Bioinspired lubrication: from fundamentals to joint protection

Introduction: We describe the design of bioinspired lubricating and wear protecting fluids based on synergistic mixtures of bottle brushes (BB) and linear polymers solutions. To illustrate this concept we used hyaluronic acid (HA) – a naturally occurring linear polyelectrolyte, and water soluble synthetic BB polymers. Individually, these two polymers exhibit poor wear protecting capabilities compared to saline solutions. Mixture of the two polymers in pure water or in saline allows to drastically increase wear protection of surfaces under a wide range of shearing conditions. We demonstrate that this synergy between the BB and HA polymer emerges from a strong, yet transient, cohesion between the two components forming the boundary film due to entanglements between both polymers. We show that this concept can be applied to other types of linear polymers and surfaces and is independent of the chemical and mechanical properties of the surfaces. Most importantly, we show that these fluids can be injected into articular joints to improve chondroprotection and wear protection. Methods: We used the surface forces apparatus (SFA) to elucidate the molecular conformation and the interaction forces of the BB polymers and their mixtures with hyaluronic acid. These experiments were complemented with larger scale tribological measurements on a lab-made tribometer. In vivo testing of the fluids was performed on rats with surgically induced osteoarthritis (anterior cruciate ligament transection). Results: Force measurements show that the BB polymers conformation can be tuned by the architecture of the polymer. Triblocks polymers tend to form loop on surfaces while monoblock and diblocks adopt a brush like conformation. When mixed with HA, nanotribology and macro tribology results show a strong improvement of wear protection compared to components alone. In vivo testing show that these polymer mixtures have the remarkable capacity to stop cartilage degradation and to preserve joints mechanical properties.Introduction:We describe the design of bioinspired lubricating and wear protecting fluids based on synergistic mixtures of bottle brushes (BB) and linear polymers solutions. To illustrate this concept we used hyaluronic acid (HA) – a naturally occurring linear polyelectrolyte, and water soluble synthetic BBpolymers. Individually, these two polymers exhibit poor wear protecting capabilities compared to saline solutions. Mixture of the two polymers in pure water or in saline allows to drastically increase wear protection of surfaces under a wide range of shearing conditions. We demonstrate that this synergy between the BB and HA polymer emerges from a strong, yet transient, cohesion between the two components forming the boundary film due to entanglements between both polymers. We show that this concept can be applied to other types of linear polymers and surfaces and is independent of the chemical and mechanical properties of the surfaces. Most importantly, we show that these fluids can beinjected into articular joints to improve chondroprotection and wear protection. Methods: We used the surface forces apparatus (SFA) to elucidate the molecular conformation and the interaction forces of the BB polymers andtheir mixtures with hyaluronic acid. These experiments were complemented with larger scale tribological measurements on a lab-made tribometer. In vivo testing of the fluids was performed on rats with surgically induced osteoarthritis (anterior cruciate ligament transection). Results: Force measurements show that the BB polymers conformation can be tuned by the architecture of the polymer. Triblocks polymers tend to form loop on surfaces while monoblock and diblocks adopt a brush like conformation. When mixed with HA, nanotribology and macro tribology results show a strong improvement of wear protection compared to components alone. In vivo testing show that these polymer mixtures have the remarkable capacity to stop cartilage degradation and to preserve joints mechanical properties.