Non-hazardous cleaning solution and process for cleaning blackened needles

Abstract

A non-toxic cleaning solution / process has been developed to remove oxide residue from the surface of blackened needles. A low concentration citric acid solution is mixed with the blackened needles and treated briefly (less than 5 minutes) in an ultrasonic bath. The oxide residue is substantially removed. Surprisingly and unexpectedly, the penetration performance of the cleaned needles is significantly improved by up to 50% over other tested cleaning solutions.

Description

[Technical field]

[0001] The technical field to which this invention pertains is the manufacturing process for surgical needles, and more specifically, processes for the removal of metal oxide residue from surgical needles. [Background technology]

[0002] Surgical needles are typically made from conventional metals such as surgical stainless steel and other biocompatible metal alloys. It is desirable for the needle to have a smooth outer surface to facilitate passage through tissue and minimize adhesion of contaminants or foreign bodies. The needle surface is typically polished to provide a smooth surface that is bright, shiny, and reflective. Surgical needles are typically coated with a silicone coating to improve the penetration of the needle through multiple passes through tissue.

[0003] In certain types of surgical procedures, such as endoscopic and laparoscopic surgery, surgeons remotely view the surgical site via a camera and screen display of the surgical field. In such procedures, it is known that surgical teams may find it difficult to see conventional surgical needles due to their shiny, reflective surfaces. This is especially true for the distal end of the needle, which has the tissue penetration point. The inability to quickly and efficiently locate the needle and needle tip when performing laparoscopic suturing procedures has led to the development of surgical needles with blackened surfaces. Blackened needles have been proven to have better visibility in the surgical field and are often preferred in minimally invasive surgical procedures utilizing indirect visualization.

[0004] Blackening processes are known in the art for blackening the bright and shiny surface of surgical needles. Processes may include chemical baths, exposure to plasma, laser energy, oxidizing fumes, etc. The purpose of the blackening process is to form an iron oxide (Fe3O4) based layer on the surface of the stainless steel needle to provide a blackened appearance.

[0005] A problem with some blackening processes is that loose black oxide residue or particles may remain on the needle after the blackening process. Removal of the loose particles is important as it is not desirable for the particles to interfere with further coatings on the needle as this can compromise the adhesion integrity of the needle coating itself. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need in the art for new methods and processes for removing metal oxide residues from blackened surgical needles that are environmentally friendly, safe, and cost effective. [Means for solving the problem]

[0007] A non-toxic cleaning solution / process has been developed to remove oxide residues from the surface of blackened needles. A low concentration citric acid solution is mixed with the blackened needles and treated briefly (less than 5 minutes) in an ultrasonic bath. The oxide residues are substantially removed. Surprisingly and unexpectedly, the penetration performance of the cleaned needles is significantly improved by up to 50%.

[0008] One embodiment of the present invention is a method of preparing a blackened surgical needle, comprising the steps of: a. placing at least one blackened surgical needle having free black oxide particles on its surface into a bath, the bath comprising: i. an effective amount of citric acid, and ii. positioning an ultrasonic source; b. applying ultrasonic waves to the bath for a time sufficient to remove loose black oxide particles from the surface of the needle.

[0009] Another embodiment of the present invention relates to a system for treating blackened surgical needles having loose black oxide particles, comprising an ultrasonic bath and citric acid.

[0010] These and other aspects and advantages of the present invention will become more apparent from the following description. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Blackened needles Surgical needles that may be blackened and treated according to the present invention include conventional surgical needles having conventional shapes made from conventional surgical grade stainless steel alloys, including, but not limited to, type 455, type 316, type 4310, type 420, and the like. Another type of stainless steel alloy that may be blackened using the process of the present invention is the proprietary alloy "ETHALLOY" available from Ethicon, Inc. (Somerville, NJ 08876 USA). The composition of ETHALLOY alloy is described in U.S. Patent No. 5,000,912, which is incorporated herein by reference. In addition to needles, the process, baths, and systems of the present invention may also be used to blacken the surfaces of other types of medical devices made from such alloys.

