Product Update
Surface Treatment Technologies
From the enhancement of a product's mechanical characteristics to the incorporation of pharmaceutical agents into micron-thin coatings to improve biocompatibility, an abundance of surface modification options are available to device manufacturers.
A number of methods have been developed to modify the surface properties of polymers and other biomaterials used in the device industry. Along with conventional coating processes such as spraying or dipping and vacuum deposition techniques, such surface modification technologies as diffusion, laser and plasma processes, chemical plating, grafting or bonding, hydrogel encapsulation, and bombardment with high-energy particles are commonly used. Plasma treatments seem to be especially popular among device manufacturers.
"Plasma-based and equivalent surface treatments are the future, especially in the medical industry," says Poul Jansen of Tantec a/s (Lunderskov, Denmark), a supplier of plasma and electrical surface treatment equipment. "The reason is quite simple--they offer the user a high degree of process control at the micron level." Fabienne Tortelli of Coating Industries (Vaulx-en-Velin, France), a contract supplier of plasma treatment services, concurs. In fact, business is so good for the company that it recently moved to a larger facility."We were obligated to grow," says Tortelli, "to accommodate our clients." Those clients, she notes, are increasingly drawn toward the company's recently developed vacuum plasma spraying (VPS) unit. "Compared to air plasma spraying, VPS seems to work better with metallic coatings. It improves the mechanical properties of the material as well as some chemical characteristics," says Tortelli. Interest in VPS, she adds, is particularly on the upswing in Germany and Switzerland.
The goal of most coating and surface treatment technologies is to achieve improved physical or mechanical properties in a component or device, enhancing the lubricity of a catheter, for example. Increasingly, though, surface modification also aims at inducing a specific desired bioresponse or inhibiting a potentially adverse reaction.
Spire Corp.'s (Bedford, MA, USA) Ioncide treatment creates a permanent infection-resistant and thromboresistant surface on temporary or permanent implantables. The company recently announced an exclusive agreement with St. Jude Medical Inc. (St. Paul, MN, USA) to develop a line of antibacterial heart-valve sewing cuffs using Spire's proprietary Spi-Argent process, a silver-based coating that is part of the company's Ioncide technology. According to Spire, in vitro testing has shown Spi-Argent to be an effective antimicrobial agent against a wide range of bacteria, including those that commonly cause endocarditis. The coating has been successfully used on a number of medical devices including catheters and orthopaedic products.
Medicated coating technology is a specialty at STS Biopolymers (Henrietta, NY, USA), and the company was recently notified that a European patent will be issued for its site-specific drug-delivery surface-coating technology. Antithrombogenic and antimicrobial agents that are incorporated into thin-surface coatings are released into proximal body fluids over time. According to the company, effective drug concentrations result at the device surface while systemic concentrations remain extremely low. STS is currently developing versions of the coatings for use on stents as well as on such devices as Foley and central venous catheters, where surface interactions often occur.
A selection of companies that offer a variety of surface treatment techniques are profiled in this section. All these companies can claim substantial expertise in meeting the specific needs of medical device manufacturers.
Diavac ACM Ltd.
Part of the Manufacturing and Engineering Systems Department of Brunel University, Diavac ACM Ltd. (London, UK) coats components with diamond-like carbon (DLC) and custom builds DLC coating systems. DLC coatings are biocompatible and resist wear, corrosion, and diffusion. Unlike diamond, which shares these properties but requires deposition temperatures in the 900°C range, DLC can be deposited at near-ambient temperatures. The technology, says managing director Joe Franks, has numerous applications in the medical sector. "DLC coatings can improve biocompatibility in stents, lubricity in catheters and other inserts, and wear and corrosion resistance in hip joints and other prostheses," says Franks.
Diamond-like carbon is produced when carbon is deposited under energetic bombardment: The instantaneous local high temperature and pressure induce a proportion of the carbon atoms to bond as diamond. Components to be coated are placed on an electrode that is capacitively coupled to a radio-frequency source. First an inert ionized gas such as argon is used to clean the substrate. That is followed by the deposition stage, in which a carbon containing gas such as acetylene is introduced to generate energetic carbon ions.
