BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Lecture 9: Polyelectrolyte Hydrogels Last Day: Physical hydrogels Structure and chemistry Toda polyelectrolyte hydrogels, complexes, and coacervates rolyte multilayer theory of swelling in ionic hydrogels Reading S.K. De et aL., 'Equilibrium swelling and kinetics of pH-responsive hydrogels: Models experiments, and simulations, J. Microelectromech. Sys. 11(5)544 (2002) Supplementary Reading L. Brannon-Peppas and N.A. Peppas, 'Equilibrium swelling behavior of pH-sensitive hydrogels, Chem Eng. Sci. 46(3)715-722(1991) USE DEMO OF AMINOETHYL METHACRYLATE HYDROGEL TO SHOW PH-DEPENDENT SWELLING? Covalent polyelectrolyte hydrogels Response of polyelectrolyte gels to pH of environment o Reminder of the response of ionizable groups to pH changes ionization of charged groups 14 o Presence of ionizable groups makes polyelectrolyte hydrogels sensitive to p o lonic strength o Electric fields o D Lecture 9-polyelectrolyte hydrogels 1of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 9: Polyelectrolyte Hydrogels Last Day: Physical hydrogels Structure and chemistry Today: polyelectrolyte hydrogels, complexes, and coacervates Polyelectrolyte multilayers theory of swelling in ionic hydrogels Reading: S.K. De et al., ‘Equilibrium swelling and kinetics of pH-responsive hydrogels: Models, experiments, and simulations,’ J. Microelectromech. Sys. 11(5) 544 (2002). Supplementary Reading: L. Brannon-Peppas and N.A. Peppas, ‘Equilibrium swelling behavior of pH-sensitive hydrogels,’ Chem. Eng. Sci. 46(3) 715-722 (1991). USE DEMO OF AMINOETHYL METHACRYLATE HYDROGEL TO SHOW PH-DEPENDENT SWELLING? Covalent polyelectrolyte hydrogels Response of polyelectrolyte gels to pH of environment o Reminder of the response of ionizable groups to pH changes: ionization of charged groups 1.2 1 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH o Presence of ionizable groups makes polyelectrolyte hydrogels sensitive to: o pH o Ionic strength o Electric fields o (T) Lecture 9 – polyelectrolyte hydrogels 1 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 o Observed swelling as a function of ph o Data for poly(2-hydroxyethyl methacrylate-co-acrylic acid)gels cross-linked with ethylene glycol dimethacrylate Data for poly (HE MA-Co-AA) covalent hydrogel CH -CH-CH-Im-CH2-C C-O CH2 CH, OH Cl- OH Na+ (1) H2O (4)II OH Physical chemistry of swelling at high pH (example for anionic gels) o Stepwise process in basic solutions 1. lonization of carboxyl groups, releasing H a. At high ionic group density, carboxylate anions repel one another, driving swelling- but this is not the main driving force for swelling in typical conditions . Electrostatic force decays as 1/, too weak at typical charged group separation to have a significant effect i. In water: F=g12 4er=-e214ter=2.04x10-39/(r in m) e=1602×1019c ⅲi.F1nmF0.2nm=0.04! 2. H recombines with OH to give water 3. Charge is compensated by diffusion of cations (e.g. Na)and OH into gel 4. Influx of new ions creates osmotic pressure that drives swelling Lecture 9-polyelectrolyte hydrogels 20f17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Observed swelling as a function of pH: o Data1 for poly(2-hydroxyethyl methacrylate-co-acrylic acid) gels cross-linked with ethylene glycol dimethacrylate o Physical chemistry of swelling at high pH (example for anionic gels): o Stepwise process in basic solutions:1 1. Ionization of carboxyl groups, releasing H+ a. At high ionic group density, carboxylate anions repel one another, driving swelling- but this is not the main driving force for swelling in typical conditions i. Electrostatic force decays as 1/r2 , too weak at typical charged group separation to have a significant effect ii. In water: F = q1q2/4πεr 2 = -e2 /4τεr 2 = 2.04x10-39/r2 (r in m) 1. ε = 80 in water 2. e = 1.602x10-19 C iii. F1 nm/F0.2 nm = 0.04! 