[0012] Processing fixtures useful for blackening needles include conventional processing fixtures such as open tubs, tanks, mixers, and baskets. The fixtures may include tanks specially designed and adapted to receive needles on a strip when using high speed needle manufacturing processes. The fixtures will be made of conventional corrosion resistant materials such as nylon, glass, PEEK, Teflon, PVDF, etc. The fixtures may also be made of conventional metals such as aluminum and stainless steel with contact surfaces coated with conventional corrosion resistant coatings such as ceramic, PTFE, FEP, etc.

[0013] The needles may be pretreated in a bath containing an aqueous composition. These pretreatment baths will have a sufficient amount of bath ingredients to provide an effective pretreatment. The pretreatment baths will typically contain about 8% to about 20% by weight, more typically about 10% to about 18% by weight, and preferably about 15% to about 17% by weight of a water-soluble chloride salt. The pretreatment baths will also contain about 5% to about 15% by weight, more typically about 6% to about 10% by weight, and preferably about 7% to about 8% by weight of an inorganic acid. The pretreatment baths will also typically contain about 60% to about 90% by weight, more typically about 70% to about 80% by weight, and preferably about 75% to about 78% by weight of water. Water-soluble chloride salts useful in the pretreatment baths include, but are not limited to, sodium chloride, potassium chloride, lithium chloride, and the like. Inorganic acids useful in the pretreatment baths include, but are not limited to, phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, and the like. The pH of the pretreatment bath will typically be in the range of about 0.1 to about 1.2, more typically about 0.3 to about 1, and preferably about 0.5 to about 0.8.

[0014] The blackening bath composition is preferably an aqueous composition. The blackening bath will have a sufficient amount of bath ingredients to provide effective blackening of the needle surface. The blackening bath will typically contain about 18% to about 38% by weight, more typically about 20% to about 35% by weight, and preferably about 26% to about 30% by weight of a strong base. The blackening bath of the present invention will typically contain about 3% to about 20% by weight, more typically about 5% to about 15% by weight, and preferably about 11% to about 13% by weight of a highly soluble nitrate salt. The blackening bath will also typically contain about 50% to about 75% by weight, more typically about 55% to about 70% by weight, and preferably about 58% to about 65% by weight of water. Nitrates useful in the blackening bath of the present invention include, but are not limited to, sodium nitrate, potassium nitrate, lithium nitrate, and the like. Strong bases useful in the blackening bath of the present invention include, but are not limited to, sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like.

[0015] The blackening bath may contain components containing two different precursors to form transition metal sulfides. The first precursor is a transition metal salt of a strong acid. Such precursors include, but are not limited to, nickel nitrate, cobalt nitrate, nickel sulfate, cobalt sulfate, iron nitrate, copper perchlorate, nickel perchlorate, perchlorate ions, cobalt perchlorate, and the like. The second precursor is a sulfur-containing reducing agent. Such second precursors include, but are not limited to, N,N'-diethylthiourea, sodium thiocyanate, sodium sulfide, sodium dimethyldithiocarbamate, and the like. Transition metal sulfide compounds formed may include, but are not limited to, NiS, CoS, Ag2S, and the like. The amount of transition metal salt of a strong acid included in this embodiment of the blackening bath of the present invention is typically about 0.1% by weight to about 3% by weight, more typically about 0.2% by weight to about 2% by weight, and preferably about 0.3% by weight to about 1% by weight. The amount of sulfur-containing reducing agent included in this embodiment of the blackening bath of the present invention is typically from about 0.1% to about 3% by weight, more typically from about 0.2% to about 2% by weight, and preferably from about 0.3% to about 1% by weight.

[0016] In an alternative embodiment, the blackening bath may also contain a manganese-containing oxidizer, also referred to as highly soluble permanganate, including but not limited to potassium permanganate, sodium permanganate, and lithium permanganate. The bath of the second embodiment will also contain a thiocyanate. Thiocyanates useful in this embodiment of the blackening bath include but are not limited to sodium thiocyanate, potassium thiocyanate, lithium thiocyanate, and the like. The amount of manganese-containing oxidizer (highly soluble permanganate) in this second embodiment of the blackening bath of the invention is typically about 0.1% to about 5% by weight, more typically about 0.2% to about 3% by weight, and preferably about 0.3% to about 1% by weight. The amount of thiocyanate included in this embodiment of the blackening bath of the invention is typically about 0.1% to about 5% by weight, more typically about 0.2% to about 3% by weight, and preferably about 0.3% to about 1% by weight.