The equipment (pictured), which may be operated manually, semi-automatically, or automatically, is designed to introduce up to four gases during different stages of the coating process. In automatic operation, process controls can be preset to 20 programmable steps corresponding to 20 time periods within a 0.01 second to 99 hour range. Up to eight control outputs may be used during any of those 20 periods. "In addition to DLC," adds Franks, "the equipment can be used to deposit other types of coatings or for etching applications."
Coating Industries
A specialist in the surface treatment of implants, Coating Industries (Vaulx-en-Velin, France) treated more than 30,000 products last year with titanium, cobalt-chromium, hydroxyapatite, and alumina, according to Fabienne Tortelli of the export department. The company recently moved to a larger facility, which will enable it to meet the growing demand for its services and introduce additional quality control procedures, says Tortelli. "For example, we now manufacture our own hydroxyapatite powders," she says. "This will allow us to exercise greater control over the materials and to select our own parameters."The company employs two coating techniques: air plasma spraying, which is performed under atmospheric conditions, and vacuum plasma spraying, a newer technology that is gaining favour worldwide, according to Tortelli. "Our German and Swiss clients, in particular, are requesting it," she says. Vacuum plasma spraying, explains Tortelli, ensures the purity of the coating agent and enhances mechanical bonding properties. It also eliminates oxidation.
Plasma-based systems, adds Tortelli, constitute the best available technology for the deposition of micron-thin layers on devices.
Coating Industries is certified to ISO 9002 and EN 46002.
Tantec a/s
Plasma systems produced by Tantec a/s (Lunderskov, Denmark) enhance wettability and adhesion in catheter tubing, needle hubs, disposable syringes, tissue culture products, and related devices. Tantec supplies both electrical surface treatment (EST) and plasma treatment machines. Both systems produce essentially the same result, says Poul Jensen, but they are designed to be used in different environments. "Because they operate in free air, electrical discharge systems are suited for in-line surface treatment on extrusion lines, assembly lines, and so forth," he says. "Plasma systems, which necessitate placing the products in a vacuum chamber, are for batch processing."
The company's plasma treatment system (pictured) creates a high-frequency electrical discharge under low pressure to treat the surface of moulded or extruded plastic parts, profiles, and containers. A 2120-second charge is generated through integrated electrodes under vacuum conditions of approximately 5 mbar.
Spire Corp.
A proprietary surface treatment process provides infection resistance and thromboresistance to a variety of temporary and permanently implanted devices. The Ioncide treatment, which was developed by Spire Corp. (Bedford, MA, USA), is optimized for each client's specific design; it has been used successfully on several products that have been approved for marketing by US FDA, including external fixation pins, catheters, and Class III permanent implants. Its antimicrobial properties are supported by numerous scientific studies.
The company supplies a variety of other surface treatment services based on ion-beam-assisted deposition (IBAD) that improve the surface characteristics and performance of orthopaedic devices.
Ionguard, which enhances the mechanical and chemical surface properties of titanium-alloy devices, reduces friction and improves wear, fretting, fatigue, and corrosion resistance. To reduce polyethylene wear in articulating cobalt-chromium orthopaedic devices, the company has developed Ionguard II; to enable polymeric cross-linking on the surface of ultra-high-molecular-weight polyethylene, Ionguard III is available.
STS Biopolymers
A company has developed a process that incorporates pharmaceutical agents into thin surface coatings. STS Biopolymers (Henrietta, NY, USA) has applied the technology to plastic, metal, and various other substrates and is currently developing antithrombogenic versions of the coatings for use on stents as well as antimicrobial coatings for Foley and central venous catheters.
"The process can be used in two ways," says company chairman Richard J. Whitbourne. "The way that it has been conceived up until now," he says, "is as a surface treatment to prevent proliferant cell growth or clots from forming on the device. But we are beginning to see applications where drugs are entrapped in polymer matrices, which are then used to deliver the drugs to tissues." Its potential use in cancer treatments is being widely explored right now, according to Whitbourne. "It's very likely that we will see devices such as this commercially available in the not too distant future," he adds.
The coatings can be applied to most conventional plastic materials as well as such metals as stainless steel, nickel titanium, and titanium, and the types of agents that can be bound into the materials appear to be limitless, according to Whitbourne. In addition to anticancer agents, "we have looked at antibiotics, antimicrobials, antithrombogenic and anti-inflammatory drugs . . . a real spectrum of materials," says Whitbourne.
