polyion-induced liposome aggregation: specific interactions, kinetic arrest and structural...

Polyion-induced liposome aggregationPolyion-induced liposome aggregation

specific interactions, kinetic arrest & structural properties.specific interactions, kinetic arrest & structural properties.

Domenico TruzzolilloDomenico Truzzolillo

Università degli Studi di Roma “La Sapienza”Università degli Studi di Roma “La Sapienza”Dipartimento di FisicaDipartimento di Fisica

SUPERVISORS: Prof. Federico Bordi, Prof. Cesare Cametti Prof. Federico Bordi, Prof. Cesare Cametti

Materials: Liposomes and Polyelectrolytes

Observed Phenomenology: Aggregation with “charge inversion and reentrant condensation”

Colloidal Stability: Classical DLVO Theory and superficial charge heterogeneity

Kinetically arrested states and typical electrostatic parameters. Simulation and experiments.

Thermally activated processes: an experimental evidence.

Detailed Simulations: description of the model, appearence of the patch attraction and polarization effects.

Summary and Perspectives

Polyelectrolytes and Liposomes: Polyelectrolytes and Liposomes: structures and interactionstructures and interaction

Cell Modeling, Cell Modeling, drug delivery and many drug delivery and many

biotechnological biotechnological applicationsapplications


Sequence of ionizable Sequence of ionizable monomers: monomers:

concentration dependence ofconcentration dependence of free counterion fractionfree counterion fraction

D.Truzzolillo et al. D.Truzzolillo et al. PRE, 79 011804, PRE, 79 011804, (2009)(2009)

DNA and proteins DNA and proteins are a typical example are a typical example of polyelectrolytes of of polyelectrolytes of

biological interestbiological interest

Flexible polyelectrolytes:Strong dependence of equilibrium conformational state on

temperature and quality of the solvent.


ElectrostaticallyElectrostaticallydriven adsorption ofdriven adsorption ofpolyelectrolyte onpolyelectrolyte onliposome surfaceliposome surface

Amount of adsorbed Amount of adsorbed polymer polymer

influenced byinfluenced by

TemperatureTemperature

Quality of the solventQuality of the solvent

Discretization of charge on Discretization of charge on macroion surfacemacroion surface

Valence of ionizable Valence of ionizable groupsgroups

Formation of aFormation of acharge inhomogenety charge inhomogenety

ononmacroion surfacemacroion surface

A composite colloid : A composite colloid : pd-Liposomepd-Liposome

1- Aggregation in aqueus solution1- Aggregation in aqueus solution2- Charge inversion2- Charge inversion

3- Reentrant condensation3- Reentrant condensation







Conclusions and Perspectives

Reentrant condensation and charge inversionReentrant condensation and charge inversion

DLS measurements: DLS measurements: standard correlation standard correlation

function analysis.function analysis.

RRhh=k=kbbT/6T/6πηπηDD

ExponentialExponentialdecay decay

2(1) ( , ) iD qi

i

g t q Ae τ−= ∑

Electrophoretic Electrophoretic measurementsmeasurements

Electrophoretic Electrophoretic MobilityMobility

ζζ-potential-potential Information about the Information about the net charge on the surface net charge on the surface

of aggregatesof aggregates

( )2

3E F Rεζµ κη

=

ξ ξ = N= N--/N/N++ Stoichiometric charge ratioStoichiometric charge ratio

Reentrant condensation and charge inversionReentrant condensation and charge inversion

Position of the neutralization point dependent on the

charge discretization of the system and on the chemical nature of P/L

G. Gilles et al. J.Phys. Chem. B 111, 8626, 2007G. Gilles et al. J.Phys. Chem. B 111, 8626, 2007

J. Kleimann et al., Langmuir 2, 13 688, 2005J. Kleimann et al., Langmuir 2, 13 688, 2005F. Bordi et al. PRE 71, 050401(R), 2005F. Bordi et al. PRE 71, 050401(R), 2005

Close to the neutralization point…



Colloidal Stability: Classical DLVO theories and superficial charge heterogeneity





Observed aggregation: limitations Observed aggregation: limitations and problems with Classical DLVO and problems with Classical DLVO

theorytheory

Screening length for TypicalScreening length for Typicallipoplexes system: lipoplexes system:

PAA+Dotap LiposomesPAA+Dotap Liposomesclose to isoelectric pointclose to isoelectric point

DLVO theories do not take into account double DLVO theories do not take into account double layer interactions and chargelayer interactions and charge

heterogeneity effects. (Patch attraction)heterogeneity effects. (Patch attraction)

Local attraction Local attraction between positive and between positive and negative domains on negative domains on

different approaching different approaching particlesparticles

liposom

e

+

adsorb

ed

polymer

Liposome+adsorbedpolymer

What’s the stabilization process???What’s the stabilization process???Two screening lengths?Two screening lengths?

