U.S. patent application number 10/226616 was filed with the patent office on 2003-03-13 for method of producing textured surfaces on medical implants.
Invention is credited to Robinson, Mark L., Staab, Michael L..
Application Number | 20030047253 10/226616 |
Document ID | / |
Family ID | 23223640 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047253 |
Kind Code |
A1 |
Robinson, Mark L. ; et
al. |
March 13, 2003 |
Method of producing textured surfaces on medical implants
Abstract
Methods of texturizing medical implants are provided which
involve embossing the surface of these implants to create a
textured pattern. Preferred roll embossing techniques are disclosed
for improving scratch resistant properties, minimizing glare,
improving lubricant retention and/or creating random or uniform
patterns on medical implants, such as the outer shield of
pacemakers and defibrillators, as well as orthopedic implants.
Inventors: |
Robinson, Mark L.; (West
Lawn, PA) ; Staab, Michael L.; (Lititz, PA) |
Correspondence
Address: |
DUANE MORRIS, LLP
ATTN: WILLIAM H. MURRAY
ONE LIBERTY PLACE
1650 MARKET STREET
PHILADELPHIA
PA
19103-7396
US
|
Family ID: |
23223640 |
Appl. No.: |
10/226616 |
Filed: |
August 23, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60315271 |
Aug 28, 2001 |
|
|
|
Current U.S.
Class: |
148/516 |
Current CPC
Class: |
A61B 17/80 20130101;
A61N 1/365 20130101; B23P 15/00 20130101; B21H 8/005 20130101; A61N
1/375 20130101; A61F 2310/00023 20130101; A61F 2310/00071 20130101;
A61F 2/3094 20130101; A61F 2310/00017 20130101; A61F 2/82 20130101;
A61F 2/30771 20130101; A61B 17/86 20130101; A61N 1/37512 20170801;
A61B 17/866 20130101 |
Class at
Publication: |
148/516 |
International
Class: |
C22F 001/00 |
Claims
What is claimed:
1. A method of manufacturing an outer shield of a medical implant
comprising: (a) providing a sheet metal substrate having first and
second planar surfaces thereon; (b) embossing said sheet metal
substrate to provide an embossed textured pattern on said first
planar surface; and (c) forming the embossed sheet metal substrate
into an outer shield of said medical implant, said outer shield
having an inside and outside surface, whereby said embossed
textured pattern is located at least on said outside surface for
helping to conceal small surface defects thereon.
2. The method of claim 1 wherein said sheet metal substrate
comprises a metal selected from the group containing titanium,
nickle, and alloys thereof, and stainless steel.
3. The method of claim 1 wherein said sheet metal substrate
comprises cold rolled titanium or titanium alloy coil.
4. The method of claim 3 wherein said titanium or titanium alloy
coil is provided in a thickness of about 0.005-0.04 inches.
5. The method of claim 1 wherein said textured pattern comprises a
leather grain, wood grain, stucco grain or a combination
thereof.
6. The method of claim 1 wherein said textured pattern comprises a
non-directional, non-reflective surface texture.
7. A method of manufacturing an outer shield of a medical implant
comprising: (a) providing a sheet metal substrate having first and
second planar surfaces thereon; (b) embossing said sheet metal
substrate to provide a textured pattern on said first surface; (c)
cleaning said sheet metal substrate with an alkaline solution; (d)
annealing said sheet metal substrate at an elevated temperature;
and (e) forming the embossed sheet metal substrate into an outer
shield of a medical implant having an inside and outside surface,
whereby said textured pattern is located on at least said outside
surface for helping to conceal small surface defects thereon.
8. The method of claim 7 further comprising pickling said sheet
metal substrate.
9. The method of claim 7 whereby said sheet metal substrate is slit
to final width prior to said forming step (e).
10. A method of manufacturing an outer shield of a medical implant
comprising: (a) providing a sheet metal substrate having first and
second planar surfaces thereon; (b) cleaning said sheet metal
substrate with an alkaline solution; (c) annealing said cleaned
sheet metal substrate at an elevated temperature; (d) embossing
said cleaned and annealed sheet metal substrate to provide an
embossed surface thereon having a textured pattern; and (e) forming
the embossed sheet metal substrate into an outer shield which
exposes said textured pattern to help conceal small surface defects
thereon.
