Purpose

To determine effects of mechanical forces on chondrocytes response using an injectable hydrogel

that can be used to plaster eroded cartilage surfaces and / or to fill up focal cartilage defects.

Methods and Materials

We have develop an injectable hydrogel from naturally occurring polymers such as dextran and HA, that crosslinks under the influence of HRP and H₂O₂. Using a cartilage-on-chip platform, we determined chondrocyte migratory behavior, viability and catabolic response upon mechanical stimulation after 3 days of culture. The model consist of a mechanical actuation chamber, a 3D cell-hydrogel unit and a perfusion channel to provide nutrients to the structure. Human chondrocytes were embedded in the Dex-HA hydrogel and physiological mechanical stimulation (cell deformation 5-10%) was applied for 1 h x day at 1 Hz. Next, in vivo studies in focal cartilage defect with a duration of 2 weeks and 7 months were performed in an equine joint model.

Results

Chondrocytes embedded in different ratios of the injectable hydrogel (Dex/HA 5% & 10%) showed migratory behavior upon cyclic mechanical stimuli respect to static conditions and our agarose control in the cartilage-on-chip model. Increased mRNA expression of several catabolic markers (HYAL-1, MMP-1, MMP-3, ADAMTS-4 & -5) was detect at day 3 in mechanically stimulated samples. Nonetheless, chondrocytes did not show significant reduction in viability upon stimulation (Figure 1). The chondrocyte migratory behavior was detected also in the two week horse study. After 7 months the ICRS-II scoring system showed significantly better scores compared to microfracture treatment with presence of chondrocytes within the entire hydrogel.

Conclusion

The outcome of the study suggest that mechanical stimulation enhance catabolic activation and migratory behavior of chondrocytes both in vivo and in vitro. Additionally, the use of the injectable hydrogel enhance the regenerative properties of the cartilage in respect to current procedures.