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PubMedDate not supplied

Cellular control of membrane permeability. Implications for a bioartificial renal tubule.

A hemofiltrate processor, which consists of a cultured monolayer of renal epithelial cells on a permeable membrane, displayed transport functions that mimicked the renal tubule. Two cell lines, LLC-PK1 (a proximal tubule-like cell) and MDCK (a distal tubule-like cell), were cultured on microporous cellulose nitrate membranes and studied in a diffusion chamber. Dual-label tracer experiments revealed that inulin, glucose, and para-aminohippurate (PAH) moved across unseeded membranes with similar rates in either direction. Solute concentrations in both compartments reached equilibrium in less than 12 hours. MDCK cell-covered membranes were impermeable to all three solutes, as expected from a distal tubule-like cell. LLC-PK1 cell-covered membranes were impermeable to inulin and PAH, but demonstrated a net apical to basal glucose flux of 150 to 350 ng/cm2/min, depending on the conditions. This led within 72 hours to a zero glucose concentration in the compartment on the apical side of the cells, versus 4.6 mg/ml on the basal side. This glucose transport function was inhibited by 0.5 mmol/L phlorizin. Highest glucose flux was obtained using extracellular matrix as the cell attachment substrate on the membrane, suggesting the highest degree of cell differentiation. Based on estimates of the surface area of the normal kidney, the glucose reabsorption capacity of the LLC-PK1 cell line was about 20% that of the normal tubule. The absence of PAH secretion may have been due to the heterogeneity of cells derived from the proximal tubule. Different cell types, culture conditions, and attachment substrates may enhance the transport capacity of the bioartificial renal tubule.

Animals↗
PubMed1992

Bioartificial organs.

Bioartificial organs combine the physical aspects of implantable prostheses with the biological advantages of organ transplantation. Enclosing live cells in a permselective, synthetic envelope avoids rejection by an immunoincompatible host while the geometric limitation of the closed polymer capsule prevents overgrowth of the transplanted material. As a tenet bioartificial organs widen the range of therapeutics based on the biological activity of cell transplants and open an alternative path to gene therapy.

Animals↗
PubMed1991

Computer-aided mechanogenesis of skeletal muscle organs from single cells in vitro.

Complex mechanical forces generated in the growing embryo play an important role in organogenesis. Computerized mechanical application of similar forces to differentiating skeletal muscle myoblasts in vitro generate three-dimensional artificial muscle organs. These organs contain parallel networks of long unbranched myofibers organized into fascicle-like structures. Tendon development is initiated and the muscles are capable of performing directed, functional work. Kinetically engineered organs provide a new method for studying the growth and development of normal and diseased tissue.

Animals↗
PubMed1980

Design of an artificial skin. II. Control of chemical composition.

Detailed methodology is described for the reproducible preparation of collagen--glycosaminoglycan (GAG) membranes with known chemical composition. These membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Such membranes have effectively protected these wounds from infection and fluid loss for over 25 days without rejection and without requiring change or other invasive manipulation. When appropriately designed for the purpose, the membranes have also strongly retarded wound contraction and have become replaced by newly synthesized, stable connective tissue. In our work, purified, fully native collagen from two mammalian sources is precipitated from acid dispersion by addition of chondroitin 6-sulfate. The relative amount of GAG in the coprecipitate varies with the amount of GAG added and with the pH. Since coprecipitated GAG is generally eluted from collagen fibers by physiological fluids, control of the chemical composition of membranes is arrived at by crosslinking the collagen--GAG ionic complex with glutaraldehyde, or, alternately, by use of high-temperature vacuum dehydration. Appropriate use of the crosslinking treatment allows separate study of changes in membrane composition due to elution of GAG by extracellular fluid in animal studies from changes in composition due to enzymatic degradation of the grafted or implanted membrane in these studies. Exhaustive in vitro elution studies extending up to 20 days showed that these crosslinking treatments insolubilize in an apparently permanent manner a fraction of the ionically complexed GAG, although it could not be directly confirmed that glutaraldehyde treatment covalently crosslinks GAG to collagen. By contrast, the available evidence suggests strongly that high-temperature vacuum dehydration leads to formation of chemical bonds between collagen and GAG. Procedures are described for control of insolubilized and "free" GAG in these membranes as well as for control of the molecular weight between crosslinks (Mc). The insolubilized GAG can be controlled in the range 0.5--10 wt. % while "free" GAG can be independently controlled up to at least 25 wt. %; Mc can be controlled in the range 2500--40,000. Studies by infrared spectroscopy have shown that treatment of collagen--GAG membranes by glutaraldehyde or under high-temperature vacuum does not alter the configuration of the collagen triple helix in the membranes. Neither do these treatments modify the native banding pattern of collagen as viewed by electron microscopy. Collagen--GAG membranes appear to be useful as chemically well-characterized, solid macromolecular probes of biomaterial--tissue interactions.

Amino Acids↗
PubMed1980

Design of an artificial skin. Part III. Control of pore structure.

