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MPMD
TM
Materials and Processes
for Medical Devices
www.asminternational.org/amp
APRIL 2009
Characterization
of Medical
Devices
TECHNICAL
AND
BUSINESS
NEWS
FOR THE
MEDICAL
DEVICE
INDUSTRY
Environmental SEM
Chemical analysis
Metallography
Industry News
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A new spin on
materials and
manufacturing.
Sandvik medical manufacturing facilities deliver
millions of components every year.
In the production of orthopedic implants and instruments, you want to be sure to get to market rapidly
and efficiently with an innovative product.
As one of the largest manufacturers in the field, and
a world leader in machining, cutting tools and new
materials development, Sandvik can give you greater
competitiveness. We have an extensive range of capabilities including materials development, machining,
investment casting, forging, powder technology and
surface modifications. We will support you to add
value to your product, identify the optimum method
of manufacture as well as customize machining and
tooling programs. Represented in more than 130
countries, Sandvik has a proven record in supporting
medical device manufacturers in meeting key commercial objectives with our advanced materials science,
rapid prototyping and manufacturing efficiency. We work
in focused teams drawing on global resources and can
respond to the urgent need for a quick turnaround,
equally meeting the demands of a worldwide launch.
sandvik.com/medical
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APRIL 2009
TM
Editorial Staff
A publication of ASM International
9639 Kinsman Road
Materials Park, OH 44073
Tel: 440/338-5151; Fax: 440/338-4634
www.asminternational.org/amp
Eileen De Guire
Editor
eileen.deguire@
asminternational.org
Barbara L. Brody
FEATURES
Art Director
Joanne Miller
Production Manager
joanne.miller@
asminternational.org
Joseph M. Zion
Publisher
joe.zion@asminternational.org
Please send news releases to
magazines@
asminternational.org
Editorial Committee
Roger Narayan
North Carolina State University
and the University of North
Carolina, Chair
Ishaq Haider
BD Techologies
Harold Pillsbury
University of North Carolina
Ray Harshbarger
Walter Reed Army Medical Center
Sebastien Henry
Porex
The MPMD Editorial Committee is
strictly an advisory group,
and membership on the
committee in no way implies
endorsement of any of the
publication’s content.
Sales Staff
Kelly Thomas, CEM.CEP
National Account Manager
Materials Park, Ohio
tel: 440/338-1733
e-mail: kelly.thomas@
asminternational.org
On the Cover
Biosensors made of
gold-palladium nanocubes
tethered by SWCNTs
Purdue University researchers, Dr. Timothy Fisher and Dr. Marshall Porterfield,
have created a high-precision biosensor
for detecting blood glucose and potentially many other biological molecules by
using single-wall carbon nanotubes
(SWCNT) anchored to gold-coated palladium “nanocubes.” The device resembles
a tiny cube-shaped tetherball. Each cube
is a sensor and anchored to electronic circuitry by a nanotube, which acts as both
a tether and an ultrathin wire to conduct
electrical signals.
The tetherball design lends itself to
sensing applications because the
sensing portion of the system extends
out far from the rest of the device so that
it can come into contact with target molecules more easily. The system does not
have to wait for target molecules to diffuse to the surface, and it can move into
other regions within the range of the
tether for enhanced sensing. The technology may have applications detecting
other types of biological molecules or in
future biosensors for scientific research.
(Image by Jeff Goecker, Discovery Park,
Purdue University.)
For more information: Timothy Fisher,
Purdue University, West Lafayette, IN
47907; tel.: 765/494-5627, tsfisher@
purdue.edu; www.purdue.edu.
ADVANCED MATERIALS & PROCESSES/APRIL 2009
CHARACTERIZATION
OF MATERIALS
FOR MEDICAL
DEVICES
Chemical analysis 7
Metallographic 9
preparation of
medical devices
Environmental 10
SEM
DEPARTMENTS
Industry News 2
Products 12
and Services
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INDUSTRY NEWS
MPMD Database: Spring 2009 update
Billions of dollars
10
House
Senate
Final
8
6
4
2
0
NIH
NSF
DOE
Science
NIST
NASA
DOE
Energy
2009 Supplemental recovery funding for R&D (House,
Senate, and Final bills) Source: AAAS analysis of R&D in
House, 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 Advancement
of Science (AAAS, Washington, D.C.) estimates that
the final version of the 2009 economic stimulus appropriations bill that President Obama signed into
law on Feb. 17, 2009 contains $21.5 billion in federal R&D funding. Basic competitiveness-related
research, biomedical research, energy R&D, and climate change programs are high priorities in the
final economic recovery bill.
