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Journal of Exposure Science &... Mar 2022Silicone personal samplers are increasingly being used to measure chemical exposures, but many of these studies do not attempt to calculate environmental concentrations.
BACKGROUND
Silicone personal samplers are increasingly being used to measure chemical exposures, but many of these studies do not attempt to calculate environmental concentrations.
OBJECTIVE
Using measurements of silicone wristband uptake of organic chemicals from atmospheric exposure, create log K and k predictive models based on empirical data to help develop air equivalency calculations for both volatile and semi-volatile organic compounds.
METHODS
An atmospheric vapor generator and a custom exposure chamber were used to measure the uptake of organic chemicals into silicone wristbands under simulated indoor conditions. Log K models were evaluated using repeated k-fold cross-validation. Air equivalency was compared between best-performing models.
RESULTS
Log K and log k estimates calculated from uptake data were used to build predictive models from boiling point (BP) and other parameters (all models: R = 0.70-0.94). The log K models were combined with published data and refined to create comprehensive and effective predictive models (R: 0.95-0.97). Final estimates of air equivalency using novel BP models correlated well over an example dataset (Spearman r = 0.984) across 5-orders of magnitude (<0.05 to >5000 ng/L).
SIGNIFICANCE
Data from silicone samplers can be translated into air equivalent concentrations that better characterize environmental concentrations associated with personal exposures and allow direct comparisons to regulatory levels.
Topics: Air Pollutants; Environmental Monitoring; Humans; Silicones; Volatile Organic Compounds
PubMed: 33953340
DOI: 10.1038/s41370-021-00332-6 -
Journal of Dentistry Nov 2023As jaw-tracking systems integrate into digital prosthetic workflows, their accuracy remains underexplored. This study aimed to evaluate the in vitro accuracy of a novel...
OBJECTIVES
As jaw-tracking systems integrate into digital prosthetic workflows, their accuracy remains underexplored. This study aimed to evaluate the in vitro accuracy of a novel digital jaw-tracking system (Modjaw, Villeurbanne, France) by comparing its precision and trueness to that of an industrial scanner.
METHODS
Upper and lower typodont models were scanned with an industrial-grade optical scanner (ATOS Q, Carl Zeiss GOM Metrology GmbH, Germany) to produce master scans. The models were placed in a phantom head with artificial joints to replicate five different intermaxillary relationships (IMRs). The 1, 2, 3, 4, and 5 mm IMR distances were stabilized by five silicone bites. The silicone bites were repositioned after each measurement. ATOS scanned the whole artificial joint with the models three times in each IMR to assess the precision of the repositioning (i.e., bite precision). The master scans were uploaded to Modjaw. Modjaw recorded the five IMR positions three times each to assess the precision of the Modjaw. Precision was calculated by aligning the scans within the same group, whereas Modjaw trueness was evaluated by aligning ATOS and Modjaw scans. The mean absolute distance (MAD) between aligned surfaces was calculated. The effect of IMR on the MAD was evaluated using a linear mixed model.
RESULTS
The mean bite precision across the IMRs was 7.6 ± 0.53 µm. Modjaw precision over the IMRS was 9.7 ± 1.76 µm, and the trueness was 10.8 ± 1.40 µm. Increased IMRs up to 4 mm significantly increased the MAD from 6.5 to 8.5 µm for the bite precision, 4.8 to 15.7 µm Modjaw precision, and 7.1 to 14.9 µm for trueness.
CONCLUSIONS
Modjaw excelled in accuracy, comparable to industrial scanners and superior to traditional methods. IMR elevation marginally deteriorates the accuracy. Future studies should extend to varied movements beyond centric relations and encompass the influence of intraoral scanners.
Topics: Dental Impression Technique; Models, Dental; Computer-Aided Design; Imaging, Three-Dimensional; Silicones
PubMed: 37777084
DOI: 10.1016/j.jdent.2023.104730 -
Journal of Visualized Experiments : JoVE Jan 2022Intravital microscopy (IVM) enables visualization of cell movement, division, and death at single-cell resolution. IVM through surgically inserted imaging windows is...
