STERILIZATION PAPER FOR WRAPPING MEDICAL DEVICES AND METHOD OF MANUFACTURING THE SAME

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application is an international filing which claims priority to and the benefit of European Patent Application Number EP23170210.1, which was filed on Apr. 26, 2023. The entire contents of the foregoing application are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a sterilization paper for wrapping medical devices, barrier to microorganism. In addition, the disclosure relates to a method for manufacturing a sterilization paper according to the disclosure and the use thereof as a sterile barrier system.

BACKGROUND OF THE DISCLOSURE

Sterile barrier systems are of primary importance for healthcare facilities. Reusable or single use medical devices typically must be sterilized and preserve sterility up to the time of use. Sterile barrier systems can be defined as in the ISO 11607-1 standard. This standard outlines the different requirements for the design of sterile barrier system and packaging system for terminally sterilized medical devices. For a given substrate to be used as a sterilization wrap it generally must comply with stringent requirements in terms of physical properties but most importantly with barrier properties against microorganisms. EN 868-2 outlines the requirements and test methods to evaluate a sterilization wrap used for packaging terminally sterilized medical devices.

A sterilization wrap can be multilayered or single layered. There are two main categories of sterilization wraps: reusable sterilization wraps, mostly woven and single-use sterilization wraps, mostly non-woven. Single-use sterilization wraps are the most commonly used. Since these sterilization wraps do not lose efficacy with time, they are often deemed safer compared to reusable ones. Non-woven sterilization wraps are generally made either from synthetic fibers, from natural fibers, or a mixture thereof. For example, sterilization wraps made of wet-laid nonwoven usually comprise a mixture of natural fibers and synthetic fibers such as polyethylene terephthalate (PET) fibers. Sterilization wraps made of Spunbond-Meltblown-Spunbond (SMS) contain exclusively synthetic fibers. Another type of sterilization wrap is crepe paper, which is almost exclusively made from natural fibers. Crepe paper used during a sterilization process usually have a basis weight of at least 60 grams per square meter (g/m²) or greater. When the basis weight is increased the tortuous path for microorganisms to reach the sterilized device is also increased. Finally, a less commonly used type of sterilization wrap is made of plain paper. Sterilization wraps made of plain paper are almost exclusively made from natural fibers.

After use sterilization wraps are typically considered as medical waste because of potential contamination. Medical waste cannot generally be recycled following recovery routes used for non-medical wastes. In particular, EN 643 defines grades of paper and board used as raw material for recycling in the manufacture of paper and board products. This standard excludes medical waste from being used as a raw material for paper making. Medical wastes are mostly incinerated to minimize risks of contamination. Accordingly, single-use sterilization wraps can be an important source of waste in a healthcare facility.

There is a need to improve the environmental impact of sterilization wraps while maintaining barrier properties as well as other properties, such as physical strength.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure provides improved sterilization paper to address the drawbacks of conventional sterilization wraps. The exemplary embodiments disclosed herein are illustrative of advantageous sterilization papers, and systems of the present disclosure and methods/techniques thereof. It should be understood, however, that the disclosed embodiments are merely exemplary of the present disclosure, which may be embodied in various forms. Therefore, details disclosed herein with reference to exemplary sterilization papers and associated processes/techniques of assembly and use are not to be interpreted as limiting, but merely as the basis for teaching one skilled in the art how to make and use the advantageous sterilization papers and/or alternative sterilization papers of the present disclosure.

In a first aspect, the present disclosure relates to a sterilization paper for wrapping medical devices having a basis weight of less than 52 g/m², preferably less than 50 g/m² and being a microbial barrier to microorganisms according to ISO 11607-1, wherein said paper is a crepe paper and comprises at least 80 wt % of cellulosic fibers of the total weight of the paper, and wherein the cellulosic fibers comprise 40-80 wt % of softwood pulp fibers and/or 20-60 wt % of hardwood pulp fibers of the total weight of the cellulosic fibers.

In a second aspect, the present disclosure relates to a method of manufacturing a sterilization paper according to the first aspect, wherein the method comprises the following steps: a) dispersing cellulosic pulp in an aqueous solution; b) refining the cellulosic pulp at a level of at least 30° SR, preferably at least 45° SR, more preferably at least 50° SR; and c) forming the sterilization paper preferably on a paper machine using the refined cellulosic pulp, wherein the paper machine comprises a creping step.

In a third aspect, the present disclosure relates to a use of the sterilization paper according to the first aspect or the second aspect as a sterile barrier system.

