Positron annihilation and differential scanning calorimetry studies of polyacrylamide and poly(dimethylacrylamide)/poly(ethylene glycol) blends

Tuning the softness of poly(2-hydroxyethyl methacrylate) nanocomposite hydrogels through the addition of PEG coated nanoparticles

HYPOTHESIS

In nanocomposites, several factors govern the enhancement of properties when a nanofiller is added into a polymer matrix. Previously, our group have demonstrated that stabilizing nanoparticles improves the dispersion of nanoparticles in a hydrogel, but their effect on viscoelastic properties remain unclear. We hypothesized that coating the nanoparticles will block matrix-nanoparticle interactions, which would then affect the transfer of stress when the hydrogel is subjected to stress.

EXPERIMENT

To this end, we investigated the effects that nanofillers coated with polyethylene glycol (PEG) of variable molar mass have on the properties of physical hydrogels made from poly(2-hydroxyethyl methacrylate). PEG with molar masses of 6, 20, and 35 kDa were used at different concentrations and the viscoelastic properties of the resulting hydrogels were studied and compared with control hydrogels with and without nanofillers.

FINDINGS

The coated nanofiller resulted in enhanced dispersion stabilization as the molar mass and concentration of the PEG increased. However, there were noticeable changes in viscoelastic properties. In general, the nanocomposite hydrogels exhibited reduced shear modulus, greater creep, and more accentuated shear thinning behaviour. These effects were attributed to hindered matrix-nanoparticle interactions because of the PEG coating, an increased slippage of the PHEMA chains as well as a plasticizing effect.

pH-responsive polymeric micelles of poly(ethylene glycol)-b-poly(alkyl(meth)acrylate-co-methacrylic acid): Influence of the copolymer composition on self-assembling properties and release of candesartan cilexetil

The objective of the present study was to investigate the influence of chemical structure and molecular weight of pH-sensitive block copolymers on their self-assembling properties, the loading and the release of candesartan cilexetil (CDN). Block copolymers of poly(ethylene glycol) and t-butyl methacrylate, iso-butyl acrylate, n-butyl acrylate or propyl methacrylate were synthesized by atom transfer radical polymerization. pH-sensitivity was obtained by hydrolysis of t-butyl groups. The poorly water-soluble drug CDN was incorporated in the micelles and the in vitro drug release was evaluated as a function of pH. The critical aggregation concentration of hydrolyzed copolymers (pK(a)=6.2-6.6) was higher compared to the unhydrolyzed ones. Dynamic light scattering studies and atomic force microscopy images revealed uniform size micelles with aggregation numbers ranging from 60 to 160. The entrapment efficiency of CDN was generally found to be above 90%, with drug loading levels reaching approximately 20% (w/w). Differential scanning calorimetry studies showed the amorphous nature of entrapped CDN. The release of CDN from pH-sensitive micelles was triggered upon an increase in pH from 1.2 to 7.2. These findings suggest that the PEG-b-poly(alkyl(meth)acrylate-co-methacrylic acid)s can self-assemble to form micelles which exhibit high loading capacities for CDN and release the drug in a pH-dependent fashion.