~8IO ED I CAL Biomedical materials must do no damage to the body, must sustain minimal damage from the body, and must provide required strength and toughness for joints and other implants.

Titanium housings for implantable infusion drug pumps

Implantable infusion drug pumps with titanium housings are produced by Arrow International Inc., through its Implantable Drug Delivery System Di­vision. The Model3000 Series Constant Flow Im­plantable Infusion Pump's unique design assures an extremely accurate infusion of drugs and safe bolus dose injections. The pumps significantly im­prove the quality of life for patients requiring chemotherapy for colorectal cancer metastasized to the liver, for chronic pain management, and for the treatment of spasticity.

The pumps have fully contoured circular tita­nium housings that provide smooth, sloping edges between surfaces. The housings are hydroformed to

.----- - --- --- ----. close tolerances by Hudson Med-Non-coring ical Products, div. of Hudson Tool

Drug reservoir

Safety valve open

needle with tubing set & Die Co., Ormond Beach, Fla. The

housing has a unique palpable raised septum with a large target area that is easy to locate and ac­cess. This access makes reservoir refill and bolus injections a matter of simply changing needles rather than searching for injection ports on conventional pumps.

Bolus safety . ,... __ ,,

Bolus valve pa

The titanium pump housings consist of two parts - the can or body and the top or upper cover. The can ranges from 61.2 mm to 86.4 mm in diameter and 19.7 mm to 27.4 mm in height, depending on pump capacity. The can also has four small suture loops at­tached. The upper cover ranges in height from 12.3 mm to 10.0 mm; the smaller diameter can is matched with a higher upper

Safety valve closed -

Hyd oforming, the wave of f.te futu e

cover. A small recess along the top lip of the can assures a tight seal with the upper cover.

The raised septum design provides a large target area that simplifies the process for refilling the reser­voir. For a bolus injection a special needle that has a side hole allows the medication to bypass the drug reservoir and flow into the patient's system.

For more information: Jim Wagner, Hudson Tool & Die Company, 1327 Highway US #1, Ormond Beach, FL 32174, tel: 904/ 672-2000; fax: 904/672-0388, www.hudsontool.com. Circle 145

Specialty alloys designed for biomedical applications

Specialty alloys that have been designed to meet the latest requirements of the medical and dental industries for hand-held instruments, implanted fixation devices, replacement, and orthodontic ma­terial are available from Carpenter Technology Corp., Reading, Pa.

Instrument manufacturers are looking for alloys with more corrosion resistance during autoclaving . They also would like alloys that enable extended instrument life, especially longer edge retention for shaping and cutting instruments, and improved magnetic properties for MRI environments. Im­provements in mechanical properties such as tensile strength, torsional strength, fracture toughness, and ductility are also needed. In response to these re­quests, Carpenter has developed the following biodmedical alloy families.

• BioDur TrimRite stainless for instrument appli­cations, has been found superior to stainless Type 410 and Type 420 in terms of corrosion resistance, ease of fabrication, and edge retention.

• Custom 465 stainless has been established as a candidate alloy for instruments because it has better corrosion resistance and fracture toughness than Custom 455 stainless at the same strength level.

• BioDur CCM Plus alloy, a premium high­carbon steel grade made by powder metallurgy, has combined several attributes that have helped to produce longer joint life. The alloy has homoge­neous chemistry and microstructure with very fine, uniformly distributed carbides that give the mate-

Hydroforrning, sometimes called fluid forming, was developed in the late 1940s in response to escalating costs of pro­ducing deep drawn parts. Replacing conventional matched die forming with a draw ring (blank holder) and a male punch allows metal fabricators the flexibility to produce either low volume or irregular contoured parts cost effectively. The hydroforming process forms a metal blank into shape via hydraulic pressure. Basic components include a lower

die, guides, a rubber diaphragm, and an upper ram/ punch. The metal blank is placed on the lower die and held in place by the guides. The rubber diaphragm is placed on top of the blank and the punch compresses the diaphragm against the metal blank. The metal blank flows into the lower die forming the shape. Altering hydraulic pressures during the hydroforrning process allows the fabricator to form extreme profiles that were

not economically achievable with conventional forming.

26 ADVANCED MATERIALS & PROCESSES/SEPTEMBER 2001

ATE rial superior wear properties when mating with ultra-high molecular-weight poly­ethylene or when mating with itself in a metal-to-metal joint. It also has exhibited high strength and corrosion resistance in such applications. Based on customer re­sults, metal-to-metal joints appear to be a viable, long term solution to metal-to-poly­ethylene joints which, in time, tend to gen­erate wear debris at the bearing surface.

