Microfabrication of Chip-sized Scaffolds for Three-dimensional Cell cultivation

Hello, my name is Stefan Re.I'm working at the Institute of Biological Interfaces and in the following article you will see the fabrication process of a micro structured scaffold called ship, and we're using two different methods to produce this chips. Currently a heart embossing process combined with certain subsequent processes and a microthermal forming process, which was recently developed here at the research center called Squi, And now we're in a clean room tent and what you can see here on the right side is a typical vacuum hotted boxing machine, and we we're using this equipment for the fabrication of the micro structured cell chip. First of all, we're introducing a micro structured mode.

This is mounted here in such a plate, and you can see here two molds. This mold is fabricated by micro machining and it is made from breath. Now I'm mounting the microstructure mold into the machine.

For the hotboxing process, we're using polymer plates like this one here, and typically we're using polycarbonate or PMA for the production of the cell chip. Now we're inserting the polymer plate into the machine into the center of the plate, closing the tool. After closing the machine, the chamber is evacuated, then the pole mold is, or the whole tool is heated up to forming temperature, and then the warm polymer is pressed into the mold with the microstructure.

Then after this molding procedure, the whole mold is cooled down and we have an automatic demoing process within this machine. What you can see here is such a molded cell chip with the molded parts, two cell chips and a typical residual layer, which results from the Hot and bussing process. After the hot and busing steps, the residual layer of The parts have to be thin down and finally completely eliminated.

So for this, the parts are trimmed, the mold parts, and then frozen on this mounting plate. After the mounting, we are milling the residual layer down to a certain thickness of the part so that the microstructure grid is opened on the back. During the milling process, the micro container walls are stabilized by frozen water.

Finally, we obtain two molded cell chips with freestanding grids of MicroCon containers that are open on both sides on top, and at the bottom we are bonding. Then after the milling process, a porous membrane to the back of these open MicroCon container arrays. We're bonding a perforated, Commercially available polycarbonate membrane to the back of the open cell ship to obtain microporous container arrays.

For this, we're inserting thin polymer track edge membranes into this chamber. The membranes are in a thickness range of about 10 microns, and then we're putting the cell chip on top of these membranes. We're closing then this cavity, and in the first step the chamber is evacuated.

Then we're injecting vaporized solvent to solve the surface of the polymer, and by applying force to this stack, the membrane is bonded to the cell ship. In the final step, the chamber is rated and we take out the finalized cell ship. Recently we've developed a new fabrication Technique for the sechi based on a thermoforming process, and it is adapted to the microscale and therefore we called it micro thermoforming.

For the fabrication of a porous sechi, we're using polyfils that were irradiated with accelerated heavy ions. This is done in a corporation with the case at at the Unilog in, and these heavy ions are producing Latin tracks in the poly of film by penetrating completely through the polymer film. And during thermoforming process, these Latin tracks are preserved and to produce these pores.

Then after the forming process where etching these Latin tracks To pores with a defined size. Here you can see on the right side The adapted machine. A hot embossing machine adapted for this microthermal foing process.

The tool consists mainly of three parts, an upper plate and a low plate. They keep with connectors for gas pressure and evacuation, and a third part is here such as ceiling. In the first step, we're putting in a thin form of film in the range of about 50 to a hundred microns and thickness.

Then we're closing the tool and and a second step. The chamber built by these two plates and the ceiling is evacuated. After the evacuation, the polymer film is pressed between those two plates and we're heating it up then to forming temperature.Forming.

Temperature here is in the range of the glass transition temperature, which means that the polymer is not melted, but we have a polymer in a whi elastic state or in a rubber elastic state. In a subsequent step, then we applying a gas pressure. Here we are using nitrogen as a gas, and by this gas, the rubber elastic polymer film is then stretched into the previously evacuated micro molds.

After this forming step, the whole tool is cooled down and the tool is opened. Finally, the microstructure polymer foam is then demold manually. The advantage of this new process is that the number of process steps can be dramatically reduced compared to the standard micro injection molding process or the Hot embossing process.

After thermoforming of the heavy ironed polymer films, we're etching these Latin track selectively to pores with a defined size. For this, we're using a simple glass speaker set up, and with the Latin tracks are etched with sodium hydroxide, gently steered and heated up to a temperature of approximately 60 degrees. Thatching procedure lasts about one to several hours and to obtain pores with a different pore size.

Here we have now the two finished products, the hot and bused cell chip with the micropores membrane on the back of the molded cell chip. And here in my left hand the thermoformed thin walled flexible cell chip. And before we use them in cell culture, they're cleaned and sterilized by gumma irradiation.