Note: Descriptions are shown in the official language in which they were submitted.
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PARTIALLY COATED ELECTRODES~ MANUFACTURE AND USE
1. Field of the Invention This relates to partially coated electrosurgical
electrodes for the app' c-tion of el~ct~r~,agnetic energy to tissue of animal and human
and more particularly to the cleanability of such tips.
2. Backqround of the Disclosure Tips for electrosurgical use are subject to
high temperature at least whereat the electrosurgical arc emanates during, e. 9.fulguration or coagulation. The heat thus provided by ohmic coupling through aircauses the proteins in the bodily fluids to coagulate and adhere to the tips.
Coatings have been used to increase the ease of cleanability of the
electrosurgical tips. U. S. Patent 4,785,807 has a primer and top coating of Teflon
polymer over an etched or abraded stainless steel tip. The coating is thin and during
application of electromagnetic energy it is said that there is c~pP~citive coupling to allow
passage of power to the tissue being treated. Thus, the Teflon polymer surface should
remain largely intact and so the cleanabiiity of the tip is good.
U.S. Patent 4,492,231 discusses temperature, tip conductivity and sticking of
desiccated blood in a bipolar forceps.
U.S. Patents 4,232,676 and 4,314,559 assigned to Corning Glass Works,
disclose mechanically cutting knives or scalpel tips that have areas for electrocautery
and other areas which do not conduct high frequency power. The '676 patent has
20 bipolar electrodes on the same tip so that power passing therebetween will cauterize
bleeders thereagainst. The '559 patent is an electrically conductive coating over a glass
scalpel to which a silver brazing paste has been applied forming a surface finish having
interstices to be filled with Teflon polymer for providing non-stick properties. Alternately,
platinum is applied with a rough and Teflon polymer filled surface. Only portions of the
25 scalpel that are covered have an electrical connection between them and the tissue; the
silver or platinum conductors have numerous problems. Most importantly, these noble
metals are expensive and applied in a relative thin layer which must be mechanically
compatible with the electrosurgical blade or tip. In use the surgeon may flex the blade
during cleaning as for example, while wiping the used tip on a cleaning pad, patient
30 drape or the like. Good mechanical connection between the conductive layer and the
glass substrate is essential to prevent fracture of the coating or stil! worse flaking of the
coating into the wound. The glass substrate is not a deformable material and would
fracture under bending and therefore be unacceptable for use in surgery. In addition,
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biocompatability of the conductive layer and the tissue is critical to a commercial
product and silver is not an endorsed material for contact with a wound. No
commercially viable method of making is taught in '559. Consequently, a conductive
layer that is metallurgically, mechanically and electrically compatible and biocomp~t~hl~
5 has not been known. The platinum conductive layer in the '559 patent was found to
adhere poorly, be expensive and therefore unacceptable.
The Teflon polymer fills interstices, inclusions and the like at the surface
providing non-stick areas on the cutting, cauterizing or coagulating instrument. The
'559 patent teaches of a surface which provides areas of Teflon polymer and raw metal
10 and so recognizes the conductive nature of the tip and permits energy flow without
capacitive coupling or the need to overcome the electrical insulative properties of the
polymer coating. Specifically, interstices along the conductive layer on the substrate
of the metal tip are filled with primer and a top coat of Teflon polymer. The surface is
thus partly conductive metal and partly cleanable Teflon polymer but the problems of
15 compatibility with known conductive layer materials have hampered commercially
successful blades.
Cookware has been made with filled fluoropolymer to reinforce the relatively soft
polymer against scrapes and abrasions. In particular, fillers such as mica and other
minerals, metals, ceramics and other materials have been used for that purpose and
20 to improve the appearance of the coated cookware. There is no electrosurgical energy
conducted in cookware. No partially coated electrosurgical electrodes exist wherein
an easily cleaned electrosurgical electrode having a partial coating of fluorinated
polymer including areas of exposed and compatible metallic conductor therethrough
and uniformly distributed thereabout for providing an effective conductive and cleanable
25 electrode are known in the prior patents. It has been found that the cleanability of the
electrosurgical tips is a function of surface finish as well as the surface free energy of
the partial coating. The burning through the fully coated electrosurgical electrodes has
been a problem which is corrected by the partially coated electrode disclosed and
claimed herein. Significant reductions of adherence of coagulum to the electrosurgical
30 electrode is possible with the partially coated blade.
