biomechanics

The essence of mechanobiology is, probably, the interrelation between mechanical and biochemical factors.  An exciting example of such phenomenon is signaling associated with the interaction between the cell and extracellular matrix (EM).  While some purely biochemical pathways initiated in the area of contact of the cell and EM are known, there are interesting ideas how the mechanical forces, stresses and strains can be involved too. This view goes back to works of Donald Ingber's group in the 90s that showed how perturbations of the adhesion area as a whole and of an individual integrin result in deformation of the cell nucleus. Interestingly, a distinguished oncologist at Johns Hopkins, Donald Coffey, published similar experimental results about the same time, and he also demonstrated that the observed cytoskeleton/nucleus interaction is different in tumor cells. There are several separate pieces of the puzzle that have been resolved: mechanical forces are generated at focal adhesions, the cytoskeleton is involved, nucleus deforms, gene expression changes as a result of perturbation of the adhesions, however, the whole picture of the interrelated mechanical and biochemical factors has yet to be understood. We recently published some results on this topic in the Journal of Biomechanical Engineering (Jean et al., 2004 and 2005). I was glad to find an interest in the same problem from some participants of this website (e.g., N. Wang, Z. Suo,   Long-distance propagation of forces in a cell, 2005 and P.R. LeDuc and R.M. Bellin, Nanoscale Intracellular Organization and Functional Architecture Mediating Cellular Behavior, 2006). This aspect of mechanotransduction is important for many areas beyond mechanics such as cancer, wound healing, cell adhesion and motility, effect of surface micro- and nanopatterning, etc.

What might be the differences, if there is any, between mechanical signaling and chemical signaling in a living cell?

In a recent article in Physical Review Letters, Alain Goriely and Sébastien Neukirch offer a mechanical model of how the free tip of a twining plant can hold onto a smooth support, allowing the plant to grow upward. The model also explains why these vines cannot grow on supports of too large a diameter. Read more.

The mechanics involves large deflection and bifurcation of a rod. I hope to hear opinions from people who know about the mechanics of plants.

Biomechanics is a reasonably well-developed field of study, with a modern history usually linked to the pioneering work of Prof. Y.C. Fung in the 1960s. There are a number of dedicated biomechanics journals (including but not limited to the Journal of Biomechanics and the Journal of Biomechanical Engineering). The field is well-enough established to have several generations of researchers working on the subject at universities across the world.

Symposium DD at the upcoming Materials Research Society Annual Meeting (Nov. 26-Dec. 1, Boston, MA) will be the latest in a series of MRS symposia on the mechanics of biological materials and materials designed following natural principles ("biomimetic" or "bio-inspired").   The full program is available at the MRS website (www.mrs.org).  This topic was also the subject of the August, 2006 focus issue of the Journal of Materials Research, which contained over 30 articles on the subject.

A viscous-elastic-plastic indentation model was used to assess the local variability of properties in healing porcine bone. Constant loading- and unloading-rate depth-sensing indentation tests were performed and properties were computed from nonlinear curve-fits of the unloading displacement-time data. Three properties were obtained from the fit: modulus (the coefficient of an elastic reversible process), hardness (the coefficient of a nonreversible, time-independent process) and viscosity (the coefficient of a nonreversible, time-dependent process). The region adjacent to the dental implant interface demonstrated a slightly depressed elastic modulus along with an increase in local time-dependence (lower viscosity); there was no clear trend in bone hardness with respect to the implant interface.

Cells function based on a complex set of interactions that control pathways resulting in ultimate cell fates including proliferation, differentiation, and apoptosis. The interworkings of his immensely dense network of intracellular molecules are influenced by more than random protein and nucleic acid distribution where their interactions culminate in distinct cellular function.

The Department of Engineering Science and Mechanics (ESM) at Virginia Tech seeks applications for two tenured or tenure-track faculty colleagues. The ideal candidates are expected to interface mechanics with the domain of biology (cellular mechanics, soft tissue biomechanics, macro-molecular biology, biodynamics, biofluids); the domains of nanotechnology or nanobiotechnology (mechanics of self-assembly, nanocomposites, functional nanodevices, biological and biomedical applications); or the domain of energy, with an emphasis on nanoscale and microscale problems or biological principles (fuel cells, renewable energy, energy conversion, clean energy, energy storage). However, intellectual depth is more important than the specific area of specialization, since ESM faculty members are expected to have a broad scholarly interest in engineering with a special emphasis on the fundamental mechanics.

Snoring is defined as sounds made by vibrations in the soft palate and their adjacent tissues during sleep. Heavy snoring can result in sleep-related upper airway narrowing, which leads to respiratory flow limitation and increased respiratory effort. If untreated, heavy snoring may be complicated by excessive daytime sleepiness. Hence, snoring has received a great deal of clinical attention in recent years.

OSTEONECROSIS is the death of bone that results in the collapse of the bony structure, leading to joint pain, bone destruction, and loss of function. Destruction of the bone frequently is severe enough to require joint replacement surgery. Osteonecrosis is a common disorder and accounts for 10% or more of the 500,000 total joint replacement procedures performed annually in the United States. Approximately 75% of patients with osteonecrosis are between 30 and 60 years of age.

From the point of view of mechanics, osteonecrosis means deterioration of mechanical properties of the bone. Decrease of the magnitude of the elastic modulus of the bone leads to its inability to bear the external load and culminates in bone damage and fracturing. For a couple of decades the engineers were trying to estimate the critical stress-strain state of the femoral head using the available data on the osteonecrotic bone properties, finite element analysis based on 3D elasticity, and Von Mises stress as a criticality condition. The fact that the cortical shell of the femoral head is significantly stiffer than the underlying cancellous bone did not attract much attention yet. However, from the solid mechanics point of view the difference in the stiffness of the cortical and cancellous parts of the femoral head under both normal and necrotic conditions is important. This difference allows for considering the femoral head as an elastic cortical shell on an elastic cancellous foundation. This, in its turn, suggests the buckling of the cortical shell as a possible starting point of the overall head collapse. The purpose of the study, described here, was to assess the cortical shell buckling scenario as a possible mechanism of the femoral head collapse at the various stages of osteonecrosis.