Page 136 - IJB-4-2

Mandt D, et al.

Figure 7. Cell Layer adhered to the walls of a GelMOD-AEMA placental membrane.(A) Fluorescence images show the cell layer
formation of HUVEC on the membrane wall. The image enlargement on the right side shows a two-dimensional image of HUVECs
growing on the channel wall. Furthermore, BeWo B30 cells were recognized on the other side of the membrane. (B) Light microscope
images taken after 7 days of incubation clearly show a continuous dense cell layer. (C) In the enlargement, it becomes clear that cells are
attached to the membrane at different heights, which is demonstrated by the fact that cells out of focus appear blurry.

research. Therefore, flow profiles of the maternal and of maternal high blood pressure in vitro. The chip
fetal blood, and its changes in course of the pregnancy, molds were made of a PEGdma hydrogel. The main
have to be considered [1,3,22,23] . advantage of using this material is its permeability. After
In this study, three-dimensional geometries within chip finalization, components of the structure material
a microfluidic channel were produced from a gelatin- diffused into the mold material. This feature guarantees
based hydrogel material, mimicking the basal membrane a seamless transition between mold and structure
of the placenta. Gelatin, used as substrate or scaffold material. Furthermore, the attachment of the membrane
material, is reported in various studies in the field of to the cover and bottom glass surfaces was ensured
tissue engineering [24–27] . The material used in this study through their methacrylation via silanization. This
was a methacrylamide- and methacrylate-modified pretreatment step was performed, as silanization of glass
gelatin hydrogel. GelMOD is reported to be applicable surfaces is known to improve the adhesion properties of
[11]
for cell based experiments, as polymerized GelMOD polymer materials by covalent bonding . The complete
mimics the cellular microenvironment and thus favors sealing of the membrane resulted in two separated
the cell attachment and proliferation [8,10,28] . Preliminary cul tivation channels. As a consequence, the two
biocompatibility experiments have shown a slight different compartments of the placental interface were
decrease in viable cell count when cells were plated mimicked. This is also important to make the model
on GelMOD-AEMA only, but this drawback was visible for the use in transportation studies later on, as
successfully tackled by using fibronectin coatings. The it is a prerequisite to guarantee that changes are due
improved proliferation of both cells can be explained to active cell transport and not leakage at connections
by the fact that the extra cellular matrix (ECM) proteins points. The complete tightness of the membrane, and
gelatin and fibronectin promote cell adhesion and thus its adhesion to the bottom and cover material as
spreading . Several studies have shown that fibronectin well as its connection to the mold, was verified with
[29]
plays a predominant role in adhesion processes, to a large molecular weight dextran solution. Membrane
neighboring cells as well as to substrate material, in permeability to sugar-sized substances was demonstrated
various cell types [30–33] . The coating layer facilitates the with riboflavin. Fluorescence intensity analysis con-
attachment of the cell as the applied fibronectin can firmed the selective transport of small molecules across
firmly bind to fibronectin deposits in the ECM . the membrane in a time-dependent manner. We proved
[33]
The photosensitive gelatin material was polymerized that measured diffusion of nutrient in subsequent
induced by two-photon absorption of precisely focused experiments is only dependent on the semi-permeable
laser irradiation. Photo-induced crosslinking was there- properties of the membrane and not a result of leakages
by depending on the presence of photoinitiators. One in the construct itself. Thereby, the barrier thickness
of the demands placed on this compound was its water in the tested range does not noticeably influence the
solubility. Sodium dipropanoate-based P2CK fulfills diffusion behavior.
this requirement and proved to be efficient in material The barrier model with its two separated channels
formulations containing up to 90% water [36] . The has the advantage that two cell types can be cultivated
x-shaped cultivation chamber not only facilitates the in their respective cell culture media at the same time.
addition of the viscous material GelMOD-AEMA but Nevertheless, diffusion and mixing of media components
also allows the separate perfusion of the two generated through the membrane may take place. Therefore, the
culture channels, allowing for instance the simulation effect of mixed media, here termed co-culture media,

International Journal of Bioprinting (2018)–Volume 4, Issue 2 9