CN111513925B

CN111513925B - High-strength waterproof breathable composite dressing and preparation method thereof

Info

Publication number: CN111513925B
Application number: CN202010394009.0A
Authority: CN
Inventors: 郑汶江; 邹伟; 陈骞; 杨帆; 刘波; 杨虎; 颜杰
Original assignee: Zhonghao Chenguang Research Institute of Chemical Industry Co Ltd; Sichuan University of Science and Engineering
Current assignee: Zhonghao Chenguang Research Institute of Chemical Industry Co Ltd; Sichuan University of Science and Engineering
Priority date: 2020-05-11
Filing date: 2020-05-11
Publication date: 2021-10-08
Anticipated expiration: 2040-05-11
Also published as: CN111513925A

Abstract

The invention discloses a high-strength waterproof breathable composite dressing and a preparation method thereof. The composite dressing prepared by the invention adopts the expanded polytetrafluoroethylene film as an outer layer structure, so that the dressing has good waterproof and antifouling performances, and the special pore structure can effectively prevent bacteria from penetrating into a wound and effectively prevent wound infection; meanwhile, wound exudate and sweat on the skin can be rapidly evaporated through the special pore structure, and the composite dressing keeps the excellent performance of expanded polytetrafluoroethylene, so that the dressing can meet the requirements of wound treatment under complex conditions in battlefields and fields.

Description

High-strength waterproof breathable composite dressing and preparation method thereof

Technical Field

The invention relates to the technical field of medical dressings, in particular to a high-strength waterproof breathable composite dressing and a preparation method thereof.

Background

Traditional surgery covers the wound with gauze, but the gauze needs to be replaced every few hours before the wound becomes scabbed. And the yarn is easy to adhere to the wound, so that the wound is easy to be secondarily damaged during replacement, a chronic wound is formed, healing is delayed, and even the life is possibly threatened. For this purpose, hydrogel dressings have been developed for modern medicine to cover the wound directly, the inner layer of which is often a hydrogel that promotes wound healing and adheres directly to the skin, and the outer layer of which is a nonwoven or polyurethane fabric. Has good air permeability, but the material has poor water resistance and does not have the capability of isolating bacteria.

The wound can be polluted by rainwater, muddy water, blood and the like at any time after being treated in the fields such as battlefields, fields and the like, and pollutants such as soil and the like are easily adhered to the surface of the dressing. Bacteria in these contaminants are easily penetrated to cause wound infection. The surface treatment is carried out on the dressing, so that the waterproofness of the dressing can be effectively improved, but the waterproof coating can reduce the air permeability of the dressing, and wound exudate and sweat cannot be quickly discharged to influence the healing of the wound. Therefore, the novel wound dressing which has high waterproof capacity, can resist the pollution of other dirt and can quickly discharge wound exudate and sweat has important practical significance for battlefield and field rescue.

In the prior art, although polytetrafluoroethylene has good waterproofness and air permeability and is an ideal waterproof material, hydrogel is also commonly used as an inner layer material of a wound dressing, but the polytetrafluoroethylene has extremely low surface energy and a contact angle with water of more than 140 degrees, so that the polytetrafluoroethylene cannot be effectively combined with hydrogel called solid water. Patent CN201810087777.4 discloses a preparation method of medical hydrogel capable of being eluted and hydrogel dressing thereof, wherein although polytetrafluoroethylene film is also used as a base material, the hydrogel and the base material are bonded together by using a tackifier, and the addition of the tackifier can block the pore channels of the polytetrafluoroethylene film, so that the dressing prepared in this way has the defect of poor air permeability. Therefore, to realize the preparation of the high-strength waterproof and breathable dressing, the effective connection between the two must be realized.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a high-strength waterproof breathable composite dressing to solve the technical problem that the breathable effect is affected by using a tackifier to connect polytetrafluoroethylene and hydrogel in the prior art.

The invention also provides a method for preparing the composite dressing, which aims to solve the technical problem that the combination of the polytetrafluoroethylene and the hydrogel is difficult.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the utility model provides a waterproof ventilative composite dressing of excelling in, includes skin and inlayer, and the skin is the polytetrafluoroethylene film, and the inlayer is aquogel, the polytetrafluoroethylene film has mesh structure, the polytetrafluoroethylene film links to each other through grafting hydrophilic macromolecular compound and inlayer aquogel complex.

