Composite absorption pad and preparation method thereof

Abstract

The invention discloses a composite absorption pad and a preparation method thereof, and relates to the technical field of sanitary absorption products. The composite absorption pad comprises a first composite functional layer, an absorption layer and a second composite functional layer which are sequentially arranged in a laminated mode from bottom to top, each of the first composite functional layer and the second composite functional layer comprises a hydrophobic silk fibroin nanofiber layer and a hydrophilic silk fibroin nanofiber layer, and the absorption layer is sodium hyaluronate; wherein the difference value of a static contact angle between the hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer is greater than or equal to 30 degrees, so that one-way diversion from the hydrophobic silk fibroin nanofiber layer to the hydrophilic silk fibroin nanofiber layer is formed. According to the composite absorption pad, the absorption performance can be improved, meanwhile, rapid liquid conduction, back seepage prevention, lightness, thinness, comfort, long-term use safety and environmental friendliness are considered, and the composite absorption pad does not depend on chemical auxiliaries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sanitary absorbent products, in particular to a composite absorbent pad and a preparation method thereof. BACKGROUND

[0002] The existing absorbent pads for nursing, such as medical dressings, adhesive bandages and sanitary products, usually adopt a layered structure composed of a surface non-woven fabric, an absorbent core layer and a bottom film, wherein the absorbent core layer is mostly a mixed system of fluff pulp and high molecular water-absorbing resin to realize the functions of liquid absorption and storage. In order to improve the fluid conduction and dryness performance, some existing technologies introduce hydrophilic treated non-woven fabric, embossed groove structure in the surface layer or fluid conduction layer, or set a hydrophilic coating on the surface of the absorbent layer to promote the penetration of liquid into the core body. However, the difference in wettability between the functional layers in the above structures usually depends on the intrinsic properties of the materials or simple modification of the surface, and lacks quantitative design for the wetting gradient, making it difficult to form a stable and controllable one-way fluid conduction effect between the layers, and the liquid is still prone to horizontal diffusion and backflow after being pressed or used for a long time.

[0003] In the prior art, some schemes have tried to introduce bioactive materials such as silk fibroin and sodium hyaluronate into sanitary products, but they are mostly applied to the surface care or functional additional layer in the form of coating, impregnation or adding additives, mainly focusing on skin soothing, moisturizing or antibacterial performance, and their structural morphology is mostly continuous film layer, gel layer or functional coating, and they are not used as the core structural unit of the absorbent pad for multi-layer collaborative design.

[0004] In addition, the existing absorbent core mostly relies on the high liquid absorption ratio of high molecular water-absorbing resin particles to realize the water locking effect, and its absorption process mainly relies on local swelling and pore blockage, which easily leads to uneven absorption, hardening of the structure and increase in thickness, which is contradictory to the demand for lightness, softness, adhesion and long-term dryness. Therefore, how to realize the rapid introduction, effective locking and backflow inhibition of liquid without relying on traditional high molecular water-absorbing resin particles through the structural design of hydrophilic and hydrophobic cooperation is still a technical problem to be solved in the prior art. SUMMARY

[0005] One object of the first aspect of the present application is to provide a composite absorbent pad to solve the technical problems in the prior art that the absorbent core composed of high molecular water-absorbing resin and non-woven fabric in the existing sanitary absorbent products is difficult to balance the functions of rapid liquid conduction, backflow prevention, lightness, comfort, safety and environmental friendliness during long-term use while improving the absorption performance, and is limited in function improvement and relies on chemical additives and non-degradable materials.

[0006] Another object of the first aspect of the present application is to further improve the structural reliability of the composite absorbent pad.

[0007] The second aspect of this invention aims to provide a method for preparing a composite absorbent pad.

[0008] According to a first aspect of the present invention, the present invention provides a composite absorbent pad, comprising a first composite functional layer, an absorbent layer, and a second composite functional layer arranged sequentially from bottom to top. Each of the first and second composite functional layers includes a hydrophobic silk fibroin nanofiber layer and a hydrophilic silk fibroin nanofiber layer located on the side of the hydrophobic silk fibroin nanofiber layer near the absorbent layer. The absorbent layer is sodium hyaluronate. The static contact angle of the hydrophilic silk fibroin nanofiber layer with water is smaller than that of the hydrophobic silk fibroin nanofiber layer with water, and the difference in static contact angle between the hydrophilic and hydrophobic silk fibroin nanofiber layers is greater than or equal to 30°, so as to form a unidirectional flow from the hydrophobic silk fibroin nanofiber layer to the hydrophilic silk fibroin nanofiber layer.

[0009] Optionally, the average pore size of the hydrophilic silk fibroin nanofiber layer is smaller than that of the hydrophobic silk fibroin nanofiber layer, and the average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer is smaller than that in the hydrophobic silk fibroin nanofiber layer.

[0010] Optionally, the hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer are each composed of a nanofiber membrane, wherein the porosity of the nanofiber membrane is any value between 60% and 90%; wherein, The average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer is any value between 100nm and 400nm, and the average pore size is any value between 0.1μm and 3μm. The average diameter of the nanofibers in the hydrophobic silk fibroin nanofiber layer is any value between 200nm and 600nm, and the average pore size is any value between 1μm and 5μm.

[0011] Optionally, the hydrophilic silk fibroin nanofiber layer and / or the hydrophobic silk fibroin nanofiber layer are nanofiber layers formed by electrospinning with a silk fibroin spinning solution; wherein, The electrospinning process has a propulsion rate of 0.3 mL / h to 0.8 mL / h, an applied voltage of 15 kV to 20 kV, and a receiving distance of 12 cm to 18 cm between the spinning nozzle and the receiving device.

[0012] Optionally, the composite absorbent pad is prepared by sequentially stacking the hydrophobic silk fibroin nanofiber layer, the hydrophilic silk fibroin nanofiber layer, the absorbent layer, the hydrophilic silk fibroin nanofiber layer, and the hydrophobic silk fibroin nanofiber layer to form a preform, and then subjecting the preform to hot pressing; wherein, The hot pressing treatment is performed at any temperature between 55℃ and 65℃, at any pressure between 0.3MPa and 0.8MPa, and for any hot pressing time between 5s and 30s.

[0013] Optionally, the amount of sodium hyaluronate used in the absorbent layer is 20 g / m². 2 -80g / m 2 Any value in the range, with a molecular weight of any value between 1000KDa and 3000KDa.

[0014] Optionally, the silk fibroin spinning solution used in the hydrophobic silk fibroin nanofiber layer is derived from a regenerated silk fibroin solution, which is treated by enzymatic hydrolysis to form a precipitate, and then the precipitate is dissolved in a calcium chloride / formic acid binary solvent system.

[0015] Optionally, the concentration of calcium chloride in the calcium chloride / formic acid binary solvent system is any value between 4wt% and 10wt%.

[0016] Optionally, the protease used in the enzymatic hydrolysis reaction is selected from one or more of trypsin, α-chymotrypsin, pepsin, alkaline protease, papain, and proteinase K.

[0017] According to a second aspect of the present invention, the present invention also provides a method for preparing the composite absorbent pad described in any one of the above claims, comprising the following steps: A hydrophilic silk fibroin spinning solution was prepared by dissolving degummed silk fibroin in a calcium chloride / formic acid binary solvent system. The regenerated silk fibroin solution was enzymatically hydrolyzed to obtain a precipitate, which was then dissolved in a calcium chloride / formic acid binary solvent system to prepare a hydrophobic silk fibroin spinning solution. The hydrophilic silk fibroin spinning solution and the hydrophobic silk fibroin spinning solution are respectively injected into an electrospinning device for spinning to prepare the hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer respectively. The hydrophobic silk fibroin nanofiber layer, the hydrophilic silk fibroin nanofiber layer, the absorbent layer, the hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer are sequentially stacked to form a preform, and the preform is subjected to hot pressing treatment to obtain the composite absorbent pad.

[0018] This invention employs a composite absorbent pad arranged in a bottom-to-top configuration of a hydrophobic silk fibroin nanofiber layer, a hydrophilic silk fibroin nanofiber layer, an absorbent layer, another hydrophilic silk fibroin nanofiber layer, and a hydrophobic silk fibroin nanofiber layer, with the static contact angle difference between the hydrophobic and hydrophilic silk fibroin nanofiber layers being greater than or equal to 30°. This creates a unidirectional flow channel between adjacent nanofiber layers, allowing liquid to flow rapidly from the hydrophobic layer to the hydrophilic layer while significantly limiting reverse permeation. Furthermore, the middle absorbent layer is made of sodium hyaluronate powder, which can quickly absorb and gel in situ to lock in the liquid. Thus, the two sets of composite functional layers further form a physical leak-proof barrier, while providing dynamic adhesion responsive to humidity. This allows for the simultaneous realization of four functions—efficient liquid flow, absorption, locking, and leak prevention—within a single composite unit.

