Implications of vehicle roll direction on occupant ejection and injury risk.

Vehicle roll direction and occupant position have been shown to affect occupant kinematics. Data from NASS-CDS were analyzed for risk of serious or greater injuries and ejection with respect to the position of the occupant (near side or far side). The risk of AIS 3+ injuries was higher for unrestrained occupants, for ejected occupants, for occupants involved in rollovers with higher numbers of quarter turns, and for far side occupants. Near side occupants had an increased risk of partial ejection in rollovers consisting of one complete roll or less. Occupant roll direction did not affect risk of complete ejection.

Biaxial mechanical properties of muscle-derived cell seeded small intestinal submucosa for bladder wall reconstitution.

Bladder wall replacement remains a challenging problem for urological surgery due to leakage, infection, stone formation, and extensive time needed for tissue regeneration. To explore the feasibility of producing a more functional biomaterial for bladder reconstitution, we incorporated muscle-derived cells (MDC) into small intestinal submucosa (SIS) scaffolds. MDC were harvested from mice hindleg muscle, transfected with a plasmid encoding for beta-galactosidase, and placed into single-layer SIS cell culture inserts. Twenty-five MDC and/or SIS specimens were incubated at 37 degrees C for either 10 or 20 days. After harvesting, mechanical properties were characterized using biaxial testing, and the areal strain under 1 MPa peak stress used to quantify tissue compliance. Histological results indicated that MDC migrated throughout the SIS after 20 days. The mean (+/-SE) areal strain of the 0 day control group was 0.182 +/- 0.027 (n=5). After 10 days incubation, the mean (+/-SE) areal strain in MDC/SIS was 0.247 +/- 0.014 (n=5) compared to 10 day control SIS 0.200 +/- 0.024 (n=6). After 20 days incubation, the mean areal strain of MDC/SIS was 0.255 +/- 0.019 (n=5) compared to control SIS 0.170 +/- 0.025 (n=5). Both 10 and 20 days seeded groups were significantly different (p=0.027) than that of incubated SIS alone, but were not different from each other. These results suggest that MDC growth was supported by SIS and that initial remodeling of the SIS ECM had occurred within the first 10 days of incubation, but may have slowed once the MDC had grown to confluence within the SIS.

Changes in the biaxial viscoelastic response of the urinary bladder following spinal cord injury.

In order to gain a deeper understanding of bladder function, it is necessary to study the time-dependent response of the bladder wall. The present study evaluated and compared the viscoelastic behaviors of normal and spinal cord injured (SCI) rat bladder wall tissue using an established rat model and planar biaxial stress relaxation tests. Bladders from normal and spinalized (3 weeks) rats were subjected to biaxial stress (either 25 or 100 kPa in each loading direction) rapidly (in 50 ms) and subsequently allowed to relax at the constant stretch levels in modified Kreb's solution (in the absence of calcium; with no smooth muscle tone) for 10,000 s. We observed slower and therefore less stress relaxation in the SCI group compared to the normal group, which varied with the stress-level. These experimental results were fitted (r2 > 0.98) to a reduced relaxation function. Furthermore, biochemical assays revealed that the collagen content of SCI rat bladders was significantly (p < 0.05) lower by 43%, while the elastin content was significantly (p < 0.001) higher by 260% than that of normal bladders. These results suggest that SCI and the associated urologic functional changes induce profound tissue remodeling, which, in turn, provided the structural basis for the alterations in the complex, time-dependent mechanical behavior of the urinary bladder wall observed in the present study.

Passive biaxial mechanical properties of the rat bladder wall after spinal cord injury.

PURPOSE: Changes in the mechanical properties of the bladder wall after spinal cord injury can alter bladder compliance and wall tension, leading to changes in afferent nerve activity and to abnormal reflex mechanisms. To our knowledge we report the first application of biaxial mechanical testing to the normal bladder wall and demonstrate how these properties change after spinal cord injury. MATERIALS AND METHODS: Whole bladders were harvested from mature female Sprague-Dawley rats weighing 250 to 300 gm. Test group animals underwent complete spinal cord transection at the T9 to T10 level and normal animals comprised the control group. The bladders were cut open longitudinally, the trigone and apex were removed and the remaining tissue was trimmed to a square of 9 to 13 mm. per side. Mechanical properties of the tissue sample were tested using planar biaxial testing, in which a stress was applied in the circumferential and longitudinal (base-apex) directions, and resulting axial strains were measured. RESULTS: In normal and spinal cord injured rats bladder wall tissue demonstrated isotropic mechanical behavior when equal stress levels were applied in anatomical directions. However, under nonequi-biaxial loading bladder specimens were not truly isotropic but displayed anisotropic-like behavior. Spinal cord injured tissues were consistently more compliant than normal controls. CONCLUSIONS: Biaxial mechanical testing can detect differences in normal control and hypertrophied rat bladders 10 and 14 days after spinal cord injury. These changes represent an important component of the bladder response to spinal cord injury.