Huge increasing of Yukawa potental Huge increasing of Yukawa potental amplitudes?amplitudes?

Stabilization process via Stabilization process via surface interactionssurface interactions

Random charge distribution: HHF model Random charge distribution: HHF model revisited.revisited.

Velegol and Thwar (2001)Velegol and Thwar (2001)Random potential fluctuationRandom potential fluctuation

Mean value of theMean value of thesurface potentialsurface potential

Derjaguin approximation Derjaguin approximation can be appliedcan be applied

What’s new………What’s new………The presence of chargeThe presence of charge

heterogeneities introduces an heterogeneities introduces an attractive term of attractive term of purely purely

electrostatic natureelectrostatic nature..

A potential barrier appears A potential barrier appears whose stregth depends on the whose stregth depends on the

electrostatic parameter of electrostatic parameter of macroions (macroions (ζζ,,σσ))

The larger the variance of surface potentialThe larger the variance of surface potentialthe smaller barrier height .the smaller barrier height .

2 2

max 2

1lnH

ζ σκ ζ

+=

((ζ,σζ,σ)-)-dependence of the dependence of the range of interactionrange of interaction

0σ → max 0H → HHF resultHHF resultDependence on curvature Dependence on curvature

radius of interacting particlesradius of interacting particles

Kinetically arrested statesKinetically arrested statesIncreasing of the barrier height

upon clustering Slowing down of theaggregation

kinetics

Stable cluster phase as a kinetically arrested Stable cluster phase as a kinetically arrested aggregation process.aggregation process.

Typical energies required Typical energies required to arrest the aggregationto arrest the aggregation

Size distributionsSize distributions

How to simply simulate the systemHow to simply simulate the system

CompactnessCompactnessof the aggregatesof the aggregates

Oil drop-like processOil drop-like process

( ) 30R N NR=

R0

R(N)

The size of the uniform The size of the uniform potentialpotential

regions on the particle surface regions on the particle surface is independent on the cluster is independent on the cluster

size.size.

Brownian dynamics in the MC algorithm: theBrownian dynamics in the MC algorithm: theiithth particle is selected with a probability proportional to particle is selected with a probability proportional toRR00/R/Rii, where R, where R00 is the initial radius and Ri is the radius is the initial radius and Ri is the radius

of the iof the ithth aggregate aggregate

When two approaching particlesWhen two approaching particles(A and B) overcome the (A and B) overcome the

potential barrier (surface gappotential barrier (surface gapdistance H < Hmax), they distance H < Hmax), they

aggregate forming an uniqueaggregate forming an uniqueparticle with radius particle with radius

Rp=(RRp=(RAA33+R+RBB

33))1/31/3 and positioned and positionedin the center of mass of two in the center of mass of two

aggregating spheres.aggregating spheres.

Let’s start withLet’s start withSimulations!!!Simulations!!!

““Equilibrium” size and Temperature Equilibrium” size and Temperature dependencedependence

10000 particles10000 particles

In all cases the In all cases the aggregation aggregation

stops when barrier height stops when barrier height reaches 10 kTreaches 10 kT

ExperimentalExperimentalconditionsconditions

φ= = 0.010.012R=80 nm2R=80 nmT= 298 KT= 298 K

D.TruzzolilloD.Truzzolillo, F. Bordi, F. Sciortino, C. Cametti., F. Bordi, F. Sciortino, C. Cametti. Eur. Phys Jour. E , 29, 229 (2009) Eur. Phys Jour. E , 29, 229 (2009)

Experimental evidence of thermal activated processExperimental evidence of thermal activated process

Two evident effectTwo evident effectof the increasingof the increasingtemperature : temperature :

Net incrementNet incrementof the mean of the mean

cluster radius cluster radius close to theclose to the

isoelectric point isoelectric point

Shifting of Shifting of ζζ-potential-potentialcurves curves

Temperature dependence Temperature dependence of the amount of the of the amount of the

adsorbed adsorbed polyelectrolytepolyelectrolyte

S.Sennato,S.Sennato,D. TruzzolilloD. Truzzolillo, F.Bordi, C.Cametti, Langmuir 24, 12181 (2008)., F.Bordi, C.Cametti, Langmuir 24, 12181 (2008).

