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www.asminternational.org/ampAPRIL 2009

MPMD

TECHNICAL AND BUSINESSNEWS FOR THE MEDICALDEVICEINDUSTRY

TM

Materials and Processesfor Medical Devices

Characterization of Medical

Devices

Environmental SEMChemical analysisMetallographyIndustry News

MPMDNEWS.qxp 3/21/2009 2:32 PM

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Editorial StaffEileen De Guire

Editoreileen.deguire@

asminternational.org

Barbara L. BrodyArt Director

Joanne MillerProduction Manager

[email protected]

Joseph M. ZionPublisher

[email protected]

Please send news releases tomagazines@

asminternational.org

Editorial CommitteeRoger Narayan

North Carolina State Universityand the University of North

Carolina, Chair

Ishaq HaiderBD Techologies

Harold PillsburyUniversity of North Carolina

Ray HarshbargerWalter Reed Army Medical Center

Sebastien HenryPorex

The MPMD Editorial Committee isstrictly an advisory group,

and membership on the committee in no way implies

endorsement of any of the publication’s content.

Sales StaffKelly Thomas, CEM.CEP

National Account ManagerMaterials Park, Ohio

tel: 440/338-1733e-mail: [email protected]

ADVANCED MATERIALS & PROCESSES/APRIL 2009 43

APRIL 2009

On the CoverBiosensors made of gold-palladium nanocubes tethered by SWCNTs

Purdue University researchers, Dr. Tim-othy Fisher and Dr. Marshall Porterfield,have created a high-precision biosensorfor detecting blood glucose and poten-tially many other biological molecules byusing single-wall carbon nanotubes(SWCNT) anchored to gold-coated palla-dium “nanocubes.” The device resemblesa tiny cube-shaped tetherball. Each cubeis a sensor and anchored to electronic cir-cuitry by a nanotube, which acts as botha tether and an ultrathin wire to conductelectrical signals.

The tetherball design lends itself tosensing applications because thesensing portion of the system extendsout far from the rest of the device so thatit can come into contact with target mol-ecules more easily. The system does nothave to wait for target molecules to dif-fuse to the surface, and it can move intoother regions within the range of thetether for enhanced sensing. The tech-nology may have applications detectingother types of biological molecules or infuture biosensors for scientific research.(Image by Jeff Goecker, Discovery Park,Purdue University.)

For more information: Timothy Fisher,Purdue University, West Lafayette, IN47907; tel.: 765/494-5627, [email protected]; www.purdue.edu.

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FEATURESCHARACTERIZATION

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DEVICES

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medical devices

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2009 Supplemental recovery funding for R&D (House,Senate, and Final bills) Source: AAAS analysis of R&D inHouse, Senate, and Final stimulus appropriations bills(HR1), Feb. ’09. 2009 AAAS

Record-breaking support for R&D in federal stimulus package

The American Association for the Advancementof Science (AAAS, Washington, D.C.) estimates thatthe final version of the 2009 economic stimulus ap-propriations bill that President Obama signed intolaw on Feb. 17, 2009 contains $21.5 billion in fed-eral R&D funding. Basic competitiveness-relatedresearch, biomedical research, energy R&D, and cli-mate change programs are high priorities in thefinal economic recovery bill.

Highlights for agencies active in medical deviceR&D:

• National Science Foundation - $3.0 billion. Re-search grants distributed through NSF’s regularpeer review are receiving a $2.0 billion bump withthe balance funding instrumentation and academicresearch infrastructure programs. Depending onfinal FY 2009 appropriations, the stimulus puts NSFwell ahead of the $7.3 billion authorized for FY 2009in the America COMPETES Act of 2007.

• National Institutes of Health - $10.4 billion. Thefinal bill allocates $7.4 billion to be distributed pro-portionally among the NIH’s institutes and centersthrough regular, already scheduled grant review cy-cles. Another $800 million remains in the Office of theDirector, with priority given for 2-year, short-termspecial research grants to be awarded competitively.The enormous stimulus appropriation gives NIH atotal FY 2009 budget of $39.9 billion, a total that couldgo even higher in final FY 2009 appropriations.

For more information: www.aaas.org.

MPMD Database: Spring 2009 updateASM International brings to your desktop a com-

prehensive andauthoritative setof mechanical,physical, biolog-ical response,and drug compatibility properties for materials andcoatings used in medical implants. Update high-lights include:

Cardiovascular Module: In a major new exten-sion to the database, information has been addedfor all FDA classifications of catheters and other re-lated interventional devices.

• Diagnostic Devices: Catheter cannula, Contin-uous flush catheter, Electrode recording, Guidewires, Percutaneous catheter

• Therapeutic Devices: Embolectomy, Sep-tostomy

• Surgical Devices: Vascular clamps • Materials information and links to specific

devices: Fused silica. Ni-Cr-Mo, Polycarbonate,Porcine small intestinal submucosa

Orthopaedic Module• New Material with Bioresponse Information:

Poly(lactic acid)/hydroxyapatite (HAPLA)• Materials information and links to specific

devices: Alumina– zirconia toughened, Bioactiveglass, Bovine cortical bone, Calcium sulfate hemi-hydrate, Fe-23Mn-21Cr-1Mo, Poly(lactic acid)/tricalcium phosphate, Poly(lactic-glycolic acid)/tricalcium phosphate, Poly(lactide-co-trimethyl-enecarbonate), Poly(L-lactide-co-caprolactone)/tricalcium phosphate, Polycarbonate, Polyether-imide, Polymethylpentene (TPX), Polyphenylsul-fone, Polysulfone, Pyrolytic carbon, Ti-3Al-2.5V

• Schematic Diagram Added: Constrained Toe(General)

Updated information for both Modules• New information about ISO Standard: ISO

10993 Biological Evaluation of medical devices –Part 5: In vitro Cytotoxicity.

• PMA/510(k) Updates: This latest version of thedatabase features all the new PMA and 510(k) ap-provals up to February 6th, 2009, in both the Or-thopaedic and Cardiovascular modules, fully inte-grated for ease of searching, and linked to materials.

