A method for preparing a degradable medical abdominal pad

Abstract

The application relates to the technical field of medical dressings and discloses a preparation method of a degradable medical abdominal pad. The abdominal pad is made of a homogeneous precursor sol of polyvinyl alcohol, sodium carboxymethyl cellulose, D-sorbitol, anhydrous citric acid, itaconic acid, sodium hypophosphite monohydrate and ammonia water, and is prepared through cold freeze drying forming, thermal induced phase crosslinking and radiation crosslinking in sequence. In the preparation process, the homogeneous dispersion is maintained by neutralizing polycarboxylic acid with ammonia water, and a porous physical skeleton is constructed through freeze drying; then, heating is performed to decompose the ammonium salt and release ammonia gas, in-situ pore forming and catalytic dehydration esterification reaction are performed, and internal residues are removed through cyclic pulse degassing treatment; finally, high-energy rays are adopted to trigger addition polymerization of carbon-carbon double bonds. The application realizes stage triggering of chemical crosslinking and physical forming, constructs a double crosslinking network of ester bonds and carbon chains, improves the wet mechanical strength of the polysaccharide-based dressing after absorbing body fluid, and inhibits excessive swelling and disintegration.

Description

Technical Field

[0001] This invention relates to the field of medical dressing technology, specifically to a method for preparing a biodegradable medical abdominal pad. Background Technology

[0002] In surgical procedures, medical abdominal pads are commonly used to absorb wound exudate, stop bleeding, and isolate organs. Biodegradable medical sponges, based on polysaccharide polymers such as polyvinyl alcohol and sodium carboxymethyl cellulose, are widely used due to their excellent biocompatibility and absorbency. To prevent these water-soluble polymers from rapidly dissolving upon contact with bodily fluids, a chemical cross-linking mechanism is typically introduced during the manufacturing process.

[0003] Existing processes for preparing polysaccharide-based dressings often employ esterification and crosslinking with polycarboxylic acid crosslinking agents under acidic catalytic conditions. However, directly introducing an acidic system during the preparation and mixing of the precursor solution can lead to protonation of anionic groups on polysaccharide molecular chains such as sodium carboxymethyl cellulose. This change weakens the electrostatic repulsion between molecular chains, triggering disordered association of intermolecular hydrogen bonds, which in turn causes phase separation and premature gelation of the solution. This localized crosslinking in the liquid phase not only severely hinders the molding of homogeneous sols but also makes it difficult to form a uniform and stable porous framework structure during subsequent freeze-drying.

[0004] On the other hand, biodegradable sponges prepared using traditional processes often rely on a single cross-linked network. When the abdominal pad absorbs large amounts of blood or tissue exudate within the surgical cavity, this single network is insufficient to effectively restrict the slippage and disentanglement of the polymer macromolecular chains. This leads to uncontrolled volume swelling of the material in a humid environment, a significant decrease in mechanical strength, and even structural disintegration and fragmentation before the expected degradation cycle. This not only results in the loss of physical isolation and support functions but also increases medical safety risks.

[0005] Therefore, this invention proposes a method for preparing a biodegradable medical abdominal pad to address the shortcomings of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing a biodegradable medical abdominal pad, which solves the problems of strong acid catalysis leading to substrate phase separation, easy collapse of internal pore structure, excessive swelling and disintegration of material after absorption by body fluid, and insufficient wet mechanical strength in existing biodegradable polysaccharide-based medical dressings.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a biodegradable medical abdominal pad, which adopts the following technical solution:

[0009] A biodegradable medical abdominal pad, wherein the biodegradable medical abdominal pad is made of homogeneous precursor sol through freeze-drying molding, thermally induced phase crosslinking, and radiation crosslinking;

[0010] The homogeneous precursor sol is composed of a mixture of a phase A solution and a phase B solution comprising the following components by weight: 750-1100 parts purified water; 8-12 parts polyvinyl alcohol; and 65-75 parts sodium carboxymethyl cellulose.

[0011] The B-phase solution comprises the following components in parts by weight: 402.6–572.0 parts purified water; 10–15 parts D-sorbitol; 2–5 parts anhydrous citric acid; 2–4 parts itaconic acid; 1–3 parts sodium hypophosphite monohydrate; and 3.0–12.0 parts ammonia water suitable for adjusting the pH of the B-phase solution.

[0012] The amount of ammonia added is such that the pH value of the homogeneous precursor sol after mixing the A-phase solution and the B-phase solution is stabilized between 6.0 and 6.6. The specific amount of ammonia added depends on the actual amount of polycarboxylic acid components added and the slight pH fluctuations of the purified water, and is usually controlled between 3.0 and 12.0 parts by weight to ensure that the final pH value reaches the target value.

[0013] By adopting the above technical solution, using polyvinyl alcohol and sodium carboxymethyl cellulose as the basic framework, combined with a multi-component aqueous phase reaction system, and employing a dual curing method of thermally induced crosslinking and radiation crosslinking, a medical dressing material with a porous structure and high wet mechanical stability is obtained. The specific reaction process and principle are as follows:

[0014] During the initial liquid-phase mixing stage, anhydrous citric acid and itaconic acid, among other polycarboxylic acid components, in phase B solution neutralize with ammonia water to form their corresponding ammonium salts. The system pH is controlled within a slightly acidic range of 6.0–6.6. This environment prevents the carboxylate ions in the sodium carboxymethyl cellulose structure from protonating under low pH conditions, thus eliminating the risk of precipitation due to weakened electrostatic repulsion and hydrogen bonding between molecular chains. Consequently, the liquid-phase system maintains a homogeneous dispersion, preserving suitable rheological processing viscosity and high light transmittance.

[0015] As the system enters the freeze-drying and sublimation drying process, the internal moisture is gradually removed. At this time, D-sorbitol precipitates microcrystals at the interface of the polysaccharide polymer network, providing rigid physical support for the macromolecular skeleton to resist capillary contraction tension, and limiting the volume shrinkage and pore collapse that occur during the drying and dehydration process.

[0016] To impart a preliminary cross-linked structure to the material, the precursor was subsequently placed in a heated environment for thermally induced phase cross-linking. The increased system temperature caused the previously formed polycarboxylic acid ammonium salt to decompose thermally. Ammonia gas escaped from the ammonium salt network, constructing distributed and interconnected microporous channels in situ within the polymer matrix. Simultaneously, the ammonia gas release caused the reaction microenvironment to release protons, resulting in a rapid decrease in pH and the formation of a locally acidic catalytic environment. Under spontaneously formed acidic conditions and the reducing catalysis of sodium hypophosphite monohydrate, the carboxyl groups of anhydrous citric acid and itaconic acid underwent a dehydration esterification reaction with the hydroxyl groups on the main chain and side chains of polyvinyl alcohol and sodium carboxymethyl cellulose macromolecules. The basic reaction formula is as follows:

[0017] R-COOH + R'-OH → R-COOR' + H2O;

[0018] This esterification process constructs the first thermocovalently crosslinked network for the polysaccharide substrate.