[0017] Alternative embodiments of the blackening bath may optionally include some additives to enhance the color of the black oxide layer and allow repeated use of the blackening bath. The additives include, but are not limited to, 1. molybdates, including ammonium molybdate, sodium molybdate, and potassium molybdate, and 2. sodium chloride. The amount of molybdate optionally present in this embodiment is sufficient to provide effective blackening enhancement, typically ranging from 0.1% to about 3% by weight. The amount of sodium chloride optionally present in this embodiment is sufficient to provide effective blackening enhancement, typically ranging from 0.3% to about 1% by weight.

[0018] The pretreatment bath composition and the blackening bath composition may be prepared in a conventional manner using conventional processes and mixing equipment. For example, the blackening and pretreatment bath compositions may be prepared in the following manner: all components are mixed using a mechanical mixer for a sufficient effective period of time until all solid components are completely dissolved in the aqueous solution, up to about one hour.

[0019] The preferred method for blackening surgical needles consists of two major steps. The initial step is a pretreatment step which is performed prior to the blackening step of the needle. In the pretreatment step, surface oxides are removed from the surface of the needle. The second step is the blackening step of the needle. In the blackening step, a black oxide coating is formed on the surface of the needle.

[0020] The pretreatment step is carried out to remove surface oxides. The stainless steels are covered with a layer of chromium oxides that makes them corrosion resistant. This oxide layer consequently passivates the surface and makes it resistant to further chemical treatments. The activation solution reacts with the chromium oxides, making the stainless steel needle surface chemically receptive to the various blackening solutions utilized in the second blackening step. Any surface contaminants present on the needle surface, such as machine oils and greases, are also removed in this step. Various acids, such as hydrochloric acid, phosphoric acid, and sulfuric acid, are commonly used at high temperatures for this purpose. Thus, the first step is also referred to as the pickling process step, which typically lasts from about 10 minutes to about 1 hour. The pretreatment bath formulations listed in Table 1 below were developed for a 30 second activation process adapted for an in-line process and a 3 minute large scale batch process. The process temperature for this bath formulation is 80°C, well below the boiling point of the solution to prevent the formation of fumes of harmful substances.

[0021] In the pretreatment process, the pretreatment bath solution described above is prepared using conventional mixing and process equipment. The solution is transferred to a conventional bath vessel having the desired dimensions and volume. The pretreatment process steps can be performed as a batch or continuous process. It will also be appreciated that the bath configuration will vary depending on whether the pretreatment process is batch or continuous. In a batch process, the needles are typically loaded into a basket and immersed in a bath of the bath solution. The needles are maintained in the bath at a temperature sufficient to effectively pretreat the needle surfaces for a sufficient time. The time will typically range from about 30 seconds to about 1 hour, more typically from about 1 minute to about 30 minutes, and preferably from about 2 minutes to about 5 minutes, depending on the amount of needles in the batch. The temperature of the pretreatment bath will typically range from about 60°C to about 100°C, more typically from about 70°C to about 90°C, and preferably from about 75°C to about 85°C.

[0022] In a continuous process, the needles are typically attached to a strip for rapid movement between manufacturing stations in a high speed needle operation. In such a process, the needles attached to the strip are moved through a pretreatment bath while attached to the strip. The needles are maintained in the bath for a sufficient time and at a sufficient temperature to effectively pretreat the surface of the needles. The time will typically range from about 20 seconds to about 60 seconds, more typically from about 25 seconds to about 45 seconds, and preferably from about 30 seconds to about 40 seconds. The temperature of the pretreatment bath will typically range from about 60°C to about 100°C, more typically from about 70°C to about 80°C, and preferably from about 75°C to about 85°C.

