NANOTECHNOLOGY: A TOOLKIT FOR CELL BEHAVIOR - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 14

FIGURE 1.6
Several typical 3D printing systems. Image is from O'Brien et al. (2014).
A quickly growing fabrication method for more detailed structures is a technique called two-
photon polymerization. Here, two light sources are used: one to excite the material to an inter-
mediate state, and another to initiate crosslinking. Through this method, scaffolds can be created
with feature sizes of less than 10 m m, allowing researchers to generate CAD models on a smaller
scale, and print constructs in various specific geometries with high resolution. Femtosecond laser
two-photon polymerization is one of the highest-resolution 3D printing technologies in use today.
Initially, only commercially available polymers ( Ovsianikov et al . , 2007 ) could be printed, which
may have lacked necessary physical, chemical, and cell favorable characteristics needed for biomi-
metic tissue engineering. Some materials, such as 4,4 9 -bis(dimethylamino)benzophenone (SZ2080),
can support cell growth and migration ( Raimondi et al . , 2013 ), and have effectively demonstrated
that cells can react to microgeometries with pores varying from 10 to 30 m m. Scaffolds with graded
microporosity outperformed single-dimension microporous scaffolds, and cells tended to migrate
to designed niches on the surface of the scaffold, as opposed to flat surfaces. The biocompatible
PEG was used in two-photon polymerization printer to produce engineered 3D scaffolds ( Torgersen