Manufacturer of pressure-sensitive adhesives, MACtac, Stow, Ohio, says patient comfort can be a difficult goal when it comes to adhesives used on bandages for covering wounds or holding catheters in place.
“Sometimes medical devices must stick to skin for long periods of time while withstanding showering and exercising,” says Aaron Smith, technical marketing manager. “So we developed our new Silk adhesives with good skin adhesion that can be removed cleanly and gently without hurting the skin. In addition, the adhesives are okay for sustained skin contact and remain stable after sterilization.”
For manufacturing techniques, one method perhaps not familiar to some is two-shot molding. Companies like Northeast Mold & Plastics Inc., Glastonbury, Conn., take two-piece designs and redesign components for a manufacturing process that uses two separate injectors. Two-shot injection lets engineers combine two parts into a single component, include seals for water protection, and make parts with movable features using in-mold assembly. The twoshot technique is for parts such as soft-touch handles and multicolor knobs.
In contrast, metal stamping is a familiar operation. But what if medical parts must be shaped from films, foams, adhesives, or nonwoven materials? Companies like Plitek LLC, Des Plaines, Ill., say, “Think precision die cutting.” An example might come from flat-bed die cutting for large-format and thick parts. The company says this can include in-line material cutting and kiss cutting (i.e., die cutting a laminated substrate’s face material without cutting the support material). Another example is rotary die cutting which can handle intricate parts with many layers including in-line laminating, slitting, and adhesive coating.
A technique somewhat similar to plastic injection molding is rubber injection molding. Although the design of rubber parts has long been considered an art, it is actually a science. So says Vernay Laboratories Inc., Yellow Springs, Ohio. According to National Account Manager Scott Pakenham, the company uses proprietary software to extract needed data from a large online library of test data. Designs that conform to typical part families have already been analyzed, so new designs can be generated by interpolation without full FEA simulations. To pinpoint undesired flow, cavitation and noise, pressure loss, and turbulence, the company uses CFD and FEA. Of interest in the near future is using a 3D physics program to model rubber molding. This would include cross-linking and simultaneous thermal analysis of heaters, mold, cavities, and rubber.
Innovative equipment for inspecting parts includes software that lets users check items based on color. For example, Dalsa in Ontario, Canada, now includes iNspect Color software with its Vision Appliances. The software can, for example, confirm the correct color cap or label is applied on drug bottles or verify the number and color of pills in a blister pack for pharmaceutical packaging. The software includes scriptlike programming and network commands for OEMs and system integrators.
For an unusual business view, Ed Goldman, senior vice president of Foster-Miller Inc., Waltham, Mass., says “Medical products that must be made on customized equipment can actually lead to higher profits. Commodities such as crutches, cotton swabs, and disposable exam gowns are often differentiated only on price, which tends to force profit margins lower,” he says. “In contrast, devices such as syringes from Becton- Dickinson (Franklin Lakes, N. J.) are successful because making them requires custom-engineered equipment. This protects the company’s investment and patents on manufacturing equipment. A competitor would have to overcome brand-name recognition and develop an alternate way to make an equivalent device, a cost barrier higher than most are willing to pay.”
Finally, in one of several technical conferences, Anthony Walder, a research chemist at Lubrizol Advanced Materials Inc., Cleveland, Ohio, talked about engineering polyurethanes. “Polyurethanes are made of what are called ‘hard’ and ‘soft’ domains. Varying the domains’ ratios formulates materials ranging from soft to hard (72 Shore A to 84 Shore D). Medical-grade polyurethanes are designated aromatic or aliphatic, but there is not much difference between the two as far as having a high tensile strength (4,000 to 10,000 psi), high ultimate elongation (250 to 700%), good biocompatibility, high abrasion resistance, and other features. And both materials soften considerably within minutes of insertion in the body, a big plus for patient comfort.”
Lubrizol Advanced Materials
Northeast Mold & Plastics Inc.
Vernay Laboratories Inc.