Intravital microscopy (IVM) enables visualization of cell movement, division, and death at single-cell resolution. IVM through surgically inserted imaging windows is particularly powerful because it allows longitudinal observation of the same tissue over days to weeks. Typical imaging windows comprise a glass coverslip in a biocompatible metal frame sutured to the mouse's skin. These windows can interfere with the free movement of the mice, elicit a strong inflammatory response, and fail due to broken glass or torn sutures, any of which may necessitate euthanasia. To address these issues, windows for long-term abdominal organ and mammary gland imaging were developed from a thin film of polydimethylsiloxane (PDMS), an optically clear silicone polymer previously used for cranial imaging windows. These windows can be glued directly to the tissues, reducing the time needed for insertion. PDMS is flexible, contributing to its durability in mice over time-up to 35 days have been tested. Longitudinal imaging is imaging of the same tissue region during separate sessions. A stainless-steel grid was embedded within the windows to localize the same region, allowing the visualization of dynamic processes (like mammary gland involution) at the same locations, days apart. This silicone window also allowed monitoring of single disseminated cancer cells developing into micro-metastases over time. The silicone windows used in this study are simpler to insert than metal-framed glass windows and cause limited inflammation of the imaged tissues. Moreover, embedded grids allow for straightforward tracking of the same tissue region in repeated imaging sessions.
Topics: Animals; Cell Movement; Diagnostic Imaging; Intravital Microscopy; Mice; Silicones; Skull
PubMed: 35068483
DOI: 10.3791/62757 -
Nano Letters Sep 2022Cells migrate through channel-like tracks. While polydimethylsiloxane devices emulate such tracks , their channel walls are impermeable and have supraphysiological...
Cells migrate through channel-like tracks. While polydimethylsiloxane devices emulate such tracks , their channel walls are impermeable and have supraphysiological stiffness. Existing hydrogel-based platforms address these issues but cannot provide high-throughput analysis of cell motility in independently controllable stiffness and confinement. We herein develop polyacrylamide (PA)-based microchannels of physiological stiffness and prescribed dimensions for high-throughput analysis of cell migration and identify a biphasic dependence of speed upon confinement and stiffness. By utilizing novel four-walled microchannels with heterogeneous stiffness, we reveal the distinct contributions of apicolateral versus basal microchannel wall stiffness to confined versus unconfined migration. While the basal wall stiffness dictates unconfined migration, apicolateral stiffness controls confined migration. By tracking nanobeads embedded within channel walls, we innovate three-dimensional traction force measurements around spatially confining cells at subcellular resolution. Our unique and highly customizable device fabrication strategy provides a physiologically relevant platform to study confined cells.
Topics: Cell Movement; Dimethylpolysiloxanes; Hydrogels; Mechanical Phenomena; Traction
PubMed: 36112517
DOI: 10.1021/acs.nanolett.2c01261 -
International Journal of Environmental... Feb 2022Humans are exposed to numerous potentially harmful chemicals throughout their lifetime. Although many studies have addressed this issue, the data on chronic exposure is... (Review)
Review
Humans are exposed to numerous potentially harmful chemicals throughout their lifetime. Although many studies have addressed this issue, the data on chronic exposure is still lacking. Hence, there is a growing interest in methods and tools allowing to longitudinally track personal exposure to multiple chemicals via different routes. Since the seminal work, silicone wristbands (WBs) have been increasingly used to facilitate human exposure assessment, as using WBs as a wearable sampler offers new insights into measuring chemical risks involved in many ambient and occupational scenarios. However, the literature lacks a detailed overview regarding methodologies being used; a comprehensive comparison with other approaches of personal exposure assessment is needed as well. Therefore, the aim of this review is fourfold. First, we summarize hitherto conducted research that employed silicone WBs as personal passive samplers. Second, all pre-analytical and analytical steps used to obtain exposure data are discussed. Third, we compare main characteristics of WBs with key features of selected matrices used in exposure assessment, namely urine, blood, hand wipes, active air sampling, and settled dust. Finally, we discuss future needs of research employing silicone WBs. Our work shows a variety of possibilities, advantages, and caveats associated with employment of silicone WBs as personal passive samplers. Although further research is necessary, silicone WBs have already been proven valuable as a tool for longitudinal assessment of personal exposure.
