What Are Smart Polymers?
How Stimulus-Responsive Polymers Are Used in Biotechnology
Smart polymers, or stimulus-responsive polymers, are materials composed of polymers that respond in a dramatic way to very slight changes in their environment. Scientists studying natural polymers have learned how they behave in biological systems and are now using that information to develop similar man-made polymeric substances with specific properties. These synthetic polymers are potentially very useful for a variety of applications including some related to biotechnology and biomedicine.
How Smart Polymers Are Used
Smart polymers are becoming increasingly more prevalent as scientists learn about the chemistry and triggers that induce conformational changes in polymer structures and devise ways to take advantage of and control them. New polymeric materials are being chemically formulated that sense specific environmental changes in biological systems, and adjust in a predictable manner, making them useful tools for drug delivery or other metabolic control mechanisms.
In this relatively new area of biotechnology, the potential biomedical applications and environmental uses for smart polymers appear to be limitless. Currently, the most prevalent use of smart polymers in biomedicine is for specifically targeted drug delivery.
Classification and Chemistry of Smart Polymers
Since the advent of timed-release pharmaceuticals, scientists have been faced with the problem of finding ways to deliver drugs to a particular site in the body without having them first degrade in the highly acidic stomach environment. Prevention of adverse effects to healthy bone and tissue is also an important consideration. Researchers have devised ways to use smart polymers to control the release of drugs until the delivery system has reached the desired target. This release is controlled by either a chemical or physiological trigger.
Linear and matrix smart polymers exist with a variety of properties depending on reactive functional groups and side chains. These groups might be responsive to pH, temperature, ionic strength, electric or magnetic fields, and light. Some polymers are reversibly cross-linked by noncovalent bonds that can break and reform depending on external conditions. Nanotechnology has been fundamental in the development of certain nanoparticle polymers such as dendrimers and fullerenes, that have been applied for drug delivery. Traditional drug encapsulation has been done using lactic acid polymers. More recent developments have seen the formation of lattice-like matrices that hold the drug of interest integrated or entrapped between the polymer strands.
Smart polymer matrices release drugs by a chemical or physiological structure-altering reaction, often a hydrolysis reaction resulting in cleavage of bonds and release of drug as the matrix breaks down into biodegradable components. The use of natural polymers has given way to artificially synthesized polymers such as polyanhydrides, polyesters, polyacrylic acids, poly(methyl methacrylates), and polyurethanes. Hydrophilic, amorphous, low-molecular-weight polymers containing heteroatoms (i.e., atoms other than carbon) have been found to degrade fastest. Scientists control the rate of drug delivery by varying these properties thus adjusting the rate of degradation.