Peptide-Induced Biomineralization of Tin Oxide (SnO₂) Nanoparticles for Antibacterial Applications

Recently, there has been growing attention and effort to search for new microbicidal drugs which present different mode of action from those already existing, as an alternative to the global threat of fungal and bacterial multi drug resistance (MDR). Here we propose biological synthesis of SnO₂ nanoparticles using mammalian cells as an economic and ecofriendly platform. This presents a novel biogenic method for SnO₂ synthesis using metal binding peptides extracted from MCF-7 human cancer cells, which induces the biomineralization of SnO₂ nanoparticles. A series of electron donor functional groups and metal binding sites in these peptides reacts with Sn²⁺ ions and directs the growth of SnO₂ nanoparticles without addition of toxic redox and capping agents in the reaction system. Since peptides present reactive sites in aqueous solution at room temperature, a facile reaction environment can be easily achieved. Furthermore, by tuning the reactants' concentration and pH, the size, shape and 3D-structures of SnO₂ nanoparticles can be controlled. Peptides also ensure biocompatibility, and SnO₂ nanoparticles provide antibacterial properties, which broadens their applications in biomedical fields.

Multifunctional and biodegradable self-propelled protein motors

A diversity of self-propelled chemical motors, based on Marangoni propulsive forces, has been developed in recent years. However, most motors are non-functional due to poor performance, a lack of control, and the use of toxic materials. To overcome these limitations, we have developed multifunctional and biodegradable self-propelled motors from squid-derived proteins and an anesthetic metabolite. The protein motors surpass previous reports in performance output and efficiency by several orders of magnitude, and they offer control of their propulsion modes, speed, mobility lifetime, and directionality by regulating the protein nanostructure via local and external stimuli, resulting in programmable and complex locomotion. We demonstrate diverse functionalities of these motors in environmental remediation, microrobot powering, and cargo delivery applications. These versatile and degradable protein motors enable design, control, and actuation strategies in microrobotics as modular propulsion sources for autonomous minimally invasive medical operations in biological environments with air-liquid interfaces.

Thrust and Hydrodynamic Efficiency of the Bundled Flagella

The motility mechanism of prokaryotic organisms has inspired many untethered microswimmers that could potentially perform minimally invasive medical procedures in stagnant fluid regions inside the human body. Some of these microswimmers are inspired by bacteria with single or multiple helical flagella to propel efficiently and fast. For multiple flagella configurations, the direct measurement of thrust and hydrodynamic propulsion efficiency has been challenging due to the ambiguous mechanical coupling between the flow field and mechanical power input. To address this challenge and to compare alternative micropropulsion designs, a methodology based on volumetric velocity field acquisition is developed to acquire the key propulsive performance parameters from scaled-up swimmer prototypes. A digital particle image velocimetry (PIV) analysis protocol was implemented and experiments were conducted with the aid of computational fluid dynamics (CFD). First, this methodology was validated using a rotating single-flagellum similitude model. In addition to the standard PIV error assessment, validation studies included 2D vs. 3D PIV, axial vs. lateral PIV and simultaneously acquired direct thrust force measurement comparisons. Compatible with typical micropropulsion flow regimes, experiments were conducted both for very low and higher Reynolds (Re) number regimes (up to a Re number = 0.01) than that are reported in the literature. Finally, multiple flagella bundling configurations at 0°, 90° and 180° helical phase-shift angles were studied using scaled-up multiple concentric flagella thrust elements. Thrust generation was found to be maximal for the in-phase (0°) bundling configuration but with ~50% lower hydrodynamic efficiency than the single flagellum. The proposed measurement protocol and static thrust test-bench can be used for bio-inspired microscale propulsion methods, where direct thrust and efficiency measurement are required.

Multi-functional soft-bodied jellyfish-like swimming

The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot's soft body and incurred fluidic flows due to the robot's body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.

