This micromolded filter features more than 76-µm squares.
Big Things Come in Small Packages
It seems as though the prefixes micro and nano are on every member of the medical community’s lips. The advent of nanotechnology, the popularity of minimally invasive surgery, and the efficacy of implantables in delicate body tissue are all spurring the shrinking of devices. And though prospects for the future appear exciting and wide-ranging, one pressing issue is much less discussed: the manufacture of these minute medical components.
Micromolding is recognized as a process capable of churning out some miniature products on the horizon. Already relied upon for many small applications, micromolding will most likely expand significantly in conjunction with the swelling demand for miniaturization.
Donna Bibber, vice president of sales and marketing for Miniature Tool & Die (MTD; Charlton, MA), attests to the rapid growth of the micromolding sector. “We have been in business for 34 years, doing micromolding for 8,” she says. “It was kind of frustrating at first, but we put in a lot of effort. About 6 months ago, the floodgates opened and I have barely been able to take a minute to breathe since!”
Despite a flourishing market, the industry is plagued by an inconsistency. Many companies disagree as to what constitutes a micromolded part. Some firms vaguely define one as having a mass of less than a gram. MTD defines a micropart as one molded from fractions of a pellet, weighing less than a gram, and featuring a wall thickness of 0.005–0.010 in.
MTD has made its mark in the industry, having laid claim to the smallest molded component in the world. The firm creates 520 of the parts per pellet, each with a weight of 0.00012. The firm has also released what it touts as one of the world’s smallest single-piece injection–molded filters. The micromolded filter features 76-µm squares with wall thicknesses of 0.006 in. and offers ranges of 18–36% open area for use in nylon and polypropylene filtration products. According to Bibber, the micromolding of the filter converted an eight-step process into a one-step process.
Beyond filters, MTD micromolds resorbable polymers for implantable materials. Despite a hefty price tag that can range from $3000 to $12,000 per pound, the materials are considered desirable because the implantable device market is thriving. Properties of the materials include heat and moisture sensitivity. They are designed to degrade in the body.
In addition to its use for small applications, micromolding boasts other advantages as well. “It is advantageous because you use a small amount of a very expensive material; in the medical market you can’t reuse or regrind materials,” says Bibber. “In big-scale molding you are basically throwing away material. Also, in a conventional press the mold is baking in a huge barrel, sitting there degrading and becoming brittle and losing its properties.”
The field of micromolding is growing by leaps and bounds. Right now, it is still somewhat of a niche field. However, as the trend toward miniaturization rolls onward, many more companies are likely to jump on the bandwagon.
Breaking the Mold
Liquid silicone–injection molding can enable reduced lead times and is suited for medical use due to the material’s biocompatible properties.
Though liquid silicone–injection molding has been a major player in the European molding market, it has yet to burst into the spotlight of the stateside arena. Its use has, however, begun to spread in the U.S. market and is increasing, according to Jim Meier, vice president of new business development for Scientific Molding Corp., Ltd. (SMC; Somerset, WI).
Inspired by its success in Europe and Asia, SMC adopted liquid silicone– injection molding capabilities. Since then, the firm has enjoyed its own success, attributing an estimated 10% of its business to the process. SMC acknowledges that this process is its fastest growing sector. “It has had a significant impact. As a matter of fact, within the last year the capacity of SMC has doubled,” Meier notes.
Rather than using conventional plastic pellets, liquid silicone–injection molding, as its name implies, forms parts from the liquid form of silicone. A two-part material, liquid silicone exhibits a consistency that Meier compares to motor oil or soft putty. The material is injected into a hot mold that serves as a curing element.
In the past, silicone has been molded through a rubber vulcanization process, which entails a long cycle time. Liquid silicone allows for reduced compressed cycle times, resulting in reduced unit costs, says Meier. He adds that with this process, the firm was able to produce some tools in 6 weeks that typically would have taken 20 weeks.
Owing to its biocompatible, inert, and flexible nature, silicone is well suited for the medical industry. Among the advantages of silicone–injection molding are repeatability, limited contamination and human contact, flash-free precision, and rapid curing cycles.
“It’s the perfect material for the medical world,” Meier asserts. “When we combine the benefits of silicone with the process of liquid–injection molding, the results in terms of components, and especially in terms of economies, is very beneficial to our customers.”
Along with liquid silicone–injection molding capabilities, SMC also specializes in two-shot injection molding. Two-shot molding is performed for enhanced aesthetic and textural value. Because tools with features such as flexible grip handles are often preferable to users, demand for two-shot and multishot injection molding is on the rise, according to Meier.
“The user demand, in most cases, is from surgeons in an operating room or clinic that are holding on to a surgical device,” says Meier. “And if there’s a better feel or grip imparted to a product by using two-shot elastomeric compounds, that creates more sales for the producer and more two-shot molding applications for us.”
The availability of bright colors and different textures may not be vital to the use of a product. However, aesthetics differentiate products and appeal to the senses, hence the growing popularity of two-shot injection molding. And the cost effectiveness and repeatability of the process are added incentives.