Eric A. Schmitt

Influence of formulation methods on the in vitro controlled release of protein from poly(ester) microspheres

Abstract Poly ( dl -lactide/glycolide, 50:50) microspheres containing bovine serum albumin (BSA) were pre-pared with and without Carbopol® 951 (a potential adjuvant agent) by o/o, o/w and (w/o) /w emul-sion methods. The protein loading of the microspheres reached 50%–70% of the theoretical amount of protein put into the formulation medium. The microsphere particle size was approximately 500 μm, 25–100μm, 10–20/nn using o/o, o/w, or (w/o)/w emulsion techniques, respectively. The release of BSA was dependent on the preparation method. The greatest burst of release was found for vacuum-dried microspheres formulated using the (w/o)/w method. This burst effect could be eliminated by lyophilizing the microspheres following their preparation. BSA was released at a higher initial rate from microspheres prepared by the o/w emulsion method that contained Carbopol® 951 than from micro-spheres not containing Carbopol® 951. Release studies also suggested that the release of BSA could be sustained for 54, 36, or 34 days for microspheres prepared by o/o, o/w, or (w/o)/w methods, respectively.

Degradation of poly(ester) microspheres

Biodegradable polymeric microspheres have been prepared by spray drying, precipitation, rotary evaporation and press grinding methods. Erosion of microspheres of poly(lactide), poly(3-hydroxybutyrate), copolymers of lactide and glycolide, and copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate at 85 degrees C and 37 degrees C have been studied using ion chromatography, nuclear magnetic resonance, residual mass measurements, viscometry and gel permeation chromatography. Such studies demonstrated that these polyester matrices degraded via (1) random chain scission and (2) release of soluble monomeric and oligomeric products. Protein release from microspheres prepared by these methods indicated that most of the protein is released before the polymer matrix loses weight.

Preparation and Drug Loading of Poly(Ethylene Glycol)-block-Poly(ε-Caprolactone) Micelles Through the Evaporation of a Cosolvent Azeotrope

AbstractPurpose. The aim of this work was to study the assembly, drug loading, and stability of poly(ethylene glycol)-block-poly(∈-caprolactone) (PEG-b-PCL) micelles. Methods. Three PEG-b-PCL compositions with PCL number average molecular weights of 1000, 2500, and 4000 g/mol were used. The assembly of PEG-b-PCL micelles, induced by the addition of water to acetonitrile (ACN), was characterized with 1H nuclear magnetic resonance spectroscopy (1H-NMR) and dynamic light scattering (DLS) with and without the presence of fenofibrate, a poorly water-soluble drug. PEG-b-PCL micelles with encapsulated fenofibrate were prepared through the removal of a negative ACN-water azeotrope under reduced pressure. Fenofibrate content was measured using reverse-phase high-performance liquid chromatography (HPLC), whereas the kinetic stability of PEG-b-PCL micelles with and without encapsulated fenofibrate was evaluated using size exclusion chromatography (SEC). Results. The critical water content (CWC), the water content at which amphiphilic block copolymer (ABC) micelle assembly begins, was determined using DLS and ranged from 10% to 30% water, depending on both PCL molecular weight and PEG-b-PCL concentration. As the water content was increased, the PEG-b-PCL unimers assembled into swollen structures with hydrodynamic diameters ranging from 200 to 800 nm. The 1H-NMR peaks associated with the PCL block exhibited line-broadening, following the addition of D2O, indicating that the PCL blocks reside in the core of the PEG-b-PCL micelle. With further addition of water, the PCL cores collapsed to form fairly monodisperse PEG-b-PCL micelles (20-60 nm). In the presence of fenofibrate, the CWC value was lowered, perhaps due to hydrophobic interactions of fenofibrate and the PCL block. Further addition of water and subsequent evaporation of the negative ACN-water azeotrope resulted in fenofibrate-loaded PEG-b-PCL micelles of under 50 nm. The extent of fenofibrate encapsulation was dependent on PCL block size. At a polymer concentration of 1.0 mg/ml, PEG-b-PCL (5000:4000) and (5000:2500) micelles could encapsulate more than 90% of the initial loading level of fenofibrate, whereas PEG-b-PCL (5000:1000) micelles encapsulate only 28%. SEC experiments revealed that PEG-b-PCL (5000:4000) and (5000:2500) micelles eluted intact, indicating kinetic stability, whereas PEG-b-PCL (5000:1000) micelles eluted primarily as unimers. Conclusions. PEG-b-PCL in ACN assembles with fenofibrate into drug-loaded polymeric micelles with the addition of water and the subsequent removal of a negative ACN-water azeotrope.

Thermodynamics, molecular mobility and crystallization kinetics of amorphous griseofulvin.

Griseofulvin is a small rigid molecule that shows relatively high molecular mobility and small configurational entropy in the amorphous phase and tends to readily crystallize from both rubbery and glassy states. This work examines the crystallization kinetics and mechanism of amorphous griseofulvin and the quantitative correlation between the rate of crystallization and molecular mobility above and below Tg. Amorphous griseofulvin was prepared by rapidly quenching the melt in liquid N2. The thermodynamics and dynamics of amorphous phase were then characterized using a combination of thermal analysis techniques. After characterization of the amorphous phase, crystallization kinetics above Tg were monitored by isothermal differential scanning calorimetry (DSC). Transformation curves for crystallization fit a second-order John-Mehl-Avrami (JMA) model. Crystallization kinetics below Tg were monitored by powder X-ray diffraction and fit to the second-order JMA model. Activation energies for crystallization were markedly different above and below Tg suggesting a change in mechanism. In both cases molecular mobility appeared to be partially involved in the rate-limiting step for crystallization, but the extent of correlation between the rate of crystallization and molecular mobility was different above and below Tg. A lower extent of correlation below Tg was observed which does not appear to be explained by the molecular mobility alone and the diminishing activation energy for crystallization suggests a change in the mechanism of crystallization.

Controlled Release of Protein and Vaccines from Poly(Ester) Microspheres in Vitro

Biodegradable microspheres of poly(L-lactide) and copolymers of lactide and glycolide have been prepared by spray drying. Degradation studies of these microspheres using residual mass measurements, viscometry and gel permeation chromatography indicated the entire mass of polyester matrices was maintained for 10, 30 days and 6–10 months for 50:50 and 85:15 copolymers and poly(L-lactide), respectively. The continuous drop in polymer intrinsic viscosity and molecular weight during hydrolysis suggested that matrix degradation began as soon as these microspheres were placed in the buffer and that their degradation proceeded through random-chain scission. Protein release, using bovine serum albumin micro-spheres, showed that release from 50:50 copolymer was independent of polymer molecular weight over a range from 31,000 to 93,000. The release was, however, dependent on the polymer composition and BSA loading in the microspheres. A burst-effect was found in the release study for microspheres prepared from copolymers. The identity and integrity of the released protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis on the release products of polymeric microspheres containing BSA, FPL-R and EcoBacR-Plus vaccines. These results suggested that the release BSA (or vaccine) from polymeric microspheres could be sustained for up to one month.

Biodegradable Polymers for the Controlled Delivery of Vaccines

New methods for the efficient and effective administration of vaccines are required particularly with the advent of new synthetic subunit vaccines. This chapter describes the approaches of several research groups to administer vaccines using biodegradable polymer carriers. Delivery systems composed of synthetic poly[esters] and poly[iminocarbonates] and natural (crosslinked serum albumin) biodegradable polymers are described. The antibody levels in response to these systems are presented, and possible mechanisms responsible for the observed effects are discussed. The important questions that need to be answered before this technology can be successfully applied are also discussed.