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Self-assembled bionanostructures

Nanostructures refer to materials that have the relevant dimensions of internal structure defined at the nanometer scale. These materials have unique physical properties that are distinctly different from bulk materials. Self-assembly has aroused an interest in the contexts of natural and synthetic materials, as it can lead from nanoscale structures to functional or responsive materials (Kosonen, 2004).

Self-assembly is a process by which molecules spontaneously assemble into some structure or molecular machine under the appropriate conditions and adopt a defined arrangement in space. The fundamental advantage over mechanically directed assembly is that it requires no tools to move and orient components (Sweeney et al, 2008). Selective binding between matching surfaces is uniquely defined with attractive forces between components that prevail random connections.

Biological systems are almost entirely driven by self-assembly. This is an essential process for many of the key activities of living cells. These include the formation of protein and nucleic acid complexes necessary to protein, RNA, and DNA synthesis and degradation, formation of plasma membrane, flagella, cytoskeleton assembly as well as pathological conditions such as the formation of prions and viral particles, and many others. Biological molecules forming these systems range from nucleic acids, polypeptides and polysaccharides. They can even be regulated by multiple chemical and biological stimuli (Lu et al., 2007; Bromley et al., 2008; Sweeney et al., 2008). Fiber forming proteins are fundamental building blocks of life. They play an essential role in motility (flagellin), elasticity (elastin, collagen), scaffolding (actin), stabilization (keratins) and protection of the cells, tissues and organisms (spider and insect silks). They also form a tight stable structure that has the tendency to self-assemble. These proteins are widely used in many medical and technical applications (Scheibel, 2005).

Natural polymers are all candidates for the components of self-assembled bionanostructures. The main characteristics of nucleic acids, polypeptides, polysaccharides and lipids such as stability, functional versatility, flexibility, manipulation ability and occurrence in natural materials are compared in Table 1.

Table 1: Characteristics of biological molecules as nanostructure building blocks

stability + ++ +++ +
functional versatility + +++ + +
structural versatility ++ +++ + +
ease of manipulation +++ ++ - -
use as structural
materials in nature
- +++ +++ +

Therefore biological systems offer many different molecules (peptides, nucleic acids, polysaccharides) that can be used to form bionanostructures / bionanomaterials. By the regulation of assembly of these components, the smart bionanomaterials are only a step away. Polysaccharides, such as cellulose represent the majority of biomass, however nucleic acids are the most easy to modify and synthesize. Polypeptides seem to represent the best balance of structural and functional versatility, and allow ample possibility of modifications so it is no wonder that most of the natural nanomachines and also dynamic structural elements are made of polypeptides.

Potentials of self-assembled bionanostructures are almost limitless. In fact we are limited mainly by our knowledge and imagination. We can take the structural paradigms from nature but on the other hand we can only use the cell factory to produce nanomaterials that have structure and properties unlike any structures existing in nature. It is in this field that we can have the most productive synthesis of engineering and biological philosophy.

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