With the onset and progression of osteoarthritis (OA), articular cartilage (AC) mechanical properties are altered. These alterations can serve as an objective measure of tissue degradation. Although the mouse is a common and useful animal model for studying OA, it is extremely challenging to measure the mechanical properties of murine AC due to its small size (thickness < 50 μm). In this study, we developed novel and direct approach to independently quantify two quasi-static mechanical properties of mouse AC: the load-dependent (nonlinear) solid matrix Young's modulus (E) and drained Poisson's ratio (ν). The technique involves confocal microscope-based multiaxial strain mapping of compressed, intact murine AC followed by inverse finite element analysis (iFEA) to determine E and ν. Importantly, this approach yields estimates of E and ν that are independent of the initial guesses used for iterative optimization. As a proof of concept, mechanical properties of AC on the medial femoral condyles of wild-type mice were obtained for both trypsin-treated and control specimens. After proteolytic tissue degradation induced through trypsin treatment, a dramatic decrease in E was observed (compared to controls) at each of the three tested loading conditions. A significant decrease in ν due to trypsin digestion was also detected. These data indicate that the method developed in this study may serve as a valuable tool for comparative studies evaluating factors involved in OA pathogenesis using experimentally induced mouse OA models.
Cell and tissue alignment
is a defining feature of periodontal
tissues. Therefore, the development of scaffolds that can guide alignment
of periodontal ligament cells (PDLCs) relative to tooth root (dentin)
surfaces is highly relevant for periodontal tissue engineering. To
control PDLC alignment adjacent to the dentin surface, poly(ethylene
glycol) (PEG)-based hydrogels were explored as a highly tunable matrix
for encapsulating cells and directing their activity. Specifically,
a composite system consisting of dentin blocks, PEG hydrogels, and
PDLCs was created to control PDLC alignment through hydrogel swelling.
PDLCs in composites with minimal hydrogel swelling showed random alignment
adjacent to dentin blocks. In direct contrast, the presence of hydrogel
swelling resulted in PDLC alignment perpendicular to the dentin surface,
with the degree and extension of alignment increasing as a function
of swelling. Replicating this phenomenon with different molds, block
materials, and cells, together with predictive modeling, indicated
that PDLC alignment was primarily a biomechanical response to swelling-mediated
strain. Altogether, this study describes a novel method for inducing
cell alignment adjacent to stiff surfaces through applied strain and
provides a model for the study and engineering of periodontal and
other aligned tissues.
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