## 4 Discussion  
The morphologies observed by optical and scanning electron microscopy (SEM) demonstrate that this biomimetic PILP process leads to a smooth, and continuous mineral shell that has formed a thick coating around the liquid-like particles. Importantly, SEM also demonstrates the robustness of core-shell particles when subjected to storage in ethanol, centrifugation, and air-dry storage. This suggests that these core-shell suspensions may be dried down to a powder and retain core-shell integrity. Using polarized light microscopy (PLM), we demonstrate the possibility of controlling the phase of the CaCO\({}_{3}\) shell (i.e., crystalline vs. amorphous). Control over the final phase could be a means to tailor the degradation properties of the microcapsules since amorphous calcium carbonate is metastable and far more soluble than the crystalline form. The core-shells' ability to entrap and protect active agents is demonstrated by the confocal microscopy results shown in Figures 7 and 8. This data allows one to discern between fluorescence originating from within the microcapsule and fluorescence originating from within the CaCO\({}_{3}\) shell or surrounding solution. Nile Red has the useful property of fluorescing only in very hydrophobic environments. Although it is conceivable that a small portion of the model compound could become entrapped within the mineral shell itself, the fluorescence seen in Figure 7 indicates that the interior of the microcapsules indeed contains the stored model agent. The results also show that the generated microcapsules retain the active agent even under the stress of centrifugation and resuspension in anhydrous ethanol. The presence and overlap of fluorescence originating from both oil soluble Nile Red and water-soluble rhodamine 110 (Figure 8C) demonstrates that the liposome-derived core-shell microcapsules can simultaneously entrap very different compounds in a single liposome-based microcapsule. Finally, the possibility of tailoring the degradation properties of these calcium carbonate coated core-shell microcapsules is also demonstrated by the altering of the polymorph of the calcium carbonate coating through adjustments in the magnesium-to-calcium ion ratio. Much of the previous work developing calcium carbonate core-shell technology has focused on strategies to address loss of active agent activity while embedded within calcium carbonate [46], lack of affinity for calcium carbonate precipitation on/around active agent [47], and difficulties controlling the smoothness and morphology of the mineral coatings [48]. The work presented herein presents a means by which these challenges may be bypassed by coating an active agent-containing liquid droplet with a smooth, continuous calcium carbonate coating. A smooth calcium carbonate coating addresses premature agent release because there are no pores in the continuous shell. The mineral coating over an internal liquid reduces activity loss concerns because the active agent is stored in a favorable liquid environment during the benign (room temperature, aqueous based) coating process and during delivery. Figure 9: Particle degradation study. (**A**,**B**) Scanning electron micrographs of emulsion-based core-shell microcapsules after being exposed to a pH 6.8 nanopure water for 2 min, and (**C**,**D**) after exposure to a pH 4.0 HCl solution for 15 s. The rounded and particulate character of the remaining shells may be showing a memory effect of the PILP droplets that had initially coalesced to form the shells.