[0019] However, a single esterification network is insufficient to cope with the complex environment of bodily fluid infiltration. Considering that the itaconic acid molecule contains active carbon-carbon double bonds that have not participated in the esterification reaction, this invention utilizes high-energy rays to trigger the opening of carbon-carbon double bonds on the itaconic acid monomers within the crosslinking network during the later radiation crosslinking stage, generating polymeric free radicals. These free radicals further initiate addition polymerization reactions between double bonds, adding direct carbon chain covalent crosslinking nodes within the primary ester bond network, forming a second-layer solidification network. This dual crosslinking mechanism effectively restricts the slippage and disentanglement of polysaccharide molecular chains in the bodily fluid contact environment, controls the mass loss rate of the material in simulated bodily fluids, and improves wet tensile strength.

[0020] Preferably, the polyvinyl alcohol has an average degree of polymerization of 500-600 and a degree of alcoholysis of 87.0%-89.0%; the sodium carboxymethyl cellulose has a degree of substitution of 0.7-0.9 and a dynamic viscosity of 2 wt% aqueous solution of sodium carboxymethyl cellulose at 25°C of 200-500 mPa·s.

[0021] By adopting the above technical solution, polyvinyl alcohol with a specific degree of polymerization and degree of hydrolysis provides sufficient free hydroxyl groups to participate in the esterification reaction during the thermal crosslinking stage, while also taking into account the water solubility after gelation; sodium carboxymethyl cellulose with a degree of substitution and dynamic viscosity limited within the above range ensures the rheological properties of the homogeneous precursor sol in the degassing process, prevents excessively high viscosity from hindering the migration of internal entrained gas to the liquid surface, improves physical degassing efficiency, and reduces the residual rate of molding bubbles.

[0022] Preferably, the mass fraction of the ammonia water is 25wt% to 28wt%; and the total solid content of the homogeneous precursor sol is controlled to be 5.0wt% to 9.0wt%.

[0023] By employing the above technical solution, the pH value of the system can be adjusted using a limited mass fraction of ammonia water without introducing excessive free water; the total solid content is set in the range of 5.0wt% to 9.0wt%, maintaining the three-dimensional skeleton density of the sponge substrate after drying and molding. A solid content below 5.0wt% will lead to insufficient skeleton support material, causing significant volume shrinkage, while a content above 9.0wt% will cause a surge in sol rheological viscosity, hindering the molecular-level dispersion of liquid phase raw materials.

[0024] Secondly, the present invention provides a method for preparing a biodegradable medical abdominal pad, which adopts the following technical solution:

[0025] A method for preparing a biodegradable medical abdominal pad includes the following steps:

[0026] S1. Prepare phase A solution and phase B solution respectively, mix phase A solution and phase B solution and let stand to remove bubbles to obtain homogeneous precursor sol;

[0027] S2. Inject the homogeneous precursor sol into the mold, and then subject the homogeneous precursor sol to pre-freezing and vacuum drying to obtain a porous sponge.

[0028] S3. The porous sponge after vacuum drying is placed in a closed reaction chamber and thermally activated under normal pressure exhaust. Then, the porous sponge is subjected to alternating vacuuming and vacuum breaking treatment with inert gas. After the cyclic pulse treatment is completed, it is naturally cooled out of the chamber to obtain the cooled porous sponge.

[0029] S4. After the cooled porous sponge is cut and sealed, it is irradiated with high-energy rays to trigger the addition polymerization of carbon-carbon double bonds in itaconic acid in the cooled porous sponge, thus obtaining a biodegradable medical abdominal pad.

[0030] By adopting the above technical solution, the core of this method lies in separating chemical crosslinking from physical molding and triggering it in stages in subsequent steps. This design avoids the problem of traditional polysaccharide gels failing to be molded due to crosslinking occurring during the liquid-phase mixing stage. The specific preparation mechanism and process are as follows:

[0031] In the initial liquid-phase mixing and freeze-forming process, ammonia water is used to mask the polycarboxylic acid molecules in the system, ensuring that the mixture remains in a homogeneous dispersion state. During the pre-freezing treatment of the homogeneous precursor sol, internal water crystals form ice nuclei, and the subsequent vacuum drying process causes the ice crystals to vaporize directly, leaving a porous physical framework inside the substrate.

[0032] After the porous framework is formed, it needs to be cured and purified through thermally induced phase crosslinking and pulsed degassing. Heating induces the thermal decomposition of the polycarboxylic acid ammonium salt network, releasing ammonia and protons. The protons catalyze the esterification reaction between hydroxyl and carboxyl groups, constructing a primary thermally crosslinked network. It is important to note that the free ammonia released during the crosslinking process tends to remain deep within the porous medium with its high specific surface area, and simple atmospheric pressure convection is insufficient to overcome the gas diffusion resistance within the porous network. Therefore, a cyclic pulse treatment is introduced into the process to establish periodic pressure difference changes inside the closed reaction chamber. Vacuuming forces the volatile ammonia trapped in the deep micropores of the porous sponge to diffuse outward, while inert gas filling to break the vacuum introduces inert gas into the pores for gas phase replacement. Repeated alternating cycles reduce the residual ammonia content inside the material and eliminate oxygen in the chamber, inhibiting the oxidative browning reaction of polysaccharide macromolecules under high-temperature conditions.

[0033] As a final reinforcement method, high-energy rays penetrate the packaging material, simultaneously sterilizing itaconic acid monomers on the macromolecular chain. Under the influence of the ray energy, the carbon-carbon double bonds in itaconic acid generate polymeric free radicals, initiating an addition polymerization reaction between the double bonds. The chemical reaction process of double bond polymerization can be represented as follows:

[0034] nCH2=C(COOH)-CH2-COOH→-[CH2-C(COOH)(CH2COOH)] n -;

[0035] This reaction establishes a second carbon chain network based on the first esterification network, which increases the cohesive force of the polymer skeleton in the liquid-wetting state by adding covalent crosslinking nodes.

[0036] Preferably, in step S1, the preparation method of phase A solution is as follows: heat purified water to 85℃~95℃, add polyvinyl alcohol to purified water and stir until dissolved and transparent; lower the temperature of purified water to between 45℃~65℃, add sodium carboxymethyl cellulose under shear stirring at 300~500rpm, continue stirring until sodium carboxymethyl cellulose is completely dissolved, cool and keep warm to 25℃~35℃ to obtain phase A solution;

[0037] The preparation method of phase B solution is as follows: D-sorbitol, anhydrous citric acid, itaconic acid and sodium hypophosphite monohydrate are dissolved in purified water at 20℃~25℃ in sequence, and ammonia water is added dropwise under continuous stirring until the pH value of phase B solution reaches the predetermined target, thus obtaining phase B solution.

[0038] By adopting the above technical solution, the amphiphilic polymer is dissolved in stages by controlling the temperature and stirring speed, preventing polyvinyl alcohol from clumping at low temperatures and sodium carboxymethyl cellulose from undergoing macromolecular chain degradation at high temperatures; phase B is prepared at room temperature and ammonia is added dropwise to precisely control the pH value of the solution and inhibit the early hydrolysis of polybasic acids.

