Effect of binder additives on terbutaline hydrogels of a‐PVA/NaCl/H 2 O system in drug delivery: I. Effect of gelatin and soluble starch

In order to prepare ecologically and biologically safety physical cross‐linked hydrogel of a‐PVA/NaCl/H₂O system, we prepared blend hydrogel of natural polymeric binders like gelatin and starch in above system, and effect of these binder additives were evaluated on terbutaline release kinetics. Terbutaline (1%) hydrogels of a‐PVA(7%)/NaCl(11%)/H₂O and a‐PVA(7%)/H₂O system (Cyclic FT process) were prepared along with various concentrations of gelatin and soluble starch by feed‐mixture dissolving method. In case of a‐PVA/NaCl/H₂O system only one cycle gelation was done at −20°C for 24 h. On the other hand 3 cycles were done by freezing at −30°C for 16 h followed by thawing at room temperature for 8 h. Drug release was done by paddle method (USP type II) with a rotation of 50 rpm at 37°C in distilled water. Swelling of the gel was done at 37°C for 45 h and melting temperatures of the gel were also studied using the upside‐down test tube method. Comparatively lower values of release rate, diffusion coefficient and kinetic constant were found from the blend hydrogel of a‐PVA/starch/NaCl/H₂O system. When % cumulative release was plotted vs. square root of time it showed straight lines, which indicated Higuchi Matrix Dissolution Model. Inclusion of starch binder increased the degree of swelling compared with that of gelatin. 15 h was found as equilibrium swelling time. A Fickian swelling of this blend hydrogel system indicated the swelling controlled Fickian diffusion type of drug release. Melting temperatures of the blend hydrogels were characteristically higher (94–95°C) than that of cyclic FT (72–76°C), resulting a thermostable hydrogel for biological system. SEM morphological studies of gel surface indicated the well‐developed interpenetrating macromolecular network structure like fish net in starch blend gel prevails over other hydrogel studied here. Gelatin has got characteristic tunnel (200 μm in diameter) inside the macromolecular network that contributes this system higher release kinetics than that of starch.