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SUMMARY OF THE INVENTION
A partially coated electrosurgical electrode pr~t~rably applies ele_t,u~,,aylletic
energy in either a monopolar or a bipolar circuit to and through the tissue and the
bodily fluids of an animal or human. The partially coated electrosurgical electrode may
5 have an electrically conductive electrode for connection to a source of elec~, or, ,ayl ,etic
electrosurgical energy and for l,ansl"ission of the electromagnetic ~le_~,osurgical
energy in the circuit to and through the tissue and the bodily fluids of the animal or
human. A portion of the electrically conductive electrode is most pr~f~rably a medical
grade biocompatâble metallic material as a substrate thereof. The portion can be10 located for the application of electromagnetic energy in either a monopolar or a bipolar
circuit to and through the tissue and the bodily fluids of an animal or human.
Conductive sites preferably pass electrosurgical energy located on the portion of the
medical grade biocompatable metallic material substrate. The conductive sites may
include peaks defining valleys thereby. The conductive sites are pr~e,~bly formed of
15 the medical grade biocompatable metallic material substrate or alloys thereof. A partial
coating may reside primarily in the valleys disposed for contact with the tissue and the
bodily fluids of the animal or human during electrosurgical application of the partially
coated electrosurgical electrode. The partial coating could have a low surface free
energy. A treated surface is preferably substantially across the peaks and generally
20 over the filled valleys of the partially coated electrically conductive electrode. The
treated surface might be relatively smooth for non stick mechanical characteristics
during application of electrosurgical effects to tissue and bodily fluids. Openings are
most preferably in the treated surface through the partial coating. The openings formed
in the treated surface might be substantially at the peaks of conductive sites thereby
25 exposing the medical grade biocornr~t~lE metallic material or alloys thereof. The
openings are most preferably located primarily about and among the valleys filled with
the partial coating so that the smooth treated surface formed of the openings and the
filled valleys permits the direct passage of electromagnetic electrosurgical energy by
conduction of electrons through the circuit between the openings therein and the tissue
30 and the bodily fluids. It is preferred that the filled valleys can provide the partial
coating having an easily cleaned low surface free energy. The partial coating is
preferably a fluorinated polymer rnaking direct passage of electrosurgical energy
impossible without a breakdown of the dielectric properties of the fluorinated polymer.
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The fluorinated polymer may be conductive. The conductive sites are in the preferred
embodiment carried on the substrate and electrical couple to l,~nsl"il electrosurgical
energy. The treated surface can be reduced to a relatively even level that is not flat
whereon the openings and the filled valleys of partial coating form a generally
5 undulating surface for reducing mechanical coupling of co~g~ n for lowering the
surface free energy thereacross while increasing the size of the openings relative to the
peaks. The openings are p,~er,ed to be in the range of about three to 20 percent of
the area of the portion of the electrically conductive electrode having a medical grade
biocompatable metallic material as a substrate thereof. The treated surface might have
10 peaks reduced to nearly the level of the filled valleys.
The medical grade biocompatable metallic~ material substrate may be
substantially an alloy of stainless steel. The medical grade biocompatable metallic
material substrate could be primarily an iron nickel chrome alloy. The conductive sites
might be formed as a plasma deposition of the conductive material as the substrate.
15 A mechanically deformed surface finish on the medical grade biocornr~t~hle metallic
material electrically conductive electrode substrate could be used to produce the peaks
and valleys of the conductive sites. A vapor deposition of the medical grade
biocompatable metal can form the conductive sites on the medical grade
biocompatable metallic material electrically conductive electrode substrate as the peaks.
20 The partial coating might include a solid lubricant compounded to the fluorinated
polymer. The partial coating need only be a low surface energy polymer. The medical
grade biocompatable metallic material conductive sites might have a high nickel content
at the openings.
