Journal of Mechanics in Medicine and Biology

A biomechanical model was generated in order to investigate the possible mechanisms behind reductions in muscle performance due to muscle bulging. It was shown that the proportion of fiber force contributing to the total muscle force is reduced with fiber bulging and that the cause of this reduction is due to the intramuscular pressure (IMP) created by the bulging fibers. Moreover, it was established that the amount of IMP generated muscle force reduction is determined by the extent to which muscle thickening restricts muscle fibers from shortening, thereby limiting their power contribution. It was shown that bulging can set a limit to the maximal size a muscle can take without losing force and power producing capability. Possible effects, due to bulging, on maximal muscle force in relation to both muscle length and muscle shortening velocity were also demonstrated by the model.

Characteristic emission from gadolinium-doped amorphous aluminum nitride thin films deposited on Si(111) substrate are studied, with cathodoluminescence and photoluminescence, for their suitability as tissue compensators in radiation treatment planning. These films are deposited by reactive sputtering at liquid nitrogen temperature, using 100–200 W rf power, 5–8 mTorr nitrogen, and a metal target of aluminum and gadolinium. Thermal annealing was performed at a temperature of 900°C. A sharp ultraviolet peak is observed at 314 nm, corresponding to ⁶P_7/2 → ⁸S_7/2 transition. The ultraviolet emission is intense enough to harm human tissues if it is used as a tissue compensator. Thermal annealing further enhances the intensity of ultraviolet emission, indicating that its longer use as tissue compensator will provide more harm and damage to the human body.

Although little is known about the transport mechanism of bile in the human biliary system, clinical studies suggest that it may be a contributing factor in the pathogenesis of cholelithiasis. This paper reports an investigation of the steady flow in two-dimensional human biliary system models using flow visualization. The geometries of these two-dimensional models were described based on actual patients' operative cholangiograms. Two models were used: one represented biliary system of a patient suffering from gallstones, while the second represented the biliary system of a healthy person. The streamlines of the flow in the cystic duct of the patient suffering from gallstones were highly winding, compared with those of the healthy person. This is an indication of a higher resistance to the flow in the cystic duct of the gallstone patient, which is a contributing factor of the formation of gallstones. The work presented here is a part of an ongoing project aimed at understanding the functions of human cystic duct and the role of bile flow in the formation of gallstones.

The time-dependent mechanical properties of porcine esophagus were investigated experimentally and theoretically. It was hypothesized that the viscoelasticity was quasi-linear. The incremental stress-relaxation test was conducted to identify the material constants included in the quasi-linear viscoelastic (QLV) model. To verify the predictive ability of the model, the incremental cyclic test was performed. Hysteresis was calculated and compared with that predicted by the model. Results showed that stresses relaxed by 20–30% within the first 10 s and stabilized at 50% at 300 s. The QLV model was shown to be able to describe the viscoelasticity of esophagus across various stretch levels. The model could also predict the hysteresis during cyclic test well. It suggested that the QLV could be used as the material characterization of esophageal tissue.

This paper describes a signal processing technique aimed at complementing cardiac auscultation in the detection of heart valve disease. The method provides a means for keeping objective records by analyzing the characteristics of the cardiac murmurs. The Short-time Fourier Transform (STFT) is used here to provide a graphic representation of the time-frequency information of the cardiac murmurs from eight different pathology cases. The graphic representation obtained shows the variation in frequency and intensity during the murmur. Some interesting observations show characteristic rising and falling tones, suggesting degrees of the pathology severity.

Advances in molecular biology have produced a wide range of protein and peptide-based drugs. Equally, it is required to explore various technologies and capabilities to deliver those drugs. A unique medical device, the hand-held biolistics, is developed for powdered pharmaceuticals/biologicals transdermal delivery. The underlying principle is to accelerate micro-particles by means of a high-speed helium gas to an appropriate momentum to penetrate the outer layer of the skin to elicit desirable pharmaceutical/biological effects. The novelty of this hand-held biolistics is using the venturi effect to entrain micron-sized protein and peptide drugs into an established quasi-steady transonic jet flow and accelerate them toward the target. In this paper, computational fluid dynamics is utilized to characterize prototype biolistic system. The key features of gas dynamics and gas–particle interaction are presented. The overall capability of the biolistic delivery system is discussed and demonstrated. The statistical analyses show that the particles have achieved a mean velocity of 628 m/s as representatives of extracellular vaccine delivery applications.

Mechanisms of unidirectional flow generation and gas transport enhancement in oscillatory flow of avian lungs were numerically studied with bifurcation models of avian trachea. Model systems of right-angled branched tubes with single and multi-bifurcating tubes were adopted for the numerical simulation. The effect of constriction near the bifurcation was also investigated. Main concern was placed on the effects of bifurcation structure on unidirectional flow generation and axial gas transport enhancement. Oscillatory flow fields as well as concentration fields were numerically analyzed with a developed code based on SIMPLE and CIP methods. Similar to the previous experiment by the authors, unidirectional net flow was observed from side-daughter tube to daughter tube. Strongly affecting on the oscillatory flow fields and flow distribution, the constriction and the multi-bifurcation structure were found to improve unidirectional net flow generation. In particular, multi-bifurcation structure was found not only to improve the unidirectional flow generation and gas transport but also to reduce the total pressure drop of the system.

A mathematical model for the rupture of cerebral saccular aneurysms is developed through the analysis of three-dimensional stress distribution in the aneurysm wall. We assume in this paper that a saccular aneurysm resembles a thin spherical shell (a spherical membrane), and then develop a strain-energy function valid for finite strain to analyze three-dimensional stress distribution in the aneurysm wall. We find that rupture occurs when the ratio of the wall thickness to the radius of the aneurysm is 6.1 × 10^-3. We also conclude from our analysis that rupture can occur when the ratio of thickness to radius of the parent aneurysm equals the ratio of thickness to radius of the daughter aneurysm. These findings may be helpful to the neurosurgeon for predicting the rupture potential in patients presenting with unruptured aneurysms.