[0039] Preferably, in step S1, the specific implementation of mixing and standing for degassing is as follows: the B phase solution is pumped into the A phase solution which is kept at a constant temperature of 25℃~35℃, stirred at a speed of 100~200rpm for 20~40min, and then allowed to stand for degassing at 25℃~35℃ and an absolute pressure of 10~20kPa for 30~45min.

[0040] By adopting the above technical solution and limiting the mixing temperature and absolute pressure parameters, the apparent dynamic viscosity of the polymer solution is reduced, the aggregation and floating removal of microbubbles entrained in the liquid phase are accelerated, the optical transmittance of the precursor sol is improved, and the residual rate of formed bubbles is reduced.

[0041] Preferably, in step S2, the specific process parameters for pre-freezing and vacuum drying are as follows: the liquid thickness of the homogeneous precursor sol injected into the mold is controlled to be 5-15 mm; the temperature of pre-freezing is -45℃ to -35℃, and the time of pre-freezing is 3-5 h; the conditions for vacuum drying are to uniformly raise the temperature to 0℃ to 10℃ within 4-6 h under a vacuum of less than 15 Pa and maintain it for 24-36 h.

[0042] By adopting the above technical solution, the liquid thickness and quick-freezing parameters were controlled to limit the nucleation rate and size distribution of ice crystals, thus determining the final pore structure of the sponge. Low-temperature sublimation was maintained at a vacuum of less than 15 Pa to ensure that solid water vaporized directly across the triple point, thus maintaining the physical integrity of the three-dimensional porous skeleton.

[0043] Preferably, in step S3, the process parameters for the thermal escape activation treatment are as follows: the temperature of the sealed reaction chamber is set at 100℃~105℃, and baking is carried out continuously for 20~30 minutes under normal pressure exhaust conditions; the specific implementation method of the cyclic pulse treatment is as follows: maintain the temperature of the sealed reaction chamber at 100℃~105℃, turn on the vacuum pump to pump the pressure of the sealed reaction chamber to -0.09MPa~-0.08MPa and maintain it for 3~8 minutes; close the vacuum valve and fill it with high-purity nitrogen to restore the sealed reaction chamber to normal pressure and maintain it for 1~3 minutes; the process of vacuuming and filling with high-purity nitrogen to break the vacuum is considered as one cycle, and the cycle is repeated continuously for 3~6 cycles.

[0044] By adopting the above technical solution and setting a heat treatment window of 100℃~105℃, the activation energy requirements for initiating the thermal dehydration and esterification reaction of polybasic acids are met, while avoiding the high temperature range where polysaccharide materials undergo caramelization degradation, thus maintaining the whiteness of the material's appearance. By using continuous and repeated deep negative pressure pumping and alternating replacement with atmospheric pressure high-purity nitrogen, gas exchange inside and outside the pores is forced, reducing the content of volatile free ammonia inside the sponge micropores to within the qualified index of biosafety assessment.

[0045] Preferably, in step S4, the high-energy rays are cobalt-60 gamma rays or electron beams, and the set absorbed dose for irradiation treatment is 15–20 kGy.

[0046] By adopting the above technical solution, cobalt-60 gamma rays or electron beams have strong penetrating power and can achieve uniform energy deposition inside the product without damaging the packaging seal. The absorbed dose is controlled at 15-20 kGy, which is sufficient to trigger the addition polymerization of itaconic acid double bonds and the terminal sterilization of medical consumables. At the same time, it avoids excessive radiation dose from causing a large number of glycosidic bonds in the polysaccharide backbone to break, thus maintaining the gel fraction and mechanical strength of the material.

[0047] This invention provides a method for preparing a biodegradable medical abdominal pad. It has the following beneficial effects:

[0048] 1. This invention introduces an alkaline regulator during the liquid-phase mixing stage to neutralize and mask the polycarboxylic acid crosslinking agent, effectively inhibiting premature association and phase separation precipitation of polysaccharide macromolecular chains under acidic conditions due to weakened electrostatic repulsion. This design maintains the homogeneous dispersion of the precursor sol during processing and molding, solving the problem of local crosslinking and gelation that easily occurs in the premixing stage of traditional polysaccharide-based medical materials, and ensuring the uniformity of spatial distribution of the components in the substrate.

[0049] 2. This invention utilizes the thermal decomposition mechanism of the crosslinking agent to release gas in situ and free catalytic protons. Simultaneously, this drives a dehydration and esterification reaction between molecular chains, and the gas escape process spontaneously constructs three-dimensional interconnected microporous channels within the substrate. Combined with alternating pressure cyclic pulse degassing, volatile residues trapped deep within the porous network are forcibly expelled and replaced by a gas phase. This not only increases the porosity of the abdominal cavity to facilitate absorption by bodily fluids but also eliminates potential biotoxicity risks and inhibits oxidative degradation of the material under thermal conditions.

[0050] 3. This invention employs a dual curing strategy combining thermally induced crosslinking and radiation crosslinking. After constructing a preliminary covalent ester bond network between the polysaccharide backbone, addition polymerization is further achieved by utilizing the pre-reserved active carbon-carbon double bonds in the system through high-energy radiation excitation. This process simultaneously completes the construction of the second carbon chain network during conventional medical radiation sterilization, increasing the crosslinking density of the polymer backbone, restricting the slippage of polysaccharide molecular chains, effectively inhibiting excessive swelling and disintegration of the medical abdominal pad after absorbing large amounts of body fluid, and ensuring the structural integrity and mechanical support performance of the dressing in a moist medical environment. Attached Figure Description

[0051] Figure 1 This is a schematic diagram for verifying the rheological parameters and pH evolution mechanism of liquid phase processing in this invention; wherein, Figure (a) shows the apparent dynamic viscosity and transmittance distribution of Examples 1 to 5 and Comparative Examples 1, 2, and 7 in the liquid phase state before degassing and molding; Figure (b) shows the microenvironment pH distribution of each test object at three key nodes: preparation of B phase solution, multiphase mixing and degassing, and final high-temperature curing and molding.

[0052] Figure 2 This is a schematic diagram of the evaluation of the physicochemical and safety indicators of the dry-state finished sponge of the present invention; wherein, Figure (a) shows the macroscopic deformation data and surface optical properties of each group of materials after dehydration and thermosetting; Figure (b) reflects the distribution of volatile chemical residues inside each group of samples;

[0053] Figure 3 This is a schematic diagram of the dual network evolution and wet mechanical evaluation of the present invention; wherein, Figure (a) shows the trajectory of the change in internal crosslinking density of each group of materials before and after sterilization irradiation treatment; Figure (b) shows the stability of the finished sponge after process treatment in a simulated body fluid environment;

[0054] Figure 4 This is a schematic diagram illustrating the evaluation of the body fluid absorption kinetics performance of the present invention. Detailed Implementation

[0055] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0057] Sodium carboxymethyl cellulose, CAS No. 9004-32-4, with a degree of substitution of 0.7 to 0.9, has a dynamic viscosity of 200 to 500 mPa·s in a 2% aqueous solution at 25°C.

