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In a subcutaneous implant rat model, Collagraft alone (n=8), Collagraft plus isologous bone marrow (n=8), and marrow alone (n=8) were evaluated. Twelve rats were euthanized at 11 days and 12 at 21 days. Explants were evaluated histologically for evidence of bone formation, and osteogenic activity was determined by an assay for alkaline phosphatase. Histological bone formation was absent in all groups at 11 days. At 21 days, in the Collagraft alone and bone marrow alone groups, no bone induction was noted. In contrast, 21-day specimens from the Collagraft plus bone marrow group showed newly formed bone. Alkaline phosphatase activity was negligible (<0.05 units/mg) in all 11-day specimens. Activity in Collagraft plus bone marrow specimens at 21 days (0.38 units/mg) was significantly higher than any other group (P<.001 for all comparisons). This study demonstrates that Collagraft plus bone marrow is an osteoinductive matrix.

Objective This study aimed at assessing the risks associated with human exposure to heat-stress conditions by predicting organ- and tissue-level heat-stress responses under different exertional activities, environmental conditions, and clothing. Methods In this study, we developed an anatomically detailed three-dimensional thermoregulatory finite element model of a 50th percentile U.S. male, to predict the spatiotemporal temperature distribution throughout the body. The model accounts for the major heat transfer and thermoregulatory mechanisms, and circadian-rhythm effects. We validated our model by comparing its temperature predictions of various organs (brain, liver, stomach, bladder, and esophagus), and muscles (vastus medialis and triceps brachii) under normal resting conditions (errors between 0.0 and 0.5 °C), and of rectum under different heat-stress conditions (errors between 0.1 and 0.3 °C), with experimental measurements from multiple studies. Results Our simulations showed that the rise in the rectal temperature was primarily driven by the activity level (~ 94%) and, to a much lesser extent, environmental conditions or clothing considered in our study. The peak temperature in the heart, liver, and kidney were consistently higher than in the rectum (by ~ 0.6 °C), and the entire heart and liver recorded higher temperatures than in the rectum, indicating that these organs may be more susceptible to heat injury. Conclusion Our model can help assess the impact of exertional and environmental heat stressors at the organ level and, in the future, evaluate the efficacy of different whole-body or localized cooling strategies in preserving organ integrity.