Tunable and Robust Nanostructuring for Multifunctional Metal Additively Manufactured Interfaces.

Novel processing phenomena coupled with various alloying materials used in metal additive manufacturing (AM) have opened opportunities for the development of previously unexplored micro-/nanostructures. A rationally devised structure nanofabrication strategy of AM surfaces that can tailor the interface morphology and chemistry has the potential for many applications. Here, through an understanding of grain formation mechanisms during AM, we develop a facile method for tuning micro-/nanostructures of one of the most used AM alloys and rationally optimize the morphology for applications requiring low surface adhesion. We demonstrate that optimized AM structures reduce the adhesion of impaling water droplets and significantly delay icing time. The structure can also be altered and optimized for antiflooding jumping-droplet condensation that exhibits significant enhancement in heat transfer performance in comparison to nanostructures formed on conventional Al alloys. In addition to demonstrating the potential of functionalized AM surfaces, this work also provides guidelines for surface-structuring optimization applicable to other AM metals.

Pathway specific activation of ventral hippocampal cells projecting to the prelimbic cortex diminishes fear renewal.

The ability to learn that a stimulus no longer signals danger is known as extinction. A major characteristic of extinction is that it is context-dependent, which means that fear reduction only occurs in the same context as extinction training. In other contexts, there is re-emergence of fear, known as contextual renewal. The ability to properly extinguish fear memories and generalize safety associations to multiple contexts provides therapeutic potential, but little is known about the specific neural pathways that mediate fear renewal and extinction generalization. The ventral hippocampus (VH) is thought to provide a contextual gating mechanism that determines whether fear or safety is expressed in particular contexts through its projections to areas of the fear circuit, including the infralimbic (IL) and prelimbic (PL) cortices. Moreover, VH principal cells fire in large, overlapping regions of the environment, a characteristic that is ideal to support generalization; yet it is unclear how different projection cells mediate this process. Using a pathway-specific (intersectional) chemogenetic approach, we demonstrate that selective activation of VH cells projecting to PL attenuates fear renewal without affecting fear expression. These results have implications for anxiety disorders since they uncover a neural pathway associated with extinction generalization.

Effects of Methamphetamine Self-Administration and Extinction on Astrocyte Structure and Function in the Nucleus Accumbens Core.

Astrocytes provide support for neurons, regulate metabolic processes, and influence neuronal communication in a variety of ways, including through the homeostatic regulation of glutamate. Following 2-h cocaine or methamphetamine self-administration (SA) and extinction, rodents display decreased levels of basal glutamate in the nucleus accumbens core (NAcore), which transitions to elevated glutamate levels during drug seeking. We hypothesized that, like cocaine, this glutamate 'overflow' during methamphetamine seeking arises via decreased expression of the astroglial glutamate transporter GLT-1, and withdrawal of perisynaptic astroglial processes (PAPs) from synapses. As expected, methamphetamine self-administration and extinction decreased the level of contact made by PAPs in the NAcore, yet did not impact glutamate uptake, GLT-1 expression, or the general structural characteristics of astrocytes. Interestingly, systemic administration of N-acetylcysteine (NAC), a drug that both upregulates GLT-1 and promotes glial-glutamate release, reduced cued methamphetamine seeking. In order to test the impact of astrocyte activation and the induction of glial glutamate release within the NAcore, we employed astrocyte-specific expression of designer receptors exclusively activated by designer drugs (DREADDs). We show here that acute activation of Gq-coupled DREADDs in this region inhibited cued methamphetamine seeking. Taken together, these data indicate that cued methamphetamine seeking following two-hour SA is not mediated by deficient glutamate clearance in the NAcore, yet can be inhibited by engaging NAcore astrocytes.

Glucocorticoid enhancement of dorsolateral striatum-dependent habit memory requires concurrent noradrenergic activity.

