Evaluation of the diffusion coefficient for controlled release of oxytetracycline from alginate/chitosan/poly(ethylene glycol) microbeads in simulated gastrointestinal environments.
Diffusion studies of OTC (oxytetracycline) entrapped in microbeads of calcium alginate, calcium alginate coacervated with chitosan (of high, medium and low viscosity) and calcium alginate coacervated with chitosan of low viscosity, covered with PEG [poly(ethylene glycol) of molecular mass 2, 4.6 and 10 kDa, were carried out at 37+/-0.5 degrees C, in pH 7.4 and pH 1.2 buffer solutions - conditions similar to those found in the gastrointestinal system. The diffusion coefficient, or diffusivity (D), of OTC was calculated by equations provided by Crank [(1975) Mathematics in Diffusion, p. 85, Clarendon Press, Oxford] for diffusion, which follows Fick's [(1855) Ann. Physik (Leipzig) 170, 59] second law, considering the diffusion from the inner parts to the surface of the microbeads. The least-squares and the Newton-Raphson [Carnahan, Luther and Wilkes (1969) Applied Numerical Methods, p. 319, John Wiley & Sons, New York] methods were used to obtain the diffusion coefficients. The microbead swelling at pH 7.4 and OTC diffusion is classically Fickian, suggesting that the OTC transport, in this case, is controlled by the exchange rates of free water and relaxation of calcium alginate chains. In case of acid media, it was observed that the phenomenon did not follow Fick's law, owing, probably, to the high solubility of the OTC in this environment. It was possible to modulate the release rate of OTC in several types of microbeads. The presence of cracks formed during the process of drying the microbeads was observed by scanning electron microscopy.
Universidade Estadual de Campinas, Faculdade de Engenharia Química, Departamento de Tecnologia de Polímeros, Caixa Postal 6066, CEP 13081-970, Campinas-SP, Brazil.
Maria C Pinto
MC
Cruz
Sergio P
SP
Ravagnani
Fabio M S
FM
Brogna
Sérgio P
SP
Campana
Galo Cardenas
GC
Triviño
Antonio C Luz
AC
Lisboa
Lucia H Innocentini
LH
Mei
D000464:Alginates / Q000737:chemistry*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000737:chemistry; D048271:Chitosan / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D003198:Computer Simulation; D003692:Delayed-Action Preparations / Q000737:chemistry*; D004058:Diffusion; D004337:Drug Carriers / Q000737:chemistry; D005766:Gastrointestinal Contents / Q000737:chemistry*; D020723:Glucuronic Acid / Q000737:chemistry*; D006603:Hexuronic Acids / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008863:Microspheres; D008956:Models, Chemical; D010118:Oxytetracycline / Q000008:administration & dosage* / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*
D000464:Alginates; D000900:Anti-Bacterial Agents; D020099:Coated Materials, Biocompatible; D003692:Delayed-Action Preparations; D004337:Drug Carriers; D006603:Hexuronic Acids; D011092:Polyethylene Glycols; D020723:Glucuronic Acid; D048271:Chitosan; D010118:Oxytetracycline