11. The method of claim 10 wherein said sheet metal comprises
titanium or titanium alloy having a thickness of about 0.005-0.04
inches.
12. The method of claim 10 wherein said annealing step (c) achieves
a temperature of about 1400-1800.degree. F.
13. The method of claim 12 wherein said annealing step (c) is
followed by a water quench or air cool.
14. The method of claim 10 wherein said medical implant comprises a
cardiac pacemaker or defibrillator.
15. An outer shield for a medical implant comprising a sheet metal
substrate having first and second surfaces thereon; said first
surface including an embossed, textured pattern having a
non-reflective appearance for helping to conceal small surface
defects on said implant.
16. The outer shield of claim 15 wherein said medical implant
comprises a pacemaker or defibrillator;
17. The outer shield of claim 15 wherein said sheet metal substrate
comprises stainless steel, or nickel, titanium, or alloys
thereof.
18. The outer shield of claim 15 having a thickness of less than
about {fraction (3/16)} inches (4.76 mm).
19. A medical implant comprising the outer shield of claim 15.
20. A method of manufacturing an outer shield of a medical implant
comprising: (a) providing a sheet metal substrate comprising
titanium having first and second planar surfaces thereon; (b)
cleaning said sheet metal substrate in an alkaline solution; (c)
annealing said sheet metal substrate at an elevated temperature;
(d) embossing said sheet metal substrate to provide an embossed
textured pattern thereon; said embossing step being provided either
before said alkaline cleaning step or thereafter; and (e) forming
the embossed sheet metal substrate into an outer shield having an
inside and outside surface whereby said textured pattern is located
on at least said outside surface for helping to conceal small
surface defects thereon.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method of embossing strip
material used for medical implants, and more particularly, to
methods of producing textured surfaces on implant quality titanium
strip.
BACKGROUND OF THE INVENTION
[0002] Medical implant applications, such as implantable
pacemakers, defibrillators, drug infusion pumping devices, and
orthopedic implants, are commonly made from, or housed within,
corrosion-resistant metal, such as titanium, titanium alloys,
nickel alloys or stainless steel.
[0003] Medical implants have often been finished by a variety of
techniques, including hand polishing, media blasting, and
electrolytic and chemical polishing. It is difficult to effectively
polish all surfaces of medical implants, since they often have
small features and intricately curved surfaces. Additionally,
mechanical and electrolytic polishing can produce a surface finish
that is bright and light reflective. Such a surface can sometimes
lead to glare under the bright light of a surgical procedure, and
reveal scratches and blemishes which are, at a minimum,
aesthetically undesirable, and which can sometimes lead to a part's
rejection on purely cosmetic grounds.
[0004] Matte or "scratch resistant" surfaces have been produced by
chemical polishing and media blasting techniques. Such surfaces are
in demand, since they are less light-reflective and conceal
scratches and blemishes, rather than literally resisting them as
the term "scratch resistant" suggests.
[0005] Recent artisans have attempted to create matte surfaces on
medical implants. Baswell et al., U.S. Pat. No. 4,704,126, issued
Nov. 3, 1987, discloses a method of chemically polishing medical
implants by immersing them in a mixed acid solution to produce a
smooth, matte surface. This acid polishing technique is principally
designed to minimize tissue fixation on titanium or titanium alloy
medical implants, while preventing reflective glare from
interfering with surgical procedures. While smoothing the exterior
of medical implants offers some advantages, such surfaces do not
conceal scratches and blemishes well enough, and are not known to
retain metal working lubricants in any significant way during metal
working processes, which is a disadvantage in deep drawing metal
working operations. In addition, acid baths generate a considerable
amount of hazardous waste, and require time consuming cleaning,
washing and acid neutralization steps in the manufacture of medical
implants.
