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Biomedical subjects

B Amsden

Publications and source records attributed to B Amsden.

10 recordsLinked to original sources
PubMed2005

Preparation and characterization of blends of star-poly(epsilon-caprolactone-co-D,L-lactide) and oligo(epsilon-caprolactone).

Polymer blending provides a relatively facile means of combining the separate desirable properties of different polymers into a single material. In this paper blends of a low-molecular-weight star co-polymer of epsilon-caprolactone and D,L-lactide with a linear oligo(epsilon-caprolactone) are prepared and characterized as a possible biodegradable injectable drug-delivery vehicle. The melting characteristics, melt viscosity and degree of crystallinity of the blends were measured, and an in vitro degradation study was performed over a period of 12 weeks. The blends all had a single glass transition temperature and an onset of melting point near body temperature, with the melting point range decreasing as the star co-polymer content increased. The melt viscosity of the blends increased as the star co-polymer content increased, in a manner consistent with miscible blend behavior. The star co-polymer degraded fastest, with a more than 60% mass decrease over the 12-week period. As the oligo(epsilon-caprolactone) content increased, the degradation rate decreased, with the oligo(epsilon-caprolactone) exhibiting a mass loss of only 12% over the 12-week period.

Crystallization↗
PubMed2004

A biodegradable injectable thermoplastic for localized camptothecin delivery.

Camptothecin is an example of a potent drug with a short half-life that would benefit from a localized drug depot system that maintains its stability prior to being released. For this reason, a thermoplastic, biodegradable polymer drug depot was prepared and characterized, and the in vitro release of camptothecin examined. epsilon-Caprolactone oligomers were prepared by ring-opening polymerization initiated by various alcohols. The polymers were characterized via differential scanning calorimeter (DSC) for thermal transitions, and via a parallel plate rheometer for melt viscosity. Camptothecin was loaded into the oligomers and released into PBS buffer. The viscosity of the oligomers was alterable by the initiator used. The oligomers were semi-crystalline with melting points between 37 and 45 degrees C. Camptothecin was released from the oligomers in a diffusion-controlled manner, with the release rate increasing as the melt viscosity of the oligomer decreased. The unreleased camptothecin remained in its active lactone form for a period of up to 16 weeks.

Biocompatible Materials↗
PubMed2002

Biodegradable injectable in situ forming drug delivery systems.

The ability to inject a drug incorporated into a polymer to a localized site and have the polymer form a semi-solid drug depot has a number of advantages. Among these advantages is ease of application and localized, prolonged drug delivery. For these reasons a large number of in situ setting polymeric delivery systems have been developed and investigated for use in delivering a wide variety of drugs. In this article we introduce the various strategies that have been used to prepare in situ setting systems, and outline their advantages and disadvantages as localized drug delivery systems.

Animals↗
PubMed2002

Camptothecin delivery methods.

Camptothecin has shown significant antitumor activity to lung, ovarian, breast, pancreas, and stomach cancers. Camptothecin, however, like a number of other potent anticancer agents such as paclitaxel, is extremely water insoluble. Furthermore, pharmacology studies have determined that prolonged schedules of administration given continuously are required. Thus, this insolubility has restricted its clinical application. For these reasons, a number of water-soluble analogs have been synthesized and a number of different formulation approaches have been investigated. In this review, we examine each of these approaches and discuss their advantages and limitations.

Animals↗
PubMed1999

Diffusion characteristics of calcium alginate gels.

The diffusivity of a protein solute (bovine serum albumin) within calcium alginate gels made from sodium alginate of different guluronic acid content was determined. It was found that protein diffusion within alginate gels, prepared to be isotropic in structure, was greatest for gels prepared from sodium alginate of low guluronic acid content as opposed to those prepared from sodium alginate of high guluronic acid content. This finding was explained in terms of the difference in flexibility of the polymer backbone of the two alginates. The greater the polymer backbone flexibility, the greater the solute diffusivity within the gel.

Alginates↗
PubMed1994

Controlled release of albumin from chitosan-alginate microcapsules.