[0023] The blackening process is carried out similarly to the pretreatment process. In the blackening process, the blackening bath solution described above is prepared using conventional mixing and process equipment. The solution is transferred to a conventional bath vessel having the desired dimensions and volume. The blackening process steps can be carried out as a batch or continuous process. It will also be understood that the bath configuration will vary depending on whether the blackening process is batch or continuous. In either case, the bath may be optionally stirred by conventional equipment. In a batch process, the needles are typically loaded into a basket and immersed in a bath of the bath solution. The amount of needles in a batch can vary depending on the size of the system and can range, for example, from less than 10 needles to more than 10,000 needles. The needles are maintained in the bath at a sufficient temperature and for a sufficient time to effectively treat the surface of the needles to obtain a blackened surface. The time will typically range from about 1 minute to about 60 minutes, more typically from about 2 minutes to about 30 minutes, and preferably from about 2 minutes to about 4 minutes. The temperature of the blackening bath will typically range from about 90°C to about 140°C, more typically from about 95°C to about 110°C, and preferably from about 98°C to about 105°C. In a continuous process, the needles are typically attached to a strip for rapid movement between manufacturing stations in a high speed needle operation. In such a process, the needles attached to the strip move through the blackening bath while attached to the strip. The needles are maintained in the bath at a temperature sufficient to effectively blacken the surface of the needles for a sufficient time. A typical number of needles in the treatment bath can range, for example, from 20 or less to 100 or more at a time. Treatment times will typically range from about 5 seconds to about 40 seconds, more typically from about 10 seconds to about 30 seconds, and preferably from about 15 seconds to about 25 seconds. The temperature of the blackening bath will typically range from about 90°C to about 140°C, more typically from about 95°C to about 110°C, and preferably from about 98°C to about 105°C.

[0024] Harmless cleaning solutions and processes A method for the oxide residue cleaning process has been developed to ensure complete or substantially complete removal of oxide residue from the surface of the blackened needles. A unique feature of the novel method is its short process time (only 30 seconds) for each of its steps. This makes it ideal for fully automated batch processing and robotic equipment for large scale needle blackening processes, where a batch of 15,000 needles is blackened in 2 minutes. The novel method and composition of the present invention address the removal of large amounts of black oxide by-product that forms and deposits on the interior surfaces of the coating bath and on the blackened needles during production.

[0025] Furthermore, the loose oxide layer on the surface of the blackened needle affects the adhesion between the silicone lubricant layer and the needle. The silicone coating on the new black needle tends to peel off more easily than the conventional needle with the same geometric shape, resulting in poor penetration performance.

[0026] To overcome this problem, the entire batch of blackened needles was placed in an ultrasonic batch containing 1% citric acid at the end of the blackening process. The needles were treated with ultrasonic conditions for 1 minute and rinsed twice in water. Short washing times are important for an automated process.

[0027] With regard to a suitable ultrasonic bath, any commercially available ultrasonic bath system is suitable, provided that the system is capable of generating cavitation (forming microbubbles) in the citric acid solution and implosion of the formed microbubbles. The size of the bath may vary depending on the number of needles to be processed. For example, a half-gallon size ultrasonic bath is large enough to process 300 core needles. Commercial ultrasonic cleaners provided by Branson Ultrasonics of Danbury, Connecticut are available in half-gallon, three-quarter gallon, 1.5 gallon, 2.5 gallon, and 5.5 gallon sizes and operate at a frequency of about 40 kHz with power ratings of about 80, 130, 130, 185, and 320 watts, respectively, in the above-mentioned size units. EXAMPLES

[0028] 6000 6 mil taper point core needles (BV050606D01) were blackened according to the procedure described in Example 5 of US Patent Publication No. 2017 / 0370004, the disclosure of which is incorporated herein by reference in its entirety. The blackened needles were divided into several sets of approximately 300 needles each. Each set of needles was placed in a 1% aqueous solution of various formulations listed in Table 1 for 1 minute at ambient temperature in a half-gallon ultrasonic bath Branson ultrasonic cleaner (Model: 1510R-MTH). The ultrasonically cleaned needles were further rinsed twice in water before being coated with a 4.5% Nusil MED4162 heptane solution. The silicone-coated needles were cured at 200C for 4 hours, and the silicone coating process was repeated three times. Each set of needles received four layers of silicone coating.

