1、Chapter 6 Functional Polymers 6.8 Smart Hydrogel,Xie Xingyi, Ph. D College Polymer Sci. & Eng., Sichuan University,1. Introduction,Gels cross-linked polymer networks that can absorb enough solvent to swell.Hydrogels hydrophilic polymer networks which swell in water.,Linear polymer,Aqueous gel,Hydrog
2、el,Dissolve,Swell,Entanglement,Crosslink,Water,1. Introduction,Hydrogel: Ways of Crosslinking,1. Introduction,Smart Hydrogelsundergo strong conformational changes when only small changes in the environment occur.,1. Introduction,Volume phase transitionChemical gels: abruptly swell to many times its
3、original size-or collapse into a compact mass with a small change in solvent concentration or temperature,Sol-gel transitionA physical gel: often change from a solution state to a gelation state (above CGC at LCST) with a small change of temperature or concentration,Transition of a Smart Hydrogel,Vo
4、lume phase transition,Glucose Sensitive Hydrogel,Sol-gel transition,Phase diagram of a PEGPLGAPEG (5502810550).,Turbid line,CGC: Critical Gelation Concentration,LCST: Low Critical Solution Temperature,2. History of Smart Hydrogel,1975, Toyoichi Tanaka discovered smart hydrogelionized gels immersed i
5、n water-acetone solutions : volume dramatically changed. First commercial product in 1994GelMedliquid at room T; viscous at body T at 1 to 3%.,3. Classification and property,Classified based on the type of stimuli. The physical stimulitemperature, electric fields, composition, light, pressure, sound
6、 and magnetic fields Chemical or biochemical stimuli pH, ions and specific molecular recognition events.,3.1 Temperature-sensitive Hydrogels,Structure: possess moderately hydrophobic groups (Chemical Hydrogel),Temperature-sensitive Hydrogels,Structure: hydrophilic & hydrophobic segments (physical Hy
7、drogel),Properties,At lower temperaturehydrogen bonding between hydrophilic segments of the polymer chain dominates swelling or solution state At higher temperature hydrophobic interactions among hydrophobic segments become strengthened, while hydrogen bonding becomes weaker shrinking or gelation oc
8、cur,Physical hydrogel,3.2 pH-sensitive Hydrogels,Properties of pH-sensitive Hydrogel,Ionization on polyelectrolytes more difficult due to electrostatic effects exerted by other adjacent ionized groups. Swelling mainly due to the electrostatic repulsion among charges present on the polymer chain. the
9、 extent of swelling : influenced by any condition that reduce electrostatic repulsion, such as pH, ionic strength, and type of counterions.,3.3 Electric Signal-sensitive Hydrogels,Usually made of polyelectrolytesthe same as pH-sensitive hydrogels Propertieshydrolyzed polyacrylamide contact with both
10、 the anode and cathode electrodes undergo volume collapse sodium acrylic acid acrylamide copolymer is placed in aqueous solution without touching the electrodes: low electrolytes, shrinking; high concentration of electrolytes, bending.,3.4 Light-sensitive Hydrogels,UV-sensitive , bis(4-(dimethylamin
11、o) phenyl)(4-vinylphenyl)methyl- lencocyanide,Light-sensitive Hydrogels,Visible light-sensitive light-sensitive chromophore (e.g. trisodium salt of copper chlorophyllin, 488nm) to poly(N-iso-propylacrylamide) hydrogels. Light heat local polymer, then shrinkage occur IR sensitivepoly(N-isopropylacryl
12、amide) hydrogels without any chromophores are irradiated by a CO2 laser infrared, the volume phase transition, together with a gel bending toward the laser beam,3.5 Pressure-sensitive Hydrogels,Based on uncharged hydrogel theory According to the theory, hydrogels which are collapsed at low pressure
13、would expand at higher pressure Common characteristic of temperature-sensitive gelsPressure sensitivity due to an increase in their LCST value with pressure,4 Application 4.1 Controlled drug delivery,Drug level profiles achieved by conventional (A) and controlled release (B) drug delivery systems.,S
14、mart HydrogelTM for eye drug delivery,Graft copolymer of Pluronic and poly(acrylic acid), Smart hydrogelTM,Network formation at 37 , temperature, pH, and Pressure sensitive,Easy to delivery drug to eye, also to nose,Molecular gate for insulin delivery,graft copolymer of poly(methacrylic acid) (PMAA)
15、 and PEG that is a pH-sensitive hydrogel. Incorporated with glucose oxidase which converts glucose into gluconic acid,4.2 Molecular Recognition,Do what proteins dorecognize a specific molecule, capture it, then release it when appropriate . An examplecopolymer of poly(acrylic acid) and poly(N-isopro
16、pyl-acrylamide) : swollen below 37 and collapses abruptly when heated to 50.,Molecular Recognition,-COO-,Metal ions Absorption,The phase transition temperature of the gel is different for different metal ions,4.3 Antigen-responsive Hydrogels,4.4 Shape Memory Hydrogel,Responsive gel strips made in Hu
17、s lab straight at room temperature ;when modulated design, they bend into alphabet letters at 39; the black bar represents 10 mm.,5. Conclusion and Future Trend,Polymer gels can be stimulated and controlled by changes in pH, solvents, temperature, and electric field strength. Depending on the type o
18、f polymer used and the way it has been actuated, the gels either change volumes, bend or contract. Applications of such devices can range from medical implants for drug delivery to microfluidic systems, which act as mini laboratories to perform experiments. Soft machines will probably never replace hard ones, but wetware may soon take its place next to hardware and software in the designers lexicon.,