Sarthak Misra

• University of Twente

Microorganisms, such as spermatozoa, exhibit rich behaviours when in close proximity to each other. However, their locomotion is not fully understood when coupled mechanically and hydrodynamically. In this study, we develop hydrodynamic models to investigate the locomotion of paired spermatozoa, predicting the fine structure of their swimming. Expe...

Combining local magnetic actuation with fluorescence imaging modalities promises to introduce significant advances in microrobotic-guided procedures. This review presents the advantages and challenges of this approach, emphasizing the need for careful design considerations to optimize performance and compatibility. Traditional microrobotic actuatio...

Robotic manipulators are used across various surgical tasks, including endoscopic and laparoscopic procedures. Operating in small and constrained spaces during these procedures requires the manipulators to have high dexterity and control over the motion path but with a small footprint. In this work, we propose a modular design of a magnetically-gui...

The functional principle behind extrusion‐based printing is the capability of flowing material through a nozzle on demand, which must solidify upon deposition, a behavior exhibited only by some materials. Embedded printing offers a solution to maintain shape fidelity during the deposition of a wider range of materials. However, the use of a moving...

Microfluidics has enabled the miniaturization of fluidic systems for various biomedical and industrial applications, including small-scale robotic propulsion. One mechanism for generating propulsive force through microfluidics is by exploiting the solutal Marangoni effect via releasing surfactant on the air-water interface. Surfactants locally redu...

Programmable and self-assembled magnetic pillars are essential to expanding the application domain of magnetic microparticle collectives. Typically, the collective behavior of self-assembled magnetic pillars is carried out by generating uniform and time-varying magnetic fields. However, magnetic field-shaping capabilities employing non-uniform fiel...

The emergence of miniaturized medical robots capable of performing targeted therapeutic procedures in deep-seated anatomical regions presents an alternative to conventional medical treatments. However, it remains a significant challenge to accurately locate the miniaturized robots in the complex environments of living organisms. Taking advantage of...

The fabrication of thermo-magnetic dual-responsive soft robots often requires intricate designs to implement complex locomotion patterns and utilize the implemented responsive behaviors. This work demonstrates a minimally designed soft robot...

In minimally invasive surgery, grippers are essential for tissue manipulation. However, in commercial tendon‐driven systems, challenges remain, including tendon fatigue and bulkiness. Promising alternatives are magnetically actuated systems, offering contactless steering but limited forces. To overcome this, a miniaturized, locally actuated magneti...

Thermal ablation treatments (TATs) are promising alternatives to traditional surgery for bone cancer eradication. Among several TATs, radiofrequency ablation (RFA) has gained considerable ground in treating bone cancer. Therefore, tracking temperature is paramount in ensuring complete tumor destruction without injuring adjacent structures. Despite...

The precise manipulation of microrobots presents challenges arising from their small size and susceptibility to external disturbances. To address these challenges, we present the experimental evaluation of a haptic shared control teleoperation framework for the locomotion of multiple microrobots, relying on a kinesthetic haptic interface and a cust...

Bubble‐driven microsystems inspired by the therapeutic use of microbubbles under clinical ultrasound actuation offer innovative remote manipulation in biological settings. Ultrasound‐powered microrobots, benefiting from a distribution of vibrating microbubbles (1–100 μm in diameters), exhibit localized fluid flow for self‐propulsion. Microbubbles a...

Guiding catheters assist in delivering hazardous equipment such as needles through non-solid mediums like cavities and vasculature. Traditionally, metallic needles are passed through metallic guiding catheters, which are limited to linear paths or require anatomy-specific designs. Recently, variable stiffness active guiding catheters (AGCs) made of...

Magnetic actuation of untethered small-scale helical devices (USHDs) shows great potential for targeted drug delivery or as minimally invasive surgical tools in the human body. However, ensuring the success of therapeutic interventions in anatomically challenging regions, such as neck vascular networks with winding pathways and branching, demands t...

Minimally-invasive surgery (MIS) for stent implantation is a complex procedure requiring specialized instruments. It often leads to prolonged patient recovery, and interrupted operations due to incorrect instrument selection and complex anatomy. This study presents a novel magnetic navigation system that addresses these challenges by using magnetic...