• Producers: 80 new producers with links to spe-cific devices.

• Contributing Authors Table: Biographical de-tails of experts from the medical device industrywho have authored information in this database have been updated.

Full details of the Spring 2009 update can befound at http://products.asminternational.org/meddev/index.aspx.

44 ADVANCED MATERIALS & PROCESSES/APRIL 2009

INDUSTRY NEWS2

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MPMD e-Newsletter begins monthly publicationBecause quarterly access to information is not enough tostay current with the dynamic medical device industry,ASM International is proud to introduce the MPMD e-Newsletter. Published monthly, the e-Newsletter is a nimblevehicle for getting the latest news to the medical devicecommunity. To subscribe to this free e-Newsletter, visithttp://asm.asminternational.org/asm/n.asp.

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INDUSTRY NEWS 3

Diamond coatings decrease blood clotting in heart pumps

Using a process originally developed for indus-trial equipment, Advanced DiamondTechnologies, Inc. (ADT, Romeoville,Ill.) and Jarvik Heart, Inc. (JHI, NewYork, N.Y.) are collaborating to de-velop improved blood contacting sur-faces using ADT’s form of diamond,

known as UNCD. Because the coating is both thinand exceptionally smooth, it is expected to inhibitthe formation of blood clots inside the device, andto reduce the need for blood thinning medications.Freed from anticoagulation medication, the heartassist device could be used for tens of thousandsmore patients suffering from heart failure.

In a relatively small percentage of patients withheart pumps, blood clots may form on the titaniumor ceramic components such as rotors and bearings.If this occurs, the ability of the device to pumpenough blood can be reduced. Also, blood clots canbreak free and cause a stroke.

Other potential applications for the UNCDcoating include artificial heart valves, cardiac stents,and metal and ceramic components of intravascular

prostheses. JHI is investigating using the diamondcoatings on heart pumps for infants and children.Because the pumps are so small, about the size of aAAA battery, flow channels are tiny and the risk ofblood clotting is even higher than with adult pumps. The market for heart pumps is estimated to be $580million a year by 2015 with a compound annualgrowth rate of 16.6 percent according to Medtech In-sight, November 2008.

For more information: www.thindiamond.com,www.jarvikheart.com.

Feasibility of carbon nanotubes brainsProfessors Alice Parker and Chongwu Zhou at the

University of Southern California (Los Angeles, Calif.)are taking the first steps to build neurons from carbonnanotubes that emulate human brain function.

Unlike computer software that simulates brainfunction, a synthetic brain will include hardwarethat emulates brain cells, their amazingly complexconnectivity, and their “plasticity,” which allowsthe artificial neurons to learn through experienceand adapt to changes in their environment the wayreal neurons do.

Using mathematical models, the researchers

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have shown that portions of a neuron can be modeled electronically using carbon nanotube circuitmodels. A single archetypical neuron, including excitatory and inhibitory synapses, has been modeledelectronically and simulated. A small network of interconnected neurons will be simulated using thecarbon nanotube models.

Engineering challenges that could benefit from technological solutions that involve artificial neuralstructures include autonomous vehicle navigation, identity determination, robotic manufacturing, andmedical diagnostics. This technology could revolutionize neural prosthetics, and yield some amazing bio-mimetic devices.

For more information: Alice Parker, [email protected], http://ee.usc.edu.

Cardo Medical’s Press-Fit Total Hip system

Cardo Medical (Los Angeles, Calif.) has released itsPress-Fit Total Hip system. The Press-Fit Total Hipsystem incorporates a dual taper design which has along, proven clinical history with great implant suc-cess rates. As a complement to the Press-Fit Total Hipsystem, Cardo Medical is also preparing to release its Bipolar Hip system within the next month.

For more information: www.cardomedical.com.

Doing the math to reduce stent blood clot riskDrug-releasing stents have proven to be a “double-edged sword.” The drugs successfully block tissue

growth that could impede blood flow, but can have the unforeseen side effect of increasing the risk of bloodclots and heart attacks. Stents affect the fluid dynamics of blood flowing past them and cause drugs to ac-cumulate in certain areas. Too much drug build-up promotes clot formation. A mathematical model de-veloped by MIT engineers can predict whether particular types of stents are likely to cause life-threateningside effects. The model shows that the dynamics of blood flowing around a stent is similar to white-

water rapids, according to Dr.. Elazer Edelman, professor in the of HealthSciences and Technology Department, Massachusetts Institute of Tech-nology, Cambridge, Mass.

This is the first time that a mathematical model has successfully pre-dicted stent performance based on changes in arterial blood flow anddesign. Researchers hope the model and concepts it establishes couldaid efforts to design stents that allow drugs to be more evenly distrib-uted throughout the area; the model could also help the FDA with itsapproval processes.

