## 4 Discussion
Although free-standing flat films of CaCO\({}_{3}\) had been deposited on the anionic head groups of fatty acid monolayers in our previous studies [41; 49], here we show that analogous surfaces containing the charged head groups of stearic acid and DSPC phospholipid are effective at templating the deposition of PILP precursors onto templating particles, even when there is significant curvature, which one might anticipate could create a large amount of strain on the mineral precursor, and particularly in the case of the tiny liposomes. The particles consist of a \"hard\" mineral shell and \"soft\" fluidic oil core, in which a chemical of interest can be stored/protected at moderately high pH, in organic solvent, or dried down as a powder, until pH or mechanically triggered release. Although not examined here, one should be able to achieve the high encapsulation efficiencies analogous to what can be obtained by the core droplet emulsion and liposome systems to begin with, but with much easier separation and storage of the microcapsules once coated with a robust calcium carbonate shell. Storage and transport of a powder provides a major advantage over transport of the large amount of volume required in emulsions and liposome suspensions. The continuous coating allows even small molecular weight active agents to be stored in the interior of the core-shell without fear of early diffusion-release, and without having to design a new shell with different pore sizes. The non-faceted morphology of the mineral shells allows for easier deposition of further surface materials, such as polymeric coatings to further tailor core-shell functionality. The generated microcapsules retain the active agent even under the stress of centrifugation and suspension in anhydrous ethanol, suggesting they might readily allow for various chemical methods of surface modification. In addition, the liposome-derived microcapsules reported in this study demonstrate versatility in entrapment of either or both hydrophilic and hydrophobic compounds of interest. Due to the versatility of the PILP-derived core-shell microcapsules described herein, we envision a wide-range of potential pharmaceutical, environmental, and industrial applications are possible. We anticipate that the release of the entrapped compound would be a relatively rapid or even a burst-type of release in the physiological environment. This might be useful for inhalant systems with dry powders that rapidly release the pharmaceutic agent into the moist environment of nasal or lung tissues [50] or for intragastric drug release systems that utilize the dissolution product of calcium carbonate to trigger pharmaceutical release and enhance pharmacokinetics [51]. Although not examined here, the benign processing conditions might also enable encapsulation of sensitive biological agents such as proteins, enzymes, growth factors, DNA, etc. Other applications might include environmental release of pesticide or fertilizer, or body care lotions that incorporate exfoliating particles, etc. These microcapsules may also be suitable for incorporation into composite materials where future rupture can release catalysts or other agents that lead to strengthening of the composite [52], and/or trigger self-healing in the material [53; 54]. The core-shell particles shown in this study demonstrate that the PILP process can be used as a method coating emulsions and liposomes to enhance the properties of many different nano/microparticle systems. Stearic acid/n-dodecane (O/W) emulsion and 1,2-distearoyl-sn-glycero-3-phosphotidyl choline (DSPC)/cholesterol liposomes were chosen for use in this study because they are generally available and similar to many potential nano/microcapsule substrates in use. Due to the coating nature of this method, many of the resultant core-shell particle properties are largely substrate- and environment-dependent.