FRAP experiments showed that the permeability of cartilage was enhanced after enzymatic treatment. The increase in the diffusion coefficient may result from the disruption of the ECM by enzymatic digestion. The size of dextran examined in this study was selected to mimic certain physiologically relevant molecules. The large 500 kDa dextran was similar in size to fibronectin or cartilage oligomeric protein which have molecular weights of 550 or 500 kDa. The 70 kDa dextran was similar in size to some of the smaller matrix molecules such as biglycan and decorin, and the 10 kDa dextran was similar in size to important growth factors such as BMP-7, BMP-3, IGF and EGF. Interestingly, diffusion coefficients of FITC-BSA in partially digested cartilage were lower than in undigested cartilage. It is possible that an aggressive and short-term partial digestion that induces disruption of the cartilage ECM may change the natural space of the ECM to a much more intricate environment with exudates of digested ECM constituents hindering BSA diffusion and it may even be possible that the partial digestion exposes non-specific binding sites on the collagen with BSA. Moreover, this finding may also imply that the enzymatic treatment preserved most of the structural ECM in cartilage.
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