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TU Berlin

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1. Microgels at surfaces


The synthesis and characterisation of microgels based on NIPAM is the main topic of the present research. Not only pure NIPAM but also microgels with different co-monomers are in the focus. The project addresses the comparison of the swelling/shrinking behavior in bulk (DLS) and after adsorption on substrates (AFM, contact angle). The characterization (size, elasticity, ...) of the synthesized particles is done by atomic force microscopy (AFM) in air and in liquid medium. Special focus is the on the viscoelastic properties studied by AFM indendation.

Contact: Marcel Richter

Selected Publications

Burmistrova, A.; Richter, M.; Üzüm, C. & von Klitzing, R.
Effect of cross-linker density of p(NIPAM-co-AAc) microgels at solid surfaces on the swelling/shrinking behaviour and the Young's modulus. Colloid Polym. Sci., 2011, 289, 613-624

Burmistrova, A.; Richter, M.; Eisele, M.; Üzüm, C. & von Klitzing, R.
The Effect of Co-Monomer Content on the Swelling/Shrinking and Mechanical Behaviour of Individual Adsorbed pNIPAM Microgel Particles. Polymers, 2011, 3, 1575-1590 

2. Microgels with gold nanoparticles

Details coming soon...

Contact: Sarah Turner, Kornelia Gawlitza

3. Microgels and proteins

Enzymes are very important as biocatalysts. For the application in industrial processes it is necessary that the used enzymes are stable at high temperatures, at different pH values and in the presence of organic solvents. One method to achieve such stable systems is the embedding of enzymes into polymer matrices. Microgels made of poly-N-Isopropylacrylamide (p-NIPAM) show a reversible shrinking above the volume phase transition temperature (VPTT). This behavior makes them a promising system as matrix for the embedding of organic particles. In order to get the possibility to make the microgels visible with a confocal laser scanning microscopy (CLSM) we synthesize p-NIPAM microgels up to a diameter of 1.7 µm using a temperature ramp during the polymerization.

Schematic process of the immobilization of enzymes wihtin p-NIPAM hydrogel particles

The enzymes lipase B and peroxidase were immobilized within large p-NIPAM microgel particles via a solvent exchange. Using CLSM it has been proven that the enzymes are immobilized within the polymer network. In comparison with the non-immobilized enzymes, the immobilized systems show an enhanced activity in organic solvents. Furthermore, immobilized Lipase B shows a high stability and reusability. The immobilization within a higher cross-linked p-NIPAM microgel leads to a system where the supply of the substrate can be controlled by the temperature. Hence, the activity can be switched on and off. These properties make the presented systems promising biocatalysts, especially for chemical synthesis.

Contact: Kornelia Gawlitza

Selected Publications

[1] Gawlitza, K.; Wu, C.; Georgieva, R.; Wang, D.; Ansorge-Schumacher, M.B.; von Klitzing, R.
”Immobilization of lipase B within micron-sized poly-N-isopropylacrylamide hydrogel particles by solvent exchange”
Phys. Chem. Chem. Phys. 2012, 26, 12980-12987.

[2] Gawlitza, K.; Wu, C.; Georgieva, R.; Ansorge-Schumacher, M.B.; von Klitzing, R.
”Temperature Controlled Activity of Lipase B from Candida Antarctica after Immobilization within p-NIPAM Microgel Particles”
Z. Phys. Chem. 2012, 226, 749-759.

[3] Gawlitza, K.; Georgieva, R.; Tavraz, N.; Keller, J.; von Klitzing, R.
”Immobilization of Water-Soluble HRP within Poly-N-isopropylacrylamide Microgel Particles for Use in Organic Media”
Langmuir 2013, 29, 16002-16009.

4. Biocompatible, thermoresponsive microgels based on Poly(Ethylene glycol) (PEG)

Due to their reversible temperature induced volume phase transition (VPT), microgels made of poly-N-Isopropylacrylamide (p-NIPAM) served as model systems for basic research and have been intensively studied, e.g. their swelling behavior and internal structure. Although this microgel system is a useful model system and seems to be promising for pulsatile drug delivery, the fact that the NIPAM monomer is carcinogenic or teratogenic limits its application in biomedical applications. The presented project deals with the synthesis and characterization of biocompatible PEG based microgels. Fundamental properties are studied in bulk as well as after deposition on Silicon wafers using Dynamic Light Scattering (DLS), Small Angle Neutron Scattering (SANS) and Atomic Force Microscopy (AFM). The synthesis was done by precipitation polymerization using 2-(2-methoxyethoxy)ethyl methacrylate (MeO2MA) as monomer, Poly(ethylene glycol) methyl ether methacrylate (OEGMA) as comonomer and Ethylene glycol dimethacrylate (EGDMA) as cross-linker.

Swelling curves of PEG microgels with 5%, 17%, 26% comonomer (a) and temperature dependent AFM images of PEG microgel with 17% comonomer measured against water at different temperatures (b).

Bulk studies offered that the size, the VPTT, the charge and the internal structure of the microgel particles can be adjusted by the amount of OEGMA. Furthermore, the synthesized PEG based microgels can be easily adsorbed onto Silicon surfaces without modification of the wafer surface. AFM measurements in aqueous environment show that the microgel particles exhibit vertical and horizontal swelling behavior even after adsorption. The combination of thermosensitivity and biocompatibility make these microgels interesting alternatives for p-NIPAM, especially for the usage in long time biomedical applications.

Contact: Kornelia Gawlitza



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