Particles 2009, Berlin. using AFM force spectroscopy. Andreas Fery

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1 Particles 2009, Berlin Mechanical characterization of microcapsules using AFM force spectroscopy Andreas Fery University of Bayreuth Faculty of Biology, Chemistry and Geosciences Department Physical Chemistry II BZKG Bayreuth Center for Colloids and Interfaces

2 Microcapsules Encapsulation : pharmaceutics, cosmetics, food design,. Biosystems : abundance of capsules (bacterial and viral capsids, ) Mechanical properties Stability Insight in physical state of the wall material Stimulus sensitivity Transport properties in flow, Rheology Adhesion (interplay mechanics-surface forces) New tools for Investigations on Single microcapsule level needed

3 Combination of AFM with optical micoscopy Layer-by-layer capsules Microballoons h thin V Air-Burst 2 Z burst 2 R Swell

4 AFM schematically Photodiode Laserdiode Mirror Sample Feedback XYZ Piezo-Scanner Force detection or imaging possible

5 AFM: Force information Usage of colloidal probe-cantilever 1 ensures well defined d deformationgeometry 1 Butt HJ. Biophysical Journal 1991; 60 (6): Colloidal probe Mi l i t i Microcapsule, axiosymmetric deformation

6 RICM: Shape Reconstruction Interferences Reflection Interference Contrast Microscopy (RICM) allows reconstruction of shape J. Rädler, E. Sackmann; J. Phys France II 3: 727 (1993) Dubreuil, F., N. Elsner, A. Fery Europhys. J. E 12(2) 215 (2003)

7 Single Microcapsule Deformation : Method H 2 O 2 Atomic Force Microscopy (AFM) Solvent, Temperature, variable Force resolution < 10 pn Force range: 100pN 100nN Deformation Resolution <1nm Optical Microscopy Microscope. Image Processing Shape information Contact areas Fluorescence Europhys. J. E, 12 (2), (2003) review article : review article : Polymer, (2007)

8 Microcapsule Systems Polyelectrolyte Multilayer Micro Bubbles Polyelectrolyte Multilayer Capsules Tubes 1 Pickering Emulsions 2 1 : R. Müller & al. Polymer (2007); R. Müller et al. J. Phys. Chem. B (2007) 2 : Russell et. al. Angew. Chem. Int. Ed (2005); Ferri et al. Soft Matter (2008)

9 Combination of AFM with optical micoscopy Layer-by-layer capsules Microballoons h thin V Air-Burst 2 Z burst 2 R Swell

10 PE-Multilayer capsules LbL Core dissolution E. Donath, G. B. Sukhorukov, F. Caruso, S. A. Davis and H. Möhwald, Angewandte Chemie, International Ed. in English. 37, , 2205 (1998) wall properties (thickness, composition) defined by multilayer shape (size, monodispersity) defined d by template t particle

11 Qualitative look at PEM capsule deformation F=k*x Eur. Phys. J. E 12(2): 215 (2003) Prog. Coll. Pol. Sci. 132: 117 (2006) Buckling transition from spherical shape to indented sphere

12 Small Deformation Approach Playing Ping-Pong : Deformations on the order of the membrane thickness 1,2 : Ping Pong Ball : plastic deformation and no volume conservation h R F d F d R Material of Young s modulus E 2 Eh E : Young s modulus R : radius of curvature h : membrane thickness 1 : L. Pauchard and S. Rica Philosophical Magazine B (1998) 2 : E. Reissner J. Mat. Phys (1946)

13 Wall-thickness effect and Young s modulus System : Polystyrenesulfonate (PSS) / Polyallylamine (PAH) in water k shell in mn/m N k shell in mn/m k 1 Eh 2 R Capsule stiffness can be controlled by wall thickness Young s modulus E = 294 ± 94 * 10 6 Pa Diffusion-coefficient D< cm 2 /sec immobile chains, glasslike material h 2 in nm 2 New Journal of Physics 6 18 (2004)

