Originally Published EMDM May/June 2002
Implant and Tissue-Replacement Products
Dermagraft Dermal-Replacement Tissue
A dermal-replacement product promotes faster and better-quality wound closure for chronic ulcers
Tissue engineering is redefining organ transplantation by providing metabolically active products that remain bioactive following implantation to impart structure and physiological function. Dermagraft dermal-replacement tissue is an example of this kind of product, speeding the healing of the various kinds of foot ulcers, including diabetic foot ulcers, which affect more than 400,000 people in the United States alone. Though many traditional treatments exist for these painful sores, including wound debridement, cleaning and bandaging, antibiotics, and special shoes, they tend to work slowly if at all. As the risk of infection and other complications increases with time, it is important for healthcare providers to seek treatments that close these wounds as soon as possible. Dermagraft tissue serves as a metabolically active solution to this problem, closing diabetic foot ulcers in just 8 weeks.
Cryopreserved and allogeneic, this replacement tissue is manufactured by seeding human dermal fibroblast cells obtained from routine circumcisions on a three-dimensional bioresorbable polymer scaffold that mimics the conditions found in the human body. As the cells proliferate, they secrete human growth factors and matrix proteins, which are assembled into a functioning tissue that is analogous to human skin. The engineered tissue is supplied in units that measure 2 x 3 x 0.008 in. and weigh 0.5 g. Each eight-course treatment of this product is grown under the same conditions to ensure uniformity. Fully packaged product dimensions measure 6.5 x 5 x 0.5 in. IDEO, Palo Alto, CA, USA; and Advanced Tissue Sciences, La Jolla, CA, USA.
Ancure Endograft System
A device treats abdominal aortic aneurysm without traditional surgical techniques
The Ancure Endograft system is used to treat abdominal aortic aneurysm—a potentially life-threatening bulge of the aorta—without traditional surgical techniques. In conventional surgery, large abdominal incisions are made to access the aorta and to attach a blood-diverting polyester sheath to the weakened aortic wall. The Ancure surgical procedure uses a catheter to insert a sheath through the femoral artery in the leg. This procedure is less invasive and causes less trauma to the body; it is normally performed in a catheter lab.
Miniaturization was the primary design challenge, according to the firm, which likens the process to building a boat in a bottle. A graft implant is passed through a 5-mm aperture, and it is remotely positioned, deployed, and fastened from the outside. Several areas of innovation are involved including Endograft suture protection, deployment, and fastening. A relatively large-diameter graft and attachment system, up to 26 mm frame, is needed for the aorta. It collapses to 23 French for delivery into the body. Stirling Design, Aptos, CA, USA; and Guidant Corp., Menlo Park, CA, USA.
Strata Shunt Valve
A shunt valve enables the noninvasive adjustment of cerebrospinal-fluid pressure after implantation
The Strata shunt valve allows adjustable control of cerebrospinal-fluid (CSF) pressure to improve the effectiveness of hydrocephalus treatments. Measuring 2.5 in. in length, the valve uses a plastic-encapsulated gold-plated samarium-cobalt magnet placed directly in the flow path to adjust liquid transmission from the brain ventricles to the peritoneal cavity. This simple noninvasive adjustment is performed using magnetic tools and helps to meet a patient's changing needs, eliminating the need for follow-up surgical implantation procedures that can cost upwards of US$20,000. Negative performance aspects caused by the siphoning effect on the distal catheter are also eliminated.
The Strata valve eliminates the need for repeated surgical implantation by enabling postoperative adjustment of pressure rates using magnetic hand tools. Suited for office use, these noninvasive tools allow a surgeon to check, adjust, and confirm the valve's setting in a matter of minutes. According to company sources, this adjustability leads to earlier intervention, a reduction of drainage-related complications, and the elimination of unnecessary surgical risks and expenditures in all but extreme cases. The Strata valve also allows a more tailored therapy than standard products. For example, a lower pressure setting could be used initially to provide rapid draining, and then be raised after a patient's condition has stabilized. Medtronic Neurosurgery, Goleta, CA, USA; and Hauser Inc., Westlake Village, CA, USA.
On-X Prosthetic Heart Valve
A prosthetic heart valve reduces costly complications using a proprietary carbon construction and improved fluid dynamics
The On-X prosthetic heart valve lowers the risk of expensive valve complications by using a proprietary carbon construction that enables improved fluid dynamics. Replacing diseased, damaged, or malfunctioning aortic valves, this product consists of a mechanical valve with two half-disk leaflets contained in an orifice made of On-X pyrolytic carbon. Though man-made, this valve mimics the function of natural human valves to provide improved functionality. The product also eliminates the durability problems associated with tissue replacements, and performs well under poorly controlled anticoagulation therapy.
The key to these dramatic improvements is the unit's On-X carbon material, a chemically pure pyrolytic carbon with improved mechanical properties and blood-contacting-surface qualities. The material purity and surface quality facilitate smooth surface contours that reduce turbulence and eliminate flow stagnation. These factors also improve the potential for thromboresistance. Compatible with tight-tolerance coating, the material minimizes unit cost by eliminating the need for expensive secondary machining operations. Medical Carbon Research Institute, Austin, TX, USA.
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