Highlights for agencies active in medical device
R&D:
• National Science Foundation - $3.0 billion. Research grants distributed through NSF’s regular
peer review are receiving a $2.0 billion bump with
the balance funding instrumentation and academic
research infrastructure programs. Depending on
final FY 2009 appropriations, the stimulus puts NSF
well ahead of the $7.3 billion authorized for FY 2009
in the America COMPETES Act of 2007.
• National Institutes of Health - $10.4 billion. The
final bill allocates $7.4 billion to be distributed proportionally among the NIH’s institutes and centers
through regular, already scheduled grant review cycles. Another $800 million remains in the Office of the
Director, with priority given for 2-year, short-term
special research grants to be awarded competitively.
The enormous stimulus appropriation gives NIH a
total FY 2009 budget of $39.9 billion, a total that could
go even higher in final FY 2009 appropriations.
For more information: www.aaas.org.
MPMD e-Newsletter begins monthly publication
Because quarterly access to information is not enough to
stay current with the dynamic medical device industry,
ASM International is proud to introduce the MPMD eNewsletter. Published monthly, the e-Newsletter is a nimble
vehicle for getting the latest news to the medical device
community. To subscribe to this free e-Newsletter, visit
http://asm.asminternational.org/asm/n.asp.
44
ASM International brings to your desktop a comprehensive and
authoritative set
of mechanical,
physical, biological response,
and drug compatibility properties for materials and
coatings used in medical implants. Update highlights include:
Cardiovascular Module: In a major new extension to the database, information has been added
for all FDA classifications of catheters and other related interventional devices.
• Diagnostic Devices: Catheter cannula, Continuous flush catheter, Electrode recording, Guide
wires, Percutaneous catheter
• Therapeutic Devices: Embolectomy, Septostomy
• 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, Bioactive
glass, Bovine cortical bone, Calcium sulfate hemihydrate, Fe-23Mn-21Cr-1Mo, Poly(lactic acid)/
tricalcium phosphate, Poly(lactic-glycolic acid)/
tricalcium phosphate, Poly(lactide-co-trimethylenecarbonate), Poly(L-lactide-co-caprolactone)/
tricalcium phosphate, Polycarbonate, Polyetherimide, Polymethylpentene (TPX), Polyphenylsulfone, 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 the
database features all the new PMA and 510(k) approvals up to February 6th, 2009, in both the Orthopaedic and Cardiovascular modules, fully integrated for ease of searching, and linked to materials.
• Producers: 80 new producers with links to specific devices.
• Contributing Authors Table: Biographical details of experts from the medical device industry
who have authored information in this database
have been updated.
Full details of the Spring 2009 update can be
found at http://products.asminternational.org/
meddev/index.aspx.
ADVANCED MATERIALS & PROCESSES/APRIL 2009
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INDUSTRY NEWS
Diamond coatings decrease
blood clotting in heart pumps
Using a process originally developed for industrial equipment, Advanced Diamond
Technologies, Inc. (ADT, Romeoville,
Ill.) and Jarvik Heart, Inc. (JHI, New
York, N.Y.) are collaborating to develop improved blood contacting surfaces using ADT’s form of diamond,
known as UNCD. Because the coating is both thin
and exceptionally smooth, it is expected to inhibit
the formation of blood clots inside the device, and
to reduce the need for blood thinning medications.
Freed from anticoagulation medication, the heart
assist device could be used for tens of thousands
more patients suffering from heart failure.
In a relatively small percentage of patients with
heart pumps, blood clots may form on the titanium
or ceramic components such as rotors and bearings.
If this occurs, the ability of the device to pump
enough blood can be reduced. Also, blood clots can
break free and cause a stroke.
Other potential applications for the UNCD
coating include artificial heart valves, cardiac stents,
and metal and ceramic components of intravascular
3
prostheses. JHI is investigating using the diamond
coatings on heart pumps for infants and children.
Because the pumps are so small, about the size of a
AAA battery, flow channels are tiny and the risk of
blood clotting is even higher than with adult pumps.
The market for heart pumps is estimated to be $580
million a year by 2015 with a compound annual
growth rate of 16.6 percent according to Medtech Insight, November 2008.
For more information: www.thindiamond.com,
www.jarvikheart.com.
Feasibility of carbon nanotubes brains
Professors Alice Parker and Chongwu Zhou at the
University of Southern California (Los Angeles, Calif.)
are taking the first steps to build neurons from carbon
nanotubes that emulate human brain function.
Unlike computer software that simulates brain
function, a synthetic brain will include hardware
that emulates brain cells, their amazingly complex
connectivity, and their “plasticity,” which allows
the artificial neurons to learn through experience
and adapt to changes in their environment the way
real neurons do.
