Substrate adhesion evolves non-monotonically with processing time in millimeter-scale aligned carbon nanotube arrays.

The advantageous intrinsic and scale-dependent properties of aligned nanofibers (NFs) and their assembly into 3D architectures motivate their use as dry adhesives and shape-engineerable materials. While controlling NF-substrate adhesion is critical for scaled manufacturing and application-specific performance, current understanding of how this property evolves with processing conditions is limited. In this report, we introduce substrate adhesion predictive capabilities by using an exemplary array of NFs, aligned carbon nanotubes (CNTs), studied as a function of their processing. Substrate adhesion is found to scale non-monotonically with process time in a hydrocarbon environment and is investigated via the tensile pull-off of mm-scale CNT arrays from their growth substrate. CNT synthesis follows two regimes: Mode I ('Growth') and Mode II ('Post-Growth'), separated by growth termination. Within 10 minutes of post-growth, experiments and modeling indicate an order-of-magnitude increase in CNT array-substrate adhesion strength (∼40 to 285 kPa) and effective elastic array modulus (∼6 to 47 MPa), and a two-orders-of-magnitude increase in the single CNT-substrate adhesion force (∼0.190 to 12.3 nN) and work of adhesion (∼0.07 to 1.5 J m-2), where the iron catalyst is found to remain on the substrate. Growth number decay in Mode I and carbon accumulation in Mode II contribute to the mechanical response, which may imply a change in the deformation mechanism. Predictive capabilities of the model are assessed for previously studied NF arrays, suggesting that the current framework can enable the future design and manufacture of high-value NF array applications.

Differences in the expression of restricted repetitive behaviors in female and male BTBR T + tf/J mice.

Autism spectrum disorder (ASD) is characterized by the expression of restricted repetitive behaviors (RRBs) and impairments in social recognition and communication. Epidemiological studies demonstrate males are three times more likely than females to be affected. Although this is the case, more recent studies suggest females may be underrepresented in these numbers due to standard clinical measures of RRBs and social behaviors. In addition, many studies examining mouse models of ASD exclude females due to the sex disparity in diagnoses. The present study examined how female and male BTBR T + Itpr3tf /J (BTBR) compare to control C57BL/6J mice on tests of RRBs (probabilistic reversal learning, repetitive grooming, spontaneous alternation, and marble burying) and social behaviors (three chambered social approach task). Utilizing a spatial reversal learning test with 80/20 probabilistic feedback, in which ASD individuals have exhibited deficits, we find that female BTBR mice do not show the same impairment found in male BTBR mice. Interestingly, control female C57BL/6J mice required more trials to reach criterion. Female BTBR mice expressed comparable rates of repetitive grooming, marble burying and spontaneous alternation compared to female C57BL/6J mice. Male BTBR mice expressed higher rates of grooming behavior and locomotor activity compared to male C57BL/6J mice, as found in previous studies. Similarly, male BTBR mice showed a reduction in both measures of social approach compared to controls. Both male and female BTBR mice showed a reduction in sniff time for the stranger mouse compared to controls. Together these findings demonstrate how female BTBR mice do not display the RRB profile expressed by male BTBR mice. Testing of repetitive behaviors in ASD needs to better reflect the sex differences in how RRBs manifest in females compared to their extensively researched male counterparts.

5-HT6 receptor agonist EMD386088 impairs behavioral flexibility and working memory.

Serotonin 6 (5-HT6) receptors are primarily expressed in the central nervous system and to an even further extent brain regions responsible for learning and memory. Recent studies have demonstrated 5-HT6 receptor involvement in pathophysiological processes highlighting their therapeutic possibilities. Most research concerning the effects of 5-HT6 receptor modulation has focused on blockade despite paradoxical findings that 5-HT6 agonists and antagonists can both have pro-cognitive effects. The current experiments examine the effects of the 5-HT6 receptor agonist EMD386088 on behavioral flexibility and working memory. C57BL/6J mice received systemic injections of either 0, 2, or 4 mg/kg EMD386088 before being tested on probabilistic reversal learning, spontaneous alternation, and locomotor activity. In the probabilistic reversal learning task, the high dose of 4 mg/kg significantly impaired performance requiring more trials to reach criterion. The same dose significantly increased perseverative type errors, suggesting that the probabilistic reversal learning impairment was due to an inability to inhibit the previously learned choice pattern, rather than maintaining the new optimal choice pattern. Acute EMD386088 administration at 2 mg/kg significantly impaired spontaneous alternation performance, while the high dose of 4 mg/kg did not reach significance. These learning impairments were not due to an overall locomotor impairment as evidenced by comparable locomotor activity scores. Acute systemic 5-HT6 receptor activation with EMD386088 led to impaired behavior flexibility and working memory performance. Current findings support previous research suggesting that novel therapeutics directed at down regulation of 5-HT6 receptors may be effective in attenuating working memory and behavioral flexibility impairments commonly found in neuropsychiatric disorders such as Alzheimer's and schizophrenia.

Long-term monitoring of molecular markers can distinguish different seasonal patterns of fecal indicating bacteria sources.

Elevated levels of fecal indicator bacteria (FIB) have been observed at Topanga Beach, CA, USA. To identify the FIB sources, a microbial source tracking study using a dog-, a gull- and two human-associated molecular markers was conducted at 10 sites over 21 months. Historical data suggest that episodic discharge from the lagoon at the mouth of Topanga Creek is the main source of bacteria to the beach. A decline in creek FIB/markers downstream from upper watershed development and a sharp increase in FIB/markers at the lagoon sites suggest sources are local to the lagoon. At the lagoon and beach, human markers are detected sporadically, dog marker peaks in abundance mid-winter, and gull marker is chronically elevated. Varied seasonal patterns of FIB and source markers were identified showing the importance of applying a suite of markers over long-term spatial and temporal sampling to identify a complex combination of sources of contamination.

Poly(dimethylsiloxane) thin films as biocompatible coatings for microfluidic devices: cell culture and flow studies with glial cells.

Oxygen plasma treatment of poly(dimethylsiloxane) (PDMS) thin films produced a hydrophilic surface that was biocompatible and resistant to biofouling in microfluidic studies. Thin film coatings of PDMS were previously developed to provide protection for semiconductor-based microoptical devices from rapid degradation by biofluids. However, the hydrophobic surface of native PDMS induced rapid clogging of microfluidic channels with glial cells. To evaluate the various issues of surface hydrophobicity and chemistry on material biocompatibility, we tested both native and oxidized PDMS (ox-PDMS) coatings as well as bare silicon and hydrophobic alkane and hydrophilic oligoethylene glycol silane monolayer coated under both cell culture and microfluidic studies. For the culture studies, the observed trend was that the hydrophilic surfaces supported cell adhesion and growth, whereas the hydrophobic ones were inhibitive. However, for the fluidic studies, a glass-silicon microfluidic device coated with the hydrophilic ox-PDMS had an unperturbed flow rate over 14 min of operation, whereas the uncoated device suffered a loss in rate of 12%, and the native PDMS coating showed a loss of nearly 40%. Possible protein modification of the surfaces from the culture medium also were examined with adsorbed films of albumin, collagen, and fibrinogen to evaluate their effect on cell adhesion.