The outer layer of the invention adopts the polytetrafluoroethylene film prepared by the biaxial tension process, the polytetrafluoroethylene film after the treatment has a uniform mesh structure, then the surface of the polytetrafluoroethylene film is activated by plasma, then the free radical reaction is directly initiated on the surface of the polytetrafluoroethylene film, the hydrophilic high molecular monomer containing double bonds is grafted, after the modification, the surface of the polytetrafluoroethylene film is changed from super hydrophobicity to hydrophilicity, and a layer of villous hydrophilic high molecular chain grows on the surface of the polytetrafluoroethylene film, thus being more beneficial to compounding with hydrogel. Meanwhile, only one side of the polytetrafluoroethylene film is modified, the unmodified side still has higher hydrophobicity, and the mesh structure is not damaged, so that the composite dressing has good waterproof, antifouling, antibacterial and breathable performances.

Further, the polytetrafluoroethylene film is obtained through expansion and biaxial stretching, and the average pore diameter of the pore channel structure on the polytetrafluoroethylene film is less than 0.5 μm. The polytetrafluoroethylene film adopted by the invention can form a uniform mesh structure after being puffed and processed by biaxial stretching, and the aperture of the mesh structure is far smaller than the diameter of bacteria, so that the bacteria can be prevented from permeating, the wound infection can be prevented, and the polytetrafluoroethylene film is very suitable for the requirements of complex scenes such as battlefields, field rescue and the like.

Furthermore, the porosity of the polytetrafluoroethylene film is more than 90%, and the thickness of the polytetrafluoroethylene film is 20-500 microns. The porosity of the polytetrafluoroethylene film reaches more than 90 percent, and the polytetrafluoroethylene film has higher porosity and good air permeability.

Further, the hydrogel includes a PVA hydrogel, a hydroxyethyl methacrylate hydrogel, a polymethacrylic acid hydrogel or a polyethylene glycol diacrylate hydrogel. The hydrogel meets medical requirements, the hydrogel in the inner layer can reduce the temperature of a wound, reduce pain of the wound, keep the wound moist, promote the wound to grow, effectively absorb wound exudates, discharge the wound exudates through a surface film, and have certain antibacterial capacity, so that the infection of the wound can be effectively avoided.

Further, the hydrophilic polymer compound includes acrylamide, methylene acrylamide, acrylic acid, methacrylic acid, vinyl pyrrolidone, or a methacrylate-based compound. The hydrophilic high molecular compounds are grafted on the surface of the polytetrafluoroethylene film by initiating free radical reaction on the surface of the polytetrafluoroethylene film, and the hydrophilic high molecular compounds are used as templates, so that the hydrogel which is favorable for wound healing can grow on the surface of the polytetrafluoroethylene film and is well connected with the polytetrafluoroethylene film, and the hydrophilic high molecular compounds have strong hydrophilicity, cannot block pore channels of the hydrophobic polytetrafluoroethylene film, and enable the composite dressing to have good air permeability.

A preparation method of a high-strength waterproof breathable composite dressing comprises the following steps:

(1) and (3) activation: selecting a polytetrafluoroethylene film with a pore structure, cutting, activating for 10-300 s by a vacuum plasma cleaning machine, adjusting the flow of plasma gas to 10-100 mL/min, and controlling a vacuum system to keep the vacuum degree at 0.01-0.1 MPa to obtain an activated base film. Wherein the plasma generation frequency is 100kHz-40MHz, and the introduced plasma generation gas can be one of nitrogen, argon, helium, carbon dioxide or air; the activation is carried out for 20-200 s preferably by a vacuum plasma cleaning machine, and the vacuum degree of the vacuum system is controlled to be 0.08-0.095 MPa preferably.

(2) Grafting: and (3) putting the activated base membrane into an aqueous solution containing a hydrophilic high molecular compound, introducing nitrogen for 5-10 min to remove oxygen, and irradiating the surface of one side of the activated base membrane soaked in the aqueous solution for 5-10 h by using an ultraviolet lamp. Wherein the ultraviolet lamp adopts a 365nm ultraviolet lamp for irradiation.

(3) Cleaning: and (3) transferring the base film treated in the step (2) into deionized water to be soaked for 12-48 h, replacing the deionized water for three times during soaking, and washing away unreacted compounds on the surface of the base film.

(4) Compounding: and (4) transferring the base membrane treated in the step (3) into a clamp, sequentially adding raw materials of hydrogel into a mold in the clamp, and synthesizing and growing the hydrogel on the grafted side surface of the activated base membrane to be compounded with the base membrane. Wherein, one side of the basement membrane treated in the step (3) is grafted with a hydrophilic high molecular compound, the basement membrane is placed in a special hydrogel clamp, the grafted side is contacted with the raw material of the hydrogel, and the hydrogel grows on the surface of the grafted side of the basement membrane in the synthesis process, so that the synthesized hydrogel can be well connected with the polytetrafluoroethylene membrane.

