Polymer Networks and Gels

Research People Equipment Publications

Department profile

Investigation of polymer networks and gels pursued in the Department includes:

  • modeling relations between formation, structure, properties and thermodynamics of polymer networks and gels, swelling changes of crosslinked polymers
  • synthesis of polymer networks and gels and their characterization by chemical and physical methods
  • design and synthesis of hydrogel systems for biomedical research and applications such as implants, structured environments for cell cultivation, hydrogels constructs for tissue engineering and drug delivery including 3D digital fabrication methods

Research

Modelling of polymer networks and gels - structures and behavior

The Department is involved in developing and validation of the theory of formation and structure development of macromolecular (polymer) networks and the relation between the network structure and its properties. We carry out research on covalently crosslinked chemical networks as well as on physical networks such as swollen gels where chain junctions are formed due to physical interactions (Fig.1).
A recent application of the statistical branching theory combined with thermodynamics concerns phase separation in polymer networks, induced by pregel and postgel cyclization and crosslinking. We developed a semiempirical model describing the relation between cyclization and a decrease in equilibrium modulus of elasticity.

Coating film formation – polymers protect surfaces

The formation of a polymeric film involves crosslinking and simultaneous solvent release and represents a complex physico-chemical and polymer engineering problem. The system must undergo liquid – solid transition superposed with the gelation process. Typically, evaporating crosslinking layers possess gradients in the normal direction with respect to substrate. Elucidating the polymer film formation process facilitates the optimization of the surface appearance and mechanical properties of the film.
We have studied swollen polymer systems with crosslinked polymer matrix, where the swelling behavior and mechanical response are determined by the molecular structure of the matrix and the surface quality at the polymer-filler interface. The filled systems behave as constrained networks and their swelling and mechanical behavior was simulated using the mean-field statistical mechanics model fed into finite-element (FEM) simulation in three dimensions (Fig. 2).

 
Figure 1: Scheme of macromolecular structure of a three-dimensional polymer network made by crosslinking of multifunctional molecules.   Fig 2: Simulated distribution of volume degree of swelling in a swollen gel calculated using finite element method (FEM) with a swelling model based on the Flory-Huggins approach. The research is conducted in collaboration with the Department of Macromolecular Physics of the Faculty of Mathematics and Physics of the Charles University.

Hydrogel spontaneous microstructuring

The formation of macromolecular networks in a diluted state in the presence of surface-active additives can be accompanied by reaction-induced phase separation that leads to diverse morphologies of the resulting materials (Fig. 3). The department is involved in investigation of methods of tailoring the gel morphology at microscopic level and in characterizing deformation the complex mechanical behavior of microstructured materials.

Fig 3: Morphologies of synthetic hydrogels. The changes in thermodynamic parameters during crosslinking lead to the spontaneous formation of various porous structure. ESEM images. 

 

Hydrogel systems for biomedical research and applications

Hydrogels homes for living cells and engineered tissues

The stiffness and porosity of gel matrix need adjustment to the “needs” of cultivated cells and vice versa; hydrogel composition and properties may trigger specific behavior of growing cell cultures such as cell type differentiation. We are investigating ways how to make gels with arranged pores communicating throughout the whole gel volume and how to precisely tune the pore architecture. Our methods also involve radical polymerization of monomers in presence of inert particulate templates. Chemical composition of the reaction mixture is optimized to control the interactions between the synthetic material and living tissue. Some hydrogels, after certain time of functioning in the living organism, need to be removed. Controlled removal of hydrogel carriers is orchestrated via hydrolytic or enzymatic degradation of incorporated molecules; the synthesis of such degradable molecules is investigated. Recently, promising results in vitro and in vivo were obtained with macroporous scaffolds containing positively charged chemical groups facilitating ingrowth of neural cells.

To attract cells to hydrogel surface, we modify it with chemical compounds, activate functional groups, and subsequently immobilize some bioactive motifs (proteins, oligopeptides, or saccharides) (Fig. 4).