Multifarious Transit Gates for Programmable Delivery of Bio-functionalized Matters

Programmable delivery of biological matter is indispensable for the massive arrays of individual objects in biochemical and biomedical applications. Although a digital manipulation of single cells has been implemented by the integrated circuits of micromagnetophoretic patterns with current wires, the complex fabrication process and multiple current operation steps restrict its practical application for biomolecule arrays. Here, a convenient approach using multifarious transit gates is proposed, for digital manipulation of biofunctionalized microrobotic particles that can pass through the local energy barriers by a time-dependent pulsed magnetic field instead of multiple current wires. The multifarious transit gates including return, delay, and resistance linear gates, as well as dividing, reversed, and rectifying T-junction gates, are investigated theoretically and experimentally for the programmable manipulation of microrobotic particles. The results demonstrate that, a suitable angle of the gating field at a suitable time zone is crucial to implement digital operations at integrated multifarious transit gates along bifurcation paths to trap microrobotic particles in specific apartments, paving the way for flexible on-chip arrays of biomolecules and cells.

Temperature Gradients Drive Bulk Flow Within Microchannel Lined by Fluid-Fluid Interfaces

Surface tension gradients induce Marangoni flow, which may be exploited for fluid transport. At the micrometer scale, these surface-driven flows can be quite significant. By introducing fluid-fluid interfaces along the walls of microfluidic channels, bulk fluid flows driven by temperature gradients are observed. The temperature dependence of the fluid-fluid interfacial tension appears responsible for these flows. In this report, the design concept for a biocompatible microchannel capable of being powered by solar irradiation is provided. Using microscale particle image velocimetry, a bulk flow generated by apparent surface tension gradients along the walls is observed. The direction of flow relative to the imposed temperature gradient agrees with the expected surface tension gradient. The phenomenon's ability to replace bulky peripherals, like traditional syringe pumps, on a diagnostic microfluidic device that captures and detects leukocyte subpopulations within blood is demonstrated. Such microfluidic devices may be implemented for clinical assays at the point of care without the use of electricity.

3D-Printed Biodegradable Microswimmer for Theranostic Cargo Delivery and Release

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.

Programmable Collective Behavior in Dynamically Self-Assembled Mobile Microrobotic Swarms

Collective control of mobile microrobotic swarms is indispensable for their potential high-impact applications in targeted drug delivery, medical diagnostics, parallel micromanipulation, and environmental sensing and remediation. Without integrated electronics for sensing and actuation, current microrobotic systems should rely on physical interactions among individual microrobots for local communication and cooperation. Here, it is shown that mobile microrobotic swarms with well-defined collective behavior can be designed by engineering magnetic interactions among individual units. Microrobots, dynamically self-assembled from magnetic microparticles into linear chains, locomote on surfaces in response to a precessing magnetic field. Control over precessing magnetic field allows engineering attractive and repulsive interactions among microrobots and, thus, collective order with well-defined spatial organization and stable parallel operation over macroscale distances (≈1 cm) and through confining obstacles. The design approach described here addresses programmable assembly, propulsion, and collective behavior of dense mobile microrobot swarms simultaneously by engineering magnetic interactions and dynamic actuation of microrobots. The presented approach will advance swarm microrobotics by enabling facile and rapid formation of self-organized and reconfigurable microrobotic swarms with programmable collective order and stability.

The near and far of a pair of magnetic capillary disks

Control on microscopic scales depends critically on our ability to manipulate interactions with different physical fields. The creation of micro-machines therefore requires us to understand how multiple fields, such as surface capillary or electro-magnetic fields, can be used to produce predictable behaviour. Recently, a spinning micro-raft system was developed that exhibited both static and dynamic self-assembly [Wang et al., Sci. Adv., 2017, 3, e1602522]. These rafts employed both capillary and magnetic interactions and, at a critical driving frequency, would suddenly change from stable orbital patterns to static assembled structures. In this paper, we explain the dynamics of two interacting micro-rafts through a combination of theoretical models and experiments. This is first achieved by identifying the governing physics of the orbital patterns, the assembled structures, and the collapse separately. We find that the orbital patterns are determined by the short range capillary interactions between the disks, while the explanations of the other two behaviours only require the capillary far field. Finally we combine the three models to explain the dynamics of a new micro-raft experiment.

