Fibrous particle deposition in human nasal passage: The influence of particle length, flow rate, and geometry of nasal airway

Man-made vitreous fibers (MMVFs) have been used as a substitute for asbestos in industrial and residential applications. This shift has raised the concerns of the potential hazards associated with inhalation of these fibers. The human nose is an important protective organ that captures harmful particles and then clears them from human respiratory tract. However, studies have shown that some or even most of the inhalable fibrous particles can penetrate human nose and deposit into the deep lung. The understanding of fibrous particle deposition in the human nasal passage has important occupational health and possible drug delivery applications. To study the deposition pattern and influential factors, three realistic human nasal models were used and a dielectrophoretic classifier was applied to generate test aerosol of glass fibers with a narrow length distribution. These models were made by using stereolithography based on MRI data from two human subjects. Regional and total deposition efficiencies were measured for five different flow rates: 4, 8, 12, 15, and 18 Lpm and four different fiber length ranges: 10–19, 20–29, 30–39, and 40–. This study found that deposition of glass fibers (with about diameter) in human nasal passage is mainly due to inertial impaction and these fibers orientated themselves normal to the flow direction before deposition occurs. An effective aerodynamic diameter is defined such that the deposition efficiencies of glass fibers are comparable with those of spherical particles. Non-dimensional parameters were defined and an empirical model based on the experimental results is proposed to calculate fibrous particle deposition efficiency in human nose. Empirical expressions were also developed to estimate the pressure drop across the nasal model. Thus, empirical equations are now available for the prediction of total deposition in the human nasal tract for the fibrous particles under constant inspiring flow rates. In addition, this study suggested that these equations can also be used to predict the deposition of spherical particles.     

Fiber Dielectrophoresis

Dielectrophoresis is the motion of an uncharged particle in a nonuniform electric field. Using prolate spheroids to model cylindrical fibers, we find that the theoretical dielectrophoretic velocity of a conducting fiber in an insulating medium is proportional to the square of the fiber length and is virtually independent of fiber diameter. This prediction has been verified experimentally using aluminum wire particles 0.5–5 mm long and 25–75 μm in diameter moving in the space between cylindrical electrodes in a medium of mineral oil. The results point to the development of a fiber length classifier based on dielectrophoresis.     

Deposition of Fiber in the Human Nasal Airway

Inhalation is the main route for aerosol entering the human body. Many occupational lung diseases are associated with exposure to fiber aerosol in the workplace. However, very few studies to date have been conducted for investigating fiber deposition in the human airway. As a result, there is a notable lack of information on the nature of the fiber deposition pattern in the human respiratory tract. With this in mind, this research consisted of a large number of experimental works to investigate the effects of fiber dimension on the deposition pattern for a human nasal airway. Carbon fibers with uniform diameter (3.66 μm) and polydispersed length were adopted as the test material. Deposition studies were conducted by delivering aerosolized carbon fibers into a nasal airway replica (encompassing the nasal airway regions from vestibule to nasopharynx) at constant inspiratory flow rates of 7.5, 15, 30, and 43.5 l/min. Fibers deposited in each nasal airway region were washed out and the length distribution was determined by microscopic measurement. The results showed that impaction is the dominant deposition mechanism. Most of the fibers with high inertia deposited in the anterior region of the nasal airway (vestibule and nasal valve). In contrast, fibers with low inertia were found to pass through the entire nasal airway easily and collected on the filter at the outlet. Comparing the deposition results between fibers and spherical particles, our data showed that the deposition efficiencies of fibers are significantly lower than that of spherical particles, which implies that the inhaled fibers could pass through the entire nasal airway comparatively easier than spherical particles. Thus, relatively more fibers would be able to enter the lower respiratory tract.     