Several methods are compared for preparing collagen-glycosaminoglycan (GAG) membranes of high or low porosity. Collagen-GAG membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Methods studied as means for controlling pore size are confined to purely physical processes which do not require use of additives or chemical reagents to form the porous membrane. We find that membranes, initially swollen in distilled water or saline, shrink linearly to no less than 94% of original dimension after freeze drying; to 75% after critical point drying (from CO2, following water-ethanol exchange); and to 41% of original dimension following air drying from the swollen state. Scanning electron microscopic study of the pore structure resulting from eah drying procedure confirms our major conclusion: A carefully designed freeze drying process, two variants of which are described in detail, yields membranes with the highest mean pore size, as measured by quantitative stereological procedures. Critical point drying gave significantly more shrinkage and a lower mean pore size than either one of the two freeze drying procedures used.

Animals↗
PubMedDate not supplied

Development of an integrated artificial heart-lung device for long-term cardiopulmonary support.

An integrated artificial heart-lung device has been developed as a long-term cardiopulmonary support system. The device is composed of gas exchange and pumping units. The gas exchange unit consists of a special hollow fiber membrane that can prevent serum leakage. The entire blood contacting surface of the gas exchange unit is treated with covalent heparin bonding. The pumping unit consists of two pusher-plate artificial hearts joined to each end of the artificial lung unit. The core size and priming volume of the device are 11 x 14 x 17 cm and 400 ml, respectively. In in vitro evaluation, the device exhibited a maximum output of 7.0 L/ min, with a pressure gradient of 10 mmHg per 1 L/min flow rate. In acute in vivo evaluation with adult goats, the device satisfactorily replaced the animals' circulation and respiration for 6 hr. Pumping output ranged from 5.5 to 6.0 L/min, whereas PaO2 and PaCO2 were kept above 500 mmHg and below 30 mmHg, respectively. The device demonstrated prominent thrombus resistant properties in nonheparin animal use trials. These results indicate that the integrated artificial heart-lung device has a potential to be a long-term cardiopulmonary support system that can be used with minimal anticoagulant therapy.

Animals↗
PubMed1996

Surface modification of silicone rubber membrane by plasma induced graft copolymerization as artificial cornea.

In this study a highly biocompatible polymer membrane was prepared by surface modification. An artificial cornea was also developed for clinical applications. Silicone rubber (SR) membrane was grafted with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and acrylic acid by plasma induced grafted polymerization. Surface properties of the SR were characterized using secondary ions mass spectra, Fourier transform infrared/attenuated total reflection, and element spectra for chemical analysis. The corneal epithelial (CE) cell was cultured in vitro, and penetrating keratoplasty of albino rabbit cornea (in vivo) was performed to evaluate biological properties of modified SR membranes. The ability of the CE cell to attach onto various SR membranes was observed by inverted microscopy. The proliferation of CE cell was conducted in approximately 96 h. Experimental results indicated that the attachment and growth of CE onto SR-g-pHEMA (75 micrograms/ cm2) is enhanced. The morphologies of an attached CE cell are similar to those of a primary CE cell. In the in vivo study, the depth of anterior chamber was maintained 2 weeks after penetrating keratoplasty was performed with a SR grafted with pHEMA (210 micrograms/cm2). This phenomenon displayed a high biocompatibility of modified SR membrane with the CE cell. Furthermore, results in this study provide a valuable reference for application of the modified SR for an artificial cornea.

Animals↗
PubMed2004

Comparison of a new heparin-coated dense membrane lung with nonheparin-coated dense membrane lung for prolonged extracorporeal lung assist in goats.

Thrombosis and bleeding are major complications in cases of prolonged extracorporeal lung assist (ECLA) with an artificial-membrane lung. Antithrombogenic treatment of the artificial-membrane oxygenator and circuits is indispensable for safe ECLA. The efficacy of a new heparin-coated membrane lung with minimal systemic heparinization was evaluated for 7 days and compared with a nonheparin-coated membrane lung in goats. The animals were randomly assigned to either the heparin-coated membrane group (HM group, n = 5) or nonheparin-coated membrane group (NHM group, n = 5). Activated coagulation time (ACT) during ECLA was controlled to below 150 s in the HM group, and to near 200 s in the NHM group. All goats in the HM group were sustained on ECLA for 7 days, but two goats in the NHM group died on the 4th and 6th days, respectively. The mean systemic administration rate of heparin during ECLA was 22.4 +/- 4.4 U/kg/h in the HM group and 39.0 +/- 10.0 U/kg/h in the NHM group. There was a significant difference between the two groups (P < 0.05). The oxygen transfer rate, the Pco(2) difference, the perfusion resistance, and platelet counts showed no significant changes. There was no plasma leakage from the artificial lung. Although several clots were observed in the stagnant areas of the artificial lung, they did not lead to deterioration of the function of the artificial lung. The excellent antithrombogenicity, gas exchange ability, and durability of this new artificial lung with circuits might contribute to successful prolonged ECLA with minimal systemic heparinization.

Animals↗