Department Chair Wayne State University Biomedical Engineering
Introduction: This study aims to determine whether freeze-preservation affects the energy density needed to penetrate the skin. As military forces studies the effects of less-lethal impact munitions (LLIMs) with cadavers, the demand for subjects leads to using freeze-preserved specimens as subjects, with the assumption that freezing and thawing has little effect on the penetration results. This study compares data with that from a previous study using the same six specimens in the fresh condition ( < 7 days post-mortem).
Materials and
Methods: Data is compared to that from a previous study, in which six newly deceased specimens (within seven days of death) were subjected to ballistic impact in the thigh at varying velocities and round sizes to identify the penetrating energy density. This study evaluates the same specimens that were frozen for at least six months. High-strength multipurpose neoprene rubber balls were used as less-lethal impact munition surrogates, projected by a house-made air cannon using nitrogen gas. Ultrasound was used to measure thickness of skin at impact locations as a covariate.
Results, Conclusions, and Discussions: The penetrating energy density in the frozen and thawed condition both increased and decreased, on a specimen-to-specimen basis. Using a logistic model in survival analysis, the ED50 (fresh) = 13.30 J/cm2, and the ED50 (frozen/thawed) = 13.19 J/cm2. The frozen/thawed condition model had a poorer goodness-of-fit than the fresh condition model (Anderson-Darlingfresh = 8.127 and Anderson-Darlingfrozen/thawed = 32.161), likely due to the bi-directional changes in penetrating energy density from fresh to frozen/thawed. Bulk tissue thickness and round size may be covariates, as the 25mm round size may be more sensitive to changes in tissue thickness. Using ED/BT (energy density divided by bulk tissue thickness) as a transform variable, at a constant energy density and the given conditions, the 25mm round will penetrate a higher bulk tissue thickness than will a 16mm round (ED/BT50, 25mm= 10.8 J/cm3; ED/BT BT50, 16mm= 29.6 J/cm3). With the available data, the effect freezing has on penetration response is unidentifiable, though bulk tissue thickness may play a role in resistance to penetration.
Acknowledgements (Optional): Thank you to the Army Educational Outreach Program for the opportunity to complete this study, along with my mentor, Dr. Karin Rafaels. An additional great thank you goes to Dr. Cynthia Bir, my primary investigator at Wayne State University, along with the rest of the Biomechanics Injury Research Laboratory for the support and guidance to complete this project.
