In Situ Monitoring and Estimation of α-Lactose Monohydrate Crystal Growth in the Microdroplets

In this study, a new microfluidic chip that generates microscale emulsion droplets to confine α-lactose monohydrate crystal (α-LM) solutions in the microdroplets was used to prepare uniform-sized crystals. In situ observations for α-LM growth were performed by using a dual-camera structured light system consisting of two cameras fixed at different angles, achieving a satisfactory three-dimensional (3D) shape reconstruction. After 3D shape reconstruction from image processing, the 3D axial size, crystal surface area, and volume of α-LM in the microdroplets were measured at different time intervals. By fitting these data, we could quantitatively estimate 3D axial growth rates, real-time concentration, and supersaturation (σ) of α-LM. The experimental results show that the growth rate of α-LM from aqueous solution is the fastest in the nucleated 100-150 min after nucleation, and the particle volume of α-LM is about 7.08 × 10^-6 cm³ at σ = 1.5. The fitted polynomial coefficients show that the growth processes of α-LM in the microdroplets are mainly between second-order growth and fourth-order growth. The nucleation and growth mechanisms of α-LM in microdroplets are also clarified. In general, the real-time monitoring of α-LM growth in the microdroplets could avoid interference and damage to the crystals from various impurities and external forces, maintaining the characteristics of the natural growth of the crystals. The results demonstrate the applicability of the proposed method by correctly predicting the experimental morphologies of α-LM grown from the solutions.