Controllable switching between planar and helical flagellar swimming of a soft robotic sperm

Sperm cells undergo a wide variety of swimming patterns by a beating flagellum to maintain high speed regardless of the rheological and physical properties of the background fluid. In this work, we develop and control a soft robotic sperm that undergoes controllable switching between swimming modes like biological sperm cells. The soft robotic sperm consists of a magnetic head and an ultra-thin flexible flagellum, and is actuated using external magnetic fields. We observe that out-of-plane wobbling of the head results in helical wave propagation along the flagellum, whereas in-plane wobbling achieves planar wave propagation. Our theoretical predictions and experimental results show the ability of the soft robotic sperm to change its swimming speed by tuning the beating frequency of its flagellum and the propulsion pattern. The average speed of the soft robotic sperm increases by factors of 2 and 1.2 in fluids with viscosity of 1 Pa.s and 5 Pa.s at relatively low actuation frequencies, respectively, when they switch between planar to helical flagellar propulsion.

Microalga-Powered Microswimmers toward Active Cargo Delivery

Nature presents intriguing biological swimmers with innate energy harvesting abilities from their local environments. Use of natural swimmers as cargo delivery agents presents an alternative strategy to transport therapeutics inside the body to locations otherwise difficult to access by traditional delivery strategies. Herein, a biocompatible biohybrid microswimmer powered by a unicellular freshwater green microalga, Chlamydomonas reinhardtii, is reported. Polyelectrolyte-functionalized magnetic spherical cargoes (1 µm in diameter) are attached to surface of the microalgae via noncovalent interactions without the requirement for any chemical reaction. The 3D swimming motility of the constructed biohybrid algal microswimmers is characterized in the presence and absence of a uniform magnetic fields. In addition, motility of both microalgae and biohybrid algal microswimmers is investigated in various physiologically relevant conditions, including cell culture medium, human tubal fluid, plasma, and blood. Furthermore, it is demonstrated that the algal microswimmers are cytocompatible when co-cultured with healthy and cancerous cells. Finally, fluorescent isothiocyanate-dextran (a water-soluble polysaccharide) molecules are effectively delivered to mammalian cells using the biohybrid algal microswimmers as a proof-of-concept active cargo delivery demonstration. The microswimmer design described here presents a new class of biohybrid microswimmers with greater biocompatibility and motility for targeted delivery applications in medicine.

Seed-mediated synthesis of plasmonic gold nanoribbons using cancer cells for hyperthermia applications

A surfactant-less, seed mediated, biological synthesis of two dimensional (2-D) nanoribbons in the presence of breast cancer cells (MCF7) is demonstrated. The diameter and yield of nanoribbons are tunable via seeds and gold precursor concentration. Such crystalline nanoribbons serve to enhance the Raman signals over MCF7 cells. The side and slopes of the triangular nanoplatelets fused as nanoribbons exhibit plasmon excitement in quadrupole resonance modes in the infrared region. Consequently, when irradiated with an infrared laser they show an excellent photothermal effect and rapid rise in temperature. The experimental results verified by finite-difference time-domain (FTDT) calculations reveal the presence of wedge-plasmon polaritons propagating along the edges of the nanoribbons. These simulations confirm that long aspect ratio nanoribbon's edges and vertices act as an active optical waveguide, allowing for heat propagation along the long axis, killing cancer cells in the process at lower power doses.

Light-Triggered Drug Release from 3D-Printed Magnetic Chitosan Microswimmers

Advances in design and fabrication of functional micro/nanomaterials have sparked growing interest in creating new mobile microswimmers for various healthcare applications, including local drug and other cargo ( e. g., gene, stem cell, and imaging agent) delivery. Such microswimmer-based cargo delivery is typically passive by diffusion of the cargo material from the swimmer body; however, controlled active release of the cargo material is essential for on-demand, precise, and effective delivery. Here, we propose a magnetically powered, double-helical microswimmer of 6 μm diameter and 20 μm length that can on-demand actively release a chemotherapeutic drug, doxorubicin, using an external light stimulus. We fabricate the microswimmers by two-photon-based 3D printing of a natural polymer derivative of chitosan in the form of a magnetic polymer nanocomposite. Amino groups presented on the microswimmers are modified with doxorubicin by means of a photocleavable linker. Chitosan imparts the microswimmers with biocompatibility and biodegradability for use in a biological setting. Controlled steerability of the microswimmers is shown under a 10 mT rotating magnetic field. With light induction at 365 nm wavelength and 3.4 × 10^-1 W/cm² intensity, 60% of doxorubicin is released from the microswimmers within 5 min. Drug release is ceased by controlled patterns of light induction, so as to adjust the desired release doses in the temporal domain. Under physiologically relevant conditions, substantial degradation of the microswimmers is shown in 204 h to nontoxic degradation products. This study presents the combination of light-triggered drug delivery with magnetically powered microswimmer mobility. This approach could be extended to similar systems where multiple control schemes are needed for on-demand medical tasks with high precision and efficiency.

