Medical Tray Design: Every Detailâ€”and Every Needâ€”Counts
From the choice of material to the last snap fit, designers and end-users must work together during tray design.
A medical tray is far from being a simple object. And the process of designing one isn't simple either. It involves selecting the right materials, customizing the design to the device, and choosing the right manufacturing and sealing equipment.
Essential to the success of the design process, those involved say, is a close collaboration between the designers and the client. The nature of the collaboration can vary greatly from customer to customer, just as each customer's requirements can vary. Some come to suppliers with specifications at or near completion. Others ask suppliers to design a tray from scratch. Either way, or any way in between, the tray needs to be customized to the client's precise needs.
Plastofilm Industries customized a thermoformed tray for FemRx's specialized tissue aspirating resectoscope.
It is important for suppliers to involve everyone from the beginning in order to design a tray that meets every possible need. "You should optimize the design early on to prevent any unnecessary changes," says Frank Schepp, vice president of Inline Plastics Corp.'s (Milford, CT) custom division. "A big problem is when you sit down with someone with no broad overview. Then marketing and engineering people get involved, and things start changing. The net effect is that it extends development."
When selecting tray materials, designers must consider how the packaged device will be sterilized, how much it weighs, and how important package clarity is. "You can't just grab a sheet of plastic and say 'I want a plastic tray,'" says George Kluzak, design manager for Perfecseal Mankato (Mankato, MN). "You have to gear the plastic to the particular need of the customer." To do that, frequent contact is necessary. Many design firms say they meet often with their clients and involve everyone from engineers to marketers to executives.
Material selection depends greatly upon the way the device will be sterilized. "There are some plastics, like PVC, that can't be gamma and electron-beam sterilized," says Larry Richards, vice president of sales and engineering for Blue Ridge Packaging Inc. (Simpsonville, SC). If EtO sterilization is to be used, designers also must consider how a tray's configuration can affect cycle times.
The design team must also consider how strong and how thick the tray must be. As with other packaging materials, a thin tray with the strength of a thick one is often preferred because it keeps costs down. But designers can't downgauge tray materials too much—the point of using a tray is to protect and support a device, and a thin tray could buckle under the weight of a heavy one.
Package clarity must also be determined. "Opaque is typically less expensive, so if we can get away with opaque, we will," says Karen Greene, project engineer for Baxter Cardiovascular Group (Irvine, CA). "But it's a combination of marketing requirements and packaging performance. Marketing may say they need a see-through tray."
Reducing Stress in Thermoformed Trays
Custom-designed medical trays often feature sharp angles or deep cavities to accommodate particular devices. Unfortunately, the more intricate the design, the greater the chance that some areas of the tray are under extreme stress, which can lead to package failure. "The amount of inherent stress in the formed tray is a result of both part design and forming conditions," explains Jennifer Lauderback, senior technical services engineer for tray material supplier Eastman Chemical Co. (Kingsport, TN). "Trays with more intricate designs tend to contain more residual stress."
To help tray manufacturers minimize such areas of stress, Eastman has teamed up with Strainoptic Technologies Inc. (North Wales, PA) to develop a method of measuring such stress during tray thermoforming. According to Eastman, qualitative analysis of stress patterns helps thermoformers correct subtle changes in processing temperatures, residence time, or cooling rates to maintain part uniformity and integrity.
The thermoformed tray shown on the left has a high level of residual stress, while the one on the right has almost no stress.
To detect stress patterns in trays, manufacturers can place a transparent part between two polarizing filters. Stress in the part splits the polarized light into fast and slow waves in a phenomenon known as birefringence, which is observed as a color pattern. Both the color and the pattern correlate to the degree of stress. To make birefringence measurement a quantifiable, reproducible quality check, manufacturers should use a polarimeter and a compensator. Users should place the compensator—a calibrated, graduated wedge—in series with the measured item. The operator should then adjust the wedge until a black fringe becomes visible at the point of interest. A scale can then be used to supply a quantitative reading. If measurements exceed thresholds, operators can immediately adjust processing parameters. The technique is easier and faster to use than x-ray, chemical analysis, or other methods. Equipment can be easily set up on-line or in a lab for testing at regular intervals during production. Strainoptic has also developed PC-based scanner systems to provide instant readouts.
"The stress pattern has significant messages in it, but most operators do not know how to interpret it, let alone derive quantitative data for quality control," explains Barbara Hoffman, Strainoptic's marketing manager. Eastman, manufacturer of Eastar PETG copolyester, offers to help its customers install and set up stress measurement instrumentation.