[0019] Furthermore, this invention defines the porosity, average nanofiber diameter, and average pore size of the hydrophilic and hydrophobic silk fibroin nanofiber layers by dividing and segmenting them into layers. While maintaining the consistency that both layers are made of silk fibroin material, a stable pore structure gradient and capillary pressure gradient are constructed at the nanoscale. This effectively amplifies the wettability difference and stably transforms it into unidirectional flow guidance and leak-proof performance, thereby providing a reliable structural basis for the composite absorbent pad.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0021] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic structural diagram of a composite absorbent pad according to an embodiment of the present invention; Figure 2 This is a schematic flowchart of a method for preparing a composite absorbent pad according to an embodiment of the present invention; Figure 3 This is a scanning electron microscope image of the hydrophilic silk fibroin nanofiber layer in Example 1 of the present invention; Figure 4 This is a scanning electron microscope image of the hydrophobic silk fibroin nanofiber layer in Example 1 of the present invention; Figure 5 This is the Fourier transform infrared spectrum of the hydrophobic silk fibroin nanofiber layer in Example 1 of the present invention; Figure 6 This is a photograph of the leak-proof effect according to Embodiment 1 of the present invention; Figure 7 This is a physical image illustrating the leak-proof effect of Comparative Example 1 according to the present invention.

[0022] Figure label: 100 - Composite absorbent pad, 10 - First composite functional layer, 20 - Absorbent layer, 30 - Second composite functional layer, 40 - Hydrophobic silk fibroin nanofiber layer, 50 - Hydrophilic silk fibroin nanofiber layer. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0025] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] Figure 1 This is a schematic structural diagram of a composite absorbent pad according to an embodiment of the present invention. Figure 2 This is a schematic flowchart of a method for preparing a composite absorbent pad according to an embodiment of the present invention.

[0028] like Figure 1As shown, the present invention provides a composite absorbent pad 100, which includes a first composite functional layer 10, an absorbent layer 20, and a second composite functional layer 30 arranged sequentially from bottom to top. Both the first composite functional layer 10 and the second composite functional layer 30 include a hydrophobic silk fibroin nanofiber layer 40 and a hydrophilic silk fibroin nanofiber layer 50 located on the side of the hydrophobic silk fibroin nanofiber layer 40 near the absorbent layer 20. The absorbent layer 20 is sodium hyaluronate. The static contact angle of the hydrophilic silk fibroin nanofiber layer 50 with water is smaller than that of the hydrophobic silk fibroin nanofiber layer 40, and the difference in static contact angle between the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 is greater than or equal to 30°, thereby forming a unidirectional flow from the hydrophobic silk fibroin nanofiber layer 40 to the hydrophilic silk fibroin nanofiber layer 50. Here, unidirectional flow refers to the rapid passage of liquid from the hydrophobic silk fibroin nanofiber layer 40 to the hydrophilic silk fibroin nanofiber layer 50, while reverse osmosis is significantly limited.

[0029] In this embodiment, the composite absorbent pad 100 is configured as follows: a hydrophobic silk fibroin nanofiber layer 40, a hydrophilic silk fibroin nanofiber layer 50, an absorbent layer, a hydrophilic silk fibroin nanofiber layer 50, and a hydrophobic silk fibroin nanofiber layer 40 are stacked sequentially from bottom to top. The static contact angle difference between the hydrophobic silk fibroin nanofiber layer 40 and the hydrophilic silk fibroin nanofiber layer 50 is greater than or equal to 30°. This forms a one-way flow channel from the hydrophobic layer to the hydrophilic layer between adjacent nanofiber layers, allowing liquid to pass quickly from the hydrophobic silk fibroin nanofiber layer 40 to the hydrophilic silk fibroin nanofiber layer 50, while reverse permeation is significantly limited. Furthermore, the middle absorbent layer 20 is made of sodium hyaluronate powder, which can quickly absorb and gel in situ to lock the liquid. Thus, the upper and lower composite functional layers further form a physical leak-proof barrier, while providing dynamic adhesion in response to humidity. In a single composite unit, the four functions of efficient liquid flow, absorption, locking, and leak prevention are simultaneously achieved.

[0030] It is worth noting that in this embodiment, both the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 are prepared from silk fibroin. They do not rely on different material combinations or chemical modifications; functional differentiation and unidirectional flow guidance are achieved simply by controlling the spinning structure and hydrophilic / hydrophobic treatment of the silk fibroin. This not only fully utilizes the natural antibacterial, biodegradable, and humidity-responsive properties of silk fibroin but also simplifies the material system and improves biosafety and environmental friendliness. Furthermore, after absorbing moisture or coming into contact with liquid, the internal nanofiber network of the hydrophilic silk fibroin nanofiber layer 50 undergoes controllable volume expansion and structural rearrangement due to the action of hydrophilic groups, exhibiting significant humidity-responsive characteristics. This allows the nanofiber membrane to undergo flexible deformation according to local humidity conditions and tightly adhere to the external contact interface. Especially when in contact with the human body surface, it can adaptively conform to the body's curves and fill tiny gaps, thus forming a stable adaptive sealing structure without relying on additional adhesives or elastic materials. This effectively suppresses lateral liquid leakage and improves wearing comfort and leak-proof reliability.

[0031] It should be noted that prior to this application, those skilled in the art generally considered silk fibroin as a coating, nanoemulsion, or hydrolyzed comonomer, used only for surface skincare, antibacterial, or modification of particulate absorbent materials. Its existence was that of a non-structural or discrete functional additive. Furthermore, in the field of absorbent pad technology for achieving liquid absorption, core absorption functions such as liquid diversion, water retention, and leak prevention typically rely on combinations of multiple materials or chemical modifications, such as nonwoven fabrics, superabsorbent polymer particles, and geomembranes, rather than utilizing the same bio-based material through differences in physical structure to achieve the function. This is because using silk fibroin simultaneously as a structural support material and a functional interface, and forming a continuous nanofiber membrane framework through precise control of hydrophilic / hydrophobic properties, is something those skilled in the art typically would not consider.

[0032] Furthermore, silk fibroin exhibits poor solubility and spinnability control. Hydrophobic silk fibroin precipitates are difficult to dissolve uniformly, while hydrophilic silk fibroin easily affects fiber continuity and mechanical properties. Simultaneously, as a natural polymer, silk fibroin possesses a highly uniform chemical composition and polar group distribution, resulting in significant consistency in surface energy and wettability after forming a continuous nanofiber membrane. Moreover, the wettability of silk fibroin is primarily controlled by its β-sheet crystalline structure, and this crystalline behavior is both abrupt and synergistic, making it difficult to achieve spatially distinguishable and stable stepwise variations within the same continuous membrane. Furthermore, capillary effects and molecular migration within the continuous nanofiber network structure further weaken the long-term stability of local wettability differences. Therefore, those skilled in the art typically achieve wettability regulation by introducing different materials or additional interfacial layers, rather than relying solely on silk fibroin nanofiber membranes of the same material to construct a wettability ladder structure.

[0033] In a further embodiment, the silk fibroin spinning solution used for the hydrophobic silk fibroin nanofiber layer 40 is derived from a regenerated silk fibroin solution. After enzymatic hydrolysis to form a precipitate, the precipitate is dissolved in a calcium chloride / formic acid binary solvent system. This allows the resulting hydrophobic silk fibroin nanofiber layer 40 to exhibit a higher proportion of β-sheet structures and a denser fiber stacking morphology at the molecular conformation and microstructure levels without introducing hydrophobic synthetic polymers or chemically modified hydrophobic groups, thereby stably exhibiting hydrophobic properties. Specifically, the enzymatic hydrolysis treatment makes the molecular weight distribution of silk fibroin more concentrated, reducing the solution instability caused by polymer chain entanglement. This is beneficial for forming a continuous and uniform nanofiber structure during electrospinning, avoiding problems such as broken fibers, bead-like defects, or uncontrolled pore structures. The calcium chloride / formic acid binary solvent system has good solubility and conformational regulation effect on silk fibroin, which can promote the rapid solidification of the internal structure of the fiber after spinning and film formation, thereby enhancing the structural stability and water resistance of the hydrophobic silk fibroin nanofiber layer 40 in a humid environment.

[0034] In this embodiment, the hydrophobic silk fibroin nanofiber layer 40 obtained based on the above preparation method has good durability and consistency in hydrophobic properties. When it is stacked with the adjacent hydrophilic silk fibroin nanofiber layer 50, it can stably maintain a significant difference in wettability, providing a reliable interface basis for forming a unidirectional flow channel from the hydrophobic layer to the hydrophilic layer between the layers, thereby further improving the overall performance of the composite absorbent pad 100 in terms of flow conduction, backflow prevention and leakage prevention.

[0035] In this embodiment, the hydrophilic silk fibroin nanofiber layer 50 is prepared by electrospinning a hydrophilic silk fibroin spinning solution, which is prepared by dissolving degummed silk fibroin in a spinning solution solvent.