Morphological intelligence counters foot slipping in the desert locust and dynamic robots

During dynamic terrestrial locomotion, animals use complex multifunctional feet to extract friction from the environment. However, whether roboticists assume sufficient surface friction for locomotion or actively compensate for slipping, they use relatively simple point-contact feet. We seek to understand and extract the morphological adaptations of animal feet that contribute to enhancing friction on diverse surfaces, such as the desert locust (Schistocerca gregaria) [Bennet-Clark HC (1975) J Exp Biol 63:53-83], which has both wet adhesive pads and spines. A buckling region in their knee to accommodate slipping [Bayley TG, Sutton GP, Burrows M (2012) J Exp Biol 215:1151-1161], slow nerve conduction velocity (0.5-3 m/s) [Pearson KG, Stein RB, Malhotra SK (1970) J Exp Biol 53:299-316], and an ecological pressure to enhance jumping performance for survival [Hawlena D, Kress H, Dufresne ER, Schmitz OJ (2011) Funct Ecol 25:279-288] further suggest that the locust operates near the limits of its surface friction, but without sufficient time to actively control its feet. Therefore, all surface adaptation must be through passive mechanics (morphological intelligence), which are unknown. Here, we report the slipping behavior, dynamic attachment, passive mechanics, and interplay between the spines and adhesive pads, studied through both biological and robotic experiments, which contribute to the locust's ability to jump robustly from diverse surfaces. We found slipping to be surface-dependent and common (e.g., wood 1.32 ± 1.19 slips per jump), yet the morphological intelligence of the feet produces a significant chance to reengage the surface (e.g., wood 1.10 ± 1.13 reengagements per jump). Additionally, a discovered noncontact-type jump, further studied robotically, broadens the applicability of the morphological adaptations to both static and dynamic attachment.

3D Nanoprinted Plastic Kinoform X-Ray Optics

High-performance focusing of X-rays requires the realization of very challenging 3D geometries with nanoscale features, sub-millimeter-scale apertures, and high aspect ratios. A particularly difficult structure is the profile of an ideal zone plate called a kinoform, which is manufactured in nonideal approximated patterns, nonetheless requires complicated multistep fabrication processes. Here, 3D fabrication of high-performance kinoforms with unprecedented aspect ratios out of low-loss plastics using femtosecond two-photon 3D nanoprinting is presented. A thorough characterization of the 3D-printed kinoforms using direct soft X-ray imaging and ptychography demonstrates superior performance with an efficiency reaching up to 20%. An extended concept is proposed for on-chip integration of various X-ray optics toward high-fidelity control of X-ray wavefronts and ultimate efficiencies even for harder X-rays. Initial results establish new, advanced focusing optics for both synchrotron and laboratory sources for a large variety of X-ray techniques and applications ranging from materials science to medicine.

Self-Sensing Paper Actuators Based on Graphite-Carbon Nanotube Hybrid Films

Soft actuators have demonstrated potential in a range of applications, including soft robotics, artificial muscles, and biomimetic devices. However, the majority of current soft actuators suffer from the lack of real-time sensory feedback, prohibiting their effective sensing and multitask function. Here, a promising strategy is reported to design bilayer electrothermal actuators capable of simultaneous actuation and sensation (i.e., self-sensing actuators), merely through two input electric terminals. Decoupled electrothermal stimulation and strain sensation is achieved by the optimal combination of graphite microparticles and carbon nanotubes (CNTs) in the form of hybrid films. By finely tuning the charge transport properties of hybrid films, the signal-to-noise ratio (SNR) of self-sensing actuators is remarkably enhanced to over 66. As a result, self-sensing actuators can actively track their displacement and distinguish the touch of soft and hard objects.