Fibrous cartilage of human menisci is less shock-absorbing and energy-dissipating than hyaline cartilage.

PURPOSE: To test meniscal mechanical properties such as the dynamic modulus of elasticity E* and the loss angle δ at two loading frequencies ω at different locations of the menisci and compare it to E* and δ of hyaline cartilage in indentation mode with spherical indenters. METHODS: On nine pairs of human menisci, the dynamic E*-modulus and loss angle δ (as a measure of the energy dissipation) were determined. The measurements were performed at two different strain rates (slow sinusoidal and fast single impact) to show the strain rate dependence of the material. The measurements were compared to previous similar measurements with the same equipment on human hyaline cartilage. RESULTS: The resultant E* at fast indentation (median 1.16 MPa) was significantly higher, and the loss angle was significantly lower (median 10.2°) compared to slow-loading mode's E* and δ (median 0.18 MPa and 16.9°, respectively). Further, significant differences for different locations are shown. On the medial meniscus, the anterior horn shows the highest resultant dynamic modulus. CONCLUSION: In dynamic measurements with a spherical indenter, the menisci are much softer and less energy-dissipating than hyaline cartilage. Further, the menisci are stiffer and less energy-dissipating in the middle, intermediate part compared to the meniscal base. In compression, the energy dissipation of meniscus cartilage plays a minor role compared to hyaline cartilage. At high impacts, energy dissipation is less than on low impacts, similar to cartilage.

Acrylamide Polymer Double-Network Hydrogels: Candidate Cartilage Repair Materials with Cartilage-Like Dynamic Stiffness and Attractive Surgery-Related Attachment Mechanics.

BACKGROUND: In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation. METHODS: Mechanical properties related to surgical use were tested in 2 types of DN gels. RESULTS: Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (~1.1 and ~1.5 MPa) approaching swine meniscus (~2.9 MPa). Dynamic impact energy-absorbing capability was much lower (median loss angles of ~2°) than swine meniscus (>10°), but it is intriguing that >90%-water materials can efficiently store energy. Also, fine 4/0 suture tear-out strength approached cartilage (~2.1 and ~7.1 N v. ~13.5 N). Initial strength of attachment of DN gels to cartilage with acrylic tissue adhesive was also high (~0.20 and ~0.15 N/mm(2)). CONCLUSIONS: DN gel strength and toughness properties stem from optimized entanglement of the 2 network components. DN gels thus have obvious structural parallels with cartilaginous tissues, and their surgical handling properties make them ideal candidates for clinical use.