Numerical Simulation of the Effect of Smooth Muscle Layer Thickening on Stress Distribution in the Airway Wall

Many chronic respiratory diseases are associated with airway remodeling such as hyperplasia and/or hypertrophy of the smooth muscle cells. It is well known that the hyperplasia and hypertrophy of the smooth muscle cells directly affects the mechanical properties of the smooth muscle layer. Consequently, it may cause uneven distribution of stress and thus local stress stimulation of the cells and tissues in the airway wall, possibly leading to pathogenesis of airway dysfunction such as airway hyperresponsiveness. However, it is difficult to experimentally study the effect of smooth muscle layer on stress distribution in the airway wall. Therefore, in the present work, we built a finite element model which simplified the anatomical structure of the airway wall as a three-layer structure that included an inner wall layer, a smooth muscle layer and an adventitia layer. Based on this model, we varied the smooth muscle layer thickness either uniformly or locally and then computed the stress distribution in the modeled airway wall. The results revealed that the minimum stress occurred in the adventitia layer, and the maximum stress occurred in the smooth muscle layer. More importantly, the smooth muscle layer thickening, occurred either uniformly or locally, led to elevated stress level and enhanced stress concentration in the smooth muscle layer. And the enhancement of stress level and concentration was variable depending on the pattern of smooth muscle layer thickening. For a given extent of smooth muscle layer thickening, the stress level and concentration appeared to be determined by the number of locations and the separation distance between the locations at which the smooth muscle layer thickening occurred. In other words, the maximum stress level in the smooth muscle layer increased from 2.712kPa to 2.842KPa depending on whether the local thickening occurred at one location, 3 or 5 equally separated locations, 2 connected and 1 distanced location, or 3 all connected locations. These simulation results provide important insight for better understanding the mechanism through which the airway smooth muscle is involved in the alteration of airway dysfunction in health and disease, which may be helpful in developing novel diagnosis/therapy via targeting smooth muscle hyperplasia and/or hypertrophy for the prevention/treatment of asthma

Cell‐extracellular matrix interactions in the fluidic phase direct the topology and polarity of self‐organized epithelial structures

Introduction: In vivo, cells are surrounded by extracellular matrix (ECM). To build organs from single cells, it is generally believed that ECM serves as scaffolds to coordinate cell positioning and differentiation. Nevertheless, how cells utilize cell‐ECM interactions for the spatiotemporal coordination to different ECM at the tissue scale is not fully understood. Methods: Here, using in vitro assay with engineered MDCK cells expressing H2B‐mCherry (nucleus) and gp135/Podocalyxin‐GFP (apical marker), we show in multi‐dimensions that such coordination for epithelial morphogenesis can be determined by cell‐soluble ECM interaction in the fluidic phase. Results: The coordination depends on the native topology of ECM components such as sheet‐like basement membrane (BM) and type I collagen (COL) fibres: scaffold formed by BM (COL) facilitates a close‐ended (open‐ended) coordination that leads to the formation of lobular (tubular) epithelium. Further, cells form apicobasal polarity throughout the entire lobule/tubule without a complete coverage of ECM at the basal side, and time‐lapse two‐photon scanning imaging reveals the polarization occurring early and maintained through the lobular expansion. During polarization, gp135‐GFP was converged to the apical surface collectively in the lobular/tubular structures, suggesting possible intercellular communications. Under suspension culture, the polarization was impaired with multi‐lumen formation in the tubules, implying the importance of ECM biomechanical microenvironment. Conclusion: Our results suggest a biophysical mechanism for cells to form polarity and coordinate positioning at tissue scale, and in engineering epithelium through cell‐soluble ECM interaction and self‐assembly

Tuning the emission properties of a fluorescent polymer using a polymer microarray approach - identification of an optothermo responsive polymer

Fluorescent polymer microarrays were prepared using inkjet printing and screened. The fluorescence intensity was found to be tunable by temperature change when the dye was immobilized in identified thermo-responsive polymer beads.</p

Development of a Small Portable Device for Measuring Respiratory System Resistance Based on Forced Oscillation Technique

Spirometry and forced oscillation technique (FOT) are two different methods that are currently used for lung function test. However, the former requires patient’s effort to cooperate, thus is often unreliable for certain patients such as the young children and the latter is always related to bulky and expensive machines. In order to overcome the limitations of current device, we developed a portable prototype of FOT device for measuring respiratory resistance. The device consisted of a small advanced voice coil actuator to generate sinusoidal oscillatory airflow with amplitude of 2.5 cmH2O and frequency of 5 Hz, which was then superimposed onto the normal breathing airflow of the patient via a mouth piece. The pressure and flow signals of the respiratory airflow after absorption and refraction by the airways and the lung tissues were detected and acquired using NI USB-6211 data acquisition card and synchronous sampling pressure and flow sensors. After the upper computer received the digital signals that the capture card converted, the signals were processed and analyzed in real-time by the proprietary LabVIEW-based software. The analysis included digital signal filtering and impedance calculation in frequency domain, resulting in respiratory system resistance (Rrs) and reactance (Xrs). The results of present experiments on healthy volunteers demonstrated that the device could measure the respiratory system resistance with good reliability and accuracy. Importantly, due to both the hardware and software design the weight and volume of this device was reduced down to 3.5kg and 2500 cm3, respectively, proving the prototype to be worth of further developing into an inexpensive and portable tool for testing or monitoring lung function at rural community clinics or homes

