SYNOPSISMacroporous hydrogels are characterized by large pore sizes, high pore volumes, and high specific surface area. Besides these characteristics, macroporous hydrogels based on thermally reversible polymers respond to temperature changes much faster than hydrogels prepared by a conventional method. Crosslinked poly ( N-isopropylacrylamide ) (polyNIPAAm) forms a thermally reversible hydrogel which shows a lower critical solution temperature (LCST) ca. 33°C in aqueous solutions. We have synthesized thermally reversible polyNIPAAm hydrogels having macroporous structures by a new method. These macroporous hydrogels have large pore volumes, large average pore sizes, and faster macromolecule permeation rates in comparison to conventional polyNIPAAm hydrogels synthesized by a conventional method. Compared with conventional polyNIPAAm hydrogels, the macroporous polyNIPAAm hydrogels have higher swelling ratios at temperatures below the LCST and exhibit faster deswelling and reswelling rates. The deswelling rates are especially rapid. These thermally reversible macroporous hydrogels may be very useful in controlled active agent delivery and toxin removal, as we11 as dewatering of solutions. Peptides or proteins may behave as if they were in bulk solution within the large aqueous pores, and this may reduce their inactivation when such gels are used for their storage and later release. The gels may also be useful in microrobotic devices due to their fast response to temperature. 0 1992 John Wiley & Sons, Inc.

A series of previously-synthesized lactic/glycolic acid polymers (PLGA) with various molar ratios of lactic to glycolic acid and various molecular weights were further studied with regard to their biodegradation behavior, and in particular, the factors affecting the biodegradation rate. The biodegradation of PLGA is affected by many factors including polymer composition, molecular weight, and nature of the incubating media. The biodegradation rate of PLGA containing higher content of lactic acid moiety is lower than those containing a lower content of lactic acid moiety. PLGAs with a higher molecular weight, degrade faster than those with a lower molecular weight, i.e. the molecular weight decreases more rapidly for higher molecular weight PLGAs than their lower molecular weight counterparts. Nature or properties of the hydrolysis/incubating media may have an effect on the biodegradation of PLGAs. A basic medium may slow down the biodegradation of PLGA in comparison with samples in an acidic medium. The rate of pH reduction for the incubating medium can be divided into three deferent phases, giving an inverted S-type pH profile for the non-buffered incubating media.

No abstract

The purpose of this work was to develop and characterize a protein and peptide injectable drug delivery system in agarose hydrogel nanoparticles. The nanoparticles were prepared by using a new emulsion-converted-to-suspension in situ method. This is an emulsifier-free method that has advantages for protein and peptide drug encapsulations. Ovalbumin, used as a model protein drug, was successfully encapsulated into nearly spherical agarose hydrogel nanoparticles under mild conditions. The nanoparticles possessed a log-normal size distribution with an average size of 504 nm. They imbibed a large amount of water (66.85% to 84.33%) and the water content was a function of temperature; the water content increased with increase in temperature. Release studies of the ovalbumin from the agarose hydrogel nanoparticles revealed a diffusion-controlled release mechanism with a temperature dependence; the ovalbumin release rate was higher at 37 degrees C than that at room temperature. The great biocompatibility of agarose hydrogel, plus the mild conditions for drug encapsulation, make the agarose hydrogel nanoparticles a potential system for protein and peptide drug delivery.

The nanoencapsulation of a model protein drug, bovine serum albumin (BSA), using gelatin as the matrix material is reported. Nanoencapsulation was conducted using a modified water-in-oil (w/o) emulsion method, which is emulsifier-free and simple. The nanoencapsulation product, BSA-containing gelatin nanoparticles, is characterized in terms of nanoparticle morphology, size and size distribution, water content, and in vitro protein release. The BSA-containing gelatin nanoparticles obtained from this nanoencapsulation process are nearly spherical and have a log-normal size distribution. The average diameter of the BSA-containing gelatin nanoparticles is approximately 840 nm. They can absorb 51-72% of water. In vitro release experiments demonstrate that BSA has been successfully encapsulated in, and can be released from the gelatin nanoparticles. The release of BSA from the gelatin nanoparticulate matrix follows a diffusion-controlled release mechanism. It is found that temperature affects both the water content and the BSA release rate of the gelatin nanoparticles.