Bacterial crystalline surface layers (S-layers) are the outermost envelope of prokaryotic organisms representing the simplest biological membranes developed during evolution. In this context, the bacterial protein SbpA has already shown its intrinsic ability to reassemble on different substrates forming protein crystals of square lattice symmetry. In this work, we present the interaction between the bacterial protein SbpA and five self-assembled monolayers carrying methyl (CH(3)), hydroxyl (OH), carboxylic acid (COOH) and mannose (C(6)H(12)O(6)) as functional groups. Protein adsorption and S-layer formation have been characterized by atomic force microscopy (AFM) while protein adsorption kinetics, mass uptake and the protein layer viscoelastic properties were investigated with quartz crystal microbalance with dissipation monitoring (QCM-D). The results indicate that the protein adsorption rate and crystalline domain area depend on surface chemistry and protein concentration. Furthermore, electrostatic interactions tune different protein rate adsorption and S-layer recrystallization pathways. Electrostatic interactions induce faster adsorption rate than hydrophobic or hydrophilic interactions. Finally, the shear modulus and the viscosity of the recrystallized S-layer on CH(3)C(6)S, CH(3)C(11)S and COOHC(11)S substrates were calculated from QCM-D measurements. Protein-protein interactions seem to play a main role in the mechanical stability of the formed protein (crystal) bilayer.

The self-assembly kinetics and nanocrystal formation of the bacterial surface-layer-protein SbpA are studied with a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Silane coupling agents, aminopropyltriethoxysilane (APTS) and octadecyltrichlorosilane (OTS), are used to vary the protein-surface interaction in order to induce new recrystallization pathways. The results show that the final S-layer crystal lattice parameters (a = b = 14 nm, gamma = 90 degrees ), the layer thickness (15 nm), and the adsorbed mass density (1700 ng cm(-2)) are independent of the surface chemistry. Nevertheless, the adsorption rate is five times faster on APTS and OTS than on SiO(2,) strongly affecting protein nucleation and growth. As a consequence, protein crystalline domains of 0.02 microm(2) for APTS and 0.05 microm(2) for OTS are formed, while for silicon dioxide the protein domains have a typical size of about 32 microm(2). In addition, more-rigid crystalline protein layers are formed on hydrophobic substrates. In situ AFM experiments reveal three different kinetic steps: adsorption, self-assembly, and crystalline-domain reorganization. These steps are corroborated by frequency-dissipation curves. Finally, it is shown that protein adsorption is a diffusion-driven process. Experiments at different protein concentrations demonstrate that protein adsorption saturates at 0.05 mg mL(-1) on silane-coated substrates and at 0.07 mg mL(-1) on hydrophilic silicon dioxide.

Pyrazole-isothiazole monomers are electrospun from solution into solid, quasi-endless micro- and nanofibers.

Biomolecules, cells and the cellular environment have characteristic mechanical properties that determine a range of biological responses. The affected responses include the differentiation and phenotypic expression of cells, an area that has gained prominence due to the current interest in the control of stem cell development. Recent research on biomaterials includes many measurements that have been made on a micro or nano-scale and which are not well described by continuum models. The focus of this review is on the integration and comparison of information obtained from different experimental techniques: mechanical properties are discussed in terms of the wide range of molecular motions and relaxation times that are characteristic of biological materials. Starting at the smaller end of the scale, one component which will be almost universally present in biomolecular samples is water; although bulk water has a relaxation time that would make it fluid in typical experiments, interfacial water and water in confined films will exhibit much slower motions and may therefore show an elastic response, depending on the experimental technique used for the measurements. Water at the surface of hydrophilic solids may thus appear elastic when characterised using high-frequency acoustic devices such as the quartz crystal microbalance (QCM), although the layer will still be fluid in AFM measurements at typical load rates. Likewise, lipid bilayers are viscous at low shear but would be elastic at a sufficiently high frequency. Supported lipid bilayers (SLB) are effectively elastic in acoustic experiments; this could be due to the relaxation time with respect to shear displacements in the bilayer. At the larger end of the size scale, whole cells can also show a frequency-dependent transition to elastic behaviour, at frequencies as low as 0.1 Hz. Other examples mentioned here include proteins and the protein networks of cells.