Date of Award
Master of Science
Roberto S. Benson
Karen Tobias, Wei He
In some breeds of dog, specifically the Yorkshire Terrier, a genetic defect exists that causes a hepatic portosystemic shunt to form. A hepatic portosystemic shunt is a vessel that when present cause blood to bypass the liver, which is responsible for filtering waste from the digestive system and moving it out of the body. An implantable polymeric device was constructed that would slowly occlude the hepatic portosystemic shunt and force the blood to stop flowing through the bypassing vessel and flow through the vessel to the liver over 3-4 months time.
The portosystemic shunt occluder device consist of three polyoxymethylene components, a swelling hydrogel (poly (acrylic acid)), and a degrading copolymer – (Poly (lactide-co-caprolactone)). The poly (acrylic acid) was used to move the piston component of the device upward to constrict the portosystemic shunt placed inside the device. Eight milligrams of poly (acrylic acid) had a swelling ratio of 20.10 ± 1.63, a swelling rate of 0.071 mm/s2, and generated 25mN of force. Eight milli-Newtons is the amount of force that is produced by blood flowing in a four milli-meter diameter vessel. The degradation properties of two compositions of poly (lactide-co-caprolactone) (40 percent lactide and 60 percent caprolactone; 86 percent lactide and 14 percent caprolactone) were analyzed and relationships were developed that would aid in determining the degradation rate of the copolymers in respect to the copolymer composition and the environmental temperature. The poly (lactide-co-caprolactone) controlled the rate that the piston moved by providing a counter force to the poly (acrylic acid). The poly (lactide-co-caprolactone) (40:60), when loaded into the device, degraded in 86 days in a phosphate buffered saline solution at a temperature of 37oC.
Washington, Tommy Lee, "Novel Design of a Portosystemic Shunt Occluder. " Master's Thesis, University of Tennessee, 2009.