Optical microscopy is frequently used to visualize microrobotic agents (i.e., micro-agents) and physical surroundings with a relatively high spatio-temporal resolution. However, the limited penetration depth of optical microscopy techniques used in microrobotics (in the order of 100 μm) reduces the capability of visualizing micro-agents below biolo...

Conformity of tumour volumes and dose plans in prostate brachytherapy (BT) can be constrained by unwanted needle deflections, needle access restrictions and visualisation limitations. This work validates the feasibility of teleoperated robotic control of an active steerable needle using magnetic resonance (MR) for guidance. With this system, pertur...

Soft bio-microrobots have the potential to execute complex tasks in unexpected and harsh environments of the human body due to their dexterity and flexibility. The architectural designs of soft bio-microrobots either replicate the motion of natural creatures or capitalize on their motility. Based on this design principle, biologically inspired micr...

The actuation of miniaturized robots through external magnetic fields has great potential for medical applications. The controllability properties of the miniaturized robots are affected by magnetic field generation modality. In this work, the magnetic field of a mobile electromagnet, notably capable to generate a desired magnetic field in large 3D...

Soft and flexible magnetic robots have gained significant attention in the past decade. These robots are fabricated using magnetically-active elastomers, are capable of large deformations, and are actuated remotely thus allowing for small robot size. This combination of properties is appealing to the minimally invasive surgical community, potential...

Electromagnetic actuation of micro-/milli-sized agents has traditionally relied on large electromagnets positioned at considerable distances from the agents. As a result, the electromagnets consume kilowatts of power to overcome the limited generation of magnetic field gradients. Miniaturized electromagnets offer an alternative approach for reducin...

Currently, gastrointestinal bleeding in the colon wall and the small bowel is diagnosed and treated with endoscopes. However, the locations of this condition are often problematic to treat using traditional flexible and tethered tools. New studies commonly consider untethered devices for solving this problem. However, there still exists a gap in th...

Continuum manipulators have found several applications in surgical interventions like endoscopy, laparoscopy, and as end‐effectors for surgical robots. Continuum manipulators coupled with magnetic actuation can be precisely maneuvered inside the human body. Recently, variable stiffness manipulators (VSMs) have been introduced for enhanced dexterity...

Magnetically‐actuated soft robots for medical applications are required to be functional, biocompatible, as well as capable of robust motion inside human organs. In this paper, a ring‐shaped magnetic soft robot, with a flexible biopolymeric film coating, capable of motion on mucus‐coated surfaces is designed and investigated. The biopolymeric film...

Magnetic continuum manipulators (MCMs) are a class of continuum robots that can be actuated without direct contact by an external magnetic field. MCMs operating in confined workspaces, such as those targeting medical applications, require flexible magnetic structures that contain combinations of magnetic components and polymers to navigate long and...

Untethered small‐scale helical devices (USHDs) have the potential to navigate blood vessels and treat vascular occlusive diseases. However, there are still many challenges in translating this method into clinical practice, both in terms of localization and wireless motion control. Herein, closed‐loop control characterization of the USHD against and...

Various locomotion strategies employed by microorganisms are observed in complex biological environments. Spermatozoa assemble into bundles to improve their swimming efficiency compared to individual cells. However, the dynamic mechanisms for the formation of sperm bundles have not been fully characterized. In this study, we numerically and experim...

In order to fabricate functional organoids and microtissues, a high cell density is generally required. As such, the placement of cell suspensions in molds or microwells to allow for cell concentration by sedimentation is the current standard for the production of organoids and microtissues. Even though molds offer some level of control over the sh...

Continuum manipulators coupled with magnetic actuation have great potential as steerable instruments for diverse surgical applications. They can be maneuvered inside the human body to reach difficult-to-access surgical sites with contactless actuation. This paper presents a new design of a compliant continuum manipulator of diameter 3 mm and length...

Optical microscopy techniques are a popular choice for visualizing micro-agents. They generate images with relatively high spatiotemporal resolution but do not reveal encoded information for distinguishing micro-agents and surroundings. This study presents multicolor fluorescence microscopy for rendering color-coded identification of mobile micro-a...

Untethered helical magnetic devices (UHMDs) have the potential to navigate bodily fluids using permanentmagnet robotic systems for minimally invasive diagnostic and surgical procedures. These devices can be actuated by robotically moving rotating permanent magnets (RPMs) to achieve controllable steering and propulsion simultaneously in a wireless m...

