Fabrication of perforated microcavities for cell cultures

Today, a variety of processes is available for the production of two-dimensional and three-dimensional microstructured polymer components. The current state of the art, however, meets with considerable problems in particular when fabricating microporous cavities that are required for e.g. 3dimensional cell cultures (Fig. 1). With a few exceptions, such as the fabrication of so-called microporous hollow fibers by extrusion and phase inversion processes, defined microperforation of already existing microcavities by laserbased or lithographic methods applied to individual, isolated structures is possible only when the structure is rotated and repositioned in the directed beam. For this, a high expenditure is required. Moreover, shadowing, diffraction, and scattering effects in components of high structural density limit a subsequent microperforation to a small proportion of the accessible areas. Here we are presenting a novel process based on the microthermoforming technique [1] in combination with the ion track technology, allowing a rapid and efficient fabrication of three-dimensional microporous components. In the macroscopic world, thermoforming is a major process applied in packaging industry. Thermoplastic semi-finished products are fixed at their edges, heated, and stretched to three-dimensional components in their viscoelastic state, as a result of which wall thickness is reduced [2]. Microthermoforming results from a special process, the so-called trapped sheet thermoforming. Here, the thin semifinished film is fixed between the two metal plates of the forming tool that are pressed onto each other. By these plates, the polymer film is heated conductively to forming temperature. One-sided application of a pressurized gas causes the elastic film to be cast into the cavities of the microstructured mold that have been evacuated in advance. By cooling down the structure, the new shape of the film is frozen and the component can be demolded.