NANOTECHNOLOGY: A TOOLKIT FOR CELL BEHAVIOR - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 2

of the tissue's and organ's function. Simultaneously, in recent years, many health professionals have
been advocating for a more active lifestyle with increased exercise and thus an increased risk of injury.
These factors, and many others, put a strain on existing treatment methods and hallmark their many
weaknesses. For most tissue damage caused by diseases or injuries, many current treatment methods
lack the ability to restore the affected area to a level of functionality equivalent to healthy native tissue.
They instead provide a stop-gap or temporary solution that either slows the progress of further degen-
eration or requires sacrifice of other healthy tissue (autografts). Many researchers and doctors hope that
by increasing understanding of how cells and tissues interact on the nano scale and creating biomimetic
nanostructured tissue constructs to better emulate natural designs, solutions that more effectively treat
diseases and injuries can be discovered.
In the following sections, we will focus on the current state of nanotechnology for a series of tissue
and organ regeneration. In addition, we will put special emphasis on integrating cutting-edge 3D nano/
microfabrication techniques with nanobiomaterials for complex tissue and organ regeneration applica-
tions. These nanobiomaterial constituents can be made of nearly any material imaginable, including
carbon nanomaterials, self-assembly nanomaterials, natural or synthetic polymers, ceramics, drug-
containing spheres, or metal particles. Researchers strive to combine the appropriate nanobiomaterials,
cells, and growth factors to create the ideal biomimetic tissue engineered construct that could surmount
traditional methods of injury mitigation.
1.2 NANOBIOMATERIALS FOR TISSUE REGENERATION
1.2.1 CARBON NANOBIOMATERIALS
1.2.1.1 Carbon Nanotubes
Carbon and carbon derivatives are some of the most versatile nanomaterials that tissue engineers have
in their arsenal ( Zhang et al . , 2009a ; Tran et al . , 2009 ). In addition to constituting 18% of the aver-
age human body by mass ( Frieden, 1972 ), carbon is a highly flexible element that can assume many
nanometer-sized structures. One of the most well-explored carbon nanomaterials is carbon nanotubes
(CNTs) ( Figure 1.1 ). CNTs have several different types, but those used in the tissue engineering field
are primarily multiwalled CNTs (MWCNTs) or single-walled nanotubes (SWCNTs). They are one of
the strongest materials known ( Yu et al . , 2000 ; Terrones, 2004 ), and can exhibit semiconducting ( Jung
et al . , 2013 ) and conducting ( Lan and Li, 2013 ) properties, making them interesting media for stimulat-
ing tissue regeneration.
One of the most prominent features of CNTs is their ability to significantly influence the electrical
conductivity of scaffolds. This trait is of particular interest to groups studying tissues that rely heav-
ily on signaling to perform functions, such as cardiac tissue. In one example, gelatin methacrylate
hydrogel scaffolds modified with incorporated CNTs expressed improved cell behavior when seeded
with rat cardiomyocytes. The tissue exhibited increased synchronous beating rate and a significantly
lower threshold for excitation when compared to control samples without incorporated CNTs ( Shin
et al . , 2013 ). Furthermore, CNTs also tend to increase cardiomyocyte proliferation and maturation in
vitro ( Martinelli et al . , 2013 ; Shin et al . , 2013 ; Martinelli et al . , 2012 ). Although CNTs are used for
several other fields within tissue engineering, they appear to selectively steer mesenchymal stem cells
(MSCs) toward a cardiac lineage when introduced into cell culture media and exposed to electrical
stimulation ( Mooney et al . , 2012 ).