....... ALS

For more information: RobertS. Brown, P.O. Box 14662, Carpenter Technology Corp., Readin~ PA 19612-4662; tel: 610/ 208-2197; fax: 610/736-7059; e-mail; Web site: www.cartech.com. Circle 148

Femoral bearing caps of Carpenter CCM alloy in four sizes fit on the ends of tapered femoral hip stem joints.

Bacteria synthesize polymer biomaterials for implants

A biomaterial synthesized by a bacterium could help lead the way in the production of better plas­tics for surgical implants, report Alexander Stein­buchel and coworket'S at the Weslfa.J.ische WilhehTt.s­Universitat Miinster, Germany. The development was published in the January 2001 issue of Micro­biology, a peer-reviewed journal produced by the

Heart valves tested for fatigue life in saline solution A replacement heart valve is being tested in a saline so­

lution in the 8872 system from Instron Corp., Canton, Mass. The system is equipped with Instron's Dynacell, an inertially compensated load cell. Its saline bath and heater are designed to test materials being considered for artifi­cial heart valves. Dynacell provides more accurate load readings during fatigue life testing of the material, while the saline bath and heater sim­ulate the environment of the human heart. The 5 kHz data acquisition feature of the elec­tronics provides greater accu­racy of results in applications where loads change rapidly, such as peel/tear and high speeds. User programming is possible via optional lAb View drivers, as well as advanced control features that provide flexibility for a wide variety of demanding test applications. For more information: Tnstron Corp., 100 Royall St., Canton, MA 02021-1089; tel: 8001564-8378; fax: 781/575-5725; Web site: www.instron.com.

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Society for General Microbiology. Called poly­thioesters, the materials are said to be more com­patible with the human body and less likely to be­come infected by microbes because they contain sulfur in the backbone.

English biopolymer expert Professor Ian Suther­land of Edinburgh University says, "This is an ex­citing breakthrough, the ability to produce these unusual polymers containing sulfur means that we might soon have surgical implants that are able to prevent bacteria from growing and causing infec­tion."The polymers also offer a renewable source of plastics.

One of the biggest problems with plastics for sur­gical implants is possible infection, which is often very difficult to treat. The infection rate in U.K. hos­pitals for children with plastic shunts that remove flu id from the brain is between 15 and 20%, and

can lead to brain damage. The infection rate in more common hip and knee replacements is about 5%. As with new medicines, the ap­plication of polythioesters for surgical im­plants has yet to be studied and confirmed with further rigorous tests.

Pyrolytic carbon heart valve receives premarket approval

Medical Carbon Research Institute (MCRI), has announced that the U.S. Food and Drug Administration (FDA) has issued a p re­market approval (PMA) for the On-X py­rolytic carbon aortic valve. With the PMA, the On-X aortic valve is now available in the United States as a replacement for diseased heart valves. Evaluation included mechan­ical testin~ structural analyses, and exten­sive clinical testing in Europe and North America.

Pyrolytic carbon is made by heating a pre­cursor material in an inert atmosphere to drive off oxygen, nitrogen, and hydrogen,

ADVANCED MATERIALS & PROCESSES/SEPTEMBER2001

-

27

Typical mechanical properties of On-X carbon Property On-Xvalue

Wear resistance Coefficient of friction Young's modulus Flexural strength Density

< 1.23x10-6 mm 3 I km 0.15 26GPa 490MPa 1.9gm/ cm3

Strain to failure Strain energy Residual stress Fracture toughness Fatigue threshold Fatigue crack velocity

1.6% 7.7 MPa-mm/ mm) 18.2MPa 1.67 MPa-m 112

1.11 MPa-m 112

3.98xlQ-15 m /cyde, DK 70.3

leaving continuous chains of pure carbon. On-X Carbon is said to be the first significant improve­ment in biomedical PyC since its introduction in 1969. At that time, it was necessary to add 3 to 8 wt% silicon as an alloying element, forming po­tentially thrombogenic silicon carbide inclusions in the highly thromboresistant carbon matrix. How­ever, alloying with silicon was needed 30 years ago to allow the consistent production of biomedical PyC with the appropriate mechanical properties. Fortunately, the presence of silicon has been toler­ated, because over this period more than 2.5 mil­lion silicon-alloyed PyC components in approxi­mately twenty mechanical heart valve designs have accumulated more than ten million patient-years clinical experience.

