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Semipermeable Membranes (semipermeable + membrane)
Selected AbstractsUseful Adjuncts to Harvest Split-Thickness Skin GraftsDERMATOLOGIC SURGERY, Issue 12p2 2004Hunter H. Sams MD Background. Split-thickness skin grafts are useful for repair of defects that are not amenable to primary closure or secondary intention healing. Because of the thinness of split-thickness skin grafts, damage to the graft and curling are common with standard harvesting techniques. Adjunctive methods for harvesting split-thickness skin grafts have not been well elucidated in the literature. Methods. Lubrication and a tongue depressor facilitate even harvesting of the split-thickness skin graft. A semipermeable membrane is applied to the split-thickness skin graft donor site before harvesting the skin graft. This aids with harvesting and minimizes trauma to the graft. Conclusion. Use of lubrication, a tongue depressor, and a semipermeable membrane are useful adjuncts to harvesting split-thickness skin grafts. [source] Neurochemistry of Trigeminal Activation in an Animal Model of MigraineHEADACHE, Issue 2006Michael L. Oshinsky PhD Research techniques such as electrophysiology, cFos protein expression, and other measurements of neuronal activation provide insights into the pathophysiology of pain processing in migraine, but they do not indicate the specific neurotransmitter systems involved. This paper summarizes data from microdialysis experiments in which changes in the neurochemistry of the trigeminal nucleus caudalis (TNC) were monitored during dural stimulation. Microdialysis allows the measurement of extracellular concentrations of neurotransmitters in a small area of the brain, in vivo, by means of a probe equipped with a semipermeable membrane. Microdialysis enables direct measurement of changes in extracellular concentrations of neurotransmitters in the intact animal over time in response to dural inflammation. Following the activation of the dural nociceptors, changes in the extracellular amino acid neurotransmitters in the deep lamina of the TNC were tracked. A 5-minute application of inflammatory soup when compared with saline to the dura of rats induced a transient decrease in extracellular glutamate in the TNC at approximately 30 minutes postapplication. This short-lived decrease was followed by a continuous increase in extracellular glutamate to a level of approximately 3 times the baseline value at 3 hours after application of the inflammatory soup. The time course of this increase in extracellular glutamate correlated with changes in sensory thresholds on the face of the rat from electrophysiological recordings of secondary sensory neurons in the TNC. No significant differences between the inflammatory soup and saline conditions were observed for extracellular concentrations of aspartate (an excitatory amino acid) or the inhibitory neurotransmitters gamma-aminobutyric acid or glutamine. Results of these experiments support an integral role for glutamate in central sensitization of neurons in the TNC, and suggest an important contribution of glutamate to allodynia and hyperalgia in this animal model of migraine. [source] Spatial and temporal patterns of bone formation in ectopically pre-fabricated, autologous cell-based engineered bone flaps in rabbitsJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2008Oliver Scheufler Abstract Biological substitutes for autologous bone flaps could be generated by combining flap pre-fabrication and bone tissue engineering concepts. Here, we investigated the pattern of neotissue formation within large pre-fabricated engineered bone flaps in rabbits. Bone marrow stromal cells from 12 New Zealand White rabbits were expanded and uniformly seeded in porous hydroxyapatite scaffolds (tapered cylinders, 10,20 mm diameter, 30 mm height) using a perfusion bioreactor. Autologous cell-scaffold constructs were wrapped in a panniculus carnosus flap, covered by a semipermeable membrane and ectopically implanted. Histological analysis, substantiated by magnetic resonance imaging (MRI) and micro-computerized tomography scans, indicated three distinct zones: an outer one, including bone tissue; a middle zone, formed by fibrous connective tissue; and a central zone, essentially necrotic. The depths of connective tissue and of bone ingrowth were consistent at different construct diameters and significantly increased from respectively 3.1 ± 0.7 mm and 1.0 ± 0.4 mm at 8 weeks to 3.7± 0.6 mm and 1.4 ± 0.6 mm at 12 weeks. Bone formation was found at a maximum depth of 1.8 mm after 12 weeks. Our findings indicate the feasibility of ectopic pre-fabrication of large cell-based engineered bone flaps and prompt for the implementation of strategies to improve construct vascularization, in order to possibly accelerate bone formation towards the core of the grafts. [source] Modeling water flux in forward osmosis: Implications for improved membrane designAICHE JOURNAL, Issue 7 2007Jeffrey R. Mccutcheon