For more information: Elazer Edelman, [email protected], www.mit.edu.

Long term durability of cementless total hip replacementsResearchers from Rush University Medical Center (Chicago, Ill.) have

found that fixation of the implant to bone is extremely durable even twentyyears after repeat or “revision” hip replacement. The implant utilized,the Harris-Galante-1 acetabular metal shell, which is designed to allowa patient’s bone to grow into the implant, remained fixed in place in 95percent of hip revision cases after a minimum follow-up of 20 years.

The implant and its bone in-growth surface, are one of the first cement-less metal cup designs. The cup’s porous surface allows bone and tissueto grow into the device to keep the hip implant in place. Earlier genera-tion implants relied on the use of bone cement to secure the implant tothe patient’s pelvis and were associated with a higher failure rate, par-ticularly in patients who had previously experienced a failed hip implant.

While the long-term fixation of the device performed very well, thestudy found an increased rate of repeat surgery for wear-related com-plications at 20 years compared to the 15-year report. Despite the in-creasing prevalence of wear-related problems, the main modes of failure

INDUSTRY NEWS4

Researchers at the Fraunhofer Institute forMachine Tools and Forming Technology andthe University of Leipzig have developed a

simulation model to calculate bone densityand elasticity from CT scanner images. The

model will help surgeons choose the bestsites for placing the screws that anchor artifi-

cial hip joints to the patient’s bone.www.fraunhofer.de

Micell Technologies has obtained the rightsto Maxcor’s Genius MAGIC Cobalt Chromium

Coronary Stent System for the purpose of developing and marketing drug-eluting

stents based on Micell’s proprietary coatingtechnology. Maxcor Inc., is a newly

incorporated subsidiary of Opto Circuits Ltd.www.micell.com

St. Jude Medical Inc. has received regulatory approval from the Japanese

Ministry of Health, Labour and Welfare for itsAtlas II implantable cardioverter defibrillator

(ICD) for patients with potentially lethal abnormal heart rhythms. The ICD is a small

device implanted in the chest to treat potentially lethal, abnormally fast heart

rhythms (ventricular tachycardias or ventric-ular fibrillation), which often lead to sudden

cardiac death. www.sjm.com


were infection and recurrent dislocations. The study authors recommend theuse of larger diameter femoral heads and more wear-resistant bearings to de-crease the risks of these complications.

For more information: www.rush.edu/rumc.

Rejection-free, bioreabsorbable scaffold for jaw implantThe Custom-Fit project, an EU-

funded research program involving 30partners from 12 European countries,is developing a bioresorbable materialfor mandibular and other joints. Onceimplanted, it is replaced with re-grown,natural bone in 6-12 months. The con-sortium is developing a new manufac-turing paradigm for customizing im-plants to the individual shape of thehuman body using CAD systems andrapid manufacturing technologies.

The process begins by studying the jaw bone geometry through comput-erized tomography images and using computer programs to distinguish thedamaged part of the bone from the healthy area. A surface model of the im-plant is designed with a CAD system that allows direct manipulation of facetmodels, and a 3D model of the implant is completed by adding the internalstructure (porosity). Finally, the model is prepared for manufacture using aspecial rapid manufacturing tool using high viscosity, bioreabsorbable resinsand is capable of printing multi-material and porous objects.

Although approval for implantation in patients is several years away, thetechnology offers several advantages: no rejection of foreign material, newbone will be able to grow over time (for children), further treatment like dentalimplants remains possible, and the implant will be completely replaced bynew natural bone.

For more information: www.custom-fit.org.

‘Lint Brush’ Captures and Kills Cancer Cells in the BloodstreamCornell University (Ithaca, N.Y.) researcher, Dr. Michael King, has devel-

oped a lethal “lint brush” for the blood that captures and kills cancer cells inthe bloodstream. In research conducted at the University of Rochester,Rochester, N.Y., King showed that two naturally occurring proteins can worktogether to attract and kill as many as 30 percent of tumor cells in the blood-stream without harming healthy cells.

The goal is to develop a tiny, implantable, tube-like device coated with pro-teins that would filter outand destroy free-flowingcancer cells in the blood-stream. Cancer cells ad-here to the selectin pro-tein on the microtube’ssurface, and are exposedto the protein, TRAIL(Tumor Necrosis FactorRelated Apoptosis-In-ducing Ligand), whichbinds to two so-called“death receptors” on thecancer cells’ surfaces, set-

ADVANCED MATERIALS & PROCESSES/APRIL 2009

INDUSTRY NEWS

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6ting in motion a process that causes the cells to self-destruct. The cancer cells are released back into thebloodstream to die, and the device is available for new cancer cells to enter.

Used in combination with traditional cancer therapies, the device could remove a significant propor-tion of metastatic cells, and give the body a fighting chance to remove the rest of them. The work will bepublished in Bioengineering and Biotechnology; “Delivery of apoptotic signal to rolling cancer cells: anovel biomimetic technique using immobilized TRAIL and E-selectin;” DOI: 10.1002/bit.22204.

For more information: Michael King, [email protected], www.news.cornell.edu.

