The effect of Rear-End collisions on triaxial acceleration to occupant cervical and lumbar Spines: An analysis of IIHS data.

Rear-end impacts are the most frequent type of the more than seven million motor vehicle collisions (MVCs) occurring annually in the United States. The cervical and lumbar spine are the most commonly injured sites as a result of rear-end collisions. The direction and magnitude of accelerations and forces to the spine are considered primary indicators of injury. Yet, there is a dearth of research regarding the relation and quantification of vehicle to occupant accelerations, as well as triaxial acceleration components (and thus, forces) to occupant spines in rear-end impacts. Therefore, the current study utilizes the Insurance Institute of Highway Safety (IIHS) test database to examine the relative relations between vehicle and occupant accelerations, as well as between component accelerations experienced at the cervical and lumbar spines in rear-end collisions. Anthropometric test device (ATD) head and pelvis accelerometer data from IIHS sled testing are used as representative measures of acceleration experienced at the cervical and lumbar spine, respectively. Peak resultant acceleration is calculated at the head and pelvis, and peak directional components (x, y, and z) of acceleration are compared to resultants. This analysis revealed significantly higher occupant head than sled (2.17 ± 0.4 × Sled; p < 0.001) and pelvis than sled (1.24 ± 0.27 × Sled; p < 0.001) accelerations. There were also significant differences across triaxial acceleration components relative to resultant at the head (x = 0.99 ± 0.02, y = 0.11 ± 0.05, z = 0.34 ± 0.06; p < 0.001 for all comparisons) and pelvis (x = 0.94 ± 0.06, y = 0.12 ± 0.14, z = 0.35 ± 0.08; p < 0.001 for all comparisons). A secondary analysis examining differences in occupant dynamics by seat designs across vehicle type revealed significant differences only between the pelvis z component accelerations in the passenger vehicle and SUV groups (passenger vehicle:SUV = 1.07, p < 0.001). Due to the uniform nature of IIHS sled testing protocols, this analysis reflects similarities in seat properties rather than between vehicle types. These results may provide a simplistic approach to quantify the magnitude of directional accelerations and forces to occupant spines in rear-end collisions.

Multi-modal characterization of polymeric gels to determine the influence of testing method on observed elastic modulus.

Demand for materials that mechanically replicate native tissue has driven development and characterization of various new biomaterials. However, a consequence of materials and characterization technique diversity is a lack of consensus within the field, with no clear way to compare values measured via different modalities. This likely contributes to the difficulty in replicating findings across the research community; recent evidence suggests that different modalities do not yield the same mechanical measurements within a material, and direct comparisons cannot be made across different testing platforms. Herein, we examine whether "material properties" are characterization modality-specific by analyzing the elastic moduli determined by five typical biomaterial mechanical characterization techniques: unconfined-compression, tensiometry, rheometry, and micro-indentation at the macroscopic level, and microscopically using nanoindentation. These analyses were performed in two different polymeric gels frequently used for biological applications, polydimethylsiloxane (PDMS) and agarose. Each was fabricated to span a range of moduli, from physiologic to supraphysiologic values. All five techniques identified the same overall trend within each material group, supporting their ability to appreciate relative moduli differences. However, significant differences were found across modalities, illustrating a difference in absolute moduli values, and thereby precluding direct comparison of measurements from different characterization modalities. These observed differences may depend on material compliance, viscoelasticity, and microstructure. While determining the underlying mechanism(s) of these differences was beyond the scope of this work, these results demonstrate how each modality affects the measured moduli of the same material, and the sensitivity of each modality to changes in sample material composition.