The material was improved in the early 1990's through newly developed production process con­trols combined with a better understanding of the relationships between processing variables, struc-­ture, and mechanical properties. It was found that the highly thromboresistant pure carbon PyC could be reliably produced free of silicon, stronger, and tougher than silicon-alloyed PyC, with the hard­ness, durability, and wear characteristics required

Gold plated coronary stents protect blood vessels

Gold-plated coronary stents made by Boston Scientific Corp., Natick, Mass., .:r<' :.aid to be benign in the body and offr.r excellent visibility under X-rays. Coro­•:...;ry 3te11ts act as scaffolds, propping up weakened blood vessels and keeping : :...::-· : <' !'t'll. For more information: Paul Donovan, Boston Scientific Corp., 1 ?-:-~· P . .rkway, Natick, MA 01760; tel: 508/650-8000; e-mail: donovap3@bsci. .:r: ; \ ·,-t , ite: wzvw.bsc:i.cvm. Circle 149

for long-term implant heart valve applications. For more information: Robert B. More, Medical

Carbon Research Institute, 8200 Cameron Rd., Suite A196, Austin, TX 78754; tel: 512/339-8000 ext. 242; e-mail: rmore@mcritx.com. Circle 147

Cobalt alloy approved for implant applications

A heat-treatable, nonmagnetic cobalt-base alloy that provides very high strength and excellent cor-rosion resistance has Havar composition* reportedly been ap-proved for medical Cobalt

Chromiwn Nickel Tungsten Molybdenwn Manganese Carbon Iron

implant compatibility. Designated Havar, the alloy is p rovided in foil and strip forms by Hamilton Precision Metals, Lancaster, Pa. Havar strip is avail­able with thickness · *ltuueigllt percent

42 19.5 12.7 2.7 2.2 1.6 0.2 Balance

ranging from 0.005 to 0.025 in., and in widths up to 7.5 in.

The company can also produce ultrathin foils as

Polymer stimulates bone growth in spinal implant

A polyareyletherketone polymer called PEEK-Optima, developed by l1wibio Inc., Greenville, S.C., has reportedly been selected for lumbar spinal fusion cages because of its biocompatibility, resistance to chemicals and hydrolysis, high strength, and excellent tribological properties. The polymer is a polyaromatic, semicrystalline thermoplastic (typically 30 to 35% crystallinity) with a melt tempera­ture of 340°C (650°F). Crystallization peak is 160°C (320°F, )and its glass transition temperature is 145°C (290°F). Three natural (unfilled) grades are available as high, medium, and /ow-viscosity variants. Elastic mod­ulus is said to be close to that of cortical bone, which results in an improved bone/implant interface.

The implants help to fuse vertebrae in which disks have been damaged btj accident, disease, or age-related wear. As an implant, the polymer cages are filled with autograft ma­terials (from the same person) and/or allograft materials (from a donor). After several months, the adjacent verte­brae begin to fuse.

For more information: Michael Callahan, lnvibio lnc., 3A Caledon Court, Greenville, SC 29615; tel: 8661468-4246; fax: 8641672-7328; e-mail: info@invibio.com; Web site: www.invibio.com. Cirde190

ADVANCED MATERIALS & PROCESSES/SEPTEMBER 200 1

Havar mechanical and physical properties

Property Annealed Cold rolled Cold rolled

and heat-treated

Ultimate tensile strength, ksi 140 Yield strength, ksi (0.2% offset) 70 Elongation in 2 in., % 40 Hardness, Rockwell C · 25 Modulus of elasticity in tension, 1()6 psi 29.5

thin as 0.000060 in., and in widths up to four inches. All foil p roduction is segregated from other oper­ations to minimize airborne contamination. Testing has reportedly shown Havar to be "innocuous for cytotoxicity, systemic toxicity, intracutaneous irri­tation, intramuscular implantation, skin sensitiza­tion, blood hemolysis, and pyrogenicity."

For m ore information: Robert Crawford, Hamilton Precision Metals Inc., 1780 Rohrerstown Road, Lancaster, PA 17601-2334; tel: 800/476-7065; fax: 717 /569-7642.; e-mail: rcrawford@h p-metals. com; Web site: www.hpmetals.com.

