In Vitro‐Induced High Sugar Environments Deteriorate Human Cortical Bone Elastic Modulus and Fracture Toughness

Abstract

Advanced glycation end-products (AGEs) have been suggested to contribute to bone fragility in type 2 diabetes (T2D). AGEs can be induced through in vitro sugar incubations but there is limited data on the effect of total fluorescent AGEs on mechanical properties of human cortical bone, which may have altered characteristics in T2D. Thus, to examine the effect of AGEs on bone directly in T2D patients with uncontrolled sugar levels, it is essential to first understand the fundamental mechanisms by studying the effects of controlled in vitro-induced AGEs on cortical bone mechanical behavior. Here, human cortical bone specimens from female cadaveric tibias (ages 57-87) were incubated in an in vitro 0.6 M ribose or vehicle solution (n = 20/group) for 10 days at 37°C, their mechanical properties were assessed by microindentation and fracture toughness tests, and induced AGE levels were quantified through a fluorometric assay. Results indicated that ribose-incubated bone had significantly more AGEs (+81%, p ≤ 0.005), lower elastic modulus assessed by traditional microindentation, and lower fracture toughness compared with vehicle controls. Furthermore, based on pooled data, increased AGEs were significantly correlated with deteriorated mechanical properties. The findings presented here show that the accumulation of AGEs allows for lower stiffness and increased ability to initiate a crack in human cortical bone. Statement of clinical significance: High sugar levels as in T2D results in deteriorated bone quality via AGE accumulation with a consequent weakening in bone's mechanical integrity.

Methods for bone quality assessment in human bone tissue: a systematic review

“…Currently, micro-indentation testing can measure bone properties at the millimeter level, and nano-indentation testing has the potential to measure the mechanical properties of bone at the level of trabeculae or osteons. These novel techniques are being used in vitro to evaluate bone quality at various anatomical sites [ 5 , 6 , 61 – 67 ].…”

A review on experimental and numerical investigations of cortical bone fracture

“…31 Numerous experimental studies determined the effect of several parameters, that is, sugar, age, hydration, mineralization, preservative method, fatigue loading, strain rate, porosity, anisotropy, demineralization, deproteinization, type of specimen, indentation, shear deformation, bone composition, etc., on fracture parameters of cortical bone. 21–23,32–64 Many researchers have validated their numerically predicted results with the experimental analysis as well. 22,40,42,47,51,62…”

Mechanical properties of cortical bones related to temperature and orientation of Haversian canals

“…Regarding the testing of bone mechanical properties [4], static testing methods, including compressive [5], tensile [6], bending [7] and indentation [8], are frequently used, such as E Lefevre et al used microindentation to assess the mechanical properties of the extracellular matrix. Combining with the influencing factors, including porosity [3], sugar content [9] and mineral content [10], these methods could obtain basic strength, anisotropy, toughness, microstructure evolution, healing behavior and gradient of mechanical properties between cortical and cancellous bones. For instance, the plastic deformation behaviors of both single lamellae and macroscopic samples was revealed by the micropillar compression inside a scanning electron microscope [11].…”

“…A large number of studies involved the effects of sampling depth and porosity on mechanical properties of cortical bones, and the finite element analysis of failure mechanism subjected to different loading conditions were also performed, such as F Khor et al analyzed the anisotropic three-point bending and axial torsion behaviors of cortical bones by using an effective human body models [12]. The in vitro environment could be established to achieve the mechanical tests under approximate service condition, such as K Merlo et al carried out the indentation and fracture toughness tests under thermostatic (37°C) ribose solution to assess the elastic modulus and fracture toughness [9]. Meanwhile, due to the ordered structures consisting of mineralized collagen fibrils with specific orientation and embedded hydroxyapatite crystals, the mechanical anisotropy of cortical bones related to axial or radial orientation was also investigated [13].…”