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Displaying publications 161 - 170 of 170 in total

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Fulltext Mechanoregulation of cardiac myofibroblast differentiation: implications for cardiac fibrosis and therapy

Yong KW, Li Y, Huang G, Lu TJ, Safwani WK, Pingguan-Murphy B, et al.

Am J Physiol Heart Circ Physiol, 2015 Aug 15;309(4):H532-42.
PMID: 26092987 DOI: 10.1152/ajpheart.00299.2015

Cardiac myofibroblast differentiation, as one of the most important cellular responses to heart injury, plays a critical role in cardiac remodeling and failure. While biochemical cues for this have been extensively investigated, the role of mechanical cues, e.g., extracellular matrix stiffness and mechanical strain, has also been found to mediate cardiac myofibroblast differentiation. Cardiac fibroblasts in vivo are typically subjected to a specific spatiotemporally changed mechanical microenvironment. When exposed to abnormal mechanical conditions (e.g., increased extracellular matrix stiffness or strain), cardiac fibroblasts can undergo myofibroblast differentiation. To date, the impact of mechanical cues on cardiac myofibroblast differentiation has been studied both in vitro and in vivo. Most of the related in vitro research into this has been mainly undertaken in two-dimensional cell culture systems, although a few three-dimensional studies that exist revealed an important role of dimensionality. However, despite remarkable advances, the comprehensive mechanisms for mechanoregulation of cardiac myofibroblast differentiation remain elusive. In this review, we introduce important parameters for evaluating cardiac myofibroblast differentiation and then discuss the development of both in vitro (two and three dimensional) and in vivo studies on mechanoregulation of cardiac myofibroblast differentiation. An understanding of the development of cardiac myofibroblast differentiation in response to changing mechanical microenvironment will underlie potential targets for future therapy of cardiac fibrosis and failure.

Matched MeSH terms: Stress, Mechanical*
Aerosol-based delivery of fibroblast cells for treatment of lung diseases

Kardia E, Yusoff NM, Zakaria Z, Yahaya B

J Aerosol Med Pulm Drug Deliv, 2014 Feb;27(1):30-4.
PMID: 23409833 DOI: 10.1089/jamp.2012.1020

Cell-based therapy has great potential to treat patients with lung diseases. The administration of cells into an injured lung is one method of repairing and replacing lost lung tissue. However, different types of delivery have been studied and compared, and none of the techniques resulted in engraftment of a high number of cells into the targeted organ. In this in vitro study, a novel method of cell delivery was introduced to investigate the possibility of delivering aerosolized skin-derived fibroblasts.

Matched MeSH terms: Stress, Mechanical
Physicochemical evaluation and in vitro hemocompatibility study on nanoporous hydroxyapatite

Ooi CH, Ling YP, Abdullah WZ, Mustafa AZ, Pung SY, Yeoh FY

J Mater Sci Mater Med, 2019 Mar 30;30(4):44.
PMID: 30929088 DOI: 10.1007/s10856-019-6247-5

Hydroxyapatite is an ideal biomaterial for bone tissue engineering due to its biocompatibility and hemocompatibility which have been widely studied by many researchers. The incorporation of nanoporosity into hydroxyapatite could transform the biomaterial into an effective adsorbent for uremic toxins removal especially in artificial kidney system. However, the effect of nanoporosity incorporation on the hemocompatibility of hydroxyapatite has yet to be answered. In this study, nanoporous hydroxyapatite was synthesized using hydrothermal technique and its hemocompatibility was determined. Non-ionic surfactants were used as soft templates to create porosity in the hydroxyapatite. The presence of pure hydroxyapatite phase in the synthesized samples is validated by X-ray diffraction analysis and Fourier transform infrared spectroscopy. The TEM images show that the hydroxyapatite formed rod-like particles with the length of 21-90 nm and diameter of 11-70 nm. The hydroxyapatite samples exhibit BET surface area of 33-45 m2 g-1 and pore volume of 0.35-0.44 cm3 g-1. The hemocompatibility of the hydroxyapatite was determined via hemolysis test, platelet adhesion, platelet activation and blood clotting time measurement. The nanoporous hydroxyapatite shows less than 5% hemolysis, suggesting that the sample is highly hemocompatible. There is no activation and morphological change observed on the platelets adhered onto the hydroxyapatite. The blood clotting time demonstrates that the blood incubated with the hydroxyapatite did not coagulate. This study summarizes that the synthesized nanoporous hydroxyapatite is a highly hemocompatible biomaterial and could potentially be utilized in biomedical applications.

