Two-Sided Photoetching Process for Needle Fabrication

1. Technical Field

This disclosure relates to surgical needles, and more particularly, to a method for photoetching multiple needles simultaneously.

2. Background of Related Art

Processes for preparing quality needles from raw stock typically include the steps of straightening spooled wire stock, cutting needle blanks from raw stock, tapering or grinding points on one end of the blank, providing a bore for receiving suture thread at the other end of the blank, flat pressing a portion of the needle barrel to facilitate easier grasping by surgical instrumentation, and curving the needle blank.

Most surgical needles are typically made one at a time. However, it is increasingly difficult to maintain the precision quality of very small needles, e.g. needles used in microscopic surgery, such as ophthalmic needles. Each needle must be cut, formed and sharpened, in order to yield uniform surgical needles.

An alternative to individually fabricating surgical needles is to simultaneously form a plurality of needles from a metal base plate using a photoetching technique.

The basics of this technique are well known in the art. The first step is to coat a thin metal sheet with a light sensitive, photoresist material. This can be done by conventional methods such as dipping or spraying the metal with any commercially available photoresist. Alternatively, a dry photoresist attached to a film may be applied to the metal sheet The metal is typically repeatedly cleaned, rinsed and briefly immersed in a diluted aqueous acid, such as 10% HCl before being coated. The coating itself should be done under safe light conditions, e.g. yellow or orange light, to prevent exposing the entire sheet. The coated sheet is lightly baked for a few minutes at about 80.degree. C. in order to speed up and ensure the drying of the coat. A negative image of the product to be fabricated is placed over the coated metal and then exposed to light. A light rich in ultraviolet radiation, such as carbon-arc or mercury vapor lamps are preferred, but any ultraviolet rich fluorescent light may be used. This typically hardens the photoresist while removing the non-exposed areas of the coating. The negative image is removed, and the metal sheet is subsequently placed in an etchant solution, such as an aqueous solution of ferric chloride and HCl, where the unwanted, uncoated metal is etched away. The desired product, such as the plurality of needle blanks are left. As a final step, these are washed, dried, and stripped of any remaining photoresist.

This technique generates a plurality of surgical needle blanks attached at their respective suture attachment ends to a carrier strip. See, e.g. U.S. Pat. Nos. 4,587,202 and 4,777,096, both to Borysko. Accordingly, a need exists for a photoetching process that results in a predetermined needle cross section without a separate pressing step while also permitting collective needle manufacturing and finishing.

A photoetching process for fabricating surgical needles is disclosed in which both a top side and a bottom side of a base material is coated with a light sensitive photoresist material. A mask in the negative image of the needle blanks to be fabricated is placed over the photoresist and then exposed to light. The unexposed areas are then etched away through just over half of the thickness of the material completely etching away those areas. The negative images are such that the needle blanks remain attached to each other at a carrier strip. A layer of an etchant resistant material with an adhesive backing is attached to the bottom etched side and the etching process is repeated on the top side leaving individual finished needles attached to the adhesive backing without the carrier strip. This process allows for the generation of predetermined needle cross-sections without pressing and permits subsequent collective electropolishing of all the needles simultaneously.

Various embodiments are described herein with reference to the drawings wherein:

FIG. 1 is a top view of a series of surgical needle blanks on an adhesive backing in accordance with the present disclosure;

FIG. 2 is a flow diagram showing the overall steps of a needle fabricating method in accordance with the present disclosure;

FIGS. 3A and 3B are flow diagrams showing an illustrative example of a needle fabricating method in accordance with the present disclosure;

FIGS. 3C and 3D are a series of sectional views corresponding to the steps of FIGS. 3A and 3B respectively;

FIG. 4 is a cross-sectional view of a single needle blank after a first etching in accordance with the method of the present disclosure;

FIG. 5A is a side view of a surgical needle blank fabricated in accordance with the present disclosure prior to milling;

FIG. 5B is a top view of the surgical needle blank of FIG. 5A;

FIG. 5C is a front view of the surgical needle blank of FIG. 5A;

FIG. 6A is a side view of an illustration of electromagnetic curving the surgical needle blanks in accordance with the present disclosure; and

FIG. 6B is an end view of an illustration of electromagnetic curving the surgical needle blanks in accordance with the present disclosure.

In the drawings and in the description which follows, the term "proximal", as is traditional, will refer to the end of the structure which is closest to the user, i.e., the suture end of the needle, while the term "distal" will refer to the end of the structure which is furthest from the user, i.e. the point. As used herein the term "surgical needle blanks" refer to a piece of needle stock material at various stages of completion but not fully formed into a surgical grade needle suitable for use during surgical procedures. Needles suitable for such procedures will be referred to as "surgical needles".