[0029] Needle Testing Procedure Coating performance on medical devices can be tested with a variety of friction or adhesion tests. In the case of surgical needles, coating performance and integrity are evaluated using a penetration test device. The coated surgical needle is held using autolocking forceps, or a similar holding device. The coated needle is then passed through a medium that represents typical human tissue. Approximately half of the needle's length is passed through the medium and then withdrawn before the next pass. The test medium is typically a type of synthetic rubber (Duraflex™, Manufactured by Monmouth Rubber and Plastic Corporation, Monmouth, NJ). A typical test involves using ten needles that are individually passed through the medium ten times each. The maximum force at each pass is recorded and used as an indicator of coating performance. Typically, the penetration force increases with each successive pass as the coating wears off the needle. Further details regarding the equipment and method can also be found in U.S. Pat. No. 5,181,416, the disclosure of which is incorporated herein by reference.

[0030] A total of five sets of coated needles were tested with this procedure along with two sets of control samples, and the results are summarized in Table 1.

[0031] [Table 1]

[0032] With reference to Table 1, it can be seen that citric acid provides the most effective cleaning for the blackened needles, as indicated by the lowest needle penetration force. The best adhesion between the silicone coating and the surface of the blackened needle was observed on needles cleaned with citric acid, as evidenced by the lower penetration force. If the adhesion of the lubricant is poor, the silicone lubricant layer on the needle will be minimal and will easily come off during the penetration test, as indicated by the higher penetration force due to the lack of lubricant on the needle. EXAMPLES

[0033] Different concentrations of citric acid were used in the cleaning process, and eight batches of needles were cleaned in an ultrasonic bath with different concentrations of citric acid for 1 minute. Two sets of control samples were also included in this experiment. The first set of control samples was immersed in 1% citric acid solution (not in ultrasonic bath, control 3). The other set of samples was cleaned in Triton™ X-100 surfactant. (Triton™ X-100 surfactant is a commercial surfactant from Dow Chemical that contains 0.06% octylphenol ethoxylate in an aqueous solution.) Similar experiments were carried out using the above-mentioned procedure to evaluate its effectiveness on penetration performance, and the results are summarized in Table 2.

[0034] [Table 2]

[0035] With reference to Table 2, at citric acid concentrations of 0.75% and above, sufficient removal of oxide residues on the surface of the blackened needles is observed as shown by the penetration test results outlined in Table 2. It was observed that the color of the cleaned needles began to fade when the concentration of the cleaning solution reached 5%. These blackened needles turned light brown when cleaned with 10% citric acid for 1 minute under ultrasonic conditions. Existing surfactant-based cleaning processes do not provide for this type of blackened needle, so an ultrasonic bath is required to provide effective cleaning.

[0036] Various sonication times were investigated for 1% citric acid solution to evaluate its effectiveness on penetration performance. The results are summarized in Table 3. A control experiment with non-sonication conditions was also included in this table.

[0037] [Table 3]

[0038] With reference to Table 3, for ultrasonic treatment times of 0.5 minutes or more, sufficient removal of oxide residue from the surface of the blackened needles is observed, as evidenced by the lower penetration forces outlined in Table 3. It was also observed that the color of the cleaned needles began to fade when the ultrasonic bath cleaning time reached 10 minutes.

[0039] In summary, a low-cost, non-hazardous cleaning method has been developed to remove oxide residues on the surface of blackened needles. A combination of citric acid and / or ultrasonic agitation provides controlled removal of loose oxide particles to provide a good balance of color and penetration performance required for surgical needles. The concentration of citric acid in the cleaning solution is safe for workers and the environment, similar to that in soft drink soda.

[0040] While the present invention has been shown and described with reference to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail of the invention may be made without departing from the spirit and scope of the invention as claimed.

[0041] [Embodiment] (1) A method for treating a blackened surgical needle, comprising the steps of: a. placing at least one blackened surgical needle having free black oxide particles on its surface into a bath, said bath comprising: i. an effective amount of citric acid, and ii. positioning an ultrasonic source; b. applying said ultrasonic waves to said bath for a time sufficient to remove loose black oxide particles from the surface of said needle. (2) The method of claim 1, wherein the concentration of citric acid is about 0.5% to 5% by weight (aqueous). (3) The method of embodiment 2, wherein the concentration of citric acid is about 0.75% by weight to 5% by weight (aqueous). (4) The method of embodiment 3, wherein the concentration of citric acid is about 1.0% by weight (aqueous). (5) The method according to any one of the preceding claims, wherein the frequency of the ultrasound is about 40 kHz.

