Adhesives, like so many materials destined for use in medical applications, need to respond to a variety of demands. Not only must they create reliable bonds, but they must do so economically, and without compromising the sensitive components with which they come into contact. Furthermore, some grades of adhesives may need to meet biocompatibility requirements. Such demands have driven the evolution of specialized medical adhesive suppliers, who, in addition to offering standard products, may find that they are called upon to improve OEMs' manufacturing processes and provide ad hoc consulting services on specific medical projects.

A line of visible-light-curable adhesives from Dymax Europe GmbH is suited to medical and optical applications such as the above lens-bonding procedure.

Cutting Cycle Times

Many adhesives are designed to facilitate the assembly and production of finished devices by reducing curing times. Tim Wendel, product manager at Dymax Europe GmbH (Frankfurt, Germany), explains that Dymax's UV-curable adhesives contribute to short cycle times. He adds that these time savings may in turn cut operation costs by as much as 50% by enabling just-in-time production and in-line inspection, slashing long drying and storage times, and eliminating the need for investments such as drying ovens and air conditioning.

This race against the clock can be problematic in a highly regulated industry. Describing the challenges of working in the medical sector, Steve Bruner, marketing director at NuSil Technology Europe (Anglet, France), says, "We're pressed into a hard corner. On the one hand, design engineers are working with very sensitive applications, and they want to use proven technologies. But at the same time, they are under enormous pressure to reduce their cycle times." Given this situation, says Bruner, suppliers of medical-grade adhesives must adapt their technology to help device OEMs find the most cost-effective way to build their products and get them to market quickly. "At the end of the day, we offer not only good materials, but also the expertise to apply them to meet the needs of our customers—that's where we can make the real cost savings come in," he says.

When time is of the essence, OEMs would be well advised to include their adhesives supplier in the early stages of product development. "Manufacturers often think about adhesives at the last stage of their process, but we can also provide advice on device engineering and design," says Thomas Naudet, European market development manager at Loctite European Group (München). "Most suppliers provide only adhesives, but we provide a full package of services," he says, adding that it is to the advantage of medical OEMs to integrate an adhesive into their process early in the design cycle.

Full-Service Suppliers

Suppliers that can offer custom capabilities in addition to standard product lines will be especially attractive to medical manufacturers. "Our strength is formulating grades for people's needs," says Mark Turner, commerical manager at Medical Engineering Technologies Ltd. (Ashford, Kent, UK). "We can adjust properties like viscosity to suit a variety of applications." Medical Engineering Technologies offers custom formulations of adhesives for a range of applications including balloons and catheters.

In addition to bespoke products, adhesives suppliers often provide a range of services that complement their core activities. One area in which adhesives suppliers can offer OEMs added value is biocompatibility testing. NuSil's Bruner notes that two of the company's new adhesives have undergone USP Class VI biological testing and have US FDA master files, which can help medical manufacturers streamline their regulatory submissions. NuSil also offers its customers on-site application support, as well as a biannual four-day conference on silicone applications held at its US headquarters in Carpinteria, CA.

As advanced adhesive products are developed and released at a dizzying pace, it can be tempting to put too much faith in the efficacy of the products themselves—sometimes at the expense of other critical factors. "We ask a lot of adhesion, but there is no 'miracle' product available," says Loctite's Naudet. "After all, adhesives are not manufactured in Lourdes," he quips, adding that manufacturers need to consider the dispensing equipment they are using, the quantity of adhesive they are applying, where it is being dispensed, and at what point in their manufacturing process they are applying it. "We try to make adhesives simple from a marketing perspective, to make it easy on the customer," he says. "But just as companies have a specific process for welding, so too must medical OEMs take into consideration all the variables that can affect an adhesive's performance in a given context."

Is your company desperately seeking a supplier of joining technology? Screw your courage to the sticking point! The following pages contain profiles of some of the industry's leading suppliers of medical-grade adhesives, as well as welding technology.

"Medical manufacturers are not married to the idea of UV products or cyanoacrylates or any specific adhesive. They just want something that works," says Thomas Naudet, European market development manager at Loctite European Group (München). The company's range of instant, light curing, and flexible adhesives allows device manufacturers to bond virtually any material rapidly. The adhesives withstand sterilization by EtO, gamma irradiation, or autoclave. All products in the range are solvent-free, and most are one-part adhesives that can be applied manually or automatically.

Instant cyanoacrylate adhesives can be used to join materials such as Santoprene, polypropylene, FEP, and polyethylene, which are traditionally difficult to bond. Viscosities ranging from 3 to 1500 cP are available.

