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Biohybrid micromotors propelled by motile cells are fascinating entities for autonomous biomedical operations on the microscale. Their operation under physiological conditions, including highly viscous environments, is an essential prerequisite to be translated to in vivo settings. In this work, a sperm-driven microswimmer, referred to as a spermbot, is demonstrated to operate in oviduct fluid in vitro. The viscoelastic properties of bovine oviduct fluid (BOF), one of the fluids that sperm cells encounter on their way to the oocyte, are first characterized using passive microrheology. This allows to design an artificial oviduct fluid to match the rheological properties of oviduct fluid for further experiments. Sperm motion is analyzed and it is confirmed that kinetic parameters match in real and artificial oviduct fluids, respectively. It is demonstrated that sperm cells can efficiently couple to magnetic microtubes and propel them forward in media of different viscosities and in BOF. The flagellar beat pattern of coupled as well as of free sperm cells is investigated, revealing an alteration on the regular flagellar beat, presenting an on–off behavior caused by the additional load of the microtube. Finally, a new microcap design is proposed to improve the overall performance of the spermbot in complex biofluids.

By combining new robot control systems with piezoelectric motors and micromechanics, we propose creating micromechanical systems which are small, cheap and completely autonomous. We have fabricated small - a few millimeters in diameter - piezoelectric motors using ferroelectric thin films and consisting of two pieces: a stator and a rotor. The stationary stator includes a piezoelectric film in which we induce bending in the form of a traveling wave. Anything which sits atop the stator is propelled by the wave. A small glass lens placed upon the stator becomes the spinning rotor. Using thin films of PZT on silicon nitride memebranes, various types of actuator structures have been fabricated.

The fast evolution of medical micro- and nanorobots in the endeavor to perform non-invasive medical operations in living organisms has boosted the use of diverse medical imaging techniques in the last years. Among those techniques, photoacoustic imaging (PAI), considered a functional technique, has shown to be promising for the visualization of micromotors in deep tissue with high spatiotemporal resolution as it possesses the molecular specificity of optical methods and the penetration depth of ultrasound. However, the precise maneuvering and function's control of medical micromotors, in particular in living organisms, require both anatomical and functional imaging feedback. Therefore, herein, the use of high-frequency ultrasound and PAI is reported to obtain anatomical and molecular information, respectively, of magnetically-driven micromotors in vitro and under ex vivo tissues. Furthermore, the steerability of the micromotors is demonstrated by the action of an external magnetic field into the uterus and bladder of living mice in real-time, being able to discriminate the micromotors’ signal from one of the endogenous chromophores by multispectral analysis. Finally, the successful loading and release of a model cargo by the micromotors toward non-invasive in vivo medical interventions is demonstrated.

L’électrochimie bipolaire est un phénomène générant une réactivité asymétrique à la surface d’objets conducteurs, sans contact électrique direct. Ce concept est basé sur le fait que lorsqu’un objet conducteur est localisé dans un champ électrique, il se polarise. Par conséquent, une différence de potentiel est générée entre ses deux extrémités, et peut être utilisée pour induire des réactions redox localisées. Dans cette thèse, l’utilisation de l’électrochimie bipolaire pour la science des matériaux et pour la locomotion d’objets est présentée.Jusqu’à présent, la plupart des méthodes ou procédés utilisés pour générer des objets asymétriques,appelés aussi objets « Janus », nécessitent l’introduction d’une interface pour briser la symétrie. Nous avons développé une nouvelle approche basée sur l’électrodéposition bipolaire pour générerce type d’objet en grande quantité. Grâce à cette technologie différents matériaux tels que des métaux, des polymères et des semi‐conducteurs ont pu être déposés sur diverses particulesconductrices. Il a été aussi démontré que l’électrochimie bipolaire pouvait être utilisée pour lamicrostructuration de substrats conducteurs.Nous avons induit des mouvements à des objets conducteurs en exploitant le phénomèned’électrochimie bipolaire. Certains objets Janus synthétisés par l’approche précédente ont pu être utilisés comme micronageurs. La brisure de symétrie qui est générée par l’électrochimie bipolaire peut être aussi utilisée directement pour générer un mouvement de particules isotropes. En employant ce concept, nous avons pu provoquer des mouvements de translation, rotation et lévitation pour des particules de carbones ou métalliques. / The phenomenon of bipolar electrochemistry generates an asymmetric reactivity on the surface ofconductive objects in a wireless manner. This concept is based on the fact that when a conducingobject is placed in an electric field, it gets polarized. Consequently, a potential difference appearsbetween its two extremities, that can be used to drive localized redox reactions. In the presentthesis, bipolar electrochemistry was used for material science and the locomotion of objects.So far, the majority of methods and processes used for the generation of asymmetric objects, alsocalled “Janus” objects, is based on using interfaces to break the symmetry. We developed a newapproach based on bipolar electrodeposition for generating this type of objects in the bulk. Using thistechnology, various materials like metals, polymers and semiconductors could be deposited ondifferent types of conducting particles. We also showed that bipolar electrochemistry can be used forthe microstructuration of conducting substrates.Motion generation by bipolar electrochemistry has also been demonstrated. Some of the Janusobjects synthesized by the previous approach can be used as microswimmers. The asymmetricreactivity that is induced by bipolar electrochemistry can also be used directly to generate motion ofnon‐hybrid objects. With this concept we induced translations, rotations and levitations of carbonand metal particles.

