Nanogels are crosslinked particles of sub-micrometer size made of hydrophilic polymers. They are soluble in water, but have properties different from linear macromolecules of similar molecular weight. Such structures, along with their bigger analogues - microgels - have a number of practical applications, mostly in medicine (for example in stomatology) and pharmacy (stimuli-sensitive drug delivery systems). They are also being used as nanocatalysts and water purification systems.

     Micro- and nanogels can be synthesized by combined polymerization and crosslinking, usually in emulsion. A drawback of this procedure, especially when the products are designed for biomedical use, is the presence of monomers and crosslinking agents that are usually toxic and have to be removed from the system after the synthesis.
 
 

     We have proposed a different synthetic approach, eliminating the use of monomer and crosslinking agents . In our method the substrates - macromolecules of high molecular weight - are subjected to short, intense pulses of fast electrons in dilute, deoxygenated aqueous solution. The primary products of radiolysis - hydroxyl radicals and hydrogen atoms - react with macromolecules and, as a result, polymer radicals are formed. When appropriate conditions are chosen these radicals undergo mainly intramolecular recombination.
The product is a macromolecule internally crosslinked with covalent C-C bonds, i.e. a stable nanogel. Under such conditions a relatively weak or even negligible increase in molecular weight is observed. Decrease in radius of gyration indicates a strong shrinkage of the polymer coils resulting from intramolecular crosslinking.
  
 

      Great advantage of this method, which is applicable both for neutral polymers and for polyelectrolytes, is the elimination of the use of monomer and crosslinking agents, which have to be removed from the system after the synthesis - especially when the products are designed for biomedical use.

The possible directions of applications of such nano(hydro)gels are being tested:

  filling of human teeth microchannels in order to prevent caries and hypersensitiveness of tooth necks

  drug delivery system (DDS) which can mimic the secretory granule action, i.e. synthetic systems that in respond to the inner signal are able the release the loaded drug in seconds (an idea proposed by other authors in Nature 1998, vol. 394, pp.459-462))

  formation of metallic catalysers in atomic spreading

The nanogel production technology has been submitted to Polish Patent Office
Application No. P-334602 (1999)