2. H+ recombines with OHto give water 3. Charge is compensated by diffusion of cations (e.g. Na+ ) and OHinto gel 4. Influx of new ions creates osmotic pressure that drives swelling2 Lecture 9 – polyelectrolyte hydrogels 2 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Kinetcs for ph change from 3 to 6: Kinetics for pH change from 6 to 3 pe ad AIn 2002 o Kinetics: deswelling faster(-10X) than swelling Swelling in -166 mi De-swelling in-16 min (300 Hm thick gels) Theory based on diffusion of ions into and out of gel semi-quantitatively predicts observed swelling behavior Swelling rate inversely proportional to square of gel size the size of the gel o Implies that response time of gels will scale inversely with th o Swelling rate can also be increased by creating greater porosity in gel-increase surface/volume ratio allows solute to diffuse into gel more rapidly Rapid swelling/deswelling of superporous gels Low pH and shrinking kinetics of I )in a ph=11.77 NaOH solution and a 1. 92 buffer with ionic strength of 0. 2 M. Three cycles of swelling inking were shown for gel 1; two cycles were shown fo o hydrogels containing basic groups show opposite pH sensitivity o swelling in acidic solutions o e.g. Peppas papers Lecture 9-polyelectrolyte hydrogels 3of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Kinetics: deswelling faster (~10X) than swelling • Swelling in ~166 min. • De-swelling in ~16 min. • (300 µm thick gels) • Theory based on diffusion of ions into and out of gel semi-quantitatively predicts observed swelling behavior o Implies that response time of gels will scale inversely with the size of the gel o Swelling rate inversely proportional to square of gel size3 o Swelling rate can also be increased by creating greater porosity in gel- increase surface/volume ratio allows solute to diffuse into gel more rapidly Rapid swelling/deswelling of superporous gels: Low pH High pH (Zhao and Moore, 2001) o hydrogels containing basic groups show opposite pH sensitivity o swelling in acidic solutions o e.g. Peppas papers Lecture 9 – polyelectrolyte hydrogels 3 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Polyion complex hydrogels Coacervates o complexation between two oppositely charged polyelectrolytes can lead to precipitation(insoluble solid phase driven by charge neutralization on hydrophobic polymers driven by macro-aggregate formation 2. coacervate formation(dense liquid phase) 3. soluble comple o mechanisms of formation Polyanion Polycation Random primary Ordered secondary 解 Complex aggregates 1. initial rapid Coulombic bonding 2. formation of new bonds/restructuring of chain distortions gregation of secondary complexes o mixing of two polyions can lead to 90% complex formation Polyelectrolytes studied as coacervates for biomaterials: Polyanions o Carboxymethylcellulose o Dextran sulfate o Carboxymethyl dextran o Pectin o Polycau chitosan(derived from crab shells) o Polyethyleneimine o Poly (4-vinyl-N-butylpyridinium) bromide o Quarternized polycations o Poly(vinylbenzyltrimethyl)ammonium hydroxide Lecture 9-polyelectrolyte hydrogels 4of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Polyion complex hydrogels4 Coacervates o complexation between two oppositely charged polyelectrolytes can lead to: 1. precipitation (insoluble solid phase) driven by charge neutralization on hydrophobic polymers driven by macro-aggregate formation 2. coacervate formation (dense liquid phase) 3. soluble complexes o mechanisms of formation 1. initial rapid Coulombic bonding 2. formation of new bonds/restructuring of chain distortions 3. aggregation of secondary complexes o mixing of two polyions can lead to 90% complex formation o Polyelectrolytes studied as coacervates for biomaterials:4 o Polyanions o Carboxymethylcellulose o Alginate o Dextran sulfate o Carboxymethyl dextran o Heparin o Carrageenan o Pectin o xanthan o Polycations o Chitosan (derived from crab shells) o Polyethyleneimine o Poly(4-vinyl-N-butylpyridinium) bromide o Quarternized polycations o Poly(vinylbenzyltrimethyl)ammonium hydroxide Lecture 9 – polyelectrolyte hydrogels 4 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 o Microstructure of coacervate hydrogels o Example structures: xanthan/chitosan coacervates(Dumitriu et al. 1998) Xanthan Chitosan omani poly o-H NH2 CH2OH SEM o Pore sizes formed 0. 