(5) And (3) post-treatment: taking out the base film after the hydrogel is cured, coating pressure-sensitive adhesive on the blank area around the hydrogel on the base film, pasting isolation paper on the back of the base film, and sealing and packaging to obtain the novel dressing.

Further, the concentration of the hydrophilic polymer compound in the aqueous solution of the hydrophilic polymer compound in the step (2) is 0.2 to 5 mol/L.

Further, raw materials for preparing the hydrogel are one or more of monomers of acrylamide, methylene acrylamide, acrylic acid, methacrylic acid or hydroxyethyl methacrylate; or the raw material for preparing the hydrogel is one or more of a plurality of high molecular compounds of hyaluronic acid, polyvinyl alcohol or polyethylene glycol diacrylate.

Further, the hydrogel is synthesized by a small molecular monomer through a free radical reaction under the action of a cross-linking agent and an initiator.

Further, the hydrogel is prepared by physically or chemically crosslinking a high molecular compound.

The high-strength waterproof breathable composite dressing prepared by the preparation method has the following characteristics:

1. the expanded polytetrafluoroethylene film is activated by a low-temperature plasma technology, and a layer of villous hydrophilic macromolecules grows on the activated surface of the expanded polytetrafluoroethylene film in a free radical polymerization mode, so that the surface of the modified expanded polytetrafluoroethylene film is changed from super-hydrophobicity to hydrophilicity, and the modified expanded polytetrafluoroethylene film is more favorable for being compounded with hydrogel.

2. Because only the single-side modification is carried out on the expanded polytetrafluoroethylene film, the unmodified side still has very high hydrophobicity, meanwhile, the reticular structure is not damaged, and the reticular structure on the modified side can allow sweat and wound exudate on the skin at the wound to permeate in a molecular form, so that the sweat and the wound exudate on the skin at the wound are discharged in time, the liquid deposition at the wound is reduced, the wound surface is kept clean, and the wound healing is promoted; the unmodified surface still has good hydrophobicity, so that the penetration of external liquid can be effectively prevented, and the net structure can prevent bacteria from extending into a wound to prevent wound infection, so that the composite dressing can meet the requirements of complex scene application in battlefields and field rescue.

3. The inner layer is hydrogel meeting medical requirements and has the following characteristics:

1) the temperature of the wound can be reduced, and the pain feeling of the wound can be reduced;

2) can keep the wound moist and promote the wound growth;

3) the wound exudate can be effectively absorbed and discharged through the surface film;

4) has certain antibacterial ability and can effectively avoid wound infection.

Compared with the prior art, the invention has the following beneficial effects:

1. the composite dressing prepared by the invention adopts expanded polytetrafluoroethyleneThe alkene film is used as an outer layer structure, the surface of the outer layer structure has a water contact angle as high as 135 degrees, the alkene film is hydrophobic, liquid is not easy to wet the outer layer structure and easily moves on the outer surface of the outer layer structure, so that the composite dressing has good waterproof and antifouling properties, and the outer layer structure has a uniform mesh structure and can effectively prevent bacteria from entering a wound and prevent the wound from being infected; meanwhile, wound exudate and sweat on the skin can be rapidly evaporated through the mesh structure, the composite dressing has excellent air permeability and capability of absorbing exudate, and the air permeability reaches 10000 g.m^-2·24h^-1The liquid absorption and seepage capacity is 40 g.100 cm^-2And the expansion rate of the thickness of the hydrogel layer is lower than 5 percent when the hydrogel layer is soaked in water, so that the composite dressing cannot deform when in use, the excellent performance of the expanded polytetrafluoroethylene is kept, and the dressing can meet the requirements of wound treatment under complex conditions in battlefields and fields; the hydrogel adopted in the inner layer can effectively reduce the temperature of the wound to relieve the pain of the wound, the wound cannot be adhered, meanwhile, the moist environment can also promote the healing of the wound, the exudate of the wound can be absorbed, and the exudate is discharged through the pore structure of the outer layer film.

2. The preparation method of the invention activates the surface of the expanded polytetrafluoroethylene film by using plasma, realizes the high-efficiency compounding between the similar expanded polytetrafluoroethylene and the hydrogel in a mode of in-situ growth on the activated surface, ensures the waterproof and antifouling performances of the surface of the expanded polytetrafluoroethylene, and also provides a new idea for compounding the expanded polytetrafluoroethylene and other materials.

