Felix Bauer

Controllable cell adhesion, growth and orientation on layered silk protein films

Due to their mechanical stability, biocompatibility and biodegradability, silks are promising materials for various biomedical applications including tissue engineering. Since the shape and the organisation of cells in and on scaffolds both affect their function, we tested patterned silk scaffolds made of three different silk proteins concerning their influence on cell adhesion, growth and orientation. Two different cell lines, BALB/3T3 fibroblasts and C2C12 myoblasts, showed controllable cell adhesion as well as orientation dependent on the silk proteins used and patterns made. Surprisingly, the presence of the integrin binding motif RGD did not influence cell adhesion and orientation on structured silk films, although it did so significantly on flat films.

Artificial Egg Stalks Made of a Recombinantly Produced Lacewing Silk Protein

Rigid threads: Lacewings protect their eggs from predators by laying them on small stalks (see picture). The stalks have good mechanical properties and, unlike most other silks, a cross β structure. An artificial egg stalk was produced using a designed recombinant variant of a sequenced lacewing egg stalk protein, and it attained 90 % of the tensile strength of a natural egg stalk.

Dependence of mechanical properties of lacewing egg stalks on relative humidity.

Silk fibers are well known for their mechanical properties such as strength and toughness and are lightweight, making them an interesting material for a variety of applications. Silk mechanics mainly rely on the secondary structure of the underlying proteins. Lacewing egg stalk silk proteins obtain a cross-β structure with individual β strands aligned perpendicular to the fiber axis. This structure is in contrast with that of silks of spiders or silkworms with β strands parallel to the fiber axis and to that of silks of honeybees with α helices arranged in coiled coils. On the basis of the cross-β structure the mechanical properties of egg stalks are different from those of other silks concerning extensibility, toughness, and bending stiffness. Here we show the influence of relative humidity on the mechanical behavior of lacewing egg stalks and propose a model based on secondary structure changes to explain the differences on a molecular level. At low relative humidity, the stalks rupture at an extension of 3%, whereas at high relative humidity the stalks rupture at 434%. This dramatic increase corresponds to breakage of hydrogen bonds between the β strands and a rearrangement thereof in a parallel-β structure.

In Situ and Ex Situ Characterization of PFSA-Inorganic Inclusion Composites for Medium Temperature PEM Fuel Cells

It is known, that by addition of zirconium layered phosphate (ZP) to perfluorinated sulfonic acid ionomers (PFSA), the proton conductivity of the composite decreases, but the high temperature stability and electrical efficiency increases as compared to the unmodified PFSA membrane. In order to clarify this finding, mechanical properties and conductivity of a commercially available PFSA ionomer (Nafion®117), PFSA-ZP and PFSA-calcium phosphate (CP) composites were examined ex-situ and in-situ under conditions similar to fuel cell application. The results indicate a strong columbic interaction between the organic and inorganic ZP phase, which at the same time increases the stiffness and Tg by ionic cross-linking and decreases conductivity. The interaction is more pronounced at low water activity. A threshold of about three water molecules per sulfonic acid group was identified, above which a significant increase in proton conductivity is achieved and, concomitantly, most of the mechanical stiffening effect has vanished. CP as inorganic additive, however, has a tendency to be washed out of the ionomer, most probably due to the high acidity of Nafion®.

Microwave Decomposition of Metal Alkoxides to Nanoporous Metal Oxides – a Mechanistic Study

Synthesis of nanoscaled TiO2 and ZrO2 by pyrolysis of metal alcoholate – paraffin emulsions using microwave heating (Colloidal Microwave Pyrolysis, CMP) as well as conventional heating (Colloidal Conventional Pyrolysis, CCP) is described. The ceramic yield of the inorganic products, the pore structure, grain size and phase composition of the nanoscaled oxides is influenced to a lesser extend by the heating method as by the organic by-products. Different reaction paths are found for Ti-alcoholate as compared to Zr-alcoholate. A mechanism is proposed for the decomposition of each alcoholate, showing that microwave heating enhances the catalytic activity of the oxide powders generated during the reaction.

Facile Photochemical Modification of Silk Protein-Based Biomaterials

Silk protein-based materials show promise for application as biomaterials for tissue engineering. The simple and rapid photochemical modification of silk protein-based materials composed of either Bombyx mori silkworm silk or engineered spider silk proteins (eADF4(C16)) is reported. Radicals formed on the silk-based materials initiate the polymerization of monomers (acrylic acid, methacrylic acid, or allylamine) which functionalize the surface of the silk materials with poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(allylamine) (PAAm). To demonstrate potential applications of this type of modification, the polymer-modified silks are mineralized. The PAA- and PMAA-functionalized silks are mineralized with calcium carbonate, whereas the PAAm-functionalized silks are mineralized with silica, both of which provide a coating on the materials that may be useful for bone tissue engineering, which will be the subject of future investigations.