Using mathematical models, the researchers
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jhunter@cartech.com
ADVANCED MATERIALS & PROCESSES/APRIL 2009
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INDUSTRY NEWS
have shown that portions of a neuron can be modeled electronically using carbon nanotube circuit
models. A single archetypical neuron, including excitatory and inhibitory synapses, has been modeled
electronically and simulated. A small network of interconnected neurons will be simulated using the
carbon nanotube models.
Engineering challenges that could benefit from technological solutions that involve artificial neural
structures include autonomous vehicle navigation, identity determination, robotic manufacturing, and
medical diagnostics. This technology could revolutionize neural prosthetics, and yield some amazing biomimetic devices.
For more information: Alice Parker, parker@eve.usc.edu, http://ee.usc.edu.
Cardo Medical’s Press-Fit
Total Hip system
Cardo Medical (Los Angeles, Calif.) has released its
Press-Fit Total Hip system. The Press-Fit Total Hip
system incorporates a dual taper design which has a
long, proven clinical history with great implant success rates. As a complement to the Press-Fit Total Hip
system, 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 risk
Drug-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 blood
clots and heart attacks. Stents affect the fluid dynamics of blood flowing past them and cause drugs to accumulate in certain areas. Too much drug build-up promotes clot formation. A mathematical model developed by MIT engineers can predict whether particular types of stents are likely to cause life-threatening
side effects. The model shows that the dynamics of blood flowing around a stent is similar to whitewater rapids, according to Dr.. Elazer Edelman, professor in the of Health
Researchers at the Fraunhofer Institute for Sciences and Technology Department, Massachusetts Institute of TechMachine Tools and Forming Technology and nology, Cambridge, Mass.
the University of Leipzig have developed a
This is the first time that a mathematical model has successfully presimulation model to calculate bone density
dicted stent performance based on changes in arterial blood flow and
and elasticity from CT scanner images. The
model will help surgeons choose the best design. Researchers hope the model and concepts it establishes could
sites for placing the screws that anchor artifi- aid efforts to design stents that allow drugs to be more evenly distribcial hip joints to the patient’s bone. uted throughout the area; the model could also help the FDA with its
www.fraunhofer.de approval processes.
For more information: Elazer Edelman, ERE@mit.edu, www.mit.edu.
Micell Technologies has obtained the rights
to Maxcor’s Genius MAGIC Cobalt Chromium
Coronary Stent System for the purpose of
developing and marketing drug-eluting
stents based on Micell’s proprietary coating
technology. 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 its
Atlas 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 ventricular fibrillation), which often lead to sudden
cardiac death. www.sjm.com
46
Long term durability of cementless total hip replacements
Researchers from Rush University Medical Center (Chicago, Ill.) have
found that fixation of the implant to bone is extremely durable even twenty
years after repeat or “revision” hip replacement. The implant utilized,
the Harris-Galante-1 acetabular metal shell, which is designed to allow
a patient’s bone to grow into the implant, remained fixed in place in 95
percent 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 cementless metal cup designs. The cup’s porous surface allows bone and tissue
to grow into the device to keep the hip implant in place. Earlier generation implants relied on the use of bone cement to secure the implant to
the patient’s pelvis and were associated with a higher failure rate, particularly in patients who had previously experienced a failed hip implant.
While the long-term fixation of the device performed very well, the
study found an increased rate of repeat surgery for wear-related complications at 20 years compared to the 15-year report. Despite the increasing prevalence of wear-related problems, the main modes of failure
ADVANCED MATERIALS & PROCESSES/APRIL 2009
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were infection and recurrent dislocations. The study authors recommend the
use of larger diameter femoral heads and more wear-resistant bearings to decrease the risks of these complications.
For more information: www.rush.edu/rumc.
Pure
Brilliance
Rejection-free, bioreabsorbable scaffold for jaw implant
The Custom-Fit project, an EUfunded research program involving 30
partners from 12 European countries,
is developing a bioresorbable material
for mandibular and other joints. Once
implanted, it is replaced with re-grown,
natural bone in 6-12 months. The consortium is developing a new manufacturing paradigm for customizing implants to the individual shape of the
human body using CAD systems and
rapid manufacturing technologies.
The process begins by studying the jaw bone geometry through computerized tomography images and using computer programs to distinguish the
damaged part of the bone from the healthy area. A surface model of the implant is designed with a CAD system that allows direct manipulation of facet
models, and a 3D model of the implant is completed by adding the internal
structure (porosity). Finally, the model is prepared for manufacture using a
special rapid manufacturing tool using high viscosity, bioreabsorbable resins
and is capable of printing multi-material and porous objects.
Although approval for implantation in patients is several years away, the
technology offers several advantages: no rejection of foreign material, new
bone will be able to grow over time (for children), further treatment like dental
implants remains possible, and the implant will be completely replaced by
new natural bone.
