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Impulse Loading on the Lower Leg using a Synthetic Bone Marley Winfield Department of Biochemical Engineering and Medical Biophysics MBP 3302 Outline Introduction Materials and Procedure Results and Discussion Conclusion Acknowledgments References Introduction Synthetic bones have recently become available as substitutes for cadaveric specimens used in testing Many advantages, including low variability as this makes them more consistent, available, easy to work with, handle and store Have been validated for quasi-static tests, but not fracture studies http://www.sawbones.com/products/bio/composite.aspx Background Upon axial loading of the lower leg during impact events, fractures of the tibia can occur Life altering injuries can take place depending on the magnitude of the axial loading Fracture analysis using synthetic bones to determine injury limits is yet to be studied Appropriate injury limits for lower limbs can be found using an apparatus designed to simulate these types of events Purpose Carrying out a fracture analysis on synthetic tibias, enables us to understand the impact that can be applied to a lower limb before fracture occurs. These experimental results can be compared with a fracture analysis of a cadaveric specimen to validate whether or not synthetic bones are suitable substitutes. Materials and Procedure Potting and Alignment of Bones Bones were potted in PVC tubing Alignment of the anterior of the tibia was done using a laser PVC tubing was filled with cement and spread equally Important for all bones to be aligned and potted the same for consistency Materials and Procedure Strain Gaging Bone was cleaned using rubbing alcohol Strain gage rosettes were placed along the tibia approximately 6 mm apart, 3 at the top and 1 at the bottom Gages were fixated to the bone using glue and a catalyst Important to make certain that the gages were completely secured and would not come off during testing Apparatus Can test Cadaveric and synthetic lower leg specimens Velocity the specimen is struck at can be varied, independent of the force applied Specimen receives a controlled impulse from a projectile using pneumatics Data Collection Bone was placed in the Data was collected chamber and hooked using a data acquisition up to operating system system The projectile was propelled causing Custom-written impact on the bone LabVIEW program calculated the momentum, energy, Projectile mass, 3.9kg, and force of impulse at acceleration, force of 16KHz impulse, exit velocity, and strain Data Collection High speed camera records the event Protocol to increase impact until failure occurred – failure when broken into 2 or more pieces Impact varied by altering pressure, which correlates to the energy, of the pneumatic device using an electrically-controlled regulator 5 sawbones were tested for comparison Results and Discussion Failure occurred at: Average Exit Velocity = 5.5m/s Energy = 60J Average Failure Force = 4609N Fracture Limitations Standard Deviation = 505N Fracture Force 6000 5000 Sawbone 1 4000 Force (N) Sawbone 2 3000 Sawbone 3 2000 Sawbone 4 Sawbone 5 1000 0 Sawbone Force and Energy Average Force at each Energy 5000 Average Force (N) 4000 3000 2000 1000 0 20 40 60 Energy (J) Principle Strain Along Bone Peak Failure Strain at each Gage 0.012 0.01 0.008 Gage 1 Strain Gage 2 0.006 Gage 3 0.004 Gage 4 0.002 0 Strain Gage Strain Strain at 20J 0.0014 0.0012 0.001 Sawbone 2 Strain 0.0008 Sawbone 3 0.0006 Sawbone 4 0.0004 Sawbone 5 0.0002 0 1 2 3 4 Strain Gage Strain at 20J 0.014 0.012 0.01 Sawbone 2 Strain 0.008 Sawbone 3 0.006 Sawbone 4 0.004 Sawbone 5 0.002 0 1 2 3 4 Strain at 40J Strain Gage 0.014 0.012 0.01 Sawbone 2 Strain 0.008 Sawbone 3 0.006 Sawbone 4 0.004 Sawbone 5 0.002 0 1 2 3 4 Strain at 60J Strain Gage 0.014 0.012 0.01 Sawbone 2 Strain 0.008 Sawbone 3 0.006 Sawbone 4 0.004 Sawbone 5 0.002 0 1 2 3 4 Strain Gage Conclusion Synthetic bones fractured at an energy of 60J Fracture of synthetic bone occurred at an average force of 4609N Current injury limit of cadaveric lower leg is 5.4kN (Yoganandan) Average exit velocity was 5.5m/s At fracture the highest principle strain was at point of impact Conclusion Fracture analysis is significant when determining the injury limits of a bone Experimental results of cadaveric and synthetic bones can be compared, allowing for appropriate fracture limits to be determined Knowledge of fracture limitations enables manufacturers to improve designs, i.e. cars, to reduce the possibility of injury Understanding the properties of synthetic bones will increase their use in testing and research Acknowledgments I would like to thank Dr. Cynthia Dunning, and Cheryl Quenneville for their guidance and support with the six week project to make it successful and enjoyable References Cristofolini, L., Viceconti, M. (1999). Mechanical Validation of whole bone composite tibia models. Journal of Biomechanics 33 (2000), 279-288. Quenneville, C., Fraser, G., Dunning, C. (2008). Development of an Apparatus to Produce Fractures From Short-Duration High- Impulse Loading With an Application in the Lower Leg. London, Ontario: University of Western Ontario, Department of Mechanical and Materials Engineering Sawbones Worldwide: A Division of Pacific Research Laboratories, Inc. (2009) Retrieved April 3, 2009, from http://www.sawbones.com/ Vishay Micro-Measurements: Strain gages and Instruments (2008). Yoganandan, N. (1997). Axial Impact Biomechanics of the Human Foot – Ankle Complex. Journal of Biomechanical Engineering Vol 119, 433-437
"Impulse Loading With an Application in the Lower Leg using a "