Repair of Full Thickness Articular Cartilage Using a 3D-Printed Acellular Polymer Implant in a Caprine Model: A Pilot Study.

ObjectiveEvaluate a 3D-printed acellular polymer scaffold combined with microfracture for repairing critical-sized cartilage defects in a goat model.MethodsSix goats received bilateral 10 mm femoral condyle defects. In a paired design, one knee received microfracture plus a scaffold (95% or 45% infill); the contralateral control received microfracture alone (final n = 6). At 16 weeks, repair was assessed via histology (modified ICRS II), immunohistochemistry, and polarized light microscopy. Histological analysis included three scaffold-treated and three control defects; others were excluded due to loosening or processing issues. The pathologist was unblinded. The scaffold contains non-resorbable, non-degradable nylon 12; remnants persist permanently.ResultsThe 95% infill scaffold handled poorly with poor integration. The 45% infill scaffold demonstrated superior handling and integration, achieving significantly higher median ICRS II scores than microfracture alone (44 vs. 33, p < 0.05), with enhanced cellularity, zonal organization, and type II collagen. Scaffold remnants were surrounded by CD68-positive macrophages, indicating a chronic foreign body response to the non-resorbable material, with associated neovascularization.ConclusionThe 45% infill scaffold improved histological cartilage repair versus microfracture alone at 16 weeks. These preliminary findings support its selection for pivotal studies with larger samples, longer follow-up, and blinded assessment. However, because nylon 12 is non-resorbable, remnants persist permanently, with important implications for long-term stability, safety, biocompatibility, and the mechanism of tissue repair. Results should be interpreted cautiously given the small sample size and short follow-up.