[0058] Polyvinyl alcohol, CAS number 9002-89-5, has an average degree of polymerization of 500 to 600 and a degree of alcoholysis of 87.0% to 89.0%.

[0059] D-sorbitol, CAS number 50-70-4, purity greater than or equal to 99.0%.

[0060] Anhydrous citric acid, CAS number 77-92-9, purity greater than or equal to 99.5%.

[0061] Itaconic acid, CAS number 97-65-4, purity greater than or equal to 99.0%.

[0062] Sodium hypophosphite monohydrate, CAS number 10039-56-2, purity greater than or equal to 99.0%.

[0063] Ammonia solution, CAS number 1336-21-6, with a mass fraction of 25% to 28%.

[0064] Preparation Example 1: This preparation example provides a method for preparing a homogeneous precursor sol, controlling the total solid content to be 7.0%, including the following steps:

[0065] Step 1, Preparation of Phase A: Weigh 863.6g of purified water into a reaction vessel, heat to 90℃, add 10g of polyvinyl alcohol, and stir until completely dissolved and transparent; then turn on the cooling system to lower the liquid temperature to between 50℃ and 60℃, and under high-speed shear stirring at 400rpm, add 70g of sodium carboxymethyl cellulose in 5 portions over 15 minutes, continue stirring for 60 minutes until completely dissolved, and finally cool down and keep the temperature constant to 30℃ to obtain the Phase A solution.

[0066] The second step is the preparation of phase B: Weigh 465.0g of purified water at 20℃~25℃, and add 12g of D-sorbitol, 3g of anhydrous citric acid, 3g of itaconic acid and 2g of sodium hypophosphite monohydrate in sequence. Stir until completely dissolved, and add 25% ammonia water dropwise at a flow rate of 10g / min while continuously stirring. A total of about 6.5g of ammonia water is consumed until the pH of the solution stabilizes at 6.3, thus obtaining phase B solution.

[0067] The third step, low-temperature mixing and degassing: the B phase solution is pumped into the A phase solution at 30°C and stirred at 150 rpm for 30 minutes. Then, it is allowed to stand for degassing at 30°C and 15 kPa absolute pressure for 40 minutes to obtain a transparent, slightly acidic homogeneous precursor sol.

[0068] Preparation Example 2: This preparation example provides a method for preparing a homogeneous precursor sol, controlling the total solid content to be 5.0%, including the following steps:

[0069] Step 1, Preparation of Phase A: Weigh 1100.0g of purified water into a reaction vessel, heat to 85℃, add 8g of polyvinyl alcohol, and stir until completely dissolved and transparent; then turn on the cooling system to lower the liquid temperature to between 45℃ and 55℃, and under high-speed shear stirring at 300rpm, add 65g of sodium carboxymethyl cellulose in 4 portions over 10 minutes, continue stirring for 50 minutes until completely dissolved, and finally cool down and keep the temperature constant to 25℃ to obtain the Phase A solution.

[0070] The second step is the preparation of phase B: Weigh 572.0g of purified water at 20℃~25℃, and add 10g of D-sorbitol, 2g of anhydrous citric acid, 2g of itaconic acid and 1g of sodium hypophosphite monohydrate in sequence. Stir until completely dissolved, and add 25% ammonia water dropwise at a flow rate of 8g / min under continuous stirring. A total of about 3.5g is consumed until the pH of the solution stabilizes at 6.0, thus obtaining phase B solution.

[0071] The third step, low-temperature mixing and degassing: the B phase solution is pumped into the A phase solution at 25°C and stirred at 100 rpm for 20 minutes. Then, it is allowed to stand for degassing at 25°C and 10 kPa absolute pressure for 30 minutes to obtain a transparent, slightly acidic homogeneous precursor sol.

[0072] Preparation Example 3: This preparation example provides a method for preparing a homogeneous precursor sol, controlling the total solid content to be 9.0%, including the following steps:

[0073] Step 1, Preparation of Phase A: Weigh 750.0g of purified water into a reaction vessel, heat to 95℃, add 12g of polyvinyl alcohol, and stir until completely dissolved and transparent; then turn on the cooling system to lower the liquid temperature to between 55℃ and 65℃, and under high-speed shear stirring at 500rpm, add 75g of sodium carboxymethyl cellulose in 6 portions over 20 minutes, continue stirring for 70 minutes until completely dissolved, and finally cool down and keep the temperature constant to 35℃ to obtain the Phase A solution.

[0074] The second step is the preparation of phase B: Weigh 402.6g of purified water at 20℃~25℃, and add 15g of D-sorbitol, 5g of anhydrous citric acid, 4g of itaconic acid and 3g of sodium hypophosphite monohydrate in sequence. Stir until completely dissolved, and add 28% ammonia water dropwise at a flow rate of 12g / min while continuously stirring. A total of about 11.2g of ammonia water is consumed until the pH of the solution stabilizes at 6.6, thus obtaining phase B solution.

[0075] The third step, low-temperature mixing and degassing: the B phase solution is pumped into the A phase solution at 35°C and stirred at 200 rpm for 40 minutes. Then, it is allowed to stand for degassing at 35°C and 20 kPa absolute pressure for 45 minutes to obtain a transparent, slightly acidic homogeneous precursor sol.

[0076] Example 1: This example provides a method for preparing a biodegradable medical abdominal pad, including the following steps:

[0077] The first step is to inject the homogeneous precursor sol obtained in Preparation Example 1 into a stainless steel mold, with the liquid thickness controlled at 10 mm. Then, the mold is sent into a freeze dryer and rapidly frozen at -40°C for 4 hours. The vacuum pump is turned on to evacuate the vacuum to below 15 Pa. The shelf temperature is raised from -40°C to 5°C within 5 hours according to the set program and maintained for 30 hours for sublimation drying to obtain a porous sponge.

[0078] The second step involves placing the dried porous sponge in a reaction oven equipped with programmed temperature control and vacuum functions. The oven temperature is set to 105°C, and the sponge is baked for 30 minutes under normal pressure with exhaust ventilation enabled for thermal escape activation. Subsequently, the oven temperature is maintained at 105°C, and the vacuum pump is turned on to evacuate the chamber pressure to -0.085MPa. This vacuum state is maintained for 5 minutes. Then, the vacuum valve is closed, and high-purity nitrogen is introduced to restore the chamber to normal pressure. This process is maintained for 2 minutes. The vacuuming and high-purity nitrogen introduction process is considered as one cycle, and this cycle is repeated 4 times. After the process is completed, the sponge is allowed to cool naturally before being removed from the oven.

[0079] The third step involves cutting the cooled porous sponge into specified sizes, sealing it in a breathable medical blister pack and Tyvek cover material, and then sending it to an irradiation center for cobalt-60 gamma irradiation treatment with an absorbed dose of 15 kGy to obtain a biodegradable medical abdominal pad.

