DESIGNING NANOFIBROUS SCAFFOLDS FOR TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 431

physiological activity of the native tissue [3]. Therefore, there is a need for alter-
native strategies to overcome the shortcomings associated with the aforemen-
tioned approaches [3].
Tissue engineering has emerged as a potential approach to overcome the
shortage of tissues and organs by combining a biodegradable scaffold [as a
temporary extracellular matrix (ECM)] and cells to create functional tissue
replacements. Tissue engineering [3] has been defi ned as: “The application of the
principles and methods of engineering and life sciences toward the fundamental
understanding of structure-function relationships in normal and pathological
mammalian tissue and the development of biological substitutes to restore, main-
tain, or improve tissue function [4,5].”
The development of a biological substitute for the restoration of tissue func-
tion can involve multiple steps. The major stages involved in any tissue engineer-
ing approach can be classifi ed as:
(1) Identifi cation and isolation of a suitable source of cells;
(2) in vitro or ex - vivo expansion of cells to generate appropriate numbers;
(3) design of a scaffold/device to either carry cells and/or encapsulate growth
factors (GFs);
(4) uniform seeding of cells onto or into the scaffold/device;
(5) appropriate culture of the seeded cells; followed by
(6) in vivo implantation of the engineered construct [6] (Figure 13.1 ).
Thus cells and scaffolds, with or without growth factors, together hold a
promise for both in vitro regeneration of neo-tissue and in vivo regeneration of
damaged tissue. Functional restoration for a large number of tissues is currently
under investigation. Of these, the musculoskeletal tissues such as bone, cartilage,
muscle and tendon have received increased attention [7].
All tissues/organs consist of tissue specifi c cells which are present in a well-
defi ned manner within a complex structural and functional network of molecules
that form the extracellular matrix. The variation in ECM composition and con-
tents along with the respective cell type governs the diverse properties and func-
tion of each tissue and organ [8]. In addition, ECM is also a key component during
dynamic events of tissue such as growth, development, repair, and regeneration.
It acts as a reservoir for signaling molecules, which in turn have the potential to
guide cell fate processes. Therefore, cells and ECM molecules along with GFs can
be considered as the most important components for tissue regeneration.
One can follow two strategies for tissue repair or regeneration: First, cell-
based therapy, wherein desired cell types can be injected directly into the defect
site, and, second, scaffold-based tissue regeneration wherein a scaffold (artifi cial
ECM) in combination with cells and/or GFs is used for tissue regeneration [9].
Cell therapy has played an important role in tissue repair including autolog-
ous chondrocyte implantation (ACI), and the commercially available carticel
[10,11,12]. However, tissues have three-dimensional (3D) structure that prompts