Optovibrometry: tracking changes in the surface tension and viscosity of multicomponent droplets in real-time

An instrument was developed for measuring real time changes in the surface tension and viscosity of multicomponent droplets of miscible liquids and other soft materials. Droplets containing glycerol and water were supported on superamphiphobic surfaces and vibrated by applying a short mechanical impulse. Laser light was refracted through the droplets and allowed to fall on the surface of a photodiode. Time dependent variations in the intensity measured by the photodiode during vibration were used to monitor the decay of the droplet oscillations. The frequencies and spectral widths of the droplet vibrational resonances were then obtained from Fourier transforms of these time dependent intensity signals. A recently developed model of viscoelastic droplet vibration was used along with these values and measurements of the drop dimensions to extract the surface tension and viscosity of the drops as they evaporated. Collection of data was automated and values of frequency, spectral width, drop size, surface tension and viscosity were obtained with a time resolution of three seconds over a period of thirty minutes. The values of surface tension and viscosity obtained were shown to be in good agreement with literature values obtained from bulk glycerol/water solutions; thus validating the technique for wider application to other multicomponent liquids and soft matter systems

Single droplet microrheology

The vibration of microlitre sized drops in partial contact with a substrate was used to extract the rheological properties of multicomponent fluids. Sessile and pendant drop vibration was triggered using a short mechanical impulse. Sessile drops were supported on superhydrophobic surfaces and their vibration monitored using laser light, refracted through the drops and focussed on the sensor of a photodiode. Pendant drops were suspended from clean pipette tips and their vibration was recorded using a high speed camera. Time dependent photodiode intensity/centre of mass variations were Fourier transformed to extract the frequency and spectral widths of vibration. The vibration of aqueous glycerol sessile drops was tracked in real time as the drops evaporated. The changing surface tension and viscosity were extracted using a simple model describing the vibration of a viscous sessile drop. The values of surface tension and viscosity obtained for initial bulk solutions were shown to be in good agreement with literature values, however evaporating drops showed signs of surface contamination after ∼300s. The vibration of sessile drops of aqueous poly(acrylamide-co-acrylic acid) solutions was used to calculate the shear storage and loss moduli using a simple theoretical model. The resulting rheological properties were found to be in agreement with microrheology measurements of the same solutions. The model was also applied to pendant drops of aqueous poly(acrylamide-co-acrylic acid). The majority of the rheological data measured for the pendant drops agreed with microrheology and sessile drop data. Drop vibration therefore provides an accurate method of quantifying the rheological properties of single drops in short time

Single droplet microrheology

The vibration of microlitre sized drops in partial contact with a substrate was used to extract the rheological properties of multicomponent fluids. Sessile and pendant drop vibration was triggered using a short mechanical impulse. Sessile drops were supported on superhydrophobic surfaces and their vibration monitored using laser light, refracted through the drops and focussed on the sensor of a photodiode. Pendant drops were suspended from clean pipette tips and their vibration was recorded using a high speed camera. Time dependent photodiode intensity/centre of mass variations were Fourier transformed to extract the frequency and spectral widths of vibration. The vibration of aqueous glycerol sessile drops was tracked in real time as the drops evaporated. The changing surface tension and viscosity were extracted using a simple model describing the vibration of a viscous sessile drop. The values of surface tension and viscosity obtained for initial bulk solutions were shown to be in good agreement with literature values, however evaporating drops showed signs of surface contamination after ∼300s. The vibration of sessile drops of aqueous poly(acrylamide-co-acrylic acid) solutions was used to calculate the shear storage and loss moduli using a simple theoretical model. The resulting rheological properties were found to be in agreement with microrheology measurements of the same solutions. The model was also applied to pendant drops of aqueous poly(acrylamide-co-acrylic acid). The majority of the rheological data measured for the pendant drops agreed with microrheology and sessile drop data. Drop vibration therefore provides an accurate method of quantifying the rheological properties of single drops in short time

Rheological properties of viscoelastic drops on superamphiphobic substrates

The rheological properties of microliter sized drops of polymer solutions were investigated using measurements of their mechanical vibrational response. Drops were suspended on superamphiphobic substrates and vibrated by the application of a short mechanical impulse. Surface vibrations were monitored by refracting laser light through the drops and focusing the refracted light onto the surface of a photodiode. Time dependent variations in the photodiode output were Fourier transformed to obtain the frequency and spectral width of the mechanical resonances of the drops. These quantities were related to the frequency dependent shear storage and loss moduli (G′ and G″, respectively) using a simple theoretical model. The resulting rheological properties were found to be in agreement with microrheology measurements of the same solutions. Drop vibration therefore provides a fast and accurate method of quantifying the rheological properties of single drops