For more information: www.custom-fit.org.
‘Lint Brush’ Captures and Kills Cancer Cells in the Bloodstream
Cornell University (Ithaca, N.Y.) researcher, Dr. Michael King, has developed a lethal “lint brush” for the blood that captures and kills cancer cells in
the bloodstream. In research conducted at the University of Rochester,
Rochester, N.Y., King showed that two naturally occurring proteins can work
together to attract and kill as many as 30 percent of tumor cells in the bloodstream without harming healthy cells.
The goal is to develop a tiny, implantable, tube-like device coated with proteins that would filter out
and destroy free-flowing
cancer cells in the bloodstream. Cancer cells adhere to the selectin protein on the microtube’s
surface, and are exposed
to the protein, TRAIL
(Tumor Necrosis Factor
Related Apoptosis-Inducing Ligand), which
binds to two so-called
“death receptors” on the
Surface
Protein G
Trail
E-selectin
cancer cells’ surfaces, setADVANCED MATERIALS & PROCESSES/APRIL 2009
Brilliant marker bands
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6
ting in motion a process that causes the cells to self-destruct. The cancer cells are released back into the
bloodstream 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 proportion of metastatic cells, and give the body a fighting chance to remove the rest of them. The work will be
published in Bioengineering and Biotechnology; “Delivery of apoptotic signal to rolling cancer cells: a
novel biomimetic technique using immobilized TRAIL and E-selectin;” DOI: 10.1002/bit.22204.
For more information: Michael King, mike.king@cornell.edu, www.news.cornell.edu.
Bioabsorbable stents show promise
A 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 and
an angiographic in-stent late loss of 0.48 mm at two years. These results fall between those commonly seen
for bare metal stents (typical in-stent late loss of 1.0 mm), and drug eluting stents (typical in-stent late loss
of 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 probable
explanation for the in-stent late loss is early recoil after stent implantation, indicating that the stent initially is not exerting enough radial force to keep the vessels perfectly open. The challenge facing stent
designers is to achieve a balance between radial strength and a structure that can be reabsorbed in a reasonable time period.
After two years the physiological function of the stented part of the vessel was almost completely restored, preventing patients from having symptoms of angina or limitations in
Researchers from the National Eye
Institute, and NASA developed a physical activity. In contrast, studies of first generation drug eluting stents have
compact fiber optic probe to shown “paradoxical vasoconstriction” in the area of the stent, where the vessel
measure alpha-crystallin, a protein constricts instead of opening during exercise. For more information:
related to cataract formation. First www.escardio.org/
developed for the space program, the
safe, 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 a
laser light technique called dynamic
light scattering. www.grc.nasa.gov,
www.nei.nih.gov
AGY’s new biomaterial, HPB glass
fiber, is suitable for long-term implant
applications, and is compatible with a
wide range of thermoplastic
polymers such as PEEK, PEI and
PPS. HPB glass fibers have 40%
more tensile strength and a 20%
higher tensile modulus than ordinary
E-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 Idaho
are engineering multifunctional and
dynamic nanowires coated in gold
that swim through the bloodstream
and attach to specific cancerous
cells. An electromagnetic fields heats
the nanowires, destroying the
cancerous cells. The research is part
of a multimillion dollar project funded
by the Korean government.
www.uidaho.edu
48
Magnetic bracelet for acid reflux management
Torax Medical (Shoreview, Minn.) is
testing its LINX System, designed to prevent gastric reflux by augmenting the
lower esophageal sphincter, the body’s
natural anti-reflux barrier. The device conLinxTM
D
evice
sists of a “bracelet” of miniature magnetic
beads made of permanent rare earth magnets encased in titanium and placed
LES
around the lower esophageal sphincter.
The band is sized to fit each patient. The
attractive force between the magnetic
Stomach
beads helps to keep the lower esophageal
sphincter closed, restoring the normal barrier function of the defective sphincter.
The ring expands to allow swallowing or to release high gastric pressures. The
device is placed via laparoscopic methods and, once in place, begins working
immediately. For more information: www.toraxmedical.com.
Future looks bright for orthopaedic
A recent report by Global Markets Direct, The Future of the Orthopedic Devices
Market to 2012, indicates that the joint reconstruction (artificial joints) market
will grow from $12.2 billion in 2008 to $17.4 billion by 2012, and will comprise 45% of the overall orthopaedeic devices market in 2012. The spinal nonfusion device market valued at $551 million in 2008 is forecast to reach $792
million by 2012, accounting for 15% of the spinal surgery market value. The
development of minimally-invasive technologies has enabled patients to choose
alternate orthopedic procedures and is likely to positively impact the growth
dynamics of the orthopaedic devices sector in the next 5 years. For more information: www.reportlinker.com/p098179/The-Future-of-the-OrthopedicDevices-Market-to-2012.html#summary
ADVANCED MATERIALS & PROCESSES/APRIL 2009
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Ensuring patient safety
through chemical analysis
7
Suppliers of medical equipment and implants
must ensure the safety of their products.
