer cell targeting. These cell-based microrobots, capable of forming dimers, trimers, or tetramers, respond to environmental cues like light, offering versatile and targeted delivery applications.
Prominent Challenges
While the technology holds immense potential, it also comes with some inherent challenges to counter. Some of them have been listed below:
- Miniaturization & Production: Space limits and scale mismatches require advanced methods like two-photon polymerization.
- Handling Fragile Objects: Flexible structures (e.g., neural electrodes) demand high precision; current methods are costly or lack accuracy.
- Feedback Limits: Visual systems fail in closed environments; alternatives include Fiber Bragg sensors, mini-endoscopes, and MRI-compatible robots.
- Automation: Over-reliance on vision reduces robustness; advanced strategies like reinforcement learning are needed for autonomous navigation.
- Safety: Metallic magnetic residue poses risks; biofriendly carriers help, but safe removal methods and standardized assessments are still lacking.
In conclusion, MFIA and magnetic microrobots provide versatile, remotely controlled tools for microassembly with strong potential in biomedical engineering. Their broader adoption and clinical use will depend on overcoming key challenges—practicality, complex geometries, reliable feedback in closed environments, higher automation, and material safety.
