Wound dressing assembly

Abstract

Wound dressing assemblies and methods of processing are described where hydrogel pads may be formed by introducing a first amount of pullulan, salt and crosslinker, introducing a second amount of collagen such that the weight ratio of pullulan to collagen is between 20:1 to 22:1. The pullulan and collagen may be mixed to form a pullulan mixture and a third amount of an initiator solution may be introduced to the pullulan mixture to form a component mixture. The component mixture may be set for a predetermined period of time whereby the pullulan crosslinks with one another and the collagen remains un-crosslinked to form a hydrogel. The hydrogel may be cooled at a predetermined cooling rate from room temperature to a first cooling temperature, and then dried at a predetermined warming rate from the first cooling temperature to a second drying temperature while exposing the hydrogel to a predetermined negative pressure.

Description

Attorney Docket No.: TTNGZ01800WO WOUND DRESSING ASSEMBLY CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Prov. 63 / 486,928 filed February 24, 2023, which is incorporated herein by reference in its entirety. FIELD OF THE INVENTION

[0002] The present invention relates generally to medical devices and methods. More particularly, the present invention relates to apparatus and methods for the production of wound dressings made from pullulan and collagen. BACKGROUND OF THE INVENTION

[0003] Compositions and methods are provided for the manufacture of pullulan- collagen pads which display excellent handling characteristics, durability, and a porous dermal-like ultrastructure that is maintained in vitro. These pullulan-collagen pads can be used as wound dressings, drug delivery platforms, skin substitute, and cell delivery scaffolds.

[0004] Conventional wound dressings utilizing collagen are manufactured using various techniques, but such techniques are typically limited by factors such as cost, ability to maintain the optimal moisture environment, short shelf life, etc.

[0005] Therefore, there exists a need for manufacturing processes which enable the efficient manufacturing of pullulan-based collagen hydrogel pads for wound dressings which are effective. SUMMARY OF THE INVENTION

[0006] Pullulan-based collagen hydrogel pads may be processed to improve their uniformity and performance in wound remodeling by altering various production process parameters such as wash duration, salt content, as well as lyophilization parameters such as heating ramp times, temperatures, and durations. A mixture of pullulan, potassium chloride (KCl), and sodium trimetaphosphate (STMP) may be initially prepared. A collagen suspension may also be prepared in dilute acid solution (e.g. in HCL) and the HCl-KCl buffer may also be added to the collagen suspension and further mixed for aAttorney Docket No.: TTNGZ01800WO period of time to provide a homogenous collagen suspension. The mixture of pullulan, KCL and STMP may be then mixed with collagen suspension. This step facilitates the precipitation of collagen fibers at a relatively high salt concentration (e.g., by KCl) and neutral pH (e.g., pH of 6-7). Finally, an initiator sodium hydroxide (NaOH) may be introduced and mixed with the component mixture.

[0007] With the component mixing completed, the aliquots of the reaction mixture may be separated into patch forms by pouring the mixture into a mold form and the tray may be shaken for a period of time to ensure that the mixture spreads evenly within each of the molds. Afterwards, the mixture may be left in the tray for pullulan crosslinking for a specified period of time (e.g., 8 hours or more) at a specified temperature (e.g., room temperature).

[0008] The mixture may undergo gel formation via pullulan polymer crosslinking by STMP in the presence of NaOH. The collagen fibers, however, may remain in a natural state and not cross linked due to the fact that collagen molecules are precipitated and protected from from crosslinking reaction.

[0009] Once the reaction has stopped, the individual pads may be washed for a period of time. The process may be optionally repeated for an additional number of times after which a final volume of deionized water may be introduced to the tray and various parameters of the decanted water (e.g., pH, conductivity, etc.) may be measured.

[0010] Once the hydrogels have been washed, they may undergo a lyophilization process where the hydrogels are first slowly cooled down and frozen to a lowered temperature with subsequent drying under a high vacuum level.

[0011] The manufacturing steps lead to pore formation within the hydrogel pad such that the pore size may range between, e.g., 100-250 μm in diameter which is shown to be within the optimal range of pore size for fibroblast infiltration and tissue regeneration when the hydrogel pad is applied as a wound dressing upon a patient. In one variation, the average pore size may be, e.g., 250 μm. Furthermore, the cooling rate during lyophilization as described results in the desired pore size and consistency in pad formation. With the lyophilization completed, the individual pads may be removed from the tray and trimmed to size depending upon the desired application.