The fabrication of transient electronic devices based on non-toxic materials is an emerging field, in which the key characteristic is the complete dissolution of the devices within a settled period of time. Usually, these devices are built in polymeric substrates or pure metals; however they show some disadvantages such as low degradation rate. The aim of this work was to investigate the feasibility of electrodeposition of FeMn-based films from green sulfate-based aqueous electrolytes without and with the use of additives toward the possible replacement of the aforementioned materials. The results obtained from the first experiments regarding the electrodeposition of Fe and Mn as single metals allowed the design of the experiment to synthesize FeMn layers. Potentiostatic deposition of metallic Mn layers from environmentally friendly aqueous manganese sulphate electrolytes with a pH value of 3 was successfully demonstrated. A continuous flow in the cathodic compartment of the electrochemical cell to control the pH value during the electrodeposition experiments was found to be essential for achieving good layer qualities. It also allowed the co-electrodeposition with a second element, Fe, which also needs an acidic pH value to be electrodeposited from aqueous electrolytes. Cyclic voltammetry analyses were performed in combination with electrochemical quartz microbalance measurements in the MnSO4 containing electrolytes and a suitable deposition potential range was identified. The electrolyte composition played an important. The addition of H3BO3 provided mechanical stability to the Mn films and avoided their disintegration. An increase of the (NH4)2SO4 concentration increases the deposit roughness but also the layer quality, without impurities and a better crystalline α-Mn structure. An increase of the deposition potential led to an increase of the film thickness. Mn-oxides/-hydroxides were identified only in a thin surface region of the films. The Mn electrodeposited films were deeply characterized by means of SEM, XRD, GD-OES and XPS. The results related to the Mn electrodeposition allowed further design of the electrolytes and experiments to electrochemically synthesize FeMn layers. The assessment of the impact of the electrodeposition parameters on the structural, morphological and magnetic properties of the obtained films was also aimed in this work. With view to possible application of FeMn-based films in transient devices, their corrosion behavior in chloride-containing solution and their cytotoxicity were also evaluated. The electrolytes were characterized by means of CV and EQCM analyses. The ratio of the metal ions Mn2+:Fe2+ and the presence of glycine as complexing agent in the electrolyte determined the layer composition. The formation of the complexes Fe(gly)+ and Mn(gly)+ established a new reduction step modifying the Fe and Mn reduction/deposition. Glycine also leaded to a better film quality. A set of magnetron co-sputtered FeMn thin films was deposited as reference in order to compare the two synthesis methods with a broader range of Mn content between 10 and 70 wt.%. Metallic electrodeposited FeMn films presented a bcc structure with a Im-3m symmetry as well as the sputtered samples with a low Mn content up to 25 wt.%. An increase of the Mn content in the electrodeposited layers yielded to the formation of oxidized compounds with a fcc structure and Fm-3m symmetry. An increase in the Mn content for the sputtered films maintained the bcc structure but the symmetry was lowered to I-43m. With view to possible application of FeMn-based films in transient devices, their corrosion behavior in chloride-containing solution and their cytotoxicity were also evaluated. Regarding their corrosion behaviour, both techniques produced FeMn films with an active dissolution behaviour in chloride containing solutions. In vitro cytotoxicity tests revealed significant biocompatible characteristics of the sputtered films regardless of their Mn content. However, electrodeposited FeMn based layers did not presented optimal biocompatible characteristics. Furthermore, template-assited electrodeposition to obtain microrobots was studied in this work. Observed confinement effect was exploited, which results in compositional gradients with Mn-rich and Fe-rich regions and tubular or mushroom-like shapes. The propulsion performance of these electrochemically prepared hybrid micromotors was studied in the presence of H2O2 fuel with Triton-X as a surfactant and a magnetic field of 23.5 mT was applied. Bubbles produced by the catalytic decomposition of the H2O2 by the MnO2 and MnFe2O4 compounds was clearly the motion mechanism. Wireless modulated trajectory by the application of an external magnetic field was possible thanks to the magnetic phases, Fe3O4 and MnFe2O4.