Rescaling radiiwith T

all the points collapse on

the same mastercurve

Typical behavour of a thermal

activated process

Agreement with the model and Agreement with the model and rescaling with T………rescaling with T………

σσ ((ξξ) is a Bell-shaped

Gaussian distribution whose width

is determined by the extention of condensation region

Deteiled MC - simulationsDeteiled MC - simulations

T= 298.16 K

εLJ=KBT/1.2

kF≈ KBT

Typical DOTAP liposome suface charge density

κ=[(2F2cs)/(εRT)]1/2

Uniform charge densityDebye constant for a 1:1 salt

Room temperature

Energy scale of excluded volume interaction

Binding coupling between adjacentmonomers

20 monomers for chain

Σ = Ne/S =1.67 nm-2 2R= 7nm, 10 nm

Deteiled MC - Deteiled MC - simulationssimulations: creation : creation of complexesof complexes

N chains + one macroion

One ComplexStabilization of the adsorption process

Replication of the PE-colloid complex

Two complexes MC-simulation: traslational moves of

single monomers and rotational moves of the whole polyelectrolyte layer around a

colloid.

Calculation of the mean force potential

Patch attraction. When does it occur?Patch attraction. When does it occur?

For κR<1 the interaction

between complexes is well fitted by the

repulsiveinteraction due to the

presence of a residual net charge

Where is the patch attraction?

Non-neutral complex (ξs= 0.57)

Patch attraction. When does it occur?Patch attraction. When does it occur?

Increasing the ionic strength short range attraction appears

Dominance of the attractive interaction

between opposite heterogeneous surfaces.

Confinement of interactions:Interacting surfaces rather

than interacting particles

Overlap of opposing PE-layer generates Repulsive steric contribution at

very short distance

The effect of charge ratio on the potential The effect of charge ratio on the potential shape . . .shape . . .

κR = 5 ≈ (κR)pd-liposomes

Existence of a potential barrier as predicted by

double layer theory.Competition between monopole-monopole

repulsions and energetic bridging.

The presence of flat PE-layer inducesEnergetic bridging between complexes

(attractive interaction)

ξs=2ξ Superficial charge ratio

on the the total pair interaction potential . . .on the the total pair interaction potential . . .

The presence of PE-layer adds a “soft” repulsive contribution

at very short distances

Reentrant behavior of the global minimum depth

The depth of the global minimumis strongly influenced by the

PE-layer structure.In presence of tails the overlap

of chains increases the repulsion.

Polarization effects: antiparallelPolarization effects: antiparalleldipolar doubletsdipolar doublets

The dipole moments are always directed in opposite directions.

Inversion at the isoelectric point.Anti-parallel doublets.

2

1s

s

Zd

ξµξ

= −+

rr

The standard deviation of the surface potentialThe standard deviation of the surface potential

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4-10

0

10

20

30

40

Protruding tails

<σ V

> [

mV

]

ξs

Flat PE-layer

Low PE content: flat layers σA with negative concavity and global maximum (stripes model).

High PE content: protruding tails monotonicincrease of σA.

0 10 20 30 40 50 60 70 80 90 100-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

<Α>

σ Α

m

From the 2D model of the adsorption:From the 2D model of the adsorption:

and the behaviour close to the and the behaviour close to the neutralization point is…neutralization point is…

and from the thermal activated process and from the thermal activated process assumptionassumption

very close to the very close to the experimental experimental divergence !divergence !

Power law divergence for Power law divergence for ξξξξ00

SummarySummaryLiposomesLiposomes, as several charged colloids, undergo condensation and charge , as several charged colloids, undergo condensation and charge

inversion induced by the addition of oppositely charge inversion induced by the addition of oppositely charge polyelectrolytespolyelectrolytes. . The The charge patch attraction charge patch attraction appears and destabilizes dispersions. appears and destabilizes dispersions.

Double layer theory Double layer theory qualitatively explains the reentrant condensation qualitatively explains the reentrant condensation phenomenon indicating that the interaction between phenomenon indicating that the interaction between

large particles (kR>>1) depends on the first two moments of the suface large particles (kR>>1) depends on the first two moments of the suface potential distribution and on the radius of the particles.potential distribution and on the radius of the particles.

Kinetic arrest Kinetic arrest occurs if the barrier between the particles is sufficiently high occurs if the barrier between the particles is sufficiently high (<Φ(<Φmaxmax≈10k≈10kBBTT>)>) Stable cluster phaseStable cluster phase

DivergenceDivergence of the right order at the neutralization point. of the right order at the neutralization point.

Dependence of cluster size on the temperature Dependence of cluster size on the temperature Evidence of a Evidence of a thermal thermal activated processactivated process. The double layer picture is confirmed.. The double layer picture is confirmed.