[0036] In this embodiment, a significant wettability difference exists between the adjacent hydrophobic silk fibroin nanofiber layer 40 and the hydrophilic silk fibroin nanofiber layer 50, with a static contact angle difference greater than or equal to 30°, thereby establishing a stable surface energy gradient at the interlayer interface. Combined with the micro-nano-scale porous network structure of the silk fibroin nanofiber layer, under the action of the surface energy gradient, capillary-driven channels are formed between adjacent nanofiber layers, pointing from the hydrophobic layer to the hydrophilic layer. This allows the liquid to achieve directional and rapid permeation without external pressure, relying on the capillary pressure difference. Specifically, when the liquid contacts the hydrophobic silk fibroin nanofiber layer 40, under the combined action of the wettability difference and the capillary pressure gradient, the liquid is preferentially drawn into the adjacent hydrophilic silk fibroin nanofiber layer 50, achieving unidirectional flow. In the reverse permeation direction, due to the wettability barrier formed by the transition from the hydrophilic layer to the hydrophobic layer and the capillary resistance effect, the backflow and reverse osmosis behavior of the liquid are significantly suppressed.

[0037] In this embodiment, through the synergistic effect of the aforementioned wettability difference and capillary drive effect, the liquid can be rapidly guided, directionally transported, and layered within the composite absorbent pad 100, providing stable and controllable liquid input conditions for the efficient absorption and in-situ gelation locking of the intermediate absorbent layer 20, thereby improving the overall leak-proof performance and reliability of the composite absorbent pad 100.

[0038] In a preferred embodiment, the difference in static contact angle between the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 is any value between 30° and 60°. That is, the static contact angle of the hydrophilic silk fibroin nanofiber layer 50 with water can be 30°, 35°, 40°, 45°, 50°, 55°, or 60° smaller than that of the hydrophobic silk fibroin nanofiber layer 40 with water, or any other value between 30° and 60°. When the difference in static contact angle between adjacent nanofiber layers is greater than 30° but less than 60°, problems such as interfacial wetting mismatch, local liquid retention, or discontinuous wetting between fiber layers caused by excessive wettability differences can be avoided, thereby maintaining the continuous capillary channel structure of the nanofiber membrane and the long-term stability of the interlayer interface. The contact angle difference within this range can provide sufficient capillary driving force and facilitate the smooth transfer and uniform distribution of liquid in the multilayer structure, further improving the flow conduction efficiency and absorption response speed, thereby achieving a better balance between unidirectional flow conduction capability, anti-backflow performance and structural stability.

[0039] In a preferred embodiment, the hydrophilic silk fibroin nanofiber layer 50 has a static contact angle with water of any value between 30° and 70°, that is, 30°, 40°, 50°, 60° or 70°, or any other value between 30° and 70°, and the hydrophobic silk fibroin nanofiber layer 40 has a static contact angle with water of any value between 80° and 120°, that is, 80°, 90°, 100°, 110° or 120°, or any other value between 80° and 120°, so that a stable and controllable wettability gradient is formed between adjacent functional layers.

[0040] In this embodiment, the thicknesses of the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 are any values ​​between 50 μm and 200 μm. That is, the thicknesses of the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 can be 50 μm, 100 μm, 150 μm or 200 μm, or any other value between 50 μm and 200 μm. This ensures that the nanofiber layer forms a continuous and stable three-dimensional porous network structure, while avoiding structural incompleteness, easy backflow or insufficient leak-proof performance caused by excessive thickness, as well as increased liquid transport resistance and reduced absorption rate caused by excessive thickness.

[0041] In a further embodiment, the average pore size of the hydrophilic silk fibroin nanofiber layer 50 is smaller than that of the hydrophobic silk fibroin nanofiber layer 40, and the average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer 50 is smaller than that in the hydrophobic silk fibroin nanofiber layer 40, further enhancing the capillary-driven flow conduction effect between adjacent nanofiber layers. Specifically, based on the established wettability difference, the smaller fiber diameter and pore size in the hydrophilic silk fibroin nanofiber layer 50 can generate higher capillary pressure, causing the liquid to be rapidly drawn and uniformly spread after entering the hydrophilic layer from the hydrophobic layer, thereby significantly improving the directional transport efficiency of the liquid. On the other hand, the relatively larger pore size and fiber diameter in the hydrophobic silk fibroin nanofiber layer 40 are beneficial for the initial entry of the liquid, but in the reverse osmosis direction, due to its lower wettability and lower capillary adsorption capacity, it is difficult to overcome the capillary pressure difference formed by the hydrophilic layer, thus significantly inhibiting the backflow of liquid.

[0042] In this embodiment, the aforementioned pore size gradient and fiber size difference work synergistically with the hydrophilic / hydrophobic wettability gradient to achieve rapid unidirectional flow of liquid from the hydrophobic layer to the hydrophilic layer, while further enhancing the barrier against reverse permeation and lateral leakage, thus improving the leak-proof stability of the composite absorbent pad 100 from a structural perspective.

[0043] In a further embodiment, the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 are each composed of a nanofiber membrane. The porosity of the nanofiber membrane is any value between 60% and 90%, that is, the porosity of the nanofiber membrane in the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 can be 60%, 70%, 80%, or 90%, or any other value between 60% and 90%. The average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer 50 is any value between 100 nm and 400 nm, that is, the average diameter of the nanofibers in the nanofiber membrane can be 100 nm, 200 nm, 300 nm, or 400 nm, or 100 nm-400 nm. The average pore size is any value between 0.1μm and 3μm, i.e., the average pore size can be 0.1μm, 0.5μm, 1.0μm, 2.0μm or 3.0μm, or any other value between 0.1μm and 3.0μm. The average diameter of the hydrophobic silk fibroin nanofiber layer 40 is any value between 200nm and 600nm, i.e., the average diameter can be 200nm, 300nm, 400nm, 500nm or 600nm, or any other value between 200nm and 600nm. The average pore size is any value between 1μm and 5μm, i.e., the average pore size can be 1μm, 2μm, 3μm, 4μm or 5μm, or any other value between 1μm and 5μm. By defining the porosity, average nanofiber diameter, and average pore size of the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 in a layered and segmented structure, a stable pore structure gradient and capillary pressure gradient are constructed at the nanoscale while maintaining the consistency that both layers are made of silk fibroin material. This effectively amplifies the wettability difference and stably transforms it into unidirectional flow guidance and leak-proof performance, thus providing a reliable structural basis for the composite absorbent pad 100.

[0044] In this embodiment, the porosity of the nanofiber membrane of the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 is limited to the range of 60%-90%. This not only ensures the formation of a continuous and interconnected pore network inside the nanofiber membrane, enabling the liquid to be rapidly transported and spread within the layer, but also avoids structural looseness and decreased mechanical stability caused by excessive porosity. This achieves a balance between liquid conduction efficiency and structural integrity, and provides the necessary channel conditions for capillary actuation formed by the difference in pore size and fiber size.

[0045] In this embodiment, the average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer 50 is any value between 100nm and 400nm, and the pore size is any value between 0.1μm and 3μm. This is because the smaller fiber diameter and pore size in the hydrophilic silk fibroin nanofiber layer 50 can significantly increase the specific surface area per unit volume, thereby enhancing the wetting and adsorption capacity of the liquid. At the same time, the smaller pore size can generate higher capillary pressure after the liquid enters, so that the liquid is quickly drawn and uniformly diffused in the layer, which is conducive to the directional transport and rapid transfer of the liquid towards the absorption layer 20, and reduces the liquid retention at the interface.

[0046] In this embodiment, the average diameter of the nanofibers in the hydrophobic silk fibroin nanofiber layer 40 is any value between 200nm and 600nm, and the pore size is any value between 1μm and 5μm. The relatively large fiber diameter and pore size structure in the hydrophobic silk fibroin nanofiber layer 40 allow the liquid to smoothly enter the layer and be transported downstream during forward flow, avoiding liquid accumulation or backflow due to the small pore size. In the reverse osmosis direction, due to the low wettability of the hydrophobic surface itself and the low capillary adsorption capacity corresponding to the large pore size, the liquid is difficult to form a stable reverse capillary traction, thereby effectively suppressing liquid backflow and leakage.

[0047] Furthermore, when the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 simultaneously satisfy the aforementioned porosity, fiber diameter, and pore size ranges, a significant gradient is formed between the different layers in terms of pore structure scale and wetting characteristics. This allows the capillary pressure difference and wettability difference to synergistically superimpose, constructing a stable unidirectional flow channel from the hydrophobic layer to the hydrophilic layer. This structure not only accelerates the directional flow of liquid and its transfer to the absorbent layer 20, but also, after the liquid is absorbed and locked, significantly reduces the probability of reverse permeation and lateral leakage through the synergistic barrier effect of the hydrophobic and hydrophilic layers, thereby comprehensively improving the flow efficiency, absorption stability, and leak-proof performance of the composite absorbent pad 100.