[0006] Johnson, U.S. Pat. No. 5,673,473, issued Oct. 7, 1997,
described a method of creating a scratch resistant surface on a
medical implant shield, by blasting the titanium metal strip
precursor with metallic media. The '473 patent reports that
metallic media blasting enhances scratch resistant properties,
while simultaneously improving manufacturing "throughput" without
sacrificing shield biocompatability. Despite the teachings of this
patent, metallic media blasting always presents a chance that
embedded media will unintentionally be retained on the implant
surface. Media blasting generally forms the same texture on all
surfaces of the metal strip and is a relatively slow operation to
perform. Media blasting is also incapable of controlling the nature
of the texture, such as the degree of roughness, randomness or
orientation.
[0007] Accordingly, there remains a need for providing textured
surfaces on implant quality metal strips which improves
manufacturing "throughput", produces a high quality scratch
resistant surface, and improves control over the nature of the
texture imparted onto the medical implant surface.
SUMMARY OF THE INVENTION
[0008] In a first embodiment, the present invention provides a
method of manufacturing an outer shield of a medical implant, which
includes providing a sheet metal substrate having first and second
planar surfaces thereon. The method further includes embossing the
sheet metal substrate to provide an embossed sheet metal substrate
having a textured pattern on at least the first surface, and
forming the embossed sheet metal substrate into an outer shield
exhibiting said textured pattern on at least an external facing
surface portion for helping to conceal small surface defects
thereon.
[0009] The present invention provides surface defect concealment on
medical implants, and especially outer shields of pacemakers and
defibrillators, and other implantable devices. The embossing
processes of this invention are more expedient than media blasting
or chemical polishing. For example, the embossing step of this
invention can provide a textured surface on a medical grade
titanium strip at speeds of ten to fifty times faster than media
blasting. Since no particulate media is used in the preferred
embossing steps to form the surface texture, there is virtually no
chance of embedding media or foreign objects in the surface of the
implant. While media blasting forms an identical texture on either
side of the strip, the embossing processes of this invention allow
for differing textures on different locations on the strip by
utilizing, for example, upper and lower rolls with different
engraving patterns. Additionally, while media blasting is, by its
very nature, a random process generating a random texture, the
embossing processes of this invention can generate either a random,
regular, periodic, or semi-periodic pattern on the strip, as
desired. Patterns simulating wood, tweed, leather, and stuccos, can
be engraved on titanium, titanium alloy, nickel alloy and stainless
steel metal strips, as desired. More preferably, a non-directional,
non-reflective surface texture which mimics media blasting, is
used. Finally, no hazardous waste is generated by embossing, since
no acid baths are required. The textured surfaces produced on the
metal surfaces of this invention conform merely to the engraved
tool design and the degree of pressure selected.
[0010] In further embodiments of this invention, medical implants
are provided having embossed textured patterns which retain
lubricants to minimize galling in subsequent metal forming
operations. Medical implants with textured embossed surfaces are
also provided which have different engraving patterns on their
surfaces. For example, a simulated leather grain can be produced on
the exterior of the shield, with a stucco-like pattern on the
interior of the shield, so as to readily distinguish these surfaces
during subsequent manufacturing operation. Additionally, the
embossed patterns of this invention can be designed to enhance
tissue implantation on the surface of the medical implant, when
desirable, such as in bone ingrowth applications of orthopedic
implants. Patterns can be developed which retain more or less metal
working lubricant, such as oil or detergent-based lubricants, for
deep drawing, stamping or shaping operations.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0011] The accompanying drawings illustrate preferred embodiments
of the invention, as well as other information pertinent to the
disclosure, in which:
[0012] FIG. 1: is a flow diagram of a preferred manufacturing
method for producing an outer shield of a medical implant;
[0013] FIG. 2: is a flow diagram of an alternative manufacturing
method for producing an outer shield of a medical implant;
[0014] FIG. 3: is a front perspective view of a roll embossing
machine in the process of engraving a metal strip;
[0015] FIG. 4: is a top planar view of a bottom hardened steel
engraving roll embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] This invention provides improved metal finishing techniques
for producing textured surfaces on medical implants, such as for
example, the outer shield of pacemakers and defibrillators. This
invention is also applicable to shields or cases for implantable
medication dispensing devices, or the surface of orthopedic
implants, stents, plates, orthopedic screws and any number of
medical devices used in contact with the human body. As used
herein, the following terms are defined:
[0017] "Sheet or strip metal" means a substantially planar thin
gauge metallic substrate having a thickness of less than about
{fraction (3/16)}" (4.76 mm) inches;
[0018] "Roll embossing" means a three-dimensional texturizing
process involving one or more engraved rolls.
