CA2059276A1

CA2059276A1 - Porous metal surface and method of production

Info

Publication number: CA2059276A1
Application number: CA002059276A
Authority: CA
Inventors: Clifford M. Bugle; Alfred L. Donlevy
Original assignee: Individual
Current assignee: Dynamet Inc
Priority date: 1990-04-20
Filing date: 1991-04-18
Publication date: 1991-10-21
Also published as: WO1991016012A1; EP0478769A1; EP0478769A4

Abstract

A porous surface (2) is selectively formed on a workpiece such as a medical implant (8) by pulsing a laser device in a controlled manner to produce a plurality of small, spaced-apart cavities (6) of uniform or variable depth. The porous surface provides a mechanical grip with bone cement as well as a medium for bone and tissue ingrowth.

Description

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Porous Met~ Surface And Method 0f Production BAC~GRO~ND OF T~ INV~N~ON
FI~LD OF T~ ~NVENTION
The present invention relates generally to porous metal surfaces and methods .or forming such surfaces, particularly for use in medical prostheses.

- BRI~:F DE8CRIP~I!ION OF T~E PRIO~
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- It is well-known in the medical implant art to provide a porous surfaca on selected areas on a medical prosthesis to permit the bone cement, or ideally the bone itself, to penetrate the voids in the surface in order to establish and maintain a strong mechanical bond with the implant. A frequently employed technique for creating such an active implant surface area involves the selective placement of a porous coating on the i~plant device. The most commonly used porous coatings are gravity or pressure sintered spherical powders, diffusion bonded metal fi~ers and plasma sprayed powder coatings. Exemplary of such sintered metal powder coatin~s are those described in our U.S. Patent Nos. 4,612,160 and 4,854,496.
Titaniu~ and titanium alloys have experienced wide usage as ~edical implant materials, especially for medical prostheses such as orthopedic devices in the form of knee and hip joints. Diffusion bonded metal fiber coatings have been producad ~from titanium wire in the form of random porous fiber metal coatings. Likewise, in plasma sprayed coatings, it is also known to utilize either commercially pure titanium or titanium alloy powders. The desirability of producing porous surfaces on medical prosthetic devices is well-known as seen, for example, in U.S. Patent No.

3,855,638 to Pilliar, U.S. Patent No. 3,605,123 to Hahn, U.S. Patent No. 4,017,911 ~o Ka~esjian and U.S. Patent No.
3,808,606 to Tronzo.
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WO91~1601~ -2- 2 0 ~ ~ ~ 7 6 PCT/US91/02672 The various medical factors involved in bone or tissue ingrowth, including those involved in bone cement adhesion, are documented and well-known to those in the medical implant art. The medical community has also clearly indicated that control of the pore size in porous coatings is highly desirable and that dimensional control of the implant itself is absolutely necessary for satisfactory prosthetic devices. In addition, careful control of the metal chemistry and the elimination of sources of ; lO contamination are also recogni2ed to be e5sential for implanted prosthetic devices. As noted previously, it has been common practi~e to produce porous surfaces by applying .; a porous coating to the implant substrate. It has been ~ found in some instances, however, that after prolonged :. 15 periods o~ use, portions o~ the porous coating ~ay break loose from the coating ~ass, When such an event occurs, the loose porous coating material becomes a contaminant in the surrounding tissue. Naturally, such contamination is highly `- objectionable since it may require surgical intervention in order to correct the problem.
It is certainly desirable to prevent such contamination while still providing sùfficient porosity i~
the implant surface to permit proper mechanical interlocking .:.
' by cement adhesion and bone or tissue ingrowth. The present ''~J ' 25 invention solves these prior shortco~ings by providing an improved porou~ sur4ace which eliminates the opportunity for surface ~reakaway an~ subsequent tissue contamination. ~he pres~nt invention provides a process for forming a porous :~.
~ surface on or in a workpiece such as a ~edical implant, ;~ 30 having closely controlled porcsity which may be uniformly ,s, dispersed or varied in spacing and in size in pre-selected areas over the implant surface. The process of the present ,; invention ~urther provides a porous surface which is more ` economical to produce than comparable processes such as the `.t 3~ commo~ y US~ po~ 2~ ~êtaI~urgy ~in-ering _r ~if4uOi~n ~ ~onding processes of the prior art. The present invention ''! also provides a medical i~plant device having extremely close dimensional tolerances with closely controlled porous ~;I
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.~.y WV g~ O12 2 ~ . 7 6 P~TJussl/o2672 surface areas having pores or cavities of selected size and spacing. Tha present invantion provides a porous surface and process for producing same in which the size of each cavity with respect to its diameter and depth may be closely controlled in either a constant or varying pattern across the workpiece to provide consistent high quality surfaces.
In addition, the cosmetic appearance of the porous surface is enhanced.

