Epitaxy: Programmable Atom Equivalents

The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle (NP) superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of NP thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm² areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in atomic thin film deposition, allowing these processes to be understood in the context of well-studied atomic epitaxy and enabling a nanoscale model to study fundamental crystallization processes. Through understanding the role of epitaxy as a driving force for NP assembly, we are able to realize 3D architectures of arbitrary domain geometry and size.United States. Air Force Office of Scientific Research (AFOSR FA9550-11-1-0275)United States. Air Force Office of Scientific Research (FA9550-12-1-0280)United States. Department of Defense (N00014-15-1-0043)United States. Department of Energy (Grant DE-SC0000989-0002)National Science Foundation (U.S.) (Award DMR-1121262

Breakdown in the Smart City: Exploring Workarounds with Urban-sensing Practices and Technologies

Smart cities are now an established area of technological development and theoretical inquiry. Research on smart cities spans from investigations into its technological infrastructures and design scenarios, to critiques of its proposals for citizenship and sustainability. This article builds on this growing field, while at the same time accounting for expanded urban-sensing practices that take hold through citizen-sensing technologies. Detailing practice-based and participatory research that developed urban-sensing technologies for use in Southeast London, this article considers how the smart city as a large-scale and monolithic version of urban systems breaks down in practice to reveal much different concretizations of sensors, cities, and people. By working through the specific instances where sensor technologies required inventive workarounds to be setup and continue to operate, as well as moments of breakdown and maintenance where sensors required fixes or adjustments, this article argues that urban sensing can produce much different encounters with urban technologies through lived experiences. Rather than propose a “grassroots” approach to the smart city, however, this article instead suggests that the smart city as a figure for urban development be contested and even surpassed by attending to workarounds that account more fully for digital urban practices and technologies as they are formed and situated within urban projects and community initiatives

Epitaxy: Programmable Atom Equivalents Versus Atoms

The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle (NP) superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of NP thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm2 areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in atomic thin film deposition, allowing these processes to be understood in the context of well-studied atomic epitaxy and enabling a nanoscale model to study fundamental crystallization processes. Through understanding the role of epitaxy as a driving force for NP assembly, we are able to realize 3D architectures of arbitrary domain geometry and size

Epitaxy: Programmable Atom Equivalents Versus Atoms

The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle (NP) superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of NP thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm2 areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in atomic thin film deposition, allowing these processes to be understood in the context of well-studied atomic epitaxy and enabling a nanoscale model to study fundamental crystallization processes. Through understanding the role of epitaxy as a driving force for NP assembly, we are able to realize 3D architectures of arbitrary domain geometry and size

Global Policy Barriers and Enablers to Exercise and Physical Activity in Kidney Care

Objective: Impairment in physical function and physical performance leads to decreased independence and health-related quality of life in people living with chronic kidney disease and end-stage kidney disease. Physical activity and exercise in kidney care are not priorities in policy development. We aimed to identify global policy-related enablers, barriers, and strategies to increase exercise participation and physical activity behavior for people living with kidney disease. Design and Methods: Guided by the Behavior Change Wheel theoretical framework, 50 global renal exercise experts developed policy barriers and enablers to exercise program implementation and physical activity promotion in kidney care. The consensus process consisted of developing themes from renal experts from North America, South America, Continental Europe, United Kingdom, Asia, and Oceania. Strategies to address enablers and barriers were identified by the group, and consensus was achieved. Results: We found that policies addressing funding, service provision, legislation, regulations, guidelines, the environment, communication, and marketing are required to support people with kidney disease to be physically active, participate in exercise, and improve health-related quality of life. We provide a global perspective and highlight Japanese, Canadian, and other regional examples where policies have been developed to increase renal physical activity and rehabilitation. We present recommendations targeting multiple stakeholders including nephrologists, nurses, allied health clinicians, organizations providing renal care and education, and renal program funders. Conclusions: We strongly recommend the nephrology community and people living with kidney disease take action to change policy now, rather than idly waiting for indisputable clinical trial evidence that increasing physical activity, strength, fitness, and function improves the lives of people living with kidney disease

Controlling structure across length scales with directed assembly of colloidal nanoparticles

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, May, 2020Cataloged from the official PDF of thesis.Includes bibliographical references (pages 319-334).One of the promises of nanotechnology is the ability to create a bulk, designer material with its structure programmed at each length scale using deterministic control over the placement of each nanoscale component. Self-assembled nanoparticle colloids, particularly those directed by sequence-specific DNA hybridizations, have emerged as a promising building block for producing these designer materials from nanoparticles that arrange themselves into precise symmetries through mechanisms analogous to atomic crystallization. However, DNA-directed colloids and other self-assembled nanoparticle systems still struggle to realize the goal of arbitrary structure control at length scales larger than a few microns due to the complexity of forces impacting different scales simultaneously.Utilizing existing atomic analogues for inspiration, this work extends the structure-defining nature of these programmable building blocks by imposing lithographic boundary conditions and devising processing techniques resembling those of atomic thin films and powders. Crystallization at an interface is explored, and preferential grain growth from a substrate is demonstrated to control large scale crystal texture. Full crystal orientation control is achieved by using standard nano-fabrication techniques to construct a lithographically-defined template for epitaxial growth that can define arbitrary macroscale shapes over millimeters. The resulting crystallization platform exhibits remarkable resiliency to lattice mismatch due to the 'soft' nature of the DNA ligands binding nanoparticles together. The understanding garnered from the DNA-grafted nanoparticle as a model system is extended to a colloid synthesized from a more scalable and robust directing polymer, polystyrene.The unique advantages of this new building block enable the fabrication of truly bulk, 3D materials with arbitrary macroscale shape on the centimeter scale via sintering and post-processing of nanoparticle-based crystallites. The results of this work are nanoparticle-based materials with dictated structure from the nanoscale (crystallographic unit cell), through the microscale (crystallite size and orientation), to the macroscale (lithographically defined shape).by Paul A. Gabrys.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineerin

