Non-monotonic speed-dependence of microswimmers on wall distance.

While substrates naturally occur in most microswimmer experiments, their impact on the swimming performance is not well understood. In the present study, we functionalize substrates with polymer brushes of varying swelling properties, grafting densities and brush lengths to systematically modify and explore the substrate-swimmer interactions. Notably, the swimming speed does not monotonically change with brush thickness, but shows a distinct maximum at a certain intermediate thickness, which results from two counteracting factors: surface charge and surface roughness. The results show that the speed of thermophoretic microswimmers does not only depend on the particle properties but is also strongly influenced by the properties of the underlying substrate. This provides a route to control the speed of microswimmers via the underlying substrate, which could be applied in the future e.g. to design complex motility landscapes by patterning substrates with polymer brushes. It is expected that similar effects would occur for diffusio- and electrophoretic particles.

Exploring water in oil emulsions simultaneously stabilized by solid hydrophobic silica nanospheres and hydrophilic soft PNIPAM microgel.

A general drawback of microgels is that they do not stabilize water-in-oil (w/o) emulsions of non-polar oils. Simultaneous stabilization with solid hydrophobic nanoparticles and soft hydrophilic microgels overcomes this problem. For a fundamental understanding of this synergistic effect the use of well defined particle systems is crucial. Therefore, the present study investigates the stabilization of water droplets in a highly non-polar oil phase using temperature responsive, soft and hydrophilic PNIPAM microgel particles (MGs) and solid and hydrophobic silica nanospheres (SNs) simultaneously. The SNs are about 20 times smaller than the MGs. In a multiscale approach the resulting emulsions are studied from the nanoscale particle properties over microscale droplet sizes to macroscopic observations. The synergy of the particles allows the stabilization of water-in-oil (w/o) emulsions, which was not possible with MGs alone, and offers a larger internal interface than the stabilization with SNs alone. Furthermore, the incorporation of hydrophilic MGs into a hydrophobic particle layer accelerates the emulsions sedimentation speed. Nevertheless, the droplets are still sufficiently protected against coalescence even in the sediment and can be redispersed by gentle shaking. Based on droplet size measurements and cryo-SEM studies we elaborate a model, which explains the found phenomena.

Acute prefrontal rTMS increases striatal dopamine to a similar degree as D-amphetamine.

Prefrontal repetitive transcranial magnetic stimulation (rTMS) has been shown to increase striatal dopaminergic activity. Here we investigated dopaminergic neurotransmission using single photon emission computed tomography (SPECT) and [(123)I]IBZM to indirectly assess the change in endogenous striatal dopamine concentration upon rTMS as compared with d-amphetamine challenge. SPECT imaging was performed twice each in five patients during rTMS, and in two patients who received 0.3 mg/kg D-amphetamine. Administration of rTMS led to a mean relative decrease in striatal IBZM binding by 9.6+/-6.2%, and d-amphetamine challenge (n=4) induced a mean relative reduction by 8+/-2.95% (difference not statistically significant). Acute rTMS challenge showed similar striatal dopaminergic effects to those associated with the administration of d-amphetamine, a substance known to increase synaptic dopamine.

Striatal dopamine release after prefrontal repetitive transcranial magnetic stimulation in major depression: preliminary results of a dynamic [123I] IBZM SPECT study.

Though there is considerable evidence that prefrontal repetitive transcranial magnetic stimulation (rTMS) exerts antidepressant effects, the neurobiological action of rTMS in patients with depression is poorly understood. Preclinical studies in animals and humans have demonstrated that prefrontal rTMS can induce dopamine release in mesostriatal and mesolimbic regions. We therefore investigated whether rTMS also modulates striatal dopaminergic neurotransmission in depressed patients using a dynamic [123I] iodobenzamide (IBZM) single photon emission computed tomography (SPECT) approach. Five patients with a major depressive episode (DSM-IV) underwent an acute 10 Hz rTMS challenge with 3000 stimuli over the left dorsolateral prefrontal cortex during an [123I] IBZM-SPECT bolus and constant infusion protocol. In four subjects the protocol was repeated after a three week rTMS standard treatment. Striatal IBZM binding to dopamine D2 receptors was assessed with a region-of-interest (ROI) technique. The change in striatal IBZM binding after the rTMS challenge was regarded as measure of change in endogenous striatal dopamine. Data of nine SPECT investigations showed a significant reduction by 9.6+/-6.2% in IBZM binding to striatal dopamine D2 receptors after rTMS challenge compared to baseline (p=0.01, Wilcoxon test). In this preliminary study, the reduction of IBZM binding observed after rTMS challenge is suggestive of a release in endogenous dopamine induced by prefrontal rTMS. In future, this approach can be used to differentiate specific and non-specific reward-related effects of rTMS on dopaminergic neurotransmission.