Microrobots have attracted a lot of attention because they are small enough to manipulate biological systems, yet they are large enough to include computerized components; which provide a higher degree of control over nanorobots. While there are many different components to these microrobots, polymer-based thin films are used across many of them. In this article, we look at the roles that polymer-based thin films play in microrobot systems.
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Many people will have heard about nanorobots - small molecular machines that perform a specific function (usually in the form of atomic manipulation), often through the control of an external stimulus (magnetic field, UV light, etc.). Microrobots are based on the same premise, with the main difference being that they are micrometers in size, not nanometers, and some can even be seen with the naked eye. Microrobots can be used as an individual entity, or as part of a microrobot collective, to perform a specific function.
Another area where microrobots differ from nanorobots is in their structure. The small size of nanorobots often limits the complexity of materials used, whereas microrobots’ size enables the incorporation of micro-electromechanical systems (MEMS) and micronized computer components. This gives the user a much higher degree of control when the microrobots are performing a specific task. Many applications benefit from the use of microrobots, but they are often used in the biomedical field.
Thin Films in Microrobots
Many different materials and components contribute to the make-up of a microrobot. One of these is polymer thin films. In this section, we look at the different types of polymer thin films used in microrobot systems.
Polymer Thin Films
There is a broad range of biohybrid microrobots. The role of polymer films is to act as a biocompatible surface that cells can adhere to, bind to and grow on. Many of the microrobots in these areas have been developed to act as a deliverable 3D scaffold that can swim through the cellular matrix, grow cells and deposit them to a target area. Although, there are also many biohybrid microrobots that are intended to act as actuators, with the most promising being muscle-cell hybrid actuators to mimic the body’s natural moving muscles.
A wide range of these systems have been developed include PDMS, elastomers with cardiomyocytes (cardiac muscle cells), polymer hydrogel films with cardiomyocytes and ultrathin thermoplastic polymer films. The advantages of using polymer films for these applications include the ability for the surface to return to their natural conformation after deformation from cell growth, interactions with extracellular environments, or physical deformations as a part of a mechanism, low cytotoxicity and high flexibility (and flexural strength).
Nanoparticle Doped Polymer Thin Films
Polymer films can be doped with magnetic nanoparticles, such as NdFeB, to create a magnetically controlled microrobot which responds to changes within an applied magnetic field. Both the polymeric matrix and the magnetic nanoparticles are low in cytotoxicity, so they are often biocompatible for biological applications.
These thin films are often fabricated as a composite material where the nanoparticles are embedded into the polymer matrix, creating a magnetic material that is responsive to magnetic field changes. This type of composite film is a step up from previous efforts which deposited magnetic nanoparticles onto the surface of a polymer, as it negates the need for particle deposition techniques; which can often lead to an uneven distribution of magnetic nanoparticles meaning that the microrobot doesn’t respond to the magnetic field as uniformly, or as effectively.
As mentioned, the composite polymer films in these systems act as the responsive material. In this instance, the polymer films are responsible for the locomotion and navigation of the microrobot, as the magnetic field is used to (wirelessly) guide the microrobot to its intended destination. This is also why magnetic uniformity across the polymer matrix is a key aspect of these composite thin films. The possible applications involving these thin films include targeted drug delivery, lab-on-a-chip, personalized medicine and the manipulation of cancer cells.
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