A method of manufacturing a partially coated electrosurgical electrode for the
25 application of electromagnetic energy in either a monopolar or a bipolar circuit through
the tissue and the bodily fluids of an animal or human can include steps. Preparing an
electrically conductive electrode of a medical grade biocompatable metallic material
substrate for connection to a source of electromagnetic electrosurgical energy at one
erld thereof and for transmission of the electromagnetic electrosurgical energy in the
30 circuit from another end thereof to and through the tissue and the bodily fluids of the
animal or human may be a step. Making the electrically conductive electrode about its
one end with an electrically conductive material for the conductive sites which are the
conductive material preferably the same medical grade biocompatable metal of the
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WO 96/20652 PCT/l~JI*_~74
substrate, the making of the electrically conductive electrode to have peaks in the range
of about 1 to 50 microns in height above the valleys for forming conductive sites for
passing electrosurgical energy through the openings at the peaks and located on the
one end of the electrically conductive electrode can be another step. Applying a partial
5 coating for residing primarily in the valleys disposed for contact with the tissue and the
bodily fluids of the animal or human during electrosurgical applic~tion of the partially
coatêd electrosurgical electrode could be a further step. Applying the partial coating
to a thickness in the range of about 5 to 100 microns might be another step.
The step of making may be performed by coining the one end. The step of
10 making could be performed by burnishing the one end. The step of making can be
performed by stamping the one end. The step of making might be performed by
embossing the one end. The step of making can be performed by threading the one
end. The step of making may preferably be performed by etching the one end. The
step of making is in a preferred method performed by knurling the one end. The step
15 of making could be performed by shot peening the one end. The step of making might
be performed by wire brushing the one end. The step of making can be performed by
grit blasting the one end. The step of making may preferably be performed by thermal
spraying the one end with a conductive material. The step of making can preferably
be performed by plasma spraying the one end with conductive powder material. The20 step of making is in another method performed by electric arc spraying the one end
with conductive wire material. The step of making may be performed by high velocity
oxygen fuel (HVOF) combustion spraying the one end with a conductive material.
Treating a surface substantially across the peaks and generally over the filled
vaileys of the partially coated electrically conductive electrode can be used as a step
25 for generating relatively smooth non stick surface of a relatively uniform level so that the
height of the partial coating and the peaks are reduced. Forming openings in thetreated surface through the partial coating at the peaks for exposing the electrically
conductive material might be another step. Locating the openings primarily among the
valleys filled with the partial coating so that the smooth treated surface formed of the
30 openings and the filled valleys could permit the direct passage of electromagnetic
electrosurgical energy through the circuit between the openings therein and the tissue
and the bodily fluids while the filled valleys provide the partial coating having an easily
cleaned low surface free energy may be an additional step.
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The step of treating may be performed by tumbling a plurality of partially coated
electrodes with abrasive material media. The step of treating could be performed by
tumbling a plurality of the partially coated electrodes together. The step of treating
might be performed by vibrating in a container a plurality of the partially coated
6 electrode with abrasive material media. The step of treating can be performed by
vibrating in a container a plurality of the partially coated electrodes together. The step
of treating is in one method preferably performed by polishing or buffing the partially
coated electrode with abrasive material. The step of treating may be performed by
buffing the partially coated electrode with abrasive material. The step of treating could
10 be performed by abrasive belt grinding or sanding the partially coated electrode with
abrasive material. The step of treating might be performed by surface grinding the
partially coated electrode with abrasive material.
A method of manufacturing a partially coated electrosurgical electrode may have
steps including coating a portion of a strip of medical grade sheet metal with a low
15 surface energy polymer and forming electrosurgical electrodes in a progressive
stamping operation including severing through the coated portion to produce at least
a raw edge metal edge for electrosurgery. The step of coating the portion of theelectrosurgical electrode with coriductive material having peaks and valleys prior to the
step of coating the strip of medical grade sheet metal with a low surface free energy
20 polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partially coated electrosurgical electrode for the application of
electromagnetic energy in either a monopolar or a bipolar circuit shown schematically
and in perspective.
Figure 2 is a side view in cross section as taken along lines 2-2 of Figure 1 ofthe preferred embodiment of a partially coated electrosurgical electrode.
Figure 3 is a side view in cross section as taken along lines 3-3 of Figure 1 ofan alternate embodiment of a partially coated electrosurgical electrode.
Figure 4 is a schematic illustration showing the relevant part of the progression
30 for producing a partially coated electrode from a sheet metal strip that has a conductive
material and thereafter covered with a low surface free energy coating that is treated.
