Conscience is the inner voice that warns us that someone might be looking. -- H. L. Mencken
BIOMECHANICS OF HEART VALVES1
Dimitrios Psalidas Rodríguez, Josie R. Bohn Sauveterre, Mariano Matos Santiago and Reyinald García Montañez2
ABSTRACT years, the field of heart valve replacement became one of
The heart is a vital part of the human anatomy because the major growth areas in cardiac surgery, and it is
it functions as a pump to circulate blood throughout the estimated that over 150,000 valves are replaced in the
body. Heart valves allow the heart to pump blood to world every year. Moreover, world demand for these
specific locations efficiently. These valves are prone to devices continues to expand at a rate of 10% to 12% per
disease and malfunction, and can be replaced by year.
prosthetic heart valves. The two main types of NATURAL AORTIC VALVE
prosthetic heart valves are mechanical and
bioprosthetic. The mechanical valves are excellent in An aortic valve consists of three leaflets and three
terms of durability, but are hindered by their tendency corresponding cavities, called sinuses of Valsalva.
to coagulate the blood. Bioprosthetic valves are less Apertures of the right and left coronary arteries are present
durable and must be replaced periodically. All valve in two of the sinuses and, accordingly, the sinuses are
types must be durable, because the body is an extremely named right coronary sinus, left coronary sinus, and non-
hostile environment for a foreign object, including coronary sinus. At the lower margin the sinuses join the
prosthetic heart valves. Today, chemical engineers are left ventricle, and at the upper margin they become part of
researching new designs of prosthetic heart valves. the ascending aorta. The leaflets are attached at the base of
Many engineers believe the future lies within the regime the valve ring (annulus fibrosus). The noduli arantii are
of tissue engineering. thickenings at the middle of the free edge of the leaflet and
are believed to be important in reducing the leakage when
KEYWORDS the valve is closed. At the commisures the free edges are
Heart Valve, Titanium, Pyrolitic Carbon, Commisures, connected to the aortic wall. The contact area between two
Elastomers, EPDM polymer, Alumina, Hemodynamics, leaflets, called coaptation area, is formed by the lunulae,
Mitral Valve, Pyrogen, Radiopacity, and Regurgitation. which are much thinner that the leaflet body. They have no
load bearing the function, but provide a safety margin for
INTRODUCTION the valve to close without regurgitation.
Heart valves are passive devices that open and close about
105,000 times a day.1 Their2 function is to maintain the
unidirectional flow of blood through the heart.
Pathological changes may result in a restriction of the
opening of a valve (stenosis) or loss of competence,
allowing back flow through the closed valve
(regurgitation). Mitral and aortic valves are most frequently
affected. In all cases, the work load for the heart is
increased and cardiac function may be compromised. For
patients with severely symptomatic valve disease, valve
replacement offers improvement of the cardiovascular
function, long term survival and quality of life.
Figure 1. Human Heart Diagram .
Artificial heart valves were first used in the late 50’s and The leaflets are made from a very pliable, spongy material
early 60’s. Following the success of these early implants, containing fibers. They consist of three layers: fibrosus,
the replacement of diseased valves with prostheses became the layer at the aortic side that contains a dense network of
rapidly a routine clinical procedure. During the next 30 collagen fibers; spongiosa, the middle layer, still containing
some Collagen fibers but mainly acid
mucopolysaccharides; ventricularis, the layer at the
This review article was prepared on May 14, 2004 for ventricular side, containing both elastin and collagen fibers.
the course on Mechanics of Materials - I. Collagen fibers are approximately organized in clearly
Course Instructor: Dr. Megh R. Goyal, Professor in visible bundles. They seem to originate mainly from the
Biomedical Engineering, General Engineering Leaflet attachment close to the commisures and run
Department, PO Box 5984, Mayagüez, Puerto Rico circumferentially. Elastin fibers, on the other hand, are
00681-5984. For details contact: randomly oriented and not visible. Collagen and elastin
firstname.lastname@example.org or visit at: fibers have remarkably different mechanical properties.
http://www.ece.uprm.edu/~m_goyal/home.htm Collagen can elongate no more than 2 to 4% from their
relaxed length, whereas Elastin can elongate up to 100%
2 from their original length.
The authors are in alphabetical order.
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 1
particularly beneficial to seek an alternative for the rigid
The specific orientation of collagen fibers and the random conduit proposed here since the large internal surface area
orientation of elastin fibers determine the material (approximately 4 500 mm²) is an order of magnitude
properties of the leaflets. In the circumferential direction greater than the exposed surface area of a typical
the main role is played by the collagen bundles, which are conventional valve of the same diameter.
very important for leaflet durability. They transfer the load
on the leaflets in the closed state to the sinuses, such that The homodynamic characteristics of the valve should be
leaflets and sinuses form a unique bearing structure. In the preserved. This involves undisturbed blood flow, a low
axial direction the leaflets are much more extensible, pressure drop over the valve, low incidence of hemolysis
indicating the elastin fibers are mainly being strained. and a gradual valve closure which starts during systole and
Indeed, the leaflets must be quite elastic in the axial is enabled by the preserve of cavities formed by the sinuses
direction to maintain the sharp curvature at the coaptation of Valsalva. As a consequence valve prosthesis should have
area without producing high stresses. leaflets made of soft material and preserve sinuses of
valsalva or replace them. Leakage is kept low in the natural
Lately leaflets have been shown to be curved in only one valve by the lunulae, which form the cooptation areas and
direction thus being cylindrical. In the cylindrical leaflets, the noduli arantii. In a synthetic valve the leaflets should
stresses in circumferential direction are higher than in axial also have the possibility to form sufficient mutual contact
direction. The structure of the leaflet is best suited to area to prevent too much regurgitation. In a stented valve,
withstand these stresses. The shape of the leaflet is also where the leaflets are attached at the outside of the stent,
critical for its ability to reverse curvature. A single curved this implies very narrow stent post with a relatively sharp
surface can reverse curvature more easily and with less edged at the top of the aortic side. For both valve types the
creasing than a doubly curved surface. Since the leaflets free edges of the leaflets should be long enough.
must reverse curvature each time the valve opens and
closes, it is advantageous for them to have a cylindrical The natural leaflets have fiber reinforced structure. They
shape rather than a spherical shape. consist of an elastin network with circumferential oriented
bundles of, much stiffer, collagen fibers causing a marked
During diastole, aortic pressure is higher than the anisotropy. Theses fibers run into the aortic wall, to form a
ventricular pressure; the valve is closed. Next, the left strongly integrated structure. The load of the leaflets in the
ventricular pressure increases causing the commisures to closed configuration, the pressure difference between the
move outward thereby pulling the leaflets to produce a aorta and the left ventricle is manly taken up by the collage
stellate orifice. The aortic valve initially opens without any fibers. The elastin network is thinner at the attached to the
detectable forward flow. After expansion of the aortic wall, this part functions as a hinge. The elastin
commisures, the entire leaflets can move to the open network function manly a very flexible seal giving a high
position without bending in the radial direction. If the base degree of mobility during opening and closing this
did not expand, the leaflets would become redundant, separation if thought to be the natural solution of the
function and geometry would become abnormal and high conflicting demands of strength and leaflet flexibility.
deformations would occur that could lead to calcification. Therefore valve prosthesis should have fiber reinforced
Next, the forward flow is responsible for the full opening of leaflets in which the combination of materials mimics the
the leaflets. natural composite. Moreover, to obtain the same
mechanical integration of the leaflets and wall, the fibers of
According to Padula [1965, 683-689.], the aortic valves the stented valve should run on the outside of the stent from
opens fully very early in systole, but only for a very short leaflet to leaflet and, for the stenless valve the fibers should
time after which the valve aperture becomes triangular. run from leaflets into the wall.
