Nano- and micro-particles are being increasingly used to tune interfacial frictional properties in diverse applications, from friction modifiers in industrial lubrication to enhanced biological fluids in human osteoarthritic joints. Here, we assessed the tribological properties of a simulated synovial fluid enriched with non-spherical, poly lactic-co-glycolic acid (PLGA) microparticles (µPL) that have been previously demonstrated for the pharmacological management of osteoarthritis (OA). Three different µPL configurations were fabricated presenting a 20 µm × 20 µm square base and a thickness of 5 µm (thin, 5H µPL), 10 µm (10H µPL), and 20 µm (cubical, 20H µPL). After extensive morphological and physicochemical characterizations, the apparent Young’s modulus of the µPL was quantified under compressive loading returning an average value of ∼ 6 kPa, independently of the particle morphology. Then, using a linear two-axis tribometer, the static (µ_s) and dynamic (µ_d) friction coefficients of the µPL-enriched simulated synovial fluid were determined in terms of particle configuration and concentration, varying from 0 (fluid only) to 6µ10⁵ µPL/mL. The particle morphology had a modest influence on friction, possibly because the µPL were fully squeezed between two mating surfaces by a 5.8 N normal load realizing boundary-like lubrication conditions. Differently, friction was observed to depend on the dimensionless parameter Ω, defined as the ratio between the total volume of the µPL enriching the simulated synovial fluid and the volume of the fluid itself. Both coefficients of friction were documented to grow with Ω reaching a plateau of µ_s ∼ 0.4 and µ_d ∼ 0.15, already at Ω ∼ 2×10⁻³. Future investigations will have to systematically analyze the effect of sliding velocity, normal load, and rigidity of the mating surfaces to elucidate in full the tribological behavior of µPL in the context of osteoarthritis.

纳米和微米颗粒越来越多地用于调节各种应用中的界面摩擦特性，从工业润滑中的摩擦调节剂到人类骨关节炎关节中的增强生物流体。在这里，我们评估了富含非球形聚乳酸-乙醇酸 (PLGA) 微粒 (μPL) 的模拟滑液的摩擦学特性，该微粒先前已被证明可用于骨关节炎 (OA) 的药理学治疗。制造了三种不同的 µPL 配置，呈现 20 µm × 20 µm 方形底座，厚度为 5 µm（薄，5H µPL）、10 µm（10H µPL）和 20 µm（立方体，20H µPL）。经过广泛的形态和物理化学表征后，在压缩负载下对 µPL 的表观杨氏模量进行了量化，返回平均值约为 6 kPa，与颗粒形态无关。然后，使用线性两轴摩擦计，根据颗粒结构和浓度确定富含 µPL 的模拟滑液的静态 ( μs ₎和动态 ( μd ₎摩擦系数，从 0（仅流体）到6μ10 ^5μPL /mL。颗粒形态对摩擦力影响不大，可能是因为 µPL 被 5.8 N 法向载荷完全挤压在两个配合表面之间，从而实现了类似边界的润滑条件。不同的是，观察到的摩擦力取决于无量纲参数Ω，定义为富含模拟滑液的μPL总体积与液体本身体积之间的比率。据记录，这两种摩擦系数都随着Ω 的增加而增长，达到µ _s ∼ 0.4 和µ _d ∼ 0.15的平台，已经达到Ω ∼ 2×10 ^-3。未来的研究必须系统地分析滑动速度、正常载荷和配合表面刚度的影响，以全面阐明 µPL 在骨关节炎中的摩擦学行为。