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DETAILED DESCRIPTION OF THE INVENTION
In Figure 1 is a partiaily coated electrosurgical electrode 10 for the ~rpO~tionof electromagnetic energy in either a monopolar or a bipolar circuit 11 and is shown
schematically in perspective and in the altemative. An electrically conductive electrode
5 12 connects to a source of electromagnetic electrosurgical energy 13 for ll~ns~..ission
of the electromagnetic electrosurgical energy to the tissue and the bodily fluids of the
animal or human, see Figure 1. The partially coated electrosurgical electrode 10applies electromagnetic energy during electrosurgery in either a monopolar or a bipolar
circuit 11 to and through the tissue and the bodily fluids of an animal or human. A
10 portion of the electrically conductive electrode 12 is a medical grade biocompatable
metallic material as a substrate 14 thereof, as in Figures 2 and 3. The preferred
material is stainless steel and alloys thereof but nickel and other highly conductive
metals have been found to work well in electrosurgical applications.
Conductive sites 15 located on the portion of the medical grade biocompatable
15 metallic material substrate 14 pass electrosurgical energy. The conductive sites 15
include peaks 16 defining valleys 17 thereby, as in Figure 2 only. Consequently, the
conductive sites 15 are formed of the medical grade biocompatable metallic material
substrate 14 or alloys thereof. A partial coating 18 is applied to reside primarily in the
valleys 17 disposed for contact with the tissue and the bodily fluids of the animal or
20 human during electrosurgical application of the partially coated electrosurgical electrode
10. The partial coating 18 has a low surface free energy to resist sticking of coagulated
tissue and bodily fluids. A treated surface 19 is substantially across the peaks 16 and
generally over the filled valleys 17 of the partially coated electrically conductive
electrode 10. The treated surface 19 is relatively smooth for non stick mechanical
25 characteristics and easy cleaning on a drape, gauze or other convenient cleaning
surface in the sterile field. That is to say that, there are no rough areas or edges on the
treated surface for tissue or bodily fluid to coagulate to or adhere at. Openings 20 are
in the treated surface 19 through the partial coating 18. In particular, the openings 20
formed in the treated surface 19 are substantially at the peaks 16 of conductive sites
30 15 thereby exposing the medical grade biocompatable metallic material or alloys
thereof. The openings 20 are located primarily about and among the valleys 17 filled
with the partial coating 18 so that the smooth treated surface 19 formed of the
openings 20 and the filled valleys 17 permits the direct passage of electromagnetic
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electrosurgical energy by conduction of electrons through the circuit 11 between the
openings 20 therein and the tissue and the bodily fluids.
It is prefe,-ed that, the filled valleys 17 provide the partial coating 18 having an
easily cleaned low surface free energy. The surface energy is prefe, c bly less than 25
5 ergs per centimeter squared with its polar less than five percent of the total surface
energy. In Figure 2, a side view in cross section as taken along lines 2-2 of Figure 1
of the preferred embodiment, the partially coated electrosurgical electrode 10 is
disclosed. Note that, in Figure 2 the cross section of the partially coated electrosurgical
electrode 10 is shown enlarged and schematically so that the concept of peaks 16 and
10 valleys 17 with the treated surface 19 forming openings 20 is readily apparent. The
partial coating 18 is a fluorinated polymer making direct passage of electrosurgical
energy impossible without a breakdown of the dielectric properties of the fluorinated
polymer. For example, Whifford, of Westchester, PA, Xylan 8820 has been found towork well. The fluorinated polymer may be made slightly conductive by the addition
15 thereto of conductive matter such as powered metal or other conductor including
carbon, molybdenum disulfide or mineral salts. Even so, the dielectric properties of the
fluoropolymer are considered an insulator as regards the flow of electrons in the circuit
11.
The conductive sites 15 are carried on the substrate 14 and electrically couple
20 therewith to transmit electrosurgical energy from the source 13 to and through the
electrode 12. The treated surface 19 can be reduced to a relatively even level that is
not entirely flat whereon the openings 20 and the filled valleys 17 of partial coating 18
form a generally undulating surface for reducing mechanical coupling of coagulum for
lowering the overall surface free energy thereacross while increasing the size of the
25 openings 20 relative to the peaks 16, as best shown in Figure 2. The openings 20 are
preferred to be in the range of about three to 20 percent of the total area of the portion
of the electrically conductive electrode 10 having the conductive sites 15 preferably of
the same medical grade biocompatable metallic material as the substrate 14. The
treated surface 19 produces peaks 16 reduced to nearly the level of the filled valleys
30 17 whereby the electrode ~12 is relatively smooth. The partial coating 18 thus produced
has a mottled appearance of the gleaming metallic openings 20 contrasting with the
coated filled valleys 17 sort of like the appearance of stars in the cloudless night sky.