8~MA~Y OF T~_IN~EN~IO~
Tha present invention is directed to the formation of porous surfaces, wherein a workpiece of, for example, commercially pure titanium, titanium alloy, or cobalt-chromium alloy has a plurality of cavities formed therein of a predet~rmined diameter, dçpth and spacing. The method of the present invention comprises the steps of providing a workpiece, such as a medical implant device, for example;
mounting the workpiece in ~a fixture, preferably having `: positioning means associated therewith; providing a laser in . spaced relation to said mounted workpiece: adjusting the power of the laser to provide a laser beam of a selected value whereby a cavity of pre-selected depth is drilled into the surface of the workpiece: and pulsing the laser at ` a selectcd frequency while simultaneou~ly moving one or both .. of the laser and workpiece relative to one another, whereby a plurality of spac~d-apart cavities of a pre selected size and spacing are formed in the workpiece surface. By selecting the proper focal point, laser power level and - indexing location, a surface with selected surface .. ; connected porosity charact~ristics is produced. The porosity may be produced in specific locations, with a pre-select~d size and density of cavities to provide a surface area of closely controlled dimensions particularly suitable for medical implant devices. A workpiece having a porous ~ u~ La~e p~oduced in accorda~ h ,he prO~ent i~ cn~ic~l is .i 35 also suitable for uses other than medical implants, such as, . ~or example, titanium components bo~ded by epoxy to other ~ . .

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W091/1601~ PCT/~S91~02672 .
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structural ele~ants. The porous surface provides an excellent base for obtaining a strong mechanical joint with castable epoxy materials.
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B~IEF DE8C~rION OF ~ D~I13GS
These, as well as other objects and advantages of the present invention, will become clearer when reference is made to the following description when taken with the drawings in which:
Figure 1 is ~n enlarged plan view of a porous : lO surface in accordance with the present invention;
~igure 2 is a side cross sectional view taken : along line II-II of Figure l;
Figure 3 is a side elevation view of an acetabular cup having a porous surface formed in accordance with the present invention;
; Figure 4 is a side elevation view o~ a hip prosthetic device having a pattQrn of surface porosity produced in accordance with the present invention; .
Figure 4A is an enlarged view of a portion of the i 20 porous surface taken from area 4A o~ Figure 4;
;~ Figure 5 ls an enlarged plan view of a porous .
~urface in accordance with the pres~nt inYention;
. Figure 6 is a cross-sectional side view of the surface taken along line VI-VI of Figure 5;
Figure 7 is a sche~atic perspective view of a ~ laser devi~e and workpiece positioning table and associated i~ controls useful in practicing a method of the present ::i invention:
.j $, : Figure 8 is a photomicrograph o~ a titanium alloy wor~piece showing a porous surface produced in accordance ~t~1 with the present invention at a magnification of 20 power;
-. Figure 8A is a photomicrograph of a cobalt-.. ~ chromium alloy showing a porous surface produced in .`
~cco.da.,c~ h .h~ prPsant i~ .'ic,. a~ ni~ic~tion c.
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': ;' WO 91/16012 ~. O ~ ~ 2 7 ~ PCT/~S9~,026,2 Figure g is a photomicrograph showing a cross-sectional side view of two cavities in a titanium alloy workpiece at a magnification o~ 50 power;
Figure 10 is a photomicrograph showing a cross-sectional view of a cavity formed in a titanium alloy at lOopower magnification; Figure 11 is a top side perspective view of a tibial knee tray useful in a knee implant system: and Figure 12 is a top side perspective view of a femoral Xnee component use~ul in a knee implant system.