[0048] In a further embodiment, the hydrophilic silk fibroin nanofiber layer 50 and / or the hydrophobic silk fibroin nanofiber layer 40 are nanofiber layers formed by electrospinning with a silk fibroin spinning solution. The electrospinning advance rate is any value between 0.3 mL / h and 0.8 mL / h, i.e., the advance rate can be 0.3 mL / h, 0.4 mL / h, 0.5 mL / h, 0.6 mL / h, 0.7 mL / h, or 0.8 mL / h, or it can be 0.3 mL / h-0.8 mL / h. The electrospinning process can be performed at any value within 0.8 mL / h, with an applied voltage of 15 kV-20 kV (the applied voltage can be 15 kV, 16 kV, 17 kV, 18 kV, 19 kV, or 20 kV, or any other value within this range). The receiving distance between the spinning nozzle and the receiving device is 12 cm-18 cm (the receiving distance can be 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, or 18 cm, or any other value within this range). This electrospinning process is used to stably construct nanofiber membranes with specific fiber diameters, pore size distributions, and pore structures in the highly sensitive biomacromolecule system of silk fibroin. By setting the electrospinning parameters within the above range, structural and functional differentiation between hydrophilic and hydrophobic nanofiber layers can be achieved in the same silk fibroin system without introducing additional chemical modification or heterogeneous materials, providing the necessary structural basis for the subsequent formation of unidirectional flow channels.

[0049] In this embodiment, by setting the advance rate of the electrospinning process to within the range of 0.3 mL / h to 0.8 mL / h, the silk fibroin spinning solution can form a stable and continuous jet under the action of an electric field. This avoids jet interruption due to insufficient liquid supply or bead-like fibers and fiber adhesion due to excessive liquid supply, which is beneficial for obtaining nanofiber membranes with uniform fiber diameter distribution and continuous structure. In addition, while ensuring the stability of filamentation, it provides a process window for subsequent fine-tuning of parameters to achieve differences in fiber diameter and pore structure between different nanofiber layers, thereby supporting the structural differentiation of hydrophilic and hydrophobic nanofiber layers.

[0050] In this embodiment, the applied voltage for the electrospinning process is set within the range of 15kV-20kV. This allows the silk fibroin jet to obtain sufficient tensile force in the electrostatic field, effectively suppressing unstable jet oscillation and promoting sufficient fiber stretching and refinement, which is beneficial for forming a nanoscale fiber network structure. Simultaneously, this voltage range avoids the problems of excessively low electric field strength leading to coarse fibers and insufficient porosity, or excessively high electric field strength causing jet breakage and fiber structure collapse. This helps to stably construct nanofiber membranes with continuous channels and controllable pore size distribution, providing a structural basis for capillary-driven transport of liquids within the fiber layer.

[0051] In this embodiment, the receiving distance between the spinning nozzle and the receiving device is set to any value between 12cm and 18cm. This allows the silk fibroin jet sufficient time to complete solvent evaporation and structural solidification during its flight, preventing fiber accumulation in an insufficiently solidified state that could cause pore blockage or membrane densification. Simultaneously, this distance range also prevents excessive drying of the jet, which could lead to fiber embrittlement or decreased film uniformity. Therefore, while ensuring the overall mechanical stability of the nanofiber membrane, the connectivity and openness of the membrane's pore structure are maintained, facilitating rapid liquid permeation and transport within the membrane.

[0052] In this embodiment, the metal roller, which serves as the fiber receiving device in the electrospinning process, is set to any value between 100 rpm and 300 rpm. That is, the rotation speed of the metal roller can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, or 300 rpm, or any other value between 100 rpm and 300 rpm. Under the premise of ensuring effective fiber reception, a moderate traction and shearing action is applied to the fiber dropping process, so that the not-fully-cured silk fibroin fibers are stretched and oriented to a certain extent in the circumferential direction, which is beneficial to obtaining a nanofiber membrane with more uniform fiber diameter, more dense structure, and good continuity.

[0053] In a preferred embodiment, a hydrophilic silk fibroin nanofiber layer 50 with a porosity of 70%-90% and an average pore size of 0.1μm-3μm is prepared by using a propulsion rate of 0.3mL / h-0.5mL / h, an applied voltage of 17kV-20kV, and a receiving distance of 15cm-18cm. The fibers are fine, the channels are continuous, and the surface energy is high, which is beneficial for rapid liquid wetting and capillary conduction. Specifically, a lower propulsion rate is beneficial for the spinning jet to be fully stretched and the solvent to evaporate in the electric field, inhibiting fiber tufting and collapse, thereby obtaining a smaller nanofiber diameter. A higher voltage enhances the electric field force and improves the degree of jet stretching, which is beneficial for forming a fine fiber structure with an average diameter of 100nm-600nm. The longer receiving distance provides sufficient flight and solidification time for the jet, which is beneficial for forming a loosely structured but small-pore-sized and uniformly distributed nanofiber membrane.

[0054] In a preferred embodiment, a hydrophobic silk fibroin nanofiber layer 40 with a porosity of 60%-80%, an average pore size of 1μm-5μm, and an average nanofiber diameter of 200nm-600nm is prepared using a propulsion rate of 0.6mL / h-0.8mL / h, an applied voltage of 15kV-18kV, and a receiving distance of 12cm-15cm. This results in a larger inter-fiber pore size and significantly reduced capillary force, thus exhibiting overall hydrophobicity or resistance to reverse osmosis. Specifically, a higher propulsion rate increases the material supply per unit time, relatively reducing the jet stretching and facilitating the formation of larger diameter fibers. A relatively lower voltage weakens the electric field traction, which helps maintain a larger fiber diameter and form a relatively open pore structure. Furthermore, a shorter receiving distance allows fibers to deposit under conditions of insufficient stretching, further promoting fiber coarsening and pore size increase.

[0055] In a preferred embodiment, the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 obtained by electrospinning are immersed in an ethanol solution for a predetermined time, which is any value between 10 min and 60 min. That is, after spinning, the nanofiber layers need to be immersed in an ethanol solution for 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, or any value between 10 min and 60 min. By utilizing the selective induction of the silk fibroin conformation by the ethanol solution, its transformation from a random coil structure to a stable β-sheet structure is promoted, thereby significantly improving the wet mechanical strength of the nanofiber membrane.

[0056] In a further embodiment, a composite absorbent pad 100 is prepared by sequentially stacking a hydrophobic silk fibroin nanofiber membrane, a hydrophilic silk fibroin nanofiber membrane, an absorbent layer 20, a hydrophilic silk fibroin nanofiber membrane, and a hydrophobic silk fibroin nanofiber membrane to form a preform, and then subjecting the preform to hot pressing. The hot pressing temperature is any value between 55°C and 65°C, i.e., the temperature can be 55°C, 60°C, or 65°C, or any value between 55°C and 60°C. Other values ​​include pressure values ​​between 0.3 MPa and 0.8 MPa (i.e., pressure can be 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, or 0.8 MPa, or any other value between 0.3 MPa and 0.8 MPa), and hot-pressing times between 5 s and 30 s (i.e., hot-pressing times can be 5 s, 10 s, 15 s, 20 s, 25 s, or 30 s, or any other value between 5 s and 30 s). Through the coordinated control of the above hot-pressing composite process parameters, each layer of the nanofiber membrane achieves a robust integrated composite while maintaining its original pore structure and wettability differences. This allows the multilayer silk fibroin nanofiber membrane and the absorbent layer 20 to form a structurally stable, continuously pore-filled, and functionally synergistic overall structure within a single composite unit, providing a reliable structural guarantee for subsequent efficient liquid conduction, rapid absorption, in-situ locking, and leak-proof functions. Here, the spinning solution used to prepare the nanofiber membrane in the hydrophilic silk fibroin nanofiber layer 50 is a hydrophilic silk fibroin spinning solution, and the spinning solution used to prepare the nanofiber membrane in the hydrophobic silk fibroin nanofiber layer 40 is a hydrophobic silk fibroin spinning solution.

[0057] Furthermore, the hot-pressing temperature is any value between 55℃ and 65℃, which moderately softens the surface of the silk fibroin nanofibers without melting or structural collapse, making the fibers deformable at the interface. This facilitates the adhesion and embedding of fibers between adjacent layers. The hot-pressing temperature, combined with a hot-pressing pressure of 0.3MPa-0.8MPa, allows the upper and lower nanofibers to form a stable physical entanglement and mechanical bonding structure at the interface, thereby significantly improving the overall structural stability and interlayer bonding strength of the composite core. At the same time, it avoids excessive compaction of the nanofiber network, maximizing the preservation of the porous structure and continuous channels. In addition, controlling the hot-pressing time within the range of 5s-30s ensures sufficient interlayer bonding while avoiding prolonged heating or pressure that could lead to pore closure, reduced wettability differences, or decreased unidirectional flow properties of the silk fibroin nanofibers. This helps maintain the predetermined wettability gradient and capillary driving conditions between the hydrophobic silk fibroin nanofiber layer 40 and the hydrophilic silk fibroin nanofiber layer 50.