Bioabsorbable stents show promiseA study published online in The Lancet presented two year data on 30 patients for the bioabsorbable

everolimus coronary stent. The study showed an overall 19 % loss in luminal diameter at 18 months andan angiographic in-stent late loss of 0.48 mm at two years. These results fall between those commonly seenfor bare metal stents (typical in-stent late loss of 1.0 mm), and drug eluting stents (typical in-stent late lossof 0.15 to 0.3 mm).

Since in-stent late loss increased by only 0.05 mm between 6 months and two years, the most probableexplanation for the in-stent late loss is early recoil after stent implantation, indicating that the stent ini-tially is not exerting enough radial force to keep the vessels perfectly open. The challenge facing stentdesigners is to achieve a balance between radial strength and a structure that can be reabsorbed in a rea-sonable time period.

After two years the physiological function of the stented part of the vessel was almost completely re-stored, preventing patients from having symptoms of angina or limitations inphysical activity. In contrast, studies of first generation drug eluting stents haveshown “paradoxical vasoconstriction” in the area of the stent, where the vesselconstricts instead of opening during exercise. For more information:www.escardio.org/

Magnetic bracelet for acid reflux managementTorax Medical (Shoreview, Minn.) is

testing its LINX System, designed to pre-vent gastric reflux by augmenting thelower esophageal sphincter, the body’snatural anti-reflux barrier. The device con-sists of a “bracelet” of miniature magneticbeads made of permanent rare earth mag-nets encased in titanium and placedaround the lower esophageal sphincter.The band is sized to fit each patient. Theattractive force between the magneticbeads helps to keep the lower esophagealsphincter closed, restoring the normal barrier function of the defective sphincter.The ring expands to allow swallowing or to release high gastric pressures. Thedevice is placed via laparoscopic methods and, once in place, begins workingimmediately. For more information: www.toraxmedical.com.

Future looks bright for orthopaedicA recent report by Global Markets Direct, The Future of the Orthopedic Devices

Market to 2012, indicates that the joint reconstruction (artificial joints) marketwill grow from $12.2 billion in 2008 to $17.4 billion by 2012, and will com-prise 45% of the overall orthopaedeic devices market in 2012. The spinal non-fusion device market valued at $551 million in 2008 is forecast to reach $792million by 2012, accounting for 15% of the spinal surgery market value. Thedevelopment of minimally-invasive technologies has enabled patients to choosealternate orthopedic procedures and is likely to positively impact the growthdynamics of the orthopaedic devices sector in the next 5 years. For more infor-mation: www.reportlinker.com/p098179/The-Future-of-the-Orthopedic-Devices-Market-to-2012.html#summary

Researchers from the National EyeInstitute, and NASA developed a

compact fiber optic probe tomeasure alpha-crystallin, a proteinrelated to cataract formation. First

developed for the space program, thesafe, simple test has proven valuable

as the first non-invasive early detection device for cataracts, the

leading cause of vision loss worldwide. The device is based on alaser light technique called dynamiclight scattering. www.grc.nasa.gov,

www.nei.nih.gov

AGY’s new biomaterial, HPB glassfiber, is suitable for long-term implantapplications, and is compatible with a

wide range of thermoplastic polymers such as PEEK, PEI andPPS. HPB glass fibers have 40%more tensile strength and a 20%

higher tensile modulus than ordinaryE-Glass fibers. The material has been

used successfully for dental composite applications such as

orthodontics, dental implants,crowns, and bridges. www.agy.com

Scientists at the University of Idahoare engineering multifunctional anddynamic nanowires coated in gold

that swim through the bloodstreamand attach to specific cancerous

cells. An electromagnetic fields heatsthe nanowires, destroying the

cancerous cells. The research is partof a multimillion dollar project funded

by the Korean government.www.uidaho.edu

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Suppliers of medical equipment and implantsmust ensure the safety of their products. Chemical analysis is used to verify that products pose no danger to patients and practitioners.

David KlukDirector of Technical Development

Carm D’AgostinoHead Chemist

NSL Analytical Services Inc.Cleveland, Ohio

Doctors and hospitals are keenly aware of pa-tient safety, and take extreme steps to ensurethat anything that comes into contact with apatient is free of toxic or harmful elements. As

a result, suppliers of medical equipment and implantstake every precaution to verify the safety of their prod-ucts. Often, this verification is done through rigorouschemical analysis by a third parting testing lab.

Cleanliness is particularly critical for any medical com-ponents that will be implanted or used during surgery.Hip and knee implants, for example, are often coated witha calcium phosphate to encourage bone growth aroundand into the implant. Any impurities in the coating couldinhibit bone growth or could cause an adverse reaction inthe body. Stents, staples, clamps, and surgical tools alsomust be tested for any residues from the manufacturingprocess. FDAguidelines require these parts to be checkedby a third-party laboratory to confirm that they are safefor use.

Tests performed vary with the type of component beinganalyzed. For example, the composition of surgical tools istypically analyzed with optical emission testing. Cleanli-ness is verified with traditional wet chemistry testing, whileInductively Coupled Plasma Mass Spectroscopy (ICP/MS)is used to check for impurities in implant coatings.

Chemical AnalysisBulk analysis determines the concentration of the major

chemical constituents of a material. Analytical instrumen-tation used for bulk analysis includes X-Ray Fluorescenceand Inductively Coupled Plasma Optical Emission Spec-troscopy.

