The surface of as-deposited, machined and polished components is shown in Fig. 8. It was found early on in experiments that clean polished pyrolytic carbon surfaces of tubes when placed within the vasculature of experimental animals accumulated minimal if any thrombus and certainly less than pyrolytic carbon tubes with the as-deposited surface. Consequently, the surfaces of pyrolytic carbon have historically been polished, either manually or mechanically, using fine diamond or aluminum oxide pastes and slurries. The surface finish achieved has roughness measured on the scale of nanometers. As can be seen from Table 2
the surfaces of polished pyrolytic carbon (30–50 nm) are an order of magnitude smoother than the as-deposited surfaces (300–500 nm). Once the desired surface quality is achieved, components are again inspected. The final component inspection may include measurement of dimensions, X-ray inspection in two orientations to verify coating thickness, and visual inspection for surface quality and flaws. In many cases, automated inspection methods with computer-controlled coordinate measurement machines are used. X-ray inspection can be used to ensure that minimum coating thickness requirements are met. Two orthogonal views ensure that machining and grinding of the coating was achieved uniformly and that the coating is symmetrical.
the machining and grinding operation after coating is not without the risk of inducing cracks or flaws in the
coating, which may subsequently affect the service life of the component. Such surface flaws are detected visually or with the aid of dye-penetrant techniques. Components may also be proof-tested to detect and eliminate components with subsurface flaws. With the advent of bed size control, which allows coating to exact final dimensions, the concerns about flaws introduced during the machining and grinding operation have been eliminated.
The polished and inspected components, thus prepared, are now ready for assembly into devices, or are packaged and sterilized in the case of stand-alone devices. Shown in Fig. 9 are the three pyrolytic carbon components for a bileaflet mechanical heart valve. The components were selected and matched for assembly using the data generated from the final dimensional inspection to achieve the dimensional requirements specified in the device design. In Fig. 10, the pyrolytic carbon components for a replacement metacarpophalangeal total joint prosthesis are shown.