D~5TAII.ED_D~8C~IPTI021 OF ~B IN~NTIO~I
: It will be readily understood that the present invention utilizing a laser enables the production of ~edical implant devices of very close dimensional tolerances and without potential contamination since the conventional porous surface layer i~ eliminated.. As is ~nown, the term laser is an acronym for light amplification by stimulated emission of radiation. Further description of lasers may be found in Van Nostrand's Scientific Encyclopedia, Seventh Edition, Douglas M. Considine, Editor. There are a number of materials that are capable of being utilized as lasers, however, those which most often are used for industrial processing are either of the C02 or YAG type. Of particular . usefulness in the pre ent invention is the YAG laser r 25 utilizing a neodymiu~-doped yktrium aluminum garnet material . operating a~ between about 25 to 50 watts of power~ The power level is adju~ted according to the size, depth, and . .
repetition rate utilized for drilling into the surfac~ layer . of the implant substrate being treated.
` 30 According to the process of the present invention, the workpiece, such as a medical implant or other workpiece . whose surface is to be modified, is positioned in the near fvcal point of a suitable laser system. The laser may be pul~ed, ~OL exa~.~le, 3~ rr. ~bout Q to abo~ 15 r-l~O~
per second at the desired power level to produce a cavity of . desired depth and diameter. Either the laser beam is moved ''! to another selected position and pulsed again, or the ,.. ~ ~ , .

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- WO 91~160~2 ~ 7 ~ pcr/us9l/o26?2 substrate is moved prior to the next laser pulse. Those skilled in the art will readily understand that a combination of concurrent movement of the su~strate and laser ~eam will accomplish the same end result. Indexing - 5 movement of the workpiece or laser device is either continuous OI' intermittent.
By selection of the focal point, laser power level and indexing parameters, a surface with any desira~le porosity is easily produced and replicated with consistent quality. The porous surface formed by the present invention ~`~ may be produced in specific locations on the workpiece and - with a selected density of cavities. The porosity produced ~` is easily distinguished from laser marking such as that utilized ~o mark ~etal and plastic items for identification or decorative purposes, as such marking is less than O.005"
"~ deep. In order for porosity to be useful for either bone ingrowth or adhesive bonding, the depressions are significantly over G.005~ deep, and pre~erably on the order of about 0.030~ deep.
Perhaps the greatest advantage of the present invention over prior art methods resides in the fact that the porous surface is integral with the implant base material so as to avoid the flaking contamination pro~lems present in prior coatings applied by sintering, plasma ~ 25 spraying, or by diffusion bonding technigues.
,'~3 ~: In Figures 1 and 2, a thin workpiece 2 is depicted ~; ~ in idealized fashion~ha~ing a flat upp~r surrace 4 and a~
`~ plurality o pores or cavities 6 drilled therein by means of ; : a laser:device such as that schematically shown in Figure 7.
~- 30 Of course, it is~understood that the scale of Figures 1 and .: 2 is enlarged approximately 10 time~ actual size so that the '. details of the cavities 6 can be easily seen. Utilizing a - pulsed laser bea~ with a controlled energy level, the ca~ities 6 are formed in the surface 4 of the workpiece 2 in .~ 35 ~ rc~ctitive ~nner as shc~. in .,~-e 1. T~ cal'y, thc ;~ operating condii~ions~ are selacted such that the cavities 6 .~ have a controlled depth ~a~ which is less than the thickness ~ of the workpiece 2 so as to avoid complete penetration .;, ,, ~,.

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wosl/16012 PCT/VS91/02672 _7~ 2 7 ~
thereo~. A typical overall th.ickness of the workpiece 2 may be on the order of about 1/8~. The cavity diameter nd" is likewise controlled as well as the cavity spacing nS" such that bone ingrowth and bone cem~nt adherence i5 enhanced.

