Originally Published May/June 2000

Product Update

Advances in Adhesives and Pressure-Sensitive Components

Norbert Sparrow

Novel technologies and increased capabilities enable suppliers to enhance final product designs.

Process validation, shadow-curing formulations, and products that permit accelerated throughput are among the primary demands of OEMs sourcing medical-grade adhesives, according to some of industry's leading suppliers. Custom adhesives that solve specific application problems continue to be a key focus among R&D personnel at many of these companies. Issues foremost in the minds of manufacturers seeking pressure-sensitive components include reductions in the coefficient of friction, advances in moisture vapour transmission rates (MVTRs), and the ability of converters to rationalize manufacturing processes.

A premixed two-component epoxy developed by Permabond cures at room temperature and has a long pot life. The adhesive is suited for the manufacture of catheters and other plastic devices.

Accelerating production while maintaining compliance with quality systems is one of the benefits of using adhesives that fluoresce. "Validation is becoming more and more of an issue," says Laurie Gibbons, medical manager at Permabond (Eastleigh, Hants, UK), who notes that many device companies are changing their process lines to accommodate adhesives with fluorescing capabilities. Fluorescing adhesives, such as Permabond's UV-cure 4L47, produce bond lines that become visible when exposed to UV light. This facilitates quality control either visually or by means of a machine vision system, explains Gibbons.

"Fluorescing is easy to introduce into standard epoxies and UV curing products; it's more difficult to do with cyanoacrylates, which require a certain amount of expertise, but it can be done," says Gibbons.

Device Manufacturers Form Strong Bond with Cyanoacrylates

Cyanoacrylates have gained popularity within industry for their rapid cure time and high bond strength. On the downside, UV-only products have curing limitations within shadowed areas, which can compromise high-speed manufacturing processes. To overcome this deficiency, Loctite Europe (München) has developed a cyanoacrylate that cures either by exposure to UV light or by means of the standard polymerization mechanism. The principal advantage of this product, according to the company, resides in a secondary cure mechanism that doesn't require heat or chemical activators.

Shadow-curing formulations are also being developed at Medical Engineering Technologies Ltd. (Ashford, Kent, UK). "Manufacturers like the convenience of UV curing because they can assemble their product, move things around, and then cure on demand," says commercial manager Mark Turner. "But what they would ideally like is to be able to give the adhesive a quick flash of light and to have it cure later, so that they don't have to wait for the product to completely cure before taking the device out of the production process." These so-called shadow-cure grades are gaining in popularity, according to Turner, especially among device manufacturers with automated processes, where extended dwell times are not desirable. "We have a couple of shadow-cure products currently available, and more are on the way."

Wound Dressings Get Smarter

Quality is a primary concern of device manufacturers sourcing pressure-sensitive products. "Our customers are demanding greater consistency in processing parameters," says Kären Olson, vice president and general manager of the medical business unit at Adhesives Research Inc. (Limerick, Ireland). "They want to know down-line and across-line that we are holding the tolerances that they require. Quality, CGMP compliance, and technical support are what our customers are looking for."

Adhesives Research has channeled considerable resources into implementing CGMP compliance, notably in facilities dedicated to the development and production of PSAs used in transdermal drug delivery systems. The pharmaceutical business unit, which manufactures these systems, features isolated manufacturing processes, controlled access to each manufacturing area, and strict gowning requirements.

For Peter Walker, medical market manager at Rexam Image Products (Wrexham, UK), technological advances in wound dressing components are a focus, notably in the development of smarter, condition-specific dressings. In essence, this refers to dressings adapted to the different phases of wound healing. According to Walker, "A smart dressing will develop a moist environment initially, allowing enough moisture to escape so that the wound doesn't become macerated. As the wound begins to heal, the moisture vapour transmission rate may shift to a lower level to maintain a moist environment."

In addition to breathability, tactile comfort is a key consideration in the development of wound-care products. Rexam recently announced the availability of a lubricious polyurethane with a 0.2 coefficient of friction. "When you rub this material," says Walker, "it's like touching wet glass."

