The study of biobinder droplet impacting on HA particle surface depending on nondimensional scale similarity theory

摘要

Instruction: The hydroxyapatite bone scaffolds fabricated with three dimensional printing techniques are considered to be applied widely in artificial bones. In order to promote the printing bone scaffold model precision .quality and mechanical properties, the binder droplet spreading performance on the surface of hydroxyapatite (HA) micro spheres should be studied. The deposition of a liquid droplet impacting on a solid surface is a topic of considerable importance in a variety of applications, and it has spawned a substantial body of theoretical, experimental, and simulation studies in recent years. However, most previous studies have focused on the impact of a droplet on a flat surface, but few studies have focused on the impact on a spherical surface. In this study, we performed a two-dimensional simulation of the spreading of a single droplet impacting on a spherical surface, and also studied the effects of impact velocity, viscosity, surface tension, and surface size on the deposition of the droplet. At last, we compared the simulation and the real experimental results to improve our inkjet spraying methodology and obtain some conclusions for controlling biobinder droplet pattern in fabricating bone scaffold process. Materials and Methods: In HA bone scaffold 3D printing, the piezoelectric nozzle diameter is about 10μm, and it can spray droplets 20μm in diameter. The HA powder particles average size is about 60μm in diameter. But for the normal experimental assessment instruments, it is difficult to watch the tiny liquid droplet flying on 1 mm distance at above 1.0 m/s velocity. On the basis of nondimensional scale similarity theory, we have adopted droplet spray system to observe a single biobinder droplet of 200μm or larger in diameter impacting on a spherical surface of HA microsphere 600μm in diameter to study the binder droplet spreading performance. The diameter of bioadhesive droplet was adopted as 200 μm in the droplet impact on the microspherial surface of HA particles which was also set 600 μm in the numerical simulation process. The process of piezoelectric droplet injection is very complex. According to Fig. 2 A, the droplet spray system consisted of a pulse function generator, a homemade piezoelectric nozzle. The impact events were observed with a high-speed video camera. Results and Discussion: (1) According to the calculation, the impact velocity, viscosity, surface tension, and surface size of the HA microsphere shows effect on the maximum spread diameter, the minimum spread thickness, the final spread diameter and the final spread thickness respectively. (2) When the impact velocity is too high, or the curvature of microspheres or surface tension of biobinder is too small, the bioadhesive droplet will break up into smaller droplets. The air at the liquid-solid interface can be entrapped at the moment of impact when the viscosity coefficient is too large. Conclusions: The simulation results are found to be consistent with the experiment data and can be used as a basis of droplet impacting on a spherical surface. The rapid prototyping fabrication parameters can be deduced from this computer simulation process.