Deposition of man-made fibers in human respiratory airway casts

New experiments of fiber deposition in the human respiratory airway were conducted by delivering aerosolized man-made fibers (TiO₂ and glass) into two different human respiratory airway casts at three inspiratory flow rates. Fiber deposition patterns and regional deposition efficiencies in the airway casts were studied and compared with previously published results acquired from carbon fiber. The results showed that very few small momentum fibers (TiO₂ and glass fibers) were deposited in the airway casts, which is significantly different from the results found for the large momentum fiber (carbon fiber). The fiber deposition pattern and deposition efficiency in the two airway casts were similar in both trend and magnitude, and all of the data revealed an overall continuity between fiber materials. Empirical models were proposed based on the experimental data acquired for estimating the fiber's regional deposition efficiency in the human respiratory airway.     

Deposition of Man-Made Fibers in a Human Nasal Airway

Many occupational lung diseases are associated with exposure to aerosolized fibers in the workplace. The nasal airway is a critical route for fiber aerosol to enter the human respiratory tract. The fiber deposition efficiency in the nasal airway could be used as an index to indicate the fraction of the inhaled fibers potentially transported to the lower airways. In this research, experiments of fiber deposition in the human nasal airway were conducted. Man-made carbon, glass, and titanium dioxide fibers in the inertia regime were used as the test fiber materials. The deposition studies were carried out by delivering aerosolized fibers into a human nasal airway replica at constant human inspiratory flow rates ranging from 15 l/min to 43.5 l/min. The deposition results were compared in detail between these fiber materials to study how the fiber characteristics affected the nasal airway deposition. The results showed that the deposition efficiency of the carbon fiber increases as the fiber impaction parameter increases. Many carbon fibers deposited in the anterior region of the nasal airway. In contrast, very few glass or titanium dioxide fibers deposited in the nasal airway, but relatively more of these two fibers deposited in the turbinate region. This result implies that, if a fiber in the inertia regime is inhaled during normal human breathing, the smaller the fiber, the more easily it could enter the human lower respiratory tract, possibly causing harm to the human respiratory tract.     

On the Effect of Fiber Shape and Packing Array on Elastic Properties of Fiber-Polymer-Matrix Composites

Abstract

In this study, three-dimensional finite element simulations on the base of the cell model and micromechanics are made to predict effective elastic properties of fibrous composites. The effects of fiber shape, packing array and volume fraction on the overall elastic behavior of an epoxy resin containing unidirectional glass fibers are examined. The geometrical structure includes three types of periodic fiber arrangements in cubic, hexagonal and rectangular cells. The fibers are assumed to be of four shapes; square, circular, elliptic and rectangular. The numerical results indicate that the overall transverse elastic properties are rather sensitive to both fiber shape and packing array while fiber geometry has no effect on the apparent overall Young's modulus in the longitudinal direction of the fibrous composite.     

In vitro cytotoxicity of Manville Code 100 glass fibers: Effect of fiber length on human alveolar macrophages

Background  

Synthetic vitreous fibers (SVFs) are inorganic noncrystalline materials widely used in residential and industrial settings for insulation, filtration, and reinforcement purposes. SVFs conventionally include three major categories: fibrous glass, rock/slag/stone (mineral) wool, and ceramic fibers. Previous in vitro studies from our laboratory demonstrated length-dependent cytotoxic effects of glass fibers on rat alveolar macrophages which were possibly associated with incomplete phagocytosis of fibers ≥ 17 μm in length. The purpose of this study was to examine the influence of fiber length on primary human alveolar macrophages, which are larger in diameter than rat macrophages, using length-classified Manville Code 100 glass fibers (8, 10, 16, and 20 μm). It was hypothesized that complete engulfment of fibers by human alveolar macrophages could decrease fiber cytotoxicity; i.e. shorter fibers that can be completely engulfed might not be as cytotoxic as longer fibers. Human alveolar macrophages, obtained by segmental bronchoalveolar lavage of healthy, non-smoking volunteers, were treated with three different concentrations (determined by fiber number) of the sized fibers in vitro. Cytotoxicity was assessed by monitoring cytosolic lactate dehydrogenase release and loss of function as indicated by a decrease in zymosan-stimulated chemiluminescence.     

