The meniscus plays a critical role in load transmission, stability and energy dissipation in the knee joint. Loss of the meniscus leads to joint degeneration and osteoarthritis. In a number of cases replacement of the resected meniscal tissue by a synthetic implant might avoid the articular cartilage degeneration. None of the available implants presents optimal biomechanics characteristic due to the fact the biomechanics functionality of the meniscus is not yet fully understood.
Mimicking the native biomechanical characteristics of the menisci seems to be the key factor in meniscus replacement functioning. This is extremely challenging due to its complex inhomogeneous microstructure, the lack of a full experimental characterization of the material properties and the lack of 3D theoretical, numerical and computational models which can reproduce and validate the experimental results.
Therefore, the aim of this work is a thorough understanding of the menisci biomechanics with the view of translating the knowledge to the orthopaedic implants arena.
The objective of the proposal be achieved through
- designing and performing a range of innovative experimental tests to characterize the behaviour of the meniscus tissue at the micro and macroscale
- building an appropriate and novel multiscale anisotropic model at the tissue level which takes into account the fractal dimension of the porous menisci’s tissue
- implementing the material model in commercial finite element (FE) software
- build and validate an accurate FE biomechanical model of the knee joint (which includes the meniscus) in order to model the biomechanical behaviour of the menisci when subjected to a range of mechanical stress which is not reproducible in an experimental context
The project focused on the biomechanics of the knee meniscus and understanding the structure-function relationship of this tissue.
This research has touched upon a number of length scales from nano-macro and on a number of research ﬁelds from advanced microscopy and imaging to experimental mechanical testing, involving new mathematical models used for large scale simulations of the knee joint.
Remarkable results towards and beyond the objectives of the project:
Discovery 1: New architecture of the meniscus at the micro/nano scale. The meniscus is a highly porous “cushion” made of macro/micro/nano channels of collagen fascicles through which ﬂuid ﬂows. The external layer is highly impermeable as large hydraulic pressures are required to force ﬂuid ﬂow through meniscal tissue.
Discovery 2: Damping properties at high frequency. It has been observed through DMA tests that the meniscus exhibits remarkable properties at high frequency which were not revealed before. The damping capability, enhanced at high frequency, is due through ﬂuid mobility which is strongly related to the breakthrough in the meniscal architecture proposed in.
Discovery 3: Material parameters are spatial dependent. Mechanical properties are clearly diﬀerent in the superﬁcial layers of the menisci (being stiﬀer to sustain the loading and the more internal layers which act as a damper. The central body of the meniscus in the vascular region exhibit higher stiﬀness with respect of the anterior and posterior horns.
Discovery 4: High resolution MicroCT scans (600nm resolution) on the meniscal tissue- currently the only-to-date. Quantiﬁcation of microstructural features (porosity, frequency of pores, tortuosity) and ﬂuid ﬂow simulations by using computational ﬂuid dynamics (CFD) on real microstructure reconstructed by MicroCT scans.
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