FDA's requirements for in-vitro performance data for prosthetic heart valves.

The Center for Devices and Radiological Health, Food and Drug Administration, has recently revised its "Replacement Heart Valve Guidance". That document lists the data FDA deems necessary to support the approval of new prosthetic heart valves of all designs, and which should be contained in Premarket Approval Applications for these devices. The Guidance covers detailed data requirements for in vitro, animal, and clinical data. This paper is intended to briefly summarize FDA's requirements for in vitro data, and, for those cases where it may not be obvious, to provide an overview of the significance of these data and how FDA interprets them in the approval decision process.

Digital acoustical analysis of normal and bimodal Björk-Shiley 60 degrees convexo-concave heart valves.

Fracture of the outlet strut of the Björk-Shiley 60 degrees convexo-concave (BS60CC) valve has been attributed to a bimodal closing pattern in certain valves in which the closing disk rotates about the inlet strut, causing upward displacement of the outlet strut and its eventual fracture. This article reports the in vivo studies of the normal BS60CC valve and the in vitro studies of the normal and bimodal BS60CC valves, using a digital acoustical signal processing technique, in which the individual collisions (impact history) of the occluder disk with the components of the valve body are revealed during each closing cycle. In vitro analysis of the closing acoustical signals of normal BS60CC valves showed impact history cluster width (IHCW) means of 2.07 +/- 0.85 ms (standard error), not significantly different from those of 1.86 +/- 0.58 ms (standard error) observed in 38 clinically normal patients with BS60CC valves (p greater than 0.1). The bimodal valves showed IHCW of 6.14 +/- 0.98 ms (standard error), in vitro, which was significantly greater than those observed in the normal in vitro valve group and in the normal patient population (p less than 0.0001).

Fracture mechanics principles applied to implant medical devices--a review.

Historically, the fatigue behavior of materials and structures, including biomaterials and implant devices, was analyzed using stress-life (S-N) techniques, i.e. by determining the number of cycles to failure at a calculated peak stress. The development of fracture mechanics technology has made the crack-growth aspect of fatigue analysis a more exact science, providing more precise data on the properties of materials, incorporating more geometric and metallurgical information from the structure, and, in some cases, providing for updated in-service lifetime predictions. Over the past decade, the medical implant industry and researchers have adopted this analytical tool to varying degrees. The result has been the development of some improved materials, operative procedures, and devices, based on a more exact knowledge of the properties most critical to assuring the long-term durability of devices. Examples of the application of fracture mechanics technology to orthopedic and cardiovascular devices and the potential for further applications are reviewed.

Long-term compressive creep deformation and damage in acrylic bone cements.

Compressive creep tests were performed on five commercially available acrylic bone cements under conditions simulating in vivo usage. Measured creep strains are quite large, generally exceeding elastic strains. Large variations in creep response were noted among the various cements, with a carbon-reinforced cement by far the most resistant to creep. The empirical model epsilon = a exp(b sigma)tn was found to predict creep strains within about 10% of the measured values. Microscopic examination of some specimens after testing revealed significant cracking, resulting from long-term loading, that could be a contributing cause of time-dependent failure.