Numerical Study of Microstructures and Roughness Design Effects on Surface Hydrophilicity through the Lattice Boltzmann Method

Hydrophilicity is one of the most vital characteristics of titanium (Ti) implants. Surface structure design is a powerful and efficient strategy for improving the intrinsic hydrophilic ability of Ti implants. Existing research has focused on experimental exploration, and hence, a reliable numerical model is needed for surface structure design and corresponding hydrophilicity prediction. To address this challenge, we proposed a numerical model to analyze the droplet dynamics on Ti surfaces with specific microstructures designed through the lattice Boltzmann method (LBM). In this work, a Shan-Chen (SC) model was applied in the simulations. We simulated droplets spreading on smooth and micropillar surfaces with various wettability and provided a comprehensive discussion of the edge locations, contact line, droplet height, contact area, surface free energy, and forces to reveal more details and mechanisms. To better tune and control the surface hydrophilicity, we investigated the effects of micropillar geometric sizes (pillar width a, height h, and pitch b) on hydrophilicity via single factor analysis and the response surface method (RSM). The results show that the hydrophilicity initially increases and then decreases with an increasing a, increases with an increasing h, and decreases with an increasing d. In addition, the interaction effects of a-d and h-d are significant. The optimization validation of the RSM also demonstrates the accuracy of our lattice Boltzmann (LB) model with an error of 0.687%. Here, we defined a dimensionless parameter ξ to integrate the geometric parameters and denote the surface roughness. The hydrophilicity of Ti surfaces improves with an increasing surface roughness. In addition, the effect of the microstructure geometry shape was investigated under the same value of surface roughness. Surfaces with micropillars show the best hydrophilicity. Moreover, this study is expected to provide an accurate and reliable LB model for predicting and enhancing the intrinsic hydrophilicity of Ti surfaces via specific microstructure and roughness designs.