MICRO METROLOGY| CASE STUDY
<< Figure 2: EXCOR blood pump with connectors. >>
Berlin Heart GmbH in Berlin, Germany, develops, manufactures and delivers implantable, continuous driving systems as well as paracorporeal, pulsating types of pulmonary assist devices (INCOR resp. EXCOR Ventricular Assist Device, VAD, figure 1). The continuous VAD-System INCOR employs a very compact and energy efficient axial pump and can be almost completely implanted, except for a power supply cable. In the case of paracorporeal systems, the blood pumps are located outside the body and are connected to the heart and to blood vessels by cannulas.
The EXCOR VAD-System consists of one or two blood pumps and a pneumatic driving unit. The blood pumps convey blood by the displacement principle, pulsating at 30 to 150 beats per minute, a flow rate between 1 and 7 liters of blood per minute, adjusted to the particular patient. Even small children can be supported this way.
Quality requirements for heart assist devices are extremely high, therefore the manufacturer examines 100% of all essential system components. This also includes connecting devices (connectors, adapters) which join the blood pump with the cannulae of the VAD system (figure 2). These cannulae are made of special plastic materials, mainly silicone. These circular symmetric, tube-like, thin- walled connectors and adapters made of a titanium alloy have to meet high specifications according to surface and edge quality in all blood carrying areas.
<< Figure 3: Measurement of edge shape and radius of a titanium adapter. >>
For the measurement of connector edge geometry, Berlin Heart adopted a new measuring principle: Phase measuring fringe projection, with a MikroCADlite made by GFMesstechnik, Germany (figure 3).
The measuring process especially concentrates on the radius of the outer connector edge which comes into direct contact with the cannula. This edge radius must comply with a minimum value, to assure an optimal connection to the cannula. In addition, there are requirements on the edge geometry in order to achieve a favorably defined blood flow between connector and cannula.
38 | commercial micro manufacturing international Vol 6 No.6
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