Previous findings indicate that post-training administration of glucocorticoid stress hormones can interact with the noradrenergic system to enhance consolidation of hippocampus- or amygdala-dependent cognitive/emotional memory. The present experiments were designed to extend these findings by examining the potential interaction of glucocorticoid and noradrenergic mechanisms in enhancement of dorsolateral striatum (DLS)-dependent habit memory. In experiment 1, different groups of adult male Long-Evans rats received training in two DLS-dependent memory tasks. In a cued water maze task, rats were released from various start points and were reinforced to approach a visibly cued escape platform. In a response-learning version of the water plus-maze task, animals were released from opposite starting positions and were reinforced to make a consistent egocentric body-turn to reach a hidden escape platform. Immediately post-training, rats received peripheral injections of the glucocorticoid corticosterone (1 or 3 mg/kg) or vehicle solution. In both tasks, corticosterone (3 mg/kg) enhanced DLS-dependent habit memory. In experiment 2, a separate group of animals received training in the response learning version of the water plus-maze task and were given peripheral post-training injections of corticosterone (3 mg/kg), the ß-adrenoreceptor antagonist propranolol (3 mg/kg), corticosterone and propranolol concurrently, or control vehicle solution. Corticosterone injections again enhanced DLS-dependent memory, and this effect was blocked by concurrent administration of propranolol. Propranolol administration by itself (3 mg/kg) did not influence DLS-dependent memory. Taken together, the findings indicate an interaction between glucocorticoid and noradrenergic mechanisms in DLS-dependent habit memory. Propranolol administration may be useful in treating stress-related human psychopathologies associated with a dysfunctional DLS-dependent habit memory system.

Evolution of dielectric function of Al-doped ZnO thin films with thermal annealing: effect of band gap expansion and free-electron absorption.

Evolution of dielectric function of Al-doped ZnO (AZO) thin films with annealing temperature is observed. It is shown that the evolution is due to the changes in both the band gap and the free-electron absorption as a result of the change of free-electron concentration of the AZO thin films. The change of the electron concentration could be attributed to the activation of Al dopant and the creation/annihilation of the donor-like defects like oxygen vacancy in the thin films caused by annealing.

Influence of localized surface plasmon resonance and free electrons on the optical properties of ultrathin Au films: a study of the aggregation effect.

The contributions of localized surface plasmon resonance (LSPR) and Drude (free electrons) absorption to the complex dielectric function of ultrathin Au films were investigated with spectroscopic ellipsometry. When the Au film thickness is thinner than ~10 nm, Au nanoparticles (NPs) are formed as a result of the discontinuity in the films, leading to the emergence of LSPR of Au NPs; and the LSPR exhibits a splitting when the films thinner than ~8 nm, which could be attributed to the near-field coupling of the Au NPs and/or the inhomogeneous polarizations of the Au NPs. On the other hand, the delocalization of electrons in Au NPs due to the aggregation of Au NPs in a thicker film leads to an increase in the free-electron absorption and a suppression of the LSPR.

Thermoporometry characterization of silica microparticles and nanowires.

We present the results of a systematic study on the porosity of silica microparticles and nanowires prepared by glancing angle deposition-metal-assisted chemical etching (GLAD-MACE) and interference lithography-metal-assisted chemical etching (IL-MACE) techniques using the thermoporometry (TPM) method. Good agreement was obtained between our TPM results and published data provided by the suppliers of silica microparticles. TPM characterization of the GLAD-MACE and IL-MACE nanowires was carried out on the basis of parameters obtained from TPM experiments on microparticles. Our nanowires showed a similar trend but lower values of the pore volume and surface area than nanowires prepared by MACE with AgNO3 solution. We attribute the enhanced bioanalysis performance of the GLAD-MACE nanowires based devices to the increased pore volume and total surface area of the nanowires.

Effects of free electrons and quantum confinement in ultrathin ZnO films: a comparison between undoped and Al-doped ZnO.

Band gaps and exciton binding energies of undoped and Al-doped ZnO thin films were determined from optical absorption measurement based on the Elliott's exciton absorption theory. As compared to the undoped films, the doped films exhibit a band gap expansion and a reduction in the exciton binding energies due to the free electron screening effect, which suppresses the excitonic absorption and results in a blue shift of the absorption edge. The undoped and doped films show the same quantum size dependence, i.e. both the exciton binding energies and band gap energies increase with decreasing grain size of the oxides.

