Effect of glutaraldehyde fixation on the frictional response of immature bovine articular cartilage explants

Abstract

This study examined functional properties and biocompatibility of glutaraldehyde-fixed bovine articular cartilage over several weeks of incubation at body temperature to investigate its potential use as a resurfacing material in joint arthroplasty. In the first experiment, treated cartilage disks were fixed using 0.02, 0.20 and 0.60% glutaraldehyde for 24h then incubated, along with an untreated control group, in saline for up to 28d at 37°C. Both the equilibrium compressive and tensile moduli increased nearly twofold in treated samples compared to day 0 control, and remained at that level from day 1 to 28; the equilibrium friction coefficient against glass rose nearly twofold immediately after fixation (day 1) but returned to control values after day 7. Live explants co-cultured with fixed explants showed no quantitative difference in cell viability over 28d. In general, no significant differences were observed between 0.20 and 0.60% groups, so 0.20% was deemed sufficient for complete fixation. In the second experiment, cartilage-on-cartilage frictional measurements were performed under a migrating contact configuration. In the treated group, one explant was fixed using 0.20% glutaraldehyde while the apposing explant was left untreated; in the control group both explants were left untreated. From day 1 to 28, the treated group exhibited either no significant difference or slightly lower friction coefficient than the untreated group. These results suggest that a properly titrated glutaraldehyde treatment can reproduce the desired functional properties of native articular cartilage and maintain these properties for at least 28d at body temperature.

Keywords: Cartilage; Damage; Friction; Osteoarthritis; Wear.

Fig. 1

Schematic representation of bovine calf articular cartilage harvest location and friction testing schematic. (A) Study 1 includes articular cartilage discs harvested from the tibial plateau, fixed with glutaraldehyde, and tested against a smooth glass counterface. (B) Study 2 includes articular cartilage strips harvested from the tibial plateau, fixed with glutaraldehyde, and tested against unfixed convex discs from the opposing condyles.

Fig. 2

Representative biocompatibility culture dish with viable and glutaraldehyde treated articular cartilage explants. Explants were cultured for 28 days in cell culture media at 37°C and 15% CO₂. Samples from each treatment group were sectioned and stained for chondrocyte viability at 1, 7, 14, and 28 days.

Fig. 3

Representative FEBio curve-fit of experimental stress-relaxation test (5% strain) used to obtain model parameters for E_−Y, k, and ξ (0% control sample at day 14, R²=0.988).

Fig. 4

Summary of mechanical properties for Study 1 as a function of glutaraldehyde concentration. μ_eq = equilibrium friction coefficient; t_μ = time constant for the rise of the friction coefficient to its equilibrium value; μ_min = minimum friction coefficient, typically achieved at the earliest time point of the friction response; E_−Y = equilibrium compressive modulus; E_+Y = equilibrium tensile modulus; k = hydraulic permeability. Significant differences (p ≤ 0.05) from native day 0 values indicated with †, differences between groups indicated with *.

Fig. 5

Qualitative and quantitative biocompatibility from chondrocyte viability in sectioned co-cultured explants at day 1 and day 28 for 0.0% control, 0.02, 0.2, and 0.6% glutaraldehyde treated explants. Samples from each treatment group were sectioned and stained for chondrocyte viability at 1, 7, 14, and 28 days. No significant differences were detected between groups for the ratio of viable to non viable cells normalized to tissue area.

Fig. 6

Frictional properties for Study 2, migrating contact configuration. μ_initial = friction coefficient at start of test; μ_final = friction coefficient at end of test (1 h). Significant differences (p ≤ 0.05) from day 0 values indicated with †, differences between groups indicated with *.

Fig. 7

India ink staining of representative Study 2 tibial plateau strips shows surface fibrillation of the control (CTRL) group without any apparent superficial zone damage to the 0.2% glutaraldehyde (GLUT) treated sample group after friction testing at day 28.

Fig. 8

(A) Intact immature bovine knee condyles. (B) ‘Popped’ condylar articular layer. (C) Cross-section of popped articular layer, showing the underlying surface.

Fig. 9

Potential clinical approach for bioprosthetic arthroplasties, using glutaraldehyde-fixed xenografts. (A) Natural shoulder joint. (B) A glutaraldehyde-treated bovine articular layer may be affixed to a hemispherical stainless steel substrate supported on a metal stem, and inserted into the humerus in analogy to standard hemiarthroplasties.