Detailed MC simulation: Detailed MC simulation: 1) 1) Patch attraction Patch attraction exists only if exists only if κκR>1R>1

2) Dependence on the charge ratio: 2) Dependence on the charge ratio: potential barrier potential barrier between not neutral complexes. between not neutral complexes. 3) Steric repulsion governed by PE-layer thickness3) Steric repulsion governed by PE-layer thickness

4) 4) Dipolar orientation and inversionDipolar orientation and inversion. . 5) 5) Standard deviation Standard deviation of the surface potential.of the surface potential.

Perspectives and future Perspectives and future developmentsdevelopments

Further investigations on the second virial coefficient close to the Further investigations on the second virial coefficient close to the isoelectric point. isoelectric point. SLS tecnique SLS tecnique Zimm plot + lipoplexes static form factor. Zimm plot + lipoplexes static form factor.

AFM measurements: Structural properties of adsorbing AFM measurements: Structural properties of adsorbing polyelectrolytes.polyelectrolytes.

Possible biomedical applications: developing a new class of vectors for Possible biomedical applications: developing a new class of vectors for multi-drug deliverymulti-drug delivery . . Anti-HIV therapy.Anti-HIV therapy.

Simulations: Study of the effect of the size of spherical macroions, Simulations: Study of the effect of the size of spherical macroions, temperature and valence of chains (charge mismatch);temperature and valence of chains (charge mismatch);Extension to Polyampholytes.Extension to Polyampholytes.

Thank you for your Thank you for your attention!attention!

Acknowledgments:

Dr. S. Sennato,Prof. F. Bordi,

Prof C. Cametti, Prof. F. Sciortino, Dr. E. Zaccarelli.

Grazie, Roma!

…and now let’s go to

Crete!

11. D.Truzzolillo, F.Bordi, C.Cametti, S.Sennato. Phenomenological surface characterization of cationic-lipid monolayers in the presence of oppositely charged polyions. Coll. Surf. A, 319, 51. (2008)

2. F.Bordi, C.Cametti, S.Sennato, D.Truzzolillo. Strong repulsive interactions in polyelectrolyte-liposome clusters close to the isoelectricpoint: a print for an arrested state. Phys. Rev. E, 76, 061403, (2007)

3. D.Truzzolillo, F.Bordi, F.Sciortino, C.Cametti. Kinetic arrest ininhomogeneously-charged particle aggregation. Eur. Phys. J. E 29 2 (2009) 229-237.

4. S. Sennato, D.Truzzolillo, F. Bordi, C. Cametti. Effect of Temperature on the Reentrant Condensation in Polyelectrolyte-Liposome complexation. Langmuir, 24 (21), 12181-12188, (2008).

5. D. Truzzolillo, F. Bordi, C. Cametti, S. Sennato. The counterion condensation of differently flexible polyelectrolyte aqueous solutions in the dilute and semidilute regime. Phys. Rev. E, 79 011804, (2009).

6. D.Truzzolillo, C.Cametti, S.Sennato. Dielectric properties of differently flexible polyions: a scaling approach. Phys. Chem. Chem. Phys., 11, 1780, (2009).

7. S.Sennato, D.Truzzolillo, F.Bordi, F.Sciortino, C.Cametti.Colloidal particle aggregates induced by particle surface charge heterogeneity. Coll. Surf. A, 343, 34. (2009)

8. F. Bordi, S. Sennato, D. Truzzolillo. Polyelectrolyte induced aggrega-tion of liposomes: a new cluster phase with interesting applications.REVIEW - J. Phys: Condensed Matter, 21, 203102, (2009)

9. C. Cametti, S. Sennato, D. Truzzolillo. Deviations from a simple Debye relaxation in aqueous solutions of differently flexible polyions induced by polymer concentration. J. Chem. Phys. 131, 034901 (2009)

Publications

In Preparation:10- D. Truzzolillo, F. Bordi, F. Sciortino, S. Sennato.

Interaction between polyelectrolyte-colloid complexes: a Monte Carlo simulation study in the

Debye-Huckel approximation.

Nota linguisticaNota linguisticananòmetro o nanomètro[comp. di nano- e metro; 1981]s. m.* (fis.) Unità di misura di lunghezza pari a 10-9 m. SIMB. nm.fonte: Zingarelli

polyion-induced liposome aggregation: specific interactions, kinetic arrest and structural...

Technology

charge inversionclose

net charge

classical dlvo theories

polarization effects

patch attraction

experimental evidence

activated processes

detailed simulations