A polymeric delayed-release protein delivery system was investigated with albumin as a model drug. The polysaccharide chitosan was reacted with sodium alginate in the presence of calcium chloride to form microcapsules with a polyelectrolyte complex membrane. Variables believed to be important for membrane formation were examined; these included reaction time, chitosan molecular weight, alginate concentration, chitosan concentration, and solution pH. An alginate-chitosan reaction time, in the range of 10 to 45 min, had no effect on the release of albumin. Increasing the alginate concentration, however, resulted in a decreased rate of release of albumin (from 37% release at 4 h with 1.5% alginate to 20% release with 2.5% alginate). Another key variable was the chitosan molecular weight. The molecular weight of chitosan was varied from 1.25 x 10(6) to 0.25 x 10(6) through a nitrite oxidation reaction with sodium nitrite. Decreasing the molecular weight increased the release of albumin (from 37% release at 4 h with high molecular weight chitosan to 77% release with low molecular weight chitosan). The pH of the extracapsular environment was found to affect the release of albumin significantly (15% release over 24 h at a pH 3.0 and 73% release at pH 8.0). Capsules produced with high molecular weight chitosan and a combination of high and low molecular weight chitosan gave the best results for reducing elution of albumin in the first 4 h and increasing elution in the following 20 h.

Albumins↗
PubMedDate not supplied

Development of biodegradable injectable thermoplastic oligomers.

Injectable thermoplastic oligomers represent a promising biomaterial for drug delivery provided they possess a melting point at or very near physiologic temperature, as well as a low melt viscosity. One approach would be to prepare an oligolactone. In this paper, we examine the role of different alcohol initiators used in the ring-opening polymerization of epsilon-caprolactone oligomers on the melting point and melt viscosity of the resultant thermoplastics. We found that the initiator used plays a significant role in the final properties of the final oligomer. For primary alcohols, the longer the chain length of the oligomer the lower its melt viscosity, until a chain length of 8 carbons, after which there was no noticeable effect. There was no significant effect observed of primary initiators on the melting point. The use of secondary alcohols produced oligomers with higher viscosities but with reduced overall crystallinity. The use of an unsaturated alcohol, oleyl alcohol, not only reduced the melting point and overall crystallinity but also reduced the melt viscosity of the oligomer. The oleyl alcohol initiated oligomer appears to be a promising vehicle for localized, sustained drug delivery applications.

Biocompatible Materials↗
PubMedDate not supplied

Synthesis and characterization of thermoset biodegradable elastomers based on star-poly(epsilon-caprolactone-co-D,L-lactide).

Biodegradable elastomers represent a useful class of biomaterials. In this paper, we synthesize thermoset elastomers by utilizing the living nature of ring-opening polymerization of a star copolymer of D,L-lactide and epsilon-caprolactone initiated with glycerol and catalyzed by stannous 2-ethylhexanoate. The star copolymers were synthesized of varying molecular weight and monomer composition and cross-linked by compression molding using a dilactone, bis(epsilon-caprolactone-4-yl)propane dissolved in epsilon-caprolactone monomer. The elastomers were then characterized by differential scanning calorimetry and uniaxial tensile testing and their physical properties related to the nature of the star copolymer prepolymers. The results demonstrate a means of predictably altering the elastomer physical properties by adjusting the star copolymer prepolymer initial molecular weight and monomer ratio.

Biocompatible Materials↗
PubMedDate not supplied

Modulation of protein release from chitosan-alginate microcapsules using the pH-sensitive polymer hydroxypropyl methylcellulose acetate succinate.

The release characteristics of protein from chitosan-alginate microcapsules prepared using an electrostatic droplet generator were evaluated. The release studies were undertaken in-vitro in simulated gastrointestinal fluids covering the pH range 1.2-8. Chitosan-alginate microcapsules showed unsatisfactory release properties, losing 94% of the encapsulated proteins (bovine serum albumin) over a 24 h period at pH 1.2. Incorporation of a pH-sensitive polymer, hydroxypropyl methylcellulose acetate succinate (HPMCAS), in the microcapsules, by coating the capsule membrane as well as blending with the capsule core polymer in varying ratios, produced significant changes in the release profiles of the microcapsules. At pH 1.2, the modified microcapsules retained up to 60% of the encapsulated protein after 24 h. The results obtained highlight the potential of HPMCAS as a release-modifier in chitosan-alginate microcapsules.

Aerosols↗