Polymers

Ch. 20 p.556

A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds.

The repeating unit of the polymer polypropylene

Natural polymeric materials such natural rubber have been in use for centuries. Biopolymers such as proteins and nucleic acids. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper.

A polymer is a material made up of small repeating structural units combined to give a very large, linear structure. These ultra-large molecules are called macromolecules. The small repeating units found within polymers come from the individual starting molecules, which are called monomers. All commercially important polymers are made up of hundreds or thousands of monomer units joined together to form one large molecule.

In many cases (e.g., polyethylene, polyvinyl chloride, polystyrene) the monomer moleculescontain C=C double bonds that are broken during the polymerization process. These arereferred to as “chain-growth polymers.” In other cases, the monomer molecules may connect while remove a molecule of water (e.g., nylon or polyethylene terephthalate [PET]). These are called “step-growth polymers.” Generic

Whether the control of oral absorption is desired or the delivery of genes to the interior of specific cells is sought ,the drug delivery macromolecule has emerged the most ubiquitous entity. In the current volume, macromolecules and their “younger (and sometimes smaller) cousins,” dendrimers, are presented as components extraordinaire of a variety of drug delivery systems. Scientific reports are peppered with polymer- or dendrimer-containing systems that:

POLYMERS IN DRUG DELIVERY

• Prolong drug action by entrapping the drug within matrices• Shift drug distribution in the direction of tumors• Shunt therapeutic genes or oligonucleotides into cells•Enable drug absorption at optimum gastrointestinal tract absorptive sites• Make the drug available only when there is a defined change in temperature or pH or when activated by an enzyme

In fact, recent reports show that polymers and dendrimers themselves demonstrate intrinsic bioactivity . The drug delivery macromolecule is alive and well, and now has both drug and drug carrier properties.