Chemical analysis is used to verify that
products pose no danger to patients and
practitioners.
David Kluk
Director of Technical Development
Carm D’Agostino
Head Chemist
NSL Analytical Services Inc.
Cleveland, Ohio
D
octors and hospitals are keenly aware of patient safety, and take extreme steps to ensure
that anything that comes into contact with a
patient is free of toxic or harmful elements. As
a result, suppliers of medical equipment and implants
take every precaution to verify the safety of their products. Often, this verification is done through rigorous
chemical analysis by a third parting testing lab.
Cleanliness is particularly critical for any medical components that will be implanted or used during surgery.
Hip and knee implants, for example, are often coated with
a calcium phosphate to encourage bone growth around
and into the implant. Any impurities in the coating could
inhibit bone growth or could cause an adverse reaction in
the body. Stents, staples, clamps, and surgical tools also
must be tested for any residues from the manufacturing
process. FDA guidelines require these parts to be checked
by a third-party laboratory to confirm that they are safe
for use.
Tests performed vary with the type of component being
analyzed. For example, the composition of surgical tools is
typically analyzed with optical emission testing. Cleanliness is verified with traditional wet chemistry testing, while
Inductively Coupled Plasma Mass Spectroscopy (ICP/MS)
is used to check for impurities in implant coatings.
Chemical Analysis
Bulk analysis determines the concentration of the major
chemical constituents of a material. Analytical instrumentation used for bulk analysis includes X-Ray Fluorescence
and Inductively Coupled Plasma Optical Emission Spectroscopy.
X-Ray Fluorescence (XRF) instrumentation determines
elemental concentration by analyzing the emission of characteristic x-rays from the material that has been excited
by bombarding it with high-energy X-rays or gamma rays.
The fluorescent radiation can be analyzed either by sorting
the photon energies emitted (energy-dispersive analysis)
or by separating the radiation wavelengths (wavelengthdispersive analysis). Once sorted, the intensity of each
characteristic radiation is directly related to the amount
ADVANCED MATERIALS & PROCESSES/APRIL 2009
XRF Instrument can detect elements at the parts per million
range.
of each element in the material. An XRF instrument can
handle materials in different forms such as solids and
powders. A number of techniques can be applied to place
the material in the proper form for the instrument.
Pressed powders consist of the sample material mixed
with a small amount of binder and pressed into pellet form
under extreme pressure. Provided the sample has uniform particle size, elements can be detected at the parts
per million (ppm) level. One challenge of using pressed
powders as a quantitative tool is acquiring matching material with known concentrations to calculate the final
concentration. These may not be available for the element
of interest.
Fused beads are created by mixing the sample with a
known amount of flux such as lithium tetraborate. The
mixture is then heated in a furnace or fusion equipment
and melted into a glass bead. The advantage of using fused
beads is that measurement standards can be created synthetically for comparison. The main drawback is that the
sample material is diluted by the flux, limiting detection
accuracy to about 0.1 to 0.5%, depending on the fusion
technique.
Inductively Coupled Plasma Optical Emission Spectroscopy (ICP/OES) instrumentation introduces an
aqueous solution into an extremely hot plasma gas. Light
emitted by the atoms of an element consumed in the
plasma is resolved into its component radiation, and the
intensity is measured with a photomultiplier tube or solid
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ICP instrument consumes the sample in a plasma flame and
detects elements with a photomultiplier, solid state chip or mass
spectrometer.
8
state detector. The intensity of the electron signal is compared to previously measured standards of known element concentration, and the concentration is computed.
Advantages of ICP analysis include the ability to match
the sample solution to a synthetically created standard once
the sample has been dissolved by various digestion techniques. Also, concentrations from trace to major levels can
be quantified using the same sample preparation technique.
Sample preparation usually entails taking 0.1 to1.0 g of
material and digesting it using various procedures. After
the sample has been broken down, it
is placed into solution by diluting
with acid by one thousand fold or
more. The use of proper analytical
techniques is critical to avoid variances in the final concentration cause
by sample dilution and by the influence of matrix interference. Also, some
materials can be difficult to analyze
because they are not readily soluble
by standard procedures.
www.ulbrich.com
Finding Trace Elements
Trace analysis involves determining
the presence of elements in minute
amounts. The usual analysis methods
used are ICP/MS and Cold Vapor
Atomic Absorption Spectroscopy.
