Mesoscale self-assembly, MESA

This chapter describes experimental and conceptual issues in mesoscale self-assembly (MESA), using examples from our work in the assembly of millimeter- and micron(micrometer)-sized polyhedral objects using capillary forces. In MESA, objects (from nm to mm in size) self-assemble into ordered arrays through noncovalent forces. Three systems that use capillary forces in MESA are described these involve the assembly of objects into two-dimensional arrays at the perfluorodecalin/H20 interface, into three-dimensional arrays at curved liquid/liquid interfaces, and into three-dimensional arrays from a suspension in water. The capillary interactions between objects can be viewed as a type of bond that is analogous to chemical bonds that act between atoms and molecules. 

The word self-assembly can be attributed to spontaneous aggregation of smaller subunits and formation of complex structures to achieve thermodynamic stability. Self-assembly can be of two types based on the size of the units molecular self-assembly and mesoscale self-assembly (MESA). The first method is suitable for encapsulating cells for delivery to a specific tissue, whereas by the second method, cells are encapsulated to engineer artificial organs. 

Mesoscale self-assembly We have not yet modeled MESA by computer, but with the wealth of experimental results we are in a position to develop believable computer simulations calibrated by experiment. The force of attraction between the objects is well understood mathematically in a number of cases [33,120] and in some systems it may be possible to measure these forces experimentally [149]. Some of the problems encountered in modeling molecular systems will also be encountered in modeling MESA. For example, finding global rather than local minima, the availability of computer time limiting how long the assembly can be modeled, and constructing potential functions for interactions that have not been determined... 

We study MESA for three reasons, (i) MESA bridges the gap between molecular self-assembly, which has been successful at the nanometer level, and conventional fabrication of machines and parts, which has been successful for scales greater than 100 pm [refs. 16-23], Few techniques exist to assemble or fabricate objects or arrays in the size region between several nanometers and hundreds of microns, and new techniques in this regime would be welcome, (ii) We wished to develop systems of self-assembly in which we could control the parameters affecting self-assembly more easily than we can with molecules, (iii) We wished to extend the ideas and methods of self-assembly in chemistry and biology to self-assembly on the mesoscale. 

MESA extends the ideas and methods of molecular self-assembly and biology from the molecular scale to the mesoscale... 

Biology and organic chemistry are replete with examples of self-assembly. Examples include lipid bilayers, the DNA duplex, proteins in their correctly folded forms, self-assembled monolayers, and crystals. In MESA, we extend ideas abstracted from molecular recognition - shape recognition, chirality, directional interactions, hierarchy of bonds, and hydrophobicity - to the mesoscale. 

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