[0080] Example 2: This example provides a method for preparing a biodegradable medical abdominal pad, including the following steps:

[0081] The first step was to inject the homogeneous precursor sol obtained in Preparation Example 2 into a stainless steel mold, with the liquid thickness controlled at 5 mm. Then, the mold was sent into a freeze dryer and rapidly frozen at -45°C for 3 hours. The vacuum pump was turned on to evacuate the vacuum to below 15 Pa. The program was set to uniformly raise the shelf temperature from -45°C to 0°C within 4 hours and maintain it for 24 hours for sublimation drying to obtain a porous sponge.

[0082] The second step involves placing the dried porous sponge in a reaction oven, setting the oven temperature to 100℃, and baking it for 20 minutes under normal pressure with the exhaust fan on for thermal escape activation. While maintaining the oven temperature at 100℃, the vacuum pump is turned on to evacuate the chamber pressure to -0.08MPa. This vacuum state is maintained for 3 minutes. The vacuum valve is then closed, and high-purity nitrogen is introduced to restore the pressure to normal, maintaining this state for 1 minute. This process of evacuating and introducing high-purity nitrogen to break the vacuum is considered a cycle, and this cycle is repeated three times. After the process is complete, the sponge is allowed to cool naturally before being removed from the oven.

[0083] The third step involves cutting, packaging, and sealing the porous sponge, then irradiating it with an electron beam at an absorbed dose of 15 kGy to obtain a biodegradable medical abdominal pad.

[0084] Example 3: This example provides a method for preparing a biodegradable medical abdominal pad, including the following steps:

[0085] The first step was to inject the homogeneous precursor sol obtained in Preparation Example 3 into a stainless steel mold, with the liquid thickness controlled at 15 mm. Then, it was sent to a freeze dryer and rapidly frozen at -35°C for 5 hours. The vacuum pump was turned on to evacuate to below 15 Pa. The program was set to uniformly raise the shelf temperature to 10°C within 6 hours and maintain it for 36 hours for sublimation drying to obtain a porous sponge.

[0086] The second step involves placing the porous sponge in a reaction oven, setting the temperature to 105℃, and baking it for 30 minutes under normal pressure with the exhaust fan on for thermal escape activation. While maintaining the oven temperature at 105℃, the vacuum pump is turned on to evacuate the chamber pressure to -0.09MPa and held for 8 minutes. The vacuum valve is then closed, and high-purity nitrogen is introduced to restore the pressure to normal, held for 3 minutes. This process is repeated 5 times, followed by natural cooling before removing the sponge from the oven.

[0087] The third step involves cutting, packaging, and sealing the porous sponge, then irradiating it with cobalt-60 gamma rays at an absorbed dose of 20 kGy to obtain a biodegradable medical abdominal pad.

[0088] Example 4: This example provides a method for preparing a biodegradable medical abdominal pad, including the following steps:

[0089] In the first step, except for the sequential addition of 12g D-sorbitol, 2g anhydrous citric acid, 4g itaconic acid and 2g sodium hypophosphite monohydrate during the preparation of phase B, the remaining steps and process parameters were exactly the same as in preparation example 1, resulting in a homogeneous precursor sol.

[0090] The second step involves injecting the homogeneous precursor sol obtained in the first step into a stainless steel mold, controlling the liquid thickness to 10 mm, and then rapidly freezing it at -40°C for 4 hours. Subsequently, under a vacuum of less than 15 Pa, the temperature is uniformly raised to 5°C within 5 hours and maintained for 30 hours for sublimation drying to obtain a porous sponge.

[0091] The third step involves placing the porous sponge in a 105°C reaction oven and baking it under normal pressure for 30 minutes. Then, the oven is evacuated to -0.085 MPa at 105°C and held for 5 minutes. High-purity nitrogen is then introduced to break the vacuum and held for 2 minutes. This process is repeated 4 times, followed by cooling and removal from the oven.

[0092] The fourth step involves cutting and sealing the porous sponge, then subjecting it to irradiation with cobalt-60 gamma rays at a dose of 15 kGy to obtain a biodegradable medical abdominal pad.

[0093] Example 5: This example provides a method for preparing a biodegradable medical abdominal pad, including the following steps:

[0094] The first step involved using the same procedure as in Example 1 to form the homogeneous precursor sol from Preparation Example 1 into a porous sponge by freeze-drying.

[0095] The second step is to place the dried porous sponge in a reaction oven, set the temperature to 105℃, and bake it for 25 minutes under normal pressure and exhaust conditions. Maintain the temperature at 105℃, turn on the vacuum pump to evacuate the chamber pressure to -0.08MPa and hold for 4 minutes, then close the vacuum valve and fill it with high-purity nitrogen to restore it to normal pressure and hold for 2 minutes. Repeat this cycle 6 times and allow it to cool naturally before removing it from the oven.

[0096] The third step involves cutting and sealing the porous sponge, then irradiating it with cobalt-60 gamma rays at a dose of 15 kGy to obtain a biodegradable medical abdominal pad.

[0097] Comparative Example 1:

[0098] Compared with Example 1, the difference is that in the preparation of the homogeneous precursor sol, ammonia water is not added to adjust the pH value during the preparation of phase B. Instead, a strongly acidic aqueous solution containing D-sorbitol, anhydrous citric acid, itaconic acid and sodium hypophosphite monohydrate is directly mixed with the phase A solution. All other aspects are the same.

[0099] Comparative Example 2:

[0100] Compared with Example 1, the difference is that in the preparation of the homogeneous precursor sol, an equivalent amount of sodium hydroxide aqueous solution was used instead of ammonia to adjust the pH of the solution to 6.3 during the preparation of phase B; all other aspects are the same.

[0101] Comparative Example 3:

[0102] Compared with Example 1, the difference is that D-sorbitol was completely removed from the homogeneous precursor sol preparation formula and made up with an equal mass of purified water, while the rest are the same.

[0103] Comparative Example 4:

[0104] Compared with Example 1, the difference is that itaconic acid containing carbon-carbon double bonds was completely removed from the preparation formula of the homogeneous precursor sol, and it was replaced with anhydrous citric acid according to the equimolar equivalent of carboxyl groups, while the rest are the same.

[0105] Comparative Example 5:

[0106] Compared with Example 1, the difference is that the oven setting temperature and reaction temperature in the thermal escape activation and pulsed vacuum curing steps are increased from 105°C to 120°C for conventional thermal crosslinking, while the rest are the same.

[0107] Comparative Example 6:

[0108] Compared with Example 1, the difference is that in the thermal escape activation and curing steps, the cycle of pulse vacuuming and filling with high-purity nitrogen to break the vacuum is completely eliminated. The entire process is carried out by baking continuously at 105°C and normal pressure exhaust for 50 minutes. All other steps are the same.