X-Ray Fluorescence (XRF) instrumentation determineselemental concentration by analyzing the emission of char-acteristic x-rays from the material that has been excitedby bombarding it with high-energy X-rays or gamma rays.The fluorescent radiation can be analyzed either by sortingthe photon energies emitted (energy-dispersive analysis)or by separating the radiation wavelengths (wavelength-dispersive analysis). Once sorted, the intensity of eachcharacteristic radiation is directly related to the amount

of each element in the material. An XRF instrument canhandle materials in different forms such as solids andpowders. A number of techniques can be applied to placethe material in the proper form for the instrument.

Pressed powders consist of the sample material mixedwith a small amount of binder and pressed into pellet formunder extreme pressure. Provided the sample has uni-form particle size, elements can be detected at the partsper million (ppm) level. One challenge of using pressedpowders as a quantitative tool is acquiring matching ma-terial with known concentrations to calculate the finalconcentration. These may not be available for the elementof interest.

Fused beads are created by mixing the sample with aknown amount of flux such as lithium tetraborate. Themixture is then heated in a furnace or fusion equipmentand melted into a glass bead. The advantage of using fusedbeads is that measurement standards can be created syn-thetically for comparison. The main drawback is that thesample material is diluted by the flux, limiting detectionaccuracy to about 0.1 to 0.5%, depending on the fusiontechnique.

Inductively Coupled Plasma Optical Emission Spec-troscopy (ICP/OES) instrumentation introduces anaqueous solution into an extremely hot plasma gas. Lightemitted by the atoms of an element consumed in theplasma is resolved into its component radiation, and theintensity is measured with a photomultiplier tube or solid

7Ensuring patient safety through chemical analysis

XRF Instrument can detect elements at the parts per millionrange.


8


state detector. The intensity of the electron signal is com-pared to previously measured standards of known ele-ment concentration, and the concentration is computed.

Advantages of ICP analysis include the ability to matchthe sample solution to a synthetically created standard oncethe sample has been dissolved by various digestion tech-niques. Also, concentrations from trace to major levels canbe quantified using the same sample preparation technique.

Sample preparation usually entails taking 0.1 to1.0 g ofmaterial and digesting it using various procedures. After

the sample has been broken down, itis placed into solution by dilutingwith acid by one thousand fold ormore. The use of proper analyticaltechniques is critical to avoid vari-ances in the final concentration causeby sample dilution and by the influ-ence of matrix interference. Also, somematerials can be difficult to analyzebecause they are not readily solubleby standard procedures.

Finding Trace ElementsTrace analysis involves determining

the presence of elements in minuteamounts. The usual analysis methodsused are ICP/MS and Cold VaporAtomic Absorption Spectroscopy.

Inductively Coupled Plasma MassSpectroscopy (ICP/MS) is a highlysensitive type of mass spectrometrythat can determine element concen-trations below one part per trillion. Itis based on coupling an ICP source (toproduce ions) with a mass spectrom-eter (to separate and detect the ions).

Coupling the mass spectrometrywith ICP allows for low-level detec-tion, from parts per trillion to 0.5% orgreater. Advantages of ICP/MS in-clude the ability to identify and quan-tify a large group of elements, and thatmeasurement standards are readilyavailable.

Cold Vapor Atomic AbsorptionSpectroscopy (CVAAS) takes advan-tage of the characteristic of volatileheavy metals, such as mercury, that al-lows vapor measurement at room tem-perature. In the technique, free mer-cury atoms in a carrier gas are absorbedby the ultraviolet light radiation sourceat 253.7 nm. The change in energy isdetected by a UV sensitive phototube.The technique is linear over a widerange of concentrations. MPMD

For more information: David Kluk,NSL Analytical Services, 4450 CranwoodParkway, Cleveland, OH 44128; tel.:216/643-5200; [email protected];www.nslanalytical.com.

ICP instrument consumes the sample in a plasma flame and detects elements with a photomultiplier, solid state chip or massspectrometer.

www.ulbrich.com

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9


Specimen preparation for metallographic examination of medical devicesGeorge F. Vander Voort, FASMBuehler Ltd.Lake Bluff, Illinois

Metallographic work is usually conducted onnew implant materials and devices to guar-antee their quality or to determine if themanufacturing approach is satisfactory; or,

it is conducted on implants removed from animals to eval-uate suitability or bone in-growth development. Obtainingspecimens for metallographic analysis requires optimalsectioning procedures to minimize damage to the implantmaterial. As surfaces are a prime subject for examination,encapsulation is required to promote edge retention. Thiscan be complicated if a foam or a medicinal coating hasbeen applied to the surface. The void space within thefoam must be infiltrated with a low-viscosity epoxy topreserve the pore geometry and protect the foam duringpreparation.

Once the specimens have been encapsulated and thedesired surfaces are ready to be prepared for examina-tion, the metallographer may be faced with a relativelystraightforward preparation sequence if the implant hasno formidable surface coatings. However, in the case ofimplants with bonded foam surfaces or medicinal coat-ings, the preparation sequence is more challenging. Foamsare often made from tantalum, a difficult refractory metalto prepare. Revealing both the substrate, which may bemade from a variety of highly corrosion-resistant metalsand alloys, and the tantalum foam, will test the mettleof all metallographers. Medicinal coatings on metallic sub-strates may be water soluble, and dealing with non-aqueous abrasives, extenders, and cleaning solutions isalways challenging.