Converters Focus on Specific Application Solutions

Suppliers increasingly are called on to offer product design support, to manage processes that free up OEMs and allow them to concentrate on their core technologies, and to provide an array of ancillary services. As in other contract service categories, the trend among OEMs is to look for "single-source suppliers with a range of capabilities," notes Svein Harvang, European marketing manager at 3M, Medical Specialties Dept. (Bracknell, Berks, UK).

"We are noticing a heightened demand for customized components suited for unique applications," says Olson. "The best solution may not be to design a finished device around a standard industrial tape. OEMs want the flexibility of having us design around their specifications or needs and putting together all the different component parts."

Leveraging a supplier's expertise early in the process can lead to considerable cost savings down the road, adds Acutek International (Brussels) vice president Karen Kline. "A contract manufacturer can help the medical device designer to avoid costly mistakes," says Kline. "A material or configuration can look great in the prototype phase and perform well in clinical trials and clear the regulatory process. But then you may discover that the design does not support the speed or precision needed for economical high-volume production methods." An experienced converter can also offer the designer expanded options for product refinements that are simply not available by using in-house manufacturing processes, Kline adds.

To further streamline product development and manufacture for their OEM customers, many suppliers are adding secondary services to their portfolios. "It's more and more common to have printed information directly on the device," says Harvang. 3M has a full-service converting module for medical products in Germany designed to fulfill OEM demands for single-source suppliers, he adds. Acutek offers multicolour printing among its array of secondary services at facilities in the United States and Ireland.

Ultimately, all of these companies share a common goal, summed up best by Walker: "What we hope to provide are novel technologies that will take the final product to a higher level." If your sourcing responsibilities encompass adhesives and pressure-sensitives, we invite you to read the company profiles on the following pages. You will almost certainly find a supplier able to meet your needs, and possibly even surpass them.

Permabond

A low-viscosity UV-cure adhesive that facilitates in-line quality control and a cyanoacrylate bonding agent that increases throughput while eliminating stress cracking are among the newer products offered by Permabond (Eastleigh, Hants, UK).

The 4L47 adhesive cures instantly when exposed to UV light and is compatible with plastics typically used by device OEMs, such as polycarbonate, PVC, polystyrene, and acrylics, as well as steel. "It is suited for high-volume applications such as needle bonding," says medical manager Laurie Gibbons. A wicking-grade adhesive, 4L47 can also be used to bond housings and plastic components. The resulting bond lines are colourless and transparent but fluoresce under the influence of UV light. "This is a growing demand among device manufacturers who perform quality control either visually or by means of in-line machine vision systems," explains Gibbons.

Also suited for high-speed production, the 4C50 cyanoacrylate can be used for bonding, sealing, and fixturing parts and substrates routinely used in the medical device industry. "Unlike ethyl or methyl cyanoacrylates, our product is an alkoxyalkyl cyanoacrylate," notes Gibbons, "which will not stress plastic parts." The adhesive bonds a variety of substrates including steel, brass, plaster, stone, and aluminium as well as a range of plastics from ABS to PVC within 5 to 20 seconds. The single-component adhesive has a viscosity of 100 cP at 77°F.

Permabond offers a variety of other formulations for diverse applications, but most of what emerges from the lab is never commercialized, says Gibbons. "We tailor the technology for specific applications," she says, "and actually only market a small portion of what we produce."

Rexam Image Products

Wound dressing components are developed, formulated, and produced to suit specific medical and pharmaceutical applications. The company can control characteristics such as MVTRs, adhesion, coefficient of friction, and wear profiles through selective formulation. One product developed by the firm that has become very popular with device manufacturers is a lubricious polyurethane film.

The film developed by Rexam Image Products (Wrexham, UK) achieves a low coefficient of friction while retaining desired MVTR levels. "Through formulation adjustments, Rexam has been able to reduce the coefficient of friction of its standard polyurethane from a region of one down to 0.2," says medical market manager Peter Walker. "Our film allows the patient's clothing and bedding to move freely over the wound dressing. The film's MVTR of 10,000 g/m²/24 hr remains unchanged," explains Walker.

