Research Opportunities

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Laboratory Philosophy.  Conducting research under the guidance of a faculty advisor means much more than simply implementing the ideas and efforts of your advisor.  It means learning how to think for yourself, trusting yourself in the knowledge that you have acquired, and recognizing when and knowing how to acquire new knowledge, including sharing your experience with your lab mates.  You can learn much from your fellow students just by explaining the problems you have encountered and the solutions you have discovered.  Being a member of a lab group means being part of a team and sharing in an identity:  your lab mates will most likely be lasting friends.  One way to foster such close interactions is to provide a "home" to students in the lab.  The Biomechanics Laboratory has been designed with this in mind:  the north end is devoted to conducting experimental and computational work and the south end is devoted to accommodate several students with their own work space (see below figures).

The undergraduate research experience, while ordinarily a requirement for your degree, provides you with an opportunity to develop your research, technical, and presentation skills, and to enable your informed decision as to the pursuit of a graduate degree.  Undergraduate students participate as voluntary advisees, for academic credit, or as paid research assistants.  In any capacity, a primary goal is to provide students the opportunity to generate publication quality data and to present their work at technical conferences and possibly as a co-author on a refereed journal publication.  Students interested in participating should contact me and be prepared to present electronically a brief summary of their academic background and reasons for pursuing undergraduate research opportunities in the Biomechanics Laboratory.

North end of lab for experimental work.	South end of lab with student work spaces.

Specific Projects

Proviso.  In the following project descriptions, the explicit "we" is used and denotes Dr. Rapoff, his students, and his faculty and industrial collaborators.  Successful research is almost never completed by a single person.

Structural Implications about Natural Holes.  The objective of the proposed research is to explore the structural implications of material properties, compositions, and architectures near natural holes and defects of various geometries in bones and woods.  We previously determined in the vicinity of an equine metacarpus nutrient foramen (a 1 to 2 mm diameter hole through the thick outer shell of a horse forearm bone through which blood vessels pass) that, in addition to a stress concentration reduction, compositional variations are such that everywhere a failure index (loosely, the ratio of stress to strength) is maximized.  In this way, the bone is as strong as it needs to be and as light as it can be.  To our surprise, the hole was shielded by a stiff region away from the hole, an approach normally not used in engineering structures.  The superiority of this pattern was verified by performing structural optimization of the bone composition for maximum strength.  We also found a unique microstructure about the foramen that infers a greater resistance to cyclic loading such that occurs over the lifetime of the horse.  It is unknown if such serendipitous enhancements apply for other geometries subjected to more complex loading in other bones or woods.  Students undertaking projects in this area will prepare specimens, probe them mechanically, and quantitatively observe them under the microscope.  The specimens will include the oblique nutrient foramina of the canine tibia (dog shin bone), the nutrient foramina of the bovine metacarpus, and knots and knotholes in various woods.

Biomimetic Structures.  The root words of biomimetics are biology, the study of living organism, and mime, to mimic.  Structures is a term used by engineers to denote constructions designed to support and transmit loads.  Biomimetic structures are those structures whose design is in some way informed by the quantitative analysis of the matter of living organisms.  We have designed, built, and mechanically tested structural plates containing central holes that mimicked the composition we discovered surrounding the nutrient foramen of the equine metacarpus.  These plates were constructed of discrete rings of polyethylene of varying densities and, thus, varying stiffnesses and strengths, and were twice as strong as conventionally designed plates of the same weight.  Students undertaking projects in this area will design, build, and test plates of more continuously varying compositions about central holes in plates.  Based upon the unique microstructure that infers a greater cyclic loading resistance, students may also design, build, and test fibrous composite plates containing fibers of varying diameter and stiffness.

Image-Based Weighted Measure of Skeletal Element Torsion Stiffness.  We previously developed weighted measures of structural stiffness by including the distribution of not only bone quantity, in terms of structural geometry, but heterogeneous bone quality, in terms of computed tomography (CT) derived stiffnesses, to determine the resistance to bending provided by skeletal elements.  The result was a set of weighted measures akin to heterogeneous mass moments of inertia.  We applied these weighted measures to CT images at three locations along the mandibular corpus in the Great Apes Gorilla, Pongo, and Pan.  Our results suggested that the use of these weighted measures may spur different interpretations of comparative datasets that rely upon stiffness measures as estimates of biomechanical competence.  A persistent question in masticatory mechanics is whether the distinct dietary regimens of the Great Apes are reflected in jaw morphology, and its answer is tied to the development of appropriate biomechanical measures of function.  We found that our weighted measures do not consistently document meaningful structural stiffness differences among taxa thus supporting two alternative hypotheses:  (1) the alleged dietary differences among Great Apes are not accompanied by important differences in masticatory loads, or (2) jaw form in the Great Apes, analyzed morphometrically, is not reflective of the mechanical demands of their respective diets.  Students undertaking projects in this area will participate in the extension of this type of analysis to consider torsional loading, development and validation of the analysis software, and application of the software in the analysis of CT image data sets.

Web-Based Analysis of Skeletal Element Bending Stiffness.  The previously described analysis using image-based weighted measures of skeletal element bending stiffness is accomplished via a MATLAB code for which grayscale bitmap images are the inputs.  An ideal contribution to the research community at large would be to make available a web-based capability for this type of image analysis.  Thus, researchers around the world would be able to submit their images for analysis and visualize their results through a dedicated web site.  Students undertaking this project will develop this web-based capability.

