Preparation and evaluation of microspheres prepared from novel polyester-ibuprofen conjugates blended with non-conjugated ibuprofen.

A novel polyester, poly(glycerol-adipate-co-omega-pentadecalactone) (PGA-co-PL), was conjugated with a model drug, ibuprofen, through the free hydroxyl groups of the former and the free carboxyl group of the latter at various levels of substitution. The conjugated material was processed into microspheres by both emulsion solvent evaporation and spray-drying methods. Samples of conjugated material were also blended with non-conjugated drug and the microspheres produced were evaluated by various methods. Morphologically, the microspheres produced were satisfactory. However, there was some initial burst drug release from all samples, probably due to the presence of non-conjugated drug. Subsequent drug release was very slow due to the relative stability of the covalent bonding of the drug-polyester conjugate. Stability tests showed that storage at high relative humidity resulted in increased burst release.

Synthesis and evaluation of novel polyester-ibuprofen conjugates for modified drug release.

Ibuprofen was conjugated at different levels to a novel polyester, poly(glycerol-adipate-co-omega-pentadecalactone) (PGA-co-PL), via an ester linkage to form a prodrug. The conjugates were characterized by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), infrared (IR), gel permeation chromatography (GPC), ultraviolet (UV), and high-performance liquid chromatography (HPLC). The conjugates had a molecular weight between 18 and 24 kDa, and there was a suppression of the free hydroxyl groups within the conjugated polymer. DSC scans showed a lowering of the melting point (T(m)) when compared with the polyester alone and a difference in the number and area of T(m) peaks. Drug release studies showed an initial burst release (13-18%) followed thereafter by very slow release (maximum 35% after 18 days). Continuous work may produce ester-linked conjugates that are sufficiently labile to allow for complete release of ibuprofen over the time period studied.

Evaluation of ibuprofen-loaded microspheres prepared from novel copolyesters.

The utility of two novel linear random copolyesters to encapsulate and control the release of ibuprofen, via microspheres, was investigated. Various manufacturing parameters, including temperature, disperse phase volume and polymer:ibuprofen ratios were altered during the microsphere production. The effects of these changes on the morphological characteristics of the microspheres, yield, drug loading, encapsulation efficiency and drug release rates were examined. The diameter of the microspheres ranged from 36 to 89 microm and showed both smooth and ridged surfaces. Microsphere diameter was probably determined by the internal phase volume, while surface morphology was controlled by manufacturing temperature. Greater encapsulation efficiency was obtained by increasing the polymer:ibuprofen ratio and by reducing the internal phase volume. For all batches there was an initial burst drug release into phosphate buffer (pH 7.4) over the first 2-4h, which was followed by a much slower release rate over the remaining time period. Drug release rates during both these phases were dependent upon the amount and nature of the polymer in the microspheres, noting that the more hydrophilic polymer provided faster release rates. Ibuprofen solubility appeared to play a dominant role in controlling release, although both encapsulation efficiency and microsphere morphology were also contributing factors.

Uptake and metabolism of novel biodegradable poly (glycerol-adipate) nanoparticles in DAOY monolayer.

A useful route for the development of antitumour therapies is by creating improved methods for delivering therapeutic agents to tumour cells or subcellular compartments and increasing retention of drugs within target cells. In this study, we have characterized nanoparticle (NP) uptake and metabolism by DAOY cells, a human medulloblastoma cell line. NPs were formed from a novel polymer, poly (glycerol-adipate) (PGA), containing Rhodamine B Isothiocyanate (RBITC) as a fluorescent marker. It was observed that the cellular uptake of NPs depends on the incubation time and the concentration of NPs in the culture medium. The studies of retention and metabolism of NPs within cells indicated that 1) faster degradation of NPs within cells compared with that in cell culture medium in vitro; 2) a small fraction of NPs were recycled back to the outside of cell, whereas most NPs entered endosomes and lysosomes; and 3) recycled NPs were re-taken up in the following 2 h incubation time. These studies thus suggested that PGA NPs could be used for localising therapeutic agents into cells, and could provide prolonged drug effects because of their long sustained release in physiological conditions and their rapid release when taken up into cells.

