Attapulgite Nanocomposites for Cartilage and Osteochondral Repair: Material–Tissue Matching, Evidence-Graded Mechanisms and Translation

Attapulgite (ATP; palygorskite) is a fibrous magnesium aluminum silicate that can reinforce hydrated polymer networks, provide a surface for molecular interactions, and participate in formulation-dependent ion or drug delivery. Although ATP has been studied most extensively in bone-oriented composites, its more distinctive role in cartilage repair may be as a spatially controlled regulator of the scaffold microenvironment rather than as a uniformly distributed bioactive filler. This review therefore examines ATP from a cartilage-first perspective. Direct ATP evidence, effects of modified ATP, performance of complete drug-loaded formulations, and cross-material extrapolations are considered separately. Current cartilage data support injectability, shear-thinning, photocrosslinking, mechanical reinforcement, and sustained intra-articular delivery but do not yet establish durable hyaline cartilage regeneration. In osteochondral constructs, ATP is more plausibly restricted to the calcified-cartilage interface or subchondral region, where reinforcement and mineral-associated functions may be beneficial, while high or uniform cartilage-side loading could increase stiffness, hypertrophy, or ectopic mineralization. This interpretation leads to testable design rules: define the ATP material fingerprint, map dose and spatial distribution, distinguish the true carrier phase, and assess cartilage matrix quality, lubrication, anti-hypertrophic stability, interface mechanics, persistence, and synovial safety. ATP should thus be developed as a dose-controlled and spatially restricted component whose value depends on material–tissue matching and direct mechanistic validation.