Biomedical Engineering Reference
In-Depth Information
self-assembly, molecules are often complex polymers which can assemble from the random coil into
a well-defined stable structure (secondary and tertiary structure). Protein folding to form second-
ary and tertiary amine structures is a good example of intramolecular self-assembly. Intermolecular
self-assembly is the ability of molecules to form supramolecular assemblies (quaternary structure).
Supramolecular micelle formation by surfactant molecules in solution and self-assembled monolay-
ers (SAMs) on a substrate are classic examples of intermolecular self-assembly. Magnetic, capillary,
electrostatic, and gravitational forces play a vital role in self-assembly of structures on the meso- and
macroscale level
[8]
.
13.4
SELF-ASSEMBLY OF PROTEINS AND PEPTIDES
Proteins are fundamental components and building blocks of all living cells. Proteins have been
classified as a group of complex organic macromolecules containing carbon, hydrogen, nitrogen,
oxygen, and sulfur. They are composed of one or more chains of amino acids. Amino acids contain
an amino (-NH
2
) and a carboxyl (-COOH) group. Two or more amino acids linked by a peptide
bond form a peptide molecule. Large numbers of peptide molecules arrange themselves in different
fashions to make up different kinds of proteins. Enzymes, hormones, and antibodies are few exam-
ples of biological substances that are made up of proteins and are required for the proper function-
ing of a living organism. Structural analysis of protein molecules has revealed that they take up
various shapes to form a stable macroscopic structure. Nature has used self-assembly of proteins
and peptides to build a vast array of structures like keratin, collagen, coral, pearl, shell, etc. In the
past few decades numerous researches have been done to understand the structural characteris-
tics that influence the self-assembly of protein and peptide molecules. The self-assembly process is
highly dependent on the peptide sequence, concentration, pH, presence of salts, and time or kinet-
ics. Self-assembling proteins and peptides have been effectively utilized to design novel biomimetic
nanomaterials which have tremendous applications in the fields of bionanotechnology and biomedi-
cine
[9-20]
.
13.5
BIONANOTECHNOLOGY APPLICATIONS
As understood from the word “bionanotechnology,” it is the emerging field of science which uti-
lizes biological molecules for nanotechnological applications. Bionanotechnology takes advantage
of the unique properties of biological molecules like amphiphilic peptides by utilizing their self-
assembling property for the nano-engineering of molecular templates and supramolecular structures
[9]
. Amphiphiles are molecules containing a nonpolar hydrophobic region and a polar hydrophilic
region will self-assemble in aqueous solution to form distinct structures such as micelles, vesicles and
tubules. When suspended in an aqueous solution, the nonpolar hydrophobic regions of amphiphilic
molecules are attracted toward each other and away from water (hydrophobic effect). The shape
and dimensions of supramolecular structures formed from such assemblies will then depend on dif-
ferent factors, such as the structure of the polar head group and the shape of each amphiphile
[11]
.
Several self-assembling amphiphilic peptide and protein systems that self-assemble to form various
nanostructures like nanofibers, nanotubes, vesicles, helical ribbons, and fibrous scaffolds have been
described extensively for their potential applications in the field of bionanotechnology
[12]
.
