Most of the lab-scale instruments currently available in the industry are fully capable of producing test strips in a low- to moderate-volume manufacturing environment. When selecting instruments for this application, there are two primary factors to watch for: equipment quality and scalability.
As with most things in life, the quality and durability of the tools used to produce a product will more than pay for themselves over time. Quality equipment usually costs a little bit more initially, but the real cost of ownership is more dependent on how reliable and stable it is in extended use. Problematic equipment can cost more in repairs and lost production than the original cost of purchase. As product demand increases, so too will the demand on the machinery used to produce it. For this reason, it is very important to maintain a view toward scale-up in the early stages of product development.
Lab-scale to moderate-volume liquid reagent-dispensing instruments generally consist of a small bench-top module that secures the membrane in place and moves it beneath several precision dispense tips. An individual sheet of membrane is placed on a flat surface (platen) and secured by vacuum. Precision liquid-metering pumps are utilized to deliver a very precise and uniform volume per unit time of reagent to the individual dispense tips. Then, as the vacuum platen is moved uniformly beneath these dispense tips, fine lines are dispensed onto the surface of the membrane. Once a sheet of membrane has been successfully dispensed, it must be removed from the instrument and dried. This can generally be done by allowing it to sit for an extended period of time in ambient atmosphere. Alternatively, drying can be accelerated by placing each sheet in a heated drying chamber.
Small-scale lamination systems provide a means to accurately place the various filters and membranes to create a laminated card containing a multitude of individual test strips. Commercially available card laminators are usually designed to secure pre-cut sections of the components on a vacuum platen. Each individual component must be manually positioned using precision guide features on the instrument. Once accurately positioned, each component is secured in place by vacuum and then assembled onto the exposed adhesive of the plastic backing material while maintaining its precision alignment. Such small-scale lamination systems are not particularly high throughput instruments, but they do serve to create accurate laminations so long as the operator is careful to accurately place each component relative to the guide surfaces provided.
There are two different approaches to test-strip cutting—guillotine shear cutting and rotary slitting. Each process has distinct advantages and disadvantages relative to the other. Guillotine shear cutting has a distinct advantage over rotary in that it is highly flexible—strip widths can be changed at will. In a matter of seconds, a different strip width can be entered via a programming keypad. It is this flexibility that makes guillotine shear cutters such an important part of every development lab. One problem with guillotine cutters is that adhesive can build up very quickly on the cutting surfaces, causing significant problems and requiring frequent cleaning. Depending on the type and amount of adhesive present in the product, this problem can be quite severe and can be disastrous in a production environment. Another issue with guillotine cutters is that of blade sharpening. Because each strip produced comes from one blade action, there is a one-to-one correlation of blade cycles to test strips produced— millions of blade actions are required to produce millions of strips. The blade wears down over time, especially if the laminate being cut contains glass fibers or other tough or abrasive materials. As the blade wears, adhesive buildup problems become more acute, requiring more frequent cleaning. Ultimately, the blade must be removed and sharpened.
Rotary shear cutters mitigate the two primary issues with guillotine shears. However, this too comes at a cost. Rotary shears are inflexible—to change a strip width requires a change of tooling. Rotary cutters are dedicated to a specific strip width. As such, they are extremely accurate and repeatable, but they are designed to cut only one strip width. Rotary shears are designed to cut many strips at one time—as many as 50 strips. This means less adhesive buildup, because for one action of the shear, 50 strips are produced as opposed to only 1 from a guillotine. Additionally, the strips are not cut at the same place on the rotary shear blades each time. This means the adhesive buildup is even less. So, whereas in extreme cases (depending on adhesive) a guillotine blade may require cleaning after as few as 2500 to 5000 strips (10 to 20 min), a rotary shear module might require cleaning after 500,000 strips (8 h) or even more. On the other hand, the guillotine blade can be cleaned in a minute or two, whereas, the rotary cut module may require as much as 30 min or more to clean. The same goes for sharpening—the guillotine shear blade may require sharpening as frequently as every other month or so, whereas the rotary cut module may go a year or more between sharpenings. All this obviously depends upon usage and types of materials being cut.
Another significant advantage of rotary shear cutting is the tremendous output capability of the process. Assuming 50 strips per card and 20 cards per minute being processed, output is easily 1000 strips per minute. Compare this to guillotine cutting—the fastest guillotine cutter on the market cuts 360 strips per minute. Allowing for manual placement of cards and the trimming of the leading and trailing ends of each card, the net output is no better than about 250 strips per minute from a guillotine shear.
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