Cross-linked hydrophilic gels from ABA block copolymeric surfactants

The influence of gamma irradiation on the physicochemical properties of a novel triblock copolymer of epsilon-caprolactone and ethylene oxide

A novel triblock copolymer of epsilon-caprolactone (CL) and ethylene oxide (E), CL6E90CL6, intended for use in implantable drug-delivery systems, has been subjected to gamma irradiation, in the solid state and in aqueous solution, under different controlled environmental conditions, to assess its stability to a radiation sterilization process. When copolymer matrices were irradiated with doses of irradiation up to 72 kGy in the presence of oxygen, negligible changes were observed in the molar mass, molecular mobility (assessed by pulsed nuclear magnetic resonance spectroscopy) and thermal properties. However, irradiation of matrices in the absence of oxygen (anoxia) induced the formation of cross-links, as indicated by a reduction in the molecular mobility of the copolymer, but without affecting its molar mass and thermal properties. Gamma irradiation of aqueous solutions of CL6E90CL6 in the presence of oxygen induced random polymer chain scission, as evidenced by a reduction in the molar mass, and the formation of a distribution of copolymer chain lengths in solution. Nuclear magnetic resonance relaxation studies showed that irradiation of solutions of CL6E90CL6 at concentrations greater than 4% w/v under anoxic conditions with doses of 54 kGy produced polymer gels with a network structure. These differences in the effects of gamma irradiation on the physicochemical properties of CL6E90CL6 might be germane to the method selected for sterilization of the polymer before its use in implantable drug-delivery systems.

Stabilization of water/oil/water multiple emulsions by polymerization of the aqueous phases

In order to improve the stability of w/o/w multiple emulsions which have isopropyl myristate as the non-aqueous 'oil' phase, either the internal aqueous phase of the multiple system or the secondary (outer or continuous) aqueous phase can be gelled. Production, by gamma-irradiation, or cross-linked polyacrylamide or poloxamer gels in the aqueous phases of the emulsions leads to systems which have a greater intrinsic stability than untreated multiple emulsions. If the internal aqueous phase is gelled this prevents coalescence. When the continuous outer phase is gelled an opaque emulsion is produced in which the disperse w/o droplets are held in a hydrophilic polymer network from which the droplets are released on contact with water.