The optimal method to integrate scaffolds with articular cartilage has not yet been identified, in part because of our lack of understanding about the mechanobiological conditions at the interface. Our objective was to quantify the effect of mechanical loading on integration between a scaffold and articular cartilage. We hypothesized that increased number of loading cycles would have a detrimental effect on interface integrity. The following models were developed: (i) an in vitro scaffold–cartilage explant system in which compressive sinusoidal loading cycles were applied for 14 days at 1 Hz, 5 days per week, for either 900, 1800, 3600, or 7200 cycles per day and (ii) an in silico inhomogeneous, biphasic finite element model (bFEM) of the scaffold–cartilage construct that was used to characterize interface micromotion, stress, and fluid flow under the prescribed loading conditions. In accordance with our hypothesis, mechanical loading significantly decreased scaffold–cartilage interface strength compared to unloaded controls regardless of the number of loading cycles. The decrease in interfacial strength can be attributed to abrupt changes in vertical displacement, fluid pressure, and compressive stresses along the interface, which reach steady-state after only 150 cycles of loading. The interfacial mechanical conditions are further complicated by the mismatch between the homogeneous properties of the scaffold and the depth-dependent properties of the articular cartilage. Finally, we suggest that mechanical conditions at the interface can be more readily modulated by increasing pre-incubation time before the load is applied, as opposed to varying the number of loading cycles.

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.

INTRODUCTION: Models aimed at characterizing the response of chondrocytes to mechanical forces are designed as displacement-controlled systems th |