Macroencapsulation involves filling a hollow, usually cylindrical, selectively permeable membrane with cells, generally suspended in a matrix, and then sealing the ends to form a capsule.[4] Polymers used for macroencapsula-tion are biodurable, with a thicker wall than that found in microencapsulation. While thicker wall and larger implant diameters can enhance long-term implant stability, these features may also impair diffusion, compromise the viability of the tissue, and slow the release kinetics of desired factors. In theory, macrocapsules can be retrieved from the recipient and replaced if necessary.

Macroencapsulation is generally achieved by filling preformed thermoplastic hollow fibers with a cell suspension. The hollow fiber is formed by pumping a solution of polymer in a water-miscible solvent through a nozzle concurrently with an aqueous solution. The polymer solution is pumped through an outer annular region of the nozzle, while the aqueous solution is pumped through a central bore. Upon contact with the water, the polymer precipitates and forms a cylindrical hollow fiber with a permselective inner membrane. Further precipitation of the polymer occurs as the water moves through the polymer wall, forcing the organic solvent out and forming a trabecular wall structure. The hollow fiber is typically collected in a water bath, allowing complete precipitation of the polymer and dissolution of the organic solvent. The ends of the hollow fiber are sealed using a biocompatible fast-curing adhesive manually applied to the ends of the device. A second method of macroencapsulation, called coextru-sion, avoids the sealing problem by entrapping cells within the lumen of a hollow fiber during the fabrication process. Pinching the fiber before complete precipitation of the polymer causes fusion of the walls, providing closure of the extremities while the cells are inside.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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