Abstract

The microenvironment of cells in vivo is defined by spatiotemporal patterns of chemical and biophysical cues. Therefore, one important goal of tissue engineering is the generation of scaffolds with defined biofunctionalization in order to control processes like cell adhesion and differentiation. Mimicking extrinsic factors like integrin ligands presented by the extracellular matrix is one of the key elements to study cellular adhesion on biocompatible scaffolds. By using special thermoformable polymer films with anchored biomolecules micro structured scaffolds, e.g. curved and µ-patterned substrates, can be fabricated. Here, we present a novel strategy for the fabrication of µ-patterned scaffolds based on the “Substrate Modification and Replication by Thermoforming” (SMART) technology: The surface of a poly lactic acid membrane, having a low forming temperature of 60°C and being initially very cell attractive, was coated with a photopatterned layer of poly(L-lysine) (PLL) and hyaluronic acid (VAHyal) to gain spatial control over cell adhesion. Subsequently, this modified polymer membrane was thermoformed to create an array of spherical microcavities with diameters of 300 µm for 3D cell culture. Human hepatoma cells (HepG2) and mouse fibroblasts (L929) were used to demonstrate guided cell adhesion. HepG2 cells adhered and aggregated exclusively within these cavities without attaching to the passivated surfaces between the cavities. Also L929 cells adhering very strongly on the pristine substrate polymer were effectively patterned by the cell repellent properties of the hyaluronic acid based hydrogel. This is the first time cell adhesion was controlled by patterned functionalization of a polymeric substrate with UV curable PLL-VAHyal in thermoformed 3D microstructures.

A novel high-temperature micro-tensile setup allows the characterization of the elastic and plastic as well as creep behavior of free-standing thin films at temperatures of up to 1000 °C. Correspondingly, a new layout for free-standing thin film tensile test structures has been developed, enabling accurate self-alignment upon loading. Furthermore, a differential optical strain measurement technique as well as optimizations of the optical path has been implemented, providing a strain resolution of well below 1 × 10(-4) at 1000 °C. Two different polycrystalline SiC free-standing thin films have been investigated in tension to acquire stress-strain data and corresponding Young's modulus at up to 1000 °C. The high sensitivity of the strain measurement technique makes it also possible to identify creep strains in the high-temperature regime.

Abstract