Nature-inspired soft robotics: On articial cilia and magnetic locomotion

Inspired by micro-organisms in nature, people imagined using micro-scale soft robots to work inside the human body for therapeutic drug delivery, minimally invasive surgery, or diagnostic biochemical sensing. To create these robots is challenging due to their small size, viscosity environment, and soft constituting materials. In addition, the mechanisms of operation are quite different from the conventional rigid macro-scale robots that we are familiar with. In this PhD project, we focused on the computational analysis and design of micro-scale soft robots. Working closely with experimental groups, we studied artificial cilia and micro-swimmers that can realize particle manipulation, fluid transport, fluid mixing, or magnetic locomotion. Various cilia systems are considered, including soft inflatable cilia which could be controlled individually and programmable magnetic cilia featuring phase shifts and collective metachronal patterns. We also analyze micro-swimmers that are soft and adaptive in confined spaces. Driven by different external magnetic fields, the swimmer's motion can be changed between undulation crawling, undulation swimming, and helical crawling. By using computational modeling, we analyze the transport mechanisms of the soft robots and study the effect of different parameters to provide guidelines for the design of the robots in specific applications. By studying the physical mechanisms of micro-organisms in nature, we are not only able to understand more clearly their functional behaviour, it also opens the possibility of biomimetic design of soft robotic cilia and micro-swimmers

Metachronal patterns by magnetically-programmable artificial cilia surfaces for low Reynolds number fluid transport and mixing

Motile cilia can produce net fluid flows at low Reynolds number because of their asymmetric motion and metachrony of collective beating. Mimicking this with artificial cilia can find application in microfluidic devices for fluid transport and mixing. Here, we study the metachronal beating of nonidentical, magnetically-programmed artificial cilia whose individual non-reciprocal motion and collective metachronal beating pattern can be independently controlled. We use a finite element method that accounts for magnetic forces, cilia deformation and fluid flow in a fully coupled manner. Mimicking biological cilia, we study magnetic cilia subject to a full range of metachronal driving patterns, including antiplectic, symplectic, laeoplectic and diaplectic waves. We analyse the induced primary flow, secondary flow and mixing rate as a function of the phase lag between cilia and explore the underlying physical mechanism. Our results show that shielding effects between neighboring cilia lead to a primary flow that is larger for antiplectic than for symplectic metachronal waves. The secondary flow can be fully explained by the propagation direction of the metachronal wave. Finally, we show that the mixing rate can be strongly enhanced by laeoplectic and diaplectic metachrony resulting in large velocity gradients and vortex-like flow patterns.</p

Collaborative Online Education: A Case Study of an Ed.D. Program

This dissertation discusses collaborative teaching and learning models of online courses. Four research questions guide the study: How do instructors design online courses to facilitate instruction using collaborative teaching and learning models? When instructors co-teach online, how do they utilize collaborative teaching and learning models? How do students build online learning communities from collaborative teaching and learning models? and How do instructors and students evaluate online collaborative teaching and learning models? We conducted a case study of an Ed.D. cohort of Chinese students in the College of Education of the University of Missouri-St. Louis (UMSL). We employed a qualitative approach to this study, using a sample of seven students and four instructors who participated in online courses that used collaborative approaches to learning and teaching. We collected data from three primary sources: interviews, questionnaires, and relevant documents. The data analysis and discussion focus on the perspectives of instructors and students on collaborative learning and teaching in online contexts and offer insights into improving the design and implementation of collaborative online education. Our findings revealed that collaborative approaches in online settings are relatively complex and can effectively support instructors and students in achieving teaching and learning goals. The findings provide support for the following arguments, that professional development for instructors, effective communication, varied strategies to increase classroom interaction, and clear roles and expectations are all factors that influence successful approaches to online teaching and learning. Finally, this study may be a valuable resource for instructors who intend to implement successful collaborative education in an online setting

