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Biomedical subjects

J M Pollok

Publications and source records attributed to J M Pollok.

8 recordsLinked to original sources
PubMed1998

Formation of spheroidal aggregates of hepatocytes on biodegradable polymers under continuous-flow bioreactor conditions.

Our laboratory has investigated heterotopic hepatocyte transplantation on biodegradable polymer matrices as an experimental treatment for end-stage liver disease. One of the limitations has been survival of sufficient cell mass after transplantation. We hypothesize that in vitro conditioning of cells within polymer matrices prior to implantation may increase hepatocyte survival and function. In this preliminary study we investigated the effect of continuous flow on hepatocytes and sinusoidal endothelial cells on poly-L-lactic acid (PLLA) discs in vitro. Highly porous PLLA discs were manufactured measuring 18 mm diameter by 1 mm thickness using previously described techniques. Hepatocytes were isolated from adult, male Lewis rats (200-300 g) using a two-step collagenase digestion. Sinusoidal endothelial cells were isolated using a two-step collagenase digestion, differential sedimentation, Percoll gradient centrifugation, and selective adherence. PLLA discs were seeded with hepatocytes alone or with co-cultures of hepatocytes and sinusoidal endothelial cells. Seeded discs were then secured within a flow bioreactor chamber and exposed to continuous flow of culture media at a rate of 20 ml/minute through the chamber. Seeded discs placed in static culture conditions served as controls. Specimens seeded with only hepatocytes were harvested at 24 hours, 48 hours, and 168 hours after seeding. Co-culture specimens were harvested after 168 hours. Specimens were viewed under phase-contrast microscopy and then formalin-fixed and prepared for histologic sectioning. Sections were stained with Hematoxylin and Eosin and then analyzed with light microscopy. Hepatocytes under flow conditions formed spheroidal aggregates of cells of 50 to 200 microns in diameter by 24 hours in culture. Hepatocytes in static conditions showed decreased aggregation of cells and spheroid formation was absent. Co-cultured specimens under flow also showed spheroid formation with endothelial cells lining the outside of hepatocyte spheroids. Co-cultured specimens in static culture showed no spheroid formation and no organization between sinusoidal endothelial cells and hepatocytes. These results suggest that continuous flow increases organization of hepatocytes cultured within biodegradable polymer matrices.

Animals↗
PubMed1998

[Immuno-isolation of xenogenic islands of Langerhans in a tissue engineered autologous cartilage capsule].

Islet transplantation is a potential cure for diabetes mellitus. The major problem for clinical application remains the prevention of transplant rejection without major side effects. Broad application in early disease will make the usage of xenogeneic tissue necessary. Immunoisolation is an experimental strategy to prevent rejection, by separating the transplanted allogeneic or xenogeneic cells from the host immune system using a barrier device. Current methods of immunoisolation use artificial, not completely inert materials as barrier devices and induce an unwanted foreign body reaction. Using recipient own cells for encapsulation the foreign body reaction could be prevented. This study describes a new method of encapsulation of islets of Langerhans within a capsule of chondrocytes, which may serve as an immunoisolation barrier utilizing the immunoprivileged properties of the chondrocyte matrix and demonstrates the functional survival of the encapsulated islets in vivo.

Animals↗
PubMed1997

The effect of donor and recipient age on engraftment of tissue-engineered liver.

A novel treatment for end-stage liver disease using heterotopic hepatocyte transplantation on biodegradable polymers has been investigated. Survival and repopulation of adequate cell mass to replace hepatic function has been the principal difficulty of this method. Hence the authors have begun to investigate the role of donor and recipient age on the efficiency of hepatocyte transplantation. Lewis rats were used as donors and recipients. Hepatocytes were isolated with a collagenase digestion, both for the adult and fetal livers (17 days estimated gestational age). After digestion, the hepatocytes were seeded onto 95% porous poly-(L)-lactic acid matrices. The polymer-cell constructs with adult or fetal cells were then implanted between mesenteric leaves of three different recipient groups: adults (approximately 200 g), 2-week, and 4-week neonates (two to five animals per group, depending on litter size). The specimens were harvested at 4 weeks, stained with Hematoxylin and Eosin (H&E), and the cell area of each specimen (24 sections per group) was quantitated using morphometric analysis. Results were statistically analyzed using an unpaired, two-tailed Student's t test. At 4 weeks, all specimens showed survival of groups of hepatocytes, especially along the periphery of the polymers and near blood vessels. The hepatocyte cell area for the six groups was calculated in square micrometers: the adult cells transplanted into adult recipients, 0.16 x 10(5) microns2; fetal cells into adults, 0.47 x 10(5) microns2; adult into 4-week neonates, 1.17 x 10(5) microns2; fetal into 4-week neonates, 4.54 x 10(5) microns2; adult into 2-week neonates, 2.98 x 10(5) microns2, and fetal into 2-week neonates, 5.81 x 10(5) microns2. In all three recipient groups, the area of fetal hepatocytes was approximately two to three times the area of the adult hepatocytes (P < .05 for 2-week and 4-week neonatal recipients, P = .06 for adult recipients). Also, as the recipient age decreased, there was an increase in the hepatocyte cell area (P < .05 for fetal or adult groups). The authors conclude that fetal hepatocytes heterotopically transplanted have a significant survival advantage over adult hepatocytes, independent of recipient age. The authors further conclude that the neonatal environment is more favorable than the adult environment for implantation of hepatocytes.

Age Factors↗
PubMed1997

[Complicated amebic liver abscess--course and therapy].

We report on a case of an amoebic liver abscess acquired during a holiday in Bali. Transdiaphragmatic migration and consecutive atelectasis of the right lung caused respiratory insufficiency, requiring immediate surgical intervention. Complications consisted of massive bleeding into the colon concomitant with a reactivated CMV-infection. In addition, toxins of Clostridium difficile and enterohaemorrhagic E. coli were seen in the faeces. In contrast to the majority of uncomplicated cases of amoebic liver abscess, usually treated with amoebicidal drugs only, surgical intervention was clearly indicated in our patient.

Combined Modality Therapy↗
PubMed1996

Tissue engineering.

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Current treatment modalities include transplantation of organs, surgical reconstruction, use of mechanical devices, or supplementation of metabolic products. Tissue engineering is the application of the principles and methods of engineering and the life sciences to the fundamental understanding of structure/function relationships in normal and pathological tissues and the development of biological substitutes to restore, maintain, or improve function. This article discusses the challenges of this interdisciplinary field and its attempts to provide solutions to tissue creation and repair.

Artificial Organs↗