Medical Microrobots

: Scientists around the world have long aimed to produce miniature robots that can be controlled inside the human body to aid doctors in identifying and treating diseases. Such microrobots hold the potential to access hard-to-reach areas of the body through the natural lumina. Wireless access has the potential to overcome drawbacks of systemic therapy, as well as to enable completely new minimally invasive procedures. The aim of this review is fourfold: first, to provide a collection of valuable anatomical and physiological information on the target working environments together with engineering tools for the design of medical microrobots; second, to provide a comprehensive updated survey of the technological state of the art in relevant classes of medical microrobots; third, to analyze currently available tracking and closed-loop control strategies compatible with the in-body environment; and fourth, to explore the challenges still in place, to steer and inspire future research

Magnetic Field-Based Technologies for Lab-on-a-Chip Applications

In the last decades, LOC technologies have represented a real breakthrough in the field of in vitro biochemical and biological analyses. However, the integration of really complex functions in a limited space results extremely challenging and proper working principles should be identified. In this sense, magnetic fields revealed to be extremely promising. Thanks to the exploitation of external magnetic sources and to the integration of magnetic materials, mainly high aspect ratio micro-/nanoparticles, non-contact manipulation of biological and chemical samples can be enabled. In this chapter, magnetic field-based technologies, their basic theory, and main applications in LOC scenario will be described by foreseeing also a deeper interaction/integration with the typical technologies of microrobotics. Attention will be focused on magnetic separation and manipulation, by taking examples coming from traditional LOC devices and from microrobotics

Millimeter-Scale Magnetic Carrier for On-Demand Delivery of Magnetic and Non-Magnetic Microparticles Suspensions

The use of magnetic microparticles (MMPs) has recently proven a great potential for biomedical applications, i.e. for drug delivery or magnetic hyperthermia. However, MMPs are typically delivered passively through systemic injection or exploiting tethered drug delivery systems which require percutaneous medical procedures. Here we propose an untethered magnetic carrier for MMPs suspension delivery. This wireless millirobot is capable of precisely releasing MMPs that after delivery are completely decoupled from the carrier and can be manipulated independently by separate magnetic sources. Experiments were performed in an aqueous environment to validate carrier locomotion and controlled release capabilities. The prototyped carrier (overall 41 mm long and 10 mm in diameter) can be wirelessly moved by an external magnet at a distance larger than 10 cm, and, when fixed magnetically, can be triggered by another external magnet (around 6 mm apart) to release a cargo. Magnetic navigation and release activation well fit model predictions with actuation distance errors below 10% based on experimental performance. The carrier proved able to perform controlled release of non-magnetic and magnetic cargoes and was recorded to release approximately 25% of the loaded MMPs suspension with no premature release

A Bioinspired Fluid-Filled Soft Linear Actuator

In bioinspired soft robotics, very few studies have focused on fluidic transmissions and there is an urgent need for translating fluidic concepts into realizable fluidic components to be applied in different fields. Nature has often offered an inspiring reference to design new efficient devices. Inspired by the working principle of a marine worm, the sipunculid species Phascolosoma stephensoni (Sipunculidae, Annelida), a soft linear fluidic actuator is here presented. The natural hydrostatic skeleton combined with muscle activity enables these organisms to protrude a part of their body to explore the surrounding. Looking at the hydrostatic skeleton and protrusion mechanism of sipunculids, our solution is based on a twofold fluidic component, exploiting the advantages of both pneumatic and hydraulic actuations and providing a novel fluidic transmission mechanism. The inflation of a soft pneumatic chamber is associated with the stretch of an inner hydraulic chamber due to the incompressibility of the liquid. Actuator stretch and forces have been characterized to determine system performance. In addition, an analytical model has been derived to relate the stretch ability to the inlet pressure. Three different sizes of prototypes were tested to evaluate the suitability of the proposed design for miniaturization. The proposed actuator features a strain equal to 40–50% of its initial length—depending on size—and output forces up to 18 N in the largest prototypes. The proposed bioinspired actuator expands the design of fluidic actuators and can pave the way for new approaches in soft robotics with potential application in the medical field

Medical Imaging of Microrobots: Toward In Vivo Applications

Medical microrobots (MRs) have been demonstrated for a variety of non-invasive biomedical applications, such as tissue engineering, drug delivery, and assisted fertilization, among others. However, most of these demonstrations have been carried out in in vitro settings and under optical microscopy, being significantly different from the clinical practice. Thus, medical imaging techniques are required for localizing and tracking such tiny therapeutic machines when used in medical-relevant applications. This review aims at analyzing the state of the art of microrobots imaging by critically discussing the potentialities and limitations of the techniques employed in this field. Moreover, the physics and the working principle behind each analyzed imaging strategy, the spatiotemporal resolution, and the penetration depth are thoroughly discussed. The paper deals with the suitability of each imaging technique for tracking single or swarms of MRs and discusses the scenarios where contrast or imaging agent's inclusion is required, either to absorb, emit, or reflect a determined physical signal detected by an external system. Finally, the review highlights the existing challenges and perspective solutions which could be promising for future in vivo applications

Infiltration of Cell-Inspired Ultra-Deformable Magnetic Microrobots in Restrictive Environments

Microscale robotics represents a promising future for minimally invasive medicine. However, one of the biggest challenges of microrobots moving through the human body is represented by the complex 3D structure of biological lumina and tissues, which obstructs the navigation of micron-sized devices. Here, we fabricate ultra-deformable magnetic microrobots, consisting of ferrofluid-loaded lipid vesicles, and we magnetically pull them through chambers that exert upon them a gradually more forceful confinement. We thus analyze their capability to face interstices comparable to or smaller than their characteristic size and their consequent behavior in terms of stability, velocity, and deformation. The results show that the inherent compliance of these vesicle-based magnetic microrobots allows them to infiltrate successfully in interstices slightly smaller than their size. Further enhancement of their compliance and the development of specific control strategies may lead to microrobots able to move through interstices and traverse complex biological environments