Short fiber reinforced thermoplastics. I. Rheological properties of glass fiber reinforced Noryl

An experimental study on the flow behavior of glass fiber reinforced Noryl (a commercial poly(phenyleneoxide)/polystyrene blend) using a capillary rheometer is described. The effect of fiber concentration on shear viscosity and die swell was studied at various temperatures. Breakage of glass fibers during flow through the rheometer is discussed; it was found that the average fiber length (about 230 μm) was not significiantly altered, except at the highest shear rate (575 s⁻¹) studied. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity without changing the basic rheological character-shear rate dependency. No discernible viscosity changes were measured by incorporating 10 weight percent fibers, and upon further increase of fiber concentration from 20 to 30 weight percent no appreciable increase in viscosity was noted. It is shown that short glass fibers cause a large reduction in extrudate swell. The presence of voids and fiber orientation contribute to the decrease of the die swell, an effect greater than expected from volumetric considerations alone.     

Performance Evaluation of a Fiber Length Classifier

A performance evaluation was conducted on a differential mobility classifier that separates fibers according to length using dielectrophoresis. The classifier had been constructed and used for several applications in previous studies. The performance of the classifier was predicted using a two-dimensional axisymmetric model of the flow field and then calculating particle trajectories for a variety of conditions. Based on the flow calculations, several regions of the classifier were improved to reduce likelihood of turbulent losses. For a given total flow through the classifier and a maximum voltage across the electrodes, the performance of the classifier was found to depend on the ratios of the aerosol flow to the inner and the outer sheath flows. It was found that the minimum classifiable length, the minimum length distribution width, and the throughput of classified fibers can each be optimized, but not independently. Several approaches to testing the resolution of the classifier were tried. The first was to measure the length distribution of fibers passing through the classifier under different conditions using electron microscopy. However, this was a slow and imprecise measure of performance. Two approaches using monodisperse latex spheres were used; one operated the instrument as an electrical mobility (electrophoresis) analyzer and the other evaluated only the flow system accuracy. All measures indicate that the classifier operates close to theoretical performance, but improvements are still possible. Suggested improvements require redesign of the flow system and improved electrode alignment.     

Direct Numerical Simulation of Curly Fibers in Turbulent Channel Flow

Wall deposition of rigid-link fibrous aerosols in a turbulent channel flow is studied. The instantaneous turbulent velocity vector field is generated by the direct numerical simulation of the Navier-Stokes equation with the aid of a pseudospectral code. It is assumed that the fiber is composed of five rigidly attached ellipsoidal links. The dynamic behavior of these elongated and irregular shaped particles is markedly different from the spherical ones. The hydrodynamic forces and torques acting on the fiber are evaluated and the equations governing the translational and rotational motions of the fiber are analyzed. Euler's four parameters are used, and motions of fibrous particles in the turbulent channel flow field are studied. Ensembles of 8000 fiber trajectories are generated and are used for evaluating various statistics. Root mean-square fiber velocities and fiber concentrations at different distances from the wall are evaluated and discussed. Empirical models for the deposition rate of curly fibers are also developed. The model predictions are compared with the simulation data and good agreement is observed.     

Collection efficiency of airborne fibers on nylon mesh screens with different pore sizes and configurations

