Strain-Engineered PVA Hydrogels for Anisotropic Load-Bearing Fibrocartilage: Mechanical and Microstructural Characterization in a Meniscal Model

Poly(vinyl alcohol) (PVA) hydrogels are promising for meniscal replacement, but reproducing native meniscal anisotropy remains unsolved. We developed a fabrication strategy for imparting controlled anisotropy to PVA hydrogels. We hypothesized that modulus and alignment would increase with applied strain, and that circumferential strain would produce direction-dependence in a meniscal-like geometry. Dogbone specimens at three PVA concentrations were strained 0–200% during freeze–thaw processing. Meniscal-like specimens were fabricated at 27.5% PVA under 200% circumferential strain. Constructs were characterized by tensile testing, stress-relaxation compression, and polarized light microscopy. In dogbone specimens, tensile modulus rose exponentially and coherency linearly with applied strain (adjusted R² > 0.92; R² ≥ 0.96). In meniscal-like specimens, stretching increased circumferential peak stress (587 ± 173 vs 439 ± 96 kPa), and direction-dependence appeared only after stretching. Stretched constructs showed higher optical coherency (p = 0.002, r = 0.77), concentrated in the outer third of the cross-section. Compressive moduli trended lower in stretched constructs, reaching significance anteriorly. Strain applied during freeze–thaw processing programs direction-dependent stiffness and alignment into a homogeneous hydrogel, though absolute stiffness remains below native tissue. More strain during processing is the most direct route to a stiffer construct, and further development is required before functional replacement.