According to van Steenhoven, the shape of the fully opened
valve is related to peak flow and stroke volume. The The leaflets are attached to the aortic wall which acts as a
higher the peak flow the more a circular geometry is flexible suspension. This determines to large extent the
approximated. shape of the leaflets during opening and closure: the very
unfavorable wrinkling of the leaflets which causes high
CHOICE OF MATERIAL strain and bending stresses is prevented. Moreover a
flexible suspension is expected to reduce stress peaks just
after valve closure. In conclusion a stenless valve is
The general approach in materials selection for mechanical
heart valves is to try and produce a surface which is so
smooth that blood cells will roll along them and not
A maximum resistance against fatigue is required to
become attached. Hence pyrolitic carbon, with its
maximize the lifer span. Thus is translated in choosing
inherently dense, glassy structure and its ability to be
durable materials, and the need form minimum stresses or,
highly polished, is a popular choice. Furthermore its
at least concentrate stresses in specially incorporated load
electrical conductivity is useful in allowing it to become
carrying parts and finally Appling design rules known for
electrostatically charged so that it can repel the blood cells.
improving the fatigue behavior of a structure and causing
Nevertheless, it is customary to use chronic anticoagulant
safe behavior. The latter means the along with the fiber
therapy with all mechanical valves, even those constructed
reinforcement that mimics the collagen fiber structure a
largely from pyrolitic carbon, indicating that this approach
is not necessarily the best one to pursue. It would be
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 2
random network of fibers is required that further lowers in polyethylene fibers (HP-PE, DSM) are applied as
the matrix and acts as a crack arresting medium. continuous fibers. Their diameter is 0.06 mm and
relatively low Young’s modulus of 30 GPa. Also other
Fiber reinforcements are not a new idea however one fibers were tested, for instance Lycra fibers, but their
should look for the optimal fiber layout within the limits of strength to break was too low for our application. Chopped
the manufacturability of theses layouts. Such a layout can Pe fibers, with a length of about 5 cm and diameter less
only be found if a numerical model of the valve is available than 0.05 mm were considered. However, nylon fibers were
as a design tool. All important aspects must be incorporated found to bee too stiff for our application, so chopped PE
in the model. fibers were chosen.
The design of a complex structure such as a synthetic Knitted Nylon and polyethylene networks were also tested
leaflet prosthesis, which has to function under very for reinforcement instead of continuous fibers. Knitted
complex and demanding conditions, is a very difficult task composites are in general easier to manufacture than wound
which asks for a deliberate approach. Not all problems can composites. To manufacture a composite with continuous
be solved at once, they have their own ranking. For fibers the fiber winding method. Various fiber layouts can
example, when the design and manufacturing procedure are be made and combined. The fist one is unidirectional fiber
such that materials are interchangeable, studying layout. Fibers run parallel to the circumferential direction,
biocompatibility and in vivo testing can be postponed until imitation the distribution of collagen fibers in a natural
a mechanical and hemodyamical optimal design is leaflet. Such layout influences mostly the composite
obtained. Typical dimensions are shown in figure 1. behavior in the circumferential direction (Figure 3).
EPDM MATERIAL The second one is a sinusoidal lay out (Figure 4).
Depending on the angle between the fibers and the axis of
The synthetic material for the matrix should be the cylinder, the composite has different material
biocompatible, flexible and easy to process in any desired properties. If the angle is 45, for instance the properties will
shape. EPDM rubber can be used as it matches these be the same in the circumferential direction and more
requirements, but polyurethane or silicon rubber could also complaint in the axial direction in this example the
be used. EPDM (Ethylene-Propylene-Diene-monomer) sinusoidal fiber layout has an angle of circa 70 with respect
rubbers belong to the family of the ethylene-propylene to the circumferential direction. This kind of layout
rubbers. Copolymerization of ethylene with propylene prevents propagation of cracks in the leaflets. The effect of
gives an EPM rubber, which needs to be cross linked. For reinforcement with different layouts on the most important
that a third monomer, diene is added in small amounts. The mechanical properties of EPDM is shown in Table 1.
diene used in EPDM rubber is mostly dicyclopentadiene
(DCPD). To cross link the rubber peroxide is used.
Activated by temperature, the peroxide molecules break
and form free radicals, which react with the polymer
molecules, creating cross links between them. EPDM
rubber is suitable to make bioprosthesis because it has a
low swell grade in blood, a good biocompatibility, high
chemical stability, and favorable mechanical properties.
Moreover, as the polymer chain of EPDM is completely
saturated, the resistance to degradation from oxygen and
chemicals is excellent. For this reason products made of
EPDM are very durable.
The properties of polyurethane plastic are similar to the Figure 2. Typical dimensions of a synthetic leaflet
issue that the human body uses in the valve construction. prosthesis. .
So far the EPDM is a material that assimilates the natural
tissue but it is also reinforced by collagen distributed in the
same direction as the circumference of the valve
(unidirectional) the purpose if this is to transfer the stress
the base and walls of the valve were it can hold more stress.
This why fiber reinforcement is the main stress reducing
expedient in the natural valve. By means of the fibers, the
leaflets transfer the load to the aortic walls. Not only fibers
can be used to reduce stresses. A flexible aortic base and
leaflet attachments also seem to improve the performance
and life span of a valve. The goal of this valve is the same Figure 3. Ethylene-Propylene-Diene-monomer .
concept of the original human valve. To accomplish this
polymer is combined with strong, high modulus
reinforcement; the resulting material has superior properties
compared to the matrix material alone. High performance
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 3
a. Manufacturing of a stented valve developed. EPDM rubber was chosen as matrix material,
continuous and chopped PE fibers were used as
reinforcement. It is possible to reinforce the material with
Valves are made on a mold. The first mold used to make a different fiber layouts. The unidirectional layout reinforces
stented valve, was of Teflon, an auto-lubricant material. the material in the circumferential direction and it should
The mold had a conical shape, designed to enlarge the be combined with another layout that reinforces the leaflet
cooptation area between the leaflets. A nylon stent was in the axial direction. A possible solution is applied on the
inserted in a stent shaped cavity. mold during dipping. The manufacturing procedure
described here can be used to manufacture prototypes with
Using Teflon for the mold ensures easy removal of the other matrix fiber materials, such as polyurethane or silicon
valve when the vulcanization process is completed. On the rubber instead of EPDM rubber.
other hand, Teflon is a soft material that gets easily
scratched and damaged; also the mold can become
deformed after a few vulcanization cycles, due to relaxation
of internal stresses. For these reasons, it was replaced by a
stainless steel shaped cavity. To avoid sticking of the
rubber on the steel, the mold was covered with polymeric
coating. Such coating does not influence the manufacturing
procedure of the properties of the rubber. In this way
removing the valve form the mold becomes as easy as in
the case of the Teflon mold. After insetting the stent in the
stent cavity, the mold is ready for valve manufacturing.