Aerodynamic behavior of airborne fibers including high-aspect ratio particles plays an important role in aerosol filtration and lung deposition. Fiber length is considered to be an important parameter in causing toxicological responses of elongate mineral particles, including asbestos, as well as one of the factors affecting lung deposition. In order to estimate the toxicity of fibers as a function of fiber length, it is required to separate fibers by length and understand mechanisms related to fiber separation for use in toxicology studies. In this study, we used nylon mesh screens with different pore sizes as a separation method to remove long fibers and measured screen collection efficiency of glass fibers (a surrogate for asbestos) as a function of aerodynamic diameter with the aim to prepare toxicology samples free of long fibers and/or harvest long fibers from the screen. Two screen configurations ([i] without a laminar flow entrance length, and [ii] with the entrance length) were tested to investigate the effect of screen pore size (10, 20, and 60 µm) and screen configuration on collection efficiency of fibers. Screen collection efficiency (η) was obtained based on measurements of downstream concentrations of a test chamber either without or with a screen. The results showed that screen collection efficiency increases as screen pore size decreases from 60 to 10 µm for both cases with and without entrance lengths. For the screen configuration without entrance length, higher collection efficiency was obtained than the case with entrance length probably due to increased impaction caused by the close proximity of inlet to screen. In addition, the difference between the collection efficiencies for the different configurations was small in the aerodynamic size range below 3 µm while it increased in the size range from 3 to about 7 µm, indicating that as large aerodynamic diameter is associated with longer fibers, some differential selection of fibers is possible. Modified model collection efficiency for 10 and 20 µm screens based on the interception predicts well the measured data for the case with entrance length, indicating that the fiber deposition on these screens occurs dominantly through the interception mechanism in the micrometer size range under a given flow condition.     

Transport and deposition of ellipsoidal fibers in low Reynolds number flows

The motion of elongated, ellipsoidal fibers in low Reynolds number flows was studied using a computational modeling approach. The computer model resolved the coupled translational and rotational motion of fibers in laminar flows. The computational model was applied in a circular duct and the transport and deposition of ellipsoidal fibers with different sizes and aspect ratios were simulated. An experimental setup was also developed and deposition of glass fibers in a pipe flow in laminar flow regime was measured. A fiber classifier was used to generate fibers with different aspect ratios in controlled condition. The computational model predictions were compared with the experimental data and good agreement was observed. It was found that the flow shear rate, the fiber aspect ratio, and the particle-to-fluid density ratio significantly affect the transport and deposition of ellipsoidal fibers. It was also found that the computational model should account for the duct flow entrance region in order to provide physically realistic predictions. Attention was given to comparing the effectiveness of using equivalent spheres to approximate the elongated fibers. Several commonly used equivalent spheres were studied, and their suitability for characterizing motion of ellipsoidal fiber particles in the laminar flow was studied.     

Characterization of an anisotropic hydrogel tissue substrate for infusion testing

Artificial tissue models that capture specific transport properties are useful for investigating physical phenomena important to drug delivery. In this study, an in vitro tissue model was developed and characterized with the goal of mimicking aligned tissue. An anisotropic porous medium was developed by the construction of a 1% agarose hydrogel implanted with different volume fractions (～ 5, 10, and 20%) of 10‐μm‐diameter glass fibers. The developed substrate was able to capture anisotropic transport after the direct infusion of a macromolecular tracer, Evans blue albumin (EBA). To further characterize the test substrate, the diffusion tensor of water was measured by diffusion tensor imaging, and the ratios of the diffusivities in the directions parallel and perpendicular to the glass fibers were 1.16, 1.20, and 1.26 for 5, 10, and 20% fiber volume fractions, respectively. The hydraulic conductivity was estimated by the measurement of pressure gradients across samples under controlled microflow conditions in the direction parallel to implanted fibers. The hydraulic conductivities at various hydrogel concentrations without fibers and in a 1% hydrogel with various fiber volume fractions were measured; for example, K_∥ = 1.20 × 10^?12 m⁴ N^?1 s^?1 (where K_∥ is the conductivity component in the direction parallel to the glass fibers) for 20% fiber volume fractions. Also, EBA distributions were fit to porous medium transport models to estimate hydraulic conductivity in the direction perpendicular to glass fibers. The estimated ratio of directional hydraulic conductivity, K_∥/K_? (where K_? is the conductivity component in the direction perpendicular to the glass fibers), ranged from approximately 3 to 5, from 6 to 10, and from 40 to 90 for 5, 10, and 20% fiber volume fractions, respectively. These agarose hydrogel models provided convenient media for quantifying infusion protocols at low flow rates. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Inertial Impactors to Measure Aerodynamic Diameters of Man-Made Organic Fibers

