5th Annual Workshop on
"Finite Element Modeling in Biology"
June 5 - 11, 2011 - UMass Amherst

Maria-Grazia Ascenzi (University of California, Los Angeles)
The specialty of my lab is bone micro-mechanics. We are comparing the mechanical properties bone of two genetic mutant mice. Because bone is a hierarchical material, we first develop a macro-level finite elementa subdivision within the material that is relatively simple in shape, such as a tetrahedral or hexahedral, defined by vertices called nodes. model from the microCT scan of the femur to simulate  the three-point bending test that we have conducted. Then we will develop meso- and micro- models at specific regions of high strain.

Jonah Choiniere (American Museum of Natural History)
Cranial kinesis, or the differential displacement of bones of the skull, is an important component of vertebrate feeding strategy. Prokinesis (cranial kinesis between the bones of the face and the braincase) is common in birds and has also been hypothesized in the alvarezsauroid (Dinosauria: Theropoda) taxon Shuvuuia. Alvarezsauroids have particularly weak jaws relative to other theropod dinosaurs and they share many features of the postcranial skeleton with birds. Thus, the feeding strategies and the phylogenetic affinities of this group remain unclear.  By reconstructing CT scans of the skull of Shuvuuia, I hope to quantitatively assess the bite strength and the prokinetic ability in this taxon, and in doing so compare the skull architecture to that of birds.

Abigail Curtis (University of California, Los Angeles)
I am interested in how the internal architecture of the skull contributes to skull function. My research focuses specifically on the frontal sinuses, which are air-filled cavities within frontal (forehead bone) of mammals. These structures are highly homoplastic, and extremely variable among species. I aim to test how sinus size and shape vary with skull shape in mammalian carnivores, and how this affects skull performance, such as ability to transmit muscle force into bite force, and deal with stresses imposed by prey.

Christine Dzialo (UMass Amherst)
The purpose of my project is to build an additional Cebus skull model in order to perform a statistical comparison.  A complete set of data (in vivo strains, EMG, PCSA, and material properties) is required to construct this model and apply probabilistic FE analysis.   Increasing the population of Cebus skull models will allow for experimental comparison of different skulls of the same species.  The long term goal of this research is to further validate the FE model and quantify the effect of material property and muscle load variability on the response of the skull structure.

Sander Gussekloo (Wageningen University and Research Centre)
At the base of the evolutionary tree of modern birds is a clear split between the Palaeognathae (ratites and tinamous) and the Neognathae. Many palaeognathous species, especially the ratites, are strikingly different from most neognathous birds because of their lack of flight, but one of the most important characters that distinguishes the two groups is hidden within the skull. The ventral side of the skull, where the bony elements lie that play an important role in kinesis of the upper bill, is very different in the two groups. Because the differences are in the part that plays a role in the movement of the upper bill, it can be expected that this is a functional adaptation to a specific feeding behaviour. However, analyses of the feeding behaviour showed no differences in behaviour that could explain the difference in morphology. As the overall structure of the palaeognathous skull seems more robust, an alternative hypothesis is that it is an adaptation to withstand large internal forces within the skull. I will try to use FEM to determine whether differences in morphology can be explained by a difference in stress-distribution within the skull.