Mechanical Characterization of Released Thin Films by Contact Loading

The design of reliable micro electro-mechanical systems (MEMS) requires understanding of material properties of devices, especially for free-standing thin structures such as membranes, bridges, and cantilevers. The desired characterization system for obtaining mechanical properties of active materials often requires load control. However, there is no such device among the currently available tools for mechanical characterization of thin films. In this paper, a new technique, which is load-controlled and especially suitable for testing highly fragile free-standing structures, is presented. The instrument developed for this purpose has the capability of measuring both the static and dynamic mechanical response and can be used for electro/magneto/thermo mechanical characterization of actuators or active materials. The capabilities of the technique are demonstrated by studying the behavior of 75 nm thick amorphous silicon nitride (Si_3N_4) membranes. Loading up to very large deflections shows excellent repeatability and complete elastic behavior without significant cracking or mechanical damage. These results indicate the stability of the developed instrument and its ability to avoid local or temporal stress concentration during the entire experimental process. Finite element simulations are used to extract the material properties such as Young's modulus and residual stress of the membranes. These values for Si_3N_4 are in close agreement with values obtained using a different technique, as well as those found in the literature. Potential applications of this technique in studying functional thin film materials, such as shape memory alloys, are also discussed

Transport and mixing by metachronal waves in nonreciprocal soft robotic pneumatic artificial cilia at low Reynolds numbers

Cilia are widely employed by living systems to manipulate fluid flow in various functions, such as feeding, pumping, and locomotion. Mimicking the intricate ciliary asymmetry in combination with collective metachronal beating may find wide application in fluid transport and mixing in microfluidic systems. Here, we numerically analyze the metachronal beating of pneumatic artificial cilia. We specifically address three aspects of ciliary motion: (i) pumping in the backflow region, (ii) mixing in the cilia region, and (iii) the transport—mixing transition region. Our results show that antiplectic metachrony leads to the highest mixing efficiency and transport rate in two distinct regions, i.e., below and above the ciliary surface, respectively. We find that the ciliary motion strongly enhances the diffusivity when advection is dominant at high Péclet numbers, with a factor 3 for symplectic metachrony and a factor 4 for antiplectic metachrony and synchronous beating. In addition, we find an increase with a factor 1.5 for antiplectic metachrony and a decrease with a factor 2.5 for symplectic metachrony compared with synchronous beating for fluid pumping. To investigate the higher transport rate compared to symplectic metachrony, we develop a simple two-cilia model and demonstrate that the shielding of flow between neighboring cilia is the main reason for the higher antiplectic transport rate

Visualization of Flagella during Bacterial Swarming

When cells of Escherichia coli are grown in broth and suspended at low density in a motility medium, they swim independently, exploring a homogeneous, isotropic environment. Cell trajectories and the way in which these trajectories are determined by flagellar dynamics are well understood. When cells are grown in a rich medium on agar instead, they elongate, produce more flagella, and swarm. They move in coordinated packs within a thin film of fluid, in intimate contact with one another and with two fixed surfaces, a surfactant monolayer above and an agar matrix below: they move in an inhomogeneous, anisotropic environment. Here we examine swarm-cell trajectories and ways in which these trajectories are determined by flagellar motion, visualizing the cell bodies by phase-contrast microscopy and the flagellar filaments by fluorescence microscopy. We distinguish four kinds of tracks, defining stalls, reversals, lateral movement, and forward movement. When cells are stalled at the edge of a colony, they extend their flagellar filaments outwards, moving fluid over the virgin agar; when cells reverse, changes in filament chirality play a crucial role; when cells move laterally, they are pushed sideways by adjacent cells; and when cells move forward, they are pushed by flagellar bundles in the same way as when they are swimming in bulk aqueous media. These maneuvers are described in this report.Molecular and Cellular Biolog