A core strength of the company is the scope of polyurethane chemistry it has at its disposal. Polyurethanes reportedly possess performance characteristics that are crucial for the functioning of smarter and more condition-specific dressings. "A smart dressing, for example, will develop a moist environment initially, allowing enough moisture to escape so that the wound doesn't become macerated," explains Walker. "As the wound begins to heal, the MVTR may shift to a lower level to maintain a moist environment."

Certified to ISO 9001, the company has plants located throughout Europe and the United States. All of the coating lines are housed in temperature-controlled, air-conditioned, positive-pressure rooms with air filtration systems effective to 0.5 µm.

Alpharma AS

A company with 15 years' experience supplying specialty medical-grade tapes to European and US device companies provides pressure sensitives based on nonwoven materials, films, foams, and adhesive-coated fabrics. Located in Vennesla, Norway, Alpharma AS owes its success to a responsive business philosophy, according to export manager Helge Muggerud. "We are quite a small company," he explains, "and this allows us to be very flexible with our customers. We do a lot of niche work and are especially skilled at accommodating short lead times."

The company's forte is the development of custom adhesive materials to suit converted applications. "We can satisfy most customer requirements, from products used in wound-care applications, where gentleness and breathability are desirable, to more-aggressive formulations," says Muggerud.

Materials routinely processed by the converter include polyethylene and polyurethane foams, polyamide and polyester nonwovens, polyethylene and polyurethane films, and elastic or nonstretching woven fabrics. In addition to wound-care and surgical products, applications include diagnostic devices, ostomy bags, electrodes, and IV components.

Acutek International

Recently acquired by Scapa Group plc (Blackburn, Lancs, UK) and now a member of Scapa Medical, a business unit of Scapa Tapes North America, Acutek International (Brussels) is a custom converter that specializes in the manufacture of pressure-sensitive adhesive components. The company processes materials for use in pulse oximetry, wound care, incontinence, transdermal drug delivery, diagnostic testing, drug infusion therapy, and a range of other applications. Commonly used materials include polyethylene and polyurethane foams, nonwovens and wovens, laminated foils, antifog films, hydrogels and hydrocolloids, and mineral oil polymers.

One of the core strengths of the company, according to vice president of marketing Karen Kline, is the expertise it has gained converting an array of materials for more than a quarter century. "We can provide informed guidance to our customers in terms of materials selection," says Kline. "Plus our versatile equipment and converting expertise offers medical device designers greater options that may not be available at their in-house manufacturing facilities. They can turn over a good part of the pressure-sensitive component design to us," Kline explains, "and free themselves up to work concurrently on other aspects of their projects."

The company's capabilities at manufacturing facilities in Ireland and the United States include flexographic printing, precision rotary or flat-bed die-cutting, and multilayer lamination. Quality systems are certified to ISO 9001 and EN 46001 and the firm is registered with US FDA.

Scapa Medical also manufactures component materials for the medical device industry including foams, extruded film, and coated products.

Tapemark Medical/Industrial Fabricating Div.

"We specialize in complex applications," says Jeff Noren, business development manager at Tapemark Medical/Industrial Fabricating Div. (West St. Paul, MN, USA). The company was founded in 1952 and is an experienced converter of foams, gels, hydrocolloids, foils, and films. For the past 15 years, Tapemark has produced diagnostic kit components, wound dressings, and pressure-sensitive labels for the device industry. Additional divisions specializing in label printing and specialty coatings augment the company's work in the medical field.

Medical projects are completed in the company's Class 100,000 and Class 100 cleanrooms, where machine vision systems control die-cutting processes. Much of the company's equipment—which includes rotary laser die-cutting machines—can be modified for customer-specific applications. According to Noren, Tapemark has made efforts to match its technical inventory with human expertise: "We realized that if we were serious about the European medical sector, we needed to offer design assurance," he says. The company has an on-site engineering staff to assist customers with design and to shepherd components through production in an efficient manner.

Tapemark is both drug and device registered with US FDA, and operates according to quality systems certified to ISO 9001/EN 46001. Noren comments that the company is more than just a converter: "Our technical development group helps customers speed new products through the necessary approval phases, even providing prototypes and short initial runs for clinical evaluation samples." He adds that Tapemark's status as a preferred converter with companies such as 3M allows it to acquire raw materials at competitive prices.

Adhesives Research Inc.

