Barium

The experimental composites were composed of Bis-phenol A diglycidyl dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) at a 50:30:20 mass ratio. All monomers were purchased from Esstech (Essington, PA, USA). Photoinitiators were added to the monomers as follows: 0.2 wt.% of dl-camphoroquinone (Polysciences Inc., Warrington, PA, USA), 0.8 wt.% of a tertiary amine (EDMAB – ethyl 4-dimethylaminobenzoate; Avocado, Heysham, England), and 0.2 wt.% inhibitor (BHT – 2,6-di-tert-butyl-4-methylphenol; Sigma–Aldrich, St. Louis, MO, USA).
Six thiourethane oligomers were synthesized in solution in the presence of catalytic amounts of triethylamine. Two multi-functional thiols – pentaerythritol tetra-3-mercaptopropionate (PETMP) or trimethylol-tris-3-mercaptopropionate (TMP) – were combined with three di-functional isocyanates – 1,6-hexanediol-diissocyante (HDDI) or 1,3-bis(1-isocyanato-1-methylethyl) benzene (BDI) (aromatic) or 1-isocyanato-4-[(4-isocyanatocyclohexyl) methyl] cyclohexane (DHDI) in 60 ml of methylene chloride. In addition, 1 mol of 3-(triethoxysilyl)propyl isocyanate was also added to each of the six combinations described above – this is the source of trimethoxy silane to be used for the subsequent silanization step. The reaction was catalyzed by triethylamine. The isocyanate:thiol mol ratio was kept at 1:2.5 (with thiol in excess) to avoid macro-gelation of the oligomer during reaction, according to the Flory–Stockmayer theory²¹ , leaving pendant thiols and trimethoxy silanes. Oligomers were purified by precipitation in hexanes and rotoevaporation, and then characterized by mid-IR and NMR spectroscopy^{6 (link)}. The disappearance of the isocyanate mid-IR peak at 2270 cm⁻¹ and the appearance of NMR resonance signals at 3.70 ppm were used as evidence for completion of isocyanate reaction and thiourethane bond formation, respectively³⁶ .
For the silanization procedures, thiourethane oligomers were combined with 65 ml of an ethanol: distilled water solution (80:20 vol%), previously acidified by the addition of glacial acetic acid (pH = 4.5). Thiourethane was added at 2 wt%, in relation to the solution mass. Five grams of neat barium silicate glass filler (average size = 1.0 μm; Kavo Kerr Corporation, Orange, CA) was added to the solution, kept under magnetic stirring for 24 hours, filtered, and dried for 4 days in an oven at 37 °C.
The TU fillers were introduced at 50 wt% to the monomer matrix with a centrifugal mixer (DAC 150 Speed Mixer, Flacktek, Landrum, SC, USA) operated for 2 min at 1800 rpm. All procedures were carried out under yellow light.
Control groups were prepared with a commercially available unsilanized (UNS) and methacrylate-silanized (SIL-MA) barium glass filler particles (average size = 1.0 μm; Kerr Corporation, Orange, CA). All photocuring procedures were carried out using a mercury arc lamp (EXFO Acticure 4000 UV Cure; Mississauga, Ontario, Canada) filtered at 320–500 nm (light guide diameter = 5 mm). In order to verify the achieved functionalization and its efficiency, the different filler particles were analyzed by thermogravimetric analysis (TGA) over a temperature range of 50 °C to 850 °C at 10 °C/minute.

A total of 20 participants with GOLD Stage II–IV moderate-to-severe COPD who were enrolled in the SPACE in the Boston area agreed to participate in a NELF pilot study; further details of recruitment have been described elsewhere [8 (link)].
For this pilot study, we measured indoor air pollution exposure in the home as well as long-term exposure using a portable air monitor (PAM). Short-term indoor PM_2.5 was measured with cascade impactor samplers [10 (link)] in the home for the seven days preceding nasal sampling. Gravimetric filter samples were collected using Teflon filters and PM_2.5 concentration for the seven day sampling period was determined by measurement of pre- and post-sampling filter weights and sampler flow rate as previously described [10 (link)]. BC was determined from the PM_2.5 fraction by the optical absorbance measurement using the SootScan OT21 Transmissometer (Magee Scientific, Berkeley, CA, USA), which is a cost-effective, non-destructive method that quantifies filter particles using optical measurements at the wavelength of 880 nm [11 (link)]. Participants also measured personal long-term PM_2.5 exposure by PAM for 4 months over a 12 month period. We estimated long-term PM_2.5 exposure by taking the average daily measurement over all four months of data collection for each participant.
At the end of the seven day indoor air sampling period, NELF was sampled once in both nares using an absorbent fibrous matrix (Leukosorb medium) soaked in sterile saline solution [9 (link)]. 16 out of 20 nasal samples were collected during fall and winter months. Following a previously described procedure [9 (link)], Ergonomic Leukosorb strips were inserted in both nostrils for 2 min, then removed and placed in sterile vials for storage.
For the NELF metals analysis, elements were selected based on previously reported associations with indoor and outdoor pollution sources, including motor vehicle exhaust and road dust (barium [Ba], copper [Cu], Fe, lead [Pb], zinc [Zn]) [12 (link)–14 (link)], oil combustion (Ni, vanadium [V]) [15 (link), 16 (link)] and cooking (Fe, Zn) [12 (link), 13 (link), 17 (link), 18 (link)].
The concentration of these metals was determined in the NELF using inductively coupled plasma mass spectrometry [19 (link)] at the Wisconsin State Laboratories. Each of the elements used in the analysis had minimal detection on blank fibrous matrices. Samples from both nares were averaged for each participant and reported as the average concentration (ng per nasosorption strip). To evaluate whether metals from the same sources were present within NELF, we assessed correlations between metal concentrations in the NELF samples using Spearman correlations.
Using linear regression models, we examined if seven day PM_2.5 and BC in the home and long-term (four month average) PM_2.5 by PAM were associated with per-person averaged nasal fluid metal concentrations. We also examined models using log-transformed nasal fluid metal concentrations. The primary models were unadjusted. We also evaluated models adjusted for participant sex and age at baseline visit. Additionally, we performed a sensitivity analysis to determine whether nasal metal concentration may serve as a predictor of air pollutant exposure using linear regression models with nasal metal concentration as the primary predictor and log-transformed pollutant concentrations as the outcome.