Because these metals and alloys tend to be highly cor-rosion resistant, etching them so that the microstructureis fully and clearly revealed may be quite difficult. In gen-eral, there are well-known, highly successful etchants foraustenitic stainless steels. However, etching the Ni-free,

high-Mn austenitic stainless steels is very difficult, es-pecially when they have been cold worked in manufac-ture. Cobalt alloys are very popular for implants and,while etchants for them exist, it is still a challengeto reveal their structure with clarity. Grain size ratingof any twinned FCC metal is always difficult asmany etchants reveal only a portion of the grain andtwin boundaries. Cobalt alloys are FCC, althoughpure cobalt is HCP, and as they are highly corrosionresistant, etching them properly is difficult. Com-mercial purity (CP) titanium can be examined as-polished using polarized light, but only if all thepreparation-induced damage is removed. Speci-mens must be totally free of any preparation-in-duced damage; “just good enough” preparation isnot acceptable for this work.

To illustrate the challenge facing the metallog-rapher, Figure 1 shows a Ti-6Al-4V acetabular cupwhere CP Ti wire has been diffusion bonded to thesubstrate to promote bone in-growth. The specimenwas encapsulated using vacuum impregnated Epo-Heat epoxy resin which has a viscosity of ~32 cps.It was prepared using Buehler’s three-step methodfor titanium, and color etched with a modificationof Weck’s reagent for titanium (100 mL water, 25 mLethanol, 2 g NH4F×HF). The micrograph was takenusing polarized light with a sensitive tint filter. Colormetallography revealed the structure far better than thestandard black & white etching with Kroll’s reagent. Figure2 shows examples of Nitinol, a very difficult alloy to pre-pare damage free and to etch. Figure 2a shows theaustenitic structure as processed and Figure 2b shows themartensitic structure after going through the shape-memory affect transformation.

For more information: Rick Wagner, Buehler, Ltd., 41Waukegan Road, Lake Bluff, IL 60044; tel.: 847/295-4546;[email protected]; www.buehler.com.

CorrectionThe January issue of MPMDlisted incorrectcontact information for Buehler, Inc.The correctcontact details for more information are:Rick WagnerBuehler, Ltd. 41 WaukeganRoadLake Bluff, IL60044 tel.: 847/[email protected]

Fig. 1 — Ti-6Al-4V acetabular cup Fig. 2a — Austenitic Nitinol Fig. 2b — Martensitic Nitinol

MPMDNEWS.qxp 3/24/2009 7:35 AM

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Environmental SEM for medical devices —

An interview with ESEM expert, Scott Robinson Environmental SEM is a useful tool for examining delicate, vacuum-sensitive specimens.

Angele Sjong, Ph.D.Sjong Consulting LLC Boulder, Colorado

Medical devices increasingly use materialswith drug release properties, swellingability, and surfaces designed to promotebiocompatibility. Examining such materials

via electron microscopy can be challenging, particularlywhen those properties essential to their function, such asswelling and drug dissolution, make them vacuum in-compatible. The traditional limitation of scanning elec-tron microscopy (SEM) is that the specimen must be ableto withstand a high vacuum and be either electrically con-ductive or rendered conductive by modifying it with avery fine coating of metal (usually gold–palladium). En-vironmental SEM (ESEM), which permits the observationof nonconductive samples by providing a humid envi-ronment in the sample chamber and using water vaporas a cascade amplifier for secondary electrons, was firstintroduced in 1989 by the company ElectroScan, whichwas purchased in 1996 by the FEI Company (Hillsboro,Oreg.) ESEM has been used extensively since then by bi-ologists for imaging specimens such as insects and plantsamples, and by materials engineers for imaging vacuum-incompatible specimens and for following dynamicprocesses as a function of temperature, humidity, or both.Following the launch of ESEM, other companies intro-duced low vacuum and variable pressure (LVSEM andVPSEM) instruments. These also allowed for the imagingof nonconductive samples, including polymeric substratesthat outgas.

Recently ESEM has garnered attention for the analysisof medical devices, particularly in the evaluation of ma-terial properties such as cell adhesion (Ref. 1), tissue cal-cification (Ref. 2), and osseointegration into implants(Ref. 3). Following is an overview of the ESEM methodand an interview with Scott Robinson from the Univer-sity of Illinois’ Imaging Technology Group. ScottRobinson has extensive experience in electron mi-croscopy, including the use of ESEM for imaging of med-ical device components.

Background of ESEMFor ESEM to work, it must be possible to introduce

water vapor into the sample chamber without posing athreat to the electron gun. The gun chamber must main-tain its relatively high vacuum (<10-10 torr in a field-emis-sion instrument) while delivering the electron beam tothe poor vacuum (between 0.7 and 10 torr) of the samplechamber. This is accomplished by placing a series of pres-sure-limiting apertures (PLAs), approximately 400 µm indiameter, between the high and low vacuum regions inthe electron column. At least five stages of increasingvacuum separate the sample chamber from the gunchamber.

The PLAs work in conjunction with a gaseous sec-ondary electron detector (GSED), which is usually locateddirectly above the sample and contains the final aperturethrough which the electron beam passes. The diameter ofthat aperture determines how poor the vacuum can be inthe sample chamber. For a 500 µm GSED aperture, thechamber pressure can be as high as 10 torr. Imaging oc-curs as the electron beam (‘primary electrons’) enters thechamber, passes through the aperture of the positivelycharged GSED, through the water vapor, and impingeson the sample surface, generating secondary electronsfrom that surface. The secondary electrons collide withthe water vapor molecules and form electron-ion pairs.Through the repeated process of acceleration, collision,and ionization, the original secondary electron signal is“cascade amplified” when it reaches the GSED, which col-lects the amplified signal as it repels the positively chargedions. The repelled positive ions combine with excess neg-ative charge on the sample, neutralizing it, and therebypreventing surface charging.