[0019] "Embossing" means any method useful in providing a pattern
or shape to a metal sheet material, including one-sided embossing
(coining), roll forming of deep ridges (corrugation) and rotary or
roll embossing.
[0020] With reference to the figures, and in particular FIGS. 1 and
2 thereof, there is shown a pair of manufacturing sequences 100 and
200 for texturing the implant quality metal strips of this
invention. While these preferred steps can be used in a different
order, the disclosed sequence embodiments 100 and 200, provide a
favorable combination of texture and metal properties.
[0021] Sequence 100 begins with a source of strip metal, such as a
cold rolled coil of titanium, titanium alloy, nickle, nickel alloy
or stainless steel. Titanium and its alloys are often used in
corrosive environments, as in contact with body fluid, such as
blood. Titanium has a light weight, high strength-to-weight ratio,
and non-magnetic properties. Depending on the predominate phase or
phases in the microstructure, titanium alloys are categorized as
alpha, alpha-beta, and beta. This natural grouping not only
reflects basic titanium production metallurgy, but also indicates
general properties peculiar to each type. Chemically pure ("CP")
titanium and Ti-6Al-4V alloys are commonly selected for medical
implant applications, since they are extremely biocompatable
materials. While CP titanium may contain small amounts (<1 wt %)
of O.sub.2 or iron, it is an alpha alloy type having a coefficient
of thermal expansion of 5.4.times.10.sup.-6 in/in-.degree. F.,
within the range of 32-1000.degree. F., and a tensile modulus of
elasticity of about 14.9.times.10.sup.6 psi. Ti-6Al-4V is an
alpha-beta alloy type, having a coefficient of thermal expansion of
about 3.9.times.10.sup.6 in/in-.degree. F. over the same
temperature range, and a tensile modulus of elasticity of about
16.5.times.10.sup.6 psi. CP titanium has excellent corrosion
resistance and excellent ductility for maximum formability during
the drawing of medical implant shields. Ti-6Al-4V is one of the
more versatile titanium alloys, and is used in many corrosion
resistant applications. It has much greater electrical resistivity,
having a RT electrical resistivity of 171 micro-ohms-cm, whereby
the high purity titanium has a RT electrical resistivity of 56
micro-ohms-cm. Other titanium alloys that are useful for this
invention include Ti-15Mo-2.7Nb-3Al-0.2Si, beta-21S alloy, which is
an ideal candidate for orthopedic implants, due to its extremely
low hydrogen uptake efficiency levels. Like stainless steel, which
is also a candidate for this invention, titanium sheet work hardens
significantly during forming, even during media blasting and
embossing. Minimum bend-radius rules are nearly the same for both,
although spring back is greater for titanium. CP grades of heavy
titanium plate are cold formed or, for more severe shapes, warm
formed at temperatures of about 800.degree. F. Alloy grades can be
formed at temperatures as high as 1400.degree. F. in inert gas
atmospheres.
[0022] Despite their high strength, some alloys of titanium have
superplastic characteristics in the range of 1500-1700.degree. F.
The alloy used for most superplastically formed parts is the
standard Ti-6Al-4V alloy.
[0023] Selected titanium alloys useful in the methods of this
invention are disclosed below in Table I.
1TABLE I Titanium alloys properties Tensile Coef. of thermal RT
Yield Strength Modulus expansion RT Thermal Electrical Nominal
alloy (10.sup.3) Minimum of Elasticity (32-1,000.degree. F.)
conductivity resistivity composition at room temp. (10.sup.6 psi)
(10.sup.-6 in./in.-.degree. F.) (Btu-ft/h-ft.sup.2-.degree. F.)
