Materials Engineering Research

Leads are designed for in vivo applications, however, for a definite period of time. In-vivo environment affects the mechanical behavior of implantable devices, therefore, there is a need to evaluate the residual properties of implantable leads used with pacemakers, defibrillator and neuro-stimulators. Silicone (MED-4719) lead is widely used in cardiac implantable electronic devices made by different manufacturers. . We collected 150 devices (with or without leads) from Anatomical Gift Program of the Wright State University. The objective of this study was to investigate the residual properties of Silicone (MED-4719) lead with different in vivo exposure time and compare the properties of a new, unused lead supplied by Medtronic for the purposes of this research. The tensile test was performed by applying specific load on the samples, percentage elongation at 5N and the corresponding displacement measured. Load to failure, percentage elongation, ultimate tensile strength, and modulus of elasticity were determined for each lead. Methods to collect and compile data were standardized, and statistical models were used to assess the sensitivity of measured parameters with in vivo performance. Load to failure, elongation to failure, ultimate tensile strength, and percentage elongation at 5N showed a significant decrease after 94 months (P = 0.0063), 8 months (P = 0.0136), 94 months (P = 0.0244) and 71 months (P-value = 0.0326) after implantation, respectively. On the other hand, modulus of elasticity was found proportional to the number of months device was exposed and showed significant increase after 71 months (P = 0.0446) of in-vivo environment.

Hearing aid devices are powered by the oxidation of zinc that occurs within zinc-air batteries. Zinc-air batteries have an average discharge time of 7 days. Therefore, hearing-aid devices need frequent battery replacement. In this paper, degradation mechanisms of zinc-air batteries investigated where a competition mechanism between zinc passivation and dendritic formation dictates the battery life. This research included exposure time from none to 9 days and to document dendritic growth with time. Scanning electron microscope images were taken to quantify the damage growth as well energy dispersive X-ray tests were conducted to comment on the composition changes. The results confirmed an increase in oxygen in exposed batteries from unexposed. These results matched findings from past literature. Exposure time was investigated to optimize battery lifespan. In conclusion, life of zinc-air batteries depends on the competition mechanism of zinc passivation and dendritic formation caused by oxidation and our investigation shows that this occurs within the first 7 days.

Failure of critical engine components such as compressor, fan, and turbine disks during flight can cause the loss of the engine, aircraft, or even life. To reduce the risk of this failure during flight, different methodologies and tools have been developed to determine the safe operating life of these critical disk components. The two most widely used lifing methods, safe-life and damage tolerance, are inherently conservative, retiring all components when a predetermined operating limit is reached. Both methods retire components with theoretical useful life remaining. Additional lifing methods can be used to reduce this conservatism and extend the life of these components. Retirement for cause, developed within the United States Air Force is a lifing method that can extend the life of components by retiring a component only when there is cause to do so. Military and industry standards on lifing methodologies were reviewed. Both deterministic and probabilistic approaches to disk lifing methods are discussed as well as current tools. This paper provides a comparison of the methodologies and tools currently being used today by both the government and industry.

Ethicon Coated Vicryl absorbable sutures of different diameters were studied in order to determine if a relationship exists between the load and measured clearance. A prototype was designed to simulate knot location. Tensile tests were conducted on the suture knots followed by clearance measurements after each load level was applied. From the results it was concluded that the measured clearance was directly proportional to the amount of load applied to the suture knot. Also, based on the diameter of the suture, the smaller the diameter, the lower was the total displacement of the knot or the clearance.

This article was prepared from a project assigned in a graduate class, BME 7371, Failure Assessment of Medical Devices, taught at Wright State University by the senior author. The device was donated for the study which was successfully retrieved after 93 days in-vivo. Even-though the mechanical integrity of the device held in-tact, the microscopic observations revealed that the damage via corrosion and scratching took place on the surface of the device. The image reconstructed in 3D using image-J software to determine device roughness and depth-of-pits. Results presented in this paper show that damage starts developing in these devices after the implantation that resulted in premature failure in many cases as reported in the media and literature.