Inductively Coupled Plasma Mass
Spectroscopy (ICP/MS) is a highly
sensitive type of mass spectrometry
that can determine element concentrations below one part per trillion. It
is based on coupling an ICP source (to
produce ions) with a mass spectrometer (to separate and detect the ions).
Coupling the mass spectrometry
with ICP allows for low-level detection, from parts per trillion to 0.5% or
greater. Advantages of ICP/MS include the ability to identify and quantify a large group of elements, and that
measurement standards are readily
available.
Cold Vapor Atomic Absorption
Spectroscopy (CVAAS) takes advantage of the characteristic of volatile
heavy metals, such as mercury, that allows vapor measurement at room temperature. In the technique, free mercury atoms in a carrier gas are absorbed
by the ultraviolet light radiation source
at 253.7 nm. The change in energy is
detected by a UV sensitive phototube.
The technique is linear over a wide
range of concentrations.
MPMD
info@ulbrich.com
50
For more information: David Kluk,
NSL Analytical Services, 4450 Cranwood
Parkway, Cleveland, OH 44128; tel.:
216/643-5200; nsl@nslanalytical.com;
www.nslanalytical.com.
ADVANCED MATERIALS & PROCESSES/APRIL 2009
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Specimen preparation for
metallographic examination
of medical devices
George F. Vander Voort, FASM
Buehler Ltd.
Lake Bluff, Illinois
M
etallographic work is usually conducted on
new implant materials and devices to guarantee their quality or to determine if the
manufacturing approach is satisfactory; or,
it is conducted on implants removed from animals to evaluate suitability or bone in-growth development. Obtaining
specimens for metallographic analysis requires optimal
sectioning procedures to minimize damage to the implant
material. As surfaces are a prime subject for examination,
encapsulation is required to promote edge retention. This
can be complicated if a foam or a medicinal coating has
been applied to the surface. The void space within the
foam must be infiltrated with a low-viscosity epoxy to
preserve the pore geometry and protect the foam during
preparation.
Once the specimens have been encapsulated and the
desired surfaces are ready to be prepared for examination, the metallographer may be faced with a relatively
straightforward preparation sequence if the implant has
no formidable surface coatings. However, in the case of
implants with bonded foam surfaces or medicinal coatings, the preparation sequence is more challenging. Foams
are often made from tantalum, a difficult refractory metal
to prepare. Revealing both the substrate, which may be
made from a variety of highly corrosion-resistant metals
and alloys, and the tantalum foam, will test the mettle
of all metallographers. Medicinal coatings on metallic substrates may be water soluble, and dealing with nonaqueous abrasives, extenders, and cleaning solutions is
always challenging.
Because these metals and alloys tend to be highly corrosion resistant, etching them so that the microstructure
is fully and clearly revealed may be quite difficult. In general, there are well-known, highly successful etchants for
austenitic stainless steels. However, etching the Ni-free,
Fig. 1 — Ti-6Al-4V acetabular cup
high-Mn austenitic stainless steels is very difficult, especially when they have been cold worked in manufacture. Cobalt alloys are very popular for implants and,
while etchants for them exist, it is still a challenge Correction
to reveal their structure with clarity. Grain size rating The January
of any twinned FCC metal is always difficult as issue of MPMD
many etchants reveal only a portion of the grain and listed incorrect
twin boundaries. Cobalt alloys are FCC, although
contact
pure cobalt is HCP, and as they are highly corrosion
information
resistant, etching them properly is difficult. Commercial purity (CP) titanium can be examined as- for Buehler, Inc.
polished using polarized light, but only if all the The correct
preparation-induced damage is removed. Speci- contact details
mens must be totally free of any preparation-in- for more
duced damage; “just good enough” preparation is information are:
not acceptable for this work.
Rick Wagner
To illustrate the challenge facing the metallog- Buehler, Ltd.
rapher, Figure 1 shows a Ti-6Al-4V acetabular cup 41 Waukegan
where CP Ti wire has been diffusion bonded to the Road
substrate to promote bone in-growth. The specimen Lake Bluff, IL
was encapsulated using vacuum impregnated Epo60044
Heat epoxy resin which has a viscosity of ~32 cps.
tel.:
It was prepared using Buehler’s three-step method
for titanium, and color etched with a modification 847/295-4546
of Weck’s reagent for titanium (100 mL water, 25 mL richard.wagner
ethanol, 2 g NH4F×HF). The micrograph was taken @buehler.com
using polarized light with a sensitive tint filter. Color www.buehler.com
metallography revealed the structure far better than the
standard black & white etching with Kroll’s reagent. Figure
2 shows examples of Nitinol, a very difficult alloy to prepare damage free and to etch. Figure 2a shows the
austenitic structure as processed and Figure 2b shows the
martensitic structure after going through the shapememory affect transformation.