A solution of EPDM rubber was prepared in the following
way: 30 gr. K520 were cut in small pieces and dissolved in
400 gr. Xylene. This gave a solution an appropriate
viscosity for dip coating. Next the solution was mixed at a
temperature of 80 C for about 12 hours to get a
Figure 4. Sinusoidal Fiber lay out .
homogeneous mixture. When the solution had retuned to
room temperature, the cross linker debenzoyl peroxide was
added (1% in weight).After the Xylene has evaporated,
Figure 5. Unidirectional Fiber layout. .
leaving a dry rubber layer, the dipping procedure is
repeated. When the second rubber layer is also dry, we can
proceed with the winding procedure.
Given a fiber layout, a data file containing the velocities of
the two motors is created. A motor keeps the mold rotating
while the other motor moves the eye that guides the PE
fiber, coming from a spool. The fiber is kept in position on
the mold with a pressing cylinder. After the winding
procedure is completed it is appropriate to press manually
the fibers on the mold, using again some rubber solution
with low viscosity, to remove air bubbles below the fibers.
Next, the dipping step can be repeated, in order to create a
symmetrical structure of fibers between the rubber layers.
Dipping four times and using a rubber solution for
preweting the fiber, we obtain leaflets with thickness of
abut 0.2 mm, which gives a good compromise between
strength and stiffness of the leaflets. Table 1. Mechanical Properties of EPDM .
When the manufacturing of the valve is completed the Sample E (MPa) SF (MPa) EB (%)
mold is put in an oven to vulcanize the rubber. A curing EPDM 1.5 7 611
time of two hours at 120 ˚C is enough to make the rubber non-
suitable for our application. The valve is then carefully reinforced
removed from the mold with the aid of soapsuds. A valve Sin-long 110 14 16
produced in this way is free in its open configuration. From Sin-tran 16 13 45
in vitro tests, it became clear that regurgitation of such a
Uni-long 93 10 10
valve is higher than biological or polyurethane valves.
Uni-tran 1.5 2.9 419
Another way to increase the cooptation area is to make the
leaflets a bit longer that stent posts. Starting from design
criteria, synthetic prosthesis with three leaflets is
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 4
If fibers other that PE are used, probably the winding mold can be then dipped and wounded as described before.
procedure should be adapted to the fiber mechanical Eventually, the mold is put in. an oven to vulcanize the
properties. For instance, if lira fibers are used, it is rubber, and then the valve can be removed from it with the
advisable to prestrain the fibers to a certain degree and then aid of soapsuds.
wind them on the mold, because of their great extensibility.
The manufacturing procedure for a stentless valve is more Starting from design criteria, synthetic valve prosthesis
complicated because the irregular shape of the mold does with three leaflets is developed. The manufacturing method
not allow the use of a pressing cylinder to keep the fiber in for making a stented and stentless, fiber-reinforced,
place, during the winding procedure. The fiber must be synthetic heart valve prosthesis is presented. Fiber-
kept in place manually. Despite this difficulty with reinforcement is believed to be an important step in
manufacturing, stentless valves are believed to have reducing stress peaks in the leaflet matrix material, which
superior Hemodynamics and probably long term are believed to cause indirectly calcification and eventually
performance. valve failure. EPDM rubber was chosen as matrix material,
and continuous and chopped PE fibers were used as
b. Manufacturing of a Stentless valve reinforcement.
Manufacturing a stentless valve (Figure 5) is quite more It is possible to reinforce the material with different fiber
complicated than a stented one. Two manufacturing layouts. The unidirectional layout reinforces the material in
procedures are developed applying two different molds. the circumferential direction and it should be combined
The dipping and winding procedures, as described for the with another layout that reinforces the leaflet in the axial
stented valve, are followed. The winding procedure is direction. A possible solution is the use of chopped PE
performed to reinforce the leaflets, with the difference that fibers, which are easily added to the rubber solution and
fibers must be pressed manually on the mold, because of its applied on the mold during dipping.
irregular shape, which does not allow the use of a pressing
cylinder. The mold is then partially covered with Teflon The sinusoidal layout reinforces the material in both axial
tape and put in an oven to vulcanize the leaflets. The Teflon and circumferential direction. The optimal fiber layout, that
tape prevents the covered rubber from vulcanization gives the highest reduction of stresses, is determined by
computer simulations different leaflet shapes and
Next, the mold is removed from the oven and cooled. The geometries are possible for the stented valve. The
Teflon tape is removed together with part of the rubber. manufacturing procedure described here can be used to
The leaflets are now covered with Teflon tape. The dipping manufacture prototypes with other matrix and fiber
procedure is continued to make the aortic root with the materials, such as Polyurethane or Silicon rubber instead of
sinuses of Valsalva and a piece of the aorta, creating EPDM rubber.
continuity between aortic base, commisures and aorta, A
winding procedure is also required to reinforce this outside If fibers other than PE are used, probably the winding
structure, with a sinusoidal fiber layout. procedure should be adapted to the fiber mechanical
properties. For instance, if Lycra fibers are used, it is
The valve is put in the oven again for the vulcanization. advisable to prestrain the fibers to a certain degree and then
There after, it is removed from the mold with the help of wind them on the mold, because of their great extensibility.
soapsuds, and the Teflon tape is taken out, leaving the
leaflets free from the sinus cavities. Two problems inherent The manufacturing procedure for a stentless valve is more
to this design are: complicated because the irregular shape of the mold does
not allow the use of a pressing cylinder to keep the fiber in
• The leaflets are made in an open configuration, and
as a consequence, the regurgitation is too high;
• The attachment between leaflets and sinus cavities, place, during the winding procedure. The fiber must be
at the commisures, is too weak as no fibers run from kept in place manually. Despite this difficulty with
the leaflets into the sinuses of the valve.
These problems are solved with a new design for the
stentless mold. Mold II consists of two parts. Part I is used
to make the leaflets. They are not completely open, but in
an half closed configuration. Dipping and winding
procedure are the same as before, except that some PE fiber
ends are left free.
Part II of the mold, representing the sinus cavities and a
piece of the aorta, are dipped separately in the rubber
solution in order to create a rubber layer on the outside.
Next, it is mounted on part I and the free fiber ends can
now be pressed on part II, creating in this way a direct
connection of the leaflet fibers with the sinuses. The whole Figure 5: Stentless heart Valve .