Light-curable adhesives cure in 2–60 seconds to depths of 3–13 mm, and provide rigid or flexible joints. This product line, which has been successfully applied in needle-bonding processes, includes viscosities ranging from 100 to 10,000 cP to suit various applications and designs.

A flexible light-cure silicone sealant completes the Loctite range for sterile device assemblies. Applied to extruded or moulded silicone parts in combination with stainless steel, glass, or aluminium, it provides an enduring seal with high resilience. Typical applications include colostomy bags, endotracheal tubes, and Foley catheters.

Loctite is also active in the nondisposable medical market, and supplies adhesives to manufacturers of fibre-optic surgical equipment. "In such applications, we are not only bonding two parts, but also ensuring that small crevices in devices are filled to prevent the growth of bacteria," says Naudet, adding that these applications call on the company's expertise in stainless-steel adhesion.

NuSil Technology Europe

"For years, design and manufacturing engineers have coped with the slow cure rates of room-temperature-vulcanizing silicone adhesives," says Steve Bruner, marketing director at Nusil Technology Europe (Anglet, France). The company's 4213 product line was developed to offer fast-curing alternatives. The flowable, platinum-catalyzed, addition-cured adhesives are available in two grades. MED1-4213 has a working time of 15–20 minutes and is suited for components that are sensitive to heat. MED2-4213 features a working time of 4–6 hours and can be used on components that are more resistant to heat. NuSil has US FDA master files for both of these products, which were also tested to meet USP Class VI requirements.

NuSil is an ISO 9001–certified company that operates state-of-the-art research, manufacturing, and technical marketing facilities in Europe and North America. The company recently announced its opening of a new European technical centre in Sophia Antipolis, France.

Permabond

Launched at the MEDTEC 2000 show in Amsterdam, the 4L36 light-cure adhesive and 4E99 epoxy from Permabond (Eastleigh, Hants, UK) are tailored to the needs of the device sector.

Used to bond various medical-grade plastics, the 4L36 photocurable adhesive cures within a fraction of a second on demand. Laurie J. Gibbons, medical adhesive manager, explains that the adhesive's unique chemistry allows it to bond highly plasticized PVC and the large variety of plastics used in tube set assemblies. "It has very good wetting capabilities, so it produces excellent adhesion to difficult-to-bond materials," she says. The adhesive forms clear, colourless bonds that fluoresce under black light to provide high-speed, automated quality testing in-line. When fully cured, the product meets ISO 10993 standards for cytotoxicity, haemolysis, acute systemic toxicity, intracutaneous reactivity, and implantation.

The company's 4E99 single-component epoxy provides a quick, low-temperature cure and is well suited for high-speed needle bonding. The white epoxy fluoresces under black light for quality control. Curing times are between 10 and 20 minutes, at temperatures ranging from 120° to 90°C. The epoxy withstands EtO and E-beam and gamma irradiation sterilization.

Medical Engineering Technologies Ltd.

UV-curable and cyanoacrylate adhesives have been specially developed for the requirements of the medical market. Grades include materials specifically formulated for the bonding of highly plasticized PVC, materials for bonding polyamides and polyimides, and adhesives for the joining of steel to plastic. Medical Engineering Technologies Ltd. (Ashford, Kent, UK) also offers a range of low-bloom cynaoacrylates for applications where clear surface appearance is critical.

A formulation service is offered to tailor adhesives to customers' particular needs. According to commercial manager Mark Turner, the company has been able to solve difficult problems for medical clients with this service, providing exceptionally strong bonds while refining material properties to suit specific production processes. Examples include balloon bonding, multilumen catheter assembly, needle bonding, and the bonding of PTFE and polyethylene. "We're an engineering firm that works exclusively with medical companies," says Turner, adding that the company also offers its own laboratory services, including quality testing.

Dymax Europe GmbH

A company specializes in UV- and visible-light-curable adhesive resins for the medical device and other industries. Dymax Europe GmbH (Frankfurt, Germany) offers more than 3000 adhesive formulations. The company's adhesives have found applications in medical devices, optical components, electronics, and microelectronics for more than 20 years. Dymax's specialized medical-grade adhesives were specifically developed to meet the requirements of various medical assembly applications.

A case in point is the company's new 140-series line of high-performance UV/visible-light-curable adhesives, which was developed for optical applications in medical devices that require Class VI biocompatibility. The adhesives undergo curing in seconds under UV or visible light, bond stress-free with exceptional clarity, and feature low shrinking and low outgassing characteristics. Suited for single-component products, they also have fluorescing properties for in-line inspection and are 100% solvent free.

