Method for determining resin cure kinetics with low-frequency Raman spectroscopy.

Characterizing resin extent of cure kinetics is critical to understanding the structure-property-processing relationships of polymers. The disorder band present in the low-frequency region of the Raman spectrum is directly related to conformational entropy and the modulus of amorphous materials, both of which change as the resin polymerizes. Normalizing the disorder band to its shoulder (∼85 cm-1) provides structural conversion kinetics, which we can directly correlate to chemical conversion kinetics for methacrylate and epoxy-amine based resin systems. In addition to fitting both the structural and chemical conversion data to a phenomenological kinetic rate equation, we also demonstrate a relationship between the chemical and structural kinetics which appears to relate to the softness of the material. Lastly, we use the method to investigate a methacrylate/epoxy interpenetrating polymer network resin system. We find that the structural and chemical conversions occur simultaneously during the formation of the primary (methacrylate) network, but there is a lag between the two during the formation of the secondary (epoxy-amine) network.

Return to work and lost earnings after acute respiratory distress syndrome: a 5-year prospective, longitudinal study of long-term survivors.

BACKGROUND: Delayed return to work is common after acute respiratory distress syndrome (ARDS), but has undergone little detailed evaluation. We examined factors associated with the timing of return to work after ARDS, along with lost earnings and shifts in healthcare coverage. METHODS: Five-year, multisite prospective, longitudinal cohort study of 138 2-year ARDS survivors hospitalised between 2004 and 2007. Employment and healthcare coverage were collected via structured interview. Predictors of time to return to work were evaluated using Fine and Grey regression analysis. Lost earnings were estimated using Bureau of Labor Statistics data. RESULTS: Sixty-seven (49%) of the 138 2-year survivors were employed prior to ARDS. Among 64 5-year survivors, 20 (31%) never returned to work across 5-year follow-up. Predictors of delayed return to work (HR (95% CI)) included baseline Charlson Comorbidity Index (0.77 (0.59 to 0.99) per point; p=0.04), mechanical ventilation duration (0.67 (0.55 to 0.82) per day up to 5 days; p<0.001) and discharge to a healthcare facility (0.49 (0.26 to 0.93); p=0.03). Forty-nine of 64 (77%) 5-year survivors incurred lost earnings, with average (SD) losses ranging from US$38 354 (21,533) to US$43 510 (25,753) per person per year. Jobless, non-retired survivors experienced a 33% decrease in private health insurance and concomitant 37% rise in government-funded coverage. CONCLUSIONS: Across 5-year follow-up, nearly one-third of previously employed ARDS survivors never returned to work. Delayed return to work was associated with patient-related and intensive care unit/hospital-related factors, substantial lost earnings and a marked rise in government-funded healthcare coverage. These important consequences emphasise the need to design and evaluate vocation-based interventions to assist ARDS survivors return to work.

Healthcare Resource Use and Costs in Long-Term Survivors of Acute Respiratory Distress Syndrome: A 5-Year Longitudinal Cohort Study.

OBJECTIVE: To evaluate the time-varying relationship of annual physical, psychiatric, and quality of life status with subsequent inpatient healthcare resource use and estimated costs. DESIGN: Five-year longitudinal cohort study. SETTING: Thirteen ICUs at four teaching hospitals. PATIENTS: One hundred thirty-eight patients surviving greater than or equal to 2 years after acute respiratory distress syndrome. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Postdischarge inpatient resource use data (e.g., hospitalizations, skilled nursing, and rehabilitation facility stays) were collected via a retrospective structured interview at 2 years, with prospective collection every 4 months thereafter, until 5 years postacute respiratory distress syndrome. Adjusted odds ratios for hospitalization and relative medians for estimated episode of care costs were calculated using marginal longitudinal two-part regression. The median (interquartile range) number of inpatient admission hospitalizations was 4 (2-8), with 114 patients (83%) reporting greater than or equal to one hospital readmission. The median (interquartile range) estimated total inpatient postdischarge costs over 5 years were $58,500 ($19,700-157,800; 90th percentile, $328,083). Better annual physical and quality of life status, but not psychiatric status, were associated with fewer subsequent hospitalizations and lower follow-up costs. For example, greater grip strength (per 6 kg) had an odds ratio (95% CI) of 0.85 (0.73-1.00) for inpatient admission, with 23% lower relative median costs, 0.77 (0.69-0.87). CONCLUSIONS: In a multisite cohort of long-term acute respiratory distress syndrome survivors, better annual physical and quality of life status, but not psychiatric status, were associated with fewer hospitalizations and lower healthcare costs.

EXPRESS: Influence of Rheological Modifications on Primary Network Chemical and Structural Cure Kinetics for an Interpenetrating Polymer Network Resin.

