Automated Indentation Demonstrates Structural Stiffness of Femoral Articular Cartilage and Temporomandibular Joint Mandibular Condylar Cartilage Is Altered in FgF2KO Mice

Abstract

Objective Employ an automated indentation technique, using a commercially available machine, to assess the effect of fibroblast growth factor 2 (FGF2) expression on structural stiffness over the surface of both murine femoral articular cartilage (AC) and temporomandibular joint (TMJ) mandibular condylar cartilage (MCC). Design Experiments were performed using 3-month-old female homozygote Fgf2KO mice with wild type (WT) littermates. After euthanization, isolated mandibles and hindlimbs were either processed for histology or subjected to automated indentation on a Biomomentum Mach-1 v500csst with a 3-axis motion controller in a phosphate buffered saline bath using a 0.3 mm spherical tip indenter. The effect of indentation depth on normal force was characterized, then structural stiffness was calculated and mapped at multiple positions on the AC and MCC. Results Automated indentation of the AC and TMJ MCC was successfully completed and was able to demonstrate both regional variation in structural stiffness and differences between WT and Fgf2KO mice. Structural stiffness values for Fgf2KO AC were significantly smaller than WT at both the medial/anterior ( P < 0.05) and medial/posterior ( P < 0.05) positions. Global Fgf2KO also lead to a decrease in MCC thickness of the TMJ compared with WT ( P < 0.05) and increased structural stiffness values for Fgf2KO at both the posterior and anterior location ( P < 0.05). Conclusions Automated indentation spatially resolved differences in structural stiffness between WT and Fgf2KO tissue, demonstrating FGF2 expression affects femoral AC and TMJ MCC. This quantitative method will provide a valuable approach for functional characterization of cartilage tissues in murine models relevant to knee joint and TMJ health and disease.

High spatial resolution analysis using indentation mapping differentiates biomechanical properties of normal vs. degenerated mouse articular cartilage

“…Using a novel microscale instrumented apparatus, we were able to reliably detect and quantify spatial variations in biomechanical parameters across murine cartilage surfaces, both within healthy and degenerated femoral condyles. Compared to recent mouse studies using this commercially available apparatus 26,42 , the optimization of sample mounting and needle probing protocols allowed for unprecedented quantitative mapping of the mechanical behavior and associated cartilage thickness on load-bearing regions of distal femurs with high spatial density.…”

“…Male C57Bl6 mice were purchased from Jackson Laboratories (Bar Harbor, ME). We based on sample on a recent paper that used indentation (but not needle probing) in mice 26 , however, because of the addition of needle probing we decided to increase the sample size. Animals were housed under a standard light cycle and had free access to feed (standard diet) and water.…”

“…As such, it can map entire cartilage surfaces using a single setup with high spatial density, and has been previously shown to discriminate between healthy and diseased human cartilage samples 23,25 . This apparatus has been recently employed by Woods and colleagues 26 to evaluate altered biomechanics in a mouse model of cartilage degeneration. However, the study was conducted in the non-load-bearing region of the mouse knee joint.…”

“…Woods and colleagues 26 were also unable to account for site-specific cartilage thickness variations in their measurements, instead using the mean cartilage thickness obtained via histological analysis in their assessment 26 . Other studies have employed mean cartilage thickness values retrieved through histology or imaging techniques to characterize and model tissue mechanical parameters in mice 13,15 .…”

High spatial resolution analysis using automated indentation mapping differentiates biomechanical properties of normal vs. degenerated articular cartilage in mice

“…As such, it can map entire cartilage surfaces using a single setup with high spatial density and has been previously shown to discriminate between healthy and diseased human cartilage samples ( Sim et al, 2017 ; Seidenstuecker et al, 2019 ). This apparatus has been recently employed by Woods and colleagues ( Woods et al, 2021 ) to evaluate altered biomechanics in a mouse model of cartilage degeneration. However, the study was conducted in the non-load-bearing region of the mouse knee joint.…”