Magnetic actuation of minimally invasive medical tetherless devices holds great promise in several biomedical applications. However, there are still several challenges in noninvasive localization, both in terms of sensing detectable signals of these devices and estimating their states. In this work, a magnetic milli-roller is actuated in a viscous...

Magnetically-actuated soft robots have potential for medical application but require further innovation on functionality and biocompatibility. In this letter, a multi-segmented snake-inspired soft robot with dissolvable and biocompatible segments is designed. The actuation response under external magnetic field is investigated through simulations a...

Recent advances in contactless micromanipulation strategies have revolutionized prospects of robotic manipulators as next-generation tools for minimally-invasive surgeries. In particular, acoustically-powered phased arrays offer dexterous means of manipulation both in air and in water. Inspired by these phased arrays, we present SonoTweezer: a comp...

Magnetic actuation is a versatile technology, widely applied in medical robotics for non-contact steering of flexible instruments and untethered agents. In this paper, we exploit the benefits of this technology by developing a magnetically-actuated flexible catheter capable of the controlled ejection and retrieval of an untethered magnetic capsule....

Control of tetherless magnetically actuated helical microrobots using rotating dipole fields has a wide variety of medical applications. The most promising technique in manipulation of these microrobots involves a rotating permanent magnet controlled by a robotic manipulator. In this work, we study the open-loop response of helical microrobots (in...

Bubble-powered acoustic microsystems span a plethora of applications that range from lab-on-chip diagnostic platforms to targeted interventions as microrobots. Numerous studies strategize this bubble-powered mechanism to generate autonomous self-propulsion of microrobots in response to high frequency sound waves. Herein, we present two micro-propel...

In the previous chapter, we have shown that the motion of a soft microrobot in a viscous medium is governed by at least two sets of forces. Viscous forces oppose the motion of each element and elastic forces tend to straighten the elastic body to its natural position. These forces determine the form and rate of propagation of transverse waves along...

Arterial stenosis is a high-risk disease accompanied by large amounts of calcified deposits and plaques that develop inside the vasculature. These deposits should be reduced to improve blood flow. However, current methods used to reduce stenosis require externally-controlled actuation systems resulting in limited workspace or patient risks. This re...

Multicolor fluorescence microscopy is a powerful technique to fully visualize many biological phenomena by acquiring images from different spectrum channels. This study expands the scope of multicolor fluorescence microscopy by serial imaging of polystyrene micro-beads as surrogates for drug carriers, cancer spheroids formed using HeLa cells, and m...

Medical ultrasound (US) systems are widely used for the diagnosis of internal tissues. However, there are challenges associated with acquiring and interpreting US images, such as incorrect US probe placement and limited available spatial information. In this study, we expand the capabilities of medical US imaging using a robotic framework with a hi...

This paper introduces and validates a real-time dynamic predictive model based on a neural network approach for soft continuum manipulators. The presented model provides a real-time prediction framework using neural-network-based strategies and continuum mechanics principles. A time-space integration scheme is employed to discretize the continuous...

Technical design features for improving the way a passive elastic filament produces propulsive thrust can be understood by analyzing the deformation of sperm-templated microrobots with segmented magnetization. Magnetic nanoparticles are electrostatically self-assembled on bovine sperm cells with nonuniform surface charge, producing different catego...

Objective: In this study, we introduce a multi-modal sensing and feedback framework aimed at assisting clinicians during endovascular surgeries and catheterization procedures. This framework utilizes state-of-the-art imaging and sensing sub-systems to produce a 3D visualization of an endovascular catheter and surrounding vasculature without the ne...

Current surgical devices are mostly rigid and are made of stiff materials, even though their predominant use is on soft and wet tissues. With the emergence of compliant mechanisms (CMs), surgical tools can be designed to be flexible and made using soft materials. CMs offer many advantages like monolithic fabrication, high precision, no wear, no fri...

This paper presents a technique to acquire measurements of curvature, twist and pose for two multi-core fibers; one with straight cores and the other with helical cores. Both the fibers have multiple fiber Bragg grating (FBG) sensors inscribed in the cores and the fibers are placed in known configurations in order to compare their measurement accur...