14 Stimulus sensitivity : Temperature 4,5 incubation time: 20 min Effect of temperature ( T > 35 C ) : System Poly-diallyl-dimethyl-ammonium /PSS Capsule dia ameter / μm 4,0 3,5 3,0 2,5 2,0 1,5 A B C Incubation temperature / C Shrinking and thickness increase (irreversible) Köhler, K.; Shchukin, D. G.; Sukhorukov, G. B.; Möhwald, H. J. Phys. Chem. B 109, (2005)

15 Change of Young s Modulus with temperature stiffness s k [pn/nm m] blue : room temperature red : at 70 C time [min] Upon, cooling, shape is frozen Change in k ~ Change in E E changes by two orders of magnitude upon cooling, E is in MPa range at high temperature R. Müller, K. Köhler, R. Weinkamer, G. B. Sukhorukov and A. Fery Macromolecules (2005)

16 Rate dependency of elastic constants norm malized stiffn ness , open symbols : high temperature, pronounced rate dependency 2 filled symbols: low temperature, 1 little l variation i over 2 decades of deformation rate extension/retraction rate [Hz] Transition from frozen to viscoelastic state

17 Gold-NP containing capsules System: Sukhorukov, Skirtach Au-NP PDADMAC/PSS Talk M. Bedard Tue, 15:30 for details Here : Shrinking process stops at well defined radius, depending on Au-NP content 1. Bedard MF, Munoz-Javier A, Muller R, del Pino P, Fery A, Parak WJ, Skirtach AG and Sukhorukov GB. Soft Matter 2009; 5 (1):

18 Mechanical characterization Nonlinear dependency Of mechanical properties on Au-NP content (nn N) Regime 1: gold embedded in PDADMAC/PSS matrix, surface tension dominates Regime 2: gold NPs percolate, shrinking stops

19 Combination of AFM with optical micoscopy Layer-by-layer capsules Microballoons h thin V Air-Burst 2 Z burst 2 R Swell

20 Microballoons in Theragnostics Micro-balloons = gas filled microcapsules Micro-balloons act as strong scatterers for ultrasound in the body (large density difference) contrast t enhancement therapy by encapsulation and release of therapeutic gases

21 PVA Microballoons Microballoon Synthesis (G. Paradossi / F. Cavallieri) Polymerization of poly(vinyl alcohol) under agitation Macroscopic creaming Shelf lifetime months Cavalieri, Hamassi, Chiessi and Paradossi, Langmuir 2005, 21, 8758 Soft X-ray Microscopy: Langmuir 2008, 24, 13677; Soft Matter 2008, 4, 510

22 Micro-Balloon Deformation - Bursting Gas filled MB (strong scattering) Same MB after Bursting (weak scattering) Force (μn De eflection N) (µn) Bubble Burst Piezo Displacement Piezo Displacement (μm) (µm) 9 <<< trace >>> retrace 10 h thin V Air-Burst 2 R Swell 2 Z burst

23 Deformation rate dependency N) Force (µ 10 Hz 1.0 Large deformation: 8 Hz 6 Hz pronounced rate dependency 4 Hz Permeability effects? 2Hz Hz 0.5 Hz 0.05 Hz Small deformation: Weak rate dependency Deformation (µm)

24 Conclusions Combination RICM-AFM: Shape information can be obtained in situ Fewer assumptions on deformation Mechanism necessary PE-Multilayer capsules: deformation described by shell theory shrinking effects upon melting composite shells show two destinct regimes Deflection (µn) Bubble Burst 8 9 <<< trace >>> retrace 10 Microballoons: gas release can be monitored in situ Compressible interior, volume forces dominant Piezo Displacement (µm)

25 Coworkers : F. Dubreuil (microcapsule mechanics) R. Müller (microcapsule T-effects) N. Elsner (microcapsule ph-effects) P. Fernandes, M. Pretzl, C. Hanske (Micro-balloons) Cooperations : PE Capsules: G.B. Sukhorukov (Queen Mary Coll.) H. Möhwald, A. Skirtach (MPI Golm) Micro-balloons: G. Paradossi, F. Cavallieri (University of Rome Tor Vegata ): MB preparation Financial support : DFG, European Framework Program 6 Thank you for your attention!