Topics: Dust; Environmental Monitoring; Humans; Silicones
PubMed: 35206121
DOI: 10.3390/ijerph19041935 -
Medicina (Kaunas, Lithuania) Nov 2022Developing a prosthetic heart valve that combines the advantageous hemodynamic properties of its biological counterpart with the longevity of mechanical prostheses has...
Developing a prosthetic heart valve that combines the advantageous hemodynamic properties of its biological counterpart with the longevity of mechanical prostheses has been a major challenge for heart valve development. Anatomically inspired artificial polymeric heart valves have the potential to combine these beneficial properties, and innovations in 3D printing have given us the opportunity to rapidly test silicone prototypes of new designs to further the understanding of biophysical properties of artificial heart valves. TRISKELION is a promising prototype that we have developed, tested, and further improved in our institution. Materials and STL files of our prototypes were designed with FreeCad 0.19.2 and 3D printed with an Agilista 3200W (Keyence, Osaka, Japan) using silicones of Shore hardness 35 or 65. Depending on the valve type, the support structures were printed in AR-M2 plastics. The prototypes were then tested using a hemodynamic pulse duplicator (HKP 2.0) simulating an aortic valve cycle at 70 bpm with 70 mL stroke volume (cardiac output 4.9 L/min). Valve opening cycles were visualized with a high-speed camera (Phantom Miro C320). The resulting values led to further improvements of the prototype (TRISKELION) and were compared to a standard bioprosthesis (Edwards Perimount 23 mm) and a mechanical valve (Bileaflet valve, St. Jude Medical). : We improved the silicone prototype with currently used biological and mechanical valves measured in our setup as benchmarks. The regurgitation fractions were 22.26% ± 4.34% (TRISKELION) compared to 8.55% ± 0.22% (biological) and 13.23% ± 0.79% (mechanical). The mean systolic pressure gradient was 9.93 ± 3.22 mmHg (TRISKELION), 8.18 ± 0.65 mmHg (biological), and 10.15 ± 0.16 mmHg (mechanical). The cardiac output per minute was at 3.80 ± 0.21 L/min (TRISKELION), 4.46 ± 0.01 L/min (biological), and 4.21 ± 0.05 L/min (mechanical). The development of a heart valve with a central structure proves to be a promising concept. It offers another principle to address the problem of longevity in currently used heart valves. Using 3D printing to develop new prototypes provides a fast, effective, and accurate way to deepen understanding of its physical properties and requirements. This opens the door for translating and combining results into modern prototypes using highly biocompatible polymers, internal structures, and advanced valve layouts.
Topics: Humans; Heart Valves; Printing, Three-Dimensional; Polymers; Heart Valve Prosthesis; Silicones
PubMed: 36422234
DOI: 10.3390/medicina58111695 -
Journal of Biomedical Optics Apr 2015Photoacoustic imaging is an emerging technique. Although commercially available photoacoustic imaging systems currently exist, the technology is still in its infancy....
Photoacoustic imaging is an emerging technique. Although commercially available photoacoustic imaging systems currently exist, the technology is still in its infancy. Therefore, the design of stable phantoms is essential to achieve semiquantitative evaluation of the performance of a photoacoustic system and can help optimize the properties of contrast agents. We designed and developed a polydimethylsiloxane (PDMS) phantom with exceptionally fine geometry; the phantom was tested using photoacoustic experiments loaded with the standard indocyanine green dye and compared to an agar phantom pattern through polyethylene glycol-gold nanorods. The linearity of the photoacoustic signal with the nanoparticle number was assessed. The signal-tonoiseratio and contrast were employed as image quality parameters, and enhancements of up to 50 and up to 300%, respectively, were measured with the PDMS phantom with respect to the agar one. A tissue-mimicking (TM)-PDMS was prepared by adding TiO2 and India ink; photoacoustic tests were performed in order to compare the signal generated by the TM-PDMS and the biological tissue. The PDMS phantom can become a particularly promising tool in the field of photoacoustics for the evaluation of the performance of a PA system and as a model of the structure of vascularized soft tissues.