E~AMP~E 1 A flat titanium workpiece of ncP~ or commercially pure titanium was prepared having a planar surface 4 as in Figures 1 and 2. The titanium substrate 2 was positioned on a moveable work table spaced from a YAG laser. The alignment of the workpiece 2 was calibrated using a red ruby ; laser alignment beam produced by the laser machine in conventional fashion. After alignin~ the laser focusing lens approximately 5~ from the titanium substrate 2, a -~ shielding or inert cover gas o~ argon was turned on and the YAG laser was activated in a pulsating mode having a frequency of approximately 11 pulses per second. The table with the C~ titanium ~ubstrate 2 mounted thereon was moved beneath the stationary pulsating laser beam and a series of cavities 6 were formed therein along a first row ~A~, Figure 1. The table and attached workpiece were moved at a ; constanl rate; the laser, whi.ch aliso was pulsed at a constant frequency, formed cavi~.ies 6 in an equally spaced manner. Rather than moving at a constant rate, the table , - and workpiece can be intermittently ~oved. After the row ~A~ of cavities 6 wa for~ed, the laser was turned off and the table returned to the starting position and indexed one ^~ cavity spacing ~s~ perpendicular to the first row ~A~ o~ the newly produced cavi~ies. At this pointl a second row ~Bn of cavities was formed. This procedure of row indexing was ~, 30 repeated for rows ~C~ through ~Hn until the desired modified '.' ar~a of surface porosity was producedO A typical diameter ~d~ ~or the cavities 6 is be~ween about 0.020~ and about ,.i - , .
;~ 0.030n, with a preferred depth ~a~ between about 0.020" and 0 ~ (33~ ahd a ~en.e~-t~-cen~Gr ca-i~t~i spa~ b2twesn ;;
about 0.025~ and 0.030~. A pre~erred range for the cavity ' spacing is greater than 1/2 a cavity diameter, but preferably less than 0.125~

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WO91/16012 2 0 ~ ~ 2 7 g PCT/US91102672 As se~n in Figures 5 and 6, the rows of cavities 22 and 24 may be formed of different depths a, a' to provide a porous sur~ace of varying yet controlled porosity across a predetermined width thereof. In this example, depth a is about 0.020~ and a' is about 0.030~.
Photomicrographs of actual porous surfaces and - individual cavities formed by the invention are depicted in Figures 8, 8A, 9 and lO. It will be readiiy observed from the photomicrographs that a typical cross-sectional cavity geometry is not completely concentric as indicated in - Figures l, 2, 5 and 6 of the drawings. Rather, the cavities are slightly skewed from the vertical axes in the direction o~ the travel dirPction of the positioning table. This slightly skewed configuration is actually beneficial in that it presents a greater opportunity ~or stronger mechanical bondiny between the ce~ent and~or bone structure and the implant than is the case with a ~mooth, concentrically `~. formed cavity ~urface. The small melted and frozen ~, protrusions at the top surface of the cavities can also be readily removed ior cosmetic purposes through a simple .` tumbli~g operation after the laser drilling step is completed. The photomicrographs of Figures 8, 9 and lO show a plurality of cavities having a diameter o~ about 0.024n, a depth of about 0. 025n l with a spacing of about 0.030" from cavity center to cavity center.

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.~. A femoral st~m of a hip prosthesis 8 constructed, ~or example, of a Titanium-6 Aluminum-4 Vanadium ELI alloy is depicted in Figure 4 having a porous surface portion lO
. 30 formed in accordance with the present invention. The pore pattern lO, as seen in Figure 4AI is triangular in plan view . configuration and was applied to selected areas to enhance . bone ingrowth on the anterior and posterior surfaces of the .~ ` implant~ e~-ire 3.: ~s s en in t~2 ~c~ual ~1 35 photomicrographs of Figures 8 and 9, and in- Figure 4A, -~ cavities 12 were formed in surface lO having a diameter of ~1 0.024n and a depth of 0.025~ with a center-to-center cavity , ~

WO91/16012 2 ~ 2 7 ~ PC~/U~9~`~026,2 spacing of 0.03~ average. The cavities 12 were formed using a co2 laser with an argon cover gas to protect the surface of the oxygen reactive titanium alloy during the laser drilling operation.
Curved or other complex surface geometries may also be utilized in the method of the invention. As seen in Figure 3, an acetabular hip cup 14 in the shape of a thin-walled hemisphere has its outer surface treated according to the present invention ~herein a porous surface 16 is formed around a selected portion thereof. A typical acetabular hip cup 14 includes spaced screw holes 18, 18' formed therein for securement of screws directly to the bone. The cup 14 possesses a thin wa}l, on the order of about 0.125~ thick, which makes laser drilling of the cavities to a controlled lS depth of about 0.030~ particularly desirable. In this ; manner, a porous surface 16 of controlled depth is formed on the outer surface of the cup 14 without drilling through the ~ -thin wall and without impairing the load bearing structural ~- integrity of the GUp. The dangex of tissue contamination potentially present in prior art porous surface coatin~
techniques is, likewise, eliminated~
Examples of other complex sur~ace geometries are shown in Figures ll and 12. A tibial knee tray 50 having a porous surface 52 formed in accordance with the invention is shown in Figure ll. A femoral knee component 60 having a poro~s surface 62 formed in accordance with the presen~
; invention is depicted in Figure 12~ The femoral knee component 60 and the tibial knee tray 50 are useful components in a kne~ implant system.

