Biomedical subjects

M V Sefton

Publications and source records attributed to M V Sefton.

95 records · Page 6Linked to original sources

PubMedDate not supplied

Maintenance of normoglycemia in pancreatectomized dogs with a controlled release micropump.

A diffusion-based insulin micropump was capable of sustaining normoglycemia in diabetic, pancreatectomized dogs for as long as 10 months. Basal insulin delivery was provided by diffusion into the peritoneal cavity from the insulin reservoir across a silicone rubber porous outlet, while the delivery of insulin was augmented for 35 minutes at mealtimes by repeated squeezing of a polyurethane foam disk; the latter was initiated 15 minutes prior to the start of the meal. In the best implant, which functioned for more than 10 months before it was deliberately terminated, the mean glucose level was 126 +/- 24.7 mg/dl (+/- SD) and the mean Schlichtkrull M value was 2.8. In the other three implants, the mean and standard deviations were a little higher. The basal insulin supply was sufficient to restore normoglycemia each morning, while the augmented supply substantially reduced the size of the postprandial period of hyperglycemia. Over the 10 month period studied, the maximum concentration was 150 mg/dl approximately 6 hours after the beginning of the meal, based on the mean of the approximately 200 glucose profiles determined for this implant. Despite this ability to maintain reasonable normoglycemic profiles for long periods, the pump performance deteriorated over this time period, presumably from a tissue reaction to the porous outlet of the implant. This deterioration was evident in the higher levels of glycemia associated with an insulin delivery program that was maintained for too long or in the need to readjust the program to achieve similar levels of glycemia. Nevertheless, the biocompatibility and efficacy of the controlled release micropump demonstrates the feasibility of this approach.

Animals↗

PubMedDate not supplied

Agarose enhances the viability of intraperitoneally implanted microencapsulated L929 fibroblasts.

To achieve immunoisolation, mouse L929 fibroblasts were encapsulated in approximately 400 microm poly(hydroxyethyl methacrylate-co-methyl methacrylate) (HEMA-MMA) microcapsules and were subsequently implanted in the peritoneal cavity of syngeneic C3H mice. As a baseline for the use of genetically engineered cells in cell encapsulation therapy, the L929 cells were transfected to express a secreted form of human alkaline phosphatase (SEAP). Implantation of empty microcapsules in a PBS suspension resulted in deformation, aggregation, and poor retrievability of the microcapsules. Incubation of microcapsules with medium containing xenogeneic horse serum prior to implantation increased the thickness of the fibrous tissue surrounding the microcapsules. However, immobilization of the microcapsules in a 4% (w/v) SeaPlaque agarose gel prior to implantation allowed complete recovery of the microcapsules and prevented their aggregation and deformation. As a result, approximately 50% of the encapsulated cells remained viable 21 days postimplantation. Moreover, once the viable cells were released from retrieved microcapsules and regrown as monolayers, they expressed SEAP at a level similar to their encapsulated but nonimplanted counterparts.

Alkaline Phosphatase↗

PubMedDate not supplied

Metabolic activity and proliferation of CHO cells in hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) microcapsules.

To better understand encapsulated cell behaviour, Chinese Hamster Ovary (CHO) fibroblasts were encapsulated in HEMA-MMA microcapsules and short-term (<2 wks) proliferation and changes in metabolic activity were investigated in vitro. CHO cells were observed to undergo rapid proliferation in the first week following encapsulation after which a growth arrest was obtained at approximately 3500 cells/capsule. The cell growth was localized in aggregates in the capsule core, resulting in high local cell density but low cell density in the whole capsule interior (approximately 10(7) cells/mL). The total metabolic activity, as determined by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium) assay, within the microcapsules increased in the first week, with no significant change afterwards. A broad variation in metabolic activity among the individual capsules was obtained. Supplementing the cell suspension with 20% Ficoll 400 during the encapsulation process resulted in significantly higher morphological uniformity among the individual capsules (with reduced capsule wall thickness and eccentricity); however, this did not change the extent of heterogeneity in metabolic activity. We conclude that viability and proliferation ability (at least to a limited extent) of CHO cells are maintained in HEMA-MMA microcapsules. The local cell growth and subsequent growth arrest remain issues to be addressed in order to obtain better utilization of the microcapsule core volume. Alternatively, small diameter (< 400 microns as opposed to the present approximately 750 microns diameter) capsules are necessary.

Animals↗

PubMedDate not supplied

Microencapsulation of pancreatic islets in a water insoluble polyacrylate.

Rat pancreatic islets were encapsulated in a water insoluble polyacrylate (Eudragit RL), a model polymer, by coaxial extrusion and interfacial precipitation. Despite exposure to organic solvents and nonsolvents (diethyl phthalate, corn oil, and mineral oil) and to shear, the islets survived encapsulation. They continued to secrete insulin into the tissue culture medium and responded to glucose in both static glucose challenges and perifusion assays as well and as long as control islets which were not encapsulated, but were maintained in tissue culture alongside the encapsulated islets. Unfortunately, there was a great deal of variability in the performance of all islets studied, making unequivocal conclusions difficult. Some encapsulated islets survived more than 140 days in vitro and histologically appeared healthy. However, there appeared to be a general deterioration in insulin secretion capacity following prolonged culture in all islets, with corresponding changes (e.g., central necrosis) visible by microscopy. Although Eudragit RL is not practical as an encapsulation polymer, this study was useful in demonstrating that islets may be encapsulated in materials other than alginate-polylysine, and ultimately in materials that may have a more optimum blend of the desired properties: biocompatibility, permselectivity, and mechanical durability.

Acrylic Resins↗

PubMedDate not supplied

A chronic arteriovenous shunt for the testing of biomaterials and devices in dogs.

A technique is described for an extracorporeal arteriovenous shunt in dogs which allows the testing of biomaterials in the shunt for several months in the same animal. The details of the preparation of the tubes and of the surgical technique are given. In contrast to other techniques, encircling ligatures are not placed around the cannulated blood vessels.

Animals↗