Unlike a pouch or a stock tray, a custom tray features cavities, snap fits, and undercuts, which are often the tray's most crucial features because they are responsible for positioning the device. "You have to think about product placement and ergonomics," says Tom Wetsch, product development manager, Alloyd Company, Inc. (Chicago).
Tray designers must therefore talk to product designers to find out "the sequence of use of components, how [the tray] will be opened, where it will be used, and how it will be disposed of," says Dick Simmons, vice president of medical marketing at Plastofilm Industries (Wheaton, IL). Answering these questions incorrectly during the design process can result in an inappropriate or too-costly package and could even confuse end-users. If the instruments are placed in the wrong sequence, a doctor could pick up the wrong one. If the package is hard to open, valuable time could be lost during surgery. "All that plays an important part as to whether a physician may want to use that product again," says Perfecseal's Kluzak.
THE DESIGN PROCESS
Tray design may begin with sketch drawings, but it always progresses to a computer model, usually produced by CAD software. Open-architecture design software is helpful in this situation, because it allows all design team members to access drawings over the computer, which smoothes and speeds up the process. "Communication over the Internet is expected, not just a nice option," says Randall Loga, director of engineering at Tek Packaging (Huntley, IL, and Stockton, CA).
Alloyd's Wetsch also finds Internet communication useful. "You can obtain documents, files, and drawings from the customer" that way, says Wetsch. "You can take product drawings, pull the numbers off, and transfer the data into the design of a part," even if the device hasn't been manufactured yet.
There are several ways of handling computer design, but Loga says his company has found a particularly efficient way. "A fully integrated system is the best way to approach packaging development," he says. "We use the same exact CAD program—Pro Engineer—to do the concept sketch, the preliminary part drawing, the prototype mold, the production tool, and the program to cut tooling. So if you modify one, you modify all. This means huge time and cost savings to the customer."
As accurate as the computer models may be, end-users often like to see a solid prototype because "people like to see 3-D models; they want to be able to touch things," says Greene of the Baxter Cardiovascular Group.
With a 3-D solid modeling package, "we can draw the exact tray they want and then do a rapid prototype," says Shawn Hartmann, senior design engineer for UFP Technologies (Georgetown, MA, and Raritan, NJ). "We can send the file out in 3-D and get a quick mold in a day."
Designers must also make sure the tray materials are compatible with the tray manufacturing process. Most trays are produced through thermoforming, but some are made by injection molding. The latter is more expensive—the production costs are often about the same, but the mold itself can often be as much as five times more costly. "There are limits to what you can do with thermoforming," Greene says. "We have had people at our company who require injection molding. They are looking for peculiar dimensions or using heavy-gauge materials."
Many designers use a wide range of thermoformers to produce trays, and machine selection is based on tray material, gauge, size, and production volume.
The sealing process also needs to be considered because the way the package should be opened does affect design. Anthony Giovannone, president of Sencorp Systems (Hyannis, MA), a member of the DT Industries Packaging Group, says that while heat-sealing machinery manufacturers like Sencorp are not heavily involved in the design of the tray's form, they do make sure they understand the customer's requirements and suggest which machine will provide the best seal. "We have specific models that are ever more precise in setting the flatness of the platens, the tolerance of toggles, and the pressure per square inch in the seal area," he says. "You need repeatability of that seal." Adds Kent Hevenor, Sencorp's product manager of laboratory machinery, "If there's unevenness in the thickness of the flange, we can make up the difference."
There are more than a hundred health-care tray thermoformers in North America, so tray suppliers must distinguish themselves by offering quality customized trays quickly and economically. "Speed, cost, and accuracy are all number one," says Simmons of Plastofilm. Hartmann of UFP agrees. "Technological advances have enabled us to work more quickly than in the past," says Hartmann. "People see that you work quicker, so they ask for it quicker."
Such heavy competition among tray thermoformers definitely benefits packaging engineers, because it forces each tray supplier to do everything it can to meet client needs. But speed and quality alone shouldn't solidify a relationship. What element matters most and ultimately leads to the other two is a supplier's willingness to work closely with its client. The end result is a tray that accommodates every conceivable requirement from appearance to sterilization to handling. And only by involving everyone—packagers, sterilizers, marketers, and end-users—can a supplier incorporate such requirements into the tray design process.