Drawings

Fig. 1 is a schematic structural diagram of a high-strength waterproof breathable composite dressing.

Fig. 2 is a photograph of the prepared wound dressing.

Fig. 3 is a contact angle of the surface of the dressing of fig. 1.

In the figure: an outer layer 1 and an inner layer 2.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

High-strength waterproof breathable composite dressing

Referring to fig. 1, the high-strength waterproof breathable composite dressing comprises an outer layer and an inner layer, wherein the outer layer is a polytetrafluoroethylene film, the inner layer is hydrogel, the polytetrafluoroethylene film is a biaxially oriented polytetrafluoroethylene film and has a uniform mesh structure, and the polytetrafluoroethylene film is connected with the hydrogel of the inner layer in a composite mode through grafting a hydrophilic high molecular compound. In actual use, the polytetrafluoroethylene film may be coated with an organic material film on the outer surface, i.e., the surface on the side not activated, and the organic material film such as polyamide, PU, PP cloth may be hot-pressed and laminated on the side surface, so that the strength of the polytetrafluoroethylene film can be improved after coating.

TABLE 1 major Components of a high-strength, waterproof, breathable composite dressing

Second, preparation method of high-strength waterproof breathable composite dressing

Example 1: composition of expanded polytetrafluoroethylene and PVA hydrogel

(1) And (3) activation: selecting a 150-micron-thick double-drawn expanded polytetrafluoroethylene film with the pore diameter of 0.1 micron, and cutting the film into a square shape with the thickness of 10cmx10 cm; fixing the expanded polytetrafluoroethylene film on plate glass, and putting the plate glass into a vacuum plasma generation bin with the frequency of 20 MHz; vacuumizing, introducing argon gas flow of 20mL/min, adjusting the power of equipment to be 115w, controlling the vacuum degree of a system to be 0.095MPa, and treating plasma for 100 s.

(2) Grafting: immediately transferring the membrane into a special mould, adding 1mol/L of vinyl pyrrolidone aqueous solution, introducing nitrogen to remove oxygen, and transferring to an ultraviolet lamp for irradiation grafting for 6 h.

(3) Cleaning: the membrane is immersed in deionized water, and water is changed every 8 hours for 24 hours.

(4) Compounding: transferring the cleaned basement membrane to a professional hydrogel fixture, adding 10% PVA aqueous solution (wherein the mass fraction of the quaternary ammonium salt chitosan is 5 wt%), pouring the aqueous solution into a glass mold, introducing nitrogen to remove oxygen, freezing the glass mold in a refrigerator at 18 ℃ below zero, and then unfreezing the glass mold.

(5) And (3) post-treatment: coating polyacrylate pressure-sensitive adhesive on the edge position which is not covered with hydrogel, attaching release paper, and shearing to obtain the required wound composite dressing.

Wherein, the polyvinyl alcohol solution can be better spread on the surface of the expanded polytetrafluoroethylene film after grafting modification, and the polyvinyl alcohol solution is solidified by a freezing-melting method to form hydrogel. Through physical winding and van der waals force between polyvinyl alcohol and polyvinylpyrrolidone, effective compounding of hydrogel and the expanded polytetrafluoroethylene film is achieved, and the technical problem that the compounding effect of finished hydrogel and the expanded polytetrafluoroethylene film is poor in the prior art is solved.

Example 2: compounding of expanded polytetrafluoroethylene and hydroxyethyl methacrylate hydrogel

In example 2, the pretreatment method for the expanded polytetrafluoroethylene membrane was the same as in example 1, except that the preparation of the hydrogel, that is, step (4), was different.

(4) Compounding: the plasma activated and PVP grafted base membrane was transferred to a hydrogel preparation jig. Preparing 1mol/L hydroxyethyl methacrylate solution, and adding a crosslinking agent N, N-methylene bisacrylamide (the concentration is 1mol percent of the monomer concentration) and an initiator alpha-glutaric acid (the concentration is 0.1 mol percent of the monomer concentration). And introducing nitrogen into the solution to remove oxygen, transferring the solution into a mold with a base film, and irradiating for 12 hours under 365nm ultraviolet light. Taking out and soaking in deionized water for 24h, and replacing the deionized water for three times during the soaking period to prepare the composite hydrogel.

Example 3: compounding expanded polytetrafluoroethylene with polymethacrylic acid hydrogel

In example 3, the pretreatment method for the expanded polytetrafluoroethylene membrane was the same as in example 1, except that the preparation of the hydrogel, that is, step (4), was different.