Water absorption and surface properties of novel poly(ethylmethacrylate) polymer systems for use in bone and cartilage repair.

The surface and bulk properties of novel methacrylate polymers prepared by gelling poly(ethyl methacrylate) (PEMA) powder with different ratios of tetrahydrofurfuryl methacrylate (THFMA) and hydroxyethyl methacrylate (HEMA) monomers were investigated. The water adsorption and desorption characteristics of these polymers were measured in water and phosphate buffered saline (PBS). The desorption diffusion coefficients were higher than the adsorption coefficients in both water and PBS. Linear relationships between the equilibrium mass of water taken up and the mass of water desorbed with the concentration of HEMA in the polymer were established. Polymer surfaces were analysed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Surface features varied with polymer composition; during hydration only selective areas of the surface hydrated indicating a heterogeneous surface. Contact angle data showed no trend between the different polymers indicating that contact angles are not an acceptable method of assessing hydrophobicity/wettability of a material which does not have a homogeneous surface. The effect of these bulk and surface characteristics on biological interactions were examined using bovine chondrocytes and human osteoblast (HOB) cell cultures. Cell attachment decreased when HEMA was present in the copolymer.

Measuring enzyme motility in organic media using novel H-D exchange methodology.

A novel deuterium ((2)H) NMR technique as developed for measuring the total number of deuterons exchanged by lyophilised protein samples following hydrogen-deuterium (H-D) exchange. Using this methodology differences in the H-D exchange behaviour of the proteolytic enzyme subtilisin Carlsberg hydrated either in air or an organic solvent were probed as a function of hydration. At low thermodynamic water activity (a(w)), the degree of H-D exchange increased rapidly with hydration (from anhydrous to a(w) 0.22). At a(w) 0.22, subtilisin powders hydrated in air were found to have reached an H-D exchange level comparable to that found upon aqueous dissolution and in agreement with previous studies using lysozyme. Lyophilised subtilisin hydrated in either dichloromethane (DCM) or diisopropyl ether (DIPE) showed a pattern of exchange (vs. a(w)) comparable to that found for powders hydrated in air. However, subtilisin hydrated in n-hexane showed a significant reduction in H-D exchange at all a(w) studied. Control experiments demonstrated that the reduction in H-D exchange observed for subtilisin in n-hexane was not a kinetic effect. This lower level of exchange in n-hexane implies that hydrated subtilisin Carlsberg has a lower conformational motility and more rigid protein matrix.

Interactions of chondrocytes with methacrylate copolymers.

Copolymers of poly(ethylmethacrylate) (PEMA) and tetrahydrofurfurylmethacrylate (THFMA) have been shown to exhibit potential as a biomaterial for use in cartilage repair. However, the interactions of chondrocytes with the polymer surface is not well understood. A series of novel methacrylate copolymers containing PEMA, THFMA and hydroxyethylmethacrylate (HEMA) were prepared and the ability of these various copolymers to support chondrocytes attachment in vitro has been assessed by the Alamar blue assay for cell number and environmental scanning electron microscopy (ESEM). As the mole fraction of HEMA in PEMA/THFMA/HEMA copolymers increased, chondrocyte attachment to the polymer surface in 24 h decreased. Chondrocytes maintained a rounded morphology and were strongly attached on the THFMA/PEMA polymer surface, but as the mole fraction of HEMA increased the cells present became much smaller with fewer cell to cell interactions. The effect of pre-adsorbing fibronectin on to the polymer surface on cell attachment was assessed both in the presence and absence of serum. Chondrocyte attachment was significantly reduced in serum-free medium. Pre-adsorption of fibronectin on to the copolymer surface substantially increased cell attachment in all cases. In conclusion, chondrocyte attachment and proliferation on these copolymers may be controlled by changes in the polymer surface chemistry and is highly sensitive to the presence of proteins either in the culture media or pre-adsorbed on to the copolymer surface.