, 30 ~M~L~ 3 A substrate 20 o~ a co~alt-chromium medical implant alloy designated ASTM F-75-87 was treated in accordance with the present invention. The cobalt-chromium ~ ~''o~ o,'-2iece was~ posi~io.~Od _~ a movOable ~cr~ t~ 2 ; 35 spaced ~rom a YAG laser and rows of cavities were formed in the surface thereof. Figure 8A depicts a photomicrograph of the cobalt-chromium medical implant alloy at 20 power '~ .;
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magnification showing controlled porosity pr~duced with the YAG laser beam~ The cavities are typlcally 0.027" in diameter and 0.021~ average depth with a center-to-center spacing of about 0.030~. The ASTM type F-75-87 cobalt-chromium alloy is a cast material ~nd it is understood thatthe wrought cobalt-chromium alloy designated ASTM F-799-87 is also suitable.
A single cavity formed in a Titanium~6 Aluminum-4 Vanadium ELI alloy is depicted in the photomicrograph of . 10 Figure lO, at a lOO power ma~ni~ication. It is observed in `~ Figure lO that the laser drilling technique of the present : invention utilizing a quickly pulsed beam produces a very thin heat affected zone surrounding each cavity. The heat affected zone is shown as a white layer in the photomicrograph, with the haIance of the micro structure una~fected by the highly localized melting effectad by the pulsed laser beam. Thus, the metallurgical tructure and mechanical propertie~ of the adjacent titanium alloy material are substantially unaffected by the laser drilling tec~nique of the present invention.
One presently preferred arrangemPnt of the basic `~ equipment for practicing the methQd of the present invention is depicted in Figure 7. A conventional laser electrical control system 26 for regulating the power and pulse ~requency of ~he laser beam is operably coupled by conduits 28 to a conventional laser beam generator 30.~ The laser beam genera~or 30 is mounted on a cross ~race 3l carried by a support stand 32 to position the laser beam generator in a ., spaced loca~ion above a workpiece positioning unit 34. The laser beam generator 30 is conventional and may include a ~AG, C02, or like laser source for producing a coherent laser beam 36 use~ul for causing localized melting in metal or other materials. ~ conventional lens 37 is mounted on an arm 38 carried by the cross brace 31 for focusing the laser ~, 35 beam 3~ ~. a s~u~fac2 o~ a ~vi-~pi~c~ 40, s~!t, ~s tne medical ', implan~ a~etabular cup 14 or femoral stem 8, as previously described.

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: ,;, wos1~16012 ~ O~ PCT/USs1/02672 The workpiece positioning unit 34 includes a moveable work table 42 carrying a rotatable platen 44 which together are moveable in the three x, y and z axes and rotatable about the y and z axes, as shown in the representation of the x, y and z axes identified by : reference numeral 45 in Figure 7. In this manner, the work positioning unit 34 provides five degrees of freedom for positioning the workpiece 40 relative to the laser beam 36 whereby surfaces of any contour can be treated in accordance with the invention. Movement of the workpiece positioning ; unit 42 is controlled by a conventional numerical controlled or ~NC~ positioning system control 46 of the type commonly used in the computer controlled machine ~ool art. The positioning system control 46 is operably coupled to the workpiece positioning unit 42 by way of conduits 48.
Through appropriate programming of the positioning system control 46, the workpiece 40 is moved a proper distance and/or at a proper speed relative to the pulse rate of the laser beam 36 controlled by the laser control system 26 to . 20 provide proper spacing between the cavities formed in the workpiece 40 by the laser beam 36. Likewise, when drilling non-planar s~rfaces, a proper focal length is maintained by . vertical movement of the workpiece positioning unit effected ~ by the pre-programmed commands supplied by the positioning 7 25 system control 46 which also controls the hori~ontal -`~ indexing mo~ement of the workpiece positioning unit 34. As .. a result, high quality and consistent dimensional accuracy is acsured.
Of course, it is understood that the workpiece can remain stationary and the laser beam generator 30 can be ~-, moved to accomplish similar results. Also, while the ~i invention has been dsscribed in connection with only one ~ laser beam, it will occur to those skilled in the art that '.i multiple laser beams could be employed simultaneously to form a porous surface accordin~ to the invention.
Having described presently preferred embodiments, it is to be understood that it may be otherwise embodied within the scope of~ the appended claims.