[0042] (6) The method of embodiment 5, wherein the ultrasonic power is in the range of about 80 watts to about 320 watts. (7) The method of embodiment 5, wherein the ultrasonic treatment time is less than 5 minutes. (8) The method of embodiment 7, wherein the ultrasonic treatment time is less than 3 minutes. (9) The method of embodiment 8, wherein the ultrasonic treatment time is less than 1 minute. (10) A system for treating blackened surgical needles comprising an ultrasonic bath and citric acid.

[0043] 11. The system of claim 10, wherein the concentration of citric acid is about 0.5% to 5% by weight (aqueous). (12) The system of embodiment 11, wherein the concentration of citric acid is about 0.75% by weight to 5% by weight (aqueous). (13) The system of embodiment 12, wherein the concentration of citric acid is about 1.0% by weight (aqueous). (14) A system described in any one of embodiments 10 to 13, wherein the frequency of the ultrasound is about 40 kHz. (15) The system of embodiment 14, wherein the ultrasonic power is in the range of about 80 watts to about 320 watts.

[0044] (16) The system of embodiment 14, wherein the ultrasonic treatment time is less than 5 minutes. (17) The system of embodiment 16, wherein the ultrasonic treatment time is less than 3 minutes. (18) The system of embodiment 17, wherein the ultrasonic treatment time is less than 1 minute.

Claims

1. 1. A method for treating a blackened surgical needle, comprising: a. placing at least one blackened surgical needle having loose black oxide particles on its surface into a bath, said bath comprising: i. 0.5% by weight or more and less than 5% by weight of citric acid, and ii. an ultrasound source; b. applying ultrasonic waves from said ultrasonic source to said bath for greater than or equal to 0.25 minutes and less than 10 minutes to remove said loose black oxide particles from said surface of said blackened surgical needle and to maintain the black color of said blackened surgical needle.

2. The method of claim 1 , wherein the citric acid is in an aqueous solution.

3. The method described in claim 2, wherein the concentration of citric acid is greater than or equal to 0.75% by weight and less than 5% by weight (aqueous).

4. The method of claim 3, wherein the concentration of the citric acid is 1.0 wt% (aqueous).

5. The method according to any one of claims 1 to 4, wherein the frequency of the ultrasound is 40 kHz.

6. The method of claim 5, wherein the ultrasonic power ranges from 80 watts to 320 watts.

7. 6. The method of claim 5, wherein the duration of sonication is less than 5 minutes.

8. 8. The method of claim 7, wherein the duration of sonication is less than 3 minutes.

9. 9. The method of claim 8, wherein the duration of sonication is less than 1 minute.

10. A system for use in a method for treating blackened surgical needles, comprising: an ultrasonic source; and a citric acid bath, the method comprising: a. placing at least one blackened surgical needle having loose black oxide particles on its surface into said citric acid bath, said citric acid bath comprising greater than or equal to 0.5% and less than 5% by weight citric acid; b. applying ultrasound from said ultrasound source to said citric acid bath for at least 0.25 minutes and less than 10 minutes to remove said loose black oxide particles from said surface of said blackened surgical needle and maintain a black color of said blackened surgical needle.

11. The system of claim 10 , wherein the citric acid is in an aqueous solution.

12. The system described in claim 11, wherein the concentration of citric acid is greater than or equal to 0.75% by weight and less than 5% by weight (aqueous).

13. The system of claim 12, wherein the concentration of citric acid is 1.0% by weight (aqueous).

14. The system according to any one of claims 10 to 13, wherein the ultrasonic frequency is 40 kHz.

15. The system of claim 14, wherein the ultrasonic power is in the range of 80 watts to 320 watts.

16. 15. The system of claim 14, wherein the duration of sonication is less than 5 minutes.

17. 17. The system of claim 16, wherein the duration of sonication is less than 3 minutes.

18. 20. The system of claim 17, wherein the duration of sonication is less than 1 minute.

19. The method of claim 1, wherein the blackened surgical needle has a black oxide coating.

20. The method of claim 19, wherein the black color of the blackened surgical needle comes from the black oxide coating.

21. The method of claim 19, wherein the black oxide coating comprises an iron oxide (Fe 3 O 4 ) based layer.

22. The system of claim 10, wherein the blackened surgical needle has a black oxide coating.

Images