Cross-linked Microspheres Research Articles

Synthesis of cross-linked polymer microspheres in supercritical carbon dioxide

Synthesis of cross-linked polymer microspheres in supercritical carbon dioxide

Anti-Tumor Effect of Mitoxantrone-Loaded Bovine Casein Microspheres on Ehrlich Ascites Carcinoma in Mice

AbstractThis work was supported with a grant SP/SO/D-21/89 from the Department of Science and Technology, Government of India. A. J. thanks the Director, TBG&RI for collaboration and Prof. E. P. Goldberg of the University of Florida, USA for a generous gift of mitoxantrone.Glutaraldehyde cross-linked bovine casein microspheres loaded with the antineoplastic agent mitoxantrone were prepared and in vitro release of the drug into phosphate buffer was examined at 37°C. In the absence of any proteolytic enzymes, the release reached a steady state within a week, releasing only 17–40% of the incorporated drug, depending on the initial payload. In the presence of an enzyme such as protease, however, 100% release was seen in vitro in 2–3 days. The antitumor effect of mitoxantroneloaded microspheres was evaluated in Swiss albino mice bearing Ehrlich ascites carcinoma (EAC) by intraperitoneal injections. The mean survival time of mice receiving 1 mg of mitoxantrone as free drug was 4.6 ± 0.67 days as opposed 37.7 ± ...

Solvent effects on the formation of cross-linking microspheres in γ-irridiated solutions

Solvent effects on the formation of cross-linking microspheres by the radiation-induced polymerization are described. Polymerization of some bi- and tri-vinyl monomers in several organic solvents was tested. Diethylene glycol dimethacrylate (2G) is the unique monomer that gives microspheres. The distance between two vinyl groups of monomer molecules is one of the important factors for the formation of microspheres. The comparison of the solvent properties for the preparation of microspheres suggests that the forms of the monomer molecules in the solutions are also important, that is, the stretched form is favorable. Alcohols, except t-butanol, are not favorable as the solvents for the preparation of microspheres because of not only solubility but also an occurrence of the chain transfer reaction. The chain transfer reactions to the solvents and additives interfere with the formation of microspheres.

Formation of polymeric microspheres using electron beam radiation

AbstractPolymeric particulates are currently being produced by a variety of different techniques. This new approach illustrates the formation of cross‐linked polymeric microspheres by incorporating trimethylolpropane propoxylate triacrylate (a radiation‐sensitive monomer) into a polyaphron system and exposing it to electron beam radiation. Polyaphrons are essentially a collection of droplets encapsulated in a very thin aqueous film dispersed in a aqueous matrix. This film gives extreme stability to the system, which allows for extremely high dispersed‐phase concentrations. The formation of polyaphrons requires the presence of a surfactant in both the dispersed (monomer) and continuous (aqueous) phases. The effects of monomer‐phase concentration, monomer‐ and acqueous‐phase surfactant concentration, aqueous‐phase surfactant type, and preparation temperature were studied to gain an understanding of the conditions that promote the formation of polymeric microspheres with a narrow size distribution. Polymeric microspheres ranging from 2 to 40 microns in diameter were formed with monomer concentrations as high as 67 vol % without any aphron bridging occurring or need for agitation to keep the monomer‐phase dispersed in the aqueous matrix. In addition, the ability to reduce the wettability of the microspheres is demonstrated through incorporation of a polymerizable fluorinated acrylate in the dispersed phase.

Controlled Release of Fibroblast Growth Factor: Activity in Cell Culture

ABSTRACTBasic fibroblast growth factor is a multi-potent cell regulatory factor that stimulates proliferation and angiogenesis. Controlled studies of basic fibroblast growth factor in animals have been hindered by the instability of this protein. In addition, many cells appear to require the continuous addition of basic fibroblast growth factor for optimal growth and function in culture. A system for the sustained delivery of active basic fibroblast growth factor might provide both a means to conduct log-term studies on activity and provide a practical alternative to multiple growth factor additions to cell cultures. Basic fibroblast growth factor was incorporated into standard polymer matrices, but the released growth factor had lost over 99% of its bioactivity. Loss of basic fibroblast growth factor activity was found to result from both physical inactivation and adsorption of the protein to surfaces. These problems were avoided by incorporating the growth factor into calcium cross-linked alginate microspheres containing heparinsepharose beads. Basic fibroblast growth factor was incorporated into these microspheres with 71% efficiency and active growth factor was released with predictable kinetics for up to 7 weeks. Release from these microspheres was controlled by the amount of heparin within the device and could be manipulated by simply altering the heparin content during fabrication. Alginate/heparin-sepharose microspheres were placed into growing cultures of bovine aortic endothelial cells and no cytotoxic effects were observed. Furthermore, microspheres containing growth factor provided long-term stimulation of cell proliferation and maintenance of endothelial cell morphology.

In vitro release of adriamycin from drug-loaded albumin and haemoglobin microspheres.

Release of adriamycin from albumin and haemoglobin microspheres has been determined in vitro using a flow through system. Release from cross-linked albumin microspheres is controlled by the percentage of glutaraldehyde used but release profiles of spheres of 23, 41 and 60 microns diameter were virtually superimposable. Not all of the adriamycin is released from the microspheres over 20 h; as biodegradation occurs in vivo after 24 h the amount of drug remaining in the system at 20 h is likely to be principally released by degradation of the protein matrix in vivo. Estimates of the retained adriamycin vary from 16-26 per cent for albumin (n = 3) and 30 per cent for haemoglobin (n = 1).