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 5
manufacturing, stentless valves are believed to have Product liability concerns eventually lead to Ethicon's
superior Hemodynamics and probably long term decision to terminate the manufacture and sale Biomer in
performance. the late 1980s.
c. Recommendations: The Polymer Technology Group, Inc. (PTG) developed
Biospan segmented polyurethane in response to the crisis
• EPDM rubber not very tear resistant, if not created by the withdrawal of Biomer. Although designed as
reinforced by fibers, and therefore it could a direct replacement for Biomer, PTG made several
be replaced with Polyurethane or Silicon improvements to the manufacturing process of Biospan,
rubber, which also should be reinforced by including scaling up the reaction from 5 to 100 gallons,
fibers. using glass-lined reaction vessels and depth filters that
• The nylon stent should be substituted by a minimize contamination, and implementing rigorous
PE stent, to avoid creep problems during quality control and documentation of the manufacturing
fatigue tests. procedures. As a result, PTG consistently produces Biospan
• The pulse duplicator system should be batches of precise molecular structure. This consistency,
adapted to test stentless valves. It has been combined with an extensive FDA Master File, has
observed that regurgitation values for the facilitated the approval process for clinical applications of
stentless valve are rather high, but from high Biospan. In its first eight years on the market, the total
speed video recordings it seems that the number of clinical VAD and artificial heart cases utilizing
closure of the valve is complete. Analyzing Biospan, under branded and private label, has surpassed
the duration of opening and closing, it has that of Biomer by thousands of cases.
been seen that this valve stays open too
long, and this could be the reason for high For device components that require high strength,
regurgitation values. Attempts to increase flexibility, and fatigue resistance, Biospan should be
the stiffness of the sinuses and the aortic considered as a candidate biomaterial. Whereas typical
walls of the valve do not change much the urethanes lose stability with increasing soft segment
results. It is believed that the pulse concentration, Biospan SPU has excellent physical
duplicator system should be adapted to test properties at nominal 65A Shore hardness. In the absence
stentless valves. of (cobalt) corrosion products, Biospan not only resists
• The numerical model should include fluid- degradation, but actually increases in molecular weight in
structure interaction, to correctly simulate vivo in certain applications. Thus, Biospan is the most
the behavior of a heart valve. elastomeric biomaterial available today with a proven
• The prototypes have to be tested for fatigue combination of biocompatibility, biostability, and flex life
and in vitro. in many critical applications.
In addition to the proven Biospan polymer (i.e., the original
BIOSPAN MATERIAL Biomer replacement), PTG also offers experimental grades
and variations of Biospan with a variety of bulk and surface
Biospan segmented polyurethane (SPU) is the critical properties to satisfy specific requirements. For example,
biomaterial used in the majority of clinical ventricular Biospan® C has an aliphatic polycarbonate soft segment
assist devices and artificial heart cases. It is one of the that may impart additional oxidative stability to long-term
most extensively tested biomaterials on the market, backed implants, such as pacemaker leads, catheters, and stints,
by a comprehensive FDA Master File. Biospan is the most where metal oxide-induced oxidation (MIO) is a potential
elastomeric biomaterial available that simultaneously degradation mechanism. Variations of Biospan and
exhibits an impressive combination of physical and Biospan C are also available with surface properties similar
mechanical properties together with biological to silicone, fluorocarbon, polyethylene oxide, or
compatibility. hydrocarbon polymers. By incorporating PTG's proprietary
Surface-Modifying End Groups™, desirable surface
SPUs have been used as biomaterials (e.g., in heart assist properties may be obtained, including reduced coefficient
devices) since the late 1960s, when it was shown by of friction, improved abrasion resistance,
Boretos and Pierce that Lycra spandex, the SPU thromboresistance, and control of wettability. PTG has also
manufactured by DuPont (as textile fiber), has flex-fatigue developed and patented a new generation of Biospan that
resistance superior to silicone rubber. Ethicon, a Johnson incorporates silicone into the soft segment, thus delivering
and Johnson subsidiary, licensed the technology from the biocompatibility and stability of silicone to an
DuPont for medical applications. Ethicon introduced a extremely soft biomaterial with unique bulk properties.
batch-synthesized version of Lycra spandex under the
tradename Biomer SPU. For 20 years, Biomer was used to Certain Biospan materials are available unconfigured in a
fabricate a variety of experimental blood pumps, such as dimethylacetamide (DMAc) solution, suitable for
ventricular assist devices and artificial hearts, including the fabrication processes such as casting, dipping, spinning,
well-known "Jarvik Heart," implanted in Dr. Barney Clark. and spraying. Alternatively, PTG has the GMP/cleanroom
Although Biomer performed well in most of these early facilities to fabricate devices and device components from
applications, it was used in relatively few clinical cases. Biospan, according to your specifications.
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 6
CHEMISTRY OF BIOSPAN SPU Table 2. Properties of Biospan .
Biospan SPU is similar in chemistry to Dupont’s Lycra Procedure
Properties Value Units
Spandex. This series of solvent-based elastomers is based ASTM
on an aromatic polyetherurethaneurea with a soft segment
of polytetramethyleneoxide (PTMO) and a hard segment of Initial Modulus D-1708 850 psi
diphenylmethane diisocyanate and mixed diamines. It
contains an additive package consisting of an antioxidant Tensile
D-1708 6000 psi
and a copolymer of decyl methacrylate and Strength
diisopropylaminothyl methacrylate. Surface properties can
be tailored to the specifications with surface modifying end Ultimate
D-1708 850 %
groups. Properties of Biospan are listed in Table 2. Elongation
1. Applications of Biospan Hardness D-2240 70A -
Numerous medical devices and technologies have benefited Glass
from the combination of softness, excellent mechanical Transition D-3418 -65 ˚C
properties, stability, and good biocompatibility of Biospan Temperature
segmented polyurethane. Several clinical applications are
presented below where Biospan is used with continued D-570 1.5 %
a. Vascular Prostheses Average D-3593 180,000
Synthetic vascular grafts are used to replace damaged Appearance NA Translucent
vessels in the body, or to by-pass blocked arteries and -
veins. Large-diameter vascular grafts fabricated from
Biospan have been shown to retain their elastic Solution NA < 25
characteristics long after repeated immersion in hot water, Concentration %
and also exhibit better thromboresistance than materials
such as PET and e-PTFE.
Table 3. Properties of polyurethane and Stainless Steel .
b. Left Ventricular Assist Devices (LVADs)
The left ventricle accounts for 80 percent of heart Property Units Polyurethane
functions, making bypass of the left side of the heart one of
the most common methods of heart assist. Biospan is used N/A 0.40 0.27– 0.30
in this application to fabricate blood pump diaphragms
because of its excellent flexure and wear properties. A Hardness GPa 50 5 – 8.50
blood sac of a totally implantable LVAD fabricated from Young’s
Biospan was implanted for 244 days with no GPa 0.16 196
thromboembolic complications. Shear
GPa 1–2 75 – 80
c. Total Artificial Hearts (TAH) Tensile
Mpa 49.7 875
Development of a totally implantable artificial heart Compressive
remains one of the greatest challenges in biomedical GPa 50 – 70 0
engineering. Biospan is currently being used as a bladder
material in a number of different artificial heart programs, Yield stress MPa 11.9
showing a good degree of blood compatibility and physical
stability. Biospan also displays low lipid absorption, a MPa 50 59.3
distinct advantage of over similar devices manufactured
from silicone rubber. Coefficient
of thermal MPa 25 N/A
2. Processing of Biospan expansion
To prepare films or components from Biospan solution,
PTG recommends the following protocol:
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 7
1. The only materials that should ever come into
contact with Biospan solution are glass, stainless a. Do NOT use On-X Carbon heart valve if:
steel, or Teflon.
