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Biomedical subjects

M F Goosen

Publications and source records attributed to M F Goosen.

27 records · Page 2Linked to original sources
PubMed1982

Insulin-albumin microbeads: an implantable, biodegradable system.

A feasibility study on developing an implantable, biodegradable insulin delivery system was carried out. Insulin-albumin microbeads (50-1,000 microns diameter) were implanted in diabetic rats. After a single subcutaneous implant of the glutaraldehyde crosslinked microbeads, elevated blood-insulin levels were detected in the diabetic animals for longer than two months. While the blood-insulin levels of the treated animals were sustained between 10 and 67 microU/ml during the initial two month post-implantation period, complete in-vivo biodegradation of the microbeads took longer than five months. The diabetic animals, with the insulin-albumin microbead implants, gained weight. In contrast, untreated diabetic controls lost weight. Fibrous capsules were found to have surrounded the microbeads when the implants were recovered at one and two months post-implantation. The results suggest that the fibrous capsules played a role in retarding insulin release from the albumin microbead system. Cross-linked serum albumin microbeads have the clinical potential of providing long-term in-vivo drug release. This system has the additional advantage of being biodegradable and also provides more options for the method and site of implantation.

Animals↗
PubMed1979

Heparinized styrene-butadiene-styrene elastomers.

A heparinized high-strength elastomer has been developed which is potentially useful as a nonthrombogenic vascular prosthesis. A surface hydroxylated styrene-butadiene-styrene (SBS) block copolymer with at least 40% extent of reaction after glow-discharge cleaning was coated with a 20% acetylated polyvinyl alcohol/heparin mixture containing glutaraldehyde and magnesium chloride. After curing at 80 degrees C for 100 min, the polyvinyl alcohol, heparin, and hydroxylated SBS were covalently bound to each other by acetal bridges. The effects of the various substrate and coating parameters were optimized to achieve very strong adhesion between the coating layer and the surface hydroxylated SBS. Heparin was not leached from the surface of the new material using 3M saline at pH 7.4 despite a detection limit of 10(-5) micrograms heparin/cm2 min. Prolonged partial thromboplastin times of greater than 1200 sec were observed (control: PTT = 120 sec). Preliminary ex vivo testing using a simple arteriovenous shunt in the leg of a rabbit showed good thromboresistance. The heparinized SBS shunt chamber remained patent for more than two hours without desorption of heparin. It was concluded that surface hydroxylated SBS heparinized by acetal coupling owed its thromboresistance to the heparin covalently bound to the surface and not to a microenvironment of heparin in solution at the blood/material interface.

Biocompatible Materials↗
PubMedDate not supplied

Recombinant beta-galactosidase production in serum-free medium by insect cells in a 14-L airlift bioreactor.

Spodoptera frugiperda (Sf9) insect cells were successfully cultured in serum-free medium in a 14-L airlift bioreactor. Cell densities as high as 1 x 10(7) cells/mL were achieved with specific growth rates of approximately 0.0286 h-1 (doubling time of 24 h). This system was also used to demonstrate the expression of a reported gene, beta-galactosidase (beta-gal), when cells were infected with a recombinant baculovirus. Approximately 0.33 mg of beta-gal/mL (i.e., 104,000 units/mL) of medium were obtained at the 14-L scale, while about 0.95 mg of beta-gal/mL (i.e., 285,000 units/mL) of medium were obtained in small-scale shaker flasks. The difference was attributed to a suboptimal infection in the large scale. Specific oxygen consumption rates decreased from 5.58 x 10(-17) mol O2/cell.s in early exponential growth to 3.13 x 10(-17) mol O2/cell.s at 3 days post-infection.

Animals↗
PubMedDate not supplied

Protective effects of polymer additives on animal cells exposed to rapidly falling liquid films.

The protective effects of polymer additives on insect cells against fluid mechanical damage was investigated in a falling film-flow device. The falling liquid film creates rapidly moving air-liquid interfaces and high fluid shear stress, mimicking the characteristics of a bursting bubble in aerated cell culture. The additives tested included a group of surface-active polymers, (i.e., Pluronic F68, poly(ethylene glycol)s, and Tween 80) and a group of viscosity-enhancing polymers (i.e., dextrans, methyl-cellulose, and (carboxymethyl)cellulose). We found that methylcellulose, which was previously considered a viscosity-enhancing polymer, actually had significant surface-active properties. All of the surface-active polymers exhibited significant protective effects, with Pluronic F68 and the higher molecular weight poly(ethylene glycol), PEG 20M, providing the best protection. In contrast, the viscosity-enhancing polymers, with the exception of methylcellulose, showed little or no protection for insect cells in the film flow. All of the protective polymers had surface-active properties, even though some of them did not change the surface tension in the actual insect cell medium. There was no correlation between the protective effect and the changes in liquid viscosity and surface tension due to the polymer additives. The level of protection was shown to be dependent upon the type of polymer, its concentration in the culture medium, and the polymer molecular weight. We concluded that the mechanism of protection of these surface-active polymers was through interaction of the polymer molecules with the cell plasma membranes: a fast-acting biological mechanism.

Animals↗
PubMedDate not supplied

Electrostatic encapsulation and growth of plant cell cultures in alginate.

The growth of callus tissue from African Violets, encapsulated in alginate using electrostatics, was investigated as well as the mechanism of alginate droplet formation. Alginate microbeads as small as 500 (+/-50) microns in diameter could be produced by electrostatic extrusion directly from a plastic syringe (1900 micron extrusion orifice), in the absence of a needle. Video analysis of the mechanism of electrostatic alginate droplet formation from the syringe showed the development of a Taylor cone-like droplet which extended to form a thin strand that then broke up into droplets. Autoclaving of the alginate/medium solution significantly reduced its viscosity, giving smaller beads. Calculated microbead diameters agreed well with experimental values. Callus tissue from leaf explants was successfully immobilized and cultured using electrostatic extrusion. Tissue immobilized using 4% alginate in medium and cultured on agar grew best, producing a complete plantlet within four months. The long-term aim is to develop an effective method for large production of artificial seeds.

Alginates↗
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↗