We are synthetized thermo- and pH-sensitive gels, which are then tested as skin extenders.
Our aim is the development of copolymer and composite hydrogels that, when implanted
under the human skin, swell osmotically and thereby induce skin growth. During the
polimerization reaction we are produced copolymers with varyable composition, which
are proceed from two acrylic compounds [N- isopropyl- acrylamide (NIPAAm), and acrylamide
(AAm)]. The mechanical strength and the swelling stability of the gels are enhanced
by the addition of fillers [Na- montmorillonite (Na- m.) and with alkyl- ammonium
ion organophilized Na- montmorillonites [(C n - m.), n = 4, 12, 18]. With this method
we are synthetized composite- hydrogels. The filler content of composites varies between
1 and 25 wt%. We observed that in the case of composites synthesized with the addition
of fillers, relatively low filler contents (1-5 wt%) resulted in more extensive swelling
and stronger gel structure. In the course of the experiments the monomer composition
of the gels (0/100-100/0 mol% NIPAAm/AAm) and in the case of composites, the quality
(montmorillonite and organophilized montmorillonite) and quantity (1-25 wt%) of fillers
are varied. The extent of swelling and the viscoelastic properties can be manipulated
through the ratios of these parameters. In the case of certain copolymer and composite
gels, values of desorption enthalpy (ΔH m ) corresponding to the actual water contents
were also determined by thermoanalytical measurements (DSC). Swelling values determined
by gravimetry and enthalpies calculated from DSC measurements were found to be in
good correlation. Evaluation and comparison of the rheological and DSC results also
allowed conclusions to be drawn concerning the types of interaction operating among
the three components of the system, i.e. the polymer skeleton, the filler and water
molecules. We found that water molecules within the gel matrix are bound to the 3-D
polymer lattice with bonds of different strengths and the strength of these interactions
are dependent on both hydrophilicity and charge conditions. In the case of hydrophobic
NIPAAm composites a more extensive swelling can be achieved by applying montmorillonite
fillers with hydrophobized surfaces, whereas in the case of hydrophilic AAm-based
composites the use of hydrophilic montmorillonite fillers ensure more extensive swelling.