Droplet spreading on a two-dimensional wicking surface.

The dynamics of droplet spreading on two-dimensional wicking surfaces were studied using square arrays of Si nanopillars. It was observed that the wicking film always precedes the droplet edge during the spreading process causing the droplet to effectively spread on a Cassie-Baxter surface composed of solid and liquid phases. Unlike the continual spreading of the wicking film, however, the droplet will eventually reach a shape where further spreading becomes energetically unfavorable. In addition, we found that the displacement-time relationship for droplet spreading follows a power law that is different from that of the wicking film. A quantitative model was put forth to derive this displacement-time relationship and predict the contact angle at which the droplet will stop spreading. The predictions of our model were validated with experimental data and results published in the literature.

Dynamics of wicking in silicon nanopillars fabricated with interference lithography and metal-assisted chemical etching.

The capillary rise of liquid on a surface, or "wicking", has potential applications in biological and industrial processes such as drug delivery, oil recovery, and integrated circuit chip cooling. This paper presents a theoretical study on the dynamics of wicking on silicon nanopillars based on a balance between the driving capillary forces and viscous dissipation forces. Our model predicts that the invasion of the liquid front follows a diffusion process and strongly depends on the structural geometry. The model is validated against experimental observations of wicking in silicon nanopillars with different heights synthesized by interference lithography and metal-assisted chemical etching techniques. Excellent agreement between theoretical and experimental results, from both our samples and data published in the literature, was achieved.

Creation of nanostructures by interference lithography for modulation of cell behavior.

Emerging evidence of the striking differences that can be induced in the behavior of biological cells through topographical modulation of physically and chemically patterned nanostructured surfaces provides a great impetus for developing novel cellular-scale and sub-cellular-scale nanopatterned substrates and for employing them for exciting new applications in life and medical sciences and biotechnology. However, the lack of availability of cost-effective, large-surface-area nanofabricated substrates of appropriate dimensions and features has proved to be a major impediment for research in this area. Here, we demonstrate a simple and cost-effective method based on interference lithography to produce spatially precise and wide-surface-coverage silicon- and polymer-based nanostructures to study how cells react to nanoscale structures or surfaces.

Mimicking both petal and lotus effects on a single silicon substrate by tuning the wettability of nanostructured surfaces.

We describe a new method of fabricating large-area, highly scalable, "hybrid" superhydrophobic surfaces on silicon (Si) substrates with tunable, spatially selective adhesion behavior by controlling the morphologies of Si nanowire arrays. Gold (Au) nanoparticles were deposited on Si by glancing-angle deposition, followed by metal-assisted chemical etching of Si to form Si nanowire arrays. These surfaces were chemically modified and rendered hydrophobic by fluorosilane deposition. Au nanoparticles with different size distributions resulted in the synthesis of Si nanowires with very different morphologies (i.e., clumped and straight nanowire surfaces). The difference in nanowire morphology is attributed to capillary force-induced nanocohesion, which is due to the difference in nanowire porosity. The clumped nanowire surface demonstrated the lotus effect, and the straighter nanowires demonstrated the ability to pin water droplets while maintaining large contact angles (i.e., the petal effect). The high contact angles in both cases are explained by invoking the Cassie-Baxter wetting state. The high adhesion behavior of the straight nanowire surface may be explained by a combination of attractive van der Waals forces and capillary adhesion. We demonstrate the spatial patterning of both low- and high-adhesion superhydrophobicity on the same substrate by the simultaneous synthesis of clumped and straight silicon nanowires. The demonstration of hybrid superhydrophobic surfaces with spatially selective, tunable adhesion behavior on single substrates paves the way for future applications in microfluidic channels, substrates for biologically and chemically based analysis and detection where it is necessary to analyze a particular droplet in a defined location on a surface, and as a platform to study in situ chemical mixing and interfacial reactions of liquid pearls.

Learning resources and activities: students' feedback from two Malaysian medical schools.