Christopher Marshall (Texas A&M University)
We are currently investigating the ontogeny of bite force in loggerhead (Caretta caretta) sea turtles and whether durophagy is related to fishery bycatch from commercial longlines. It has been demonstrated that fishery bycatch of loggerhead sea turtles is a major factor responsible for their population decline. Since loggerhead sea turtles excel in biting, their feeding biomechanics may render make them vulnerable to longline fishery gear. As a first step we wish to understand the normal distribution of stress through loggerhead skulls, lower jaws, and jaw joints during feeding events by integrating modern functional biological methods (morphology, physiology, and behavioral performance) with Finite Element AnalysisAnalysis of the physical behavior of a finite element model. In this analysis a given physical "treatment" is applied (such as force loading on some elements), followed by computation of the effects of this treatment on other elements of the FEM. More specifically, the analysis phase involves solving a set of simultaneous algebraic equations in which the unknown variables that are solved for in this system of equations are the unknown nodal degrees of freedom. Once the values of the unknown nodal degrees of freedom are found, the unknown reaction forces are determined. Next, the spatial variation of the primary field variables within each element is computed using the element's predefined interpolating polynomials and the element’s nodal values. Thus, for solid elements this results in mathematical functions that completely define the displacement field within every finite element. These functions are then differentiated to obtain the complete strain field within each element which, when combined with known material properties of the element, yields the element stress field. In summary, the finite element solution will yield 1) the reaction forces necessary to maintain static equilibrium of the system, 2) the displacement field ( i.e. displacements of the material through out the 3-D domain), the complete strain tensor field, and the complete stress tensor field. . Ultimately, we would like to model the stress distribution during simulated hooking events to get a better appreciation for its impact on the health and rehabilitation of sea turtles.

Karen Poole (George Washington University)
My plans for using FEA in my dissertation research are to examine the fore- and hindlimb elements of various ornithopod dinosaurs in order to better understand the transition to quadrapedality in this group.  Unfortunately, I haven't collected any of this data yet, so during the workshop I will be examining the limb elements of Rahonavis.  While the forelimbs of this taxon are quite different from those of ornithopods, I'm hoping FEA will help to differentiate between weight-bearing and non-weight-bearing bones.

Caroline Rinaldi (University of Missouri, Kansas City)
My colleagues and I have a fairly large-scale project underway investigating the phylogeny and functional morphology of the Pleistocene giant beaver, Castoroides. One of our areas of focus is the function of the incisors.  Giant beaver incisors are unusual among rodents in that the enamel is characterized by the presence of longitudinal ridges. I hypothesize that the ridges function by creating serrations at the incisor's occlusal edge, enhancing its ability to cut through fibrous vegetation. I plan to use FEA to investigate whether the ridges may also have an important role in strengthening the enamel.

Andy Smith (UMass Amherst)
In a classic paper on mammalian cranial morphology, Cartmill (1974) hypothesized that a high degree of flexion between the facial skeleton and cranial base increases the efficiency with which forces generated during heavy loading of the incisors are transferred between the two regions. Many studies of monkeys have investigated this idea, but none have studied the species that Cartmill described. During this workshop we will build a model of the skull of an aye-aye (Daubentonia madagascarensis), a strepsirhine primate with exaggerated basicranial flexion. We will  compare the performance of this model to one of the the striped opossum (Dactylopsila trivigada), a marsupial from Australia and New Guinea whose skull resembles that of the aye-aye in many respects. Ultimately, we will compare these models to those of close relatives that lack the cranial specializations. These comparisons within and between primates and marsupials will provide a test of Cartmill's hypothesis.

Daphne Soares (University of Maryland)
I am interested in the evolution of sensory systems and my project will be to create reconstructions of endocasts of turtles, although I will be working on cavefishes when I get home.

Josef Steigler (George Washington University)
Recent studies have revealed archosaur craniofacial ontogeny as a confounding factor for taxonomy and systematics. Therefore, exploration of internal skull architecture and the production of brain and sinus endocasts has the potential to clarify ontogenetic processes and may lead to the discovery of more conservative characters for phylogenetic analysis. At this workshop I will work on building cranial models for three theropod dinosaur taxa: an alvarezsauroid, an oviraptorid, and a troodontid.   

Evelyn Unger (Mercer University School of Medicine)
The impact of craniofacial sutures on both local and global strain patters during dynamic loading is still unclear at best.  A recent sensitivity study using dynamic finite element analysis (FEA) with one suture found that sutures might have a minimal effect on global strain patterns in a macaque cranium. The goal of this project is to clarify the role of sutures in stress/strain distribution by building and testing a finite element model that incorporates more craniofacial sutures located in their correct anatomical positions.  We hypothesize that sutures are mechanically significant only insofar as they are weak points on the cranium that must be shielded from unduly high stresses so as not to disrupt vitally important growth processes.