EFD

In critical medical assembly operations where thin fluids like solvents and cyanoacrylates are applied, a company's microprocessor-based 2000XL-PR5 dispenser provides complete fluid control. "Typical medical applications include the securing of marker bands to heart catheters, the attachment of balloons to angioplasty catheters, and the bonding of medical-grade tubing and fittings," says Gary Cordier, UK sales manager at EFD (Dunstable, Beds, UK).

The 2000XL-PR5 allows for precise adjustments of time and pressure, providing a high degree of process control, and the digital readouts for all dispenser settings (time, pressure, and vacuum) work to simplify process documentation. Consistent microdeposits as small as 0.008 in. can be produced by placing the dispense tip in position and pressing an electric foot pedal. In facilities with multiple workstations, all dispensers can be programmed with the same settings so that every operator produces identical results. Dispensing tips are available in different styles and sizes to meet a wide variety of applications, ranging from microdots to beads.

Bielomatik Leuze GmbH + Co.

The Laser-Tec 200, developed by Bielomatik Leuze GmbH + Co. (Neuffen, Germany), can weld rigid plastic parts at high speeds without vibration or the creation of debris. Other products that stand to benefit from laser welding include housings for sensitive electronics, or any components sensitive to heat or vibration. Flash-free joints and short cycle times are among the advantages of the Laser-Tec system. In addition, the elimination of debris in the welding process reduces the risk of contaminating critical media such as liquid medicines or blood, which may come into contact with the welded devices.

Most plastics can be welded with the system, if one of the parts is transparent and the other contains a heat-absorbent additive. Weld-joint width can be adjusted from 0.1 mm to several millimetres. Tests conducted using materials such as polycarbonate, polypropylene, POM, and PA6 have shown that the weld-joint strength produced by this process is equal to that of the materials being bonded.

Weldan a/s

A new generation of welding machines for the production of medical bags has been developed by Weldan a/s (Lynge, Denmark). The machines are designed to provide easy access and operator-friendly controls. Both high-frequency and thermocontact welding systems are available.

Along with a new focus on design, the machines abandon pneumatic operation in favour of electrical servomotors that act as drive units. According to managing director Henrik Nyborg, this gives more flexibility and greater accuracy in all operations, and also offers the advantage of appreciable reduction in energy consumption.

Weldan has also used advanced PLC design to outfit the machines with 100% touch screen control systems, which give access to all control parameters together with a full error/fault display. External communication via modem or Ethernet is available as an option.

Jenton International

"Most of the UV lamps for cleanroom use are large, and the small ones tend to be rather low-tech," says Jeremy Woodbridge, sales manager at Jenton International (Whitchurch, Hants, UK). "What we're offering is a small, high-performance lamp with minimized cooling requirements that is suited for cleanroom production."

The new V0 UV curing lamp system available from Jenton is based on an 85-mm cure lamp running at 1200 W (350 W/in.) in a small, modular housing suitable for mounting in conveyor and automation applications. The lamp is highly focussed and can be supplied with a dichroic reflector for cool operation.

Woodbridge explains that the system is suited for the in-line production of small, high-volume products, such as syringes and catheters. Furthermore, he notes, the V0 "has been designed with the medical industry and cleanroom operation in mind." The system features low-volume positive-pressure air cooling for minimum disturbance of cleanroom air. Stainless-steel construction is optional. The power supply is remote, and because the lamp igniter is mounted in the lamp housing, the connection wires avoid high voltages. Remote control is possible for automated operation, as is remote alarm connection.

I & J Fisnar France S.A.

An adhesive dispenser is designed for the accurate release of all assembly fluids, including adhesives. The SMD602A-CE, supplied by I & J Fisnar France S.A. (Pontoise, France), has a manually activated vacuum pick-up system with controls integrated into the front panel of the dispenser. With the vacuum system, the unit can be used for "pick-and-place" operations that involve precision bonding of small assembly components.

With timing intervals from 0.01 to 30 seconds, the SMD602A-CE can dispense microdots or be used for potting components. The unit includes a vacuum system on the fluid line for the nondrip application of low-viscosity fluids. The unit's repeat tolerance is less than 0.5%, with cycle speeds exceeding 600 cycles per minute.

The SMD602A-CE, which is well suited for production and laboratory applications in the device sector, is shipped complete with all accessories, fittings, input hoses, and a storage stand.