Evaporation of particle-stabilised emulsion sunscreen films

We recently showed (Binks et al., ACS Appl. Mater. Interfaces, 2016, DOI: 10.1021/acsami.6b02696) how evaporation of sunscreen films consisting of solutions of molecular UV filters leads to loss of UV light absorption and derived sun protection factor (SPF). In the present work, we investigate evaporation-induced effects for sunscreen films consisting of particle-stabilized emulsions containing a dissolved UV filter. The emulsions contained either droplets of propylene glycol (PG) in squalane (SQ), droplets of SQ in PG or droplets of decane in PG. In these different emulsion types, the SQ is involatile and shows no evaporation, the PG is volatile and evaporates relatively slowly, whereas the decane is relatively very volatile and evaporates quickly. We have measured the film mass and area, optical micrographs of the film structure, and the UV absorbance spectra during evaporation. For emulsion films containing the involatile SQ, evaporation of the PG causes collapse of the emulsion structure with some loss of specular UV absorbance due to light scattering. However, for these emulsions with droplets much larger than the wavelength of light, the light is scattered only at small forward angles so does not contribute to the diffuse absorbance and the film SPF. The UV filter remains soluble throughout the evaporation and thus the UV absorption by the filter and the SPF remain approximately constant. Both PG-in-SQ and SQ-in-PG films behave similarly and do not show area shrinkage by dewetting. In contrast, the decane-in-PG film shows rapid evaporative loss of the decane, followed by slower loss of the PG resulting in precipitation of the UV filter and film area shrinkage by dewetting which cause the UV absorbance and derived SPF to decrease. Measured UV spectra during evaporation are in reasonable agreement with spectra calculated using models discussed here

Spectrophotometry of thin films of light absorbing particles

Thin films of dispersions of light absorbing solid particles or emulsions containing a light absorbing solute all have a non-uniform distribution of light absorbing species throughout the sample volume. This results in non-uniform light absorption over the illuminated area which causes the optical absorbance, as measured using a conventional specular UV-vis spectrophotometer, to deviate from the Beer-Lambert relationship. We have developed a theoretical model to account for the absorbance properties of such films which are shown to depend on the size and volume fraction of the light absorbing particles plus other sample variables. We have compared model predictions with measured spectra for samples consisting of emulsions containing a dissolved light absorbing solute. Using no adjustable parameters, the model successfully predicts the behaviour of non-uniform, light absorbing emulsion films with varying values of droplet size, volume fraction and other parameters

Activity-dependent signaling mechanisms regulating adult hippocampal neural stem cells and their progeny

Adult neural stem cells (NSCs) reside in a restricted microenvironment, where their development is controlled by subtle and presently underexplored cues. This raises a significant question: what instructions must be provided by this supporting niche to regulate NSC development and functions? Signaling from the niche is proposed to control many aspects of NSC behavior, including balancing the quiescence and proliferation of NSCs, determining the cell division mode (symmetric versus asymmetric), and preventing premature depletion of stem cells to maintain neurogenesis throughout life. Interactions between neurogenic niches and NSCs also govern the homeostatic regulation of adult neurogenesis under diverse physiological, environmental, and pathological conditions. An important implication from revisiting many previously-identified regulatory factors is that most of them (e.g., the antidepressant fluoxetine and exercise) affect gross neurogenesis by acting downstream of NSCs at the level of intermediate progenitors and neuroblasts, while leaving the NSC pool unaffected. Therefore, it is critically important to address how various niche components, signaling pathways, and environmental stimuli differentially regulate distinct stages of adult neurogenesis

Cerebellar granule neuron progenitors are the source of Hk2 in the postnatal cerebellum

A response to Leprince: The role of Bergmann glial cells in cerebellar development. Cancer & Metabolism 2013, 1:14 We recently demonstrated that developmentally regulated aerobic glycolysis is integral to the normal process of postnatal neurogenesis and becomes co-opted in medulloblastoma. In our work, we concluded that Hexokinase 2 (Hk2), which we found to be required for Shh-induced aerobic glycolysis, was expressed specifically by cerebellar granule neuron progenitors (CGNPs). We observed altered migration of CGNPs in hGFAP-cre;Hk2f/f mice and attributed this aspect of the phenotype to premature differentiation of CGNPs caused by loss of aerobic glycolysis. In response to our work, LePrince draws attention to the role of Bergmann glia in cerebellar development

Spatial ecology of a range-expanding bumble bee pollinator

Molecular methods have greatly increased our understanding of the previously cryptic spatial ecology of bumble bees (Bombus spp.), with knowledge of the spatial ecology of these bees being central to conserving their essential pollination services. Bombus hypnorum, the Tree Bumble Bee, is unusual in that it has recently rapidly expanded its range, having colonized much of the UK mainland since 2001. However, the spatial ecology of B. hypnorum has not previously been investigated. To address this issue, and to investigate whether specific features of the spatial ecology of B. hypnorum are associated with its rapid range expansion, we used 14 microsatellite markers to estimate worker foraging distance, nest density, between‐year lineage survival rate and isolation by distance in a representative UK B. hypnorum population. After assigning workers to colonies based on full or half sibship, we estimated the mean colony‐specific worker foraging distance as 103.6 m, considerably less than values reported from most other bumble bee populations. Estimated nest density was notably high (2.56 and 0.72 colonies ha−1 in 2014 and 2015, respectively), estimated between‐year lineage survival rate was 0.07, and there was no evidence of fine‐scale isolation by distance. In addition, genotyping stored sperm dissected from sampled queens confirmed polyandry in this population (mean minimum mating frequency of 1.7 males per queen). Overall, our findings establish critical spatial ecological parameters and the mating system of this unusual bumble bee population and suggest that short worker foraging distances and high nest densities are associated with its rapid range expansion

