Microtubular cells

The molecular weight or size of an optimal delivery system in vivo is imposed by the physiology of circulation and excretion. The lower limit of the molecular weight is about 30 kDa because the microtubular cells in the kidney readily excrete hydrophilic molecules whose molecular weight is 30 kDa or less.23 In fact, this is the major route of elimination for many small-molecule drugs after they are transformed into more hydrophilic metabolites. Therefore, a drug delivery system should have a combined molecular weight of 30 kDa to avoid such a quick renal clearance. 

The single tubular cell with 1.6-mm diameter and 1-cm length, generated about 140, 300, and 350 mW at 500, 550, and 570°C with Hj fuel, has been reported. This indicates that a cell stack of 55-cell arrangement whose volume is about 1 cm can possibly generate 3.5, 7.5, and 8.7 W at 500, 550, and 570°C, respectively, using the microtubular cells [8]. 

Paclitaxel (Taxol, NSC-125973), obtained from Taxus species, is a diterpene with intense antitumoral activity because of its tmique mode of action on the microtubular cell system. It is one of the most successful anticancer drugs developed in the past 50 years. Due to several difficulties associated with obtaining Taxol and related taxoids firom plants growing in nature, plant cell cultures are considered to be the most favorable and environmentally sustainable approach for its production of at an industrial level. Some pharmaceutical companies, such as the... 

Two general types of tubular cells are currently being pursued, cells with a large diameter (>15 mm), and microtubular cells with a very small diameter ( < 5 mm) the microtubular cells are discussed in Section 8.4. 

Co-extruding a strip of lanthanum chromite based interconnect along the length of a YSZ microtube has also been demonstrated [45], although a number of difficulties remain. Firstly, the tubes are much weakened by the interconnect strip, and secondly the mixing of lanthanum chromite and YSZ at the boundary of the co-extruded materials leads to a dead-zone of material, about 350 pm in extent. Thus any microtubular cell design with co-extruded interconnect will require much further development to be successful. 

Figure 8.28 Cross-section ofal 000 microtubular cells unit.

In 2000, Acumentrics Corp built a 1000-cell stack to illustrate the possibility of providing reliable power for computer systems back up. Since then, Acumentrics has designed and built several 2-5 kW systems using microtubular cells for use as back up power sources for broadband and computer systems. 

Acumentrics Corporation of Westwood, Massachussetts, USA, has produced several 2 kW size fully integrated rapid-start SOFC systems using microtubular cells, and delivered them to prospective customers. These systems operate on natural gas, and the intended application is as uninterruptible power supplies for broadband, computer and telecom backup. 

Microtubular cells were first made in 1990 by Michaela Kendall which were 1-5 mm in diameter, possessed 100-200 pm wall thickness and were made from extruded yttria-stabilised zirconia. After this achievement, Kendall and his co-workers demonstrated 20 cell, 200 cell, and 1000 cell reactors. Only a hot-air-fed reactor could heat up to the desired operating temperature and the cell could withstand an increase of temperature up to 200°C/min. Professor Kendall set up the first company in 1996 for microtubular (MT) cells known as Adelan (UK) Ltd. It was demonstrated by Bujalski that the operational temperature of these MT cells could be ramped at a rate of 4000°C/min, which indicates the rapid start-up time of 12 s for SOFC without any operational or structural damage to these cells. Second, these cells could be cooled extremely fast without any damage. The typical design of MT-SOFC and a 50 W portable MT is shown in Fig. 4.19a, b. The YSZ tube of thickness 150 pm and... 

Table 4.1 Microtubular cells stack designs by various firms...

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