Nanomedicine - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 146

located. The roots are growing in each microchannel and, depending on the media
in a specific microchannel, the roots display different characteristics of growth. The
roots are further treated with plant pathogens, and their interaction with living roots
is observed.

4.3 Artificial Tissues and Organs

The growth of artificial tissues and organs built using nanotechnologies and
nanomaterials is one of the most important tasks of nanomedicine. The transplant of
organs has always two main drawbacks: (1) the very limited availability of organs
to be transplanted, which generate very long waiting lists and (2) the high cost of
transplants. Therefore, there are very serious researches and tests aimed at recreating
human organs based on the principles of micro- and nanotechnologies. The most
striking example is the nanomedicine domain termed as tissue engineering.
The aim of tissue engineering is the implementation of an artificial media able to
allow the development and organization of cells into tissues with the same properties
as the in vivo tissue to be replaced ( Dvir et al. 2011 ). In this way, the engineering
of liver ( Uygun et al. 2010 ), arteries ( Gui et al. 2009 ), bones ( Grayson et al. 2010 ),
and lungs were achieved ( Petersen et al. 2009 ).
So, the main task of tissue engineering is to create artificial scaffolds, which
imitate the extracellular matrix (ECM), which represents the extracellular part of a
tissue that provides structural support to the cells and allows intercellular commu-
nication. A direct way to engineer delicate tissues and organs is to decellularize
an organ or a tissue to get the ECM, and then reseed the ECM scaffold with
new cells. The new cells recognize their natural environment and start to self-
organize so that, after few days, they are able to perform the pump function of
a decellularized rat heart after applying electrical and physiological stimuli, for
example ( Ott et al. 2008 ). In this way, a bioartificial heart is born again.
The ECM is a biomolecular fibrous mesh in which the cells grow, differentiate,
and travel. Therefore, there are strong interactions between cells and ECM. The
ECM is synthesized by the cell; cells self-assemble and decompose various ECM
components, and at the same time, ECM dictates various cell functions. Cells are
attached to ECM through specific molecules termed as integrins, which recognize
amino acid sequences using surface receptors (see Fig. 4.25 ).
The ECM is composed from various molecular components ( Biondi et al. 2008 ):

• Collagen, which is a fibrillar protein that forms the backbone of the ECM and has

multiples roles in cell-cell interaction and cell-ECM interaction while providing
mechanical resistance to ECM at tensile mechanical stresses

• Proteoglycans, which are carbohydrate polymers, with the role of filler substance

between cells, resistance to compressive stress transport of molecules in ECM,
cell adhesion, migration, and signaling