DETAILED DESCRIPTION OF THE DISCLOSURE

Conventional plain paper or crepe paper with a basis weight of less than 52 g/m² cannot generally be used satisfactorily as sterilization wrap. Papers with a basis weight less than 52 g/m² are typically used only as an overwrap because said products do not comply with ISO 11607-1 and EN 868-2. Additional microbial barrier wraps are generally needed to be compliant with said standards.

In the context of the present disclosure “microbial barrier to microorganisms” should be understood as defined ISO 11607-1 section 5.2.3, which indicates “Evaluation of the microbial barrier properties of porous materials can be done by challenging samples with an aerosol of bacterial spores or particulates, under a set of test conditions which specify the flow rate through the material, microbial or particulate challenge to the sample, and duration of the test. The microbial barrier properties of the material, under these specified test conditions, are determined by comparing the extent of bacterial or particulate penetration through the material with the original challenge. Data from a validated physical test method that correlates with a validated microbiological challenge method are considered acceptable for determining the microbial barrier properties. For testing of microbial barrier, see Table B.1.” Table B.1 lists the following standards: ASTM F1608, DIN 58953-6, ASTM F2101 and SS 876 0019 for challenging samples.

In the context of the present disclosure “paper” should be understood as a cellulosic fibrous substrate forming a sheet like structure that can be made on a paper machine.

In the present application, when reference is made to a standard such as ISO 11607-1, the applicable version is the one in force on the filing date of the priority application.

As mentioned above, in a first aspect, the present disclosure relates to a sterilization paper for wrapping medical devices having a basis weight of less than 52 g/m², preferably less than 50 g/m² and being a microbial barrier to microorganisms according to ISO 11607-1.

In a preferred embodiment, the sterilization paper may be a crepe paper. Crepe paper has improved elongation properties, softness and drapability compared to plain paper. Paper creping can be carried out on a paper machine before the drying step by wet creping or after the drying step by dry creping.

In one embodiment, the sterilization paper may have a basis weight greater than 40 g/m², preferably greater than 43 g/m². A paper having a basis weight above this threshold may have sufficient water repellency properties to insure adequate microbial barrier and minimize risk of contamination. The basis weight of the paper is determined according to ISO 536.

In one preferred embodiment, the sterilization paper may have a mean pore diameter of less than 25 micrometers (μm), preferably less than 23 μm and more preferably less than 20 μm. When the mean pore diameter is less than 25 μm it may reduce the chance of microbial contamination.

In another preferred embodiment, the sterilization paper may advantageously have a maximum pore diameter of less than 50 μm, preferably less than 40 μm and more preferably less than 35 μm to form a physical barrier against microorganisms.

In one embodiment, the paper may comprise at least 80 weight percent (wt %) of cellulosic fibers, preferably 90 wt % of cellulosic fibers and more preferably at least 95 wt % relative to the total weight of the paper. Cellulosic fibers are preferably native cellulosic fibers that are obtained from natural sources such as fibrous plants including hardwood and softwood trees. The high cellulosic fibers content in the paper according to the disclosure makes it more sustainable.

The cellulosic fibers may comprise 40-80 wt % of softwood pulp fibers and/or 20-60 wt % of hardwood pulp fibers relative to the total weight of the cellulosic fibers. Softwood pulp fibers tend to be longer than hardwood pulp fibers and contribute to general cohesion of the paper whereas hardwood pulp fibers contribute to the barrier properties by forming tighter pores.

In one embodiment, the paper may comprise a wet strength agent and preferably chosen from the group comprising polyamine epichlorohydrin (PAE), glyoxalated resins, such as glyoxalated polyamide (GPAM), and formaldehyde-based resin. The wet strength agent may be present in an amount greater than or equal to about 0.1 wt %, greater than or equal to about 0.2 wt %. The wet strength may also be present in an amount less than or equal to about 1.5 wt %, less than or equal to about 1.3 wt %, less than or equal to about 0.8. Combinations of the previously referenced ranges are also possible (e.g., greater than or equal to about 0.2 wt % and less than or equal to about 0.8 wt %). The wt % of the wet strength agent is expressed relative to the total dry weight of cellulosic fibers.

