**3. Dendrimers**

Dendrimer is a monodisperse macromolecule with perfectly branched regular structure and having at least one branched junction at each repeat unit 3. These dendrimers are used in gene delivery. The dendrimer/DNA complexes are encapsulated in a water-soluble polymer, and then deposited on or sandwiched in functional polymer films with a fast degradation by dehydration to mediate gene transfection.

Biodegradable dendrimers are commonly prepared by inclusion of ester groups in the polymer backbone, which will be chemically hydrolysed and/or enzymatically cleaved by esterases in physiological solutions. These dendrimers are large molecular weights which accumulate and retain in higher amounts in the tumour tissues. Dendrimer fragments are eliminated safely through urine.

Dendrimers are prepared through either a divergent method or a convergent method.

In the **divergent methods**, as given in **Figure 3**, dendrimer grows from a multifunctional core molecule to outwards. The first-generation dendrimers are derived from the core molecule that reacts with monomer molecules containing one reactive and two dormant groups. This periphery molecule is then activated to react with more monomers. This step is subsequently repetitive to produce layer-by-layer dendrimers for several generations.

In the` convergent approach, stepwise dendrimer is constructed, starting from the end groups and progressing inwards. The growing branched polymeric arms are called dendrons, which can attach to a multifunctional core molecule (**Figure 4**).

**Figure 3.** Formation of dendrimer by divergent methods.

**Figure 4.** Formation of dendrimer by convergent method.

Whereas the structure Y in dendrimer is chemically active focal point and Z is the functional chemical group of another monomer.

## **3.1. Other types of dendrimers**

polymer binds to plasmid DNA, sodium ions are displaced and the electronegative charge is partially satisfied. DNA condensates are normally prepared at near-neutral pH in low ionic

Dendrimer is a monodisperse macromolecule with perfectly branched regular structure and having at least one branched junction at each repeat unit 3. These dendrimers are used in gene delivery. The dendrimer/DNA complexes are encapsulated in a water-soluble polymer, and then deposited on or sandwiched in functional polymer films with a fast degradation by

Biodegradable dendrimers are commonly prepared by inclusion of ester groups in the polymer backbone, which will be chemically hydrolysed and/or enzymatically cleaved by esterases in physiological solutions. These dendrimers are large molecular weights which accumulate and retain in higher amounts in the tumour tissues. Dendrimer fragments are

In the **divergent methods**, as given in **Figure 3**, dendrimer grows from a multifunctional core molecule to outwards. The first-generation dendrimers are derived from the core molecule that reacts with monomer molecules containing one reactive and two dormant groups. This periphery molecule is then activated to react with more monomers. This step is subsequently

In the` convergent approach, stepwise dendrimer is constructed, starting from the end groups and progressing inwards. The growing branched polymeric arms are called dendrons, which

Dendrimers are prepared through either a divergent method or a convergent method.

repetitive to produce layer-by-layer dendrimers for several generations.

can attach to a multifunctional core molecule (**Figure 4**).

**Figure 3.** Formation of dendrimer by divergent methods.

strength buffer [23, 24].

140 Advanced Technology for Delivering Therapeutics

dehydration to mediate gene transfection.

eliminated safely through urine.

**3. Dendrimers**

## *3.1.1. Amino acid-based dendrimers*

Amino acid-based dendrimers were developed to capitalize on the unique properties of the amino acid-building blocks, including chirality, hydrophilicity/hydrophobicity, biorecognition and optical properties. Optically active protein-mimetic dendrimers have been synthesized using various amino acids, such as tryptophan, phenylalanine, glutamic acid, aspartic acid, leucine, valine, glycine and alanine.

Amino acid-based dendrimers can be synthesized by


#### *3.1.2. Glycodendrimers*

Carbohydrate interactions with different receptors displayed at the cell surface control a number of normal (e.g., lymphocyte activation and cell-cell adhesion) and abnormal (e.g., cellpathogen adhesion and cancer cell metastasis) biological processes. Glycodendrimers have been synthesized by coupling isothiocyanate-functionalized glycosyl and mannopyranoside ligands as well as an *N*-hydroxysuccinimide (NHS)-activated galactopyranosyl derivative to amine-terminated dendrimers.

#### *3.1.3. Hydrophobic dendrimers*

Dendrimers with hydrophobic interiors and a hydrophilic surface are called hydrophobic dendrimers. Hydrophobic dendrimer gives better encapsulation and efficient solubilization of hydrophobic drug molecules. Specifically, dendrimers with hydrophobic cores were proved to effectively retain hydrophobic drug molecules in the voids of their branching architecture, mimicking amphiphilic polymer micelles.

## *3.1.4. Asymmetric dendrimers*

Asymmetric dendrimers are synthesized by coupling dendrons of different generations to a linear core, which yields a branched dendrimer with a nonuniform orthogonal architecture.

There are two different types of dendrimeric copolymers:

