Purpose

The zonal microstructure of articular cartilage is a key regulator in load-bearing, wear resistance, nutrient transport, and guiding matrix remodeling. In this work, we fabricated a zonal microstructured scaffold and evaluated its mechanical properties, in vitro performance, and in vivo repair in a porcine osteochondral defect model.

Methods and Materials

Zonal microstructured scaffolds were produced from poly(caprolactone) in a step-wise manner by first generating a porogen-leached/directionally-frozen integrated foam and then electrospinning layers onto the top and bottom of the scaffold. Scaffolds were then characterized by scanning electron microscopy and unconfined compression. For in vitro studies, bovine chondrocytes were isolated from the lower leg joints of calves. Scaffolds were evaluated at weeks 0, 1, 2, and 4 for sulphated glycosaminoglycans and collagen.

In twelve female pigs, two defects, 6 mm diameter and 6 mm deep, were created in the central trochlear groove. Microstructured scaffolds were compared to empty defects and MaioRegen controls. Animals were euthanized at 6 months and repair tissue morphology was visualized using Goldner’s trichrome staining. Raman spectroscopy was used as a label-free technique to quantify differences between repair tissues.

Results

The scaffolds approached physiological values for compressive modulus (~120 kPa) and supported in vitro tissue-engineering. When implanted in vivo, the zonal scaffolds yielded a more consistent (flush articular surface, bone remodeling) repair response than the controls. Furthermore, the scaffolds remained intact demonstrating their long-term suitability for defect repair. Finally, the distinct Raman scattering of repair tissue may prove to be a useful diagnostic tool for future research.

Figure 1. (A) Scaffold architecture. (B) In vitro tissue-engineered scaffolds: picrosirius red (left) and Alcian blue (right). (C) Goldner’s trichrome stain (top) and immunohistochemistry (bottom) for collagen II + DNA.

Conclusion

The results demonstrate the ability to produce zonal microstructured scaffolds with as good, if not better, outcomes than controls in a porcine osteochondral defect model.