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WO96/206!;2 PCT/~5~ o~74
The medical grade biocornr~t~hle metallic material substrate 14 is sub~l~r.lially
an alloy of :,lai"less steel but could be ,.ri"~arilr a nickel chrome alloy or pure nickel.
The conductive sites 15 might be formed as a plasma deposition of the same or
dirrerenl material as the substrate 14 wherein, for example, the substrate 14 is an iron
5 nickel chrome alloy. A mechanically deformed surface finish on the medical grade
biocompatable metallic material electrically conductive electrode 10 substrate 14 could
be used to produce the peaks 16 and valleys 17 of the conductive sites 15. In
particular, any pattern regular or not could be pl~ctic~lly formed into the substrate 14
to raise the peaks 16. A vapor deposition of the medical grade biocompatable metal
10 or any compatible metal or alloy can form the conductive sites 15 on the medical grade
biocompatable metallic material electrically conductive electrode 10 substrate 14 as the
peaks 16. It may be economically desirable to have a non-medically biocompatablesubstrate 14 with a biocompatable conductive material for the conductive site 15. The
preferred conductive material is Metec 4050C nickel chrome powder, from Metallurgical
15 Technologies, Inc. of Pearland, Texas.
The partial coating 18 might include a solid lubricant compounded to the
fluorinated polymer. Solid lubricants such as graphite, molybdenum disulfide, or the
like can be compounded with the polymer. The partial coating 18 need only be any low
surface energy polymer as described herein for example. The medical grade
20 biocompatable metallic material substrate 14 or the conductive material might have a
highly conductive metallic material such as an alloy with generous nickel content
surface at the openings 20.
A method of manufacturing the partially coated electrosurgical electrode 10 for
the application of electromagnetic energy in either the monopolar or a bipolar circuit
25 11 through the tissue and the bodily fluids of an animal or human includes steps.
Preparing an electrically conductive electrode 10 of a medical grade metallic conductor
for connection to the source 13 of electromagnetic electrosurgical energy at one end
21 thereof and for transmission of the electromagnetic electrosurgical energy in the
circuit 11 from another end 22 thereof to and through the tissue and the bodily fluids
30 of the animal or human is a step. Typically the electrosurgical electrode 12 is formed
in a progressive stamping operation at high speed from 302 stainless steel sheet 0.5
mm thick. The thin stainless sheet is blanked but carried on a progression 23 shown
in Figure 4 during a multiple forming operation which produces the hollow tubular end
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-10-
21 to connect with the source 13 of electrosurgical energy. The elongate paddle end
22 has thinned edges 24 as shown in Figures 1 and 3; the edges 24 are used by the
surgeon to apply the electrosurgical energy to the tissue or bodily fluids during cutting
or coagulating. Because of the openings 20, the end 22 can also be used to apply5 electrosurgical energy, if desired, and still be non stick and easy to clean. Different
wave forms of electrosurgical energy are used for cutting or coagulating and various
techniques can be applied by the surgeon to coagulate bleeding. The l,~h:j~r of
electrosurgical energy is by means of establishing the flow of electrons from the
electrosurgical electrode 12 to the patient and then to a return in the form of a pad 25
10 in Figure 1 when monopolar is used or another nearby electrode 26 when bipolar is
used. Making the electrically conductive electrode 12 about its end 22 with the
electrically conductive material coating that can be substantially the same as the
medical grade metallic conductor has been found to work particularly well because the
physical connection between the substrate 14 and the electrically conductive material
15 coating for conductive sites 15 is excellent when the metals are the same or similar.
