(Imax/Cmax) (p<0.001) and 38.6% (Imin/Cmin) (p<0.001) over the 4 wk culture period. Density decreased 41.6% and 53.0% (p<0.001) over the 2 and 4 wk culture periods, respectively. These findings, not surprisingly, suggest that the organ culture models, as maintained here (passive diffusion), are most effective if used for short-term studies (≤ 1 wk) and that while the bones at 2 wk of culture are more dense and stronger than their counterparts at 24 hr post-harvest, their loss of viability is significant given the comparison to the bones from the 1 wk time point. Four week results indicate a relatively dead culture that in many cases was approximately equivalent to the 24 hr controls. EVALUATION OF THE ORGAN CULTURE SYSTEM UNDER DISTRACTION To determine if the organ culture approach could be an effective model for DO studies, femurs from 5-day-old Wistar rats were utilized. Unless otherwise noted, all femurs were maintained in culture for 1 week (37°C and 5% CO2). Bones were maintained in culture in 12 well plates on stainless steel mesh inserts to maintain the bones at a liquid/gas interface and organ culture medium (BGJb, Gibco) supplemented with 15% FBS and 2% P/S was added daily to counteract evaporation. Prior to any experimentation, bones were allowed to equilibrate in culture for 24 hr. Following observation of the 24 hr acclimation period, all bones were replenished with fresh medium to minimize any harvest–induced insult culture effects [3]. Group I (GRP I) consisted of 23 bone pairs; Group II (GRP II) consisted of 21 bone pairs. From GRP I, all 23 pair were assessed for non-destructive dimension and mass changes; from GRP II, all 21 pair were assessed for non-destructive dimension and mass changes. For each group, 3 pair were assigned to viability studies and 9 pair were assigned to microCT and destructive massing. For GRP I, 11 pair were assessed for mechanical properties and for GRP II, 9 pair were assessed '$< '$< Figure 2. Normalized microCT results show the effects of a 1 month culture period on the organ culture model. Normalized results greater than 1 indicate an increase in culture time point parameter (eg, density) in comparison to the contralateral control at 24 hr post-harvest. Normalized results less than 1 indicate a decrease in culture time point parameter in comparison to contralateral controls at 24 hr. Furthermore, as demonstrated, increases that were observed at 1 wk of culture were significantly reduced by 2 wk of culture and completely lost by 4 wk of culture. These results support the short-term (≤ 1 wk) use of the organ culture system. Results are plotted as mean ± SEM. 165
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