Abstract Osmotically-driven membrane processes, such as forward osmosis and pressure retarded osmosis, operate on the principle of osmotic transport of water across a semipermeable membrane from a dilute feed solution into a concentrated draw solution. The major hindrance to permeate water flux performance is the prevalence of concentration polarization on both sides of the membrane. This article evaluates the external and internal boundary layers, which decrease the effective osmotic driving force. By modeling permeate flux performance, the role that feed and draw concentrations, membrane orientation, and membrane structural properties play in overall permeate flux performance are elucidated and linked to prevalence of external and internal concentration polarization. External concentration polarization is found to play a significant role in the reduction of driving force, though internal concentration polarization has a far more pronounced effect for the chosen system conditions. Reduction of internal concentration polarization by way of membrane modification was found to improve the predicted flux performance significantly, suggesting that alteration of membrane design will lead to improved performance of osmotically driven membrane processes. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Chromium nanoparticle exhibits higher absorption efficiency than chromium picolinate and chromium chloride in Caco-2 cell monolayersJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 2 2008L.-Y. Zha Summary This study was conducted to determine whether chromium nanoparticle (CrNano) exhibited higher absorption efficiency and possessed unique absorption mechanism in comparison to chromium picolinate (CrPic) and chromium chloride (CrCl3), as was postulated by previous reports. Twenty-one-day-old Caco-2 cell monolayers grown on semipermeable membranes in Snapwell tissue culture bichambers were incubated with CrNano, CrPic or CrCl3 to examine their transport and uptake respectively. In the concentration range of 0.2,20 ,mol/l, transport of CrNano, CrPic and CrCl3 across Caco-2 monolayers both in apical-to-basolateral and basolateral-to-apical direction was concentration-, and time-dependent, and temperature independent. The apparent permeability coefficient (Papp) of CrNano was between 5.89 and 7.92 × 10,6 cm/s and that of CrPic and CrCl3 was between 3.52 and 5.31 × 10,6 cm/s and between 0.97 and 1.37 × 10,6 cm/s respectively. Uptake of CrNano, CrPic and CrCl3 by both apical and basolateral membranes was concentration- and time-dependent. Uptake of CrNano by apical membrane was significantly (p < 0.05) decreased when the incubation temperature was reduced from 37 °C to 4 °C. The transport efficiency of CrNano, CrPic and CrCl3 after incubation for 120 min at 37 °C was 15.83% ± 0.76%, 9.08% ± 0.25% and 2.11% ± 0.53% respectively. The uptake efficiency of CrNano, CrPic and CrCl3 was 10.08% ± 0.76%, 4.73% ± 0.60% and 0.88% ± 0.08% respectively. It was concluded that the epithelial transport of CrNano, CrPic and CrCl3 across the Caco-2 cell monolayers was mainly via passive transport pathways. In addition, CrNano exhibited considerably higher absorption efficiency than both CrPic and CrCl3 in Caco-2 cell monolayers. [source] Diffusion time dependence of the apparent diffusion tensor in healthy human brain and white matter diseaseMAGNETIC RESONANCE IN MEDICINE, Issue 6 2001Chris A. Clark Abstract The diffusion time dependence of the brain water diffusion tensor provides information regarding diffusion restriction and hindrance but has received little attention, primarily due to limitations in gradient amplitude available on clinical MRI systems, required to achieve short diffusion times. Using new, more powerful gradient hardware, the diffusion time dependence of tensor-derived metrics were studied in human brain in the range 8,80 ms, which encompasses the shortest diffusion times studied to date. There was no evidence for a change in mean diffusivity, fractional anisotropy, or in the eigenvalues with diffusion time in healthy human brain. The findings are consistent with a model of unrestricted, but hindered water diffusion with semipermeable membranes, likely originating from the extracellular space in which the average extracellular separation is less than 7 microns. Similar findings in two multiple sclerosis plaques indicated that the size of the water diffusion space in the lesion did not exceed this dimension. Magn Reson Med 45:1126,1129, 2001. © 2001 Wiley-Liss, Inc. [source] An overview on the development of a bio-artificial pancreas as a treatment of insulin-dependent diabetes mellitusMEDICINAL RESEARCH REVIEWS, Issue 2 2006Ana Isabel Silva Abstract This paper presents the concept and most of the research undertaken all over the world for the development of a bio-artificial pancreas (BAP) device over the last 30 years. The devices studied, meant to mimic the insulin secretion of the natural organ, were diverse and have been reviewed. Allogeneic or xenogeneic