[0012] One method of forming a wound dressing may generally comprise setting the collagen suspension for a predetermined period of time, introducing a first amount of pullulan, introducing a second amount of collagen such that the weight ratio of pullulan to collagen is between 20:1 to 22:1, mixing the first amount of component mixture and theAttorney Docket No.: TTNGZ01800WO second amount of collagen to form a final component mixture, introducing a third amount of an initiator solution to the final mixture to form a gel, whereby the pullulan crosslinks with one another and the collagen remains un-crosslinked, cooling the hydrogel pad at a predetermined cooling rate from room temperature to a first cooling temperature, and drying the hydrogel pad at a predetermined warming rate from the first cooling temperature to a second drying temperature while exposing the hydrogel pad to a predetermined negative pressure.

[0013] One apparatus of a wound dressing may generally comprise a pullulan- collagen hydrogel, wherein the hydrogel comprises a first amount of a pullulan, potassium chloride (KCl), and sodium trimetaphosphate (STMP) mixture, a second amount of a collagen suspension, and a third amount of a NaOH initiator. The weight ratio of pullulan to collagen may be between 20:1 to 22:1 and a weight ratio of the KCl to STMP may be about 0.96:1. A pore size of the hydrogel pad may be between 100 to 250 μm.

[0014] One apparatus of a wound dressing may generally represent a cohesive hydrogel after hydration with saline. The hydrogel may generally comprise a crosslinked network of pullulan and embedded collagen fibers. The collagen fibers may be desirably organized in a reticular fashion within the network of pullulan and may provide mechanical strength for the hydrogel and as a biocompatible support for the cells. While the collagen may be generally arranged in a networked, dispersed, or interwound manner, the collagen may be arranged in alternative configurations depending upon the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates a flow diagram of one variation for manufacturing pullulan-collagen hydrogel pads.

[0016] FIGS. 2A and 2B illustrate perspective and top views of an assembly which may be used to form a homogenous component mixture.

[0017] FIG. 3 illustrates a perspective view of one variation of a manufacturing tray for producing the pads.

[0018] FIG. 4 illustrates a perspective view of one variation of an assembly for washing the pads using deionized water.Attorney Docket No.: TTNGZ01800WO DETAILED DESCRIPTION OF THE INVENTION

[0019] In processing wound dressings, pullulan-collagen pads may be processed to improve their uniformity and performance by altering various production process parameters such as wash duration, salt content, as well as lyophilization parameters such as heating ramp times, temperatures, and durations. Such processes also help to prevent the collagen in the wound dressing from cross-linking and thereby preserves the native form of the collagen.

[0020] FIG. 1 illustrates an example of a flow diagram 10 of one variation for manufacturing pullulan-based collagen pads. A mixture of pullulan, potassium chloride (KCl), and sodium trimetaphosphate (STMP) may be initially prepared 12, e.g., in a volume of water. In one example, an amount of KCl, e.g., 24.00 g ± 0.20 g, may be combined with an amount of STMP, e.g., 25.00 g ± 0.20 g, along with an amount of the pullulan, e.g., 25.00 g ± 0.20 g, within a container such as a glass beaker. The weight ratio of the KCl to STMP may be about, e.g., 0.96:1.

[0021] A collagen suspension, e.g., an insoluble collagen fiber powder derived from bovine hide, may also be prepared 14 by initially weighing an amount, e.g., 1.2 ± 0.05 g, of the collagen. The weight ratio of pullulan to collagen may accordingly range between, e.g., 20:1 and 22:1, or the weight ratio of pullulan to collagen may accordingly range between, e.g., 20.2:1 and 21.5:1, or the weight ratio of pullulan to collagen may be, e.g., 20.8:1. A volume of WFI, e.g., 60 mL, may be added to the collagen and mixed, and a volume, e.g., 60 mL, of acid having a pH of 2.20 such as the HCL solution or HCl-KCl buffer may also be added to the collagen suspension and further mixed for a period of time, e.g., greater than or equal to 12 hours or more, to provide a homogenous collagen suspension.

[0022] In mixing the collagen suspension, the pullulan, KCl, and STMP preparation 12 and the collagen suspension 14 may be mixed by the application of mechanical energy to form a homogeneous viscous suspension. FIGS. 2A and 2B illustrate perspective and top views of one example of a syringe mixing assembly 40 which may be used to form a homogenous component mixture via turbulent plug flow mixing. The assembly 40 may include one, two, three, four, or more syringes or containers 42A, 42B, 42C, 42D which may be fluidly coupled to one another via tubing couplings while being supported by a support structure. Each syringe may then be urged to pass the suspension between each of the syringes by depressing the appropriate plunger in a corresponding manner such thatAttorney Docket No.: TTNGZ01800WO application of this mechanical energy may pass the components 18 from one syringe to another a specified number of times, e.g., 1 to 16 times or more. The component mixing 18 may be repeated, e.g., 1 to 2 more times, and each of the components may be mixed against by passing them from one syringe to another, e.g., 1 to 16 times or more until the suspension has completed mixing such that a gel-type slurry is formed. Other forms of mechanical energy may also be used to mix the suspension, e.g., rotating mixer, blender, etc.