[0109] Comparative Example 7:

[0110] Compared with Example 1, the difference is that in the preparation of the homogeneous precursor sol, the medium-low viscosity sodium carboxymethyl cellulose with a dynamic viscosity of 200 to 500 mPa·s in 2% aqueous solution is replaced with an equal mass of high viscosity sodium carboxymethyl cellulose (dynamic viscosity of 2% aqueous solution is greater than 1500 mPa·s), while the rest are the same.

[0111] Test Example 1:

[0112] This test case aims to verify the rheological processing state of the present invention during the liquid phase preparation stage and the triggering of the latent acid mechanism.

[0113] The A-phase solution, B-phase solution, mixed degassed precursor sol, and finally solidified sponge of Examples 1 to 5, Comparative Examples 1, 2 and 7 were selected as test objects.

[0114] The initial apparent dynamic viscosity of the precursor sol after degassing of each group was determined using an NDJ series rotational viscometer. The test temperature was kept constant at 25℃. The appropriate rotor and rotation speed were selected according to the actual rheological state of the sample. The data were recorded after the readings stabilized.

[0115] Take an appropriate amount of the mixed and degassed precursor sol and put it into a standard cuvette. Use a UV-Vis spectrophotometer to test the transmittance at a wavelength of 600 nm. Use purified water at the same temperature as a blank control.

[0116] The degassed sol was evenly coated onto a clean glass plate to form a 1 mm thick liquid film. The number of bubbles and the projected area within a specific field of view were observed under an optical microscope equipped with image analysis software, and the bubble residual rate was calculated.

[0117] A precision pH meter with two-point calibration was used to measure the initial pH value of each group of phase B solutions after preparation, as well as the pH value of the precursor sol after degassing of phase A and phase B.

[0118] Take 1.00g of sponge samples from each group after the thermal escape activation and solidification steps, cut them into small pieces, and immerse them in 50ml of purified water at 20℃~25℃. Extract for 24 hours under magnetic stirring, and take the supernatant to determine the pH value of the water extract.

[0119] The experimental data are shown in Table 1:

[0120] Table 1: Rheological parameters of precursors and pH changes at different stages

[0121]

[0122] in conclusion:

[0123] See attached document Figure 1 Based on the data in Table 1, the rheological properties and transmittance of the liquid phase reflect the processing state of the polysaccharide substrate. In Comparative Example 1, a strongly acidic substance was directly mixed with phase A without masking, causing the system pH to drop below the isoelectric point. This protonated the carboxylate ions on the macromolecular chains, weakening electrostatic repulsion and inducing phase separation through hydrogen bonding between molecular chains. The transmittance decreased to 8.4%, producing a white flocculent precipitate with a viscosity of 15430 mPa·s. The bubble residue rate increased to 18.2%, making the sol difficult to process in subsequent molding and freeze-drying steps. Comparative Example 7 used high-viscosity sodium carboxymethyl cellulose to maintain the system framework. No significant precipitation reaction occurred within the system, but the viscosity of 28760 mPa·s hindered bubble removal, resulting in a high bubble residue rate after physical degassing. In Examples 1 to 5, ammonia was introduced during the preparation stage to maintain the pH value of the mixed sol in the slightly acidic range of 6.0 to 6.5, thus maintaining the homogeneous state of the system and a suitable processing viscosity, keeping the light transmittance above 93%, and reducing the residual bubble rate.

[0124] In the curing stage tests, Comparative Example 2 used sodium hydroxide instead of ammonia for pH adjustment, achieving a precursor transmittance of 95.2%. During the high-temperature curing step, sodium ions did not escape from the system with increasing temperature, resulting in the pH of the water extract of the cured sponge remaining around 6.14. Insufficient acidity hindered the catalytic pathway of sodium hypophosphite, slowing down the dehydration esterification reaction and affecting the construction of the material's crosslinking network. Data from Examples 1 to 5 reflect the triggering process of the latent acid mechanism. Ammonia gas escaped from the ammonium salt network in a vacuum baking environment above 100°C, releasing protons from the system. The pH of the microenvironment decreased by more than 3 units, and the pH of the sponge matrix stabilized between 2.8 and 3.5. This in-situ acid release mechanism, while meeting the processing rheological requirements in the early stages, provided the acidic catalytic conditions required for esterification crosslinking during the high-temperature phase transition period, avoiding the initial acid precipitation problem and providing a structural basis for the subsequent radiation-induced double bond polymerization of the system.

[0125] Test Example 2:

[0126] This test case aims to verify the dry molding stability, appearance and physicochemical properties, and internal chemical residue levels of each group of materials.

[0127] Sponge samples from Examples 1 to 5, Comparative Examples 3, 5 and 6 that had undergone drying and cross-linking curing but had not yet been packaged and irradiated were selected as experimental subjects.

[0128] The initial length and width dimensions of the liquid phase injected into the mold before freeze-drying were measured using a vernier caliper with an accuracy of 0.02 mm. After each group of samples underwent thermosetting and cooled to room temperature, the actual length and width dimensions of the samples were measured again. The volume shrinkage rate of the samples was calculated by converting the difference in bottom area into thickness data obtained from a thickness gauge.

[0129] The chromaticity coordinates of each sample were measured using a spectrophotometer under a D65 standard light source. Five test points were randomly selected from different areas on the surface of each sponge sample for measurement. The whiteness index was calculated using the Hunter whiteness calculation method, and the average value was recorded.

[0130] Weigh 1.00 g of each group of dry sponge samples and place them in a sealed extraction bottle containing 100 mL of 0.01 mol / L hydrochloric acid. Extract on a shaker at 37°C for 2 hours. Measure the absorbance of the supernatant at 420 nm using Nessler's reagent colorimetry on a UV-Vis spectrophotometer. Calculate the residual ammonia content per unit mass of sponge by referring to a pre-prepared standard curve.

[0131] The experimental data are shown in Table 2:

[0132] Table 2: Macroscopic Molding and Chemical Residue Test Data of Dry Sponge

[0133]

[0134] in conclusion:

[0135] See attached document Figure 2 Based on the data in Table 2, the physical and chemical test indicators during the dry molding stage reflect the limiting relationship between the formulation components and the process environment on the final state of the material. During the sublimation dehydration stage of freeze-drying, the low-solids-content polysaccharide polymer matrix struggles to resist the shrinkage tension generated at the phase interface. In Comparative Example 3, sorbitol was removed from the formulation, and the volume shrinkage rate of the material increased to 59.2%, indicating that the molecular chain entanglement of sodium carboxymethyl cellulose alone cannot support the large-pore three-dimensional framework structure. In the Example group, sorbitol was retained, and during water removal, it constructed crystalline microregions within the matrix, providing corresponding physical support for the polymer network, thus maintaining the overall shrinkage rate below 5% after drying. In clinical applications, the color of medical consumables can affect the observation of wound exudate characteristics. In Comparative Example 5, the baking temperature during the crosslinking stage was increased to 120℃, and its whiteness index decreased to 35.8, indicating that the hydroxyl groups of the polysaccharide molecules underwent Maillard reaction and caramelization degradation in a high-temperature environment, resulting in macroscopic browning on the material surface. The embodiment limits the crosslinking temperature to 100°C to 105°C, and uses the reducing properties of sodium hypophosphite to slow down the oxidation process, thus maintaining the initial whiteness of the material while achieving the energy conditions required for thermal esterification crosslinking.

