Phase Engineering of Nanomaterials: Transition Metal Dichalcogenides

Crystal phase, a critical structural characteristic beyond the morphology, size, dimension, facet, etc., determines the physicochemical properties of nanomaterials. As a group of layered nanomaterials with polymorphs, transition metal dichalcogenides (TMDs) have attracted intensive research attention due to their phase-dependent properties. Therefore, great efforts have been devoted to the phase engineering of TMDs to synthesize TMDs with controlled phases, especially unconventional/metastable phases, for various applications in electronics, optoelectronics, catalysis, biomedicine, energy storage and conversion, and ferroelectrics. Considering the significant progress in the synthesis and applications of TMDs, we believe that a comprehensive review on the phase engineering of TMDs is critical to promote their fundamental studies and practical applications. This Review aims to provide a comprehensive introduction and discussion on the crystal structures, synthetic strategies, and phase-dependent properties and applications of TMDs. Finally, our perspectives on the challenges and opportunities in phase engineering of TMDs will also be discussed.

Phase-Controlled Growth of 1T'-MoS2 Nanoribbons on 1H-MoS2 Nanosheets

2D heterostructures are emerging as alternatives to conventional semiconductors, such as silicon, germanium, and gallium nitride, for next-generation electronics and optoelectronics. However, the direct growth of 2D heterostructures, especially for those with metastable phases still remains challenging. To obtain 2D transition metal dichalcogenides (TMDs) with designed phases, it is highly desired to develop phase-controlled synthetic strategies. Here, a facile chemical vapor deposition method is reported to prepare vertical 1H/1T' MoS2 heterophase structures. By simply changing the growth atmosphere, semimetallic 1T'-MoS2 can be in situ grown on the top of semiconducting 1H-MoS2, forming vertical semiconductor/semimetal 1H/1T' heterophase structures with a sharp interface. The integrated device based on the 1H/1T' MoS2 heterophase structure displays a typical rectifying behavior with a current rectifying ratio of ≈103. Moreover, the 1H/1T' MoS2-based photodetector achieves a responsivity of 1.07 A W-1 at 532 nm with an ultralow dark current of less than 10-11 A. The aforementioned results indicate that 1H/1T' MoS2 heterophase structures can be a promising candidate for future rectifiers and photodetectors. Importantly, the approach may pave the way toward tailoring the phases of TMDs, which can help us utilize phase engineering strategies to promote the performance of electronic devices.

Reversible Semimetal-Semiconductor Transition of Unconventional-Phase WS2 Nanosheets

Phase transition with band gap modulation of materials has gained intensive research attention due to its various applications, including memories, neuromorphic computing, and transistors. As a powerful strategy to tune the crystal phase of transition-metal dichalcogenides (TMDs), the phase transition of TMDs provides opportunities to prepare new phases of TMDs for exploring their phase-dependent property, function, and application. However, the previously reported phase transition of TMDs is mainly irreversible. Here, we report a reversible phase transition in the semimetallic 1T'-WS₂ driven by proton intercalation and deintercalation, resulting in a newly discovered semiconducting WS₂ with a novel unconventional phase, denoted as the 1T'_d phase. Impressively, an on/off ratio of >10⁶ has been achieved during the phase transition of WS₂ from the semimetallic 1T' phase to the semiconducting 1T'_d phase. Our work not only provides a unique insight into the phase transition of TMDs via proton intercalation but also opens up possibilities to tune their physicochemical properties for various applications.