ESEM thus utilizes a series of tricks to permit the useof water vapor in the sample chamber, to prevent chargingfrom occurring, and to obtain an adequate signal usingthe GSED (as opposed to the photomultiplier tube, fur-ther away and with a lesser bias, used in a traditionalSEM). As with any imaging technique, there are trade-offs in resolution.

AS: What ESEM instrument do you use in your microscopy suite at the Imaging TechnologyGroup?

S.R.: We use an XL30 ESEM, with a field emission gun,from the FEI Company. The field emission gun —

ESEM images of salt with an anti-caking agent being wetted, dissolving, and recrystallizing without the anti-caking agent. Note the more cubicform. Images courtesy of the Imaging Technology Group, University of Illinois.


11


a $200,000 option—gives much better resolution.The microscope, which is 10 years old, can be usedeither as an ESEM or an SEM, and most of the timewe encourage clients to use it as an SEM even whenthey think they want to use an ESEM. Using thescope as an ESEM is definitely tricky, and it is moredif ficult to get good images. There are other con-straints, including sample size.

A.S.: What are the key things to look out for when trying to obtain high quality images in water vapor?

S.R. People ask ‘How do I get a fine image from a cloudof electrons in water vapor?’ The signal comes fromthe water vapor at the millisecond the beam is lo-cated at one specific point on the sample. The beamthen moves maybe two nanometers along to pro-duce the next signal. And all of those split-secondsignals combine into your image.

Small changes can greatly improve image quality.The closer you are to the pole piece, the better theresolution, just like SEM. But if you get too closeyou can run into the positive bias of the detector,breaking up your image. In ESEM it’s important tobe as close as possible, and keeping an optimalworking distance is crucial.

As with SEM, a higher accelerating voltage givesbetter resolution. The higher kV helps blow throughthe water vapor, so the final image doesn’t look‘cloudy,’ but there’s an increased chance you’re notgoing to neutralize excess charging. You want tomaintain a balance between the accelerating voltage,the working distance, the water vapor pressure, andthe bias on the GSED.

A.S.: When examining medical devices with drug de-livery applications, what do people need to con-sider when deciding between LVSEM andESEM?

S.R.: You definitely have trade-offs. By imaging micelles,which are sometimes formed as vehicles for drugdelivery, in the ESEM, we can avoid destroyingthem. In backscatter mode, you might have poorcontrast, go to higher voltage, and destroy the mi-celles with that extra energy. In wet mode we oftenfreeze a large emulsion droplet and then slowlydraw water away from its surface by lowering thevapor pressure, leaving the particles exposed forimaging.

For simple examinations of drug-coated stents youcan just work at low voltage with a suitable back-cattered electron detector.

A.S.: When examining medical devices with swellingproperties, what do people need to consider? S.R.: If you don’t want to see something shrivel upunder less than 100% relative humidity, ESEMworks well. With ESEM you can monitor theswelling/shrinking of devices (such as hydrogels)in response to changes in water vapor pressure. Wecan look at tissue scaffolds, made of polymer, at highwater vapor pressures, and the vacuum doesn’tdamage them. Some polymer samples are sovacuum-sensitive that the vacuum in the sputtercoater will cause them to collapse.

A.S.: How do you adjust water vapor levels during hu-midity tests if water vapor is so crucial for im-aging?

S.R.: One problem with ESEM is that to some extent thequality of your image depends on the vapor pres-sure. If you’re doing an experiment in which hu-midity is the variable, not all of your images will beperfect.

A.S.: Is ESEM useful for examining super hydropho-bicity of treated surfaces?

S.R.: With super hydrophobicity you see very round waterdroplets. We’ve also worked with extruded polymerfibers that were irradiated to control their hy-drophilicity. Images of the tiny water droplets wecondensed onto the fibers were used to obtain con-tact angle measurements at several thousand timesmagnification.

A.S.: What are the advantages of examining cell adhe-sion using ESEM?

S.R.: It’s difficult to image unfixed cells in wet mode,especially with a field emission gun. The closer youget to them, the more likely they are to be damaged.We have imaged live Shigella bacteria, which createa biofilm, making them look like hotdogs under athin blanket.

A.S.: Where do you see the ESEM utility in examiningimplant–tissue interfaces?

S.R: Such studies are better done using backscatteredelectron imaging and EDS in SEM mode.

A.S: What other time–temperature studies are per-formed using ESEM?

S.R.: We have the ability to heat small samples as high as1500°C and take images along the way. Presentlywe are working on a heating/strain stage.

With ESEM you have a lot of options. MPMD

References1. O. Craciunesescu, L. Moldovan, D. Bojin, C. Vasile,

O. Zarnescu, ESEM Observations on New Polyurethane–Based Materials for Biomedical Applications: Structureand Cell Adhesion, Acta Microscopica, Vol. 16, No. 1-2,Supp.2, 2007.