2. Heat the immediate work area to 30-35 °C. • The prosthesis has been dropped, damage, or
3. Provide HEPA-filtered air and adequate mishandled in any way;
ventilation. • The tamper evident seal is broken;
4. Dry the film or component in the temperature • The serial number tag does not match the
controlled area. The elevated temperature is container label;
required because dimethylacetamide (DMAc) is a • The expiration date has elapsed
hygroscopic solvent and will pick up moisture at
room temperature, resulting in a poor quality
part. b. Do NOT resterilize any On-X Prosthetic Heart
5. After the bulk of the solvent has evaporated (20- Valve:
60 minutes), dry the part in an oven at 60 °C (140
°F) to remove the remaining solvent. Please note • Once it is removed from its plastic container;
that if too much solvent remains when the part is • More than 3 times – resterilization of a valve
placed in the oven, bubbles may form. The oven which has passed the sterility expiration date is
time will vary depending on the dimensions of permitted, up to this limit, only if the valve has
the part. remained in the original unopened container and
6. A final water extraction may remove trace undamaged;
DMAc. Perform this water extraction at 60 °C for • With any method other than steam sterilization,
24 hours or longer, depending on sample
with the identified resterilization parameters.
ON-X PROSTHETIC HEART VALVE c. DO NOT pass a catheter, surgical instruments, or
transvenous pacing lead through the prosthesis as
The On-X Prosthetic Heart Valve is a bi leaflet mechanical this may cause valvular insufficiency, leaflet
heart valve, which consists of an orifice housing with two damage, leaflet dislodgment, and/or
leaflets. The orifice inflow area has a flared inlet designed catheter/instrument/lead entrapment.
to reduce flow turbulence, and the outflow rim consists of
leaflet guards designed to protect the leaflets while in the
closed position. The leaflets rotate around tabs located d. Handle the prosthesis with only MCRI Prosthetic
within the inner circumference of the orifice ring. In the Heart Valve Instruments, particularly during
closed position, the each leaflet forms a nominal angle of selection of the valve size, other sizers may result in
40º relative to the plane of the orifice. In the open position, improper valve selection.
the plane of each leaflet forms a nominal angle of 90º
relative to the plane of the orifice. The leaflets have a travel
arc of 50º to the closed position. e. Avoid damaging the prosthesis through the
application of excessive force to the valve orifice or
On-X Carbon is a pure unalloyed form of pyrolytic carbon. leaflet
The leaflets consist of On-X Carbon deposited on a f. Avoid contacting the carbon surfaces of the valve
graphite substrate, which is impregnated with 10 weight% with gloved fingers or any metallic or abrasive
tungsten to provide radiopacity. instruments as they may cause damage to the valve
surfaces not seen with the unaided eye that may
The sewing cuff is constructed of polytetrafluoroethylene lead to accelerated valve structural deterioration,
(PTFE) fabric mounted on the orifice using titanium leaflet escape, or serve as a nidus for thrombus
retaining and 5-0 suture material. This form of sewing cuff formation.
attachment to the orifice allows for rotation of the sewing
cuff in situ during implantation. Orientation reference Alternatives Practices and Procedures
marks are provided on the sewing ring for valve
orientation. Alternative forms of treatment other than the On-X Carbon
include medical therapy with drugs or surgical treatments
The On-X Prosthetic Heart Valve is available in aortic sizes such as annuloplasty or valvuloplasty with or without the
19, 21, 23, 25 and 27/29 mm. Valve sizes 19mm through use of implantable materials (i.e., sutures and/ or
25mm are designed for supra-annular implantation, while annuloplasty rings). When the patient requires replacement
the valve size 27/29 mm is designed for intra-annular of his/her native or previously placed prosthetic valve, the
implantation. option of choosing a mechanical or biological valve exists.
The choice of replacement valve depends upon factors that
The On-X Heart Valve is contraindicated for patients include the patient’s age, preoperative conditions, cardiac
unable to tolerate anticoagulation therapy. anatomy, and ability to tolerate anticoagulation therapy.
1. Warnings and Precaution:
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 8
Table 4. Dimensions (millimeters) of On-X Carbon .
Orifice Profile Profile
Annulus Sewing Internal
Internal Height Height
(mounting) Ring Orifice
Diameter (closed) (open)
Model Size & Diameter Diameter Area
A D S H H mm2
ONXA-19 19 Aortic 19 17.4 23.0 10.8 13.3 228
ONXA-21 21 Aortic 21 19.4 26.0 11.9 14.7 284
ONXA-23 23 Aortic 23 21.4 29.0 13.1 16.1 344
ONXA-25 25 Aortic 25 23.4 32.0 14.2 17.8 411
27-29 23.4 34.0 14.2 17.8 411
rotators are available for each size On-X valve. The
2. Magnetic Resonance imaging (MRI) instruments are reusable.
Sizers and instrument handles have metallic regions
The On-X Prosthetic Heart Valve has been shown to that are bendable. Repeated bending of these metallic
be MRI safe when tested using systems operating with regions can lead to fatigue and fracture. To avoid
shielded static magnetic field strengths of 1.5 Tesla or instrument fracture during use, the steam should be
less. Note, however, that the effects of a time-varying inspected for surface cracks are present, the sizer
magnetic field were not examined. The testing should and/or instrument handle should be discarded and
not cause significant MRI image artifacts or replaced. Leaflet probes and rotators are flexible, but
distortion- Should this occur, this phenomenon are not intented to be bent to a permanently deformed
produces no harmful effects to the patient. state.
3. Storage 5. Sizer
The On-X Prosthetic Heart Valve has been qualified The sizer is used to gauge the resulting tissue annulus
for a maximum storage life of 5 years from the date of diameter after the annulus is prepared for implant. The
manufacture. The storage life of the On-X valve is sizer has a bendable steam on each end. The sizer is
recorded on the outer package label. Appropriate cylindrical for size 19 mm through 25 mm valves and
inventory control should be maintained so that conical for size 27/29 mm valves.
prostheses with earlier expiration dates are
preferentially implanted and expiration is avoided. To 6. Profile Sizers
protect the valve, it should be stored in its outer box The aortic profile sizer models On-X aortic valve
until used. The storage environment should be clean, profile. It is used after sizing to assure fit of the aortic
cool, and dry. valve without obstruction of the coronary arteries.
Aortic profile sizer is provided for size 19 mm through
4. Accessories 25 mm aortic valves, where the valve sewing ring is
intented to remain supra-annular. The size 27/29 mm
The On-X prosthetic Heart Valve is designed to be aortic valve is an intra-annular design, thus no profile
used only with MCRI On-X instruments. The sizer is supplied for this size valve.
instruments, supplied separately, are provided in kits
which include sizers, rotators, a universal instrument 7. Instrument Handle
handle, and a universal leaflet probe. Sizers and
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 9
The instrument handle facilitates holding the valve or
the rotator during surgery. The instrument handle is Table 5. Mechanical Properties On-X Carbon 21].
comprised of a grip, a bendable stem, and tip. The
instrument handle tip is inserted into the valve holder Property Units Value
while the valve is still in the package inner container.