For more information: Rick Wagner, Buehler, Ltd., 41
Waukegan Road, Lake Bluff, IL 60044; tel.: 847/295-4546;
richard.wagner@buehler.com; www.buehler.com.
Fig. 2a — Austenitic Nitinol
ADVANCED MATERIALS & PROCESSES/APRIL 2009
9
Fig. 2b — Martensitic Nitinol
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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
M
edical devices increasingly use materials
with drug release properties, swelling
ability, and surfaces designed to promote
biocompatibility. Examining such materials
via electron microscopy can be challenging, particularly
when those properties essential to their function, such as
swelling and drug dissolution, make them vacuum incompatible. The traditional limitation of scanning electron microscopy (SEM) is that the specimen must be able
to withstand a high vacuum and be either electrically conductive or rendered conductive by modifying it with a
very fine coating of metal (usually gold–palladium). Environmental SEM (ESEM), which permits the observation
of nonconductive samples by providing a humid environment in the sample chamber and using water vapor
as a cascade amplifier for secondary electrons, was first
introduced in 1989 by the company ElectroScan, which
was purchased in 1996 by the FEI Company (Hillsboro,
Oreg.) ESEM has been used extensively since then by biologists for imaging specimens such as insects and plant
samples, and by materials engineers for imaging vacuumincompatible specimens and for following dynamic
processes as a function of temperature, humidity, or both.
Following the launch of ESEM, other companies introduced low vacuum and variable pressure (LVSEM and
VPSEM) instruments. These also allowed for the imaging
of nonconductive samples, including polymeric substrates
that outgas.
Recently ESEM has garnered attention for the analysis
of medical devices, particularly in the evaluation of material properties such as cell adhesion (Ref. 1), tissue calcification (Ref. 2), and osseointegration into implants
(Ref. 3). Following is an overview of the ESEM method
and an interview with Scott Robinson from the University of Illinois’ Imaging Technology Group. Scott
Robinson has extensive experience in electron microscopy, including the use of ESEM for imaging of medical device components.
Background of ESEM
For ESEM to work, it must be possible to introduce
water vapor into the sample chamber without posing a
threat to the electron gun. The gun chamber must maintain its relatively high vacuum (<10-10 torr in a field-emission instrument) while delivering the electron beam to
the poor vacuum (between 0.7 and 10 torr) of the sample
chamber. This is accomplished by placing a series of pressure-limiting apertures (PLAs), approximately 400 µm in
diameter, between the high and low vacuum regions in
the electron column. At least five stages of increasing
vacuum separate the sample chamber from the gun
chamber.
The PLAs work in conjunction with a gaseous secondary electron detector (GSED), which is usually located
directly above the sample and contains the final aperture
through which the electron beam passes. The diameter of
that aperture determines how poor the vacuum can be in
the sample chamber. For a 500 µm GSED aperture, the
chamber pressure can be as high as 10 torr. Imaging occurs as the electron beam (‘primary electrons’) enters the
chamber, passes through the aperture of the positively
charged GSED, through the water vapor, and impinges
on the sample surface, generating secondary electrons
from that surface. The secondary electrons collide with
the 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 collects the amplified signal as it repels the positively charged
ions. The repelled positive ions combine with excess negative charge on the sample, neutralizing it, and thereby
preventing surface charging.
ESEM thus utilizes a series of tricks to permit the use
of water vapor in the sample chamber, to prevent charging
from occurring, and to obtain an adequate signal using
the GSED (as opposed to the photomultiplier tube, further away and with a lesser bias, used in a traditional
SEM). As with any imaging technique, there are tradeoffs in resolution.
AS: What ESEM instrument do you use in your
microscopy suite at the Imaging Technology
Group?
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 cubic
form. Images courtesy of the Imaging Technology Group, University of Illinois.
52
ADVANCED MATERIALS & PROCESSES/APRIL 2009
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a $200,000 option—gives much better resolution.
The microscope, which is 10 years old, can be used
either as an ESEM or an SEM, and most of the time
we encourage clients to use it as an SEM even when
they think they want to use an ESEM. Using the
scope as an ESEM is definitely tricky, and it is more
dif ficult to get good images. There are other constraints, including sample size.
A.S.: How do you adjust water vapor levels during humidity tests if water vapor is so crucial for imaging?
S.R.: One problem with ESEM is that to some extent the
quality of your image depends on the vapor pressure. If you’re doing an experiment in which humidity is the variable, not all of your images will be
perfect.
