RESUMEN
OBJECTIVE: Deleterious impact loading to cartilage initiates post-traumatic osteoarthritis (OA). While cytokine and enzyme levels regulate disease progression, specific mechanical cues that elucidate cellular OA origins merit further investigation. We defined the dominant pericellular and cellular strain/stress transfer mechanisms following bulk-tissue injury associated with cell death. METHOD: Using an in vitro model, we investigated rate-dependent loading and spatial localization of cell viability in acute indentation and time-course studies. Atomic force microscopy (AFM) and magnetic resonance imaging (MRI) confirmed depth-wise changes in cartilage micro-/macro-mechanics and structure post-indentation. To understand the transfer of loading to cartilage domains, we computationally modeled full-field strain and stress measures in interstitial matrix, pericellular and cellular regions. RESULTS: Chondrocyte viability decreased following rapid impact (80%/s) vs slow loading (0.1%/s) or unloaded controls. Viability was lost immediately during impact within regions near the indenter-tissue contact but did not change over 7 days of tissue culture. AFM studies revealed a loss of stiffness following 80%/s loading, and MRI studies confirmed an increased tensile and shear strain, but not relaxometry. Image-based patterns of chondrocyte viability closely matched computational estimates of amplified maximum principal and shear strain in interstitial matrix, pericellular and cellular regions. CONCLUSION: Rapid indentation worsens chondrocyte death and degrades cartilage matrix stiffness in indentation regions. Cell death at high strain rates may be driven by elevated tensile strains, but not matrix stress. Strain amplification beyond critical thresholds in the pericellular matrix and cells may define a point of origin for early damage in post-traumatic OA.
Asunto(s)
Cartílago Articular/lesiones , Supervivencia Celular , Condrocitos/fisiología , Matriz Extracelular/fisiología , Estrés Mecánico , Soporte de Peso/fisiología , Animales , Cartílago Articular/citología , Cartílago Articular/diagnóstico por imagen , Cartílago Articular/patología , Bovinos , Condrocitos/patología , Matriz Extracelular/patología , Análisis de Elementos Finitos , Técnicas In Vitro , Traumatismos de la Rodilla/complicaciones , Articulación de la Rodilla/citología , Articulación de la Rodilla/diagnóstico por imagen , Articulación de la Rodilla/patología , Imagen por Resonancia Magnética , Microscopía de Fuerza Atómica , Microscopía Confocal , Osteoartritis de la Rodilla/etiologíaRESUMEN
This report describes the development of lab-on-a-chip device designed to measure changes in cellular ion gradients that are induced by changes in gravitational (g) forces. The bioCD presented here detects differential calcium ion concentrations outside of individual cells. The device includes sufficient replicates for statistical analysis of the gradients around multiple single cells and around control wells that are empty or include dead cells. In the data presented, the degree of the cellular response correlates with the magnitude of the g-force applied via rotation of the bioCD. The experiments recorded the longest continuous observation of a cellular response to hypergravity made to date, and they demonstrate the potential utility of this device for assaying the threshold of cells' g-force responses in spaceflight conditions.