Islet devices

In terms of membrane area used and doUar value of the membrane produced, artificial kidneys are the single largest appHcation of membranes. Similar hoUow-fiber devices are being explored for other medical uses, including an artificial pancreas, in which islets of Langerhans supply insulin to diabetic patients, or an artificial Uver, in which adsorbent materials remove bUinibin and other toxins. 

Walker, G.M., Piston, D.W., McGuinness, P.O., Rocheleau, J.V., A microfluidic device for partical surface treatment of islets of Langerhans. Micro Total Analysis Systems 2003, Proceedings 7th pTAS Symposium, Squaw Valley, CA, Oct. 5-9, 2003, 543-546. 

Juang, J-H. Bonner-Weir, S. Vacanti, J.P. Weir, G.C. Outcome of subcutaneous islet transplantation improved by a polymer device. Transplantation Proceedings 1995, 27 (6), 3215-3217. 

As detailed in Section 15.4, there are multiple examples of fast separations performed in microfluidic devices and the channel design and speed of the separation is ultimately dictated by the analytes to be separated. In one example, Roper et al. detected insulin secretion from islets of Langerhans using a combination of several factors designed for rapid separations. These factors included the use of shallow channels, 1 s gated injections, 15 s separations, and high-speed data processing. 

A different study realized with thin films of tin dioxide doped with platimrm has been proposed by M. Gaidi." Gaidi assesses the oxidation degree of the platinmn particles (using X-rays absorption spectroscopy), and links it to the electric measures performed in the presence of CO. These works, which describe islets of oxidized platinum (PtOx) at the surface of the metallic particles, clearly show the existence of a direct relation between the oxidation degree of the metallic particles and the electric response of the device, according to the following kind of reactions ... 

Cell Assays in Microfluidks, Fig. 4 (a) Schematic of a device for continuous perfusion of pancreatic cell islets and stimulation with glucose and monitoring of insulin release (top). Perfusion chamber with an islet (bottom) (Image reproduced, with permission, from Ref. [18]). (b) Microfluidic device for monitoring cell-cell communication via gap junctions. Fluorescent dye transfers from one cell to another only when cells are in contact (Image reproduced, with permission, from Ref. [7])... 

Microfabrication enables the creation of complex tissue-engineered products that can be used to replace or augment failing organs and tissues. The number and variety of microfabricated tissue-engineered products have increased rapidly in the last several years microporous biocapsules to provide immunological protection to pancreatic islets micropattemed hepatocytes and mesenchymal cells as key components of liver assist devices microtextures basement-membrane-type structures to create skin with proper surface texture and microspatial control of the distribution of vitronection or other extracellular matrix proteins to promote the formation of mineralized bone-like tissue in vivo (Bhatia and Chen, 1999). 

The coupling of encapsulation technologies with cell culture techniques permits the extended use of these bioreactors with complex tissue systems such as islet clusters. Existing reactor systems are also useful in obtaining the basic transport and reaction kinetics parameters necessary to design the novel devices required for biomedical applications. In summary, the relevance of this work to the biotechnology and health care-based industries is in the development, of artificial organ systems, extra-corporeal devices to... 

There are many studies on how to determine fiber dimensions, spacing, and reactor length however, commercially available units come in a relatively limited number of sizes, usually with inner liber diameters of 500 /rm or more. Several reports in the literature describe the use of hollow-flber systems in the development of a bioartiflcial pancreas, which place the islets on the shell side, while perfusing the fibers with the animal s plasma or blood. The fibers can be made relatively non-thrombogenic and of porosity sufficiently small as to avoid immune attack of the cells inside the shell. One difficulty with this configuration is that interfiber distances in the hollow-fiber device are not well controlled, so that regions within the shell space receive too little nutrients. 

A microcapsule is a minature membrane system in which the combination of high permeability and large surface area can confer some unusual properties and have made microcapsules of interest for drug release systems and for some artificial organs. Hundreds of different materials have been enclosed within microcapsules for both biomedical and non-medical use. The classic non-medical example would be the carbonless "carbon" papers which are in wide use today. Medically, microcapsules have been used to enclose various enzymes, such as catalase or L-asparaginase (which can be used to treat some forms of cancer), and have been shown to maintain the enzymatic activity for prolonged time periods. Microcapsules have been utilized as artificial cells to enclose the beta-cells from the Islets of Langerhans, and such a system can function as a source of insulin (artificial pancreas). i Other research has centered on the use of such devices for artificial red blood cells. ... 

Encapsulation of islets has been investigated by various groups of researchers employing a variety of materials. A thorough analysis of the requirements discussed in the scientific and patent literature leads us to suggest that the optimum membrane of an implantable biohybrid device for immunoisolating islets should exhibit the following characteristics ... 

Available implantable devices for the correction of diabetes have several but not all of these properties. Many researchers utilize alginate gels to microencapsulate individual islets (i-5). The fundamental disadvantage of microencapsulation, however, is that the microcapsules enveloping the islets cannot be completely and reliably retrieved. 

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