In one embodiment, the paper may comprise a sizing agent and preferably chosen from the group comprising alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), and rosin-based resin. The sizing agent may be present in an amount greater than or equal to about 0.1 weight percent (wt %), greater than or equal to about 0.2 wt %. The sizing agent may also be present in an amount less than or equal to about 1.5 wt %, less than or equal to about 1.2 wt %, less than or equal to about 0.7 wt %. Combinations of the previously referenced ranges are also possible (e.g., greater than or equal to about 0.2 wt % and less than or equal to about 0.7 wt %). The wt % of the sizing agent is expressed relative to the total dry weight of cellulosic fibers.

In one embodiment, the paper may be a microbial barrier to microorganisms as determined according to the standard DIN 58953-6 sections 3 and 4. As indicated above, to be considered a microbial barrier to microorganisms according to ISO 11607-1, a sterilization wrap must comply with at least with one of the testing methods listed in Table B.1. Unlike other methods from the list, DIN 58953-6 requires the test sample to undergo a sterilization cycle prior to contaminant exposure. This is critical to evaluate if the tested material can preserve barrier properties after sterilization. Generally, sterilization is carried out using steam at 134° C. for 18 minutes or 121° C. for 30 minutes. DIN 58953-6 section 3 covers testing carried out under humid conditions after sterilization also known as germ proofness under humidity. DIN 58953-6 section 4 covers testing carried out under dry conditions after sterilization also known as germ proofness under air permeance.

The paper according to the disclosure is permeable to sterilant and air. In a preferred embodiment, the paper may be suitable to be sterilized using steam sterilization, ethylene oxide sterilization, gamma rays sterilization or formaldehyde sterilization.

Notably, the paper according to the disclosure is suitable for steam sterilization because it has hydrophobic properties. The paper may have preferably a Cobb value at 60 seconds exposure time, of less than 20 g/m² as determined according to the standard ISO 535. The paper may have also preferably a water repellency of at least 20 seconds as determined according to the standard EN 868-2 Annex C. Even if the paper of the disclosure has hydrophobic properties, it can still maintain some moisture wicking properties and prevent wet packs formation.

In one embodiment, the paper may have an air permeability of at least 1.7 microns per pascal second (μm/Pa·s) preferably at least 4.0 μm/Pa·s as determined according to the standard ISO 5636-3 at an air pressure of 1.47 kilopascals (kPa). This can be advantageous for efficient penetration and evacuation of sterilant and air.

In one embodiment, the paper may have a dry tensile strength of between 1000 and 2500 newtons per meter (N/m) in the machine direction (MD) and/or between 500 and 2000 N/m in the cross direction (CD). The dry tensile strength is determined according to ISO 1924-2.

In one embodiment the paper has wet tensile strength of between 300 and 1000 N/m in the machine direction and/or between 250 and 500 N/m in the cross direction. The wet tensile strength is determined according to ISO 3781 after immersion in water for 60 minutes.

In a second aspect, the present disclosure relates to a method of manufacturing a sterilization paper according to the first aspect, wherein the method comprises the following steps: a) dispersing cellulosic pulp in an aqueous solution; b) refining the cellulosic pulp at a level of at least 30° SR preferably at least 45° SR and more preferably at least 50° SR; and c) forming a sterilization paper, preferably on a paper machine, using the refined cellulosic pulp.

In one preferred embodiment, the refining at step b) may be at a level of between 45° SR and 70° SR. Refining beyond 70° SR may reduce the air permeability. Sterilant and air penetration/evacuation may not be efficient. Refining below 45° SR may not be sufficient to create enough fibrillation that improve barrier properties of the paper. Schopper Riegler degrees (° SR) describes the amount of drained suspension and is the degree of drainage properties of the pulp that has been diluted in water as determined according to the standard ISO 5267-1.

In one preferred embodiment, the sterilization paper is creped on paper machine to form a creped paper at the end of step c).

In one embodiment, the method may comprise a further step wherein the cellulosic pulp is mixed with a sizing agent and/or a wet strength agent prior to step c).

In a preferred embodiment, the method may comprise a further step wherein the pH of the cellulosic pulp dispersion is adjusted to a value between 6.5 and 8 prior to step c).

In one embodiment, the method of manufacturing a sterilization paper according to the disclosure may comprise a step wherein the sterilization paper obtained in step c) is subjected to a micrexing step. The micrexing step is preferably carried out offline (i.e., not on the paper machine). Micrexing, sometimes also referred to in the art as “micropleating” or “microcreping”, includes the application of longitudinal compressive forces to the sterilization paper to produce a condensed micropleated texture web to provide a sterilization paper that has a plurality of small discontinuous pleats extending across the sterilization paper. The longitudinal compressive forces can be applied as the sterilization paper passes through the nip of superposed rolls operating at different speeds in a micrexing system. The resulting micrexed sterilization paper can be characterized as being more flexible and softer. The micrexed sterilization paper can be extensible in the lengthwise direction (transverse to the pleats), but not elastic since, once extended, it may not return to its compacted length.

