出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/11/04 20:30:42」(JST)
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Artificial kidney is often a synonym for hemodialysis, but may also, more generally, refer to renal replacement therapies (with exclusion of renal transplantation) that are in use and/or in development. This article deals with bioengineered kidneys/bioartificial kidneys that are grown from renal cell lines/renal tissue.
Kidneys are paired vital organs located behind the abdominal cavity, at about the level of the bottom of the ribcage. They perform about a dozen physiologic functions, and are fairly easily damaged. Kidney failure results in the slow accumulation of nitrogenous wastes, salts, water, and disruption of the body's normal pH balance. Until the Second World War, kidney failure generally meant death for the patient. Several insights into renal function and acute renal failure were made during the war, not least of which would be Bywaters and Beall's descriptions of pigment-induced nephropathy drawn from their clinical experiences during the London Blitz.[1]
Over 300,000 Americans are dependent on hemodialysis as treatment for renal failure, but according to data from the 2005 USRDS 452,000 Americans have end-stage renal disease (ESRD).[2] Intriguing investigations from groups in London, Ontario and Toronto, Ontario have suggested that dialysis treatments lasting two to three times as long as, and delivered more frequently than, conventional thrice weekly treatments may be associated with improved clinical outcomes[3] Implementing six-times weekly, all-night dialysis would overwhelm existing resources in most countries. This, as well as scarcity of donor organs for kidney transplantation has prompted research in developing alternative therapies, including the development of a wearable or implantable device.[4]
Hemodialysis is a method for removing waste products such as creatinine and urea,as well as free water from the blood when the kidneys are in renal failure. The mechanical device used to clean the patients blood is called a dialyser, also known as an artificial kidney. Modern dialysers typically consist of a cylindrical rigid casing enclosing hollow fibers cast or extruded from a polymer or copolymer, which is usually a proprietary formulation. The combined area of the hollow fibers is typically between 1-2 square meters. Intensive research has been conducted by many groups to optimize blood and dialysate flows within the dialyser, in order to achieve efficient transfer of wastes from blood to dialysate.
A wearable artificial kidney is a wearable dialysis machine that a person with end-stage renal disease could use daily or even continuously. Until November 2008, no wearable kidney was widely available, but many research teams were in the process of developing such devices. Now the scientists have built an artificial device which can be fitted in the failed kidney. The FDA has approved the first human clinical trials in the United States for a wearable artificial kidney designed by Blood Purification Technologies Inc. out of Beverly Hills, California. It is a tube-like structure which allows the impure blood to be passed from it and the inserted fluids purify the blood which is now pure and the bi-products are allowed to pass through the ureter to be thrown out of the body.
Currently, no viable bioengineered kidneys exist. Although a great deal of research is underway, numerous barriers exist to their creation.[5][6][7]
However, manufacturing a membrane that mimics the kidney's ability to filter blood and subsequently excrete toxins while reabsorbing water and salt would allow for a wearable and/or implantable artificial kidney. Developing a membrane using microelectromechanical systems (MEMS) technology is a limiting step in creating an implantable, bioartificial kidney.
The BioMEMS and Renal Nanotechnology Laboratories at the Cleveland Clinic's Lerner Research Institute have focused on advancing membrane technology to develop an implantable or wearable therapy for end-stage renal disease (ESRD). Current dialysis cartridges are too large and require superphysiologic pressures for blood circulation, and pores in current polymer membranes have too broad of a size distribution and irregular features. Manufacturing a silicon, nanoporous membrane with narrow pore size distributions improves the membrane's ability to discriminate between filtered and retained molecules. It also increases hydraulic permeability by allowing the mean pore size to approach the desired cutoff of the membrane. Using a batch-fabrication process allows for strict control over pore size distribution and geometry.[8]
In recent studies, human kidney cells were harvested from donated organs unsuitable for transplantation, and grown on these membranes. The cultured cells covered the membranes and appear to retain features of adult kidney cells. The differentiated growth of renal epithelial cells on MEMS materials suggests that a miniaturized device suitable for implantation may be feasible.
A UCSF-led effort to create an implantable artificial kidney for dialysis patients has been selected as one of the first projects to undergo more timely and collaborative review at the Food and Drug Administration.
The FDA announced on April 9, 2012 that it had chosen three renal device projects to pilot a new regulatory approval program called Innovation Pathway 2.0, intended to bring breakthrough medical device technologies to patients faster and more efficiently.
The artificial kidney project, which is targeted for clinical trials in 2017, was selected for its transformative potential in treating end stage renal disease and for its potential to benefit from early interactions with the FDA in the approval process.
The FDA effort will involve close contact between the federal agency and device developers early in the development process to identify and address potential scientific and regulatory hurdles and create a roadmap for project approval. The goal is to improve the projects’ overall chance of success, while reducing the time and cost of FDA review and maintaining safety. Lessons, the agency said, will inform approvals in other areas.
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