[0023] After the initial mixing, an initiator 16, e.g., 15 ± 0.1mL of 1N NaOH, may be introduced into a syringe and the initiator may be mixed with the suspension by passing the components 18 from one syringe to another a specified number of times, e.g., 1 to 16 times or more.

[0024] With the component mixing completed 18, the aliquots of the reaction mixture may be separated into patch forms 20 by pouring the mixture into a mold form. FIG. 3 illustrates a perspective view of one variation of a manufacturing tray 50 for producing the pads. The tray 50 is shown in this example as having a base 52 with multiple molds 54 defined over the surface of the tray 50 where the mixture may be introduced into each mold 54 to form an individual hydrogel 56. The example shown illustrates individual square molds (e.g., 42 x 42 x 2 mm) each holding a volume of the suspension (e.g., 3.5 mL). Once the mixture has been introduced into one or more of the molds 54, the tray 52 may be shaken for a period of time (e.g., 200 rpm for about 10 sec) to ensure that the mixture spreads evenly within each of the molds 54. Afterwards, the mixture may be left in the tray 52 to form a gel for a specified period of time (e.g., 8 hours or more) at a specified temperature (e.g., room temperature) under an airtight cover.

[0025] The mixture may undergo gel formation via pullulan polymer crosslinking. The collagen fibers, however, may remain in a natural state and not cross linked due to the fact at a relatively high salt concentration (e.g., by KCl) and neutral pH (e.g., pH of 6-7) collagen fibers precipitate. The change of the physical state protects the collagen from crosslinking by the STMP

[0026] Once the reaction is stopped, the individual gels within each mold 54 may be washed 24 using a volume of deionized water. The tray 50 including the individual hydrogel pads 56 may be placed within a container 60, as shown in the perspective view of FIG. 4. The volume of deionized water, e.g., 3 L, may be introduced to the tray 50 and the entire assembly may be exposed to a vibrational force, e.g., an orbital shaker, for a predetermined period of time, e.g., 30 minutes at 25 rpm, to wash the hydrogels 56. AfterAttorney Docket No.: TTNGZ01800WO the wash is completed, the water may be decanted from the container 60 and another volume of deionized water, e.g., 3 L, may be introduced to the tray 50 after which the assembly may be exposed to the vibration force again, e.g., 30 minutes at 25 rpm. The process may be optionally repeated for an additional number of times after which a final volume of deionized water, e.g., 1 L, may be introduced to the tray 50 and after a dwell period of time, e.g., 10 minutes, a volume of the final wash may be decanted and various parameters of the decanted water (e.g., pH, conductivity, etc.) may be measured. For instance, verifying a neutral pH level (e.g., 7.0-8.0) of the decanted water from the final wash 26 may be indicative that the washing of the hydrogel 56 is completed and the salt concentration is relatively low.

[0027] This may also be an indicator that the collagen fibers within the hydrogel pads 56 are desirably organized in a reticular fashion within the hydrogel network as the collagen fibers provide mechanical strength for the hydrogel and as a biocompatible support for the cells. Such an arrangement allows for the collagen to be targeted to skin cells in particular while having an increased mechanical strength. While the collagen may be generally arranged in a networked, dispersed, or interwoven manner, the collagen may be arranged in alternative configurations depending upon the requirements.

[0028] Once the hydrogels 56 have been washed, they may undergo a lyophilization process 28 where during the lyophilization process, the hydrogels are first slowly cooled down and frozen to a lowered temperature with subsequent drying under a high vacuum level. The hydrogel pads 56 may be cooled at a controlled rate of temperature and over a controlled period of time. For instance, as the tray is cooled, it may be cooled from room temperature down to -20° C over a first period of time, e.g., 175 minutes at 1 minute intervals, and down to -40° C over a second period of time, e.g., 40 minutes, with a 20 minute hold period at the -40° C temperature.

[0029] With the cooling completed, the tray may be subsequently brought back up in temperature and simultaneously dried under a high vacuum level. For instance, the hydrogel pads 56 may be increased in temperature to, e.g., -5° C, ramped over a first period of time, e.g., 120 minutes with a 600 minute hold, while the pressure is held between, e.g., 20 mTorr to 23 mTorr. The temperature may be further increased up to 25° C over a second period of time, e.g., 60 minutes with a 500 minute hold, while the pressure is held between, e.g., 20 mTorr to 23 mTorr.