Salt-Assisted 2H-to-1T' Phase Transformation of Transition Metal Dichalcogenides

Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Recently, transition metal dichalcogenides (TMDs) with unconventional metastable phases (e.g., 1T and 1T') have attracted increasing research interest due to their unique and appealing physicochemical properties. However, there is still a lack of a simple, universal, and controlled method for the preparation of large-scale and high-purity unconventional-phase TMD crystals, restricting their further fundamental study and practical applications. Here, a facile, one-step salt-assisted general strategy is reported for the controlled phase transformation of commercially available TMDs with conventional 2H phase, yielding a large amount of metastable 1T'-phase TMDs, including WS₂ , WSe₂ , MoS₂ , and MoSe₂ . It is found that the easily accessible metal salts, such as K₂ C₂ O₄ ·H₂ O, K₂ CO₃ , Na₂ CO₃ , Rb₂ CO₃ , Cs₂ CO₃ , KHCO₃ , NaHCO₃ , and NaC₂ O₄ , can be used to assist the 2H-to-1T' phase transformation, greatly simplifying the synthetic process for producing metastable 1T'-TMDs. Importantly, this method can also be used to prepare 1T'-TMD alloys, such as 1T'-WS_{2 x} Se_{2(1- x )} . This newly developed strategy is robust and highly effective, which can also be used for the phase engineering of other materials with various polymorphs.

Virtual reality for spinal cord injury-associated neuropathic pain: Systematic review

BACKGROUND

Treatment of spinal cord injury (SCI)-associated neuropathic pain is challenging, with limited efficacy and no definitive options, and SCI patients often show resistance to pharmacologic treatment. Virtual reality (VR) therapy is a non-invasive, non-pharmacologic alternative with minimal adverse effects.

OBJECTIVE

To investigate the effect of VR therapy on SCI-associated neuropathic pain in a systematic review.

METHODS

Articles needed to 1) be written in English; 2) include adult subjects, with at least half the study population with a SCI diagnosis; 3) involve any form of VR therapy; and 4) assess neuropathic pain by quantitative outcome measures. Articles were searched in MEDLINE/PubMed, CINAHL^®, EMBASE, and PsycINFO up to April 2018. Reference lists of retrieved articles were hand-searched. Methodologic quality was assessed by the Physiotherapy Evidence Database Score (PEDro) for randomized controlled trials and Modified Downs and Black Tool (D&B) for all other studies. Level of evidence was determined by using a modified Sackett scale.

RESULTS

Among 333 studies identified, 9 included in this review (n=150 participants) evaluated 4 methods of VR therapy (virtual walking, VR-augmented training, virtual illusion, and VR hypnosis) for treating neuropathic pain in SCI patients. Each VR method reduced neuropathic pain: 4 studies supported virtual walking, and the other 3 VR methods were each supported by a different study. Combined treatment with virtual walking and transcranial direct current stimulation was the most effective. The quality of studies was a major limitation.

CONCLUSION

VR therapy could reduce SCI-associated neuropathic pain, although the clinical significance of this analgesic effect is unclear. Clinical trials evaluating VR therapy as standalone and/or adjunct therapy for neuropathic pain in SCI patients are warranted.

Assessment of correlation between CT angiographic clot load score, pulmonary perfusion defect score and global right ventricular function with dual-source CT for acute pulmonary embolism

OBJECTIVE

The purpose of this study was to prospectively investigate the correlation between CT angiographic clot load (CTACL) score, pulmonary perfusion defect (PPD) score and the global right ventricular function in the assessment of pulmonary embolism (PE) severity.

METHODS

49 patients with acute PE, who underwent dual-source CT scan, were included in the study. CT angiography and perfusion imaging were performed. Data from electrocardiogram-gated coronary angiography scanning protocol were used for right ventricular function analysis. Two readers evaluated the CTACL and PPD scores using the Qanadli and Chae methods, respectively.

RESULTS

The PPD score had a strong positive correlation with the CTACL score (r=0.72, p<0.001) and both scores in turn had a strong positive correlation with the right ventricular/left ventricular (RV/LV) diameter ratio (r=0.60, r=0.62, p<0.001). However, the PPD score had a strong negative correlation with ejection fraction (EF) (r=-0.63, p<0.001) while the CTACL score had a low negative correlation with EF (r=-0.33, p=0.02). Between the RV/LV<1 group (n=35) and the RV/LV >1 group (n=14), the PPD score, CTACL score, pulmonary artery trunk diameter, EF and reflux of inferior vena cava were significantly different, all with p<0.001. The end-systolic volume (p=0.01) was significantly different but the end-diastolic volume (p=0.11) and stroke volume (p=0.08) showed no statistically significant difference between the two groups.