[0136] Ammonia residue is a key reference indicator for assessing the biochemical safety of this material. Free ammonia released during the crosslinking process due to heat tends to remain deep within porous media with high specific surface areas. Comparative Example 6, which underwent baking treatment with atmospheric pressure exhaust, showed a residual ammonia content as high as 192.4 mg / kg. Because conventional thermal convection struggles to overcome the gas diffusion resistance within the porous network, the flow of surface air failed to effectively replace the internal gas, leading to deep gas retention. The embodiments employed a cyclical operation of pulsed vacuuming and backfilling with high-purity nitrogen, utilizing the periodic pressure difference established between the inside and outside of the sealed chamber to induce ammonia to overflow from the sponge micropores and facilitate gas replacement. Test data showed that the residual ammonia content in the embodiments was all below 4 mg / kg, reducing the risk of bioirritation potentially caused by volatile chemical byproducts.

[0137] Test Example 3:

[0138] This test case aims to evaluate the impact of a dual-curing system on the mechanical properties and resistance to dissolution of materials in a simulated body fluid environment by measuring the evolution trajectory of the material's crosslinking density.

[0139] The sponge samples that had completed thermal cross-linking and curing but had not yet been irradiated in Examples 1 to 5, Comparative Example 2 and Comparative Example 4, as well as the finished sponges that had undergone the corresponding irradiation treatment, were selected as experimental subjects.

[0140] Accurately weigh the dried sponge sample and record its initial mass. Place it in a stainless steel mesh bag and immerse it in a constant-temperature water bath containing deionized water. Extract at 37°C for 48 hours to dissolve the soluble components that have not undergone cross-linking. After removing the mesh bag, freeze-dry to constant weight and record the mass after deswelling. Calculate the gel fraction by the ratio of the constant weight to the initial weight. The gel fraction of the sample before and after irradiation was determined independently.

[0141] The irradiated sponge samples were cut into dumbbell-shaped strips and immersed in simulated body fluid at a controlled temperature of 37°C until swelling equilibrium was reached. A universal testing machine was used to clamp both ends of the strips, and a tensile rate of 10 mm per minute was set. The maximum tensile stress data at which the strips fractured was recorded.

[0142] Weigh the initial dry weight of the irradiated sample and immerse it statically in simulated body fluid at 37°C for 30 minutes. Remove the sample and blot off any free surface moisture with qualitative filter paper. Freeze-dry the sample in a freeze dryer until constant weight. Calculate the mass loss rate by measuring the mass difference before and after immersion.

[0143] The experimental data are shown in Table 3:

[0144] Table 3: Evolution of Double Crosslinked Network and Wet Physical Properties Test Data

[0145]

[0146] in conclusion:

[0147] Polysaccharide materials often experience a decline in mechanical properties after absorbing body fluids, leading to swelling and affecting structural stability during practical operation. (See attached document.) Figure 3 Based on the test data in Table 3, the structural integrity of the material in a liquid environment is constrained by the degree of cross-linking of its internal covalent network. Comparative Example 2 used an equivalent amount of sodium salt as a substitute, resulting in a lack of free proton catalysis and hindering the esterification reaction. The results showed that the gel fraction of this sample remained low before irradiation, and a large number of uncross-linked polysaccharide molecules dissolved and became free upon contact with the simulated body fluid, leading to a high mass loss rate and low wet tensile strength. These test results reflect the role of the thermocatalytic stage in constructing the primary framework.

[0148] To assess the specific impact of radiation treatment on the polymer backbone, Comparative Example 4 was introduced as a reference. After replacing itaconic acid in the formulation with citric acid at an equimolar equivalent of carboxyl groups, the system constructed a primary network similar to that in the example during the thermal crosslinking stage, with a pre-irradiation gel fraction of approximately 45%. After high-energy irradiation, due to the lack of free radical-consuming carbon-carbon double bonds within the system, the glycosidic bonds of the polysaccharide backbone were affected by the radiation. The degradation and breakage effect of the polysaccharide molecular chain manifested as a decrease in gel fraction, varying degrees of damage to the internal network, leading to a decrease in wet tensile strength and an increase in solubility. The introduction of itaconic acid double bonds in the formulation of the example adjusted the radiation response path of the material. After irradiation treatment, the gel fraction of the samples generally showed a secondary increase, indicating that free radicals induced addition polymerization of carbon-carbon double bonds on the flexible branches, increasing covalent crosslinking nodes in the primary ester bond network. This dual curing system allows the material to disperse external mechanical stress through a relatively dense polymer network while in a fluid-swollen state, maintaining the physical strength suitable for instrument clamping operations, while limiting excessive dissolution of the substrate.

[0149] Test Example 4:

[0150] This test case aims to determine the simulated body fluid absorption kinetics of the material and evaluate the liquid absorption performance and internal pore connectivity of each group of finished sponge products.

[0151] The finished sponges prepared by the process and sterilized by irradiation in Examples 1 to 5, Comparative Example 3 and Comparative Example 7 were selected as experimental subjects.

[0152] Determine the saturated liquid absorption ratio of the material. Accurately weigh the initial mass of a dry sponge sample of uniform size and immerse it in simulated body fluid at 37°C. Allow it to stand for 10 minutes to reach liquid absorption and swelling equilibrium. Use a stainless steel mesh clamp to horizontally lift the sample out of the liquid surface and suspend it for 1 minute to allow unbound free liquid to drip off the surface. Weigh the sample again after liquid absorption. Calculate the saturated liquid absorption ratio per unit mass of sponge by the ratio of the mass difference before and after liquid absorption to the initial dry mass.

[0153] The water penetration time of the material was determined to characterize the instantaneous liquid absorption rate. A dry sponge sample was laid flat on a horizontal test stage, and a microburette was placed 10 mm above the sample surface. A simulated body fluid of 0.1 mL was vertically added to the center region of the sample. The camera and timer were turned on to record the time elapsed from the moment the droplet contacted the sponge surface until it penetrated into the material and the specular reflection on the surface disappeared. Each sample was tested five times in different regions, and the average penetration time was recorded.

[0154] The experimental data are shown in Table 4:

[0155] Table 4: Simulated Body Fluid Absorption Kinetics Evaluation Data

[0156]

[0157] in conclusion:

[0158] See attached document Figure 4 Based on the data in Table 4, the absorption kinetics of the material in a simulated body fluid environment are influenced by the connectivity of its internal porous network and the stability of the polymer skeleton. In the droplet penetration time test, the samples in the example group all absorbed droplets within 1.5 seconds, while maintaining a saturated absorption rate above 32 g / g. This absorption state is related to the in-situ pore-forming and skeleton support mechanisms during the preparation stage. Ammonia gas escapes outward during the thermal crosslinking process, constructing distributed and interconnected microporous channels within the polymer matrix. Along with the removal of water from the polysaccharide system, sorbitol precipitates a microcrystalline network at the phase interface, providing physical support for the polymer skeleton to withstand capillary contraction forces, limiting the closure or collapse of pores during drying, and preserving internal space for capillary penetration and storage of free liquids.

