There is provided a composition comprising a plurality of particles of a weight-, number-, or volume-, based mean diameter that is between amount 10 nm and about 700 µm, which particles are made up of: (a) a solid core, which solid core preferably comprises a biologically active agent; (b) one or more discrete layers surrounding said core, said one or more layer s each comprising at least one separate coating material; and (c) a final overcoating layer of a coating material, which overcoating layer surrounds, encloses and/or encapsulates said core and said previously-applied layers of coating material, and which final layer is of a thickness that is less than said previously-applied layers. Said layers (b) and (c) are preferably applied by way of a gas phase coating technique, such as atomic layer deposition. When the cores comprise biologically active agent, the compositions may provide for the delayed or sustained release of said active agent without a burst effect.