Adsorption of proteins onto solid surfaces is an everyday phenomenon that is not yet fully understood. To further the current understanding, we have performed in situ ellipsometry studies to reveal the adsorption kinetics of three different proteins, lysozyme, α-amylase and bovine serum albumin. As substrates we offer Si wafers with a controlled Si oxide layer thickness and a hydrophilic or hydrophobic surface functionalization, allowing the tailoring of the influence of short- and long-range interactions. Our studies show that not only the surface chemistry determines the properties of an adsorbed protein layer but also the van der Waals contributions of a composite substrate. We compare the experimental findings to results of a colloidal Monte Carlo approach that includes conformational changes of the adsorbed proteins induced by density fluctuations.

It is well-known that amelogenin self-assembles to form nanoparticles, usually referred to as amelogenin nanospheres, despite the fact that not much is known about their actual shape in solution. In the current paper, we combine SAXS and DLS to study the three-dimensional shape of the recombinant amelogenins rP172 and rM179. Our results show for the first time that amelogenins build oblate nanoparticles in suspension using experimental approaches that do not require the proteins to be in contact with a support material surface. The SAXS studies give evidence for the existence of isolated amelogenin nano-oblates with aspect ratios in the range of 0.45−0.5 at pH values higher than pH 7.2 and show an aggregation of these nano-oblates at lower pH values. The role of the observed oblate shape in the formation of chain-like structures at physiological conditions is discussed as a key factor in the biomineralization of dental enamel.

One of the most fascinating topics currently being discussed in the field of biomineralization is the occlusion of organic macromolecules within mineral crystals. It is already known that intracrystalline organic inclusions in biogenic calcite improve the fracture behavior and anisotropically distort the calcite lattice. However, the detailed structure of the crystals and the underlying processes leading to the incorporation of the organic molecules are poorly understood. In this work, we investigate calcite prisms extracted from the shell of Pinna nobilis by means of three-dimensional synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS). Organic–inorganic interfaces within the single crystals give rise to a strong, anisotropic SAXS signal. The results are shown as a stereographic projection of the integrated SAXS intensity (gray scale) together with the wide-angle spots (colored) of different calcite lattice planes. A comparison of native (left) and annealed (right) prisms, where the contrast for the latter is enhanced due to the removal of organics, shows a preferential orientation along the highly charged (001) lattice planes, which strongly interact with negatively charged aspartate groups of intracrystalline proteins. Our findings on the nanostructure help to understand how biogenic calcite crystals achieve their remarkable properties and thereby open up ways for the development of bioinspired hybrid materials.

The control of biofilm formation is a challenging goal that has not been reached yet in many aspects. One unsolved question is the role of van der Waals forces and another is the importance of mutual interactions between the adsorbing and the adsorbed biomolecules ͑"critical crowding"͒. In this study, a combined experimental and theoretical approach is presented, which fundamentally probes both aspects. On three model proteins-lysozyme, ␣-amylase, and bovine serum albumin-the adsorption kinetics is studied experimentally. Composite substrates are used enabling a separation of the short-and the long-range forces. Although usually neglected, experimental evidence is given for the influence of van der Waals forces on the protein adsorption as revealed by in situ ellipsometry. The three proteins were chosen for their different conformational stabilities in order to investigate the influence of conformational changes on the adsorption kinetics. Monte Carlo simulations are used to develop a model for these experimental results by assuming an internal degree of freedom to represent conformational changes. The simulations also provide data on the distribution of adsorption sites. By in situ atomic force microscopy we can also test this distribution experimentally, which opens the possibility to, e.g., investigate the interactions between adsorbed proteins.

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