DESIGNING NANOFIBROUS SCAFFOLDS FOR TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 446

engineering. Natural polymers that have been used for electrospinning can be
broadly divided into two classes: protein based materials are used, that include
collagen, gelatin, and silk; and carbohydrate like materials namely, chitin/
chitosan, and alginate. This section briefl y describes the electrospinning of these
natural polymers.
13.4.1.1 Proteins. Proteins are a major category of natural polymers that
are diffi cult to fabricate into fi brous forms [113]. This could be attributed to the
complex macromolecular and 3D structure of proteins and the presence of strong
intra- and/or inter-molecular bonding. Electrospinning has the capability to
process protein polymers into nanofi brous scaffolds, with the use of different
solvent system.
Successful attempts have been made to electrospin protein polymers from
natural ECM components as well as proteins obtained from other organisms such
as silk. Both fi brous and globular proteins have been electrospun into nanofi bers,
however, a discussion of all the proteins is beyond the scope of this chapter, hence,
this discussion has been limited to some extensively studied proteins, namely col-
lagen, gelatin, and silk.
13.4.1.1.1 COLLAGEN. Collagen is a major protein constituent of ECM of
connective tissues, such as bone, tendon, ligament and cartilage [114]. At least 27
different types of collagen which differ in their structure, function, and location
have been identifi ed in mammalian tissues, of which collagen type I is the most
abundant form [115].
All the collagen types share a common triple helical domain that has a
characteristic primary structure, with repeated sequence of (G-X-Y) n units,
where G is glycine, X is alanine or proline and Y is hydroxyproline [116]. Being
a component of the natural ECM milieu, collagen has gained popularity in
tissue engineering as a material for the synthesis of electrospun scaffolds
[89,117] .
Matthews et al. studied electrospinning of different collagen types such as
collagen type I and type III into nanofi bers [89]. Collagen type I nanofi bers were
obtained with an average diameter of 100 nm, and 1, 1, 1, 3, 3, 3 hexafl uoro - 2 -
propanol (HFP) was used as the solvent. An important observation made by
authors was the presence of 67 nm banding pattern in the nanofi bers which is a
characteristic of collagen in its native form, thereby indicating that the process of
electrospinning maintains the native structure of collagen. In another study, Shih
et al. synthesized collagen type I nanofi bers using HFP as the solvent system
and studied the infl uence of collagen concentration on fi ber diameter. Their
results demonstrated an increase in fi ber diameter with an increase in collagen
concentration [39] .
Collagen type II is a native constituent of articular cartilage. Hence, electros-
pinning of collagen type II could be a promising approach for in vitro cartilage
tissue engineering. To validate this rationale, Shields et al. fabricated collagen
type II scaffolds by electrospinning, and cross-linked the same with glutaralde-