1-1 um; fiber diameters -100 nm Polyelectrolyte multilayers(PEMs Structure of pems Assembly ayer-by-layer deposition o How is it done o Surface properties change in digital fashion with adsorption of sequential layers Lecture 9-polyelectrolyte hydrogels 5of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Microstructure of coacervate hydrogels o Example structures: xanthan/chitosan coacervates (Dumitriu et al. 1998) o Pore sizes formed 0.1-1 µm; fiber diameters ~100 nm Polyelectrolyte multilayers (PEMs) Structure of PEMs Assembly • Layer-by-layer deposition o How is it done o Surface properties change in digital fashion with adsorption of sequential layers5 Lecture 9 – polyelectrolyte hydrogels 5 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Surface properties dominated by last layer deposited 图 s Polyanion 3)Polycation 2)Was Layer igure 2, Advancing contact angle as a function of the layer number --- termost layer, whereas even number films have chitosan as the outermost layer, Assemblyfiguresourcehttp://www.chem.fsuedu/multilayers/ mbly on complex surfaces o Polyelectrolytes will adsorb to surfaces with complex topography o Polyelectrolytes themselves may have complex geometries(e.g. particles or dendrimers )6 Scheme 1. Schematic llustration for the Preparation of Hollow 时9N2N9 PSS/4G PAMAM Multilayer Capsules 3. 4G PAMAM Colloid PSS/4G PAMAM- Generation 7 poly(amidoamine) dendrimer: template colloid coated colloid steps 1-4 Cure renoval PSS/4GPAMAM SS/4GPAMAM multilayer-coated colloid hollow capsule ( Khopade and Caruso, 2002) Dendrimerimagesourcehttp://www.foresight Lecture 9-polyelectrolyte hydrogels 60f17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Surface properties dominated by last layer deposited: θ Assembly figure source: http://www.chem.fsu.edu/multilayers/ • Assembly on complex surfaces o Polyelectrolytes will adsorb to surfaces with complex topography o Polyelectrolytes themselves may have complex geometries (e.g. particles or dendrimers) 6 Generation 7 poly(amidoamine) dendrimer: (Khopade and Caruso, 2002) Dendrimer image source: http://www.foresight.org/Conferences/MNT7/Papers/Cagin3/ Lecture 9 – polyelectrolyte hydrogels 6 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 o Assembly on protein crystals to encapsulate proteins: 7 Blahblah 1,02),etc e Figure 4. TEM decomposition ule spreads out on the carbon surfare on which it i creases can be seen, Same undecomposed enzyn mulyte can still be seen in the lnterior of the capsule. layer Fah pelyleetralyle Layr units (Caruso et al., 2000) Cells as living PEM assembly substrates (F. Caruso) (soUrce:http://ww.chem.fsuedu/multilayers/ o What else Building PEMs on biomaterials Assembly of PEMs on amino-modified poly(lactide)' o Alternating adsorption of sulfonated polystyrene and chitosan(polycation Lecture 9-polyelectrolyte hydrogels 7of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Assembly on protein crystals to encapsulate proteins: 7 Blah blah (Caruso et al., 2000) • Cells as living PEM assembly substrates: SEM micrograph of multilayer-coated echinocyte blood cell (F. Caruso) (Source: http://www.chem.fsu.edu/multilayers/) o What else Building PEMs on biomaterials8 • Assembly of PEMs on amino-modified poly(lactide) 5 o Alternating adsorption of sulfonated polystyrene and chitosan (polycation) Lecture 9 – polyelectrolyte hydrogels 7 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Scheme 1. The Schematic Representation of Aminolysis and Layer-by-Layer Self-Assembly Process with Oppositely Charged Polyelectrolytes on an Aminolyzed PLLA Membrane Surface H (CH-C-O) NH HNNH, NhS IPolyanion NHS 2. Wasl NH白 -CH-C-N-CH2 CH2-NH 2+ HO 3. Polycation NHO 4. Wash sd/ NHP PEM-modified poly lactide Lecture 9-polyelectrolyte hydrogels 8of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 H2N-CH CH3 O -(CH -C-O)n - 2-NH2 CH3 O H -CH -C-N-CH2CH2-NH2 + HOPEM-modified polylactide 2CH Lecture 9 – polyelectrolyte hydrogels 8 of 17
BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Utility of polyeletrolyte gels in biomaterials/bioengineering Cell encapsulation: In situ formation with no additives, no change in pH, no change in temperature, in physiological solutions o Useful for safe encapsulation of cells o Drug delivery: lonic interactions for protein-polymer complexes prior to gel formation allow high protein entrapment o PEMs can form hollow capsules Drug release from PSS/PAMAM PEM capsules 0.154 M NaC Figure 4. Release profiles for encapsulated DOX in PSs tion of the their interior. The inset show Fluoresceno. tas used for release studies. The excitation waveteng rug-loaded PEM capsules o Enzyme immobilization: binding to ionic groups for biosensors or active biomaterials o Protein separations/recovery: some binding specificity can be achieved in certain situations to allow for selective sorption of a target protein o Addition of polycation or polyanion to solution of protein leads to protein-polyelectrolyte coacervate formation o bound proteins released by adjustment of ph/ionic strength AN减 YCAY p, 2l. wutu of a sampan. circe Fg. b The mechanisn of proein-polyelaetrohte complexes Lecture 9-polyelectrolyte hydrogels 9of17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Utility of polyeletrolyte gels in biomaterials/bioengineering o Cell encapsulation: In situ formation with no ‘additives’, no change in pH, no change in temperature, in physiological solutions o Useful for safe encapsulation of cells o Drug delivery: Ionic interactions for protein-polymer complexes prior to gel formation allow high protein entrapment efficiencies o PEMs can form hollow capsules Drug release from PSS/PAMAM PEM capsules: Fluorescent drug-loaded PEM capsules o Enzyme immobilization: binding to ionic groups for biosensors or active biomaterials o Protein separations/recovery: 9 some binding specificity can be achieved in certain situations to allow for selective sorption of a target protein o Addition of polycation or polyanion to solution of protein leads to protein-polyelectrolyte coacervate formation o Bound proteins released by adjustment of pH/ionic strength Lecture 9 – polyelectrolyte hydrogels 9 of 17
BEH. 462/3.962J Molecular Principles of Biomaterials Spring 2003 o Microvalves for bioMEMS and lab-on-a-chip applications: 10 11 Utilize fast response of swelling in microsized ge to control flow through microfluidics o Example: PHEMA-Co-AA networks patterned in microfluidic channels outto Fgure 1 A diagram of and images demonstrating a varety of shapes that were poymenaed witn 35 seaons a, The fabricatio Figure 2 Prefabricated posts in a microchannel serve as support the posts. b, The actual dece after polymerization of the hydrogel. c, The hydrogel strucure with high-aspecH-tatio feature hydroges allow fluid to flow down the sde branch. e, The imp the hydrogel jacketdesign (ardes versus analtemative design that uses a singe larger erization of mut pe structures with a single exp cylindrical structure in the same size channel squarest. Io is the fractional change in lytic agent cells Figure 4 The volume response of two different hydrogels with respect to the pH of the surounding fluid. Top, the fractional change in diameter (D)of the hydrogels wihrespect outlet detection molecules to pH Bottom, images showing a device that directs(sorts )a fluid streamon the basis of its pH. The hydrogel gating the right branch (circles) expands in base and contracts in acid. The hydrogel gating the left branch (squares behaves in the opposite manner Figure 12 Lytic agent diffuses into the cell stream, lysing the cells and releasing the (expands n acid and contracts in base). the fluid enters from the centre channelatarate otein of interest. A small volume of the proteins are routed into the detection channel of 0.05ml min. At a pH of 7. 8, the flow is directed down the left branch. At a pH of 4.7, where molecules from a stream of detection reagent diffuse into the proteins, giving the flow s directed down the right branch. Both hydrogels expand to shut off the fow of a fluorescent signal. when the pH s changed to 6. 7. Scale bars, 300 um. Schematic shows an example lab-on-a-chip analysis approach Lecture 9-polyelectrolyte hydrogels 100f17
BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Microvalves for bioMEMS and lab-on-a-chip applications: 10,11 Utilize fast response of swelling in microsized gels to control flow through microfluidics o Example: PHEMA-co-AA networks patterned in microfluidic channels: • Schematic shows an example lab-on-a-chip analysis approach Lecture 9 – polyelectrolyte hydrogels 10 of 17