THE POWER OF CAD/CAM LASER BIOPRINTING AT THE SINGLE-CELL LEVEL: EVOLUTION OF PRINTING - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 84

FIGURE 4.5
Cell center velocity during printing process ( Wang et al . , 2009 ).
It has been found that the cell can initially accelerate as high as 10 9 m/s 2 at the beginning period of
bubble expansion and then quickly approach zero in an oscillatory manner. Fortunately, this period
of high acceleration is very brief, only lasting about 0.1 m is The pressure that the cell experiences can also
be very high at the beginning period of bubble expansion, but quickly decreases to zero in an oscillatory
manner, as seen from the cell acceleration evolution. The top surface region of the cell usually experienc-
es the highest pressure level, followed by the bottom surface and then middle regions ( Wang et al., 2009 ).
4.3.1.2 Modeling Laser-Matter Interaction Induced Thermoelastic Stress
In general, and during cell deposition, localized heating and thermal expansion of a material cause
thermoelastic stress. Two confinement conditions are necessary for the prominent generation of the ther-
moelastic stress: (1) the laser pulse duration should be much shorter than the characteristic thermal
relaxation/diffusion time, and (2) the laser pulse duration should also be shorter than the characteristic
acoustic relaxation time to achieve a high-amplitude thermoelastic stress wave. If the laser beam size
is taken as finite (laser spot diameter is comparable to the optical penetration depth), the wave genera-
tion becomes 3D, which can be solved analytically using Green's function. Unfortunately, however,
this approach usually assumes the wave propagation is within a homogenous infinite medium. The
image source method has also been explored to model this wave propagation challenge when one of
the boundaries is rigid ( Paltauf et al., 1998 ). However, the coating layer during MAPLE-DW is usually
very thin. Consequently, this layer cannot be treated as an infinite medium as in a 2D case and the wave
is reflected at the free surface. To better understand the effect of thermoelastic stress on the cell injury,
the thermoelastic stress wave propagation is modeled here by considering the unique boundary conditions
which are different from other previous studies, such as Paltauf et al. (1998) .