How the sun protection factor (SPF) of sunscreen films change during solar irradiation

We have investigated how the sun protection factor (SPF) of different types of sunscreen film varies with “standard” solar irradiation due to photochemical processes. We have used a combination of chemical actinometry, measurement and modelling to estimate the overall quantum yields for the photoprocesses occurring for avobenzone (AVB) and isopentyl p-methoxycinnamate (MC) in either propane-1,2-diol (PG) or squalane (SQ) as solvent. Using the obtained parameters, we have developed models to calculate the evolution of the film spectra and derived SPF values for both non-scattering sunscreen films consisting of solutions of multiple UV filters and for highly scattering Pickering emulsion based sunscreen films. Model calculations for all films are in excellent agreement with film spectra measured as a function of irradiation time using different laboratory light sources. Finally, using the estimated parameters and experimentally validated models, we are able to quantitatively predict how the in vitro SPF values for different film types containing any set combination of UV filter concentrations will vary with time due to photochemical processes induced by irradiation with “standard” sunlight. This provides a useful tool for the rational design and optimisation of new sunscreen formulations

Evaporation of Sunscreen Films: How the UV Protection Properties Change

© 2016 American Chemical Society. We have investigated the evaporation of thin sunscreen films and how the light absorption and the derived sun protection factor (SPF) change. For films consisting of solutions of common UV filters in propylene glycol (PG) as solvent, we show how evaporation generally causes three effects. First, the film area can decrease by dewetting leading to a transient increase in the average film thickness. Second, the film thins by evaporative loss of the solvent. Third, precipitation of the UV filter occurs when solvent loss causes the solubility limit to be reached. These evaporation-induced changes cause the UV absorbance of the film to decrease with resultant loss of SPF over the time scale of the evaporation. We derive an approximate model which accounts semiquantitatively for the variation of SPF with evaporation. Experimental results for solutions of different UV filters on quartz, different skin mimicking substrates, films with added nanoparticles, films with an added polymer and films with fast-evaporating decane as solvent (instead of slow evaporating PG) are discussed and compared with model calculations. Addition of either nanoparticles or polymer suppress film dewetting. Overall, it is hoped that the understanding gained about the mechanisms whereby film evaporation affects the SPF will provide useful guidance for the formulation of more effective sunscreens

Essential Function of Dicer in Resolving DNA Damage in the Rapidly Dividing Cells of the Developing and Malignant Cerebellum

Maintenance of genomic integrity is critical during neurodevelopment, particularly in rapidly dividing cerebellar granule neuronal precursors that experience constitutive replication-associated DNA damage. As Dicer was recently recognized to have an unexpected function in the DNA damage response, we examined whether Dicer was important for preserving genomic integrity in the developing brain. We report that deletion of Dicer in the developing mouse cerebellum resulted in the accumulation of DNA damage leading to cerebellar progenitor degeneration, which was rescued with p53 deficiency; deletion of DGCR8 also resulted in similar DNA damage and cerebellar degeneration. Dicer deficiency also resulted in DNA damage and death in other rapidly dividing cells including embryonic stem cells and the malignant cerebellar progenitors in a mouse model of medulloblastoma. Together, these results identify an essential function of Dicer in resolving the spontaneous DNA damage that occurs during the rapid proliferation of developmental progenitors and malignant cells

Determining the sample size required to establish whether a medical device is non-inferior to an external benchmark

ObjectivesThe use of benchmarks to assess the performance of implants such as those used in arthroplasty surgery is a widespread practice. It provides surgeons, patients and regulatory authorities with the reassurance that implants used are safe and effective. However, it is not currently clear how or how many implants should be statistically compared with a benchmark to assess whether or not that implant is superior, equivalent, non-inferior or inferior to the performance benchmark of interest.We aim to describe the methods and sample size required to conduct a one-sample non-inferiority study of a medical device for the purposes of benchmarking.DesignSimulation study.SettingSimulation study of a national register of medical devices.MethodsWe simulated data, with and without a non-informative competing risk, to represent an arthroplasty population and describe three methods of analysis (z-test, 1−Kaplan-Meier and competing risks) commonly used in surgical research.Primary outcomeWe evaluate the performance of each method using power, bias, root-mean-square error, coverage and CI width.Results1−Kaplan-Meier provides an unbiased estimate of implant net failure, which can be used to assess if a surgical device is non-inferior to an external benchmark. Small non-inferiority margins require significantly more individuals to be at risk compared with current benchmarking standards.ConclusionA non-inferiority testing paradigm provides a useful framework for determining if an implant meets the required performance defined by an external benchmark. Current contemporary benchmarking standards have limited power to detect non-inferiority, and substantially larger samples sizes, in excess of 3200 procedures, are required to achieve a power greater than 60%. It is clear when benchmarking implant performance, net failure estimated using 1−KM is preferential to crude failure estimated by competing risk models.</jats:sec