The inner layer of the cell walls of spores and pollen, called the intine, consists mainly of cellulose and pectin, which degrades during fossilization. Their shapes and sizes are genus specific and reproducible, and range from spherical to oblate and prolate. Plant, fungal and bacterial spores and plant pollen provide a unique and extremely large collection of biological particles and microcapsules that range in size from a few microns up to millimetres depending on genus.
Comparatively, nature provides its own variety of microcapsules and particles based on cell walls and membranes, but unlike their synthetic equivalents, they possess discrete size, shape, morphology and uniform (mono) dispersity within each species. Furthermore, it has recently been noted that certain polymeric microcapsules are detrimental to the environment. Their sizes and stabilities vary depending on material selection, production, and the environment of their use. The shells of synthetic particles and microcapsules are usually composed of lipids or polymers, or materials such as alginates, gelatin and gum Arabic. Microcapsules and functional particles have a wide variety of applications, from paints, coatings, E-inks, thermochromics, time-release pharmaceuticals, to visual indicators, etc.
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