[0058] In this embodiment, the concentrations of the hydrophilic and hydrophobic silk fibroin spinning solutions are any values ​​between 5wt% and 15wt%. That is, the concentration of silk fibroin in the spinning solution can be 5wt%, 10wt%, 12wt%, or 15wt%, or any other value between 5wt% and 15wt%. This achieves a balance between the degree of molecular chain entanglement and solution fluidity, ensuring that the spinning solution does not cause fiber breakage or bead-like defects due to excessively low concentration during electrospinning, nor does it lead to spray instability or a significant increase in fiber diameter due to excessively high concentration. This is beneficial for obtaining continuous, uniform, and diameter-controllable nanofiber structures. Furthermore, constructing hydrophilic and hydrophobic silk fibroin spinning solutions within the same concentration range helps to attribute wettability differences primarily to molecular structure regulation rather than morphological fluctuations introduced by concentration differences. This ensures comparability and interlayer synergy between different functional layers in terms of fiber scale and pore structure, improving the overall structural stability of the nanofiber membrane, the wettability gradient regulation effect, and the absorption / barrier function.

[0059] In a further embodiment, the amount of sodium hyaluronate used in the absorbent layer 20 is 20 g / m². 2 -80g / m 2 Any value, that is, the amount of sodium hyaluronate used in absorbent layer 20, can be 20 g / m 2 30g / m 2 40g / m 2 50g / m 2 60g / m 2 70g / m 2 Or 80g / m 2 It can also be 20g / m 2 -80g / m 2 The molecular weight can be any value between 1000KDa and 3000KDa, meaning the molecular weight of sodium hyaluronate can be 1000KDa, 1500KDa, 2000KDa, 2500KDa, or 3000KDa, or any other value between 1000KDa and 3000KDa. By synergistically limiting the amount and molecular weight of sodium hyaluronate within the above range, the absorbent layer 20 can effectively cooperate with the hydrophilic / hydrophobic silk fibroin nanofiber layers 40 on both sides. Sodium hyaluronate can quickly receive the liquid flowing unidirectionally from the nanofiber layer and gel in situ, achieving concentrated absorption and locking of the liquid. At the same time, the gel layer formed by sodium hyaluronate can also serve as an internal barrier structure, further inhibiting the reverse permeation of liquid to the outer layer. Thus, working together with the unidirectional flow structure of the nanofiber layer, the composite absorbent pad 100 achieves efficient absorption, backflow prevention, and leakage prevention within a single structural unit.

[0060] In this embodiment, the amount of sodium hyaluronate in the absorbent layer 20 is controlled at 20 g / m². 2-80g / m 2 Within a certain range, the sodium hyaluronate can rapidly absorb water and undergo in-situ swelling and gelation upon contact with body fluids, thereby forming a stable hydrogel structure within the absorbent layer 20. This dosage range ensures that the absorbent layer 20 has sufficient liquid absorption capacity to quickly receive the liquid introduced by the upper hydrophilic silk fibroin nanofiber layer 50, while avoiding the problems of excessive gel layer thickness, increased core rigidity, or liquid retention on the surface caused by excessive sodium hyaluronate dosage. This facilitates efficient absorption and water retention while maintaining the thinness of the core. Simultaneously, limiting the molecular weight of sodium hyaluronate to the range of 1000 kDa-3000 kDa allows it to form a three-dimensional gel network with high cohesion and stability during water absorption, effectively locking in the liquid and preventing backflow. This avoids insufficient gel strength and easy liquid migration due to excessively low molecular weight, or reduced swelling rate and slower absorption response due to excessively high molecular weight. This molecular weight range helps to achieve a balance between absorption rate and water retention capacity, ensuring that the liquid is quickly fixed after entering the absorbent layer 20.

[0061] In a further embodiment, the concentration of calcium chloride in the calcium chloride / formic acid binary solvent system is any value between 4wt% and 10wt%, i.e., the calcium chloride concentration can be 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, or any other value between 4wt% and 10wt%. This ensures that the calcium chloride / formic acid binary solvent system fully disrupts the hydrogen bond network of silk fibroin, ensuring the formation of a uniform and stable spinning solution, and obtaining a nanofiber membrane with uniform fiber morphology and no beading defects. Specifically, an appropriate amount of calcium chloride can effectively disrupt the hydrogen bonds and some crystalline structures between silk fibroin molecules, improve the solubility and solution stability of silk fibroin in the formic acid system, and avoid the formation of gels or particles due to insufficient dissolution, thereby ensuring the uniformity of the spinning solution. Meanwhile, calcium chloride within the above concentration range will not cause excessive degradation or chain segment breakage of silk fibroin molecules, and can maintain a high molecular weight and good molecular entanglement state, so that the resulting spinning solution has suitable viscosity and conductivity, thereby forming a continuous, uniform diameter and fewer defects nanofiber structure during electrospinning, which is conducive to constructing a stable hydrophobic silk fibroin nanofiber layer 40 and improving its mechanical properties and structural integrity.

[0062] In a further embodiment, the protease used in the enzymatic hydrolysis reaction is selected from one or more of trypsin, α-chymotrypsin, pepsin, alkaline protease, papain, and proteinase K. Through the synergistic or selective effects of different proteases on the cleavage sites of silk fibroin peptide chains and differences in reaction conditions, the molecular weight distribution and structural composition of the regenerated silk fibroin can be controllably adjusted. In this embodiment, enzymatic hydrolysis can partially break the high molecular weight chains of silk fibroin, reduce its molecular weight, and weaken strong intermolecular hydrogen bonds and crystalline regions, thereby promoting subsequent solubility and solution homogeneity in the calcium chloride / formic acid system. Furthermore, the use of different proteases or combinations thereof helps to avoid excessive degradation caused by a single enzymatic hydrolysis method, allowing the silk fibroin to maintain a certain molecular length and molecular entanglement ability while obtaining a narrower or more suitable molecular weight distribution. This results in a spinning solution with good rheological properties and stability, ultimately facilitating the formation of a continuous, morphologically controllable hydrophobic silk fibroin nanofiber layer 40 during electrospinning, and improving its film-forming quality and functional consistency.

[0063] In this embodiment, the mass ratio of protease to silk fibroin in the regenerated silk fibroin solution is any value between 1:50 and 1:500, i.e., the mass ratio can be 1:50, 1:100, 1:200, 1:300, 1:400, or 1:500, or any other value between 1:50 and 1:500. The enzymatic hydrolysis temperature is any value between 35℃ and 45℃, i.e., the enzymatic hydrolysis temperature can be 35℃, 40℃, or 45℃, or any value between 35℃ and 45℃. Other values, the enzymatic hydrolysis reaction time can be any value between 8h and 36h, that is, the enzymatic hydrolysis reaction time can be 8h, 10h, 20h, 30h, or 36h, or any other value within 8h-36h. This allows for precise control of the molecular chain length and molecular weight distribution of silk fibroin while avoiding excessive hydrolysis, transforming silk fibroin from a high molecular weight state to a medium molecular weight range suitable for processing. This effectively weakens strong intermolecular forces and improves the solubility and homogeneity of the system. At the same time, this parameter range is beneficial for maintaining the integrity of the silk fibroin backbone structure and the molecular entanglement ability required for subsequent fiber formation. The resulting enzymatic hydrolysis product exhibits stable rheological properties during subsequent dissolution and spinning, which in turn helps to prepare silk fibroin nanofiber layers with good fiber continuity, uniform morphology, and stable performance.

[0064] In this embodiment, the composite absorbent pad 100 is suitable for hygiene care, medical dressings and other applications requiring liquid management. It can effectively inhibit liquid backflow while ensuring rapid absorption, thereby improving overall absorption efficiency and dryness during use.

[0065] like Figure 2 As shown, the present invention also provides a method for preparing the above-mentioned composite absorbent pad 100, comprising the following steps: Step S100: Dissolve degummed silk fibroin in a calcium chloride / formic acid binary solvent system to prepare a hydrophilic silk fibroin spinning solution; Step S200: The regenerated silk fibroin solution is enzymatically hydrolyzed to obtain a precipitate, and then the precipitate is dissolved in a calcium chloride / formic acid binary solvent system to prepare a hydrophobic silk fibroin spinning solution. Step S300: The hydrophilic silk fibroin spinning solution and the hydrophobic silk fibroin spinning solution are injected into the electrospinning device for spinning to prepare the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40, respectively. Step S400: The hydrophobic silk fibroin nanofiber membrane, the hydrophilic silk fibroin nanofiber membrane, the absorbent layer 20, the hydrophilic silk fibroin nanofiber membrane and the hydrophobic silk fibroin nanofiber membrane are sequentially stacked to form a preform, and the preform is subjected to hot pressing treatment to prepare the composite absorbent pad 100.

