Needle design

In this section, a variety of devices are discussed for sample introduction, i.e., ESI needle designs. 

The most important aspect of needle design is the needle point because it has to penetrate the fabric without causing any damage to the material. It is also the most diverse part of the needle due to the many different types of points used. Needle points are designed for sewing on many different fabric types and seams. An example of needle point designs can be seen in Figure 6.21. 

The microneedle concept was first proposed as a technique for transdermal drug delivery in the 1970s [1], and the recent advances in the microelectronics industry have provided the technical capability to make microneedles into reality. The first microneedle experiments were reported in 1998 [2], Since then, there has been a rapid increase of interest in the field. Much of this effort concerns the development of novel needle fabrication technologies by adopting various needle designs and materials for use in biological and pharmaceutical applications. 

Figure 6.11. Microelectrode needle design for p02 measurements in tissues (the full electrode design is shown in Said et ai, 1961, p. 1130, Figure 1).

In hepatocellular carcinomas (HCC) within cirrhotic livers in particular, the oven effect can be noticed a well-demarcated ablation, even with volumes larger than expected by the needle design can be achieved because the heat is trapped within the (pseudo) encapsulated tumor volume. 

Beside the specific needle design, and the handling and usability of the different systems, a more... 

Fig. 2.1.3a-f. Various radiofrequency (RF) electrodes a single needle design (Cool Tip, Valleylab System, Tyco), b cluster-electrode (Cool Tip Cluster, Valleylab, Tyco) multi-tined electrodes (c LeVeen, Radiotherapeutics, Boston Scientific d Star-burst XL e perfused Talon needle, AngioDynamics-RlTA) f internally cooled, bipolar single needle electrode (Olympus Celon)... 

In the field of accessories for medical devices, Ortega and Small (2007) studied the effect of a thermally deployable SMP-based adapter for kidney dialysis needles, designed to reduce haemodynamic stress on the arteriovenous grafts. This tube-shaped adapter can be delivered through the needle and thermally deployed upon blood contact. Both computational fluid dynamics simulations and in vitro flow visualization measurements show that the adapter is able to redirect the needle flow so that its impact on the vascular grafts is reduced. 

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