Visualization of the self-assembly of silica nanochannels reveals growth mechanism.

Self-assembled mesoporous structures with well-ordered nanoscale channels could be used in applications such as molecular separation, nano-optics, molecular electronics, nanomedicine and catalysis. However, the domain sizes that can be created in such systems are limited by our lack of a detailed understanding of the relevant growth processes. Here we report the real-time observation of domain growth in the self-assembly of silica nanochannels using fluorescence polarization imaging and atomic force microscopy. We show that transient lamellar structures precede the formation of hexagonal layers, and that the layer growth follows two distinct pathways. In addition, the domains are grown on a mesoporous film substrate, which acts as a sieve and allows control of the delivery of the reactive species. We use these insights and capabilities to grow layers of well-ordered silica nanochannels with domain sizes of up to ∼0.3 mm.

Single-molecule measurement of the strength of a siloxane bond.

Increasing the mechanical stability of artificial polymer materials is an important task in materials science, and for this a profound knowledge of the critical mechanoelastic properties of its constituents is vital. Here, we use AFM-based single-molecule force spectroscopy measurements to characterize the rupture of a single silicon-oxygen bond in the backbone of polydimethylsiloxane as well as the force-extension behavior of this polymer. PDMS is not only a polymer used in a large variety of products but also an important model system for highly flexible polymers. In our experiments, we probe the entire relevant force range from low forces dominated by entropy up to the rupture of the covalent Si-O bonds in the polymer backbone at high forces. The resulting rupture-force histograms are investigated with microscopic models of bond rupture under load and are compared to density functional theory calculations to characterize the free-energy landscape of the Si-O bond in the polymer backbone.

Clinical course and NPHS2 analysis in patients with late steroid-resistant nephrotic syndrome.

A small fraction of patients with initial steroid-sensitive nephrotic syndrome (SSNS) develops late steroid resistance, i.e. a lack of remission after 4 weeks of relapse treatment despite previous response to steroids. The pathophysiological basis of late resistance and the long-term prognosis remain obscure. Fourteen out of 360 patients with SSNS who were seen in our department between 1954 and 2005 developed late resistance. Median age at onset of NS was 4 years and median duration of development of late resistance 4.6 months. Histology showed minimal-change (MC) nephropathy in six patients and focal segmental glomerulosclerosis (FSGS) in three patients on initial biopsy and four patients on repeat biopsies. Late resistance was treated with cyclophosphamide in five patients, cyclosporine A in three, and both drugs in one. Eight of these nine patients went into remission. All 14 patients maintained a stable kidney function during their period of observation. NPHS2 mutation analysis in eight patients revealed no pathogenic mutations, suggesting that late resistance is not typically associated with mutations in the NPHS2 gene. With respect to the clinical course, late resistance appears to resemble SSNS and is characterized by a favorable outcome.