Mechanical evaluation of a tissue-engineered zone of calcification in a bone-hydrogel osteochondral construct

Abstract

The objective of this study was to test the hypothesis that mechanical properties of artificial osteochondral constructs can be improved by a tissue-engineered zone of calcification (teZCC) at the bone-hydrogel interface. Experimental push-off tests were performed on osteochondral constructs with or without a teZCC. In parallel, a numerical model of the osteochondral defect treatment was developed and validated against experimental results. Experimental results showed that the shear strength at the bone-hydrogel interface increased by 100% with the teZCC. Numerical predictions of the osteochondral defect treatment showed that the shear stress at the bone-hydrogel interface was reduced with the teZCC. We conclude that a teZCC in osteochondral constructs can provide two improvements. First, it increases the strength of the bone-hydrogel interface and second, it reduces the stress at this interface.

Keywords: calcification; interfacial tissue engineering; osteochondral defect; push-off test.

Figure 1

Axisymmetric model of the osteochondral defect treatment (A) and (B) model of the push-off test. 1, Bone; 2, teZCC; 3, hydrogel; 4, indenter; 5, opposing host cartilage; 6, host cartilage; 7, host ZCC and 8, host bone. Red arrow highlights that the bottom of 3 and 7 are aligned. (C) Zoom of the black doted square detailing the mesh of the teZCC and ZCC.

Figure 2

Double diffusion system with the trabecular bone sample infiltrated with agarose hydrogel adapted from our previous study (Hollenstein et al. 2011). Calcium and phosphate solutions are circulating from each end of the hydrogel with the help of a peristaltic pump.

Figure 3

Schematic of the push-off setup (A) and experimental results (B).

Figure 4

Lateral expansion of the host cartilage following the 30% compression from the opposite host cartilage in the osteochondral defect treatment model. 1, Bone; 2, teZCC; 3, hydrogel; 5, opposing host cartilage, 6, host cartilage, 7, host ZCC and 8, host bone.

Figure 5

Shear stress along bone–hydrogel interface axis (without teZCC) and along teZCC–hydrogel interface axis (with teZCC) at 30% compression in the osteochondral defect treatment model (A). Maximum shear stress (B).

Figure 6

Photography of a control sample and calcified sample after 7 days (A). Micro-CT image at 9 µm resolution (B).

Figure 7

Push-off test. Typical experimental load–displacement curve (A). Numerical shear strength with and without teZCC at failure displacements (B) (*P < 0.05).