Assessment and prevention of cartilage degeneration surrounding a focal chondral defect in the porcine model

Abstract

Focal defects in articular cartilage are unable to self-repair and, if left untreated, are a leading risk factor for osteoarthritis. This study examined cartilage degeneration surrounding a defect and then assessed whether infilling the defect prevents degeneration. We created a focal chondral defect in porcine osteochondral explants and cultured them ex vivo with and without dynamic compressive loading to decouple the role of loading. When compared to a defect in a porcine knee four weeks post-injury, this model captured loss in sulfated glycosaminoglycans (sGAGs) along the defect's edge that was observed in vivo, but this loss was not load dependent. Loading, however, reduced the indentation modulus of the surrounding cartilage. After infilling with in situ polymerized hydrogels that were soft (100 kPa) or stiff (1 MPa) and which produced swelling pressures of 13 and 310 kPa, respectively, sGAG loss was reduced. This reduction correlated with increased hydrogel stiffness and swelling pressure, but was not affected by loading. This ex vivo model recapitulates sGAG loss surrounding a defect and, when infilled with a mechanically supportive hydrogel, degeneration is minimized.

Biomimetic and mechanically supportive 3D printed scaffolds for cartilage and osteochondral tissue engineering using photopolymers and digital light processing

“…It is worth noting that a prior study, using a similar focal chondral defect model, showed cartilage degradation by sGAG loss along the defect's edge when higher strains were applied (i.e. 20% strain vs 10% strain used herein) [43]. Thus, it is possible that a higher strain environment could lead to more pronounced differences between infilling and would require a mechanically supportive structure to maintain the health of the cartilage tissue adjacent to the defect.…”

“…It is feasible that the 3D + CMH, under free swelling conditions, may have produced a similar result through forces generated by the scaffold swelling within the defect. It was previously reported that swelling resulting from a hydrogel that was in situ polymerized in a focal chondral defect, generated pressures ranging from 13 to 310 kPa depending on the hydrogel formulation [43]. This swelling pressure correlated to a protective phenomenon, which minimized sGAG loss that was observed in empty defects.…”

“…This loading protocol was repeated 5 consecutive days per week. All experimental conditions were cultured in DMEM with 10% FBS, 0.05 mg ml −1 l-ascorbic acid-2-phosphate, 0.4 mM L-proline, 0.1 nM non-essential amino acids, 0.01 M HEPES, 0.02 mg ml −1 gentamicin, 4 mM glutaGRO, 100 U ml −1 penicillin, and 50 µg ml −1 streptomycin, a standard medium culture for chondrocytes and cartilage explants [41][42][43]. Medium was changed every 2-3 d. At the end of the study, each sample was hemisectioned, with one section prepared for histology and the other prepared for microindentation.…”

“…Samples that were subjected to dynamic compression were loaded at 1 Hz and an amplitude strain of 2.5% for 1 h, 7 d a week. All conditions were cultured in an OC medium of high glucose DMEM containing 1% ITS + premix, 100 mg ml −1 sodium pyruvate, 20 mM β-glycerophosphate, 100 nM dexamethasone, 50 mg ml -1 l-ascorbic acid-2-phosphate, 1 mg ml −1 fungizone, 50 U ml −1 penicillin, 50 mg ml −1 streptomycin, and 20 mg ml −1 gentamicin [43]. To visualize hMSCs embedded in the bilayer composite, the 3D printed structure was formed with a resin containing rhodamine methacrylate (0.1 mM).…”

Mesenchymal stem cells loaded on 3D-printed gradient poly(ε-caprolactone)/methacrylated alginate composite scaffolds for cartilage tissue engineering

“…However, PCL is often composited with other polymers to overcome its hydrophobicity [ 25 , 26 ]. Hydrogels are highly absorbent, act as a buffer between the scaffold and the cartilage, and prevent cartilage degeneration [ 27 ]. It has been reported that alginate, a biocompatible polysaccharide extracted from seaweed, is widely used in cartilage regeneration, with excellent biocompatibility, injectability, and ability to support encapsulated cells differentiation, and can be quickly gelled by the addition of Ca 2+ [ 14 , 28 , 29 ].…”