(.mu.ohm-cm) *Ti (high 25 14.9 5.4 9.0 56 purity)(Alpha) *Ti (plus
70 15.1 5.4 9.8 60 O.sub.2,F)(Alpha) Ti-0.2Pd 40 14.9 5.4 9.5 56
(Alpha) Ti-5A1-2.5Sn 115 16.0 5.3 4.5 157 (Alpha) Ti-6A1-2Sn-
4Zr-2Mo 120 18.5 5.6 -- 199 (Alpha) Ti-6A1-4V 120 16.5 3.9 3.9 171
(Alpha-beta) .dagger.Ti-6A1- 4VEL1 120 16.5 5.6 4.2 171
(Alpha-beta) Ti-3A1-SV- 6Cr-4Zr-4Mo 160 15.0 5.4 -- -- (Beta)
Ti-15Mo-3Nb- 3A1-O.2Si 160 15.5 4.9 4.4 135 (Beta) *Also available
with 0.05% max Fe for superior corrosion resistance.
.dagger.Develops excellent fracture toughness properties with
special mill processing.
[0024] In the preferred manufacturing sequences 100 and 200, cold
rolled coil of titanium, titanium alloy, nickel, nickel-alloy or
stainless steel is provided at cold rolled coil step 10. The strip
within the coil should be pre-rolled to a thickness of about
0.005-0.040 in, preferably about 0.010-0.020 in, with a target
thickness of about 0.012 in. The strip material within the coil is
used generally, especially in the manufacture of implantable
medical device shields, due to its high strength, ductility,
fracture resistance, biocompatability and corrosion resistance.
However, if the manufacturing methods of this invention are used
with thicker substrates, such as for medical implants, the roll
embossing techniques of this invention can be provided with larger
nip spacing to enable larger materials to be texturized.
[0025] In the manufacturing sequence 100 of FIG. 1, the cold roll
strip is embossed at roll embossing step 30. While it is
anticipated that other embossing technique could be useful for
certain end-uses associated with this invention, such as
single-sided embossing (coining), for thicker substrates, roll
forming for deep ridges, for added strength, roll embossing is the
preferred technique for medical device shields. Ideally, the
embossing machine 300 shown in FIG. 3 is situated directly after an
uncoiler in the processing line and may be followed by a number of
different operations. Typically, these operations include
recoiling, slitting or cutting-to-width, slitting, roll forming,
stamping, or any combination thereof.
[0026] The preferred embossing machine 300 can either be a
stationary fixture in the metal processing line, or it can be made
movable with wheels, rails, or a crane and lifting bolt assembly.
While most machines are driven with an integral motor and drive
package, embossing can also be performed using the power of a
recoiler or other device and an unpowered pull-through embossing
stand. Horsepower requirements depend on line speed and, to a
lesser degree, material thickness, pattern, and roll size.
[0027] Located within the embossing stand of the preferred
embodiment are two engraved and mated hardened steel rolls 320 and
330, geared together to maintain top-to-bottom pattern
registration. The engraved metal embossing rolls 320 and 330 are
preferably manufactured from high quality 52100 modified steel
forgings, through hardened to 62-65 Rockwell C. While this may take
a little more time and be slightly higher in cost, it yields
dividends in increased longevity and wear. The width and diameter
of these rolls 320 and 330 depends on the strip width, material
thickness, pattern depth, and material tensile strength and
hardness.
[0028] In FIG. 4 a preferred embossing roll 330 is shown with
protuberances 340 and flat regions 335. While not presently
committed to any particular pattern, leaving flat areas in the
engraved roll can preserve the original sheet thickness in certain
areas to maintain full mechanical strength. One or both rolls 320
and 330 can be engraved with a common or different pattern.
[0029] The engraved roll journals are housed in a bearing and block
assembly (not shown). In most machines, the upper roll blocks are
stationary, while the bottom roll blocks are movable. The pressure
with which the bottom roll is raised is referred to as the tonnage
capacity. This figure also depends on the aforementioned
parameters.