Referring now to the drawings wherein like reference numerals identify similar structural or procedural elements, there is illustrated in FIG. 1 a sheet 10 of surgical needle blanks fabricated in accordance with a preferred embodiment. As will become readily apparent to those having ordinary skill in the art, surgical needle blanks are fabricated in such a manner so as to reduce the costs associated with this fabrication as compared to prior art surgical needle blanks. It will also become readily apparent that the surgical needle blanks do not require a tree or carrier strip connecting the needle blanks. The needles are fabricated by chemically etching away unwanted material from both sides of a sheet of base material, for example, metal, plastic, engineering plastics or composites, attaching an etch-resistant adhesive backing to the bottom etched side and then etching away remaining unwanted material as a chemical milling step.

Because of their symmetry, needle blanks of similar types are fabricated next to each other in order to maximize the number of needle blanks fabricated on any one sheet. Therefore, as shown in FIG. 1, slightly curved needle blanks 20 can be fabricated on the same sheet as highly curved needle blanks 40 and straight needle blanks 30. These needle blanks may vary in size, as well as in shape.

FIG. 2 shows the overall flow of the various steps making up a preferred embodiment of the present disclosure. Each step is shown in parentheses in the following example and further shown in each of the subsequent figures.

Initially, a metal sheet, preferably Sandvik 1RK91 or Carpenter 455 stainless steel, as disclosed in U.S. Pat. No. 5,411,613, is coated with a photoresist material (100), such as "KMER" or "RISTON", available from DuPont. The photoresist material is of a type which, when exposed to light and subsequently developed, becomes hard and resistant to an etching solution, but unless exposed to light, can be readily removed by washing. This coating step is done either in darkness, or in a safe-light condition, e.g. yellow or orange light, typically by dipping the metal sheet into the photoresist, but can also be sprayed or brushed on the metal sheet. This safe-light condition prevents the entire surface from being exposed and acted upon before it has been completely prepared.

A mask having a negative image of the series of needle blanks to be fabricated is positioned over the coated top surface of the material (102). A second mask having a negative image of the series of needle blanks is positioned over the bottom surface of the material (104). The image of the second mask must be properly aligned with the image of the first mask. This is done, for example, by placing identical registration holes near each of the four corners of the two negative images and the metal sheet as illustrated in FIG. 1. The negative images used for the photoresist process can be made on, for example, glass plates, increasing the amount of times they can be reused. A rod approximately equal to the diameter of the hole is placed through all three materials, thus fixing and maintaining the alignment between the top and bottom images. The surface metal sheet is then exposed to preferably an ultraviolet rich light through the negatives so that the light only acts on those areas aligned with the reproduction of the needle blanks (106).

The exposed sheet is then developed in any one of several commercially available developers, and washed to remove the light-sensitive material not acted on by the light. The sheet thus has imposed on it a positive image of the shape of the desired needles. The negative images are then removed (108).

As shown via a cross-sectional view of an individual needle blank in FIG. 4, the sheet 10 is immersed in an etchant solution (110), such as 36 to 42 degrees Celsius Baume aqueous ferric chloride, or an aqueous solution of hydrochloric acid and either ferric chloride or nitric acid, where the metal is dissolved from the areas not covered by the etchant-resistant, photo-sensitive material 120. The sheet is immersed just long enough so that approximately 50% of the thickness of metal 130 on each side is etched away. The masks are slightly larger than the desired needles in order to compensate for the subsequent loss due to the etching as shown in 140. This will form an almost squared off hexagonal shape. The additional side edges will improve the ease of penetration into the tissue and the like. The metal sheet is washed, dried and stripped of any remaining photoresist by any suitable commercial stripper.

The entire bottom surface is now coated with an etchant resistant material such as solutions from the vinyl copolymer group (112). This coating can be brushed or sprayed on so that it can readily be removed by, for example, immersing the sheet in a suitable dissolving solvent as described above. As an alternative, the coating can be applied as a thin layer having an adhesive backing. The metal sheet is now immersed in a weakened form of the etching solution for a short period of time (114). This will etch away only a fine layer of the metal, thus chemically milling the top surface of the needle blanks and removing the carrier strip from between the needles. This step leaves the needles as individuals adhered to the backing.

As shown in FIG. 5A, the second etching process removes a top layer of the material designated by the dotted line 305 in FIG. 5A. This milling cleanly sharpens the sides and tip of the needle blanks 210 as well as removes any rough edges, flairs or burrs left from the initial etching due to the masking process 200. This chemical milling process leaves the sides much smoother and straighter than the typical electropolishing bath of, for example, an aqueous sulfuric, phosphoric and glycolic acid bath. The further step of individually grinding and polishing the needles is thus eliminated.

