Copolymerized PEGlyated Acrylate Hydrogels for Delivery of Dicolofenac Sodium - Pharmaceutical Technology

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Copolymerized PEGlyated Acrylate Hydrogels for Delivery of Dicolofenac Sodium
Hydrogels are biocompatible drug delivery systems by which the physical properties can be controlled by the cross-linking density. Hydrogels were prepared by copolymerization of acrylic acid monomers in the presence of poly(ethylene glycol)(PEG) to form polyethylene diacrylate (PEDGA). Various molecular weights of PEGs were used for the synthesis of PEGDA to study the effect of molecular weight of PEG on the properties of hydrogels. These hydrogels were further characterized for free water, swelling..


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Characterization

Differential scanning calorimetry (DSC) . DSC studies of prepared hydrogels were performed to determine their glass-transition temperatures and confirm the formation of hydrogels. The glass-transition temperature of plain PEGDA was 56.42 C, whereas the DSC of the polyacrylate cross-linked with PEGDA showed an endothermic peak at 252.58 C. This temperature was quite higher than the glass-transition temperature of polyacrylic acid (113.6 C) (31). The change in glass-transition temperature indicates that the individuality of PEGDA and polyacrylate had been lost because of the formation of chemical linkage between PEGDA and the acrylic acid polymer. In addition, the increase in glass-transition temperature of polyacrylate from 113.6 C to 252.58 C on cross-linking with PEGDA shows that the thermodynamic stability of the acrylic acid polymer increased because of the formation of cross-linkages.

Morphology. The hydrogels were flexible solids, with somewhat transparent or translucent appearance. On swelling, these became totally transparent. After swelling, their flexibility and rigidity were found to be dependent on the concentration of the cross-linker used. As the concentration of the PEGDA was increased, the flexibility of the hydrogels increased. No significant difference in the morphology of hydrogels, however, was found with the increase in the molecular weight of PEGDA.


Figure 5
Scanning electron microscopy (SEM) was performed to study the internal structure of the hydrogels. SEM photographs (see Figure 5) showed that these hydrogels have a porous polymeric network. Drug molecules can be seen in these photographs in the form of crystals embedded in the hydrogel matrix (see Figure 5b).







Table II: Water uptake and swelling ratio of different acrylic acid hydrogel formulations (n* = 3)
Water-absorbing capacity. Swelling in the presence of aqueous solutions or body fluids is the most important property of a hydrogel. When immersed in aqueous medium, these hydrogels absorb high amounts of water and swell several times their original size. The water-absorbing (hydration) capacity of the hydrogels was studied in terms of percent equilibrium water content and swelling ratio. The hydrogels formed by copolymerization of PEG and acrylate monomers had a very high water-absorbing capacity, absorbing water roughly 2–10 times of their dry weight (see Table II). The homopolymer of acrylic acid can absorb water up to 1.5 times its dry weight.

The equilibrium water content and swelling ratio of the hydrogels formed using the same weight percentage of the PEGDA of higher molecular weight were lower than those found for lower molecular weight PEGDA. Among the hydrogels containing 75% w/w PEGDA, formulation B10 absorbed the maximum amount of water (percent equilibrium water content was 61.16%) and B60 showed minimum water-absorbing capacity (percent equilibrium water content was 55.23%). In the case of the higher molecular weight PEGDA, this result may be attributed to a lower molar percentage of PEGDA, corresponding to the same weight percentage of PEGDA.


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