[0159] Comparative Example 3, with sorbitol removed from its formulation, resulted in volume shrinkage of the three-dimensional network lacking microcrystalline support during freeze-drying, leading to closure of the original pore structure. Test results showed an extended droplet penetration time of 14.6 seconds, with fluid remaining on the outer layer of the material due to surface tension. The reduction in internal volume caused its saturated absorbance rate to decrease to 11.5 g / g. Comparative Example 7 maintained the molded matrix by increasing the proportion of high-viscosity materials. The higher apparent viscosity limited the dispersion of gas molecules in the liquid phase, resulting in closed and irregular pores. This structure increased the mass transfer resistance during fluid penetration into the matrix, reduced capillary channels, manifested as a decreased absorbance rate and a smaller overall storage space. The test data demonstrate the role of volatile pore-forming agents and microcrystalline support agents in coordinating the microstructure and macroscopic absorbance performance of the material, providing structural support for the drainage and retention needs of medical dressings for treating wound exudate.

[0160] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A biodegradable medical abdominal pad, characterized in that, The biodegradable medical abdominal pad is made from a homogeneous precursor sol through freeze-drying, thermally induced phase crosslinking, and radiation crosslinking. The homogeneous precursor sol is composed of a mixture of a phase A solution and a phase B solution comprising the following parts by weight: The A-phase solution comprises the following components in parts by weight: 750-1100 parts purified water; 8-12 parts polyvinyl alcohol; and 65-75 parts sodium carboxymethyl cellulose. The B-phase solution comprises the following components in parts by weight: 402.6–572.0 parts purified water; 10–15 parts D-sorbitol; 2–5 parts anhydrous citric acid; 2–4 parts itaconic acid; 1–3 parts sodium hypophosphite monohydrate; and 3.0–12.0 parts ammonia. The amount of ammonia added should be such that the pH value of the homogeneous precursor sol after mixing the A-phase solution and the B-phase solution is stable between 6.0 and 6.

6.

2. The biodegradable medical abdominal pad according to claim 1, characterized in that, The polyvinyl alcohol has an average degree of polymerization of 500-600 and a degree of alcoholysis of 87.0%-89.0%. The degree of substitution of the sodium carboxymethyl cellulose is 0.7 to 0.9, and the dynamic viscosity of a 2 wt% aqueous solution of the sodium carboxymethyl cellulose at 25°C is 200 to 500 mPa·s.

3. The biodegradable medical abdominal pad according to claim 1, characterized in that, The mass fraction of the ammonia water is 25wt% to 28wt%; the total solid content of the homogeneous precursor sol is controlled to be 5.0wt% to 9.0wt%.

4. A method for preparing a biodegradable medical abdominal pad according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Prepare phase A solution and phase B solution respectively, mix phase A solution and phase B solution and let stand to remove bubbles to obtain homogeneous precursor sol; S2. The homogeneous precursor sol is injected into a mold, and the homogeneous precursor sol is subjected to pre-freezing treatment and vacuum drying treatment in sequence to obtain a porous sponge. S3. The porous sponge after vacuum drying is placed in a sealed reaction chamber and thermally activated under normal pressure exhaust. Then, the porous sponge is subjected to alternating vacuuming and vacuum breaking treatment with inert gas filling in a cyclic pulse treatment. After the cyclic pulse treatment is completed, it is naturally cooled out of the chamber to obtain the cooled porous sponge. S4. After the cooled porous sponge is cut and sealed, the cooled porous sponge is irradiated with high-energy rays to trigger the addition polymerization of carbon-carbon double bonds in itaconic acid in the cooled porous sponge, thereby obtaining the biodegradable medical abdominal pad.

5. The method for preparing the biodegradable medical abdominal pad according to claim 4, characterized in that, In step S1, the preparation method of the A-phase solution is as follows: the purified water is heated to 85℃~95℃, polyvinyl alcohol is added to the purified water and stirred until dissolved and transparent; the temperature of the purified water is lowered to between 45℃~65℃, sodium carboxymethyl cellulose is added under shear stirring at 300~500rpm, stirring is continued until the sodium carboxymethyl cellulose is completely dissolved, and the temperature is lowered and kept constant at 25℃~35℃ to obtain the A-phase solution; The preparation method of the B phase solution is as follows: D-sorbitol, anhydrous citric acid, itaconic acid and sodium hypophosphite monohydrate are dissolved sequentially in purified water at 20℃~25℃, and ammonia water is added dropwise until the pH value of the B phase solution reaches the predetermined target, thereby obtaining the B phase solution.

6. The method for preparing the biodegradable medical abdominal pad according to claim 4, characterized in that, In step S1, the specific implementation of mixing and standing for degassing is as follows: the B phase solution is pumped into the A phase solution which is kept at a constant temperature of 25℃~35℃, stirred at a speed of 100~200rpm for 20~40min, and then allowed to stand for degassing at 25℃~35℃ and an absolute pressure of 10~20kPa for 30~45min.

7. The method for preparing the biodegradable medical abdominal pad according to claim 4, characterized in that, In step S2, the specific process parameters for the pre-freezing treatment and the vacuum drying treatment are as follows: the liquid thickness of the homogeneous precursor sol injected into the mold is controlled to be 5-15 mm; the temperature of the pre-freezing treatment is -45℃ to -35℃, and the time of the pre-freezing treatment is 3-5 h; the conditions for the vacuum drying treatment are to uniformly raise the temperature to 0℃ to 10℃ within 4-6 h under a vacuum degree of less than 15 Pa and maintain it for 24-36 h.

8. The method for preparing the biodegradable medical abdominal pad according to claim 4, characterized in that, In step S3, the process parameters for the thermal escape activation treatment are as follows: the temperature of the sealed reaction chamber is set to 100℃~105℃, and baking is carried out continuously for 20~30 minutes under normal pressure exhaust conditions.

9. The method for preparing the biodegradable medical abdominal pad according to claim 8, characterized in that, In step S3, the specific implementation of the cyclic pulse processing is as follows: maintain the temperature of the sealed reaction chamber at 100℃~105℃, turn on the vacuum pump to pump the pressure of the sealed reaction chamber to -0.09MPa~-0.08MPa and maintain it for 3~8min; close the vacuum valve and fill it with high-purity nitrogen to restore the sealed reaction chamber to normal pressure and maintain it for 1~3min; the process of vacuuming and filling with high-purity nitrogen to break the vacuum is considered as one cycle, and the cycle is repeated continuously for 3~6 cycles.

10. The method for preparing the biodegradable medical abdominal pad according to claim 4, characterized in that, In step S4, the high-energy ray is cobalt-60 gamma ray or electron beam, and the set absorbed dose of the irradiation treatment is 15-20 kGy.

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