Two IVD tapes for blood glucose monitoring and related devices were recently developed by Adhesives Research Inc. (Limerick, Ireland). ARcare 8876 is a clear, single-faced printable 5-mil polyester film tape that is coated on one side with medical-grade PSA, while ARcare 8868 is a 3.2-mil-thick matte polyester film coated on both sides with a medical-grade PSA and constructed with an inert acrylic adhesive. The adhesive designed for use with these diagnostic products is one of their strongest features, according to Kären Olson, vice president and general manager of the medical business unit.

"We have selected materials for the chemical composition that we believe will not interfere with the assays," she says. "The application is really individualistic, but we are addressing a variety of uses that employ a range of samples," says Olson. "So we have tried to do a broad screen brush to identify [and eliminate] chemicals that have the potential to interfere."

Olson adds that, while Adhesives Research offers a standard product line for the smaller, entrepreneurial customers—and also recently introduced pressure-sensitive adhesives in card form for diagnostic testing products geared to this market—the company's core strength is providing custom solutions. "Eighty percent of our business, in fact, involves the utilization of our technology toolbox for product customization. That is the cutting edge of the marketplace for us," says Olson.

The company offers custom capabilities in polymerization, mixing, adhesive coatings, and release liner design supported by extensive analytical technology. It has broad expertise in the development of PSAs, films, laminations, and related materials used in transdermal drug delivery systems. Adhesives Research also supplies wound-care products that employ a patented technology enabling the adhesive to absorb moisture while allowing vapour to pass through the urethane.

Medical Engineering Technologies Ltd.

UV-cure adhesives suited for bonding steel needles to plastic hubs were recently developed as easy-to-use replacement materials for epoxies. Unlike two-part epoxies, the MET UV 816 adhesives supplied by Medical Engineering Technologies Ltd. (Ashford, Kent, UK) do not require mixing. "You can avoid this by using frozen epoxies, of course," notes commercial manager Mark Turner, "but then you have storage and handling problems. With our UV-cure adhesives, you get away from all of the pot-life issues. You just dispense them as needed," he says. The adhesives come in a variety of viscosities and withstand EtO and gamma sterilization. "In addition, they are formulated to resist water ingress, making them suitable for use with prefilled syringes, and can be made to fluoresce for quality control purposes," adds Turner.

Medical Engineering Technologies offers a broad range of cyanoacrylates, epoxies, and UV curing materials for device manufacturing applications. The company has particular expertise in finding solutions for even the most exotic bonding problems, claims Turner. One recent example he cites is a request for a rapid-curing formulation for PTFE or silicone. The firm offers a system to bond low-energy surfaces using a cyanoacrylate and primer that produces a strong bond that will withstand sterilization and the rigours of use. "If we don't have a grade available to solve a particular problem, we will go into our lab, mix a few things together, and find the right material."

It also helps that the company is staffed by people who have worked in the development and manufacture of medical devices, adds Turner. "They understand the practical and regulatory requirements of our customers, and this ease of communication can save our clients quite a bit of time."

3M, Medical Specialties

Dedicated to the development, manufacture, and supply of medical-grade components, products, and services, 3M's Medical Specialties Dept. (Bracknell, Berks, UK) works in close cooperation with customers to identify components that will enhance the final product's design. The firm can provide medical-grade pressure-sensitive plastic, nonwoven, and foam adhesive tapes; liners; fabricated components; specialty films; and adhesive systems. Applications include surgical drapes and gowns, wound-care products, electrodes, procedural kits, ostomy products, diagnostic devices, disposables, allergy patch tests, and stick-to-skin products. The firm provides converting and subassembly services from its European Converting Module located in Borken, Germany.

"The converting capabilities at this facility are fairly recent," says European marketing manager Svein Harvang. "Although this facility was acquired by 3M in the early 1970s and has been developed over the years into a centre of excellence for the medical group, the converting capabilities are only about three years old." Demand for these services has increased considerably since then, adds Harvang, largely as a result of the medical device directives that have brought to the fore ISO certification issues among suppliers of components.