Precise positioning of soft microrobots can be achieved via feedback control. We have shown in the previous chapters that non-invasive localization is possible using ultrasound images or magnetic detection. Therefore, the position and orientation of the microrobot can be used to design control laws to move soft microrobots toward prescribed locatio...

The propulsion of soft microrobots is influenced by the rheological properties of the surrounding medium. These properties affect the flagellar wave form (curvature, bending amplitude, and wavelength) of the planar or helical traveling-wave. In the previous chapters we studied fundamentals of the theories of elasticity and electromagnetism. The mag...

The swimming of a bacterium or a sperm cell driven by a rotating helical flagella bundle or a flagellum is often interpreted by the resistive-force theory and the regularized Stokeslet theory. In this chapter, we will implement these theories for the ranges of helical wavelength λ, radius R, and length L relevant to bacteria and sperm flagella. The...

Sperm cells, cilia, and bacteria propel the surrounding fluid by regular bending waves along a flexible filament. They have evolved active mechanisms to internally produce bending moment and propel the cell. They can also be integrated with nonorganic structure to create a number of biohybrid microrobots such as Spermbot, sperm- and bacteria-bead a...

The translation of soft microrobot in in vivo experiments relies on the successful implementation of real-time non-invasive localization methods. Spatial resolution and the contrast to noise ratio of these methods are important factors in the selection of the appropriate non-invasive approach. The location and orientation of the microrobot have to...

Soft microrobots represent end-effectors of electromagnetic- and permanent magnet-based manipulation systems. These microrobots can navigate controllably under the action of a controlled magnetic field. We are interested in precise control of the microrobots. Therefore, the actuating field should be designed to simultaneously propel and steer the m...

Soft microrobots in the form of flexible filament or flexible film with partial magnetization are propelled in low-Re by planar or helical bending waves. In this chapter we will discuss the mechanism which initiate these transverse bending waves along the soft body of the microrobot. First, we will present the magneto-elastic and drag forces which...

Soft microrobots have to undergo undulatory motion to produce thrust that propels the body forward. To produce flagellar propulsion, we must address two significant hurdles. First, the soft microrobot must respond to an external stimulus. Second, the external stimulus must be controlled to provide predicated propulsion and steering. A magnetic fiel...

Inspired by sperm cells and bacterial flagella, a number of biologically inspired microrobots use traveling waves to achieve drag-based propulsion. This chapter addresses the magneto-elastohydrodynamic of soft microrobots during planar and helical flagellar propulsion in low-Re. We will then address the problem of helical and planar traveling waves...

In recent years, magnetism has gained an enormous amount of interest among researchers for actuating different sizes and types of bio/soft robots, which can be via an electromagnetic‐coil system, or a system of moving permanent magnets. Different actuation strategies are used in robots with magnetic actuation having a number of advantages in possib...

Acoustic actuation techniques offer a promising tool for contactless manipulation of both synthetic and biological micro/nano agents that encompass different length scales. The traditional usage of sound waves has steadily progressed from mid-air manipulation of salt grains to sophisticated techniques that employ nanoparticle flow in microfluidic n...

[This corrects the article DOI: 10.1371/journal.pone.0236121.].

Magnetically-driven screws operating in soft-tissue environments could be used to deploy localized therapy or achieve minimally invasive interventions. In this work, we characterize the closed-loop behavior of magnetic screws in an agar gel tissue phantom using a permanent magnet-based robotic system with an open-configuration. Our closed-loop cont...

Soft materials with embedded magnetic properties can be actuated in a contactless manner for dexterous motion in restricted and unstructured environments. Magnetic soft robots have been demonstrated to be capable of versatile and programmable untethered motion. However, magnetic soft robots reported in literature are typically actuated by utilizing...

Untethered soft robots have the potential to impact a variety of applications, particularly if they are capable of controllable locomotion and dexterous manipulation. Magnetic fields can provide human-safe, contactless actuation, opening the gates to applications in confined spaces — for example, in minimally invasive surgery. To translate these co...

We characterize the propulsion of externally-actuated helical robots inside a viscous heterogenous medium. The method of regularized Stokeslets is implemented in three-dimensional space for computing the Stokes flow around a helical robot and immersed obstacles (spherical microparti-cles) in the medium. The helical robot is actuated using a permane...