[0066] In this embodiment, through the synergistic effect of the above steps, hydrophilic / hydrophobic functional differentiation, nanofiber structure construction and multilayer composite molding can be completed sequentially within the same silk fibroin material system. This realizes a continuous technical path from molecular-level regulation, nanoscale structural design to stable integration of macroscopic composite structures, enabling the resulting composite absorbent pad 100 to simultaneously possess directional flow guidance, high-efficiency absorption, liquid locking and leak-proof functions while maintaining biosafety and material consistency.

[0067] In step S100, silk fibroin is composed of 18 amino acid residues. Its molecular structure consists of alternating highly ordered crystalline regions and loosely ordered amorphous regions. The crystalline regions are mainly formed by the repeating arrangement of amino acids with small side groups, such as glycine, alanine, and serine, exhibiting regular structure and hydrophobicity. The amorphous regions are rich in hydrophilic amino acids with larger side groups. Conventional degummed silk fibers dissolved in a calcium chloride / formic acid binary solvent system yield a hydrophilic silk fibroin spinning solution. The silk fibroin nanofiber layer obtained after electrospinning is hydrophilic. That is, by directly dissolving degummed silk fibroin in a calcium chloride / formic acid binary solvent system, the integrity of the silk fibroin molecular chain and the full exposure of hydrophilic groups are maintained, resulting in a stable and homogeneous hydrophilic silk fibroin spinning solution. This lays the foundation for the subsequent electrospinning to form a nanofiber layer with high wettability and high capillary driving force, ensuring rapid wetting and introduction of the liquid from the source.

[0068] In step S200, the degummed fibers are dissolved and purified to obtain a regenerated silk fibroin solution. The regenerated silk fibroin is then enzymatically hydrolyzed by a specific protease, cleaving the connection sites between the crystalline and amorphous regions of the silk fibroin. The hydrolysate is separated into a supernatant and a precipitate layer. The supernatant mainly consists of water-soluble amorphous fragments, while the precipitate layer is composed of crystalline regions with highly repetitive and regular GAGAGS sequences at their core. Because the GAGAGS fragments do not contain large side chain groups, they can form the lowest-energy antiparallel β-sheet conformation through close packing via hydrogen bonds. This gives the precipitate a regular structure and hydrophobic properties. Consequently, the precipitate layer, when dissolved in a calcium chloride / formic acid binary solvent system, yields a hydrophobic silk fibroin spinning solution. The resulting silk fibroin nanofiber membrane obtained after electrospinning is also hydrophobic.

[0069] In step S200, the regenerated silk fibroin solution is enzymatically hydrolyzed and redissolved to regulate the molecular weight distribution and secondary structure of the silk fibroin, reduce the proportion of hydrophilic groups and enhance hydrophobic interactions, thereby preparing a hydrophobic silk fibroin spinning solution without introducing an external hydrophobic modifier. This achieves functional differentiation from hydrophilic spinning solutions in terms of material properties and provides conditions for constructing wettability gradients and unidirectional flow interfaces.

[0070] In step S300, electrospinning is used to spin hydrophilic silk fibroin spinning solution and hydrophobic silk fibroin spinning solution respectively, so that silk fibroin with different wetting properties is solidified into a film in the form of a continuous nanofiber network, forming hydrophilic and hydrophobic nanofiber layers with controllable fiber diameter, pore size and pore structure. This constructs an interface structure with significant differences in wetting properties at the nanoscale, providing a physical and interface basis for the directional transport of liquids.

[0071] In step S400, by sequentially stacking the hydrophobic silk fibroin nanofiber membrane, the hydrophilic silk fibroin nanofiber membrane, the absorbent layer 20, and their symmetrical structure, and then hot-pressing them, each functional layer achieves a stable integrated combination while maintaining a porous structure. This forms an overall structure in which the upper and lower symmetrical composite functional layers work synergistically with the middle absorbent layer 20. Thus, in a single composite absorbent pad 100, rapid liquid flow, efficient absorption, in-situ locking, and reverse osmosis inhibition are comprehensively achieved, significantly improving the overall performance and reliability of the composite absorbent pad 100.

[0072] In steps S100 and S200, in the preparation method of degummed silk fibroin, silk is first added to a Na2CO3 solution of a preset mass concentration and boiled for a preset time. After being taken out, it is washed and dried to obtain degummed silk fibroin.

[0073] In step S200, in the method for preparing the regenerated silk fibroin solution, degummed silk fibroin is dissolved in a lithium bromide solution of a preset concentration, and after dialysis purification, a regenerated silk fibroin solution of a preset concentration is obtained.

[0074] The technical solution of this application will be further described below with reference to specific embodiments.

[0075] Example 1 The preparation method of composite absorbent pad 100 includes the following steps: Step S100: Dissolve degummed silk fibroin in a 4wt% calcium chloride / formic acid binary solvent system to prepare a 5wt% hydrophilic silk fibroin spinning solution; Step S200: The regenerated silk fibroin solution is subjected to trypsin enzymatic hydrolysis to obtain a precipitate, and then the precipitate is dissolved in a 4wt% calcium chloride / formic acid binary solvent system to prepare a 5wt% hydrophobic silk fibroin spinning solution. Step S300: The hydrophilic silk fibroin spinning solution is injected into the electrospinning device for spinning. The electrospinning device has a feed rate of 0.3 mL / h, an applied voltage of 18 kV, and a receiving distance of 18 cm to prepare a hydrophilic silk fibroin nanofiber layer 50 with a porosity of 75%, an average pore size of 1.5 μm, and an average diameter of 400 nm. Hydrophobic silk fibroin spinning solution was injected into an electrospinning device for spinning. The electrospinning device had a feed rate of 0.6 mL / h, an applied voltage of 16 kV, and a receiving distance of 14 cm to prepare a hydrophobic silk fibroin nanofiber layer 40 with a porosity of 65%, an average pore size of 3 μm, and an average nanofiber diameter of 600 nm. Step S400: A preform is formed by sequentially stacking a hydrophobic silk fibroin nanofiber membrane, a hydrophilic silk fibroin nanofiber membrane, an absorbent layer 20, a hydrophilic silk fibroin nanofiber membrane, and a hydrophobic silk fibroin nanofiber membrane, and then hot-pressing the preform at a temperature of 60°C, a pressure of 0.5 MPa, and a hot-pressing time of 15 s, to obtain a composite absorbent pad 100 comprising a first composite functional layer 10, an absorbent layer 20, and a second composite functional layer 30 arranged sequentially from bottom to top. In the composite absorbent pad 100, the absorbent layer 20 is sodium hyaluronate powder, and the amount of sodium hyaluronate powder used is 40g / m². 2 The molecular weight is 1500 kDa. The static contact angle of the hydrophilic silk fibroin nanofiber layer 50 with water is 50°, and the static contact angle of the hydrophobic silk fibroin nanofiber layer 40 with water is 100°.

[0076] Figure 3 This is a scanning electron microscope image of the hydrophilic silk fibroin nanofiber layer according to Example 1 of the present invention. Figure 4 This is a scanning electron microscope image of the hydrophobic silk fibroin nanofiber layer according to Example 1 of the present invention. Figure 5 This is the Fourier transform infrared spectrum of the hydrophobic silk fibroin nanofiber layer in Example 1 of the present invention.

[0077] First, scanning electron microscopy was performed on the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 in the composite absorbent pad 100, and the results were as follows: Figures 3 to 4 The scanning electron microscope image shown.

[0078] like Figure 3 and Figure 4 As shown in the scanning electron microscope images, both the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 exhibit a three-dimensional network porous structure with uniform pore distribution and nanofiber diameter distribution. This indicates that the electrospinning process parameters used in this embodiment can achieve stable fiber formation and controllable deposition of silk fibroin nanofibers. The prepared nanofiber membrane has a complete and uniform structure with a consistent microstructure. Furthermore, the uniform three-dimensional porous network structure in Example 1 facilitates the formation of continuous and stable liquid transport channels on a macroscopic scale, providing structural assurance for the subsequent rapid liquid introduction, uniform diffusion, and interlayer synergistic transport. It also lays a repeatable and controllable microstructural foundation for the differentiated wetting behavior of the hydrophilic and hydrophobic silk fibroin nanofiber layers 40.

[0079] Next, the hydrophobic silk fibroin nanofiber layer 40 in Example 1 was characterized by Fourier transform infrared spectroscopy, and the results were as follows: Figure 5 The test results are shown.

[0080] like Figure 5 As shown, according to Fourier transform infrared spectroscopy, the hydrophobic silk fibroin nanofiber layer 40 has a wavelength of 1620 cm⁻¹. -1 Amide I band and 1520cm -1 The presence of a significant β-sheet characteristic peak at the amide II band indicates a transformation of silk fibroin molecules from a random coil or α-helix conformation to a β-sheet conformation. This results in a more ordered chain segment arrangement and a significantly enhanced intermolecular hydrogen bond network. At the molecular structural level, this confirms that the hydrophobicity of the nanofiber layer originates from the increased proportion of β-sheet crystalline regions, leading to structural densification and reduced exposure of polar groups, rather than relying on exogenous hydrophobic modification. The increased β-sheet content further endows the hydrophobic silk fibroin nanofiber layer 40 with higher crystallinity, lower swelling rate, and stronger mechanical stability, making it less prone to swelling or structural collapse in liquid environments. This allows it to stably function as an anti-backflow and reverse wetting functional layer in the composite absorbent pad 100. This demonstrates that sodium hyaluronate and the hydrophobic silk fibroin nanofiber layer 40 synergistically construct a sandwich composite structure of a hydrophobic stable framework and a durable hydrophilic transport channel, providing structural and mechanistic support for unidirectional flow guidance and long-term leak-proof performance.