Matched MeSH terms: Stress, Mechanical
Experimental determination of optimal force system required for control of anterior tooth movement in sliding mechanics

Sia S, Shibazaki T, Koga Y, Yoshida N

Am J Orthod Dentofacial Orthop, 2009 Jan;135(1):36-41.
PMID: 19121498 DOI: 10.1016/j.ajodo.2007.01.034

This study was designed to determine the optimum vertical height of the retraction force on the power arm that is required for efficient anterior tooth retraction during space closure with sliding mechanics.

Matched MeSH terms: Stress, Mechanical
Influence of stenosis on hemodynamic parameters in the realistic left coronary artery under hyperemic conditions

Kamangar S, Badruddin IA, Badarudin A, Nik-Ghazali N, Govindaraju K, Salman Ahmed NJ, et al.

Comput Methods Biomech Biomed Engin, 2017 Mar;20(4):365-372.
PMID: 27612619 DOI: 10.1080/10255842.2016.1233402

The current study investigates the hyperemic flow effects on heamodynamics parameters such as velocity, wall shear stress in 3D coronary artery models with and without stenosis. The hyperemic flow is used to evaluate the functional significance of stenosis in the current era. Patients CT scan data of having healthy and coronary artery disease was chosen for the reconstruction of 3D coronary artery models. The diseased 3D models of coronary artery shows a narrowing of >50% lumen area. Computational fluid dynamics was performed to simulate the hyperemic flow condition. The results showed that the recirculation zone was observed immediate to the stenosis and highest wall shear stress was observed across the stenosis. The decrease in pressure was found downstream to the stenosis as compared to the coronary artery without stenosis. Our analysis provides an insight into the distribution of wall shear stress and pressure drop, thus improving our understanding of hyperemic flow effect under both conditions.

Matched MeSH terms: Stress, Mechanical
Fulltext The effect of bur preparation on the surface roughness and reline bond strength of urethane dimethacrylate denture base resin

Baig MR, Ariff FT, Yunus N

Indian J Dent Res, 2011 Mar-Apr;22(2):210-2.
PMID: 21891887 DOI: 10.4103/0970-9290.84288

BACKGROUND: The clinical success of relining depends on the ability of reline resin to bond to denture base. Surface preparations may influence reline bond strength of urethane-based dimethacrylate denture base resin.
AIM: To investigate the effect of bur preparation on the surface roughness (R a ) of eclipse denture base resin and its shear bond strength (SBS) to an intra-oral self-curing reline material. The mode of reline bonding failure was also examined.
MATERIALS AND METHODS: Twenty-four cylindrical Eclipse™ specimens were prepared and separated into three groups of eight specimens each. Two groups were subjected to mechanical preparation using standard and fine tungsten carbide (TC) burs and the third group (control) was left unprepared. The R a of all specimens was measured using a contact stylus profilometer. Subsequently, relining was done on the prepared surface and SBS testing was carried out a day later using a universal testing machine.
RESULTS: One-way ANOVA revealed significant differences (P<0.05) in R a and SBS values for all the groups. Post-hoc Tukey's HSD test showed significant differences (P<0.05) between all the groups in the R a values. For SBS also there were significant differences (P<0.05), except between standard bur and control.
CONCLUSIONS: 1) There was a statistically significant difference in the R a of Eclipse™ specimens prepared using different carbide burs (P<0.05). 2) There was a statistically significant difference in the relined SBS (P<0.05) when prepared using different burs, but the difference between the standard bur and the control group was not statistically significant.

Matched MeSH terms: Stress, Mechanical
Fulltext Synthesis of Radiation Curable Palm Oil-Based Epoxy Acrylate: NMR and FTIR Spectroscopic Investigations

Salih AM, Ahmad MB, Ibrahim NA, Dahlan KZ, Tajau R, Mahmood MH, et al.

Molecules, 2015;20(8):14191-211.
PMID: 26248072 DOI: 10.3390/molecules200814191

Over the past few decades, there has been an increasing demand for bio-based polymers and resins in industrial applications, due to their potential lower cost and environmental impact compared with petroleum-based counterparts. The present research concerns the synthesis of epoxidized palm oil acrylate (EPOLA) from an epoxidized palm oil product (EPOP) as environmentally friendly material. EPOP was acrylated by acrylic acid via a ring opening reaction. The kinetics of the acrylation reaction were monitored throughout the reaction course and the acid value of the reaction mixture reached 10 mg KOH/g after 16 h, indicating the consumption of the acrylic acid. The obtained epoxy acrylate was investigated intensively by means of FTIR and NMR spectroscopy, and the results revealed that the ring opening reaction was completed successfully with an acrylation yield about 82%. The UV free radical polymerization of EPOLA was carried out using two types of photoinitiators. The radiation curing behavior was determined by following the conversion of the acrylate groups. The cross-linking density and the hardness of the cured EPOLA films were measured to evaluate the effect of the photoinitiator on the solid film characteristics, besides, the thermal and mechanical properties were also evaluated.