Certified to ISO 9001 and EN 46001, the facility offers slitting, rewinding, rotary and flat-bed die-cutting, laminating, prototyping, and sheeting. Harvang adds that one of the company's strengths is that 3M is as attentive to its client's converted product needs as it is in manufacturing its own products. "That, and our rotary conversion capabilities," says Harvang. "Most converters have die-cutting capabilities, of course," says Harvang, "but the question is, how fast are the machines? High-speed die-cutting is an important asset for converters."

Loctite Europe

Instant- and light-cure adhesives along with flexible adhesives and sealants are offered to device manufacturers by Loctite Europe (München). Characteristics shared by these products include an absence of solvents, ease of use, and compatibility with most sterilization methods. The adhesives withstand EtO and gamma sterilization and can be subjected to prolonged steam sterilization cycles at 170°–175°C. They can be deposited manually or automatically, and the formulations are compatible with cleanroom assembly requirements.

Light-cure adhesives are suited for bonding applications in which one of the components is transparent. "A typical material combination would be stainless steel and polypropylene," says European market development manager Thomas Naudet. He cites a current application that involves bonding a 304-stainless-steel needle with a KR-01 resin hub. "After a 5-second UV cure, the bond is automatically tested to a 50-N pull," says Naudet. According to the device manufacturer, the pull-out force required to separate the needle and hub actually attains 120 N. The MD light-cure adhesives are available in viscosities ranging from 100 to 10,000 cP.

Instant adhesives in the company's MD family are available in viscosities from 3 to 1500 cP. "Recent technological advances have made it possible to use these products on difficult-to-join polyolefins," notes Naudet. "Meridien Medical, for example, uses our instant adhesive to bond polypropylene and silicone for a pump set used in the manufacture of radioactive drugs."

Flexible sealants and adhesives can be applied to extruded or moulded silicone parts in combination with stainless steel, glass, or aluminium to provide a hermetic seal. Typical applications, according to Naudet, include colostomy bags, endotracheal devices, and Foley catheters.

The company's 30 USP Class VI formulations are described in the most recent edition of the Loctite Worldwide Design Handbook, available in print and CD-ROM versions.

Epoxy Technology Inc.

To keep pace with advances in the design and manufacture of pacemakers, prosthetic devices, dental tools, disposables, and other medical equipment, a company has announced the availability of 13 USP Class VI–compatible epoxies. Developed by Epoxy Technology Inc. (Billerica, MA, USA), the solid adhesives have been used to successfully bond plastic tips to tubing, join fibre-optic bundles for light guides, and adhere diamond scalpel blades, among numerous other applications.

One of the adhesives is a silver-filled electrically conductive formulation suited for use in hybrid microelectronic components. The company also offers a fast-curing UV adhesive and a clear epoxy with a long pot life that cures at room temperatures. Epoxy Technology has supplied specialty polymers and epoxies to high-tech industries since 1966.

G&L Precision Die Cutting

A converter specializing in die-cutting, printing, and slitting of films, vinyls, and other nonmetallic medical and diagnostic components is equipped with a range of rotary presses and reciprocating punch presses that can accommodate cutting widths up to 215.78 mm. G&L Precision Die Cutting Inc. (San Jose, CA, USA) also has a temperature-controlled dry room and Class 1000 cleanroom on-site for the conversion of sensitive medical materials.

Materials converted include PVC, polystyrene, and clear and opaque white polyester laminated on one side with an acrylic pressure-sensitive adhesive. These products are suited for use in lateral-flow backing and dipstick applications.

Dymax Europe GmbH

A family of UV- and visible-light-curable adhesives has received ISO 10993 certification, which is considered to be the most widely accepted international standard for medical-grade products. The 1100-series, developed by Dymax Europe GmbH (Frankfurt, Germany), incorporates a second photoinitiator that accelerates curing rates, even when curing UV-blocked transparent plastics. To facilitate in-line quality control, fluorescing agents can be added. ISO 10993 was written primarily for finished medical products and that made it rather difficult to apply to adhesives, according to the company. But the effort was worth it, a spokesperson added; because 10993 is more stringent than USP Class VI guidelines, it attests to the quality of the product.

In addition to the 1100-series of products, Dymax supplies a range of USP Class VI adhesives as well as UV lamps specifically designed for use in the medical industry and in cleanroom environnments.