[0030] These lyophilization settings may lead to pore formation within the hydrogel 56 such that the pore size is between, e.g., 150 to 250 μm, in diameter or, suchAttorney Docket No.: TTNGZ01800WO that the average pore size is, e.g., 160 μm, in diameter which is shown to be within the optimal range of pore size for fibroblast infiltration and tissue regeneration when the hydrogel 56 is applied as a wound dressing upon a patient. Furthermore, the cooling rate during lyophilization as described results in the desired pore size and consistency in formation of the pad 56.

[0031] With the lyophilization completed, the individual pads 56 may be removed from the tray 50 and trimmed to size 30 depending upon the desired application. An individual pad 56 may be placed upon a cutting fixture and the pad 56 subsequently cut to size, e.g., 50 x 50 mm, or any other size as desired or needed.

[0032] The applications of the disclosed invention discussed above are not limited to certain processes or applications of a pad upon any particular regions of the body but may include any number of other treatments and areas of the body. Modification of the above-described methods and devices for carrying out the invention, and variations of aspects of the invention that are obvious to those of skill in the arts are intended to be within the scope of this disclosure. Moreover, various combinations of aspects between examples are also contemplated and are considered to be within the scope of this disclosure as well.

Claims

Attorney Docket No.: TTNGZ01800WO CLAIMS What is claimed is:

1. A method of forming a wound dressing, comprising: introducing a first amount of pullulan; introducing a second amount of collagen such that the weight ratio of pullulan to collagen is between 20:1 to 22:1; mixing the first amount of pullulan and the second amount of collagen to form a component mixture; introducing a third amount of an initiator solution to the component mixture to form a reaction mixture; setting the reaction mixture for a predetermined period of time whereby the pullulan crosslinks with one another and the collagen remains un-crosslinked to form a hydrogel; cooling the hydrogel at a predetermined cooling rate from room temperature to a first cooling temperature; and drying the hydrogel at a predetermined warming rate from the first cooling temperature to a second drying temperature while exposing the hydrogel to a predetermined negative pressure.

2. The method of claim 1 wherein introducing the first amount of pullulan comprises introducing a mixture of the pullulan, potassium chloride (KCl), and sodium trimetaphosphate (STMP).

3. The method of claim 2 wherein a weight ratio of the KCl to STMP is about 0.96:1.Attorney Docket No.: TTNGZ01800WO 4. The method of claim 1 wherein introducing the second amount of collagen where a weight ratio of the pullulan to collagen is between 20:1 and 22:

1.

5. The method of claim 1 wherein mixing the first amount of pullulan and the second amount of collagen comprises mechanically mixing.

6. The method of claim 1 wherein introducing the third amount of the initiator solution comprises introducing a volume of 1N NaOH.

7. The method of claim 1 wherein setting the collagen suspension further comprises shaking the collagen suspension for a period of time.

8. The method of claim 1 wherein setting the collagen suspension further comprises setting the collagen suspension for 8 hours or more at room temperature.

9. The method of claim 1 further comprising washing the hydrogel with water prior to cooling the hydrogel.

10. The method of claim 9 further comprising washing the hydrogel until a pH level of the water is neutral.

11. The method of claim 1 wherein cooling the hydrogel comprises cooling at a first cooling rate from room temperature to an intermediate cooling temperature and further cooling at a second cooling rate from the intermediate cooling temperature to the first cooling temperature.Attorney Docket No.: TTNGZ01800WO 12. The method of claim 1 wherein drying the hydrogel comprises warming at a first warming rate from the first cooling temperature to an intermediate drying temperature and further warming at a second warming rate from the intermediate drying temperature to the second drying temperature.

13. The method of claim 12 wherein the predetermined negative pressure.

14. The method of claim 12 further comprising controlling a pore size of the hydrogel to have a diameter of 100 to 250 μm.

15. The method of claim 1 further comprising trimming the hydrogel.

16. A wound dressing, comprising: a pullulan-collagen hydrogel, wherein the hydrogel comprises: a first amount of a pullulan, potassium chloride (KCl), and sodium trimetaphosphate (STMP) mixture, a second amount of a collagen suspension, and a third amount of a NaOH initiator; wherein a weight ratio of pullulan to collagen is between 20:1 to 22:1 and a weight ratio of the KCl to STMP is about 0.96:1, and wherein a pore size of the hydrogel is between 100 to 250 μm.

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