[0081] To verify the hydrophilic properties of the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 in Example 1, the hydrophilic contact angle of the two layers was tested. Specifically, a Dataphysics OCA series contact angle meter was used for the tests at room temperature. 5 μL of ultrapure water was dropped onto the surface of each sample, and the static morphology of the droplet was recorded using a high-speed camera. The contact angle value was calculated by automatically fitting the droplet profile using testing software. Five different locations were tested for each sample, and the average value was taken as the final test result.

[0082] Test results show that the static contact angle of the hydrophilic silk fibroin nanofiber layer 50 with water is about 50°, and the static contact angle of the hydrophobic silk fibroin nanofiber layer 40 with water is about 100°. A stable static contact angle difference of about 50° is formed between the two, indicating that by regulating the molecular structure of silk fibroin and the configuration of nanofibers, significant hydrophilic and hydrophobic functional differentiation can be achieved without introducing exogenous hydrophobic modifiers. This wettability gradient can exist continuously inside the composite absorbent pad 100 and drive the liquid to be transported rapidly in a preset direction, while effectively limiting reverse permeation.

[0083] To verify the absorption and leak-proof performance of the composite absorbent pad 100 in Example 1, the absorption ratio and absorption rate of the composite absorbent pad 100 were evaluated according to GB / T 28004-2011 standard. The results showed that the composite absorbent pad 100 in Example 1 had an absorption ratio of 8.5 g / g under deionized water conditions and reached 65 g / g under 0.9% NaCl solution conditions, demonstrating highly efficient absorption of electrolyte-containing liquids. When using 5 mL of methylene blue solution as the test medium, the absorption time was 18 s, indicating that the liquid could be quickly introduced and locked in the absorbent layer 20, effectively reducing surface residue and backflow risks, demonstrating excellent rapid absorption and leak-proof performance. Each sample was tested 5 times, and the average value was taken as the final test result.

[0084] Figure 6 This is a photograph of the leak-proof effect according to Embodiment 1 of the present invention. Figure 7 This is a physical image illustrating the leak-proof effect of Comparative Example 1 according to the present invention.

[0085] Furthermore, to verify the leak-proof performance of the composite absorbent pad 100, a slope test was conducted: 5 mL of methylene blue solution was added dropwise to the core center of the composite absorbent pad 100 prepared in Example 1 and Comparative Example 1, respectively, and the pads were placed on a 15° slope and left to stand for 10 minutes. The composite absorbent pad 100 prepared in Example 1 showed zero side leakage and zero backflow (refer to...). Figure 6 In contrast, the composite absorbent pad 100 in Comparative Example 1 exhibited significant edge backflow and side leakage (see reference). Figure 7This indicates that the composite absorbent pad 100 of Example 1 has excellent leak-proof performance. Each test sample was tested 5 times, and the average value was taken as the final test result.

[0086] Next, the humidity response deformation performance of the composite absorbent pad 100 was tested. The thickness change of the core after local wetting was measured using a laser displacement sensor. It was found that the thickness of the wetting area expanded to 120% of the original thickness within 3 minutes. The expansion mainly occurred in the thickness direction, and the expansion in the planar direction was less than 5%, which confirmed the directional controllable expansion characteristics.

[0087] In the antibacterial performance test of the composite absorbent pad 100, the shaking method was used and GB / T 20944.3-2008 was referenced. The results showed that the composite absorbent pad 100 had an inhibition rate of 99.92% against Escherichia coli (ATCC 25922) and an inhibition rate of 99.87% against Staphylococcus aureus (ATCC6538). This indicates that the composite absorbent pad 100 of Example 1 can achieve a very high inhibition rate without the addition of any antibacterial additives and has strong antibacterial properties.

[0088] Biocompatibility testing was conducted on the composite absorbent pad 100. The cytotoxicity of the material was evaluated using the MTT assay, with L929 mouse fibroblasts as the test cells. Results showed that the relative cell proliferation rates after 24 h and 72 h of treatment with the material extract were 98% and 105%, respectively, both exceeding the cytotoxicity assessment threshold, corresponding to a grade 1 cytotoxicity rating. This indicates that the composite absorbent pad 100 has no significant cytotoxicity and possesses good cell compatibility and biosafety.

[0089] In the performance test of the composite absorbent pad 100 on skin irritation, a closed patch test was conducted using domesticated rabbits. Specifically, using domesticated rabbits as experimental animals, the test sample was applied to the intact skin surface of the rabbit's back in a closed manner for a certain period of time to simulate the continuous contact between the material and the skin during actual use. After the application, the degree of skin reaction such as erythema and edema at the application site was observed and recorded at specified time points, and the primary irritation index (PII) was calculated according to the standard scoring method.

[0090] Test results show that the primary irritation index (PII) of the composite absorbent pad 100 in Example 1 is 0.2, which is lower than the skin irritation threshold. The evaluation result is non-irritating, indicating that the composite absorbent pad 100 will not cause obvious irritation during contact with the skin, has good skin compatibility, and is suitable for long-term use.

[0091] The biodegradability of the composite absorbent pad 100 in Example 1 was tested using the composting method according to ISO 14855-1:2012 standard. The test results showed that the composite absorbent pad 100 in Example 1 exhibited good biodegradability under composting conditions, with a 28-day biodegradation rate of 45%, a 90-day biodegradation rate of 82%, and a 180-day biodegradation rate reaching 95%, demonstrating a continuous increase in biodegradability over time. This indicates that the composite absorbent pad 100 in this example possesses high biocompatibility.

[0092] Example 2 The only difference between Example 2 and Example 1 is that the static contact angle of the hydrophilic silk fibroin nanofiber layer 50 with water is 50°, the static contact angle of the hydrophobic silk fibroin nanofiber layer 40 with water is 60°, and the difference in static contact angle between two adjacent nanofiber layers with water is 30°.

[0093] Example 3 The only difference between Example 3 and Example 1 is that the hydrophilic silk fibroin nanofiber layer 50 has a porosity of 60%, an average pore size of 1.5 μm, and an average diameter of 400 nm, while the hydrophobic silk fibroin nanofiber layer 40 has a porosity of 60%, an average pore size of 3 μm, and an average nanofiber diameter of 600 nm.

[0094] Example 4 The only difference between Example 4 and Example 1 is that the hot pressing temperature is 55°C, the pressure is 0.3 MPa, and the hot pressing time is 5 seconds.

[0095] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the hot pressing temperature is 50°C, the pressure is 0.2 MPa, and the hot pressing time is 5 seconds.

[0096] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the hot pressing temperature is 50°C, the pressure is 1.0 MPa, and the hot pressing time is 5 seconds.

[0097] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 have the same static contact angle with water.

[0098] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the hydrophilic silk fibroin nanofiber layer 50 has a porosity of 50%, an average pore size of 1.5 μm, and an average diameter of 1000 nm, while the hydrophobic silk fibroin nanofiber layer 40 has a porosity of 55%, an average pore size of 3 μm, and an average nanofiber diameter of 900 nm.

[0099] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the hydrophilic silk fibroin nanofiber layer 50 has a porosity of 95%, an average pore size of 1.5 μm, and an average diameter of 90 nm, while the hydrophobic silk fibroin nanofiber layer 40 has a porosity of 95%, an average pore size of 3 μm, and an average nanofiber diameter of 100 nm.

[0100] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the hydrophilic silk fibroin nanofiber layer 50 has a porosity of 40%, an average pore size of 1.5 μm, and an average diameter of 100 nm, while the hydrophobic silk fibroin nanofiber layer 40 has a porosity of 40%, an average pore size of 3 μm, and an average nanofiber diameter of 300 nm.

[0101] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is that the amount of sodium hyaluronate powder used is 20 g / m³. 2 The molecular weight is 800 kDa.

[0102] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is that the amount of sodium hyaluronate powder used is 10 g / m³. 2 The molecular weight is 1500 kDa.

[0103] Table 1 lists the results of various embodiments and comparative examples of the present invention in multiple performance tests, including absorption rate, absorption time, horizontal wetting swelling rate, thickness wetting swelling rate, Escherichia coli inhibition rate, 24-hour relative proliferation rate, and 180-day biodegradation rate. The test data are shown in Table 1.