Effect Assessment of Airflow Resistance by Local Airway Stenosis with 3D Printing Airway Model

Clinically noticing airway constriction can randomly cause small airway quickly closed and the surrouding airway occlusion happens subsequently. A phenomenon may happened called "avalanche phenomenon" inside airway [1]. But few study on how local airway stenosis affects the respiratory flow. Because the real local airway stenosis and its flow are still unable to be directly observed and measured. In this paper, narrow numerical model of the main and branched airway are established based on CT data of normal human airways. Then the trachea and bronchial branched airway constriction models are printed out on the 3D printer by PLA material. Finally, to measure airflow impedance of different airway models and analyze the impact of structural changes in the airway (shrink and narrow) airway impedance, we adopt independent research and development Forced Oscillation Technique(FOT). The test results preliminary show that the trachea stenosis has big effect on the airway viscous resistance (Rrs) and the elastic resistance (Xrs). The bronchial stenosis obviously increases the airway elastic resistance. This article provides a new method for the study on how local constriction affects the airflow inside airway in the future

Bitter Taste Receptor Agonist (Quinine) Induces Traction Force Reduction and Calcium Flux Increase in Airway Smooth Muscle Cells from Ovalbumin-Sensitized and Challenged Rats

Recently, bitter taste receptors (TAS2Rs) have been found in the lung, which can be stimulated with TAS2R agonist such as quinine to relax airway smooth muscle cells (ASMCs) via intracellular Ca2+ signaling generated from restricted phospholipase C activation. This provides a promising new therapy for asthma because enhanced contractility and impaired ability of relaxation of the ASMCs within the bronchial wall of asthmatic patients are thought to be ultimately responsible for airway constriction in asthma. However, further study is required for characterization of the effect of TAS2R agonist on the mechanical behaviors of ASMCs, in particular the traction force generation and associated mechanism in asthma model. Here, we sensitized Sprague Dawley rats with ovalbumin (OVA) for up to 12 weeks to simulate chronic asthma symptoms. Subsequently, we isolated ASMCs from these rats, and studied the traction force and intracellular Ca2+ signaling of the cells with/out treatment of quinine hydrochloride, a well-known TAS2R agonist. The results demonstrated that quinine hydrochloride relaxed the ASMC in a dose dependent manner. It also evoked dose-dependent increase of intracellular calcium ([Ca2+]i) in the ASMCs. Perhaps more importantly, the quinine-induced traction force reduction and Ca2+ flux increase were correlated. Taken together, our findings indicate that TAS2R agonists (e.g. quinine hydrochloride) could reduce the ability of ASMCs to generate traction force via activation of the intracellular calcium signaling, which may contribute as one of the mechanisms for TAS2R agonist-induced ASMC relaxation. This provides additional evidence to support TAS2R agonists as a new class of compounds with potential in treatment of chronic asthma

Stiffness of Substrate Influences the Distribution but not the Synthesis of Autophagosomes in Human Liver (LO2) Cells

Extracellular matrix (ECM) often becomes stiffer during tumor development, which not only gives the tumor's hardness feel but also actively contributes to the tumor formation. A good example is hepatocellular carcinoma (HCC) that usually develops within chronically stiffened liver tissues due to fibrosis and cirrhosis. On the other hand, HCC cells exhibit reduced autophagy in a malignancy dependent manner, suggesting autophagy is suppressed during tumor development. However, it is not known whether ECM stiffness would influence autophagy during tumor development. To investigate this issue, We cultured the human liver (LO2) cells that stably expressed autophagosome indicator LC3 on polydimethylsiloxane (PDMS) gels with stiffness varying from 11 to 1220 kPa. and on plastic cell culture dish as controls for up to 48h. We found that the total protein level of LC3-II in LO2 cells was not affected by the substrate stiffness. However the autophagosomes in LO2 cells cultured on the soft substrate (11 kPa PDMS gel) were localized and accumulated around the nucleus, while those on the stiff substrate (1220 kPa PDMS gel or plastic dish surface) were dispersed throughout the cytoplasmic space. Therefore, our data suggest that ECM stiffness may not directly synthesize nascent autophagosomes, but instead influence the location/translocation and ultimately distribution of autophagosomes in the cells