The Postpartum Specific Anxiety Scale: development and preliminary validation

Perinatal symptoms of anxiety are increasingly recognised due to their high prevalence and impact. Studies using pregnancy-specific anxiety measures have found that they may predict perinatal outcomes more effectively than general measures. However, no such measure exists to assess anxieties specific to the postpartum. This study aimed to develop and validate a measure (Postpartum Specific Anxiety Scale; PSAS) that accurately represents the specific anxieties faced by postpartum women, using a four-stage methodology: (1) 51 items were generated from interviews conducted with a group of 19 postpartum women at two time points, (2) the scale was reviewed and refined by a diverse expert panel, (3) an online pilot study (n = 146) was conducted to assess comprehensibility and acceptability and (4) an online sample of 1282 mothers of infants up to 6 months old completed the PSAS against a battery of convergent measures. A subsample (n = 262) repeated the PSAS 2 weeks later. The PSAS possessed good face and content validity and was comprehensible and acceptable to postpartum women. PSAS scores were significantly correlated with other measures indicating good convergent validity. Principal component analyses (PCA) revealed a simple four-factor structure. Reliability of the overall scale and individual PSAS factors proved to be good to excellent. A preliminary receiver operating characteristic (ROC) analysis also suggested that the PSAS may be a useful screening tool. The psychometric evidence suggests that the PSAS is an acceptable, valid, and reliable research tool to assess anxieties, which are specific to the postpartum period. Next steps in the iterative validation process are considered for both research and screening purposes

Postpartum-specific anxiety as a predictor of infant-feeding outcomes and perceptions of infant-feeding behaviours: new evidence for childbearing specific measures of mood

Studies of pregnancy-specific anxiety suggest that it is a distinct construct which predicts perinatal outcomes more effectively than other general measures of anxiety. In response, a novel measure of postpartum-specific anxiety (PSAS) has been developed and validated, but it is not yet clear whether it possesses the same predictive power as its pregnancy-specific counterparts. The aim of this short-term prospective study was to (a) test the predictive validity of the PSAS in the context of one specific perinatal outcome, infant-feeding, and (b) examine whether the PSAS may be more efficacious at predicting infant-feeding outcomes and behaviours than the more commonly used general measures. Eight hundred mothers of infants aged between 0 and 6 months completed the PSAS alongside general measures of anxiety and depression at baseline. A subsample (n = 261) returned to complete a follow-up questionnaire examining infant-feeding outcomes and behaviours two weeks later. Hierarchical regression models revealed that the PSAS was associated with lower odds of breastfeeding exclusively, and breastfeeding in any quantity in the first 6 months postpartum. PSAS scores were also significantly associated with infant-feeding behaviours including a lower perceived enjoyment of food, and greater perceived food responsiveness and satiety responsiveness in the infant. As hypothesised, the PSAS was a stronger predictor of infant-feeding outcomes and behaviours than general anxiety and depression. The findings provide evidence for the predictive validity of the PSAS and call for the use of childbearing specific measures of mood when attempting to predict perinatal outcomes. Replication of these findings across other indices of maternal and infant health is now necessary

Comparative cancer risk associated with methotrexate, other non-biologic and biologic disease-modifying anti-rheumatic drugs

OBJECTIVE: There is little information comparing the potential risk of cancer across conventional and biologic disease-modifying anti-rheumatic drugs (DMARDs) in patients with rheumatoid arthritis (RA). Methotrexate has not been the focus of most contemporary pharmacoepidemiologic studies of cancer. METHODS: We conducted a comparative effectiveness study with cancer as the outcome. A large observational cohort of RA was followed up from 2001 to 2010. Reports of any cancer prompted a confirmation process that included adjudication of the primary cancer records. We used a propensity score (PS) with relevant covariates and cohort trimming to improve the balance between DMARD cohorts. Cox proportional hazard regression models were constructed to estimate the risk of cancer with various DMARDs, all compared with methotrexate. RESULTS: We identified 6806 DMARD courses for analysis (1566 methotrexate; 904 nbDMARDs; 3761 TNF antagonists; 408 abatacept; and 167 rituximab). Non-biologic DMARDs (HR 0.17, 95% CI 0.05-0.65) and TNF antagonists (HR 0.29, 95% CI 0.05-0.65) were associated with a reduced adjusted risk of cancer compared with methotrexate. Abatacept (HR 1.55, 95% CI 0.40-5.97) and rituximab (HR 0.42, 95% CI 0.07-2.60) were similar in risk of cancer with methotrexate. These results were robust to sensitivity analyses. After controlling for DMARD exposures, risk factors for cancer included male gender, age, and alcohol consumption. CONCLUSIONS: Cancer risk was elevated for methotrexate users compared with nbDMARDs and TNF antagonists