Holographic Spatiotemporal Inspection Allows Comprehensive Characterization of Functionalized Membrane

Fabrication and characterization of Polylactic-co-glycolic acid (PLGA) membrane is a novel issue. Thanks to PLGA's non-biological toxicity and unique chemical properties, it is considered to be one of the important materials in future space travel. However, what must be faced is that the preparation process of modern functionalized materials lacks effective monitoring methods. With the complexity of membrane functional expression and the refinement of material processes, closed-loop thin film processing technology is becoming the currently focus of research. Digital holography (DH) as one of the optimal liquid film characterization methods has gradually been recognized in recent years. Since DH has excellent temporal and spatial resolution at the micron scale, it is suitable for thin film imaging. As a specialized holographic imaging method, space-time digital holography (STDH) has been used in solid PLGA membrane characterization. Here we propose an improved STDH method, which can be used for ultra-long-range PLGA membrane imaging, which fill the gap between PLGA fabrication and quantitative monitoring. A thin membrane reconstruction method based on multi-scanning lines synthesis and multi-level propagation is applied and effectively suppress the noise during long-distance scanning. Based on this improvement, a series of experiments on PLGA films are implemented. The thickness distribution of the PLGA membrane was examined under different magnifications. As the results, we first confirmed the effect of nanoparticle concentration on PLGA characterization during the functionalization process; then, by performing full-field STDH shearing measurements, we verified the differences produced by different doses of PLGA solutions during the film formation process and proved that PLGA membrane is a suitable carrier for the functionalization process; finally, functionalized PLGA membranes were measured by using improved STDH. PLGA films containing different concentrations of protein were prepared; and then, long-range STDH recording and reconstruction were performed. For the functionalized PLGA films containing 1 µg/L and 100 pg/L protein, we accurately provide information on the number and equivalent size of particle clusters. The results show proposed STDH method can effectively reveal the particle clusters and full-field thickness distribution of membrane at the same time. It also allows further statistical analysis of particle cluster distribution to determine its impact on film functionality.