In a third aspect, the present disclosure relates to the use of a sterilization paper according to the disclosure as a sterile barrier system.

Examples

Around 40 wt % of hardwood cellulosic pulp and around 60 wt % of softwood pulp were dispersed in a pulper. After dispersion, where appropriate, the fiber mix was refined and the pH of the dispersion was adjusted to about 7. The sizing agent AKD and Kymene, a wet strength agent with polyamine epichlorohydrin chemistry, were then added in the refined fiber mix. The amount of AKD was 0.4 wt % and the amount of Kymene was 0.5 wt % relative to the total dry weight of the fiber mix.

The fiber mix of Sample 1 was not refined. The fiber mix of Sample 2, 3, 5 and 6 were all refined at a level of 50° SR

The different paper samples were then made by a wet laying process on a paper machine. The different samples were creped on the paper machine and then dried. Sample 3 was subjected to an additional micrexing step.

Different physical properties of the samples were then measured and are reported in Tables 1 and 2.

Samples 1-3 were prepared at a relatively similar basis weight but as indicated above the refining level for Sample 2 and Sample 3 was 50° SR. The refining reduced the mean pore diameter but also improved the water repellency and the Cobb values. Sample 1 was not refined and had a water repellency value of less than 20 seconds and a Cobb value of greater than 20 g/m². Sample 1 is thus not compliant with ISO 11607-1 and EN 868-2, and sample 1 may not perform reliably as a sterilization wrap.

The impact of refining on hydrophobic properties of the crepe paper is an unexpected result. Refining can produce fibrils on cellulosic fibers. Without wishing to be bound by theory, refining appears to create a more specific surface area where the sizing can be anchored. Consequently, the refining step facilitates enhanced dispersion of the sizing, thus improving hydrophobic properties.

Sample 3 was prepared in a similar manner to Sample 2 but was subjected to a further step of micrexing. Micrexing can add more extensibility to the crepe paper and can make it less prone to tearing during manipulation. Sample 3 was also compliant with ISO 11607-1 and EN 868-2 even after being subjected to a micrexing step.

Sample 4 and sample 5 were made at a basis weight of less than 50 g/m². Sample 4 had a basis weight of 42.8 g/m² and Sample 5 had a basis weight of 44.6. g/m². For sample 4 the water repellency was less than 20 seconds and it was not compliant with ISO 11607-1 and EN 868-2, thus sample 4 may not perform reliably as a sterilization wrap.

Microbial barrier to microorganisms for Samples 2 and 5 were determined according to the standard DIN 58953-6 sections 3 and 4. The sample were first sterilized by steam at 134° C. for 18 minutes. The samples were then contaminated with the test germ on both material sides.

The results from the tests are presented in Table 3 for section 3 and Table 4 for section 4.

Both samples 2 and 5 were compliant with DIN 58956-6 sections 3 and 4 and accordingly provide a microbial barrier to microorganisms.

The present disclosure can be further understood with reference to the following aspects:

Aspect 1: Sterilization paper for wrapping medical devices having a basis weight of less than 52 g/m², preferably less than 50 g/m² and being a microbial barrier to microorganisms according to ISO 11607-1.

Aspect 2: Sterilization paper according to Aspect 1, wherein the sterilization paper is a crepe paper.

Aspect 3: Sterilization paper according to Aspect 1 or 2, wherein the basis weight is greater than 40 g/m², preferably greater than 43 g/m².

Aspect 4: Sterilization paper according to Aspects 1-3, wherein said paper has a mean pore diameter of less than 25 μm, preferably less than 23 μm and more preferably less than 20 μm.

Aspect 5: Sterilization paper according to any of Aspects 1-4, wherein said paper has a maximum pore diameter of less than 50 μm preferably less than 40 μm and more preferably less than 35 μm.

Aspect 6: Sterilization paper according to any of Aspects 1-5, wherein said paper comprises at least 80 wt % of cellulosic fibers, preferably 90 wt % of cellulosic fibers and more preferably 95 wt % relative to the total weight of the paper.

Aspect 7: Sterilization paper according to Aspect 6, wherein the cellulosic fibers comprise 40-80 wt % of softwood pulp fibers and/or 20-60 wt % of hardwood pulp fibers relative to the total weight of the cellulosic fibers.