It is widely accepted that the aerodynamic diameter of a particle is one of the main factors that determines particle deposition into the human respiratory system. The determination of aerodynamic diameter of spheres or near spherical objects is routinely accomplished using impactors. The aerodynamic diameter of man made organic fibers (MMOF), on the other hand, has not traditionally been measured using impactors, because fibers of the same cross section may have different lengths and a variety of shapes (straight, curved, etc.) for each length. The aerodynamic size of the fibers is thus a function of fiber orientation. Single and multiple stage impactors have been developed, calibrated, and validated specifically for the determination of the aerodynamic diameter of large fibers with circumscribed diameters between 20 and 35 w m and an aspect ratio ranging from subfiber lengths (aspect ratio < 3) up to 40. The impactor allows measurements of the aerodynamic diameter of cellulose acetate fibers released during mechanical smoking of cigarettes. The performance characteristics were evaluated by spherical particles of known diameters, fibers of known length and diameter, and computational fluid dynamic calculations. Our methodology has shown that inertial impactors can be used to determine the aerodynamic diameter of large cellulose acetate fibers.     

Direct measurement of aerosol glass fiber alignment in a DC electric field

We report non-conducting aerosol fiber (i.e., glass fiber) alignment in a DC electric field. Direct observation of fiber orientation state is demonstrated and quantitative analysis of fiber alignment is made using phase contrast microscopy in four different conditions: (i) dry air and naturally charged fibers, (ii) humid and naturally charged, (iii) humid and neutralized (Boltzmann charge distribution), and (iv) humid and neutralized with an electrostatic precipitator upstream electrodes (i.e., non-charged). The glass fiber aerosols generated by a vortex shaking method were conditioned using a Po-210 neutralizer or humidifier and were provided into a test unit where cylindrical or parallel plate electrodes are used and high voltage is applied to them. Fibers were collected on a filter immediately downstream from the electrodes and their images were taken through an optical microscope to visualize the fiber orientation and measure the alignment angles and lengths of the fibers. The results showed that under all four conditions tested, airborne glass fibers could be aligned to the electric field with different alignment quality, indicating that the glass fibers can be polarized in a steady electric field. In humid air, the fiber alignment along the field direction was observed to be much better and the number of uniform background particles (i.e., randomly oriented fibers) in angular distributions is smaller than that in dry air. Also, it was found that charged fibers in humid air could be better aligned with negligible uniform background than neutralized and non-charged fibers. Possible mechanisms about humidity and charge effects on enhanced fiber alignment are discussed to support the observations. The results indicate that the enhancement of alignment in an electric field would be possible in humid air for other non-conducting fibrous particles having surface chemistry similar to glass fibers.     

Deposition of fiber in a human airway replica

Fiber is a notorious occupational hazard. Exposures to airborne asbestos fiber in the workplace increase the incidence of lung cancer for asbestos workers. Due to the lack of experimental data, the nature of fiber deposition in the human airway is unclear. In this study, a set of experiments were carried out to investigate the effect of fiber dimension and fiber inertia on the deposition pattern in the human airway replica. The deposition study was conducted by delivering aerosolized carbon fibers into the replica at constant inspiratory flow rates of 15–60 l/min. The results showed that impaction is the dominant deposition mechanism in this study. Most of the high-inertia fibers deposited in the oropharynx and the carina ridges of the bifurcations in tracheobronchial airways. A series of fiber deposition patterns were obtained and the deposition efficiencies were acquired for certain regions in the human airway replica.     