2. S. Habesch, C. Delogne, Progressive Calcification ofBioprosthetic Heart Valve Tissue, Techniques for AssessingDifferent Morphologies and Composition of CalciumPhosphate Deposits Under Hydrated Conditions usingESEM, Low-Vacuum SEM/ESEM in Materials Science:Wet SEM- The Liquid Frontier of Microscopy, MRS Sym-posium V, November 29, 2000.

3. M. Tarcolea, F. Miculescu, S. Ciuca, R.M. Piticescu, I.Patrascu, L.T. Ciocan, ESEM Investigation on Osseo Inte-gration of Ti Alloy Implants, European Cells and Mate-rials, Vol. 16, Suppl. 1, 2008, p. 56.

For more information: Angele Sjong is a materials engineer, chemist, andowner of Sjong Consulting LLC, PMB #324, 2525 Arapahoe Ave, Ste E4,Boulder, CO 80302; tel.: 650/799-4170; [email protected].

Scott J. Robinson is in the Imaging Technology Group at the Beckman In-stitute for Advanced Science and Technology, University of Illinois atUrbana–Champaign; B650J Beckman Institute, 405 North Mathews Ave.,Urbana, IL 61801; tel.: 217/265-5071; [email protected]; www.illinois.edu.

MPMDNEWS.qxp 3/24/2009 7:37 AM

Pedicle rodsIcotec, Altstätten, Switzerland, has

developed 6 mm composite pediclerods for spine pedicle systems. Therods are compatible with most ex-isting pedicle systems and offer arte-fact free imaging in conventional ra-diology, CT and digital imagingprocedures. as well as the ability toadapt to spinal applications With a low E-Modulus of75 GPa, they adapt well to spinal applications; mechan-ical properties are comparable with the current metalsolutions. www.icotec.ch

Metal filtersMott Corp.’s, Farmington, Conn., porous metal media

control gas and liquid flows indrug delivery devices, increaseinstrument performance, andfilter micron sized impurities fromgas and liquid streams. Porousmetal products are biocompat-ible, durable, and 100% recy-

clable. The porous metal components can be removedfrom devices for cleaning and sterilizing between uses.www.mottcorp.com.

Rapid prototypingGalloway Plastics, Inc. (Lake Bluff, Ill.) has acquired

a direct metal laser-sintering system from EOS GmbHElectro Optical Systems (Munich, Germany) to expandthe orthopaedic device fabrication capabilities of its di-vision, GPI Anatomicals, a manufacturer of anatomical/medical device models. The additive manufacturingprocess can fabricate complex three-dimensional metalparts layer-by-layer in just a few hours.www.gpiprototype.com, www.eos.info

IT reference bookTo help healthcare IT professionals understand IT-in-

tensive medical equipment, ECRI Institute (PlymouthMeeting, Pa.) has released a new reference book, Med-ical Technology for the IT Professional: An EssentialGuide for Working in Today’s Healthcare Setting. Thebook examines specific medical technologies and thechallenges they present to IT. Illustrations and clear-cutlanguage allow the reader to understand componentsand functions behind technologies like infusion pumpsand RFID. http://www.ecri.org.

Metallographic specimen preparationBuehler’s EcoMet product line offers medical im-

plant manufacturers options for preparing samples insingle or central force modes when combined with anAutoMet Power Head. A selection of platens is avail-able to accommodate varying sizes and volumes ofspecimens to be prepared.www.buehler.com/biomedical.htm

12


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www.asminternational.org/meddevices

MPMD Seminars –Your Source for Medical Device Materials Knowledge.

Seminars and instructors include:

Medical Device Design Validation and Failure AnalysisBrad James, PhD, PE

Nitinol for Medical DevicesAlan Pelton, PhD

Drug Delivery TechnologyJames Arps, PhDKlaus Wormuth, PhD

Polymer Considerations in Medical Device DesignJennifer M. Hoffman, PhD

Biological Testing Methods for Combination DevicesNicholas P. Ziats, PhD

Stainless Steels, Cobalt-Chrome and Titanium Alloys for Medical DevicesPhillip J. Andersen, PhD

Meeting Functional Requirements of Medical DevicesMichael N. Helmus, PhD

Biomedical Microdevices: An Introduction to BioMEMSColin K. Drummond, PhD, MBA

Metallographic Techniques for Medical Devices (3.0 CEUs)Gabe Lucas

Seminars are being offered in several locations throughout the year.

Ft. Wayne, IN – May 18-21

Materials Park, OH – June 15-19

Newark, NJ – June 15-18

Minneapolis, MN – August 8-9(at MPMD Conference and Exposition)

Irvine, CA – November 9-12

Materials & Processesfor Medical Devices™

Conference & ExpositionConference: August 10-12, 2009Exposition: August 11-12, 2009Hilton MinneapolisMinneapolis, MN USAMPMD is your only medical devices conference this year that brings together materials scientists and engineers, metallurgists, product designers, researchers, and clinicians. Register Today.

www.asminternational.org/meddevices

Learn more about materials for medical design at MPMD educational courses, conferences and seminars.

Visit www.asminternational.org/mpmd for details or contact John Cerne, Sales Manager, at 440.338.5417 or800.336.5152, ext. 5637 for details.

ASM International has assembled the world’s foremost materials experts to provide a practical understanding of the properties, processes and applications of the materials that shape the medical device industry.

From cardiovascular, neurological and pulmonary devices to orthopaedics and dental appliances – we’ve got the training to help prepare you to lead the industry in innovation.

Multiple student discounts and customized training available.


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