Smart Hydrogels
“Smart polymeric gels constitute a new generation of biomaterials that are now being developed. Smart hydrogels respond to diverse stimuli, which can be in the form of pH, temperature, light, pressure, electric field, chemicals, or ionic strength, or a combination thereof. These hydrogels have the ability to respond to minute changes in ambient stimuli and exhibit dramatic property changes. For a biomaterial to be truly smart, the alterations in hydrogel microstructures should be fast and reversible.”
“However, the first challenge with conventional stimuli–responsive hydrogels is the slow response time to stimuli and the hysteresis associated with the on and off states. One way to eliminate this drawback is to have thinner and smaller hydrogels without significantly deteriorating their mechanical properties.”
“The second challenge is to engineer hydrogels that degrade in response to appropriate ambient stimuli in the body. This is in contrast toThis is in contrast to the current technology where hydrogels degrade at a predetermined rate when implanted in the body. For example, proteolytic stimuli, that is, biochemical signals from cells in the vicinity of an implanted biomaterial scaffold can dynamically transduce signaling cues if the scaffold can degrade and remodel its infrastructure in a stimuli responsive manner. Here, the stimulus is the cascade of biochemical signals from the cells in the vicinity of the biomaterial.”
“The third challenge in the fabrication of smart hydrogels is to make hydrogels biocompatible such that the immune system does not set off immunogenic reactions in the body. In fact, ECM–mimetic hydrogels that evade attacks from the immune system can also be viewed upon as smart hydrogels, responding dynamically to signals from the host tissue. The structure of such ECM–mimetics aims to emulate the ECM, albeit in a much simpler form, capturing the essence of the structural and functional parameters of the ECM.”
(Chaterji, Kwon and Park, Prog Polym Sci. 2007 August; 32(8-9): 1083–1122)
Recent Journal Articles
Effects of pH and temperature on assembly of multiresponsive Janus microgels
(729-737) Colloid and Polymer Science 289 #5-6 (2011)
Umeda et al of Shinshu University, Japan, fabricated the multiresponsive Janus microgels by post-polymerization modification at an oil/water interface. To prevent the microgels from wobbling at the interface during the modification process, oil droplets stabilized by microgels were solidified by cooling. By changing temperature and pH, behaviors of Janus microgels could be controlled; they dispersed individually or assembled into specific structures. The stimuli-responsive behaviors of Janus microgels may be used as microactuators or candidates in developing more precisely controlled particle clusters. (RDC 5/17/2011)
Microgel applications and commercial considerations
(625-646) Colloid and Polymer Science 289 #5-6 (2011)
Thorne, Vine and Snowden reviewed applications of microgel particles that are synthesised by polymerisation, are of colloidal size and exhibit conformational changes in response to changes in environmental conditions. A selected range of areas will be covered and the commercial implications of scaling up the production of microgels for such purposes will be discussed. A brief description of the characteristics of microgel particles is followed by discussion of applications such as enhanced oil recovery, biomaterials and catalysis, before issues of commercialising microgel production are considered. The term microgel has been used interchangeably with terms such as nanogel, microsphere and macrogel. (RDC 5/17/2011)
Combination of living anionic polymerization and ATRP via “click” chemistry as a versatile route to multiple responsive triblock terpolymers and corresponding hydrogels
(497-512) Colloid and Polymer Science 289 #5-6 (2011)
Reinicke and Schmalz of the University of Bayreuth, Germany, used a combination of anionic polymerization, atom transfer radical polymerization (ATRP) and “click” chemistry to construct trishydrophilic ABC triblock terpolymers composed of a pH-sensitive A block, a water-soluble B block and two different thermo-sensitive C blocks without any block sequence limitation problems. First, an azido end-functionalized poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO-N3) diblock copolymer was synthesized by anionic polymerization. In a second step, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) were synthesized via ATRP using an alkyne functionalized initiator. The resulting polymers were attached to the P2VP-b-PEO-N3 diblock copolymer using the 1,3-dipolar Huisgen cycloaddition (“click” chemistry. Finally, P2VP-b-PEO-b-POEGMA (with POEGMA=P(MEO2MA-co-MEO8.5MA)) and P2VP-b-PEO-b-PDMAEMA triblock terpolymers were successfully synthesized and used to construct stimuli-responsive hydrogels. (RDC 5/17/2011)
Stimuli-responsive nanocomposite gels
(455-473) Colloid and Polymer Science 289 #5-6 (2011)|
Haraguchi of Kawamura Institute of Chemical Research, Japan, synthesized a new class of polymer hydrogels, nanocomposite hydrogels (NC gels), consisting of a unique organic (polymer)/inorganic (clay) network structure, by in situ free-radical polymerization in the presence of exfoliated clay nanoparticles in an aqueous system. The resulting NC gels overcame most of the disadvantages associated with chemically cross-linked hydrogels, such as mechanical fragility, structural heterogeneity, and slow de-swelling rate. By using thermo-sensitive poly(N-isopropylacrylamide) (PNIPA) as a constituent polymer, NC gels with remarkable mechanical, optical, and swelling properties as well as thermo-sensitivity were obtained. The various properties of NC gels, such as transparency, gel volume, cell culturing, and surface friction changed significantly in response to the temperature and surrounding conditions. All the excellent properties and new stimuli-responsive characteristics of NC gels are attributed to the unique PNIPA/clay network structure. The thermo-sensitivities and the transition temperature can largely be controlled by varying the clay content and by the addition of solutes. (RDC 5/17/2011)
Review Articles
Multipurpose smart hydrogel systems
(247-262) Advances in Colloid and Interface Science 168 #1-2 (2011)
Samchenko, Ulberg and Korotychof the National Academy of Science of Ukraine, Urkaine, reviewed new hydrogel systems and nanocomposites based on acrylic monomers (acrylamide, acrylonitrile, acrylic acid, N-isopropylacrylamide etc.) with incorporated nanosized colloidal silver, hydroxyapatite and carbon nanotubes with a new set of properties. These systems can sharply change their characteristics when minor external physical (electric and magnetic fields, temperature etc.) or chemical (pH, ionic strength) stimuli are applied. Such stimulus-responsive polymeric systems are very promising from the standpoint of different medical applications, especially for the development of intelligent drug delivery systems. On the base of designed hydrogel iontophoretic transdermal therapeutic systems, endoprosthesis for the replacement of bone tissue and hydrogel burns coatings with immobilized mesenchymal cells were obtained and tested. (RDC 10/3/2011)