This paper presents the derivation and experimental validation of algorithms for modeling and estimation of soft continuum manipulators using Lie group variational integration. Existing approaches are generally limited to static and quasi-static analyses, and are not sufficiently validated for dynamic motion. However, in several applications, model...

We develop biohybrid magnetic microrobots by electrostatic self-assembly of nonmotile sperm cells and magnetic nanoparticles. Incorporating a biological entity into microrobots entails many functional advantages beyond shape templating, such as the facile uptake of chemotherapeutic agents to achieve targeted drug delivery. We present a single-step...

Advancements in medical microrobotics have given rise to an abundance of agents capable of localised interaction with human body in small scales. Nevertheless, clinically-relevant applications of this technology are still limited by the auxiliary infrastructure required for actuation of micro-agents. In this paper, we approach this challenge. Using...

The use of magnetic resonance (MR) images for needle-based interventions offers several advantages over other types of imaging modalities (e.g., high tissue contrast and no radiation). However, MR-guided interventions face challenges related to electromagnetic compatibility of medical devices and real-time tracking of surgical instruments. This wor...

A rotating two-tailed soft microrobot induces a frequency dependent flow-field in low Reynolds number fluids. We use this flow-field to achieve noncontact manipulation of nonmagnetic microbeads with average diameter of 30 $\mu {\rm m}$ in 2-D space. Our noncontact manipulation strategy capitalizes on exerting a rotational magnetic torque on the m...

The development of magnetically powered microswimmers that mimic the swimming mechanisms of microorganisms is important for lab‐on‐a‐chip devices, robotics, and next‐generation minimally invasive surgical interventions. Governed by their design, most previously described untethered swimmers can be maneuvered only by varying the direction of applied...

Accurate navigation of flexible medical instruments like catheters require the knowledge of its pose, that is its position and orientation. In this paper multi-core fibers inscribed with fiber Bragg gratings (FBG) are utilized as sensors to measure the pose of a multi-segment catheter. A reconstruction technique that provides the pose of such a fib...

Purpose Additive manufacturing (AM) is a promising alternative to the conventional production methods (i.e., machining), providing the developers with great geometrical and topological freedom during the design and immediate prototyping customizability. However, frictional characteristics of the AM surfaces are yet to be fully explored, making the...

Continuum robots have the potential to form an effective interface between the patient and surgeon in minimally invasive procedures. Magnetic actuation has the potential for accurate catheter steering, reducing tissue trauma and decreasing radiation exposure. In this paper, a new design of a monolithic metallic compliant continuum manipulator is pr...

Endovascular interventions usually require meticulous handling of surgical instruments and constant monitoring of the operating room workspace. To address these challenges, robotic- assisted technologies and tracking techniques are increasingly being developed. Specifically, the limited workspace and potential for a collision between the robot and...

Additive manufacturing (AM) is one of the emerging production methodologies transforming the industrial landscape. However, application of the technology in fluidic power transmission and actuation is still limited. AM pneumatic stepper motors have been previously introduced to the field of image-guided surgical robotics, where their disposability...

The active flagellum propels a motile sperm cell by traveling bending waves. Here, we demonstrate that non-motile cells have the capacity to be wirelessly actuated by external magnetic fields and reveal insights into their propulsion characteristics. Partial coating of the sperm head with nanoparticle aggregates is achieved by electrostatic-based s...

Positioning conventional endovascular catheters is not without risk, and there is a multitude of complications that are associated with their use in manual surgical interventions. By utilizing surgical manipulators, the efficacy of remote-controlled catheters can be investigated in vivo . However, technical challenges, such as the duration of cat...

Accurate estimation of deformed shape and reaction forces poses a significant challenge in modeling and control of continuum manipulators interacting with their environment. This paper presents a framework for the analysis of a continuum manipulator subjected to multiple external loads using pseudo rigid body (PRB) modelling method. A PRB model wit...

Pulse width modulation (PWM) is the most commonly used technique for coil drive in magnetic manipulation systems. Relatively low PWM frequencies generate high magnitude current ripple and magnetic field fluctuation. In this study, a high-frequency coil driver is developed to increase the efficiency of the magnetic manipulation systems by minimizing...