NANOTECHNOLOGY: A TOOLKIT FOR CELL BEHAVIOR - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 13

bare controls. This synergistic effect of combining a microfibrous scaffold with nanomaterial coatings
also illustrates the importance of biomimetic nanocomposites in tissue engineering.
Other even more novel methods of scaffold fabrication are constantly being explored, Fan et al .
were able to draw out superaligned CNT yarn and apply it to neural tissue engineering. The yarns de-
scribed are not only biomimetic and able to direct neural growth ( Fan et al . , 2012 ), but exist as a transi-
tion between traditional fabrication methods and customizable scaffold design. One could imagine the
customization of the weave of the yarn ( Figures 1.5 C and D ) to the dimension of a neural defect in a
particular subject, enabling researchers and medical professionals to adapt to the individual situation
present in each animal model or human patient.
1.3.2 3D PRINTING OF NANOMATERIAL SCAFFOLDS FOR TISSUE REGENERATION
1.3.2.1 3D Printing Techniques for Tissue Regeneration
As an emerging 3D tissue manufacturing technique, 3D printing offers great precision and control of
the architecture of a scaffold, and prints complicated structures that closely mirror biological tissues
( Derby, 2012 ). 3D printing has become a driving force in the tissue engineering field with the advent of
personalized medicine and the growing interest in complex tissue and organ regeneration ( Tasoglu and
Demirci, 2013 ; Lee and Wu, 2012 ; Cui et al . , 2012 ; Koch et al . , 2012 ; Catros et al.; 2012 , Fedorovich
et al . , 2012b ; Shim et al . , 2011 ; Gruene et al . , 2011 ; Catros et al . , 2011 ; Song et al . , 2010 ; Ovsian-
ikov et al . , 2010 ; Detsch et al . , 2011 ; Warnke et al . , 2010 ; Moon et al . , 2010 ; Holmes et al . , 2014a ).
Most 3D printers have micrometer resolutions far above the nano scale, but are still a viable tool for
nanomaterial fabrication and manipulation. Unlike traditional manufacturing techniques, 3D printing
can deliver materials and cells to precise locations, resulting in constructs that can take advantage of
computer-aided designed (CAD) and biomimetic morphology to create shapes that would be difficult
or impossible to manufacture traditionally. All 3D printing methods operate upon similar principles.
To fabricate a solid object, a CAD model is first input to a program that parses the solid object into a
stack of thin axial cross-sections. These cross-sections are then converted into directions that describe
the movement of the effector in 3D space. The effector deposits material, solidifies resin, or otherwise
performs an action that prints the CAD model itself and is controlled to reproduce each cross-sectional
slice delivered to the printer. Finally, all of the individual elements come together and the construct is
serially printed from the bottom up.
It is important to note that 3D printing techniques can print materials with or without incorporated
cells, and each approach comes with various advantages and disadvantages. The major defining dif-
ference between the two is that bioprinting cells must maintain an environment that facilitates cellular
survival, and mitigates contamination or infection. 3D printing will be discussed at length later in this
topic, but briely, several common methods ( Figure 1.6 ) include inkjet bioprinting ( Ferris et al . , 2013 ),
bioplotting ( Fedorovich et al . , 2012a ), fused deposition modeling ( Kundu et al . , 2013 ), selective laser
sintering, and stereolithography ( Suri et al . , 2011 ). One of the advantages of 3D printing is the ability
to create custom-designed tissue constructs with complex internal architecture and biomimetic external
architecture. As illustrated in Figure 1.7 A, an MRI image of human osteochondral tissue defects is
reconstructed into a unique CAD model. This patient-specific, osteochondral construct can be printed
to perfectly integrate with the defect site and expedite tissue regeneration. Figures 1.7 C-G show that
several custom-designed 3D poly(ethylene glycol) diacrylate (PEG-DA) hydrogel scaffolds with vary-
ing pore sizes were fabricated via a stereolithography printer in our lab.