The tip is inserted into the valve holder by placing it 1. Critical surface
directly into the slot on top of the valve holder. It Tension
snaps into place after the application of a light 2. Surface
insertion force. Upon snapping into position, the valve Roughness
and holder are firmly retained by the instrument 3. Surface
handle. Removal of the valve from the inner container Chemistry, Carbon % -85
is performed after the valve holder is snipped onto the (Atomic)
instrument handle. 4. Surface
8. Rotator 5. Surface
The valve rotator is used for reorienting an in situ % -15
valve and may be used to verify leaflet mobility. The <
rotator consists of a plastic head with a centrally 6. Wear Resistance mm³/km
located leaflet mobility probe and an attached handle. 7. Coefficient of
The rotator is properly oriented for insertation into the - 0.15
valve when the cross-bar on the head is aligned with
the leaflet pivot axis and the probe is inserted into the 8. Young’s modulus GPa 26
central orifice between the leaflets.
9. Flexural Strength MPa 490
The rotator may be used with or without the
instrument handle attached. To attach the rotator to the 10. Density gm/cm3 1.9
instrument handle, insert the instrument handle tip
directly into the slot on the end of the rotator handle. 11. Strain to failure % 1.6
The rotator snaps into place after the application of a MPa-
light insertion force. 12. Strain energy 7.7
9. Leaflet Probe 13. Residual stress MPa 18.2
The leaflet probe is a flexible rod with tapered ends.
The leaflet probe may be used to gently move the
leaflets to verify that they open and close freely. Table 6. Biocompatibility Test and Results .
Accessory Cleaning and Sterilization: Result
Instruments for implantation of the On-X Prosthetic
Cytotoxicity L-929 Non-Cytotoxicity
Heart Valve are supplied separately, NON-STERILE,
and must be cleaned and sterilized prior to use.
Standard hospital surgical instrument cleaning Sensitization ISO 0% sensitization:
procedures must be used. Note: the metallic Kligman Grade 1
instruments are made of titanium or stainless steel. sensitization rate,
The plastic instruments are made of not significant
polyphenylsulfone, polysulfone, polyetherimide, Irritation Saline CSO Negligible irritant
polytetraflueroethylene, polyetheretherketone, or
silicone. Materials used in these instruments can
Acute Systemic Toxicity Negative
withstand standard steam and flash steam sterilization.
Rabbit Pyrogen Non- Pyrogenic
USP Physical / Chemical Passes USP
Screening Tests Standards
Mutagenicity Ames Non-mutagenic
Hemolysis Direct Non-Hemolytic
Contact Rabbit Blood
Complement Activation Non-Activating
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 10
ALUMINA MATERIAL improvement, especially in the treatment of children,
where the needs for refined flow characteristics,
Bioceramics fullfil a unique function as biomedical extended wear life and complete biocompatibility is
materials. The development of biomaterials and most acute. Recent work in biomechanics has resulted
manufacturing techniques has broadened the diversity in a design for a new valve prosthesis mounted in a
of applications within the human body. Bioceramics conduit so that it can be used outside the heart as part
satisfy needs as diverse as low coefficients of friction of a surgical procedure to correct gross congenital
for lubricating surfaces in joint prostheses, surfaces on anomalies in a child’s cardiovascular system -
heart valves that avoid blood clotting, materials that essentially a replumbing operation. The success of this
stimulate bone growth and those that can harness design is evidenced by the fact that an acrylic version
radioactive species for therapeutic treatments. has been adopted for the inlet and outlet valves of a
Alumina is a traditional bioinert ceramic that has been novel ventricular assist device - a temporary
used for the last thirty years. It is a highly stable oxide mechanical heart to sustain heart failure victims until a
known for its general chemical inertness and hardness. transplant becomes available. The most significant
These properties are exploited for implant purposes, feature of the conduit valve, however, is the fact that it
where it is used as an articulating surface in hip and is to be made from alumina when it is intended for
knee joints. Its ability to be polished to a high surface permanent implantation in children. Early examples of
finish makes it an ideal candidate for this wear the use of ceramics in biomedical implants were based
application, where it operates against materials such as on the fact that ceramics such as alumina are very
ultra high molecular weight Mitral Valve resistant to wear and chemical attack. The
Replacement. Orthopedic applications include: Biomechanics Group, however, also documented that
femoral head, bone screws and plates, porous coatings alumina will grow a fine covering of non-vascular
for femoral stems, porous spacers, knee prosthesis and tissue when immersed in the blood stream. This
mechanical heart valves. covering is enough to camouflage the prosthesis from
any further interaction with the blood, but fine enough
The design of mechanical heart valves has undergone (<0.1mm thick) not to interfere with the mechanical
continuous development over the last fifty years. The function of the valve. This means that alumina valves
biocompatibility of alumina has motivated its will exhibit not just excellent wear properties but also
consideration for use in prosthetic heart valves: for unequalled biocompatibility, which will obviate the
example, as a tilting disk in a ceramic mechanical need for continued anticoagulation.
valve. Because durability and reliability are vital
requirements for such biomedical use, it is critical that Enormous problems remain, however, in producing an
the mechanical properties and anisotropy of sapphire alumina conduit valve. The two principal ones which
be well documented and understood. However, will be addressed in this work are: alumina is so hard a
because the human heart beats some 40 million times material that machining is out of the question and so
per year and cyclic fatigue resistance is considered to some molding process must be developed which can
be a limiting property for many replacement cardiac produce a finished valve with the accurate internal
valve devices, McNaney, Mitamura, and Ritchie, shape required to achieve good hemodynamic
focused on the sub critical crack-growth properties of performance. And second, the tissue covering requires
sapphire. a porous, textured alumina surface on which to anchor
itself firmly, but the main body of the conduit valve
When a man-made material is placed in the human must be in the most dense form of alumina, with
body, tissue reacts to the implant in a variety of ways virtually no porosity, in order to maintain structural
depending on the material type . Therefore, the strength. The molding process must therefore
mechanism of tissue attachment (if any) depends on accommodate variable porosity in some way. Studies
the tissue response to the implant surface. In general, show that single crystal alumina has better blood
materials can be placed into three classes that compatibility and more mechanical strength than
represent the tissue response they elicit: inert, porous alumina. Although, porous alumina doesn’t
bioresorbable, and bioactive. Alumina (Al2O3) is a inhibit crack growth under fatigue, an advantage
material that is nearly chemically inert in the body and obtained by having small grain size.
exhibit minimal chemical interaction with adjacent
tissue. A fibrous tissue capsule will normally form The general approach in materials selection for
around alumina implants. Therefore, tissue attachment mechanical heart valves is to try and produce a surface
of this material can be through tissue growth into which is so smooth that blood cells will roll along
surface irregularities, by bone cement, or by press them and not become attached. Hence pyrolitic
fitting into a defect. This morphological fixation is not carbon, with its inherently dense, glassy structure and
ideal for the long-term stability of permanent implants its ability to be highly polished, is a popular choice.
and often becomes a problem. Furthermore its electrical conductivity is useful in
allowing it to become electro statically charged so that
Artificial heart valves have progressed greatly since it can repel the blood cells. Nevertheless, it is
the first few experimental surgical implants. customary to use chronic anticoagulant therapy with
Nevertheless there is still much more scope for all mechanical valves, even those constructed largely
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 11
from pyrolitic carbon, indicating that this approach is failed because of excessive fibrin deposits on the back
not necessarily the best one to pursue. It would be of the Delrin occluded flaps, but successfully
particularly beneficial to seek an alternative for the established that the fine, firmly anchored, non-
rigid conduit proposed here since the large internal vascular tissue covering was formed rapidly on the
surface area (approximately 4 500 mm²) is an order of alumina surface. Also, the reduction in drug intake
magnitude greater than the exposed surface area of a greatly improves the quality of life for a recipient.
typical conventional valve of the same diameter.