[0030] Embossing machines are generally sized to give 2" of strip
clearance on each side of an engraved embossing roll. However, each
unit is custom-manufactured, so there are no standard widths. In
fact, machines less than 6" wide and more than 76" wide are
currently in operation.
[0031] The reasons for employing embossed metal for medical devices
can be divided into two distinct categories: aesthetic and
functional. Many applications serve both purposes.
[0032] Aesthetic uses of embossing are those which enhance the
appearance of a product, such as the elimination of glare. By
creating a series of small peaks and valleys on the implant's
shield, small surface defects, such as scratches and blemishes can
also be more effectively concealed.
[0033] The embossed medical implant applications of this invention
that begin as aesthetic, such as scratch concealment, could very
well end up with functional improvements. Functional applications
of embossing include those in which a performance characteristic is
enhanced, and can involve, for example, better liquid dispersion
and greater friction and static reduction, as in better
metalworking lubricant retention during drawing and other metal
forming operations. Deep textures on the outside of the shield can
also increase thermal conductivity by increasing the surface area.
Additionally, texturing the exterior can encourage tissue
attachment. Embossed patterns can also improve stiffness and
rigidity which improves the shield's toughness, stiffness and
impact strength.
[0034] One additional benefit of increased stiffness is the ability
to reduce weight and material to save on material costs. Reduction
of "oil canning", diffusion of light, and decreased manufacturing
rejects are other important side benefits.
[0035] The most popular embossed metal patterns include leather
grains, wood grains, and stuccos, although almost any pattern can
be engraved on the mated set of hardened rolls 320 and 330. In the
preferred implants of this invention, a non-directional,
non-reflective surface texture is used. Warnings, brand names,
installation directions and other instructions can also become a
part of the pattern. Creating a new pattern and engraving the rolls
are complex and highly skilled tasks. Engravers can take any idea,
prototype, or artwork and develop original tooling by methods
including electroforming, etching, punching, routing, laser, or
computer generated graphic enhancement.
[0036] Once tooling has been manufactured, a mill is produced
specific to the work roll that will be engraved. This mill
displaces an acid-resist coating on the rolls and exposes metal,
which is subsequently etched with acid and removed. The entire
process is repeated again and again until the full depth (usually
about 0.001-0.1 inch) and finish are obtained.
[0037] Thus, the pattern on the small mill is transferred to a
large hardened work roll. This hardened top roll is then mated with
and geared with a bottom roll in the embossing machine. Rolls can
be re-engraved on-site as long as the pattern fidelity of the rolls
and gear clearance and roll diameter parameters remain
adequate.
[0038] Three preferred methods for obtaining embossed metal strip
for the outer shields of this invention include:
[0039] 1. Purchase pre-embossed material from a service center,
coil coater, or custom embosser;
[0040] 2. Obtain a set of embossing rolls to be run in a
third-party's embossing machine for toll embossing applications;
and
[0041] 3. Procure an embossing machine and roll set for in-house
production.
[0042] In any of these cases, one can compare the additional cost
of outside embossing with the equipment and labor costs associated
with inside embossing.
[0043] While embossed metal is handled and formed in exactly the
same way as its flat counterpart, several conditions are important
to keep in mind.
[0044] Bending radii and die clearances must take into account the
material's actual cross-section thickness versus material thickness
only. Some deep draws or severe bends may distort, wash out, or
even split open sharp patterns and should, therefore, be avoided
(or tested on a small scale before production).
[0045] Shallower embossed patterns, preferred by this invention,
such as the leather grain family, may affect material flatness and,
therefore, need corrective leveling. This is especially true as the
product increases in width.
[0046] A matched set of embossing rolls will deflect during the
embossing process. While this deflection can be compensated for by
adding crown to the rolls, this crown is pertinent to one
particular gauge (usually the most commonly run). Embossing above
or below the target thickness may result in sheet shape and/or
pattern appearance anomalies. Again, this is more pronounced with
shallower patterns.
