Dendrimers created individually and then linked together inwards

Dendrimers

Dendrimers are highly branched multivalent nanostructure
usually
about 1–10 nm in size. They have unique surface functionality, versatility and
emerged as an important biomedical drug delivery molecule in past decade. It
drives its name from Greek works ‘Dendron’ (tree) and meros (part).
It is made up
of three components: a) central hydrophobic core; b) an interior branched dendritic structure (generations) radically attached to central core; c) hydrophilic exterior surface with
functional groups (Liu M,
Fréchet JMJ. Designing dendrimers for drug delivery. Pharm Sci Technolo Today. 1999;2(10):393–401).  There
are two methods for dendrimer synthesis: a) divergent method where dendron
growth starts from the core site and it grows towards outside diverging into
space; b) convergent methods where surface units are created individually and
then linked together inwards (Fig.)Dendrimers have core-shell nanostructures architect and synthesized in layer-by-layer
fashion around a hydrophobic central core, hence the size of dendrimer and
surface functionality can be controlled precisely. There is linear increase in diameter
and with increased dendrimer generation, it adopts a more bulbous shape with
closed packed surface groups on the periphery and inner voids and channels are
also formed due to this structural arrangement.  Drug molecules can be conjugated either on the
surface or occluded within enclosed cavities of dendrimer. With increase in
generation (layer) physical properties of dendrimer also changes e.g.
viscosity, flexibility, density, size and shape and terminal surface. Viscosity
of dendrimers increases up to 4th generation and declines
thereafter. Hence the properties of dendrimers can be modified according to
their therapeutic application which makes them ideal molecules for drug
delivery.

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They offer many advantages
e.g.  1) encapsulation of drug in void
space decreases the toxicity of the drug and also facilitates controlled drug
delivery 2) Surface available for conjugation (adsorption/attachment) of drug
can be modified with functional groups to augment or resist bio-permeability at
transcellular, epithelial or vascular level; 3) low generation anionic or
neutral polar terminal surface groups are more biocompatible as compared to
high generation neutral nonpolar and cationic surface groups; 4) PEGylated or
small functional group conjugated dendrimer show low or none immunogenicity; 5)
modified surfaces with receptors can be optimized for better biodistribution
and therapeutic dosing; 6) dendrimer can arrange excretion mode from body,
owing to their nanoscale diameter .