Controlled Multidirectional Particle Transportation by Magnetic Artificial Cilia

Manipulation of particles in a controllable manner is highly desirable in many applications. Inspired by biological cilia, this article experimentally and numerically demonstrates a versatile particle transportation platform consisting of arrays of magnetic artificial cilia (MAC) actuated by a rotating magnet. By performing a tilted conical motion, the MAC are capable of transporting particles on their tips, along designated directions that can be fully controlled by the externally applied magnetic field, in both liquid and air, at high resolution (particle precision), with varying speeds and for a range of particle sizes. Moreover, the underlying mechanism of the controlled particle transportation is studied in depth by combining experiments with numerical simulations. The results show that the adhesion and friction between the particle and the cilia are essential ingredients of the mechanism underlying the multidirectional transportation. This work offers an advanced solution to controllably transport particles along designated paths in any direction over a surface, which has potential applications in diverse fields including lab-on-a-chip devices, in vitro biomedical sciences, and self-cleaning and antifouling.</p

Single-cell sequencing reveals CD133+CD44--originating evolution and novel stemness related variants in human colorectal cancer

BACKGROUND: Tumor heterogeneity of human colorectal cancer (CRC)-initiating cells (CRCICs) in cancer tissues often represents aggressive features of cancer progression. For high-resolution examination of CRCICs, we performed single-cell whole-exome sequencing (scWES) and bulk cell targeted exome sequencing (TES) of CRCICs to investigate stemness-specific somatic alterations or clonal evolution. METHODS: Single cells of three subpopulations of CRCICs (CD133+CD44+, CD133-CD44+, and CD133+CD44- cells), CRC cells (CRCCs), and control cells from one CRC tissue were sorted for scWES. Then, we set up a mutation panel from scWES data and TES was used to validate mutation distribution and clonal evolution in additional 96 samples (20 patients) those were also sorted into the same three groups of CRCICs and CRCCs. The knock-down experiments were used to analyze stemness-related mutant genes. Neoantigens of these mutant genes and their MHC binding affinity were also analyzed. FINDINGS: Clonal evolution analysis of scWES and TES showed that the CD133+CD44- CRCICs were the likely origin of CRC before evolving into other groups of CRCICs/CRCCs. We revealed that AHNAK2, PLIN4, HLA-B, ALK, CCDC92 and ALMS1 genes were specifically mutated in CRCICs followed by the validation of their functions. Furthermore, four predicted neoantigens of AHNAK2 were identified and validated, which might have applications in immunotherapy for CRC patients. INTERPRETATION: All the integrative analyses above revealed clonal evolution of CRC and new markers for CRCICs and demonstrate the important roles of CRCICs in tumorigenesis and progression of CRCs. FUNDING: A full list of funding bodies that contributed to this study can be found in the Acknowledgements section

Research Hotspots and Trends in Home-Based Cardiac Rehabilitation: A Bibliometric Visualization Analysis

Objective: This research was aimed at determining research hotspots and major topics in the field of international home-based cardiac rehabilitation (HBCR) over the past 20 years, and exploring future trends in HBCR. Methods: A total of 757 research articles from 2002 to 2022, with themes of home-based cardiac rehabilitation, were included in the core collection database of Web of Science. CiteSpace software was used for literature metrology and visualization analysis. Results: (1) The total number of research articles on HBCR is increasing. (2) Research hotspots in HBCR include the effectiveness of rehabilitation after coronary heart disease or heart failure; quality of life; mental health; and home rehabilitation after COVID-19. (3) Research trends in HBCR include wearable intelligent technology; telerehabilitation; lifestyle interventions; and home-based rehabilitation prescriptions for exercise, nutrition, psychology and continuous management. Conclusion: The effects of HBCR have been continuously verified. Research has focused primarily on secondary prevention and rehabilitation after coronary heart disease and heart failure. More attention must be paid to improving patients’ quality of life by HBCR. Telerehabilitation based on wearable intelligent technology, home-based lifestyle interventions and continuous management are future trends of HBCR development