A Calibration Procedure for a Bone Loading System

Abstract

Trabecular bone tissue is a three-dimensional structure that is difficult to duplicate with in vitro cell cultures or animal models. In an attempt to better understand the underlying mechanisms of tissue response to load, a system to load isolated bone preparations was developed. This ex vivo bone culture and loading system, given the name of ZETOS, compressively loads trabecular bone (10mm diameter, 5.0mm height) to evaluate its morphological and physiological responses while keeping cells viable. Compliance of the system may change with time, thus requiring recalibration. The purpose of this research was to develop and validate a recalibration protocol for the ZETOS system. Ten reference bodies (RBs) were designed and machined out of aluminum 7075-T6, with a structural rigidity range representative of trabecular bone (0.628–28.3N∕μm, or apparent elastic modulus of 40MPa–1.80GPa). Finite element analysis (FEA) was used to calculate the rigidity of each RB and was validated with physical testing in a universal testing machine. Results from FEA were then used to calibrate the system and relate force, piezoelectric actuator expansion, and specimen compressive deformation through a surface generated by spline interpolation, thus creating a calibration table. Calibration of ZETOS was verified by testing the RBs as well as three custom-made, metal springs and comparing measured rigidity to that calculated by FEA. Mean percent difference of FEA results with respect to those from physical testing was 3.28%. The mean percent difference of RB rigidity found with ZETOS with respect to rigidity found with FEA was 1.12% and for the metal springs, the mean percent difference was 1.74%. The calibration procedure for the ZETOS bone loading system has been successfully applied and verified. The use of RBs and FEA allows users to easily and periodically evaluate and recalibrate the system. Accuracy in studies of human bone mechanotransduction in a controlled environment can therefore be achieved. The recalibration procedure is relevant for other ZETOS users and may serve as the basis for calibration of other testing systems for small specimens of compliant materials.

Combined exposure to big endothelin-1 and mechanical loading in bovine sternal cores promotes osteogenesis

“…E x vivo organ culture allows investigations of whole tissues without disrupting the interactions among neighboring cells and the extracellular matrix [43]. The ZETOS Bone Loading and Bioreactor System (ZETOS) allows isolation and maintenance of trabecular bone cores with active and viable stem cells, osteoblasts, osteocytes, osteoclasts necessary to maintain bone homeostasis [10–14, 30–32]. Bone formation in response to mechanical and biochemical stimuli during a multi-week experiment was assessed by measuring changes in axial stiffness of bone cores, using the ZETOS mechanical testing apparatus, and secretions of metabolic biomarkers [10–13, 30–32].…”

“…The ZETOS Bone Loading and Bioreactor System (ZETOS) allows isolation and maintenance of trabecular bone cores with active and viable stem cells, osteoblasts, osteocytes, osteoclasts necessary to maintain bone homeostasis [10–14, 30–32]. Bone formation in response to mechanical and biochemical stimuli during a multi-week experiment was assessed by measuring changes in axial stiffness of bone cores, using the ZETOS mechanical testing apparatus, and secretions of metabolic biomarkers [10–13, 30–32]. Static and dynamic histomorphometry was used to trace morphological changes resulting from modeling and remodeling [10, 13, 30].…”

“…The concentration of big ET1 used in the current experiment was approximately equivalent to the lowest published concentration of active ET1 used in cell culture experiments [29]. Cores in the LC and LE treatment groups were loaded (−2000 με, 120 cycles daily, “jump” waveform) through the bioreactors’ sapphire pistons using ZETOS Bone Loading and Bioreactor System (ZETOS) [9–13, 30–32]. Bone formation in the cores was assessed with ΔE app , static and dynamic histomorphometry, and PGE2 secretion.…”

“…Each core was cyclically loaded in compression to a maximum change in bulk strain of 2000 με every 0.5 seconds for 120 cycles for 23 days [9–13, 30–32]. The dynamic loading implemented in the study mimicked a “jump” waveform, the shape of which was determined from normative human jump data [33].…”

“…The axial stiffness ( K axial ) of the cores was measured with this quasi-static compression (Figure 2) through the bioreactors’ sapphire pistons using ZETOS [9–13, 30–32, 34]. To ensure contact between the loading piston and bone core, a preload of 10 N was applied before quasi-static testing and the dynamic loading stimulus.…”