Pervasive architecture and functional patterns found in nature
The Greek terms dendri-, dendrites, dendritic are root word descriptors for branching or treelike structures. These terms describe some of the most pervasive architectural patterns observed on our planet . Before the early 1980s [2–4] all dendritic architectures and networks were known only as naturally occurring structures/entities found either in the abiotic world (e.g. snow crystals, lightning patterns, erosion/tributary river network fractals) or in the biological realm. In biological systems, these dendritic patterns are found at length scales ranging from meters (trees), millimeters/centimeters (vascular/circulatory systems in plants and animals, Golgi domains (organelles), fungi), microns (neurons) to nanometers (IgM antibodies, amylopectins and proteoglycans) as illustrated in Figure 1.1. Certain randomly branched, dendritic architectures were hypothesized by Nobel Laureate P. Flory as early as the 1940s to describe theoretical polymer intermediates in crosslinking events . However, it was not until the late 1970s that the first examples of such dendritic architecture were intentionally synthesized and rigorously characterized in a laboratory. These first dendritic structures were synthesized both as core-shell-type, small molecules, and macromolecules. The widely recognized terms – dendrimers/dendrons (i.e. dendri [branched] and mer [part of] – were first coined and introduced by Tomalia in 1983  to describe these compositionally broad and diverse categories of precisely defined core-shell, dendritic structures. A typical dendrimer family derived from a core and surrounded by radial shells (i.e. generations) of covalently connected branched monomers is illustrated in Figure 1.1.
It was soon realized that these newly discovered dendritic structures could be synthesized with a very wide range of diverse elemental compositions (i.e. both organic and inorganic). Furthermore, it was found that they could be obtained with unprecedented mono-dispersity and extraordinary structure control as a function of (a) size, (b) shape, (c) surface chemistry, (d) flexibility/rigidity, (e) architecture, and (f) composition. Unlike traditional synthetic polymers, these synthetic macromolecules were routinely synthesized with structure control normally associated only with highly precise biological polymers such as proteins, DNA, and RNA.