CONCLUSION

Therefore, considering PPD scores, CTACL scores and cardiovascular manifestations together may be helpful in the evaluation of PE severity.

Abstract P1-10-10: Organizational Use of Evidence-Based Strategies To Promote Timely Mammography among Medically Underserved Clients Recruited through the Avon Breast Health Outreach Program

Background: Income-related disparities in breast cancer screening rates are due to barriers to mammography that are more prevalent among lower-income groups. To address barriers to completion of screening mammography, the US Preventive Services Task Force recommends client-oriented interventions to increase demand and improve access. While evidence-based strategies have shown increased use of mammography for lower-income populations, little is known about the use of these strategies in real-world settings. Since 2001 the Avon Foundation for Women Breast Health Outreach Program (Avon BHOP) has granted over $53 million to more than 200 organizations to promote screening for breast cancer. Data collection and reporting requirements examine the reach of the program and utilization of evidenced-based interventions in diverse settings to promote repeat use of mammography among low-income women. Methods: This cross-sectional study describes the use of evidence-based strategies among Avon BHOP grantees to promote rescreening among returning clients, age 40-64, with no history of breast cancer; and examines associations between the strategies and use of mammography within the previous two years. Data were collected from two sources: 1) online survey administered to 149 organizations in 2009 to ascertain program strategies and 2) client intake form completed by clients or staff at Avon-funded agencies when women returned for annual mammograms. Organizational-level analysis included agencies that responded to the online survey and were funded by Avon from 2006-2009.

Results: Characteristics of the 86 organizations in the sample included: US geographic location (17% Mid-West, 27% Northeast, 30% South, and 26% West); 45% clinical sites; and delivery of the program to underserved populations including a high percentage of clients that: belonged to racial or ethnic minority group (62%), reported annual income of $25k or less (72%), and/or were uninsured (62%). Use of evidence-based strategies was common across organizations, including use of client reminders to schedule appointments (83% printed reminders, 74% telephone calls) and provision of patient navigation (51%). Use of strategies did not differ between clinical sites and community groups, and the rate of recent mammogram use was similar for both (clinical sites 84%, community groups 88%) and exceeded the target rate for Healthy People 2010 (70%).

Figure 1. The Proportion of Returning Clients Age 40-64 Yeats Who Had a Mammogram Within the Past 2 Years, by Type of Organization, Avon BHOP. 2007-2009.

Discussion: Avon BHOP programs are effective in recruiting underserved women for mammography screening. Both clinical and non-clinical organizations reported high rates of use of evidence-based strategies and high rates of recent mammogram for returning clients. These results suggest that strategies used to promote use of mammography among underserved populations previously enrolled in programs may be equally effective if implemented in clinical or non-clinical settings.

Promising Practices in Mammography Recruitment, Retention and Rescreening for Breast Cancer Early Detection among Community-Based Programs Supported by the Avon Foundation Breast Care Fund

