  The degeneration of articular cartilage (AC) occurs in osteoarthritis (OA),
which is a leading cause of pain and disability in middle-aged and older
people. The early disease related changes in cartilage extra-cellular matrix
(ECM) start with depletion of proteoglycan(PG), leading to an increase in
tissue hydration and permeability. These early compositional changes are small
(<10%) and hence difficult to register with conventional non-invasive imaging
technologies (magnetic resonance and ultrasound imaging). Here we apply
Brillouin microscopy for detecting changes in the mechanical properties and
composition of porcine AC. OA-like degradation is mimicked by enzymatic tissue
digestion, and we compare Brillouin microscopy measurements against
histological staining of PG depletion over varying digestion times and enzyme
concentrations. The non-destructive nature of Brillouin imaging technology
opens new avenues for creating minimally invasive arthroscopic devices for OA
diagnostics and therapeutic monitoring.