Alumina has very high wear resistance but compared
Recent success with short term artificial heart valves to metal, it has low fracture toughness and tensile
has led to much research in the development of new strength which means it can be used in compression
long life valves. A proposed design for a porous only. Even though stainless steel is a tougher material,
alumina Mitral valve has been suggested. Because of due to potential long term release of niquel and
the bioinertness and low wear rates of alumina the chrome into the body, it is restricted to temporary
material could be expected to last many years in the devices, making alumina a better choice of material
body. A second advantage of the porous ceramic is for mechanical heart valves.
that the pores will support the mechanical attachment
of live cells which will protect the blood from In conclusion alumina is a good material to use in
mechanical damage by the implant. Experiments on heart valves because of its hardness, wear resistance
valve cages bearing a sintered porous metal coating and excellent biocompatibility. Single crystal alumina
had shown that a tissue covering could rapidly be has better blood compatibility and more mechanical
formed which would prevent any further contact strength than porous alumina, making the first a better
between the blood and the underlying surface material choice. Nevertheless, pyrolitic carbon, with its
. Since this covering stabilized at a thickness of inherently dense, glassy structure and its ability to be
about 100 microns, and therefore would not interfere highly polished, is a more popular choice.
with the action of a mechanical valve, this Furthermore its electrical conductivity is useful in
phenomenon offers many attractions for any valve allowing it to become electrostatically charged so that
intended for implant in children since there would be it can repel the blood cells. Alumina is a more popular
little need to use chronic anticoagulation after the choice in hip and knee joints rather than in mechanical
recovery period. heart valves.
This experimental evidence backed up the observation
that orthopedic prostheses made from alumina rapidly
became covered in a fine tissue coating. To confirm
this interpretation of the tissue covering phenomenon,
a series of animal trials were carried out on a
prototype twin-flap Mitral valve with the body
manufactured from DERANOX 997, a high grade
alumina with purity of 99.7%. Including chopped
strands of organic flock filler with the alumina powder
induced an additional porosity of 17%. The filler was
burnt away on firing leaving a network of randomly
connected long pores, with the idea of providing even
stronger anchorage against the surface shear stresses
found in valves of that type. Several valves with
varying features were constructed and implanted, the
test animals being specially bred mini-pigs. The valves
Figure 6. Heart Valves .
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 12
Table 7. Material Properties of Alumina .
Property Condition Units 960P 975P 995P 96S ZTA
Al2O3 % 96.0 97.5 99.7 96.0 80.0
Bulk Density 20oC g/cm3 3.67 3.75 3.96 3.77 4.1
Tensile Strength 20oC Mpa 205 205 220 nd -
Flexural 20oC >MPa 375 375 410 295 450
Elastic Modulus 20oC Gpa 300 355 375 nd 340
Hardness 20oC kg/mm2 10 12 14 nd 16
Fracture 20oC Mpa*m1 4-5 4-5 4-5 nd 7
Porosity 20 C % 0 0 0 0 0
Max. working - C 1600 1650 1700 na 1500
Coef. Thermal 25-300 oC 10-6/oC 7.1 7.2 7.8 6.7 -
Table 8. Properties of Biomaterials for Mechanical Heart Valves.
Properties Units Alumina Titanium Polyurethane Pyrolitic Stainless Polymer
Poisson’s Ration N/A 0.33 0.33 0.40 0.3-0.4 0.27-0.30 0.33-0.44
Hardness GPA 20.6 2.24 50 10 5-8.5 90
Young’s GPA 392 120 0.16 17-28 196 1.84
Shear Modulus GPA 163 44 1.2 n/a 75-80 0.744-1.58
Tensile Strength MPA 637 616 49.7 200 875 48.3
Compressive GPA 4900 n/a 50-70 900 n/a 59.6
Yield Stress MPA 15.4*103 950 11.9 100 700 59.3
Ultimate Stress MPA 119 930 50 n/a 59.3 46.5
Coefficient of 10-6 6.2 11.9 25 10 n/a 70
Thermal per oC
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 13
GENERAL OBSERVATIONS been been for this materials for example electro
charging the valve so it will repel the blood from its
Synthetic valves aim to combine the advantages of walls. On the other hand biocompatibility is still a
both mechanical and biological valve prostheses, such factor if the material is not fully compatible problems
as long durability, flexible materials and natural shape, with blood flow will occur since blood clogs will start
without the disadvantages, such as anticoagulant forming in the valve the only remedy for this is
therapy. Moreover, they provide more freedom in the anticoagulants.
design. However, until now synthetic valves, mostly important points for this materials are smoothness and
made of polyurethane or silicon rubber, have biocompatibility. For example valves of alumina or
durability problems due to calcification. carbon with a long period of installation have given
problems of blood flow due to roughness of the valve
Many studies have shown a like between calcification walls causing regurgitation some techniques have used
and stresses in the tissue. It has been observed that in for this materials for example electro charging the
the areas of the leaflets where there are the highest valve so it will repel the blood from its walls. On the
tensile ad bending stresses, calcification mostly other hand biocompatibility is still a factor if the
occurs. Although the origin of this phenomenon is material is not fully compatible problems with blood
still unclear, the aim of many researchers is to reduce flow will occur since blood clogs will start forming in
the stresses in order to reduce calcification, which will the valve the only remedy for this is anticoagulants.
increase the lifetime of prosthesis.
The fibers carry the load due to pressure difference CONCLUSIONS
and transfer it to the aortic walls, for a stentless valve,
or to the stent for stented valve. The same stress- Polyurethane seems to be a material with hi potential
reducing mechanism is present in the natural valve, for this kind of applications even do a polyurethane
where collagen fibers are the load bearing structure. valve requires much more time since it requires
For carbon or alumina worries about stress are not a special designs due to its material properties. Many
trouble big focus as for polyurethane. The most people have benefited from prosthetic heart valves
important points for this material are smoothness and over the past 30 years. Chemical engineers believe
biocompatibility. For example valves of alumina or that the future of prosthetic valves lies in the regime of
carbon with a long period of installation have given tissue engineering. This would improve the
problems of blood flow due to roughness of the valve biocompatibility factor, and increase the life
walls causing regurgitation some techniques have used expectancy of the heart valve
being for this materials for example electro charging flow will occur since blood clogs will start forming in
the valve so it will repel the blood from its walls. On the valve the only remedy for this is anticoagulants.
the other hand biocompatibility is still a factor if the
material is not fully compatible problems with blood
flow will occur since blood clogs will start forming in special designs due to its material properties. Many
the valve the only remedy for this is anticoagulants. people have benefited from prosthetic heart valves
over the past 30 years. Chemical engineers believe
CONCLUSIONS that the future of prosthetic valves lies in the regime of
tissue engineering. This would improve the
Polyurethane seems to be a material with hi potential biocompatibility factor, and increase the life
for this kind of applications even do a polyurethane expectancy of the heart valve
valve requires much more time since it requires
special designs due to its material properties. Many of tissue engineering. This would improve the
people have benefited from prosthetic heart valves biocompatibility factor, and increase the life
over the past 30 years. Chemical engineers believe expectancy of the heart valve
that the future of prosthetic valves lies in the regime of
tissue engineering. This would improve the
biocompatibility factor, and increase the life
expectancy of the heart valve
alva: A maneuver elicited by bearing down for the
Vals for this materials for example electro charging purpose of decreasing venous blood return to the right
the valve so it will repel the blood from its walls. On side of the heart. The Valsalva maneuver can
the other hand biocompatibility is still a factor if the accentuate certain cardiac abnormalities (murmurs) for
material is not fully compatible problems with blood the purpose of diagnosis.
flow will occur since blood clogs will start forming in
the valve the only remedy for this is anticoagulants.
