Microscale Freeform Integration by Directed Self Assembly

Most solid freeform fabrication (SFF) manufacturing processes assemble uniform components such as powder particles or polymer chains to produce desired geometries. Their capacity for producing highly functional parts (integrated actuation, sensing, and electronics) will dramatically increase when multiple materials and functional subcomponents can be automatically integrated. This paper addresses criteria for a system that integrates multiple materials and components through computer-controlled self-assembly. It builds complex systems from layers of self-assembled micro-components. The paper will address implementation methods, present a concept demonstration, and consider its application to micro-thermoelectric systems. This manufacturing process can be enhanced further through integration with mature additive processes.Mechanical Engineerin

Exploiting classical nucleation theory for reverse self-assembly

In this paper we introduce a new method to design interparticle interactions to target arbitrary crystal structures via the process of self-assembly. We show that it is possible to exploit the curvature of the crystal nucleation free-energy barrier to sample and select optimal interparticle interactions for self-assembly into a desired structure. We apply this method to find interactions to target two simple crystal structures: a crystal with simple cubic symmetry and a two-dimensional plane with square symmetry embedded in a three-dimensional space. Finally, we discuss the potential and limits of our method and propose a general model by which a functionally infinite number of different interaction geometries may be constructed and to which our reverse self-assembly method could in principle be applied.Comment: 7 pages, 6 figures. Published in the Journal of Chemical Physic

Current approaches for modulation of the nanoscale interface in the regulation of cell behavior

Regulation of cell behavior in response to nanoscale features has been the focus of much research in recent years and the successful generation of nanoscale features capable of mimicking the natural nanoscale interface has been of great interest in the field of biomaterials research. In this review, we discuss relevant nanofabrication techniques and how they are combined with bioengineering applications to mimic the natural extracellular matrix (ECM) and create valuable nanoscale interfaces

Designing stem cell niches for differentiation and self-renewal

Mesenchymal stem cells, characterized by their ability to differentiate into skeletal tissues and self-renew, hold great promise for both regenerative medicine and novel therapeutic discovery. However, their regenerative capacity is retained only when in contact with their specialized microenvironment, termed the stem cell niche. Niches provide structural and functional cues that are both biochemical and biophysical, stem cells integrate this complex array of signals with intrinsic regulatory networks to meet physiological demands. Although, some of these regulatory mechanisms remain poorly understood or difficult to harness with traditional culture systems. Biomaterial strategies are being developed that aim to recapitulate stem cell niches, by engineering microenvironments with physiological-like niche properties that aim to elucidate stem cell-regulatory mechanisms, and to harness their regenerative capacity in vitro. In the future, engineered niches will prove important tools for both regenerative medicine and therapeutic discoveries

High precision self-alignment using liquid surface tension for additively manufactured micro components

Self-assembly of components using liquid surface tension is an attractive alternative to traditional robotic pick-and-place as it offers high assembly accuracy for coarse initial part placement. One of the key requirements of this method is the containment of the liquid within a designated binding site. This paper looks to expand the applications of self-assembly and investigates the use of topographical structures applied to 3D printed micro components for self-assembly using liquid surface tension. An analysis of the effect of edge geometry on liquid contact angle was conducted. A range of binding sites were produced with varying edge geometries, 45-135°, and for a variety of site shapes and sizes, 0.4 - 1 mm in diameter, and 0.5 x 0.5 – 1 x 1 mm square. Liquid water droplets were applied to the structures and contact angles measured. Significant increases in contact angle were observed, up to 158°, compared to 70° for droplets on planar surfaces, demonstrating the ability of these binding sites to successfully pin the triple contact line at the boundary. Three challenging self-assembly cases were examined, 1) linear initial component misplacement >0.5 mm, 2) angular misplacement of components, 3) 2 misplacement of droplet. Across all three assembly cases the lowest misalignments in final component position, as well as highest repeatability, were observed for structures with actual edge geometries <90° (excluding 45° nominal), where the mean magnitude of misalignment was found to be 31 μm with 14 μm standard deviation

Computational studies of biomembrane systems: Theoretical considerations, simulation models, and applications

This chapter summarizes several approaches combining theory, simulation and experiment that aim for a better understanding of phenomena in lipid bilayers and membrane protein systems, covering topics such as lipid rafts, membrane mediated interactions, attraction between transmembrane proteins, and aggregation in biomembranes leading to large superstructures such as the light harvesting complex of green plants. After a general overview of theoretical considerations and continuum theory of lipid membranes we introduce different options for simulations of biomembrane systems, addressing questions such as: What can be learned from generic models? When is it expedient to go beyond them? And what are the merits and challenges for systematic coarse graining and quasi-atomistic coarse grained models that ensure a certain chemical specificity

Design for quality manufacturability analysis for common assembly process

The globalization of market economy has precipitated a dramatic increase in competition necessitating the need for higher quality products at lower cost in shorter time periods. Shorter life cycles and proliferation of products has made companies integrate all the phases of manufacturing to bring about a superior design. Design for Quality Manufacturability (DFQM) provides a technique to invoke manufacturing and assembly considerations while designing a product. The DFQM architecture identifies factors consisting of several variables that are influenced by certain error catalysts to cause one or more specific defects. A methodology is suggested to identify and quantify these error catalysts to be able to estimate the quality of the design. Some of the assembly processes that are widely used are insertion, riveting, welding, fastening, press-fit, and snap-fit. A detailed study of each of these processes is done to analyze the techniques, capabilities, and limitations. Using the DFQM architecture defect classes and specific defects are identified and analyzed. A correlation matrix is formed to identify the processes that are associated with each specific defect. Cause-Effect analysis using Ishikawa diagrams provide a means of analyzing the characteristics of the relevant processes attributing to each specific defect. These characteristics are grouped to identify the error catalysts that influence the occurrence of the specific defect

How Water's Properties Are Encoded in Its Molecular Structure and Energies.

How are water's material properties encoded within the structure of the water molecule? This is pertinent to understanding Earth's living systems, its materials, its geochemistry and geophysics, and a broad spectrum of its industrial chemistry. Water has distinctive liquid and solid properties: It is highly cohesive. It has volumetric anomalies-water's solid (ice) floats on its liquid; pressure can melt the solid rather than freezing the liquid; heating can shrink the liquid. It has more solid phases than other materials. Its supercooled liquid has divergent thermodynamic response functions. Its glassy state is neither fragile nor strong. Its component ions-hydroxide and protons-diffuse much faster than other ions. Aqueous solvation of ions or oils entails large entropies and heat capacities. We review how these properties are encoded within water's molecular structure and energies, as understood from theories, simulations, and experiments. Like simpler liquids, water molecules are nearly spherical and interact with each other through van der Waals forces. Unlike simpler liquids, water's orientation-dependent hydrogen bonding leads to open tetrahedral cage-like structuring that contributes to its remarkable volumetric and thermal properties