Short description of our field of interest

Our group has a longstanding experience in synthesizing and characterizing polymeric hydrogels and in constructing and implementing of biomaterials based on hydrogels

Hydrogels, i.e. materials consisting of a permanent, three-dimentional network of hydrophilic polymers and water filling the space between the polymer chains, have a number of biomediclal applications, such as wound care products, dental and ophthalmic materials, drug delivery systems, elements of implants, constituents of hybrid-type organs, as well as stimuli sensitive systems. According to the definition formulated above, hydrogels must be able to hold, in equilibrium, certain amount of water. This implies that the polymers used to produce these materials must have at least moderate hydrophilic character. In practice, to achieve high degrees of swelling, it is common to use synthetic polymers that are water-soluble in non-crosslinked form. Typical simple materials applied for general-purpose hydrogels are poly(ethylene oxide), poly(vinyl pyrrolidone), poly(vinyl alcohol) and poly(hydroxyethyl methacrylate).

Nowadays a new class of hydrogels, capable of reacting to various environmental stimuli as temperature, pH, ionic strength, electric filed etc., is tested for use in the so-called “intelligent biomaterials”. Rapid progress in this field, correlated with increasing demands for more effective medical treatment indicate that there is no exaggeration in including these systems in the list of the “materials of XXI century”.

Except above described macroscopic, continuous hydrogels, obtained by the intermolecular crosslinking of polymer chains, new class of gel-type products – nano- and microgels – are recently under extensive studies. To produce this type of product, it is desirable that intramolecular crosslinking prevails over intermolecular one. The main fields of current and anticipated applications of nanogels are drugs or drug carriers, carriers or cell markers for medical tests, synovial fluid substitutes, blocking agents for dental channels, fast-responsive gels for stimuli-sensitive medical devices etc.

A very efficient, fast and clean method to produce continuous hydrogels out of the variety of hydrophilic polymers basing on radiation techniques have been already developed at the Institute of Applied Radiation Chemistry (ca. 40 papers and 5 patents). So far it is used commercially to produce hydrogel wound dressings, other applications being under way.

Our division is in hold of unique radiation sources to carry synthetic and research procedures mentioned above i.e. semi industrial and research gamma radiation sources and EB radiation source – linear accelerator (6MeV) coupled with a pulse radiolysis set-up, as well as we own the whole array of highly refined research equipment for polymer materials evaluation by its physico-chemical and mechanical properties (see instruments section).

By choosing appropriate irradiation conditions (continuous or pulsed irradiation, dose, dose rate, polymer concentration, additives), one can control the yield, structure and properties of the products. In particular, it is possible either to form a continuous, macroscopic hydrogel (“wall-to-wall” gel), or to synthesize small gel particles of desired dimensions (nanogels, microgels). In order to obtain a macroscopic gel, the chosen conditions should promote recombination between radicals localized on separate macromolecules (intermolecular crosslinking), while nanogels are formed upon recombination of many radicals within a single macromolecule (intramolecular crosslinking). A combination of these two processes leads to structures of intermediate size (microgels).

Nano- and microgel particles until now have had to be produced via classical thermally initiated polymerization. A common disadvantage of this technique is the presence of toxic monomers, crosslinking agents, initiators and other auxiliary substances. Recently it has been shown in our group that a particular kind of radiation technique, namely preparative pulse radiolysis, is an interesting way of synthesizing hydrophilic nanogels (3 papers and a patent). Since the substrates are only polymer molecules and water, one can totally eliminate the use of harmful compounds, as well as the need for purification steps following the classical synthesis. A unique advantage of radiation-induced crosslinking is that by controlling the parameters of the process it is possible to obtain nano- and microgels of desired molecular weight and, independently, is of desired dimensions. This possibility, so far unmatched by classical techniques, is of utmost importance e.g. for development of therapeutic systems based on nanogels.

For more information about hydrogels and radiation-based sythetic methods read the IAEA Report on “Radiation Formation of Hydrogels for Biomedical Applications” by J.M. Rosiak in cooperation with the other Group’s members.

Basic Research Scope

  • Mechanisms and kinetics of radiation-induced (free-radical-induced) reactions of macromolecules and model compounds in solution (nano- and microsecond time-scale measurements by pulse radiolysis with three detection modes: UV-Vis, laser light scattering and conductometry, gamma-ray irradiation, product analysis)
  • Mechanisms and kinetics of radical polymerization and depolymerization in solution
  • Theory of free-radical-induced crosslinking and degradation
  • Intramolecular reactions in polymers
  • Polyelectrolytes and polyampholytes
  • Macromolecules in solution (static and dynamic laser light scattering, triple-detector gel
  • permeation chromatography – GPC(SEC), Pulsed NMR)
  • Modification of natural polymers (e.g. chitosan)
  • Ultrasound sonochemistry of polymers
  • Radical scavengers of high biological importance (e.g. melatonin)
  • Mechanistic and kinetic simulations of fast chemical reactions