Biological response of human articular chondrocytes to shear loading following changes to hydrogel surface properties

摘要

Introduction: Articular cartilage provides a nearly frictionless surface with remarkable capacity to bear and distribute loads in a synovial joint. Alterations to the articular surface may however lead to pathological loads and unbalanced metabolism, ultimately leading to the development of osteoarthritis. Here, we established a hydrogel-based cartilage model with tailorable friction coefficients and evaluated the response of human chondrocytes in these models to dynamic shear loading imparted through custom bioreactor components. Materials and Methods: Bilayered hydrogels, with a thin cell free layer and a 2 mm alginate methacrylate (ALMA) layer containing 10^7 human articular chondrocytes (3 donors, with ethical approval, Passage 2) per mL, were photocrosslinked in the presence of Irgacure 2959. The cell-free layer consisted of either ALMA or PEG diacrylate with either 40 or 80 mol % 4-styrene sulfonic acid (PEG-40S, PEG-80S), resulting in different charge densities, as verified by EPIC-μCT. Friction coefficients were assessed over a range of velocities using custom components on an Instron Microtester. Bulk compressive modulus, swelling ratio, and water content were also measured. Further, microscopic images taken during dynamic shear loading in a custom device were used to generate strain maps using digital image correlation. Constructs were cultured in chondrogenic medium for 21 days free-swelling, followed by 11 days with 0 or 1 mm shear loading (1 h/d, 1 Hz) using custom bioreactor components. Chondrocyte response was assessed by quantitative real-time polymerase chain reaction (qRT-PCR), and matrix accumulation was assessed by immunofluorescence and biochemical assays. Results and Discussion: Constructs were able to effectively model the frictional properties of healthy, damaged, and osteoarthritic cartilage, while other physical characteristics such as compressive moduli, mass swelling ratio, and water content were not affected (Figure 1). Dynamic shear stimulation of constructs with low surface friction significantly promoted chondrogenesis and extracellular matrix synthesis as assessed by gene expression, immunofluorescence, and biochemical analysis (Figure 2). In contrast, shear stimulation of constructs with high surface friction inhibited chondrogenesis to a great extent, but induced transcription of matrix metalloproteinases involved in the degradation of cartilage extracellular matrix in osteoarthritis. Shear strains during dynamic loading were higher in the high-friction constructs than low-friction constructs, which likely explains the differences in chondrocyte response. Conclusion: This study demonstrates that surface friction may act as a key regulator of chondrocyte homeostasis by governing the magnitude of shear deformation during dynamic loading.