Journal of Mechanics in Medicine and Biology

A brief retrospective of the evolution of mechanics and its reciprocal impacts on medicine and biology is offered, from the limited viewpoint of an early contributor to some aspects of biomechanics. The development of the field after World War II, and particularly in the nineteen sixties and seventies, set the foundation for today's remarkable achievements. Looking ahead, the expanding complexity and challenges of the interaction of mechanics with biology and medicine, together with the loss of centrality of the mechanistic view in the physical sciences, compel a reexamination of the role, potential and limits of mechanics in this context. Future advances call for a broader metamechanics conception encompassing forces, energies, fields, information, network and systems theory, as well as for models spanning the range of scales from atom and molecule to cell, organ and organism.

The flow dynamics through the peripheral and hinge regions of a bi-leaflet mechanical heart valve are complex and result in abnormally high shear stresses particularly during the closing phase of the valve function. It has been observed that the late stages of closure are more significant in the dynamics of platelet activation; therefore, the later stages of closure are simulated by solving the two-dimensional Navier–Stokes equations using an Eulerian Levelset-based sharp interface Cartesian grid method. Using a fixed Cartesian mesh incorporating local mesh refinement for solution accuracy and efficiency, the flow-through within a recessed hinge design and an open pivot hinge design is compared. Platelets are modeled as point particles by Lagrangian particle tracking algorithm with one way coupling. A dilute particle flow is assumed and particle–particle interactions are neglected. It was observed that the hinge region of the open pivot valve indicated a lower potential for activation of platelets compared to that in valves with a recessed hinge design.

The left ventricle (LV) is modelled as a fluid-filled, thick-walled finite-elasticity cylindrical shell, subject to internal pressure increase during isovolumic contraction. Our objective is to elucidate that the tremendous internal pressure build-up during isovolumic contraction is caused by stress development in the spirally-wound myocardial fibers due to their contraction. The LV model data consists of LV chamber pressure, LV dynamic geometry and LV twist angle. In our analysis, the LV chamber pressure increase and LV (radial, longitudinal, and twist) deformations are formatted to be caused by the contractile stresses in the LV myocardial fibers (based on the hyper-elastic constitutive property of the LV myocardial wall, expressed in terms of the strain energy density function). The LV wall stresses are expressed in terms of the strain energy density function, and hence in terms of the measured LV wall strains and the material parameters. Then, by satisfying the stress boundary conditions, from the measured data on LV deformation state and LV pressure, we first determine the LV wall's constitutive properties, and then the instantaneous stress state in the LV.

The stress generated in the LV cylindrical model is equivalent to the development of active compression force and torsion within the model, as a mechanism for the high intra-LV cavity pressure build-up during isovolumic contraction. We in turn adopt (i) the principal compressive stress to be the stresses developed in the myocardial fibers (by their contraction), and (ii) the principal stress trajectory to correspond to the orientation of the myocardial fibers. The results show that the myocardial fiber orientation changes during the isovolumic phase, as the LV contracts. Hence, an important determinant of our analysis is the orientation of the myocardial fibers. Conversely, it can be said that the fibers are so optimally oriented, that their contraction causes LV deformation to in turn cause the appropriate increase in intra-LV pressure. Another important outcome of our analysis is the determination of the "LV torque vs twist angle" relationship, which has the potential to be employed as an index of contractility.

Mathematical modeling has proven to be a viable alternative for investigating the temperature distribution inside the human eye. This is due to its ability to overcome the limitations infrared (IR) thermography; the leading method in ocular temperature measurement. A wide range of mathematical studies on the ocular temperature distribution during various conditions have been published in the literature. In this paper, we carry out an in-depth review of the various mathematical models of the eye that have been developed in the past. Various problems and the implications from the mathematical predictions of these studies are discussed. The future directions of studies in ocular temperature distribution are deliberated.

With progress of modern technology, manually-propelled wheelchairs are still of importance for individuals with mobility impairments. The repeated wheelchair propulsion and strenuous daily activities cause high loads and thus injuries on the upper extremity joints. Over the past few years, a considerable number of studies have been made on biomechanical analysis of wheelchair propulsion and wheelchair-related activities. Thorough investigation of biomechanics during wheelchair propulsion enhances comprehension of mechanism of injuries and provides information to improve wheelchair design and fitting. Numerous investigations have been made to demonstrate factors which cause low effectiveness of force application and inefficiency of movements. Emphasis was also placed on developing analytical models to simulate wheelchair propulsion.

Arteries exhibit a remarkable ability to adapt in response to sustained alterations in hemodynamic loading as well as to disease, injury, and clinical treatment. A better understanding of such adaptations will be aided greatly by formulating, testing, and refining appropriate theoretical frameworks for modeling the biomechanics and associated mechanobiology. The goal of this brief review is to highlight some recent developments in the use of a constrained mixture theory of arterial growth and remodeling, with particular attention to the requisite constitutive relations, and to highlight future directions of needed research.