Background/Significance: National guidelines recommend women age 40 and older have mammograms every 1-2 years. Since 2000, the Avon Foundation Breast Care Fund (AFBCF), a project of Cicatelli Associates Inc., has supported nonprofit community-based organizations (CBOs) to provide breast health education and outreach to link medically underserved women with free/low-cost breast cancer screening services. These organizations have developed effective strategies for recruiting, retaining and rescreening clients. This evaluation study aims to identify promising practices for effective mammography recruitment, retention and rescreening among un/underinsured, low-income, and racial and/or ethnic minority women.Methods: Twenty of 144 AFBCF-funded CBOs were selected to participate in a retrospective study to determine clients' rescreening rates.CBOs provided de-identified data on mammography screening by age and visit date to determine their rescreening rate, defined as the proportion of female outreach clients age 40+ years receiving a mammogram and subsequent mammogram through that agency within the following 6-18 and/or 18-30 months. CBOs also completed a qualitative survey about program strategies and systems. Qualitative data were linked with rescreening rates to identify promising practices. Survey results were also used to develop a discrete questionnaire administered to 144 AFBCF-funded CBOs to identify which agencies currently employ identified promising practices.Results: Data analysis will be completed in September 2009.Preliminary results indicate that rescreening rates vary widely across agencies, from 15% to over 90%. In addition, findings indicate that some CBOs lack mechanisms to routinely monitor client rescreening. Utilizing unique client identifiers in conjunction with the use of electronic data tracking systems would facilitate tracking clients over time and improve targeted outreach efforts to increase rescreening rates.Discussion: Combined qualitative and quantitative analyses of differences in practices directed at encouraging mammography rescreening among medically underserved women will enable a description of promising practices for increasing rescreening rates in this population. Analysis will include an explanation of mammography rescreening rates among medically underserved women. Agencies with high rescreening rates will be identified and discussion regarding organizational characteristics and practices will be presented. Additionally, unique and innovative strategies for reaching specific populations will be examined.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3080.

Thyroid hormone beta receptor activation has additive cholesterol lowering activity in combination with atorvastatin in rabbits, dogs and monkeys

BACKGROUND AND PURPOSE

Thyroid hormone receptor (TR) agonists are in clinical trials for the treatment of hypercholesterolaemia. As statins are the standard of clinical care, any new therapies must have adjunctive activity, when given in combination with statins. As already known for the statins, the cholesterol lowering effect of TR activation involves increased expression of the low-density lipoprotein receptor. Using animal models, we tested whether TR activation would have additive cholesterol lowering activity in the presence of effective doses of a statin.

EXPERIMENTAL APPROACH

We evaluated the activity of a liver-targeted prodrug, MB07811, of a novel TH receptor beta agonist, MB07344, as monotherapy and in combination with atorvastatin in rabbits, dogs and monkeys.

KEY RESULTS

In rabbits, MB07344 (i.v.) decreased total plasma cholesterol (TPC) comparable to that achieved with a maximally effective dose of atorvastatin (p.o.). The addition of MB07344 to atorvastatin resulted in a further decrease in TPC. Similarly, the addition of MB07811 (p.o.) to atorvastatin treatment decreased TPC beyond the level achieved with either agent as monotherapy. In dogs and monkeys, atorvastatin and MB07811 were administered as monotherapy or in combination. Consistent with the rabbit studies, the combination treatment caused a greater decrease in TPC than either MB07811 or atorvastatin administered as monotherapy.

CONCLUSIONS AND IMPLICATIONS

We conclude that the effects of MB07811 and atorvastatin in lowering cholesterol are additive in animals. These results would encourage and support the demonstration of similarly improved efficacy of combination versus monotherapy with such agents in the clinic.

Genetic exchange between Treponema denticola and Streptococcus gordonii in biofilms

Some gram-positive oral bacteria such as Streptococcus gordonii are naturally transformable. We investigated the possibility of genetic exchange among oral bacteria using an erythromycin-resistant (Erm(r)) shuttle plasmid, pKMR4PE, as an indicator. S. gordonii Challis cells were co-cultivated with purified pKMR4PE or with Trepomena denticola harboring pKMR4PE either in broth or in artificial biofilms. Transformation of S. gordonii occurred both in broth and in biofilms with pKMR4PE or T. denticola harboring pKMR4PE as donor sources. These results provide direct experimental evidence that gene transfer can occur from T. denticola to S. gordonii.

Development of shuttle vectors for spirochetes

Constructions of Escherichia coli-spirochete shuttle vectors are based on naturally occurring plasmids, broad host range plasmids or bacteriophages. This review primarily focuses on genetic tools for Treponema denticola which is associated with periodontal diseases. The T. pallidum FlaA protein, E. coli beta-galactosidase, and the green fluorescent protein were successfully expressed in T. denticola from a shuttle vector system.