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Claims

Having described the invention, what is claimed is:

1. A method of forming a porous surface on a workpiece comprising the steps of:
(a) providing a laser device for generating a laser beam;
(b) providing means for orienting said workpiece relative to said laser beam at a first location;
(c) activating said laser device to direct the laser beam to the workpiece to form a cavity in said workpiece at said first location;
(d) interrupting said laser beam and simultaneously moving one of said workpieces or laser devices to a second location;
(e) activating said laser device to direct the laser beam to the workpiece to form a cavity in said workpiece at said second location; and (f) pulsing said laser device to alternately activate and interrupt said laser device and indexing said workpiece in accordance with steps (c), (d) and (e) to form a plurality of spaced-apart cavities along a selected surface area.

2. The process of claim 1 wherein the workpiece is a medical implant device of a material selected from the group consisting of commercially pure titanium, alloys of titanium, and alloy of cobalt-chromium.

3. The process of claim 1 wherein the cavities formed are generally cylindrical in shape, having a diameter of between about 0.020" to about 0.030", a depth of between about 0.020" to about 0.030" and an index spacing of about 0.025" to about 0.030" as measured between respective centers of an adjacent pair of cavities.

4. The process of claim 1 including the step of selectively regulating a power output of said laser device whereby cavities of different size are selectively formed within said porous surface.

5. The process of claim 1 wherein the workpiece is a medical implant device in the form of an acetabular cup.

6. The process of claim 1 wherein the workpiece is a medical implant device in the form of a femoral stem hip prosthesis.

7. The process of claim 1 wherein the workpiece is a medical implant device in the form of a tibial component of a knee implant system.

8. The process of claim 1 wherein the workpiece is a medical implant device in the form of a femoral component of a knee implant system.

9. The process of claim 1 wherein the means for orienting the workpiece includes a workpiece positioning means moveable in at least three axes and a control means for selectively moving said workpiece positioning means relative to said laser beam.

10. The process of claim 1 including the step of moving the workpiece along a vertical axis to maintain a selected laser beam focal length when indexing in a horizontal axis along a non-planar workpiece surface.

11. The process of claim 1 wherein the laser device is one selected from the group consisting of YAG and CO2 lasers.

12. The process of claim 11 wherein said laser device is a YAG laser activated at a power level of between about 25 to about 50 watts.

13. The process of claim 1 wherein the laser device is moved relative to the workpiece to achieve movement between pulses.

14. The process of claim 1 wherein the workpiece is moved relative to the laser device to achieve movement between pulses.

15. The process of claim 1 wherein both the workpiece and the laser device are moved simultaneously to achieve movement between pulses.

16. The process of claim 1 wherein the workpiece is a medical implant made from a titanium alloy and wherein said laser device is a YAG laser and wherein a spacing, as measured between centerlines of adjacent pairs of cavities, is more than one-half a diameter of a cavity and less than about 0.125".

17. A workpiece produced in accordance with the process of claim 1.

18. The workpiece of claim 17 wherein the porous surface is adapted to be joined to an epoxy type material.

19. A process for producing a porous surface on a workpiece comprising the steps of:
(a) providing a laser device; and (b) pulsing said laser device and indexing said workpiece to form a plurality of spaced-apart cavities within said workpiece having a controlled depth less than a thickness of said workpiece.

20. The process of claim 19 wherein the workpiece is a thin-walled medical implant device in the shape of a hemispherical shell for forming an acetabular cup in a hip implant system.

21. The process of claim 20 wherein the hemispherical shell has a wall thickness of about 0.125".

22. A medical implant constructed of a base material comprising at least one porous surface area defined by a plurality of spaced-apart, cylindrically-shaped cavities formed in said base material adapted to provide a mechanical bonding surface between said implant and a surrounding environment.

23. The medical implant device of claim 22 wherein the cavities are formed in a predetermined array by a laser beam.

24. The medical implant of claim 23 wherein the base material is one selected from he group consisting of commercially pure titanium, alloys of titanium and alloys of cobalt-chromium.