The making of the electrically conductive electrode 12 to have peaks 16 in the range
of about 1 to 50 microns in height above the valleys 17 for forming the conductive sites
15 which pass electrosurgical energy from the one end 22 of the electrically conductive
electrode 12 can be another step. Applying the partial coating 18 for residing primarily
20 in the valleys 17 and disposed to contact tissue and the bodily fluids of the animal or
human during electrosurgical application of the partially coated electrosurgical electrode
10 could be a further step. Applying the partial coating 18 to a thickness in the
preferred range of about 5 to 100 microns is another step. Treating surfaces 19
substantially across the peaks 16 and generally over the filled valleys 17 of the partially
25 coated electrically conductive electrode 10 is used as a step for generating the relatively
smooth non stick surface of a appropriately uniform level. The level does not have to
be dead smooth or flat and so the execution is within the typical level of ordinary high
speed manufacturing processes which usually leave the finished appearance under
magnification with scratches, abrasions and other imperfections. The average
30 roughness found to work acceptably is in the range of about under RA 180 micro
inches. Forming openings 20 in the treated surface 19 through the partial coating 18
at the peaks 16 for exposing the electrically conductive material coating at theconductive sites 15 is another step. Locating the openings 20 primarily among the
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valleys 17 filled with the partial coating 18 so that the smooth treated surface 19 formed
of the openings 20 and the filled valleys 17 permits the direct passage of
electromagnetic electrosurgical energy through the circuit 11 between the openings 20
~, therein and the tissue and the bodily fluids while the filled valleys 17 provide the partial
5 coating 18 having an easily cleaned low surface free energy is an ad-lilional step.
The step of treating the surface can be performed in many ways and several are
disclosed for example but not by way of limitation. Therefore, treating the surface can
be preferably performed by mass finishing including vibratory ~inishing the partially
coated electrode 10 with abrasive material media. The preferred material media is glass
10 or ceramic but steel or plastic can also be used. It is preferred that zirconia Z1 ceramic
media with L161 deburring compound be used for treating the surface by vibratoryfinishing. The vibratory finishing process is typically performed for a period of time
such as 15 to 90 minutes and is accomplished in a container that carries and rotates
so the plurality of electrosurgical electrodes are tossed against one another, the media
15 or the container. The step of treating could be performed by tumbling a plurality of the
partially coated electrodes together with or without the media. The surface finish on
mass finished electrodes is thus generally uniform. The step of treating is performed
by polishing or buffing the partially coated electrode 10 with abrasive material, e.g.
aluminum oxide. The polishing or buffing operation can be performed while the
20 electrodes are carried on the progression 23 during or after the stamping operations.
The step of treating is alternatively performed by buffing the partially coated electrode
10 with abrasive material before, during or after the progressive stamping operation.
The step of treating could be performed by abrasive belt grinding or sanding thepartially coated electrode 10 with abrasive material. The step of treating might be
25 performed by surface grinding the partially coated electrode with abrasive material. The
step of treating might be performed by burnishing using rollers or through a die.
Similarly, the step of making the peaks 16 and valleys 17 can be accomplished
is a variety of ways and the possibilities herein are but a few examples presented to
disclose the sort of method steps potentially available. The step of making can be
30 performed by stamping the one end 22. The step of making may be performed by
coining the one end 22. The step of making could be performed by burnishing the one
end 22. The step of making might be performed by embossing the one end 22. The
step of making can be performed by threading the one end 22. The step of making
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-12-
may be performed by knurling the one end 22. The step of making is performed by
etching the one end 22. The step of making could be performed by shot peening the
one end 22. The step of making might be performed by wire brushing the one end 22.
The step of making can be performed by grit blasting the one end 22. The step of5 making can be performed by high velocity oxygen fuel spraying the one end 22 with
powder, e.g. any metallic or conductive material can be used. The step of making is
in another method performed by electric arc spraying the one end 22 with a conductive
wire material. The step of making may be performed by high velocity oxygen fuel
spraying the one end 22 with a conductive material. The preferred step of making is
10 performed by plasma spraying the one end 22 with a conductive material.
A method of manufacturing the partially coated electrosurgical electrode 10 has
steps including coating a portion 27 of a strip 28 of medical grade sheet metal with a
low surface energy polymer and forming electrosurgical electrodes 12 in a progressive
stamping operation including severing through the coated portion 27 to produce at
15 least a raw conductive edge 29 for electrosurgery, see for example Figures 3 and 4.
Figure 3 is an enlarged cross section taken transversely to the longer dimension of the
electrosurgical electrode 12. The step of coating the portion 27 of the electrosurgical
electrode 12 with conductive material having peaks and valleys prior to the step of
coating the portion 27, although this is not specifically shown. In Figure 3 the concept
20 is exactly that described for Figure 2. The step of making can be by plasma
deposition.