cells or cell clusters have been separated from the host's immune system by synthetic biocompatible semipermeable membranes to prevent the need, of the host, for immune-suppressing regimens. The biocompatible polymer used as a barrier and its intrinsic characteristics, the cell immobilization or suspension media, the existence or not of co-immobilized molecules or cells, the number of devices used and the implantation site, were addressed. © 2005 Wiley Periodicals, Inc. Med Res Rev [source] Immunoisolated Chromaffin Cells Implanted Into the Subarachnoid Space of Rats Reduce Cold Allodynia in a Model of Neuropathic Pain: A Novel Application of Microencapsulation TechnologyARTIFICIAL ORGANS, Issue 12 2004Yu Mi Kim Abstract:, Intrathecal transplants of adrenal medullary chromaffin cells relieve chronic pain by secreting catecholamines, opioids, and other neuroactive substances. Recently, macrocapsules with semipermeable membranes were used to isolate immunologically xenogenic chromaffin cells, but the poor viability in vivo of the encapsulated chromaffin cells limited the usefulness of this method. In this study, we used a novel method of encapsulation to increase the viability of chromaffin cells. We found that microencapsulated chromaffin cells that were implanted into the subarachnoid space of rats relieved cold allodynia in a model of neuropathic pain. Furthermore, microencapsulated chromaffin cells were morphologically normal and retained their functionality. These findings suggest that the intrathecal placement of microencapsulated chromaffin cells might be a useful method for treating chronic pain. [source] Development of the method for evaluating protective effect of food factors on THP-1-induced damage to human intestinal Caco-2 monolayersBIOFACTORS, Issue 1-4 2004Fumiko Watanabe Abstract Immune cells located in the intestinal epithelium interact with intestinal epithelial cells via soluble factors. In this study, a new in vitro model using a coculture system was constructed to analyze the interaction between intestinal epithelial cells and macrophage-like cells. Human intestinal epithelial Caco-2 cells were differentiated on semipermeable membranes. Human monocytic THP-1 cells were differentiated to macrophage-like cells and then cocultured on the basolateral side of the Caco-2 cell monolayers. By coculturing for 48 hours, an increased release of lactate dehydrogenase from the Caco-2 cells and a decrease in the transepithelial electrical resistance of the monolayers were observed, suggesting that the coculture with THP-1 induced some disruption of the Caco-2 cells. This disruption was significantly suppressed by adding the anti-TNF-, antibody to the medium, suggesting that TNF-, secreted from THP-1 caused damage to the Caco-2 cells. It is also suggested that this phenomenon is similar to that observed with inflammatory bowel disease (IBD). The effects of food factors on the cells in this coculture system were examined. The disruption of the Caco-2 cell monolayers was significantly reduced by adding caffeine to the medium on the apical side. It is hoped that this coculture system will be a good model for the treatment of IBD. [source] Microencapsulation of an anti-VE,cadherin antibody secreting 1B5 hybridoma cellsBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2001G. Orive Accumulating experimental evidence demonstrates that tumor growth and lethality are dependent on angiogenesis. Based on this concept, there is growing interest in the use of antiangiogenesis agents to inhibit tumor expansion. Compelling data implicate vascular endothelium (VE),cadherin (an endothelium specific protein) as a key factor in the last step of angiogenesis, where the endothelial cells join one to each other and form microtubules (future blood vessels). We propose a novel approach to the inhibition of angiogenesis by immobilizing VE,cadherin-secreting hybridoma cells in alginate,agarose microcapsules. Hybridoma cells can be protected with biocompatible and semipermeable membranes that permit exit of anti-VE,cadherin monoclonal antibodies but not entry of cellular immune mediators. Stability studies were performed to select the suitable microcapsule for cell immobilization. Alginate and agarose solid beads coated with poly- L -lysine and alginate were chosen according to their stability and diffusional properties. 1B5 hybridoma cells were grown within the microcapsules and secreted anti-VE,cadherin antibodies during the 9 days of culture, reaching a cumulative concentration of 1.7 ,g/mL. This antibody concentration inhibited microtubule formation (87%) in the in vitro angiogenesis Matrigel assay. Moreover, the antiangiogenic effect observed was antibody concentration related. These findings open a new alternative for the inhibition or prevention of angiogenesis and demonstrates the feasibility of using microencapsulated cells as a control-drug delivery system. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 76: 285,294, 2001. [source] | ||||||||||||||||