Fracture characteristics of human cortical bone influenced by the duration of in vitro glycation

Advanced glycation end products (AGEs) accumulate in various tissues, including bone, due to aging and conditions like diabetes mellitus. To investigate the effects of AGEs on bone material quality and biomechanical properties, an in vitro study utilizing human tibial cortex, sectioned into 90 beams, and randomly assigned to three mechanical test groups was performed. Each test group included ribose (c = 0.6 M) treatment at 7-, 14-, and 21-d, alongside control groups (n = 5 per group). Fluorescent AGE (fAGE) and carboxymethyl-lysine (CML) levels were assessed through fluorometric analysis and mass spectrometry, while bone matrix composition was characterized using Fourier-transform infrared and Raman spectroscopy. Mechanical properties were determined through nanoindentation and three-point bending tests on non-notched and notched specimens. The results showed significant increases in fAGEs levels at 7-, 14-, and 21-d compared to controls (119%, 311%, 404%; p = .008, p < .0001, p < .0001, respectively), CML levels also rose substantially compared to controls (383%, 503%, 647%, p < .0001, p < .0001, p < .0001, respectively). Analysis of bone matrix composition showed greater sugars/Amide I ratio at 21-d glycation compared to controls, 7-d, and 14-d (p = .001, .011, .006, respectively); and higher carbonate-to-phosphate ratios in the ribose treatment group compared with controls (p < .05) in the interstitial bone area. Mechanical testing of notched specimens exhibited a higher yield force, pre-yield toughness, and maximum force at 14-d glycation compared to controls and to both 7-d and 21-d glycation (p < .05). Nanoindentation showed that the hardness was lower at 7-d glycation compared to the controls and 21-d glycation (p < .05). In conclusion, the study found altered mechanical properties at 7 and 14 d of glycation, which then returned to control levels at 21 d, indicating a dynamic relationship between glycation duration and mechanical characteristics that deserves further exploration.