The development of non-contact in situ techniques for monitoring of cure kinetics has the potential to greatly improve both resin formulation and processing. We have recently shown that low-frequency Raman spectroscopy is a viable method for assessing resin structural cure kinetics and complements the traditional chemical conversion determined from the fingerprint region of the spectrum. In this work we further evaluate the relationship between the structural and chemical conversion by investigating two chemically identical yet rheologically different interpenetrating polymer network resin formulations. Rheological analysis demonstrates a relationship between structural conversion and storage modulus, which is not observed in the chemical conversion data. We show that one can produce master cure kinetics curves with comparable kinetic constants using both the chemical and structural conversion methodologies. Parametric analysis of the structural conversion, chemical conversion, and photorheological conversion was combined with a semi-empirical model for the storage shear modulus as a function of extent of cure.

Itaconic Acid as a Comonomer in Betulin-Based Thermosets via Sequential and Bulk Preparation.

The inherent chemical functionalities of biobased monomers enable the production of renewably sourced polymers that further advance sustainable manufacturing. Itaconic acid (IA) is a nontoxic, commercially produced biobased monomer that can undergo both UV and thermal curing. Betulin is a biocompatible, structurally complex diol derived from birch tree bark that has been recently studied for materials with diverse applications. Here, betulin, IA, and biobased linear diacids, 1,12-dodecanedioic acid (C12) and 1,18-octadecanedioic acid (C18), were used to prepare thermosets using sequential and bulk curing methods. Thermoplastic polyester precursors were synthesized and formulated into polyester-methacrylate (PM) resins to produce sequential UV-curable thermosets. Bulk-cured polyester thermosets were prepared using a one-pot, solventless melt polycondensation using glycerol as a cross-linker. The structure-property relationships of the thermoplastic polyester precursors, sequentially prepared PM thermosets, and bulk-cured polyester thermosets were evaluated with varying IA content. Both types of thermosets exhibited higher storage moduli, Tgs, and thermal stabilities with greater IA comonomer content. These results demonstrate the viability of using IA as a comonomer to produce betulin-based thermosets each with tunable properties, expanding the scope of their applications and use in polymeric materials.

Health care resource use and costs of two-year survivors of acute lung injury. An observational cohort study.

RATIONALE: Survivors of acute lung injury (ALI) require ongoing health care resources after hospital discharge. The extent of such resource use, and associated costs, are not fully understood. OBJECTIVES: For patients surviving at least 2 years after ALI, we evaluated cumulative 2-year inpatient admissions and related costs, and the association of patient- and intensive care unit-related exposures with these costs. METHODS: Multisite observational cohort study in 13 intensive care units at four academic teaching hospitals evaluating 138 two-year survivors of ALI. MEASUREMENTS AND MAIN RESULTS: Two-year inpatient health care use data (i.e., admissions to hospitals, and skilled nursing and rehabilitation facilities) were collected for patients surviving at least 2 years, via (1) one-time retrospective structured interview with patient and/or proxy, (2) systematic medical record review for nonfederal study site hospitals, and (3) inpatient medical record review for non-study site hospitals, as needed for clarifying patient/proxy reports. Costs are reported in 2013 U.S. dollars. A total of 138 of 142 (97%) 2-year survivors completed the interview, with 111 (80%) reporting at least one inpatient admission during follow-up, for median (interquartile range [IQR]) estimated costs of $35,259 ($10,565-$81,166). Hospital readmissions accounted for 76% of costs. Among 12 patient- and intensive care unit-related exposures evaluated, baseline comorbidity and intensive care unit length of stay were associated with increased odds of incurring any follow-up inpatient costs. Having Medicare or Medicaid (vs. private insurance) was associated with median estimated costs that were 85% higher (relative median, 1.85; 95% confidence interval, 1.01-3.45; P=0.045). CONCLUSIONS: In this multisite study of 138 two-year survivors of ALI, 80% had one or more inpatient admission, representing a median (IQR) estimated cost $35,259 ($10,565-$81,166) per patient and $6,598,766 for the entire cohort. Hospital readmissions represented 76% of total inpatient costs, and having Medicare or Medicaid before ALI was associated with increased costs. With the aging population and increasing comorbidity, these findings have important health policy implications for the care of critically ill patients.

Anxiety across the transition to parenthood: change trajectories among low-risk parents.

BACKGROUND AND OBJECTIVES: A number of sources suggest changes in anxiety across the transition to parenthood may be experienced by parents in different ways, yet no studies have examined whether new parents experience changes in anxiety in distinct subgroups. DESIGN: We conducted a longitudinal study of 208 first-time parents (104 couples) from a low-risk population. Parents were interviewed from the third trimester of pregnancy to nine-months postpartum. METHODS: The current study utilized latent class growth analysis to explore subgroups of change in symptoms of anxiety. Based on stress and coping theory, we also examined a number of personal and social prenatal predictors of subgroup membership. RESULTS: We identified two distinct change trajectories: (1) moderate and stable and (2) low and declining. We also found prenatal depression, expected parenting efficacy, and relationship satisfaction were significantly associated with subgroup membership. CONCLUSIONS: Our results suggest a majority of new parents adjust well to parenthood in terms of anxiety, while a smaller subgroup of parents experience continually higher levels of anxiety months after the baby is born.