Circle150

Polyamide raises strength, cuts cost in housing for ankle

The Total Concept- Ankle/Foot system from Century XXII Innovations Inc., Jackson, Mich., adjusts to vanjing

heel heights with the simple touch of a button. No tools are needed to reposition the ankle to accommo­date downhill terrain, then change it back again for level ground.

The black ankle housing on this articulated ankle/foot prosthetic was molded with a l.Jztamid 66 H2 K/40 polyamide with 40% carbon fiber reinforcement, rnade by l.Jzti USA, Mount Pleasant, S.C. The carbon fiber reinforcement gives the highest strength and stiffness and fatigue resistance, and .provides excellent thermal

L._- ..--------....1 conductivity. The materiJll en-abled the manufacturer to improve strength and dura­bility while saving 66% in material cost. For more information: Vittorio Gerola, Lati USA,

1470 Ben Sawyer Blvd., Mount Pleasant Business Center, Suite 8, Mount Pleasant, SC 29464;; tel: 843/856-8219; Web site: www.lati.com. Century XX11 Innovations Inc.: www.totalknee.com. Circle 153

Thermoplastic one-way check valves control fluid flow

270 250 1 50

330 300 1 60

Graphite/tungsten makes biocompatible heart valves

Graphites manufactured by Poco Graphite, Decatur, Texas, are said to have a unique combination of thermal expansion, uniformitt;, high strength, high purity, and machinabilitt; that meets the stringent requirements set for critical materials in the biomedical world. Graphite is a biocompatible material and is suitable for a variety of implants. Graphite is also applied in medical devices such as filters for blood dialysis ma­chines, electrodes, and mechanical parts.

Most synthetic graphite is made from petroleum coke that is ground and mixed with a binder and then put through a series of/teat-treating steps. Poco graphites are manufactured in a proprietary, high-temperature process that yields a uni­fonn, isotropic microstruchm and high physical properties. The combination of small grain size with diameter five microns or less, small and uniform porosity, and high strength, allows the graphite to be machined into sheets as thin as 0.005 in., which can be flexed without damage.

Poco AXF-5Q10W is FDA-classified as a critical material for the production of artificial heart valves. Components made from graphite are leaflets and orifice rings. This grade is used worldwide for the production of heart valves. AXF-5Q10W is specially blended with tungsten (10% by weight) to make the graphite visible to X-rays. The material has a density of1.95 g!cm3, flexural strength of 75 MPa, and thennal expansion coefficient of7.7 (mlm-(C.

Graphite can be irradiated for implantable treatment devices. Biomedical grade graphite is certified to have no more than five parts per million impurities and typically has no more than two parts per million impurities.

For more information: Steve Winters, Poco Graphite Inc., 1601 South State St., Decatur, TX 76234; tel: 8771762-6747; fox: 940/393-8366; e-mail: swinters@ poco.com; Web site: www.poco.com. Circle 191

Laproscopic instruments metal-injection molded

Metal-injection molded laproscopic instruments from Morgan Advanced Ceramics (formerly Alberox), New Bed­ford, Mass., are said to cost-effectively meet the exacting specifications of the medical industry. The MIM process is said to produce components that require no additional machining, and they are available in 17-4PH, 304L, and 216L stainless steels. Several components may

A wide variety of check valves and pressure relief valves for medical devices are available from Geneva Medical Products, Walworth, Wis. Simple three-piece check valves are said to offer minimal failure modes, and are suitable for infusion pumps, feeding pumps, and di­agnostic equipment. The valves are available in barbed, non-barbed, and threaded designs, and can withstand temperatures ranging from -40 to 250°F. Materials include polycarbonate, acn;lic, nylon, polypropylene, PVDF, fluorosilicone, and EPDM. The company also provides design assistance and material recommendations. For more information: Mike Pietsch, Geneva Medical Products,lOO Wisconsin St., Walworth, W153184; e-mail: sales@genevamedical. com; Web site: www.genevamedical.com. Circle 154

be molded together, and molds can be designed with multiple cavities to reduce tooling costs. For more information: Ken­neth Camara, Morgan Advanced Ceramics, 225 'T'heolkJre Rice Blvd., New Bedford, MA 02745; tel: 508/995-1725, ext. 319; fax: 5081995-6954; e-mail: kcamara@alberox.com.

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ADVANCED MATERIAlS & PROCESSES/SEPTEMBER 2001 2G