Image-Based Interpolation of Anisotropic Elastic Constants.  The objectives of this research include reaping from radiographic images of bone more material properties information than currently is obtained, thereby permitting high resolution mapping of properties in patient-specific computational models of skeletal elements.  Although imaging spatial resolutions continue to improve, the resolution at which material properties can be probed continually lags behind.  No matter how fine the mechanical probe resolution, specimen preparation necessarily removes material that is precluded from mechanical probing but for which imaging data exist.  We have developed an interpolation method, based on previous work on averaging elastic constants, that uses imaging data to restore missing mechanical data.  Students undertaking projects in this area will identify functions of the principal components of the elastic constants that correlate best with radiodensity and demonstrate how such a function can be used to calculate the "density distance" needed in the interpolation of the principle components.  This project is analytical in nature, with some programming required.  Students can learn about this project by reading this abstract and will learn much during this project about bone, imaging, and some higher but not insurmountable mathematics.

Structure-Function Relationships of the Hummingbird Wing.  This research aims to understand the form and function of structures of the hummingbird wing.  Its nature is basic and applied, consisting of a detailed quantification and understanding of the biologic system ‑ the hummingbird wing ‑ that will subsequently inform the design of a biomimetic system ‑ the structural components of the wings of micro aerial vehicles.  Please visit my NASA 2003 Faculty Fellowship Program participation page and, in particular, read an abstract that explains the direction of this project.

Graft and Plate Load Sharing in the Cervical Spine.  The objectives of this proposed project are to understand the mechanical environment of plates and bone grafts in the cervical spine after surgical procedures that involve multiple levels.  The cervical spine is the portion of the spine between the head and chest.  For various maladies and traumas, a procedure is required in which a surgeon carves through the bones of the neck to access the spinal cord and nerve roots that branch off of it.  Once accessed, the surgeon can then remove any bony material or adherences that are contributing to the patient symptoms.  The procedure, however, then leaves the spine in a destabilized condition, one in which, without supplemental support, can not function to carry about the head and allow motion without serious risk of subsequent injury to the spinal cord.  Therefore, instrumentation – in the form of plates and bone grafts ‑ must be added to the spine.  Up to the present, the amount of force that the plate and the graft transmit to the remainder of the spine is unknown.  This has led to a plethora of devices that have gone to market and subsequent implantation with little knowledge as to the mechanical demands to be placed upon them.  These demands turn out to influence highly the nature and course of healing after the surgical procedure.  Finally, these procedures have in many studies been reported to have poor outcomes, up to a 50% failure rate, a rate clearly not tolerated in other medical procedures.  To that end, the proposed project aims to develop a more comprehensive understanding of the mechanics of this challenging, oftentimes unsuccessful, and increasingly popular multiple level surgical procedure of the cervical spine.  The project will address various factors under the surgeons control, such as the type of surgical procedure, plate, and graft used, and the amount of precompression induced on the bone graft.  The effect of these factors on the mechanical environment at the interfaces between the graft and host bone of the spine will be determined as well, as these interfaces are the key to successful healing of the reconstructed spine.

Meta-Analysis of Orthopedic Research Studies.  Meta-analysis concerns pooling results of research studies to determine a combined effect and to resolve discrepancies and contradictions between the individual studies.  Meta-analysis techniques are well developed and include establishing study selection criteria, amassing and archiving data, statistical analyses, and reporting results.  Topics appropriate for meta-analytical projects include outcomes in adult and pediatric orthopedic surgical and non-surgical treatments, portrayal to patients of surgical risk, and correlations between bone imaging techniques and potential for fracture.

Biomechanics and Solid Mechanics Tabletop Lab Experiments.  This project involves the design and production of tabletop lab experiments for use in biomechanics, material science, and strength of materials classes to demonstrate various material and structural behaviors including the creep and relaxation behavior of materials and the effect of transverse loading and support conditions on beam bending.

Data Acquisition System for Materials Testing.  This project involves the design and assembly of a system to acquire data from a variety of transducers including load cells, extensometers, strain gages, and LVDTs used in conjunction with a servohydraulic materials testing machine.  This project also will include investigation of appropriate parameters for the robust load control testing of a variety of materials.

Test Fixture for a Microscope Stage.  This project involves the design, fabrication, and application of a biaxial test fixture for use on the stage of a transmitting light microscope.  The fixture would primarily be used on thin sections of bone to determine displacements about microscopic discontinuities.

Footprints of the "Bigfoot."  Some advocate the existence of "mystery" primates, including the North America Bigfoot.  Their advocacy is predicated on an amalgam of folklore and planted "evidence."  Descriptions of footprints purportedly made by a Bigfoot indicate that the great beast exceeds in size any known primate and therefore must exist.  A preliminary analysis conducted by us indicates otherwise:  that these footprints could indeed have been created by a human.  In the course of the development of this analysis, it became clear that little to no data exist with regard to footprint characteristics (e.g., depth), footwear, anthropometry, and soil consistencies (e.g., hydration).  Besides definitively discounting the possibility that documented footprints could have been produced by Bigfoot (as if these need to be discounted), the generation of such empirical data may have important implications in forensic science.  Students undertaking research in this area will learn about scientific skepticism, as well as soils and novel ways of characterizing such diverse materials.