Elucidating the biomechanical factors that influence fluid loss and recovery in articular cartilage
Date
2023
Authors
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Publisher
University of Delaware
Abstract
There has been steady rise in osteoarthritis (OA) incidence rates since the Industrial Revolution. This begs the question, “Why?” With increases in life expectancy, a leading hypothesis is that we are incurring ‘wear and tear’ on our joints for much longer. However, the industrial revolution has also been marked with increasing sedentary behavior. Emerging epidemiological data demonstrates that outcomes of a sedentary lifestyle— which exposes our joints to minimal ‘wear and tear’—implicate cartilage deterioration and OA development, contradicting the ‘wear and tear’ paradigm. ☐ From a mechanical perspective, sedentary behavior insufficiently loads cartilage, leading to excessive, chronic tissue strains through fluid loss—this fluid loss is associated with mechanical and biological dysfunction that can ultimately lead to joint disease. Fortunately, movement is the engine that reverses fluid loss to establish joint function. How much activity is needed, how often, and how those thresholds vary with joint forces depend explicitly on competitive rates of fluid loss and recovery, but these topics remain largely unstudied. Researchers and clinicians must understand the processes contributing to fluid loss/recovery rates to anticipate the influence of an active lifestyle on cartilage function and joint health. ☐ With a well-controlled experimental test-bed, I address the fluid loss/recovery knowledge gap in this dissertation. I leveraged several necessary experimental and theoretical tools pioneered by former researchers to quantify (1) in-situ contact mechanics and fluid loss rates and (2) relative rates of recovery. Because fluid loss depends on the magnitude of contact stress, my 1st aim investigates the predictability of cartilage contact stress and addresses the potential consequences of assumed cartilage material properties. In Aim 2, I develop an experimentally derived fluid loss model to determine how quickly cartilage loses fluid from a static load (i.e. a sedentary condition). Although cartilage loses fluid from a static load, engaging in activity or unloading the joint can rehydrate the tissue. Therefore, in Aim 3, I quantify the rates of rehydration from both activity and joint unloading to determine what behavior may better restore hydration and function. After a restoration of fluid, cartilage must sustain low fluid loss during activity to maintain its function. In Aim 4, I examine how biomechanical factors, like speeds and loads, affect magnitude of fluid loss during activity. Overall, this dissertation demonstrates that 1) material properties of cartilage must be well-defined to predict contact stresses, 2) cartilage loses fluid much faster than previous models had predicted, 3) activity rehydrates cartilage tissue ~10X faster than a strict unloading of the joint, and 4) cartilage tissue can robustly maintain its function via fluid pressurization, despite increases in contact loads. By connecting physiological biomechanics with fluid loss/recovery, outcomes from this dissertation initiate the foundational bridge between activity and the ability to predict long-term joint function.
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Keywords
Cartilage, Hydration, Interfacial permeability, Biomechanical factors, Osteoarthritis, Fluid loss, Recovery