Randall V. Sparer

Controlled release from erod1ble poly(ortho ester) drug delivery systems

Abstract Variable rate zero order release from surface erosion controlled ercdible polyfortho ester) devices was reproducibly attained with the use of latentiated acid catalysts. Various chemical and physical characteristics of the drug release system affected its erosion/drug release performance. The greatest effect was achieved with the choice of anhydride catalyst. A range in release rates of over two orders of magnitude was obtained with acid catalysts having a first pK a from 1.8 (maleic) to 4.3 (glutaric). The control over the erosion rate was extended by altering the amount of catalyst present in the device. Increasing the anhydride content increased the zero order release up to a point, thereafter having no effect. The physical properties of the polymer, such as thermal and mechanical properties, were a function of the molecular weight and composition of the copolymer. Both had an effect on release rate: increasing either molecular weight or glass transition temperature or both decreased the rate. Increasing release rates were observed at higher drug loadings, possibly due to plasticization of the matrix by the drug and/or leaching of the drug by diffusive mechanisms. Release rates were proportional to the surface area and durations were proportional to thickness of the test slabs, agreeing with the proposed surface erosion mechanism. All of these parameters were capable of being adjusted to give zero order release devices covering a wide range of useful release rates.

Effect of an applied electric field on liquid crystalline membranes: control of permeability

Abstract This paper considers the development of liquid crystalline variable permeability membranes. The electrically induced changes in permeability of a liquid crystalline membrane composed of a 23% w/v solution of poly(γ-benzyl-l-glutamate) (PBLG) in dichloromethane are described. PBLG exists in the cholesteric mesophase in solution in a suitable α-helicogenic solvent. When an electric field is applied to a thin membrane comprised of this material, a transition to the nematic mesophase is triggered, and the permeability of the membrane for small organic permeants increases. This increase takes the form of a 50-60% increase in the steady state flux through the membrane.