Matched MeSH terms: Stress, Mechanical
A novel approach to evaluate the mechanical responses of elastin-like bioresorbable poly(glycolide-co-caprolactone) (PGCL) suture

Low YJ, Kittur MI, Andriyana A, Ang BC, Zainal Abidin NI

J Mech Behav Biomed Mater, 2023 Apr;140:105723.
PMID: 36821908 DOI: 10.1016/j.jmbbm.2023.105723

Poly(glycolide-co-caprolactone) (PGCL) has become a novice to the bioresorbable suture owing to the synergistic properties taken from the homo-polyglycolide (PGA) and polycaprolactone (PCL) such as excellent bioresorption and flexibility. In addition to under conventional monotonic loading, the understanding of mechanical responses of PGCL copolymers under complex loading conditions such as cyclic and stress relaxation is crucial for its application as a surgical suture. Consequently, the present work focuses on evaluating the mechanical responses of PGCL sutures under monotonic, cyclic, and stress relaxation loading conditions. Under monotonic loading, the stress-strain behavior of the PGCL suture was found to be non-linear with noticeable strain-rate dependence. Under cyclic loading, inelastic responses including stress-softening, hysteresis and permanent set were observed. During cyclic loading, both stress-softening and hysteresis were found to increase with the maximum strain. In multi-step stress relaxation, the PGCL sutures were observed to exhibit a strong viscoelastic response. In an attempt to describe the relationship between the stress-relaxation and strain-induced crystallization (SIC) occurring during the loading and relaxation processes, a schematic illustration of the conformational change of polymer chains in PGCL sutures was proposed in this work. Results showed that SIC was dependent on the strain level as well as the loading and relaxation durations. The inelastic phenomena observed in PGCL sutures can be thus correlated to the combined effect of stress relaxation and SIC.

Matched MeSH terms: Stress, Mechanical
Nasal airflow comparison in neonates, infant and adult nasal cavities using computational fluid dynamics

Corda JV, Shenoy BS, Ahmad KA, Lewis L, K P, Khader SMA, et al.

Comput Methods Programs Biomed, 2022 Feb;214:106538.
PMID: 34848078 DOI: 10.1016/j.cmpb.2021.106538

BACKGROUND AND OBJECTIVE: Neonates are preferential nasal breathers up to 3 months of age. The nasal anatomy in neonates and infants is at developing stages whereas the adult nasal cavities are fully grown which implies that the study of airflow dynamics in the neonates and infants are significant. In the present study, the nasal airways of the neonate, infant and adult are anatomically compared and their airflow patterns are investigated.
METHODS: Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.
RESULTS: This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7 m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58 Pa for the neonates, infants and adults.
CONCLUSIONS: The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.

Matched MeSH terms: Stress, Mechanical
Mechanical and microarchitectural analyses of cancellous bone through experiment and computer simulation

Syahrom A, Abdul Kadir MR, Abdullah J, Öchsner A

Med Biol Eng Comput, 2011 Dec;49(12):1393-403.
PMID: 21947767 DOI: 10.1007/s11517-011-0833-0

The relationship between microarchitecture to the failure mechanism and mechanical properties can be assessed through experimental and computational methods. In this study, both methods were utilised using bovine cadavers. Twenty four samples of cancellous bone were extracted from fresh bovine and the samples were cleaned from excessive marrow. Uniaxial compression testing was performed with displacement control. After mechanical testing, each specimen was ashed in a furnace. Four of the samples were exemplarily scanned using micro-computed tomography (μCT) and three dimensional models of the cancellous bones were reconstructed for finite element simulation. The mechanical properties and the failure modes obtained from numerical simulations were then compared to the experiments. Correlations between microarchitectural parameters to the mechanical properties and failure modes were then made. The Young's modulus correlates well with the bone volume fraction with R² = 0.615 and P value 0.013. Three different types of failure modes of cancellous bone were observed: oblique fracture (21.7%), perpendicular global fracture (47.8%), and scattered localised fracture (30.4%). However, no correlations were found between the failure modes to the morphological parameters. The percentage of error between computer predictions and the actual experimental test was from 6 to 12%. These mechanical properties and information on failure modes can be used for the development of synthetic cancellous bone.

Matched MeSH terms: Stress, Mechanical