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The MiniMag is a magnetic manipulation system capable of 5 degree-of-freedom (5-DOF) wireless magnetic control of an untethered microrobot (3-DOF position, 2-DOF pointing orientation). The system has a spherical workspace with an intended diameter of approximately 10 mm, and is completely unrestrained in the rotational degrees-of-freedom. This is accomplished through the superposition of multiple magnetic fields, and capitalizes on a linear representation of the coupled field contributions of multiple softmagnetic- core electromagnets acting in concert. The prototype system consists of 8 stationary electromagnets with ferromagnetic cores, and is capable of producing magnetic fields in excess of 20 mT and field gradients in excess of 2 T/m at frequencies up 2 kHz.

The progress of wet age-related macular degeneration can now be controlled by intravitreal drug injection. This approach requires repeated injections, which could be avoided by delivering the drug to the retina. Intraocular implants are a promising solution for drug delivery near the retina. Currently, their accurate placement is challenging, and they can only be removed after a vitrectomy. In this paper, we introduce an approach for minimally invasive retinal drug delivery using magnetic intraocular inserts. We briefly discuss the electromagnetic-control system for magnetic implants and then focus on evaluating their ability to move in the vitreous humor. The mobility of magnetic intraocular implants is estimated in vitro with synthesized vitreous humors, and ex vivo with experiments on cadaver porcine eyes. Preliminary results show that with such magnetic implants a vitrectomy can be avoided.

The progress of wet age-related macular degeneration can now be controlled by intravitreal drug injection. This approach requires repeated injections, which could be avoided by delivering the drug to the retina. Intraocular implants are a promising solution for drug delivery near the retina. Currently, their accurate placement is challenging, and they can only be removed after a vitrectomy. In this paper, we introduce an approach for minimally invasive retinal drug delivery using magnetic intraocular inserts. We briefly discuss the electromagnetic-control system for magnetic implants and then focus on evaluating their ability to move in the vitreous humor. The mobility of magnetic intraocular implants is estimated in vitro with synthesized vitreous humors, and ex vivo with experiments on cadaver porcine eyes. Preliminary results show that with such magnetic implants a vitrectomy can be avoided.

Many current and proposed retinal procedures are at the limits of human performance and perception. Microrobots that can navigate the fluid in the interior of the eye have the potential to revolutionize the way the most difficult retinal procedures are conducted. Microrobots are typically envisioned as miniature mechatronic systems that utilize MEMS technology to incorporate sensing and actuation onboard. This chapter presents a simpler alternative approach for the development of intraocular microrobots consisting of magnetic platforms and functional coatings. Luminescence dyes immobilized in coatings can be excited and read wirelessly to detect analytes or physical properties. Drug coatings can be used for diffusion-based delivery, and may provide more efficient therapy than microsystems containing pumps, as diffusion dominates over advection at the microscale. Oxygen sensing for diagnosis and drug therapy for retinal vein occlusions are presented as example applications. Accurate sensing and therapy requires precise control to guide the microrobot in the interior of the human eye. We require an understanding of the possibilities and limitations in wireless magnetic control. We also require the ability to visually track and localize the microrobot inside the eye, while obtaining clinically useful retinal images. Each of these topics is discussed.

We demonstrate five-degree-of-freedom (5-DOF) wireless magnetic control of a fully untethered microrobot with a magnetic steering system we call OctoMag. Although only occupying a single hemisphere, this system is capable of isotropically applying forces on the order of 1–40 µN with unrestricted control of the 2 orienting DOF. These capabilities are enabled through the use of soft-magnetic-cores which provide an increase of approximately 20× that of air cores in magnetic-field strength, but comes at the cost of more complicated interactions between coils. We propose a modeling mechanism that assumes the field contributions of the individual currents superimpose linearly when using cores with large linear regions and negligible hysteresis. When designing the system, the locations and quantity of electromagnets were optimized with regards to the force generation in the worst-case direction predicted by the model. The resultant system is capable of both open and closed-loop operation over a workspace of 4 cm3. OctoMag was primarily designed for the control of intraocular microrobots for delicate retinal procedures, but also has potential uses in other medical applications or micromanipulation under an optical microscope.

In this paper we present a protocol to create artificial vitreous humor phantom tissue to be used as a test bed for in vitro experiments. The artificial vitreous consists of water, agar, and hyaluronic acid. Unlike existing vitreous replacement substances, this dummy tissue exhibits viscoelastic characteristics of in vivo natural vitreous humor. We are able to prepare artificial vitreous with a range of viscoelastic properties, which will allow us to account for the variation seen in human vitreous that comes with aging. The artificial vitreous will primarily serve as an experimental test bed for wireless magnetic control and vision-based tracking of assembled-MEMS microrobots. These microrobots will someday enable minimally invasive surgical and diagnostic intraocular procedures.

We calculate the torque and force generated by an arbitrary magnetic field on an axially symmetric soft-magnetic body. We consider the magnetization of the body as a function of the applied field, using a continuous model that unifies two disparate magnetic models. The continuous torque and force follow. The model is verified experimentally, and captures the often neglected region between weak and saturating fields, where interesting behavior is observed. We provide the field direction to maximize torque for a given field magnitude. We also find an absolute maximum torque, for a given body geometry and material, which can be generated with relatively weak applied fields. This paper is aimed at those interested in systems-level analysis, simulation, and real-time control of soft-magnetic bodies.