PubMed · 9370650
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V Pink. 1997-09-24. Getting needled.. https://doi.org/10.7748/ns.12.1.21.s40
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Interpenetrating polymer network (IPN)-structured hydrogels of gelatin (Gtn) and dextran (Dex) were prepared with lipid microspheres (LMs) as a drug microreservoir, and LM release from these hydrogels was examined in relation to their dual-stimuli-responsive degradation. A phase morphology in the IPN-structured hydrogels was varied with the preparation temperature, i.e. above or below the sol-gel transition temperature (Ttrans) of Gtn. The IPN-structured hydrogel prepared below Ttrans exhibited a specific degradation-controlled LM release behavior: LM release from the hydrogel in the presence of either alpha-chymotrypsin or dextranase alone was completely hindered, whereas LM release was observed in the presence of both enzymes. It is concluded that dual-stimuli-responsive drug release can be achieved by specific degradation of a particular IPN-structured hydrogel.
Ethylene vinylacetate polymer (EVA) has been used for many years to fabricate controlled-release polymeric implant devices with which drugs of high or low molecular weight compounds could be delivered with zero-order kinetics. However, because the known fabrication methods such as solvent evaporation, casting and possible shrinkage are not sufficiently controllable we have now developed the microextrusion method with which even small amount of clinically important and expensive drugs can be incorporated into EVA with high reproducibility. We show here that devices produced by the microextrusion method allows for a controlled delivery of several neurotoxic and neurotherapeutic compounds such as alpha-methyl-p-tyrosine, diazepam, quinolinic acid, and phencyclidine. Each substance is slowly released from the polymer, as evidenced by spectrophotometric data, for up to 120 days at daily rates varying from 18.4 microg of phencyclidine to 97.6 microg/day of diazepam. Thus, microextrusion is a valuable method for fabricating controlled-release polymers in which small amounts of scarce drugs can be incorporated. Another advantage of the current procedure is that polymers can be fabricated with very little amount of solvent.
Statistical designs were used to study the effect of certain matrix formulation variables on the vitro release of a model compound, pseudoephedrine hydrochloride, from layered diffusional matrices designed for zero-order sustained release. These matrices consist of non-swellable, hydrophobic middle layers containing the active drug to which hydrophilic and/or hydrophobic barrier layers are press-coated. In general, linear release profiles can be obtained by applying hydrophilic barrier layers on both faces of a hydrophobic matrix tablet, or by applying a hydrophilic barrier layer on one face and a hydrophobic barrier layer on the other face of the matrix tablet. However, formulation and matrix variables in the barrier layers need to be controlled in order to achieve zero-order drug release from a hydrophobic matrix tablet coated with hydrophobic barrier layers on both faces.