One approach to the controlled release of drugs involves incorporation of the drug molecules into the matrix of microscopic polymer spheres or capsules. Existing methods for preparing such microparticles do not, however, always guarantee a constant release rate, for example because drug molecules may be trapped preferentially at the surface, because they have to diffuse through an increasing thickness of polymer when the particles are non-eroding or because the surface area changes for eroding particles. In other situations pulsed release may be required--an application to which simple polymer microspheres do not readily lend themselves. Multi-walled microspheres might solve some of these problems. Here we describe a one-step process for preparing double-walled polymer microspheres with diameters ranging from about 20 to 1,000 micrometers. Our technique involves the phase separation of a polymer mixture owing to solvent evaporation: with an appropriate choice of interfacial tensions and evaporation rate, a spherical droplet of one polymer becomes coated with a highly uniform layer of the other. This process, which might be adapted to yield multi-walled microspheres, should make possible the engineering of highly specific drug-release properties.

Multilayered microspheres for drug delivery can be produced by several methods, but most techniques involve several stages and often lead to layers of non‐uniform thickness. The solcent evaporation method of producing double‐layered microspheres described here svoids these difficulties, a single step yielding micrespheres consisting of an inner core of polymer surrounded by a second polymer. The theory is presented and the characterization of the microspheres discussed.

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This paper describes the Fourier-transform infrared (FTIR) spectroscopy of a series of polyanhydrides made of the following diacids: sebacic acid (SA); 1,3-bis@-carboxyphenoxy)propane (CPP); 1,6-bis@-carboxyphenoxy)hexane (CPH); (carboxyphenoxy)methane (CPM); fumaric acid (FA); 5-@-carboxyphenoxy)valeric acid (CPV). All the polymers revealed typical anhydride peaks corresponding to aliphatic-aliphatic, aliphaticaromatic, and aromaticaromatic diads in the wavenumber range 1820-1710 cm-l. Additional paired peaks corresponding to SA-SA diads were identified in the fingerprint region at 1382,1360 and 1307,1286 cm-I. The second pair was assigned to the crystalline regions of the copolymers. This information allows easy identification of bond distribution in a variety of polyanhydrides, and correlates well with information previously presented using nuclear magnetic resonance (NMR) spectroscopy and X-ray powder diffraction.