Xylene: A color
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 14
ACKNOWLEDGEMENTS 16. www.fda.gov
We thank: Dr. Megh R. Goyal at University of Puerto
Rico for his guidance; Medical Carbon Research 17. www.iom3.org
Institute (MCRI) for information on On-X Prosthetic
Heart Valve; and “Material technology at Eidnhoven 18. MA RC Analysis Research Corporation,
University of technology Po Box 513 5600 MB 1996.
Eidnhoven, The Netherlands” 19. www.mate.tue.nl
BIBLIOGRAPHY 20. www.materials.unsw.edu
1. Abrahams, M. mechanical behavior of the
tendon in vitro. Med. BioL Engng 5 (1967), 21. Medical Carbon Research Institute, LLC
433-443. P000037. 5/3/01, Journals Based on On-X
3. ATS Medical, Inc. Heart Valve 22. www.mmat.ubc
4. www.azom.com 23. www.mse.cornell.edu
5. BELLHOUSE, B. J. Velocity and pressure 24. www.polymertech.com
distribution in the aortic valve. J. fluid
Mech. 37 (1969), 587-6OO 25. ROOM, N. D. Fatigue-induced damage in
gluteraldehyde preserved heart valve tissue.
6. Bellhousb, B. J. Biological tissue in heart J. Thorac. Cardiovasc. Surg, 76 (1978), 202-
valve replacement. In The fluid mechanics 205.
of the aortic valve. Butterworth, Heinemann,
1972, pp. 23-47. 26. www.swri.edu
7. Bernacca, G. M.. Mackay, T. G., Wilkinson, GLOSSARY
R., and Wheatley. D. Polyurethane heart
valve. Biomaterials 16 (199a), 279-285. Commisures: In nematodes: Connecting bands of
8. BLACK, M. M., AND DRURY, P. J.
Mechanical and other problems of artificial Elastomers: Polymers of silicone having properties
valves. Current topics in pathology(1994), similar to those of vulcanised natural rubber, namely
127-128 the ability to be stretched to at least twice their
original length and to retract very rapidly to
9. approximately their original length when released.
10. Carton, R. W., Dainauskas, J., and Clark,
R.E. Elastic properties of single elastic Hemodynamics: "Hemodynamics is concerned with
fibres. J. Appl. Physiology 17 (1962), 547- the forces generated by the heart and the motion of
551. blood through the cardiovascular system. It is once a
body of theory and an experimental science, to which
11. University of Technology, The Netherlands, physicists and mathematicians have contributed
1997. equally with physicians and physiologists." William
R. Milnor, Preface of Hemodynamics 1982.
Hemolysis: Hematology - Disruption of the integrity
13. Deck, J.D., Thubrikar, M.J., Schneider of the red cell membrane causing release of
(1988), 7-16. hemoglobin.
14. DOSSGHE, K, Vanermen, H., AND Mitral valve: Valve with two cusps; situated between
DaeneN, W. Hemodynamic performance of the left atrium and the left ventricle
the Prima Edwards Stentless aortic
xenograft): early results of a multi-center Mutagenicity: The degree or measure of the ability to
clinical trial. Thorac, Cardiovasc.-i. Surg, cause mutation.
44 (1996), 11-14.
Pyrogen: Any substance that can cause a rise in body
15. www.facct.ntu.ac.uk/research/- temperature.
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 15
Pyrolytic carbon: Carbon that is deposited on a Xylene: A colorless flammable volatile liquid
heated graphite substrate by vapor phase hydrocarbon used as a solvent.
decomposition of gaseous hydrocarbons, usually
methane, at 1800-2300 degrees Celsius. Valsalva: A
maneuver elicited by bearing down for the purpose of
Radiopacity: opacity to X-rays or other radiation. decreasing venous blood return to the right side of the
heart. The Valsalva maneuver can accentuate certain
Regurgitation: Backward flow of blood into the heart cardiac abnormalities (murmurs) for the purpose of
or between the chambers of the heart when a valve is diagnosis.
Xylene: A colorless flammable volatile liquid
Valsalva: A maneuver elicited by bearing down for hydrocarbon used as a solvent. Valsalva: A
the purpose of decreasing venous blood return to the maneuver elicited by bearing down for the purpose of
right side of the heart. The Valsalva maneuver can decreasing venous blood return to the right side of the
accentuate certain cardiac abnormalities (murmurs) for heart. The Valsalva maneuver can accentuate certain
the purpose of diagnosis. cardiac abnormalities (murmurs) for the purpose of
Xylene: A colorless flammable volatile liquid
hydrocarbon used as a solvent. Xylene: A colorless flammable volatile liquid
hydrocarbon used as a solvent.
maneuver elicited by bearing down for the purpose of
decreasing venous blood return to the right side of the
heart. The Valsalva maneuver can accentuate certain
cardiac abnormalities (murmurs) for the purpose of Valsalva: A maneuver
diagnosis. elicited by bearing down for the purpose of decreasing
venous blood return to the right side of the heart. The
Valsalva maneuver can accentuate certain cardiac
Xylene: A colorless flammable volatile liquid abnormalities (murmurs) for the purpose of diagnosis.
hydrocarbon used as a solvent.
Xylene: A colorless flammable volatile liquid
Valsalva: A maneuver hydrocarbon used as a solvent.
elicited by bearing down for the purpose of decreasing
venous blood return to the right side of the heart. The
Valsalva maneuver can accentuate certain cardiac
abnormalities (murmurs) for the purpose of diagnosis.
Valsalva: A maneuver elicited by bearing down for Valsalva: A maneuver elicited by bearing down for
the purpose of decreasing venous blood return to the the purpose of decreasing venous blood return to the
right side of the heart. The Valsalva maneuver can right side of the heart. The Valsalva maneuver can
accentuate certain cardiac abnormalities (murmurs) for accentuate certain cardiac abnormalities (murmurs) for
the purpose of diagnosis. the purpose of diagnosis.
Xylene: A colorless flammable volatile liquid
hydrocarbon used as a solvent.
Valsalva: A maneuver elicited by bearing down for
the purpose of decreasing venous blood return to the
right side of the heart. The Valsalva maneuver can
accentuate certain cardiac abnormalities (murmurs) for
the purpose of diagnosis.
Xylene: A colorless flammable volatile liquid
hydrocarbon used as a solvent.
May 2004 Applications of Engineering Mechanics in Medicine, GED – University Of Puerto Rico, Mayagüez 16