[0104]

[0105] Wherein, the absorption ratio refers to the absorption ratio of the composite absorbent pad 100 to 0.9% NaCl solution, the absorption time is the absorption time for the composite absorbent pad 100 to completely absorb 5 mL of methylene blue solution, the horizontal wetting expansion rate is the expansion rate of the wetting area of ​​the composite absorbent pad 100 in the horizontal direction, and the thickness wetting expansion rate is the expansion rate of the wetting area of ​​the composite absorbent pad 100 in the thickness direction.

[0106] As shown in Table 1, firstly, regarding the wettability gradient, in Examples 1-4, the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 satisfy the condition that the contact angle of the hydrophilic layer is smaller than that of the hydrophobic layer and the difference is ≥30°. This indicates that a stable surface energy gradient is constructed between the layers, which can drive the liquid to migrate directionally from the hydrophobic side to the hydrophilic side, thereby achieving unidirectional flow and inhibiting backflow. Among them, Example 1 has the largest contact angle difference, the strongest flow driving force, and the best backflow prevention ability. Although Example 2 still satisfies the difference ≥30°, the contact angle of the hydrophobic layer is reduced to 60°, indicating that the hydrophobic barrier ability is weakened, so the absorption ratio and backflow prevention performance are slightly reduced. In Comparative Example 3, the two layers have the same contact angle, and no wettability gradient is formed, indicating that the liquid diffuses in a non-directional state in the structure, resulting in a significant deterioration in the absorption ratio, absorption time, and leakage prevention performance, directly verifying the necessity of the wettability gradient structure.

[0107] Secondly, regarding the nanofiber layer pore structure, in Example 1, the porosity and fiber diameter of the hydrophilic silk fibroin nanofiber layer 50 and the hydrophobic silk fibroin nanofiber layer 40 form a multi-scale gradient structure consisting of fine fibers, a high-porosity flow-conducting layer / coarse fibers, and a low-porosity barrier layer. This indicates that it can provide strong capillary driving force for rapid introduction and also suppress collapse and backflow through structural support. In Example 3, the porosity of both layers decreased to 60% and the fiber diameter increased, indicating that the capillary effect weakened and the number of channels decreased. Therefore, the absorption rate and flow-conducting efficiency decreased slightly, but were still better than the comparative examples. In Comparative Examples 4-6, the porosity or fiber diameter deviated significantly from the parameter range set in this application. That is, too low a value resulted in insufficient channels, and too high a value resulted in a loose structure or decreased capillary force. This indicates that the flow-conducting and liquid-locking functions could not be achieved synergistically, leading to prolonged absorption time, increased expansion rate, and decreased absorption rate.

[0108] Furthermore, regarding the absorbent layer parameters, the amount of sodium hyaluronate used in Example 1 was 40 g / m². 2 The molecular weight of 1500 kDa indicates that the composite absorbent pad 100 in Example 1 has a high liquid absorption rate and a stable three-dimensional network structure, which can form a synergistic liquid storage system with the nanofiber layer. The reduced amount or molecular weight of the absorbent layer in Comparative Examples 7 and 8 indicates insufficient liquid storage space and network stability, resulting in a decrease in absorption rate, weakened liquid-locking ability, and reduced leakage prevention performance, verifying the key influence of absorbent layer parameters on overall performance.

[0109] Furthermore, regarding the interfacial hot-pressing bonding, the hot-pressing temperature of 60℃, pressure of 0.5MPa, and time of 15s in Example 1 indicate sufficient interlayer bonding without damaging the pore structure. In Example 4, the hot-pressing conditions were slightly lower, indicating a weakened interfacial bonding force, which led to a slight increase in absorption time and expansion rate. In Comparative Example 1, the temperature and pressure were too low, indicating insufficient interlayer bonding and poor structural stability. In Comparative Example 2, the pressure was too high, indicating that the pore structure underwent compaction or collapse, both of which resulted in decreased absorption performance and uncontrolled expansion.

[0110] In summary, all key parameters in Examples 1-4 are within the synergistic matching range, indicating that this application achieves a comprehensive effect of rapid absorption, unidirectional flow guidance, backflow prevention, and structural stability through a comprehensive design that utilizes wettability gradient driving, hierarchical pore structure for flow guidance, efficient sodium hyaluronate storage, and moderate thermo-pressing interface fixation. Among these, Example 1 exhibits the best parameter matching and performance. In contrast, at least one key parameter in Comparative Examples 1-8 deviates from a reasonable range, resulting in a significant decrease in absorption efficiency, leakage prevention capability, and structural stability.

[0111] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite absorbent pad, characterized in that, The system comprises a first composite functional layer, an absorbent layer, and a second composite functional layer, arranged sequentially from bottom to top. Both the first and second composite functional layers include a hydrophobic silk fibroin nanofiber layer and a hydrophilic silk fibroin nanofiber layer located on the side of the hydrophobic silk fibroin nanofiber layer closest to the absorbent layer. The absorbent layer is sodium hyaluronate. The static contact angle of the hydrophilic silk fibroin nanofiber layer with water is smaller than that of the hydrophobic silk fibroin nanofiber layer with water, and the difference in static contact angle between the hydrophilic and hydrophobic silk fibroin nanofiber layers is greater than or equal to 30°, so as to form a unidirectional flow from the hydrophobic silk fibroin nanofiber layer to the hydrophilic silk fibroin nanofiber layer.

2. The composite absorbent pad according to claim 1, characterized in that, The average pore size of the hydrophilic silk fibroin nanofiber layer is smaller than that of the hydrophobic silk fibroin nanofiber layer, and the average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer is smaller than that in the hydrophobic silk fibroin nanofiber layer.

3. The composite absorbent pad according to claim 2, characterized in that, The hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer are each composed of a nanofiber membrane, wherein the porosity of the nanofiber membrane is any value between 60% and 90%; wherein, The average diameter of the nanofibers in the hydrophilic silk fibroin nanofiber layer is any value between 100nm and 400nm, and the average pore size is any value between 0.1μm and 3μm. The average diameter of the nanofibers in the hydrophobic silk fibroin nanofiber layer is any value between 200nm and 600nm, and the average pore size is any value between 1μm and 5μm.

4. The composite absorbent pad according to claim 3, characterized in that, The hydrophilic silk fibroin nanofiber layer and / or the hydrophobic silk fibroin nanofiber layer are nanofiber layers formed by electrospinning with a silk fibroin spinning solution; wherein... The electrospinning process has a propulsion rate of 0.3 mL / h to 0.8 mL / h, an applied voltage of 15 kV to 20 kV, and a receiving distance of 12 cm to 18 cm between the spinning nozzle and the receiving device.

5. The composite absorbent pad according to claim 4, characterized in that, The composite absorbent pad is prepared by sequentially stacking the hydrophobic silk fibroin nanofiber layer, the hydrophilic silk fibroin nanofiber layer, the absorbent layer, the hydrophilic silk fibroin nanofiber layer, and the hydrophobic silk fibroin nanofiber layer to form a preform, and then subjecting the preform to hot pressing. The hot pressing treatment is performed at any temperature between 55℃ and 65℃, at any pressure between 0.3MPa and 0.8MPa, and for any hot pressing time between 5s and 30s.

6. The composite absorbent pad according to any one of claims 1-5, characterized in that, The amount of sodium hyaluronate used in the absorbent layer is 20 g / m². 2 -80g / m 2 Any value in the range, with a molecular weight of any value between 1000KDa and 3000KDa.

7. The composite absorbent pad according to claim 6, characterized in that, The hydrophobic silk fibroin nanofiber layer uses a silk fibroin spinning solution derived from a regenerated silk fibroin solution. After enzymatic hydrolysis to form a precipitate, the precipitate is dissolved in a calcium chloride / formic acid binary solvent system.

8. The composite absorbent pad according to claim 7, characterized in that, The concentration of calcium chloride in the calcium chloride / formic acid binary solvent system is any value between 4wt% and 10wt%.

9. The composite absorbent pad according to claim 8, characterized in that, The protease used in the enzymatic hydrolysis reaction is selected from one or more of trypsin, α-chymotrypsin, pepsin, alkaline protease, papain, and proteinase K.

10. The method for preparing the composite absorbent pad according to any one of claims 1-9, characterized in that, Includes the following steps: A hydrophilic silk fibroin spinning solution was prepared by dissolving degummed silk fibroin in a calcium chloride / formic acid binary solvent system. The regenerated silk fibroin solution was enzymatically hydrolyzed to obtain a precipitate, which was then dissolved in a calcium chloride / formic acid binary solvent system to prepare a hydrophobic silk fibroin spinning solution. The hydrophilic silk fibroin spinning solution and the hydrophobic silk fibroin spinning solution are respectively injected into an electrospinning device for spinning to prepare the hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer respectively. The hydrophobic silk fibroin nanofiber layer, the hydrophilic silk fibroin nanofiber layer, the absorbent layer, the hydrophilic silk fibroin nanofiber layer and the hydrophobic silk fibroin nanofiber layer are sequentially stacked to form a preform, and the preform is subjected to hot pressing treatment to obtain the composite absorbent pad.

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