Print heads

This process uses a moving laser beam, directed by a computer, to prepare the model. The model is made up of layers having thicknesses about 0.005-0.020 in. (0.012-0.50 mm) that are polymerized into a solid product. Advanced techniques also provides fast manufacturing of precision molds (152). An example is the MIT three-dimensional printing (3DP) in which a 3-D metal mold (die, etc.) is created layer by layer using powdered metal (300- or 400-series stainless steel, tool steel, bronze, nickel alloys, titanium, etc.). Each layer is inkjet-printed with a plastic binder. The print head generates and deposits micron-sized droplets of a proprietary water-based plastic that binds the powder together. 

Figure 7.4 is a photograph of a portion of the peptide controls slide printer. A stack of microscope slides, ready for printing, is at the far left. The slides are automatically ejected from the stack, one at a time. The slides are moved on a conveyer to the right, positioning them under the print head. The print head has eight nozzles, out of which microliter-sized droplets are ejected onto an underlying slide. The slide conveyer then places a new slide under the nozzles, and the process repeats. 

The Chemical Inkjet Printer (ChIP), an inkjet printer-like device which is equipped with a piezoelectric reagent-dispensing system, has been developed by Shimadzu Corporation. The ChIP can dispense picoliter volumes of matrix solution onto a tissue section, which has four printing heads and nozzles that have no contact with the tissue section surface. 

Figure 1.8 Schematic diagram of a capillary (one of hundreds) within the printing head of a bubble-jet printer. The resistor heats a small portion of solution, which boils thereby increasing the pressure. Bubbles form within 5 (rs of resistance heating after 10 xs the micro-bubbles coalesce to force liquid from the aperture and a bubble is ejected a further 10 xs later. The ejected bubble impinges on the paper moments afterwards to form a written image. Reproduced by permission of Avecia...

In this approach, NAs are directly deposited onto a glass support using a robot able to deliver with high precision a sample to a specific x y programmed location. The NA sample is loaded into a spotting pin (highly miniaturized stainless-steel fountain-pen nibs with a gap) by capillary action, and small volumes are transferred to a solid surface, such as a microscope slide, by direct physical contact between the pin and the solid substrate. Spot size depends on the acceleration of the pen towards and away from the slide, and the surface tension of the slide. After the first spotting cycle, the pin is washed and a second sample is then transferred to an adjacent address. A robotic control system and multiplexed print heads allow the automated immobilization of many different probes simultaneously onto the slide [29]. 

Finally, pins should be cleaned and inspected to ensure they are free of any obstructions of fhe bps prior to use. Manufacturers have specific recommendations on best methods of cleaning their pins. Some vendors such as TeleChem International (www.arrayit.com) offer cleaning solutions and equipment (sonic baths, holders, etc.) for their pins and print heads. In our laboratory, we routinely inspect pins under a microscope before and after cleaning and keep photographic images as records. 

Manufacturer Trade name Print head type Pin/dispenser type Number of Pins/Tips Number of slides on deck Approximate print rate (spots/sec)... 

Figure 4.4 Majer Precision print head and MicroQuill pins. (Majer Precision Engineering, Inc., Tempe, AZ.)...

The Majer Precision print head employs spring action to control pin movement. Each pin is seated in a spring coil, and this allows a similar soft-touch landing and gentle but controlled rebound of each pin upon striking the surface. The Genetix pin head seats each pin between microball bearings to achieve low friction travel and precise rebound. 

Others such as Macas et al. (1998) successfully adapted the Biomek 2000 (Beckman Coulter), a commonly used liquid handling robot, to prepare microarray slides using a specially constructed print head and quill pins. Up to 28 microscope slides could be placed on a work surface for printing. Biomek s HDRT head was adapted to accept microarray quill pins held between two parallel plates with holes drilled on 9-mm centers to dip into 96-well source plates. The quill pins were spring-loaded similar to the design... 

V P Scientific of San Diego, CA now offers a range of adapters, print heads, and slotted pins that can be used with the major commercially available liquid handling robots (Figure 4.12). These print heads can also be transformed into manual gridding devices if only a few microarrays are needed and where the cost of a robotic system is not warranted. 

The selected pin will only fit into that manufacturer s print head pins and print heads of different manufacturers cannot be interchanged without hardware modifications. Obviously, the number of pins and their configuration in the print head are determined by the print head design and this can also vary among manufacturers. Pins and print heads are expensive so choose wisely ... 

Piezo. This is the same basic print head technology as in continuous inkjet. The ink jet droplets are forced out through the nozzle after an electrical signal to the piezoelectric crystal causes a pressure wave to be set up in the ink (Figure 2.35b). The wave can be produced in the bend mode, as in Figure 2.35b or in a push or shear mode. An important variation on piezo technology is the Xaar... 

Figure 2.35 Cross sections of thermal/bubble Jet and piezo DOD print heads.

Bottom coder. A single print head, ink-jet printer for noncontact printing (marking, coding, and overprinting) on the bottom of filled containers. 

Spread the ink onto the screen between the print head and the pattern on the screen. Use enough ink to cover the length of the print stroke and an area wider than the pattern on the screen. 

Close the work-table to initiate the print stroke of the printer. When the print stroke is finished and the print head has returned to its original position, remove the substrate from the work-table and place it in the oven to dry for 2 h. 

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