Development of a system for expressing heterologous genes in the oral spirochete Treponema denticola and its use in expression of the Treponema pallidum flaA gene

The present communication describes the construction of a new Escherichia coli-Treponema denticola shuttle vector based on the naturally occurring spirochete plasmid pTS1 and the expression of the heterologous T. pallidum flaA gene from the plasmid in T. denticola. This new shuttle vector system should prove useful in characterizing virulence factors from unculturable pathogenic spirochetes.

Bartonella koehlerae sp. nov., isolated from cats

Two of the 25 Bartonella isolates recovered during a prevalence study of Bartonella henselae bacteremia in domestic cats from the greater San Francisco Bay region were found to differ phenotypically and genotypically from all prior B. henselae isolates. These isolates, C-29 and C-30, which were recovered from the blood of two pet cats belonging to the same household, grew on chocolate agar as pinpoint colonies following 14 days of incubation at 35 degrees C in a candle jar but failed to grow on heart infusion agar supplemented with 5% rabbit blood. Additional phenotypic characteristics distinguished the isolates C-29 and C-30 from other feline B. henselae isolates. The restriction patterns obtained for C-29 and C-30 by citrate synthase PCR-restriction fragment length polymorphism (RFLP) analysis as well as by genomic RFLP could not be distinguished from each other but were distinctly different from that of the B. henselae type strain. In reciprocal reactions, DNAs from strains C-29 and C-30 were 97 to 100% related under optimal and stringent DNA reassociation conditions, with 0 to 0.5% divergence within related sequences. Labeled DNA from the type strain of B. henselae was 61 to 65% related to unlabeled DNAs from strains C-29 and C-30 in 55 degrees C reactions, with 5.0 to 5.5% divergence within the related sequences, and 31 to 41% related in stringent, 70 degrees C reactions. In reciprocal reactions, labeled DNAs from strains C-29 and C-30 were 68 to 92% related to those of the B. henselae type strain and other B. henselae strains, with 5 to 7% divergence. The 16S rRNA gene sequence of strain C-29 was 99.54% homologous to that of the type strain of B. henselae. On the basis of these findings, the two isolates C-29 and C-30 are designated a new species of Bartonella, for which we propose the name Bartonella koehlerae. The type strain of Bartonella koehlerae is strain C-29 (ATCC 700693).

Experimental transmission of Bartonella henselae by the cat flea

Bartonella henselae is an emerging bacterial pathogen, causing cat scratch disease and bacillary angiomatosis. Cats bacteremic with B. henselae constitute a large reservoir from which humans become infected. Prevention of human infection depends on elucidation of the natural history and means of feline infection. We studied 47 cattery cats in a private home for 12 months to determine the longitudinal prevalence of B. henselae bacteremia, the prevalence of B. henselae in the fleas infesting these cats, and whether B. henselae is transmitted experimentally to cats via fleas. Vector-mediated transmission of B.henselae isolates was evaluated by removing fleas from the naturally bacteremic, flea-infested cattery cats and transferring these fleas to specific-pathogen-free (SPF) kittens housed in a controlled, arthropod-free University Animal Facility. B. henselae bacteremia was detected in 89% of the 47 naturally infected cattery cats. A total of 132 fleas were removed from cats whose blood was simultaneously cultured during different seasons and were tested individually for the presence of B. henselae DNA by PCR. B. henselae DNA was detected in 34% of 132 fleas, with seasonal variation, but without an association between the presence or the level of bacteremia in the corresponding cat. Cat fleas removed from bacteremic cattery cats transmitted B. henselae to five SPF kittens in two separate experiments; however, control SPF kittens housed with highly bacteremic kittens in the absence of fleas did not become infected. These data demonstrate that the cat flea readily transmits B. henselae to cats. Control of feline infestation with this arthropod vector may provide an important strategy for the prevention of infection of both humans and cats.