Release of radioactive steroids from dried down hydrogels of polyurethane networks

Abstract

SYNOPSISThe polyurethane networks were based on poly(ethy1ene glycol) 6000 (PEG), crosslinked with l,l,l-tris(hydroxy methy1)ethane and with the stoichiometric equivalence of hexamethylene diisocyanate. Radioactive steroids were incorporated into cylindrical hydrogels over a wide range of compositions. The release profiles were drawn from dried down hydrogel of polyurethane networks. The scintillation counter was used for the release study of steroids after different intervals. In viuo, the loaded hydrogels were implanted into rats. The results for constant release studies were recorded. 0 1995 John Wiley & Sons, Inc. I NTRO DUCT10 NStudies of drug release rates from polymeric materials have been made by a number of investigat o r~. ' -~ In a polymeric controlled release system the drugs are released by diffusion, chemicals, swelling, and magnetic processes. The most common mechanism is diffusion through hydrogels, whereby the drug migrates from its initial position in the plastic to the outer surface. In earlier it has been proposed that under certain conditions the rate of diffusion from the surface of the matrix to the surrounding bulk solution makes a significant contribution to the total diffusion process. Haleblian et al.7 also suggested the possibility that the rate of solute transfer across the matrix solution may control the release.In the matrix or monolithic system where the drug is distributed uniformly throughout the polymeric matrix, the drug release does not follow zero-order.8 Lee' has described a n approach to zero-order drug delivery by immobilizing non-uniform drug distribution in hydrogels. Hydrogels can absorb a significant amount of water to form a n elastic gel and a t the same time release the dissolved drug by diffusion through the swollen region.'0," CCC OOZl-8995/95/091301-05 In the present work the influence of hydrogel composition on the resulting release characteristics has been studied. In uiuo, the delivery rates of the drug were determined by surgically implanting or hypodermically injecting the polymeric materials into animals and measuring the radioactivity of steroids at fixed intervals of time. In-vitro, the delivery rates were determined by releasing the steroids in buffer solution a t fixed intervals of time.

Structure and Drug Release in a Crosslinked Poly(Ethylene Oxide) Hydrogel

“…2 In particular, PEO-PU gels have been applied for controlled or sustained release of pharmaceuticals for more than a decade. 10,11 Due to the differences in hydration capability, the PEO groups are water soluble while PU are water insoluble, though both polymers are hydrophilic. By crosslinking PEO with PU in hydrogel formation, degree of hydration in PEO can be controlled, leading to better control in PEO swellability and erodability and, hence, the drug release rate.…”

“…13 Compared with PEO system, drug release from PU hydrogels is less well studied, though examples such as steroidal compounds are available in the literature. 11 More commonly, drug is impregnated in PU stent materials, that is Chronoflex 1 , suitable for use in polymeric tracheobronchial stents, for controlled release purpose. 14 The structure and intermolecular interactions within the hydrogels define the drug-release profile, formulation stability, mechanical and biological properties of these materials.…”