Lattice Mismatch in Crystalline Nanoparticle Thin Films

For atomic thin films, lattice mismatch during heteroepitaxy leads to an accumulation of strain energy, generally causing the films to irreversibly deform and generate defects. In contrast, more elastically malleable building blocks should be better able to accommodate this mismatch and the resulting strain. Herein, that hypothesis is tested by utilizing DNA-modified nanoparticles as "soft," programmable atom equivalents to grow a heteroepitaxial colloidal thin film. Calculations of interaction potentials, small-angle X-ray scattering data, and electron microscopy images show that the oligomer corona surrounding a particle core can deform and rearrange to store elastic strain up to ±7.7% lattice mismatch, substantially exceeding the ±1% mismatch tolerated by atomic thin films. Importantly, these DNA-coated particles dissipate strain both elastically through a gradual and coherent relaxation/broadening of the mismatched lattice parameter and plastically (irreversibly) through the formation of dislocations or vacancies. These data also suggest that the DNA cannot be extended as readily as compressed, and thus the thin films exhibit distinctly different relaxation behavior in the positive and negative lattice mismatch regimes. These observations provide a more general understanding of how utilizing rigid building blocks coated with soft compressible polymeric materials can be used to control nano- and microstructure.United States. Air Force. Office of Scientific Research (Awards, FA9550-16-1-0150 (oligonucleotide syntheses and purification), FA9950-17-1-0348 (DNA-functionalization of gold nanoparticles), and FA9550-17-1-0288 Young Investigator Research Program)United States. Office of Naval Research (Grant N00014-15-1-0043)United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0000989)National Science Foundation (U.S.) (Awards DMR-1419807, DMR-1121262)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant NSF 1122374

DNA-Directed Non-Langmuir Deposition of Programmable Atom Equivalents

Particle assembly at interfaces via programmed DNA interactions allows for independent modification of both nanoparticle-surface interaction strength and the magnitude of interparticle repulsion. Together, these factors allow for modification of the deposited thin film morphology via alterations in DNA binding sequence. Importantly, both Langmuir and random sequential adsorption models yield insights into the thermodynamics of deposition but cannot fully explain particle coverage as a function of all relevant variables, indicating that the particle deposition mechanism for DNA-grafted colloids is more complex than prior adsorption phenomena. Here, it is shown that these deviations from standard behavior arise from the fact that each nanoparticle is attached to the surface via multiple weak DNA duplex interactions, enabling diffusion of adsorbed colloids across the substrate. Thus, surface migration of individual particles causes reorganization of the deposited monolayer, leading to the unusual behavior of coverage increasing at elevated temperatures that are just below the particle desorption temperature. The programmability of DNA-directed particle deposition therefore allows for precise control over the morphology of monolayer films, as well as the ability to generate crystalline materials with controllable surface roughness and grain size through layer-by-layer growth. The increased control over thin film morphology potentially enables tailoring of mechanical and optical properties and holds promise for use in a variety of applications.United States. Department of Energy. Office of Science (Contract DE-AC02-06CH11357)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant NSF 1122374

Physical activity and exercise recommendations for people receiving dialysis: A scoping review

Introduction Remaining physically active is important to patients undertaking dialysis, however, clinical recommendations regarding exercise type, timing, intensity, and safety precautions vary. The purpose of this scoping review was to analyse and summarise recommendations for physical activity and exercise for people undertaking dialysis and identify areas that require further research or clarification. Materials and methods A scoping review of literature from five bibliographic databases (Medline, Scopus, Web of Science, CINAHL, and SPORTDiscus) was conducted. Eligible articles included consensus guidelines, position statements, reviews, or clinical practice guidelines that included specific physical activity and exercise recommendations for people undertaking dialysis. Key search terms included kidney disease OR kidney failure OR chronic kidney disease OR end stage kidney disease AND guideline* OR consensus OR position statement OR prescription OR statement AND exercise OR physical activity . Hand searching for relevant articles in all first twenty quartile 1 journals listed on SCImago under ‘medicine—nephrology’ and ‘physical therapy, sports therapy and rehabilitation’ using the terms ‘exercise and dialysis’ was undertaken. Finally, home pages of key societies and professional organisations in the field of sports medicine and nephrology were searched. Results The systematic search strategy identified 19 articles met the inclusion criteria. Two were specific to pediatric dialysis and three to peritoneal dialysis. Whilst many publications provided recommendations on aerobic exercise, progressive resistance training and flexibility, few provided explicit guidance. Recommendations for the intensity, duration and frequency of aerobic and resistance training varied. Discrepancies or gaps in guidance about precautions, contraindications, termination criteria, progression, and access site precautions were also apparent. Conclusion Future guidelines should include specific guidance regarding physical activity, safety precautions, and timing and intensity of exercise for individuals who undertake dialysis. Collaborative multidisciplinary guideline development and appropriate exercise counselling may lead to increased participation in physical activity and exercise and facilitate better patient outcomes