Aspect 8: Sterilization paper according to any of Aspects 1-7, wherein said paper comprises a wet strength agent chosen from the group comprising polyamine epichlorohydrin (PAE), glyoxalated resins, such as glyoxalated polyamide (GPAM), and formaldehyde-based resin.

Aspect 9: Sterilization paper according to Aspect 8, wherein said wet strength agent is present in an amount between 0.1 and 1.5 wt %, preferably between 0.2 and 1.3 wt % and more preferably between 0.2 and 0.8 wt %, relative to the total dry weight of cellulosic fibers.

Aspect 10: Sterilization paper according to any of Aspects 1-9, wherein said paper comprises a sizing agent chosen from the group comprising alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), and rosin-based resin

Aspect 11: Sterilization paper according to any of Aspects 1-10, wherein said sizing agent is present in an amount between 0.1 and 1.5 wt %, preferably between 0.2 and 1.2 wt % and more preferably between 0.2 and 0.7 wt % relative to the total dry weight of cellulosic fibers.

Aspect 12: Sterilization paper according to any of Aspects 1-11, wherein said paper is a microbial barrier to microorganisms as determined according to the standard DIN 58953-6 sections 3 and 4.

Aspect 13: Sterilization paper according to any of Aspects 1-12, wherein said paper has a Cobb value at 60 seconds exposure time, of less than 20 g/m² as determined according to the standard ISO 535.

Aspect 14: Sterilization paper according to any of Aspects 1-13, wherein said paper has a water repellency of at least 20 seconds as determined according to the standard EN 868-2 Annex C.

Aspect 15 Sterilization paper according to any of Aspects 1-14, wherein said paper has an air permeability of at least 1.7 μm/Pa·s, preferably at least 4.0 μm/Pa·s as determined according to the standard ISO 5636-3 at an air pressure of 1.47 kPa.

Aspect 16: Sterilization paper according to any of Aspects 1-15, wherein said paper has dry tensile strength of between 1000 and 2500 N/m in the machine direction and between 500 and/or 2000 N/m in the cross direction.

Aspect 17: Sterilization paper according to any of Aspects 1-16, wherein said paper has a wet tensile strength of between 300 and 1000 N/m in the machine direction and/or between 250 and 500 N/m in the cross direction.

Aspect 18: Method of manufacturing a sterilization paper according to any of Aspects 1-17 comprising the following steps: a) dispersing a cellulosic pulp in an aqueous solution; b) refining the cellulosic pulp at a level of at least 30° SR, preferably at least 45° SR, more preferably at least 50° SR; and c) forming the sterilization paper preferably on a paper machine using the refined cellulosic pulp, preferably said paper machine comprises a creping step.

Aspect 19: Method of manufacturing a sterilization paper according to Aspect 18, further comprising a step wherein the cellulosic pulp is mixed with a sizing agent and/or a wet strength agent prior to step c).

Aspect 20: Method of manufacturing a sterilization paper according to any of Aspect 18 or 19, further comprising a step wherein the pH of the cellulosic pulp dispersion is adjusted to a value between 6.5 and 8 prior to step c).

Aspect 21: Method of manufacturing a sterilization paper according to any of Aspects 18-20, further comprising a step wherein the sterilization paper obtained in step c) is subjected to micrexing step.

Aspect 22: Use of a sterilization paper according to any of Aspects 1-21 as a sterile barrier system.

While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt %, or, more specifically, 5 wt % to 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “5 wt % to 25 wt %,” etc.). “Combinations” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” and “the” do not denote a limitation of quantity and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and/or” unless clearly stated otherwise. Reference throughout the specification to “some embodiments”, “an embodiment”, and so forth, means that a particular element described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments. A “combination thereof” is open and includes any combination comprising at least one of the listed components or properties optionally together with a like or equivalent component or property not listed.

Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

Although the sterilization paper, systems and methods of the present disclosure have been described with reference to exemplary embodiments thereof, the present disclosure is not limited to such exemplary embodiments and/or implementations. Rather, the sterilization paper, systems and methods of the present disclosure are susceptible to many implementations and applications, as will be readily apparent to persons skilled in the art from the disclosure hereof. The present disclosure expressly encompasses such modifications, enhancements and/or variations of the disclosed embodiments. Since many changes could be made in the above construction and many widely different embodiments of this disclosure could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense. Additional modifications, changes, and substitutions are intended in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.