After the final etching, the metal sheet is again washed and dried to remove any remaining etching solution. A finished set of sharpened needles on the backing is ready for use. The needles may either be removed individually from the adhesive backing or washed in a stripper as a dissolving solvent commercially available and formulated for the particular coating used to strip away the entire backing.

As FIG. 5B shows, as a further embodiment to the present disclosure, a channel or grove 220 may be etched directly into the proximal end of the needle blank to simplify attaching a suture by clamping or crimping means. This is done by including the structure of the channel or groove in one of the mask images. This eliminates the need to drill a hole or channel after the needle is formed.

In an alternate embodiment, the sides of the distal, sharpened end of the needle may be bowed out 230 in a spatula design as shown in FIG. 5B. This is in order to further ease penetration into the tissue.

In another embodiment, all the needle blanks on the sheet are etched as straight needles. These are then placed under a mandrel as illustrated in FIGS. 6A and 6B perpendicular to the mandrel's rolling surface. Typically, the needles are rolled and pressed around the mandrel using a series of belts. In one embodiment, both the sheet of needle blank and the mandrel are electromagnetically charged with opposite charges. Typically, this will be in the order of 3K-4K Gauss. The electro-magnetic attraction between the needle and mandrel will bend the needle around the mandrel without the need for direct contact. It is also contemplated that a backing sheet may be associated with the needle-containing sheet to capture and control bending of the needles. Preferably, the backing sheet is a flexible metal sheet electro-magnetically charged with the same charge as the needle-containing sheet.

FIGS. 3A through 3D represent a hypothetical example illustrating the advantages achieved by the present method. A metal sheet of Sandvik 1RK91 is cut to a specified size and thickness, and is then cleaned with a diluted solution of 10% HCL (step 200, 300). This removes any debris left from the cutting and handling of the sheet. A thin layer of a commercial photoresist is brushed onto both sides of the metal sheet (step 202, 302). The sheet is then mildly heated for a few minutes to ensure that the photoresist is dried onto the entire sheet (step 204, 304). A negative image of the top of a series of needles is placed on the top side of the sheet and a negative image of the bottom side of the series of needles is placed on the bottom side of the sheet (steps 206, 208, 306, 308). The images are slightly larger than the final configuration of the desired needles in order to compensate for any subsequent loss due to the etching and milling processes and are used as masks for areas not to be hardened by the photoresist.

The top and bottom images are aligned by way of alignment registration holes in each of the corners of the images and metal sheet (step 210, 310). Dowels are placed in each of the holes to ensure proper alignment between the top and bottom images throughout the developing stage of the process. The image encased metal sheet is subjected to a mercury vapor lamp that is high is ultraviolet light (step 212, 312).

After being exposed to the ultraviolet light, the sheet is immersed in a commercial developer, hardening those areas that were exposed to the light (step 214). Once the exposed areas have hardened, the metal sheet is washed (step 216, 314) to remove the developer and any non-hardened photoresist. The dowels are now taken out and the two negative image masks are removed (step 218, 316) from the surfaces of the metal sheet.

The metal sheet is then immersed in an aqueous solution of ferric chloride and HCL (step 220, 318) until approximately 65% of the uncoated, unprotected metal has been etched away from each side. At that point in time, the sheet is removed from the etchant solution and the solution is washed away (step 222). The needles are still attached to each other by a carrier strip at the suture end, securing the needles together. The photoresist on the non-etched areas is stripped away (step 224) by a commercial stripper appropriate for the particular photoresist used.

A thin layer of a vinyl copolymer is brushed on the bottom side of the series of needles etched from the metal sheet (step 226, 320). This coating forms an adhesive backing, further securing the needle blanks to each other. The secured needle blanks are immersed in a diluted version of the etchant solution (step 228, 322). This will have the effect of chemically milling the top side of the needle blanks, sharpening the edges and etching away the carrier strip between the needle blanks. This will leave the surgical needles individually attached to the adhesive backing. The etchant solution is washed away (step 230) stopping the etching process and leaving finished needles on the adhesive backing.

Table II shows average bend movement for commercial square bodied curved needles and square bodied curved needles photoetched in accordance with the disclosure from the preferred Sandvik 1RK91 material, with and without heat treatment. Bend movement tests were conducted in accordance with U.S. Pat. Nos. 5,022,273 and 5,297,440.

It will be understood that various modifications may be made to the embodiments disclosed herein. For example, a sheet of nylon or polyamide film can be used in the etched-metal technique described above. In this case, the photo-resist coating is, for example, by a deposition of chromium on the plastic. The etchant solution would be a solution of hydrazine hydride. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications to the disclosure within the scope and spirit of the claims appended hereto.