1st Place Award Undergraduate Research Presentation

Student Researcher: Danielle Miller

Project Title: The effects of annual periods of disuse on porous cavity densities in black bear femurs

Advisors: Seth Donahue, Biomedical Engineering


Abstract: Osteoporosis is a condition characterized by decreased bone density and increased porosity, causing reduced bone strength and increased fracture risk. In addition to the well-known age-induced condition, osteoporosis can occur as a result of reduced mechanical stresses on bone (i.e., disuse). Black bears experience disuse (hibernation) for approximately 6 months out of the year each year, but they do not suffer the adverse effects of skeletal unloading on bone mechanical properties.

The mechanisms behind this phenomenon are still unknown, yet it is likely that bears have a unique biological process that helps them maintain balanced bone remodeling during hibernation. By analyzing the porosity of black bear femurs, this study attempted to offer insight into the phenomenon of maintained bone strength in black bears despite annual hibernation. Since black bears maintain formation during hibernation and have elevated bone formation post hibernation it was hypothesized that porosity would not change with age despite annual periods of disuse with limited recovery time.

The femurs analyzed were obtained from 27 hunter-killed bears ranging in age from 2 to 20 years. Slides were prepared from the midshaft of the bone and were analyzed using semi-automated image analysis software. Porosity was defined as total porous area divided by the total cortical area (%). Total porosity did not significantly change with age in males or females. Interestingly, the males had a significantly higher porosity than females even though female bears give birth and nurse cubs every other year; this is contrary to what is seen in humans and other animals. Therefore, this study provides further evidence that black bears have a unique ability to resist the effects of disuse osteoporosis, such as increased porosity, and thus can prevent increased fracture risk.

Student Researcher: Hans Nyberg

Project Title: Computer Simulation of Human Thermoregulatory Tests

Advisors: David Nelson Biomedical Engineering

Sponsor: ThermoAnalytics, Inc. and MTU Office of Educational Opportunity

Abstract: Thermoregulatory tests on human subjects are lengthy in process, costly to complete, and restricted by regulations for human safety. If an accurate method to simulate these tests was developed, it would greatly minimize these problems, as well as provide extensive data that would otherwise be impossible to gather from live human tests. There are several studies that may be used as a foundation while undertaking this task, one of which was completed at Brooks Air Force Base in Texas. Human response to radiofrequency fields at 2450 MHz was recorded at different ambient temperatures, measuring factors such as the local sweating rate and temperatures at different body parts.

Thermoregulation, a program currently being developed by ThermoAnalytics, Inc. of Calumet, Mich., simulates this type of human response via parallel computing. The purpose of this research was to develop a small computing cluster to run Thermoregulation in order to obtain and verify the simulated results against the results of past tests on human subjects. Computers devoted solely to execute Thermoregulation were networked together, dividing the computation among all of the machines in order to expedite the process. These simulations allowed for a much more detailed analysis of the results as the modeled body is divided into 2mm cubes, called voxels. Although computed numerically, these voxels can be displayed graphically, greatly enhancing the analysis.

A number of simulations were run and inaccuracies were found when comparing the results to previous studies. These discrepancies have led to additions and modifications to the Thermoregulation code, allowing greater accuracy in future simulations. Compared with thermoregulatory tests on human subjects, the computing process requires considerably less equipment and human power, and data can be obtained in hours rather than months, especially for unsafe human conditions.

Student Researcher: Stacie Wieszczyk

Project Title: Creep Testing of Sutures

Advisors: Debra Charlesworth Biomedical Engineering


Abstract: Viscoelastic tests for sutures are performed in air and require extensive time. Sutures should be tested in an aqueous environment to better represent in vivo conditions, and this testing procedure needs to be shortened.

The overall goal of this study is to develop a fast and reproducible creep test for sutures. The first objective of this project was to determine an optimum tying method, load, and sample length for creep tests. The second objective was to test the sutures in an aqueous environment.

The material used to model the sutures was fishing line (6 lb. Trilene Fishing Line, 0.009 in diameter), which is commonly available, cost effective, and used as sutures in third world countries. Using a custom apparatus, the creep of the sutures was measured over twelve hours. Creep is the strain a specimen undergoes over time when a constant load is applied. Testing in air determined an optimum tie method (loop tie with a double-knot or strand with triple-knots tied at each end), optimum load (470-775 g), and optimum sample length (12.7 - 127 mm.) This was followed by aqueous testing. For an aqueous test, a tank of water completely surrounded the sample.

The water temperature varied between 24 and 50 °C. A four parameter viscoelastic model was fit to the data. The tie method chosen was the loop with a double knot, because the variability was lower and it had better reproducibility. The 775 g load was chosen since it produced the greatest amount of strain without breaking the sample. As the length increased, it was found that creep decreased initially, but then remained constant. As the load is placed on each sample the knot becomes taut. The deformation due to the knot tightening is constant as a function of sample length. Since the deformation due to the tightening is constant, the strain due to the knot tightening decreases as the sample length increases. A length was chosen where the strain remained constant at 76.2 mm. In air, sutures had less long term creep and behaved more elastically than in water. In water, increasing the temperature increased the long term creep and caused the sutures to creep more elastically.

During aqueous testing, it was found that it was difficult to maintain the tank at 50 ºC. In order to prevent heat loss, an insulating system was designed for future tests. The original tank will be surrounded by an outer tank with an insulating layer of sawdust. The optimum parameters for suture creep testing were a length of 76.2 mm, a load of 775 g, and a loop style tying method. Water and temperature greatly affect the creep of polymer fibers and should not be neglected when evaluating new suture materials. Future work will develop a master curve for creep of sutures using time-temperature superposition. This will shorten the time for material testing and development of new materials.