Topics: Equipment Design; Models, Cardiovascular; Organosilicon Compounds; Phantoms, Imaging; Photoacoustic Techniques
PubMed: 25894254
DOI: 10.1117/1.JBO.20.4.046008 -
Regulatory Toxicology and Pharmacology... Jun 2021This paper compares the phase-specific inhalation toxicity of the cyclic semi-volatile methylsiloxanes (cVMSs) D4, D5 and D6. The objectives of this paper are to... (Review)
Review
This paper compares the phase-specific inhalation toxicity of the cyclic semi-volatile methylsiloxanes (cVMSs) D4, D5 and D6. The objectives of this paper are to re-analyze information from acute to chronic inhalation studies on rats with these cVMSs to identify the unifying principles of phase-specific toxicity at the portal-of-entry and if they depend on acute, acute-on-chronic or chronic mechanisms. This re-analysis supports the hypothesis that concentrations must be high enough to exceed the vapor saturation at any given temperature for stabilizing the aerosol phase and evoking phase-specific effects at sites of the respiratory tract susceptible to the cVMSs-specific physicochemical properties amphiphilicity and surface tension. In summary, the portal-of-entry effects and related findings appear to be acute in nature and specific to liquid aerosol. The repeated inhalation exposure studies with D4 and D5 up to two years in duration did not reveal chronic aggravations of portal of entry outcomes. Findings at a pulmonary location where amphiphilic surfactant molecules are present appear to be caused by the acute adaptation to deposited dose. Such outcome should better be described as a high-dose liquid aerosol phenomenon imparted by the physicochemical properties "liquid" and "hydrophobic". This calls for a phase-specific human risk characterization of cVMSs.
Topics: Aerosols; Animals; Dose-Response Relationship, Drug; Inhalation Exposure; Rats; Siloxanes; Solutions
PubMed: 33831492
DOI: 10.1016/j.yrtph.2021.104923 -
Waste Management (New York, N.Y.) Jul 2023Landfill gas (LFG) is formed by microorganisms within a landfill; it can be utilized as a renewable fuel in power plants. Impurities such as hydrogen sulfide and...
Landfill gas (LFG) is formed by microorganisms within a landfill; it can be utilized as a renewable fuel in power plants. Impurities such as hydrogen sulfide and siloxanes can cause significant damage to gas engines and turbines. The aim of this study was to determine the filtration efficiencies of biochar products made of birch and willow to remove hydrogen sulfides, siloxanes, and volatile organic compounds from the gas streams compared to activated carbon. Experiments were conducted on a laboratory scale with model compounds and in a real LFG power plant where microturbines are used to generate power and heat. The biochar filters removed heavier siloxanes effectively in all of the tests. However, the filtration efficiency for volatile siloxane and hydrogen sulfide declined quickly. Biochars are promising filter materials but require further research to improve their performance.
Topics: Hydrogen Sulfide; Gases; Charcoal; Siloxanes; Biofuels; Waste Disposal Facilities
PubMed: 37230876
DOI: 10.1016/j.wasman.2023.05.006 -
Macromolecular Rapid Communications Apr 2021A modular strategy for the synthesis of dendron-linear polymer hybrids comprised of a flexible polydimethylsiloxane (PDMS) midblock with cationic...
A modular strategy for the synthesis of dendron-linear polymer hybrids comprised of a flexible polydimethylsiloxane (PDMS) midblock with cationic 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) dendron end groups is developed. The invention of a scalable methodology to access quaternary ammonium carboxylate building blocks and their direct use in esterification chemistry enables rapid access to cationic bis-MPA dendrons. The convergent click coupling of highly charged dendrons to hydrophobic PDMS chain-ends gives a 12-membered family of hybrids that are comprised of different dendron generations (G1-3) and quaternary ammonium alkyl chain lengths (C , C , C , C ). This provides a library of materials with variable hydrophobicity, charge density, and chain-end valency. The physical behavior of the dendron-linear PDMS hybrid copolymers significantly changes after introduction of the cationic dendron end-groups and leads to soft-solid materials as a result of inhibited chain mobility. These PDMS-dendron hybrids are expected to behave as surface-active antimicrobial additives in bulk cross-linked silicone systems.
Topics: Cations; Dendrimers; Dimethylpolysiloxanes; Hydrophobic and Hydrophilic Interactions; Polymers
PubMed: 33368765
DOI: 10.1002/marc.202000652