Biomechanical characteristics of bone in streptozotocin-induced diabetic rats:An in-vivo randomized controlled experimental study

AIM: To investigate the in vivo effects of type Ⅰdiabetes on the mechanical strength of tibial bone in a rodent model.METHODS: The biomechanical effect of diabetes on the structural integrity of the tibia in streptozotocin induced diabetic Wistar rats was analysed. Induction of diabetes was achieved by an intra-peritoneal injection and confirmed by measuring serial blood glucose levels(> 150 mg/d L). After 8 wk the tibiae were harvested and compared to a control group. Biomechanical analysis of harvested tibiae was performed using a threepoint bending technique on a servo hydraulic MTS 858 MiniB ionix frame. Maximum force applied to failure(N), stiffness(N × mm) and energy absorbed(N/mm) were recorded and plotted on load displacement curves. A displacement control loading mode of 1 mm/min was selected to simulate quasi-static loading conditions. Measurements from load-displacement curves were directly compared between groups.RESULTS: Fourteen streptozotocin induced diabetic Wistar rats were compared against nineteen non-diabetic controls. An average increase of 155.2 g in body weight was observed in the control group compared with only 5 g in the diabetic group during the experimental study period. Levels of blood glucose increased to 440.25 mg/d L in the diabetic group compared to 116.62 mg/d L in the control group.The biomechanical results demonstrate a highly significant reduction in the maximum load to failure from 69.5 N to 58 N in diabetic group compared to control(P = 0.011). Energy absorption to fracture was reduced from 28.2 N in the control group to 23.5 N in the diabetic group(P = 0.082). No significant differences were observed between the groups for bending stiffness.CONCLUSION: Streptozotocin-induced diabetes in rodents reduces the maximum force and energy absorption to failure of bone, suggesting a predisposition for fracture risk.

Mechanical behavior of colonic anastomosis in experimental settings as a measure of wound repair and tissue integrity

AIM: To determine the mechanical properties of anasto- motic colonic tissue in experimental settings and there- fore give a measure of wound healing. METHODS: Thirty-six male Wistar rats were used as ex- perimental models of anastomotic tissue integrity. On the 5th post-operative day, the tensile strength was measured by application of an axial force, providing a quantitative measure of anastomotic dehiscence and leakage. RESULTS: Diagrams of the load as a function of the time [P = P (t)] and of the displacement also as a func- tion of time [Δs = Δs (t)] were recorded for each test, permitting the design of the load versus the displace- ment diagram and thus providing significant data about the critical values of anastomotic failure. Quantitative data were obtained concerning the anastomotic strength of both control specimens (healthy rats), as well as spec- imens from non-healthy rats for comparison. CONCLUSION: This experimental model provides an excellent method of measuring anastomotic strength. Despite the relative small number of specimens used, this method provides an accurate way of measuring wound repair. More experimental measurements need to be performed to correlate emerging tensile strength val-ues to anastomotic failure.