Fig 4: Hydrogel scaffold for cell seeding visualized by confocal light microscopy. The hydrogel and cell nuclei were stained with green and red fluorescent dyes, respectively. 

Nanofibrous hydrogel constructs for medical research – the finest strings

Nanofibrous meshes offer enormously high pore volume and effective barrier to bacteria, viruses and macrophages yet allowing transport of small molecule gases and liquids. Number of small pores between the strings adds up to large total porosity. The architecture of nonwoven nanofibrous mats resembles build of extracellular matrix, a natural environment in which the cell to grow, proliferation and formation of tissues takes place. Department of polymer networks and gels closely cooperates with the Technical University in Liberec (Northern Bohemia) and the Nanovia Ltd., where the nanofibers are made by needle-less electrospinning which allows large-scale production. The working group tightly cooperates on the preparation procedure and designing the composition of polymeric nanofibers for various medicinal applications. Nanofibrous constructs allow incorporation and controlled release of biologically and/or pharmacologically active compounds such as antibiotics, immunosuppressants or anti-cancer agents. The research includes control of the preparation procedure, characterization of the morphology, design of the release experiments imitating physiological environment, analytical quantification of the released compounds and in cooperation with other working groups also biological experiments (Fig. 5,6).

Hydrogels can work – swelling structures for healthy life

Various surgical interventions require a surplus of soft tissue such as skin or gingiva. Current practice involves various designs of tissue expanders that are used pre-operatively to acquire such tissue. We design hydrogel materials capable of defined linear volume change due to liquid uptake in vivo after implantation. The isotropic volume change of the gel allows fine shape adjustment just immediately prior to implantation. Hydrogel also allows the incorporation and subsequent release of drugs such as anesthetics or antibiotics.

 

 

Fig 5: Nanostructured material as drug carrier. The middle layer of fine poly(vinyl alcohol) nanofibers doped with antibiotic gentamicin is embedded within two layers of polyurehtane microfibers. This structure ensures mechanical  durability as well as control of the drug release time. (SEM image)

  

Fig 6: Synthetic hydrogel interpenetrated with natural nanofibers of bacterial cellulose. Nanofibers incorporated in the gel matrix improve mechanical strength of the hydrogel composite, making it a promising material for cartilage repair, such as knee meniscus replacement. (SEM image)

Cooperation

  • Institute of Experimental Medicine of Academy of Sciences of the Czech Republic (MD. Aleš Hejčl, assoc. prof. Pavla Jendelová)
  • Faculty of Science , Charles University in Prague (prof. Zuzana Bosáková)
  • Czech Technical University in Prague
  • University of Chemistry and Technology, Prague
  • Faculty of Textile Engineering, Technical University of Liberec (prof. Lenka Martinová)
  • Faculty of Electrical Engineering and Communication, Brno University of Technology
  • Faculty of Medicine, Masaryk University, Brno
  • Synpo Pardubice, Czech Republic
  • Nanovia Ltd., Litvinov, Czech Republic
  • Chalmers University of Technology, Goteborg, Sweden (prof. Paul Gatenholm)
  • Institute of Macromolecular Chemistry Petru Poni, Academy of Sciences of Romania (Dr. Maria Valentina Dinu, prof. Ecaterina Stela Dragan)
  • Wroclaw Medical University, Poland (Dr. Witold Musial)

 

Funding support

  • Czech Science Foundation
  • Ministry of Education, Youth and Sports of the Czech Republic
  • Ministry of Industry and Trade of the Czech Republic
  • Bilateral research collaboration with Czech and foreign industrial companies

 

BIOpolymer POstdoctoral Laboratory and educational center - BIOPOL

Otto Wichterle Centre of Polymer Materials and Technologies - CPMTOW

Centre of Biomedicinal Polymers - CBMP

Centre of Polymer Sensors - CPS

Polymers for Power Engineering - Energolab


 

Institute of Macromolecular Chemistry AS CR, v.v.i.
Heyrovského nám. 2
CZ-162 06 Praha 6
Czech Republic
phone:+420 296 809 111
fax:+420 296 809 410

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