Dynamic compression of human and ovine meniscal tissue compared with a potential thermoplastic elastomer hydrogel replacement

Abstract

Understanding how human meniscal tissue responds to loading regimes mimetic of daily life as well as how it compares to larger animal models is critical in the development of a functionally accurate synthetic surrogate. Seven human and eight ovine cadaveric meniscal specimens were regionally sectioned into cylinders 5 mm in diameter and 3 mm thick along with 10 polystyrene-b-polyethylene oxide block copolymer-based thermoplastic elastomer (TPE) hydrogels. Samples were compressed to 12% strain at 1 Hz for 5000 cycles, unloaded for 24 h, and then retested. No differences were found within each group between test one and test two. Human and ovine tissue exhibited no regional dependency (p < 0.05). Human samples relaxed quicker than ovine tissue or the TPE hydrogel with modulus values at cycle 50 not significantly different from cycle 5000. Ovine menisci were found to be similar to human menisci in relaxation profile but had significantly higher modulus values (3.44 MPa instantaneous and 0.61 MPa after 5000 cycles compared with 1.97 and 0.11 MPa found for human tissue) and significantly different power law fit coefficients. The TPE hydrogel had an initial modulus of 0.58 MPa and experienced less than a 20% total relaxation over the 5000. Significant differences in the magnitude of compressive modulus between human and ovine menisci were observed, however the relaxation profiles were similar. Although statistically different than the native tissues, modulus values of the TPE hydrogel material were similar to those of the human and ovine menisci, making it a material worth further investigation for use as a synthetic replacement. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2722-2728, 2017.

Keywords: TPE hydrogel; human; meniscus mechanics; meniscus replacement; ovine.

Figure 1

Meniscus harvesting and cutting

Figure 2

Regional compressive modulus vs cycle for human (A, B) and ovine (C, D) meniscal tissue. B and D show compressive moduli (average ± std) after selected numbers of completed cycles (1, 10, 25, 50, and 5000) used for statistical analysis

Figure 3

Coefficients of power law fit for all regions of human (A) and ovine (B) meniscal tissue. Data shown as an average ± std

Figure 4

Modulus values and relaxation profile across all 5000 cycles (average ± std)

Figure 5

Modulus values (average ± std) for cycles of interest for human (A) ovine (B) and TPE hydrogel (C) as well as a comparison of all three groups (D). Coefficients from power law fit (average ± std) for all groups (E). Statistical significance denoted as the following: @ sig diff from cycle 10, # sig diff from 25, $ sig diff from 50, % sig diff from 5000, ^ sig diff between human and ovine, & sig diff between ovine and TPE hydrogel, * sig diff between human and TPE hydrogel