Thermal conductivity of a polyethylene filled with disoriented short-cut carbon fibers

Thermal conductivity of polyethylene composites, filled with randomly dispersed and disoriented (oriented at random) carbon fibers with various aspect ratios, were investigated. Orientation of fibers was quantitatively evaluated by Hermans' parameter. In specimens of isotropic composites, i.e., filled with randomly dispersed and disoriented fibers, thermal conductivity increased with an increase in the fiber length. The result is discussed in comparison with electric conductivity of the composites and explained by the contact probability of filled fibers. Further, it was confirmed that our model previously proposed could be adopted to predict thermal conductivity of the isotropic composite filled with carbon fibers. Also, the effect of fiber length of the C₂ parameter included in the model is discussed and C₂ was found to have a linear relation with the aspect ratio of fibers at a sufficiently large value. In this study, a shape factor of a filler (aspect ratio) could be directly introduced into the equation, which was shown in our previous paper.     

Characterization of the draping behavior of jute woven fabrics for applications of natural‐fiber/epoxy composites

In this study, we investigated the draping behavior of jute woven fabric to study the feasibility of using natural fabrics in place of synthetic glass‐fiber fabrics. Draping behavior describes the in‐mold deformation of fabrics, which is vital for the end appearance and performance of polymer composites. The draping coefficient was determined with a common drapemeter for fabrics with densities of 228–765 g/m² and thread counts under different humidity and static dynamic conditions. The results were compared to glass‐fiber fabrics with close areal densities. Characterization of the jute fabrics was carried out to fill the knowledge gap about natural‐fiber fabrics and to ease their modeling. The tensile and bending stiffnesses and the shear coupling were also characterized for a plain woven jute fabric with a tensile machine, Shirley bending tester, and picture frame, respectively. As a case study, the draping and resin‐transfer molding of the jute fabric over a complex asymmetric form was performed to measure the geometrical conformance. The adoption of natural fibers as a substitute for synthetic fibers, where the strength requirements are satisfied, would thus require no special considerations for tool design or common practices. However, the use of natural fibers would lead to weight and cost reductions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1453–1465, 2013     

Fibrous Particle Deposition in a Turbulent Channel Flow—An Experimental Study

The deposition rate of glass cylinders and dust paper fibers in a turbulent duct flow was studied experimentally. The glass fibers with a minimum diameter of 5 μm and the paper fibers with a minimum diameter of 1–20 μm and aspect ratios from 4 to 20 were deposited on a flat gold plate. The particle concentration at the test section was measured with the aid of an isokinetic probe in conjunction with a digital image processing technique. An oil lubricant was used on the plate to reduce the effect of particle bounce from the surface. The experimental data show that the deposition rate increases with an increase in fiber length and size. For a fixed minimum diameter or a fixed equivalent relaxation time, the deposition rate increases rapidly with fiber aspect ratio. When the equivalent spherical particle relaxation time is used, the deposition rate of the fibers was found to increase only slightly with aspect ratio and resemble those of spherical particles. The measured deposition velocities were in good agreement with the empirical model predictions and previous data.     

Effects of thermal history on mechanical behavior of PEEK and its short-fiber composites

The effect of crystallinity differences induced by mold wall temperature and annealing on mechanical behavior is evaluated for poly(etheretherketone) (PEEK) resin and its composites. The systems investigated were neat PEEK, glass fiber (GF) reinforced PEEK, and carbon fiber (CF) reinforced PEEK. Both composite systems were reinforced with 10, 20, and 30 wt% fiber. The degree of crystallinity (X_c) of PEEK was found to increase by processing at higher mold temperatures, by annealing, and by fiber length reductions, which appears to indicate the ability of short fibers to nucleate the crystallization of PEEK under favorable thermal conditions. Improvements in Young's modulus and strength together with ductility reductions are generally obtained as crystallinity increases in both neat PEEK and its composites. The contribution of crystallinity to mechanical behavior is significant only for neat PEEK and PEEK reinforced by 10% fiber. SEM micrographs reveal that this is due to a change in failure mode. When PEEK is reinforced by carbon fibers or by 20–30% glass fibers, a macroscopic brittle mode of failure is observed irrespective of matrix crystallinity, and mechanical behavior is principally determined by the nature and content of the reinforcing fibers.