In a survey of clinical students in two Malaysian medical schools, it was found that students used a wide variety of learning resources, but textbooks were still the primary source of their information. Students had positive views about clinical teaching and lectures but somewhat lower opinions on problem-based learning. They generally did not perceive lecturers as facilitators, role models and counselors. In spite of the stated curricular goals of promoting self-directed learning via problem-based learning, students in these medical schools were driven by the nature of examinations and focused mainly on clinical contents rather than the process of learning.

Upper respiratory tract infections: to what extent is the management evidence-based?

Over a 2-week period, the management of upper respiratory tract infection by 24 medical officers and medical assistants in Seremban District was studied. Each practitioner recorded clinical data and prescription for twenty consecutive patients using a structured questionnaire. The extent to which the practitioners used "predictive features" (fever, absence of cough, cervical adenopathy, enlarged tonsils and exudates on tonsils) in clinical decision-making was analysed. The mean antibiotic prescription rate was 28.7% (95% CI: 24.6%, 33.0%). The antibiotic prescription rate of medical officers and medical assistants were similar. Five features were independently associated with antibiotic prescription (phlegm, fever, cervical adenopathy, red throat and tonsillar exudates). Antibiotics were prescribed for 22.1% of patients with 0-1 predictive features. High prescribers were 5 times more likely to prescribe antibiotics in this group of patients than low prescribers. To a large extent the clinical decision-making of practitioners in this study was evidence based. However, they were unduly influenced by purulent manifestation (phlegm) and redness of throat. The antibiotic prescription rate in these government health clinics is potentially reducible by means of educational intervention.

Morbidity and process of care in urban Malaysian general practice: the impact of payment system.

BACKGROUND: The majority of primary care consultations in Malaysia occur in the general practice clinics. To date, there is no comprehensive documentation of the morbidity and practice activities in this setting. OBJECTIVES: We reported the reasons for encounter, diagnoses and process of care in urban general practice and the influence of payment system on the morbidity and practice activities. METHODS: 115 clinics in Kuala Lumpur, Ipoh and Penang participated in this study. General practitioners in these clinics completed a 2-page questionnaire for each of the 30 consecutive patients. The questionnaire requested for the following information: demographic data, reasons for encounter, important physical findings, diagnoses, investigations ordered, outpatient procedures performed, medical certificate given, medication prescribed and referral made. The morbidity (reasons for encounter and diagnoses) was coded using ICPC-2 and the medication data was coded using MIMS Classification Index. RESULTS: During 3481 encounters, 5300 RFEs (152 RFEs per 100 encounters) and 3342 diagnoses (96 diagnoses per 100 encounters) were recorded. The majority of the RFEs and diagnoses are in the following ICPC Chapters: Respiratory, General and unspecified, Digestive, Neurological, Musculoskeletal and Skin. The frequencies of selected aspects of the process of care (rate per 100 encounters) were: laboratory investigations 14.7, outpatient procedures 2.4, sick certification 26.9, referral 2.4, and medication prescription 244. Consultation for chronic diseases and acute infections were influenced more by demographic variables (age, employment) rather than payment system. Cash-paying patients were more likely to receive laboratory investigations and injections. CONCLUSION: This study demonstrated the breadth of clinical care in the general practice. Relatively fewer patients consulted specifically for preventive care and treatment of chronic diseases. The frequencies of outpatient procedures and referrals appeared to be low. Payment system results in important differences in patient mix and influences some types of practice activities.

The management of upper respiratory tract infections.

Upper respiratory tract infections are the commonest reason for consultation in primary care. Group A beta-haemolytic Streptococcus (GABHS), the most important bacterial pathogen in this condition, can be cultured from about 30% of patients, more so in children than adults. Clinical features that are predictive of positive GABHS culture are absence of cough, fever, cervical adenopathy, tonsillar enlargement and tonsillar exudate. Use of a sore throat score can help in the detection of streptococcal throat infection. Symptomatic therapies which are useful include anticholinergic, antihistamine, decongestant, humified hot air and Vitamin C. Antibiotics are universally over-prescribed in this condition as a result of high patient expectation and faulty clinical decision making. Oral Penicillin V for 10 days is the drug of choice. Effective intervention to reduce inappropriate antibiotic prescription probably require a multifaceted approach targeted at both the patients and the prescribers.