What is Self-assembly?
Note that self-assembly and self-organization are different. In self-assembling systems, individual parts move towards a final state, wheras in self-organizing systems, components move between multiple states, oscillate and may never come to rest in a final configuration. This makes self-organization much more complex to understand and duplicate. Self-assembly has become a rapidly growing science in past two decades for two reasons.
1) Self-assembly provides a major solution to the fabrication of ordered structures from nanometers to micrometers components but in principle, it is applicable at all scales. Interestingly these size fall between the sizes that can be manipulated by I) chemistry and those that can be manipulated by II) conventional manufacturing. Therefore it became a powerful tool in the window that was not touched intensively in past.
2) Self-assembly is a concept that is crucial to understand many structures important in various fundamental sciences including chemistry, biology and physics. In general, the stability of covalent bonds enables the synthesis of almost arbitrary configurations of up to 1000 atoms. Larger molecules, molecular aggregates, and forms of organized matter more extensive than molecules cannot be efficiently synthesized bond after bond. Therefore self-assembly is a powerful strategy for organizing matter larger than a molecule.
Self-assembly has introduced hope in industry too. It allows fabrication of smaller systems with better performance and facilitate the transition of current microelectronic to futuristic nanoelectronics (nanofabrication of smaller transistor or self-assembly of nanolitz wire). Self-assembly could play an important role in many other industries including pharmacudical and petrochemical sunthesis and manufacturing.
Although there are few studies about self-assembly of low aspect ratio filamentous materials including nanorods however no study on self-assembly of high aspect ratio filamentous material are conducted. This is important because high aspect ratio self-assembly in nature play very broad role from movement of cells with microtubules to transferring and storing information which happens in DNA. In general, self-assembly of high aspect ratio filamentous materials are more complicated than the low aspect ratio filamentous ones since the high aspect term convert self-assembly from a static system to a dynamic one simply because the filamentous materials can crawl on each other or make unparalleled initial bonds with many different energy state. Indeed, it can be considered as a self-organization instead of self-assembly.
Biomimetics
In the course of million years of evolution, Nature has developed strategies that provide biological processes and materials with delicate specificity, and adaptability. Biomimetics is the imitation of nature for the purpose of solving complex human problems. On the other hand, its sister’s field, Bionics is the application of biological methods and systems in nature to the study and design modern technology. Learning from Nature not only satisfies humankind's limitless curiosity for understanding the world, but also promises a paradigm shift in creating new artificial smart materials.
Living organisms have evolved well-adapted structures and materials over geological time through natural selection. Humans have looked at nature for answers to problems throughout our existence. For instance nature has solved engineering problems such as self-healing abilities, environmental exposure resistance, harnessing solar energy and most importantly self-assembly.
Self-assembly of fibers/pillars is inspired by a wide range of biological systems in which assembly of nanofibers has functional significance. For example, the Hemisphaerota Cyanea beetle uses the surface tension of an oily liquid to reversibly self-assemble or disassemble its segmented feet to control their extraordinary attachment to an arbitrary surface.
Using periodic nanopillar arrays with arbitrary shape, dimension, high aspect ratio and spatial pattern as an artificial model system, I have studied their elastocapillary chiral self-assembly. This system has potential in many applications including dynamic structural colors, dry adhesives and guiding microfluidic systems to name a few.
My research is aimed at understanding some of the basic principles of biological systems which biology solves complex problems in the design of multifunctional, smart and adaptive materials. The goal is to use biological principles as guidance in developing new, bio-inspired nanofabrication strategies that would lead to advanced materials, with broad implications in fields ranging from energy efficiency to sensors to smart dry adhesives.
Fabrication of Nano-Braid By Using DNA Origami
A braid is a topology formed by interlacing at least three strands of soft material. Note that braiding is in the same family as weaving. There are many evidences that braiding existed since prehistoric times and the oldest known reproduction of hair braiding goes back about 30,000 years. In some regions, hair braid patterns were an indication of a person’s age, marital status, wealth, social position, and religion. Nowadays, the pursuit of topology has evolved into major themes in the physical and particularly in biological sciences.
It has been predicted that self-assembly of nanowires into braided and twisted topologies could overcome the proximity effect of conductive alternative current carrying wires at high frequencies (in GHz range) and prevent skin effect due to their nanoscale diameters. These nanobraid topologies will enable the antennas of communication devices to generate and receive purer signals which reduces interference with other nearby transmissions and consequently free up spectrum by reducing the need for space between frequencies. The improved signal performance could also enable devices to transmit more data per channel, receive weaker signals and overcome interference that disrupts GPS signals.
However, the synthesis of topologically interesting structures like braid in the range of nanometer to micrometer is still very challenging, both intellectually and technically. This is because the successful design and construction of topological structures at such small dimensions requires controllable generation of nodes in the precise position, time and with the correct handedness. Obviously, this requires a fibrous material with an extraordinarily high level of programmability.
DNA is a very promising fibrous molecule for this purpose because of its extraordinary programmability, which has allowed for the creation of various sophisticated DNA topologies including knots and links which was initiated by Seeman and coworkers.
The emergence of complex topologies such as braids, knots and twists at the molecular level represents a big challenge in chemistry, physics and materials science. We have recently showed (see figure above) that ssDNA and dsDNA braids and twist can be created by delicately designing the sequence, length and toehold design of the staples at each (+) and (−) four-arm DNA junctions (nodes). Here I propose to explore; 1) the use of various braid index motifs for fabrication of microstructure with controllable texture and enhanced mechanical, optical and more importantly electrical properties and 2) Use of DNA nanobraid for templating complex pattern of braids into non-biological fibrous materials with desirable diameter through translation of braid’s nodes.