Micromotors are recognized as promising candidates for untethered micromanipulation and targeted cargo transport. Their future application is, however, hindered by the low efficiency of drug encapsulation and their poor adaptability in physiological conditions. To address these challenges, one potential solution is to incorporate micromotors with biological materials as the combination of functional biological entities and smart artificial parts represents a manipulable and biologically friendly approach. This dissertation focuses on the development of custom-designed micromotors combined with sperm and their potential applications on targeted diseases treatment. By means of 2D and 3D lithography methods, microstructures with complex configurations can be fabricated for specific demands. Bovine and human sperm are both for the first time explored as drug carriers thanks to their high encapsulation efficiency of hydrophilic drugs, their powerful self-propulsion and their improved drug-uptake relying on the somatic-cell fusion ability. The hybrid micromotors containing drug loaded sperm and constructed artificial enhancements can be self-propelled by the sperm flagella and remotely guided and released to the target at high precision by employing weak external magnetic fields. As a result, micromotors based on both bovine and human sperm show significant anticancer effect. The application here can be further broadened to other biological environments, in particular to the blood stream, showing the potential on the treatment of blood diseases like blood clotting. Finally, to enhance the treatment efficiency, in particular to control sperm number and drug dose, three strategies are demonstrated to transport swarms of sperm. This research paves the way for the precision medicine based on engineered sperm-based micromotors.

Medical micromotors have the potential to lead to a paradigm shift in future biomedicine, as they may perform active drug delivery, microsurgery, tissue engineering, or assisted fertilization in a minimally invasive manner. However, the translation to clinical treatment is challenging, as many applications of single or few micromotors require real-time tracking and control at high spatiotemporal resolution in deep tissue. Although optical techniques are a popular choice for this task, absorption and strong light scattering lead to a pronounced decrease of the signal-to-noise ratio with increasing penetration depth. Here, a highly reflective micromotor is introduced which reflects more than tenfold the light intensity of simple gold particles and can be precisely navigated by external magnetic fields. A customized optical IR imaging setup and an image correlation technique are implemented to track single micromotors in real-time and label-free underneath phantom and ex vivo mouse skull tissues. As a potential application, the micromotors speed is recorded when moving through different viscous fluids to determine the viscosity of diverse physiological fluids toward remote cardiovascular disease diagnosis. Moreover, the micromotors are loaded with a model drug to demonstrate their cargotransport capability. The proposed reflective micromotor is suitable as theranostic tool for sub-skin or organ-on-a-chip applications.

Since the highly cited paper by Purcell postulating the “Scallop theorem” almost 50 years ago, asymmetry is an unavoidable part of micromotors. It is frequently induced by self-shadowing or self-masking, resulting in so-called Janus colloids. This strategy works very reliably, but turns into a bottleneck once up-scaling becomes important. Herein, existing alternatives are discussed and a novel synthetic pathway yielding active swimmers in a one-pot synthesis is presented. To understand the resulting mobility from a single material, the geometric asymmetry is evaluated using a python based algorithm and this process is automated in an open access tool.

Micro-and nanorobots have the potential to perform non-invasive drug delivery, sensing, and surgery in living organisms, with the aid of diverse medical imaging techniques. To perform such actions, microrobots require high spatiotemporal resolution tracking with real-time closed-loop feedback. To that end, photoacoustic imaging has appeared as a promising technique for imaging microrobots in deep tissue with higher molecular specificity and contrast. Here, we present different strategies to track magnetically-driven micromotors with improved contrast and specificity using dedicated contrast agents (Au nanorods and nanostars). Furthermore, we discuss the possibility of improving the light absorption properties of the employed nanomaterials considering possible light scattering and coupling to the underlying metal-oxide layers on the micromotor’s surface. For that, 2D COMSOL simulation and experimental results were correlated, confirming that an increased spacing between the Au-nanostructures and the increase of thickness of the underlying oxide layer lead to enhanced light absorption and preservation of the characteristic absorption peak. These characteristics are important when visualizing the micromotors in a complex in vivo environment, to distinguish them from the light absorption properties of the surrounding natural chromophores.