Page 86 - IJB-9-4

International Journal of Bioprinting Laser transfer for CTC isolation

Figure 2. The physical basis of BA-LIFT transfer. The pulsed UV laser ablates a small portion of the polyimide film (a), generating a hot gas that produces
a plastic deformation in the remaining polymer layer (b). The blister generated in this way pushes the liquid layer, leading to a jet formation that, after
collapsing by surface tension, produces the droplet that is transferred to an acceptor substrate or any other receptacle (c). In this case, the droplet contains
the selected cell.

problem of avoiding direct laser irradiation of the cells. of the liquid. The process has been widely studied [53,69-72]
Therefore, set-ups comprising a transparent donor mainly for polyimide sacrificial layers with thickness up to
substrate coated with an energy absorption layer, acting 10 µm deposited by spin-coating. Some of the authors of
as a sacrificial layer, have been proposed to avoid direct this work have previously discussed the potential of this
interaction between the laser light and the liquid media approach for cell identification and sorting with very good
containing living cells. A common approach is to use a survival results for different types of cells, including mouse
thin sacrificial absorption layer made of a biocompatible hematopoietic progenitor stem cells .
[73]
metallic material (titanium, silver, gold, etc.) [52,53,64-67] . In our approach, described in detail in the Methods
This thin film acts as a dynamic release layer, whose section, we used a donor structure made with a
thermal expansion after laser irradiation propels the commercial polyimide film with a thickness of 30 µm.
liquid generating a jet that finally collapses, producing the The main advantage of using thick polyimide films is its
desired droplet transfer. Although good cell viability after high absorption in the UV range, efficiently absorbing
printing has been demonstrated with sacrificial metallic the laser beam and avoiding direct cell irradiation or even
layers, some heating and residual contamination of the heating of the liquid sample [62,69,73] . On the other hand, the
liquid is unavoidable. For that reason, when using very use of polyimide presents other advantages: the material
sensitive biological samples or when a fundamental is partially transparent to the visible light so fluorescence-
[68]
goal is to maintain the cells as intact as possible, other vision and techniques for cell recognition and selection
approaches can be envisaged. In our work, we consider it can be used, even in a compact optical arrangement in
is a priority to protect the cells not only from direct laser which fluorescence and vision arrangements share the
irradiation but also from a possible residual heating by same optical path that the laser beam used to produce the
designing a specific approach based on the standard BA- liquid transfer .
[73]
LIFT process.

2.2. Adaption of the BA-LIFT technique for single- 3. Methods
cell isolation 3.1. Cell isolation using laser direct write
Experimental set-up BA-LIFT uses an intermediate layer MDA-MB-231 cell line (derived from breast cancer),
between the donor substrate and the liquid but made of obtained from ATCC (American Type Culture Collection
a polymer that, under laser irradiation, partially vaporizes (ATCC), Manassas, VA) was cultured in Dulbecco’s
creating a vapor bubble that induces an elastic and Modified Eagle Medium (DMEM) supplemented with 10%
plastic deformation in the remaining material (Figure 2). fetal bovine serum (FBS) and 1% penicillin/streptomycin.
Consequently, a blister in the viscoelastic material is Cells were maintained in a humidified atmosphere of 5%
produced whose dynamics induces mechanical propulsion CO in air. Following culture, cells were harvested using
2

Volume 9 Issue 4 (2023) 78 https://doi.org/10.18063/ijb.720