Smart Gels

 

What is a Smart Gel and how do they work?

 

            Smart gels contain fluids (usually water) in a matrix of large, complex polymers.  These polymers are special in that they respond to stimuli in an advanced way.  Types of stimuli that affect smart gels are physical and chemical factors.  Temperature, light, electric forces, magnetic forces, and mechanical forces (shaking) are types of physical interactions on the gel that will precipitate a reaction.  Chemical stimuli are usually pH changes or solvent exchanges (Hirai).  The reaction of the smart gel is always an expansion or contraction within milliseconds upon stimulation.  Essentially, when a gel swells, it absorbs additional fluid into it.  Likewise, when it deflates, it expels this fluid out of its membrane. The expansion and contraction are usually caused by a change in the polymer; the stimulus alters the polymer by making it more or less hydrophilic.  For example a significant pH decrease will neutralize ions in the gel, precipitating the polymers to be less hydrophilic and causing the gel to contract (University of Sheffield).     

            While smart gels do not depend on nanotechnology, in many cases their effects are greatly aided by using nanoparticles.  While microparticles usually allow the gel to function properly, smaller particles at the nanoscale increase intended effects dramatically.  A great example of this is in the use of ferromagnetic particles.  Ferromagnets are tiny particles that act as little bar magnets.  In this example, scientists apply a magnetic field on a smart gel to induce the ferromagnets to move.  This movement raises the temperature of the gel and consequently causes the gel to expand.  While microparticles of iron still allow the gel to expand, nanoparticles make the gel more responsive to the magnetic field (Dagani). 

 

How can smart gels be applied?

           

Applications of smart gels permeate into many various fields including both medical and industrial.  While smart gels are in their infancy in the medical field, there is great promise for the technology.  The two main applications for smart gels are in artificial muscle fabrication and drug release.  In drug release, a smart gel containing the desired water soluble drug is injected into the patient.  After receiving a certain stimulus (usually temperature or pH), a hydrogel (a type of smart gel) will expand by allowing the water and salt in the blood to enter the gel.  Consequently, the drug will be released from the gel in the desired environment.  This concept can be used to release drugs to attack tumors or aid specific areas of the body (i.e. eye drops for the eye).  This concept is beneficial because the area, duration, and speed of the release can be better controlled with a smart gel.  Eventually hydrogels could mimic the behavior of the pancreas by releasing chemicals to achieve the optimal glucose concentration.  This could tremendously help the medical industry by aiding patients with defective pancreases (i.e. diabetes).  Nanoparticles well help this medical technology by increasing the effectiveness of the gel by increase the surface area of its constituents (Dagani).

Development in smart gels’ electrical properties could result in the future production of artificial muscles.  When an electric field is applied on certain types of gels, there is an asymmetric charge distribution within the gel.  This asymmetry yields different rates of expansion throughout the gel.  In fact, in some cases, one end might contract while the other expands.  Asymmetry can also be created by producing heterogeneous gels with different rates of expansion throughout the gel.  As a result of the electric field and asymmetry, the gel bends.  This bending is significant because it mimics the role of muscles in the body which respond to electrical signals sent from the brain by creating mechanical energy. With more development, these gels could become replacement muscles for patients.  While this technology is only in its infancy, the manifestation would aid many who are in need of artificial muscles (Dagani and Hirai).

            One example of how smart gels could help industry is in the utilization of shake gels.  Shake gels respond to forces applied on them by becoming firm.  Shake gels could tremendously aid shock absorbers.  When driving over a pothole, the shake gel would firm up based on the size of hole and the weight of the car.  This adjustment would optimize the absorber’s response to the shock (“Recipe…”) .  

 

 

Note: Citations can be found indexed in the links page.