[0047] While materials more than 0.040 inch thick can be textured
by roll embossing techniques, the result is usually a
coined/embossed hybrid. This invention recommends staying with the
0.005-0.040 inch strip thickness range for roll embossing,
preferably about 0.010-0.020 inches, with a target thickness of
0.012 inches. Uniform in-feed tension is desirable while material
can exit with or without tension.
[0048] In the next step 15, the strip 310 is treated to an alkaline
cleaning step 15, prior to an annealing step 20. The alkaline
cleaning step 15 removes organic contaminates, such as oil, which
reside on the surface of the cold roll coil 10 from forming and
handling.
[0049] The annealing step 20 is designed to stress relieve the
sheet material prior to subsequent processing. It is typically
carried out in a vacuum or inert gas atmosphere, such as argon.
While the annealing temperature and sequence depends upon the type
of alloy used, generally for titanium alloys, a temperature of
about 1400-1800.degree. F., preferably solution treated at
1750.degree. F., followed by a water quench or air cool, is
acceptable. Titanium alloys can also be aged for up to 4-6 hours at
1000.degree. F.
[0050] In addition to the annealing step 20, a pickling step 25 is
optionally employed to remove the oxide layer formed during the
annealing step, and also to clean the substrate surface without
dissolving away the surface layer produced during the cold rolling
of the coil 10. Following pickling 25, the strip is slit to final
width at slit step 35, and is then sent to a subsequent forming
step 40 (usually an intermediate manufacturer) for final
manufacture into a medical implant shield, for example.
[0051] Sizing and fitting can also be accomplished after forming
for producing the final elements of the medical device shield
itself. Sizing and trimming affects subsequent medical device
manufacturing processes, such as machining and welding
operations.
[0052] The forming step 40 of conventional medical device shields,
such as cardiac pacemakers, for example, operates by mounting one
or more textured strips in accordance with conventional methods.
Initially, the strip is used as a blank cut from the coil or strip
of embossed titanium sheet. A drawing punch (not shown) forces the
blank holder through a cylindrical opening in a dye, such that a
half shield is formed from the flat blank. After trimming, this
half-shield is mated with another half-shield. The finished medical
device can be provided by enclosing the internal electronics and
battery cell into the shield halves. The circuitry then can be
connected to the feedthroughs. Subsequent electron beam (E B),
laser or ultrasonic welding of the shield halves together along
their edges forms a substantially hermetic closure. A molded
plastic connector block assembly containing electrical connecters
for attachment to the feedthroughs is typically installed as a
final step.
[0053] In the alternative manufacturing sequence 200, shown in FIG.
2, the roll embossing step 30 is moved further down the processing
line, after the optional pickling step 25. This provides the
additional benefit of being able to emboss the sheet metal after it
is softened by the annealing step 20, which may require less
tonnage, and may provide greater detail with less effort to print.
Since a formed shield, for example, will likely be further annealed
prior to final assembly, moving the roll embossing step 30 further
on down the manufacturing line, will not lead to a wasted annealing
step.
[0054] From the foregoing, it can be realized that this invention
provides improved methods for manufacturing medical implants having
textured surfaces, and more particularly, to outer shields of
pacemakers and defibrillators, having a scratch resistant surface
manufactured in a fraction of the time currently required by media
blasting techniques. It is further possible that roll embossing
will provide shield metal that has been strengthened by the
textured surface formed to its surface. Additionally, the roll
embossing, or other embossing, techniques of this invention can
produce designed patterns for increased metal working lubricant
retention, decreased glare, and increased thermal conductivity for
suitable end-use applications. It is conceivable that the texturing
designs of this invention can be combined with more conventional
media blasting, chemical, hand or electrolytic polishing to provide
surfaces having multiple characteristics and properties on the same
implant. Also, the embossing techniques of this invention do not
contribute to the contamination of the surface of the implant, and
can be performed directly on the metal strip, without significantly
changing its planar shape. Although various embodiments have been
illustrated, this is for the purpose of describing, but not
limiting the invention. Various modifications, which will become
apparent to one skilled in the art, are within the scope of this
invention.
* * * * *