A new class of secondary emulsifying agents for use in inverted mud and other inverted system is disclosed and method for making and using same. The silica powder may be produced by the surface treatment of a silica powder with an epoxy compound and an amine compound successively or with both these compound simultaneously. The lens holder is positioned on the substrate and accommodates the sensor. The structure may also be easily separated from the bag and used for other purposes. The extracellular vesicles are used to treat or regenerate damages or injured tissue in a subject.