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 cloud
of electrons in water vapor?’ The signal comes from
the water vapor at the millisecond the beam is located at one specific point on the sample. The beam
then moves maybe two nanometers along to produce the next signal. And all of those split-second
signals combine into your image.
Small changes can greatly improve image quality.
The closer you are to the pole piece, the better the
resolution, just like SEM. But if you get too close
you can run into the positive bias of the detector,
breaking up your image. In ESEM it’s important to
be as close as possible, and keeping an optimal
working distance is crucial.
As with SEM, a higher accelerating voltage gives
better resolution. The higher kV helps blow through
the water vapor, so the final image doesn’t look
‘cloudy,’ but there’s an increased chance you’re not
going to neutralize excess charging. You want to
maintain a balance between the accelerating voltage,
the working distance, the water vapor pressure, and
the bias on the GSED.
A.S.: Is ESEM useful for examining super hydrophobicity of treated surfaces?
S.R.: With super hydrophobicity you see very round water
droplets. We’ve also worked with extruded polymer
fibers that were irradiated to control their hydrophilicity. Images of the tiny water droplets we
condensed onto the fibers were used to obtain contact angle measurements at several thousand times
magnification.
A.S.: When examining medical devices with drug delivery applications, what do people need to consider when deciding between LVSEM and
ESEM?
S.R.: You definitely have trade-offs. By imaging micelles,
which are sometimes formed as vehicles for drug
delivery, in the ESEM, we can avoid destroying
them. In backscatter mode, you might have poor
contrast, go to higher voltage, and destroy the micelles with that extra energy. In wet mode we often
freeze a large emulsion droplet and then slowly
draw water away from its surface by lowering the
vapor pressure, leaving the particles exposed for
imaging.
For simple examinations of drug-coated stents you
can just work at low voltage with a suitable backcattered electron detector.
A.S.: When examining medical devices with swelling
properties, what do people need to consider?
S.R.: If you don’t want to see something shrivel up
under less than 100% relative humidity, ESEM
works well. With ESEM you can monitor the
swelling/shrinking of devices (such as hydrogels)
in response to changes in water vapor pressure. We
can look at tissue scaffolds, made of polymer, at high
water vapor pressures, and the vacuum doesn’t
damage them. Some polymer samples are so
vacuum-sensitive that the vacuum in the sputter
coater will cause them to collapse.
ADVANCED MATERIALS & PROCESSES/APRIL 2009
11
A.S.: What are the advantages of examining cell adhesion using ESEM?
S.R.: It’s difficult to image unfixed cells in wet mode,
especially with a field emission gun. The closer you
get to them, the more likely they are to be damaged.
We have imaged live Shigella bacteria, which create
a biofilm, making them look like hotdogs under a
thin blanket.
A.S.: Where do you see the ESEM utility in examining
implant–tissue interfaces?
S.R: Such studies are better done using backscattered
electron imaging and EDS in SEM mode.
A.S: What other time–temperature studies are performed using ESEM?
S.R.: We have the ability to heat small samples as high as
1500°C and take images along the way. Presently
we are working on a heating/strain stage.
With ESEM you have a lot of options.
MPMD
References
1. O. Craciunesescu, L. Moldovan, D. Bojin, C. Vasile,
O. Zarnescu, ESEM Observations on New Polyurethane
–Based Materials for Biomedical Applications: Structure
and Cell Adhesion, Acta Microscopica, Vol. 16, No. 1-2,
Supp.2, 2007.
2. S. Habesch, C. Delogne, Progressive Calcification of
Bioprosthetic Heart Valve Tissue, Techniques for Assessing
Different Morphologies and Composition of Calcium
Phosphate Deposits Under Hydrated Conditions using
ESEM, Low-Vacuum SEM/ESEM in Materials Science:
Wet SEM- The Liquid Frontier of Microscopy, MRS Symposium V, November 29, 2000.
3. M. Tarcolea, F. Miculescu, S. Ciuca, R.M. Piticescu, I.
Patrascu, L.T. Ciocan, ESEM Investigation on Osseo Integration of Ti Alloy Implants, European Cells and Materials, Vol. 16, Suppl. 1, 2008, p. 56.
For more information: Angele Sjong is a materials engineer, chemist, and
owner of Sjong Consulting LLC, PMB #324, 2525 Arapahoe Ave, Ste E4,
Boulder, CO 80302; tel.: 650/799-4170; angelesjong@yahoo.com.
Scott J. Robinson is in the Imaging Technology Group at the Beckman Institute for Advanced Science and Technology, University of Illinois at
Urbana–Champaign; B650J Beckman Institute, 405 North Mathews Ave.,
Urbana, IL 61801; tel.: 217/265-5071; sjrobin@illinois.edu; www.illinois.edu.
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