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Microswimmers are smart devices with potential applications in medicine and biotechnology at the micrometer-scale. Magnetic micropropellers with their remote control via rotating magnetic fields are especially auspicious. Helicoidal propellers with a linear velocity-frequency dependence emerged as the standard propulsion mechanism over the last decade. However, with their functions becoming more pivotal on the way to practical uses, deviations in shape and swimming behavior are inevitable. Consequently, propellers with nonlinear velocity-frequency relationships arise that not only pose different challenges but also offer advanced possibilities. The most critical nonlinearities are the wobbling behavior with its solution branching that has potential for bimodal swimming and the swimming characteristics in the step-out regime that are essential for selection and swarm control. Here, we show experimentally and with numerical calculations how the previously unpredictable branching can be controlled and, thus, becomes utilizable with an example 3D-printed swimmer device. Additionally, we report how two step-out modes arise for propellers with a nonlinear velocity-frequency dependence that have the potential to accelerate future microswimmer sorting procedures., Max Planck Society; Deutsche Forschungs-gemeinschaft; Priority Program 1726 Microswimmers

Wireless magnetic microrobots are envisioned to revolutionize minimally invasive medicine. While many promising medical magnetic microrobots are proposed, the ones using hard magnetic materials are not mostly biocompatible, and the ones using biocompatible soft magnetic nanoparticles are magnetically very weak and, therefore, difficult to actuate. Thus, biocompatible hard magnetic micro/nanomaterials are essential toward easy-to-actuate and clinically viable 3D medical microrobots. To fill such crucial gap, this study proposes ferromagnetic and biocompatible iron platinum (FePt) nanoparticle-based 3D microprinting of microrobots using the two-photon polymerization technique. A modified one-pot synthesis method is presented for producing FePt nanoparticles in large volumes and 3D printing of helical microswimmers made from biocompatible trimethylolpropane ethoxylate triacrylate (PETA) polymer with embedded FePt nanoparticles. The 30 mu m long helical magnetic microswimmers are able to swim at speeds of over five body lengths per second at 200Hz, making them the fastest helical swimmer in the tens of micrometer length scale at the corresponding low-magnitude actuation fields of 5-10mT. It is also experimentally in vitro verified that the synthesized FePt nanoparticles are biocompatible. Thus, such 3D-printed microrobots are biocompatible and easy to actuate toward creating clinically viable future medical microrobots., European Union (EU); Horizon 2020; European Research Council (ERC); Advanced Grant; SoMMoR Project; Max Planck Society; Projekt DEAL

Background Peripheral artery disease (PAD) is a major challenge worldwide and endovascular revascularization is an important component of treatment that is affected by COVID-19 restrictions. Purpose Here, we evaluated the impact of COVID-19 restriction on angioplasty service and outcome of patients undergoing lower limb angioplasty. Methods Consecutive patients undergoing endovascular revascularisation between August 2018-March 2021 in a UK district general hospital were analysed retrospectively. Indications for angioplasty of all patients were discussed and agreed upon in multi-disciplinary teams. We compared time from referral to angioplasty, patient and procedural characteristics, technical success, peri-procedural complications, and outcome (wound healing, major amputation, target lesion revascularization, death) in patients treated 'before' and after February 2020 (“during COVID-19”). Results One hundred nineteen patients were treated 'before' (92% critical limb ischaemia [CLI]; 60% diabetes mellitus) and 72 were treated 'during COVID-19' (96% CLI; 61% diabetes mellitus). While the total monthly number of patients treated did not change, the number of outpatients treated as day cases increased (40% to 72%) and overnight stays for social reasons decreased (16% to 10%). Treatment of hospitalized patients decreased from 44% to 18%. The percentage of outpatients treated at Conclusions Adapting to COVID-19 restriction we maintained a safe and effective angioplasty service while shortening waiting times. Very high mortality rates in patients after hospitalization indicated that CLI need to be treated much earlier and more aggressively to avoid disease progression requiring hospitalization. Funding Acknowledgement Type of funding sources: None.

As precise motion-controlled applications of mobile untethered devices emerge into real-world scenarios, full manipulator dexterity will be required. In rigid bodies without joints, one such requirement will be the ability to control all six-degrees-of-freedom (DOF). Magnetic fields and their spatial gradients are ideal for micromanipulation due to their long-range strong forces and torques, but the 6-DOF closed-loop control of such devices is a current challenge. Here we present a single-body microrobot that simultaneously demonstrates all 6-DOF. We accomplish this through the magnetic shape anisotropy of the microrobot design, yielding magnetization components, which are used to generate a torque about the 6 $^\text {th}$ DOF. We show that, under our design conditions, we can independently control the magnetic field as well as the magnetic force and torque. This allows for the open-loop control of the other rotational DOFs, assuming the microrobot net magnetization vector will align with the magnetic field. We also describe a method that enables posing the 6 $^\text {th}$ DOF without feedback. These methods will enable the development of mobile submillimeter magnetic structures capable of full 6-DOF control for bioengineering, lab-on-a-chip, and desktop micromanufacturing applications.

Untethered mobile microrobots have the potential to leverage minimally invasive theranostic functions precisely and efficiently in hard-to-reach, confined, and delicate inner body sites. However, such a complex task requires an integrated design and engineering, where powering, control, environmental sensing, medical functionality, and biodegradability need to be considered altogether. The present study reports a hydrogel-based, magnetically powered and controlled, enzymatically degradable microswimmer, which is responsive to the pathological markers in its microenvironment for theranostic cargo delivery and release tasks. We design a double-helical architecture enabling volumetric cargo loading and swimming capabilities under rotational magnetic fields and a 3D-printed optimized 3D microswimmer (length = 20 μm and diameter = 6 μm) using two-photon polymerization from a magnetic precursor suspension composed from gelatin methacryloyl and biofunctionalized superparamagnetic iron oxide nanoparticles. At normal physiological concentrations, we show that matrix metalloproteinase-2 (MMP-2) enzyme could entirely degrade the microswimmer in 118 h to solubilized nontoxic products. The microswimmer rapidly responds to the pathological concentrations of MMP-2 by swelling and thereby boosting the release of the embedded cargo molecules. In addition to delivery of the drug type of therapeutic cargo molecules completely to the given microenvironment after full degradation, microswimmers can also release other functional cargos. As an example demonstration, anti-ErbB 2 antibody-tagged magnetic nanoparticles are released from the fully degraded microswimmers for targeted labeling of SKBR3 breast cancer cells in vitro toward a potential future scenario of medical imaging of remaining cancer tissue sites after a microswimmer-based therapeutic delivery operation.