(4) Compounding: the plasma activated and PVP grafted base membrane was transferred to a hydrogel preparation jig. A methacrylic acid solution having a concentration of 1mol/L was prepared, and an initiator a-glutaric acid (concentration: 0.1 mol% based on the monomer concentration) was added thereto. And introducing nitrogen into the solution to remove oxygen, transferring the solution into a mold with a base film, and irradiating for 12 hours under 365nm ultraviolet light. Taking out and soaking in deionized water for 24h, and replacing the deionized water for three times during the soaking period to prepare the composite hydrogel.

Example 4: compounding expanded polytetrafluoroethylene and polyglycol diacrylate hydrogel

In example 4, the pretreatment method for the expanded polytetrafluoroethylene membrane was the same as in example 1, except that the preparation of the hydrogel, that is, step (4), was different.

(4) Compounding: the plasma activated and PVP grafted base membrane was transferred to a hydrogel preparation jig. A0.5 mol/L hydroxyethyl methacrylate solution was prepared, and an initiator a-glutaric acid (concentration: 0.1 mol% based on the monomer concentration) was added thereto. And introducing nitrogen into the solution to remove oxygen, transferring the solution into a mold with a base film, and irradiating for 12 hours under 365nm ultraviolet light. Taking out and soaking in deionized water for 24h, and replacing the deionized water for three times during the soaking period to prepare the composite hydrogel.

Example 5: compounding expanded polytetrafluoroethylene and polymethyleneacrylamide hydrogel

In example 5, the pretreatment method for the expanded polytetrafluoroethylene membrane was the same as in example 1, except that the preparation of the hydrogel, that is, step (4), was different.

(4) Compounding: the plasma activated and PVP grafted base membrane was transferred to a hydrogel preparation jig. A methylene acrylamide solution having a concentration of 0.5 mol/L was prepared, and an initiator a-glutaric acid (having a concentration of 0.1 mol% based on the monomer concentration) was added thereto. And introducing nitrogen into the solution to remove oxygen, transferring the solution into a mold with a base film, and irradiating for 12 hours under 365nm ultraviolet light. Taking out and soaking in deionized water for 24h, and replacing the deionized water for three times during the soaking period to prepare the composite hydrogel.

The preparation methods of the embodiments 6 to 9 are the same as those of the embodiment 1, except that the pore sizes of the expanded polytetrafluoroethylene films are different, and the pore sizes of the prepared composite dressings are different. The composite dressings prepared in examples 1 to 9 were measured according to the national standard contact wound dressing test method (part 2: water vapor transmission rate of breathable film dressing) (YYT 0471.2-2004), and the contact angle of the surface of the composite dressing was measured using a contact angle instrument, and the hydrogel thickness swelling rate was measured under water immersion.

TABLE 2 Performance parameters of composite dressings prepared in examples 1-9

Examples	Air permeability (g.m)^-2·24h^-1）	Ability to absorb seepage (g.100 cm)^-2）	Contact angle (°)	Hydrogel thickness expansion ratio (%) under water immersion
					Example 1	6500	20	135	＜5
Example 2	10000	40	132	＜5
					Example 3	6500	85	130	＜10
Example 4	9500	70	136	＜10
					Example 5	9300	35	135	＜10
Example 6	6400	21	131	＜10
					Example 7	6500	19	131	＜10
Example 8	6700	22	131	＜10
					Example 9	6600	21	131	＜10

The photograph of the prepared wound dressing is shown in fig. 2, the contact angle of the surface of the dressing tested by using a contact angle meter is shown in fig. 3, and as can be seen from table 2, the contact angle of the outer side surface of the composite dressing prepared in examples 1-9 to water is as high as 135 degrees, the hydrophobic property of the polytetrafluoroethylene film is maintained, and the outer side surface of the composite dressing has excellent waterproof and antifouling properties. Meanwhile, the air permeability is 6500-10000 g.m^-2·24h^-1And has excellent air permeability.

The above examples of the present invention are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Variations and modifications in other variations will occur to those skilled in the art upon reading the foregoing description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.

Claims

1. A high-strength waterproof breathable composite dressing comprises an outer layer and an inner layer, wherein the outer layer is a polytetrafluoroethylene film, and the inner layer is hydrogel;

the composite dressing is obtained by the following method:

(1) and (3) activation: selecting a polytetrafluoroethylene film with a pore structure, cutting, activating for 10-300 s by using a vacuum plasma cleaning machine, adjusting the flow of plasma gas to 10-100 mL/min, and controlling a vacuum system to keep the vacuum degree at 0.01-0.1 MPa to obtain an activated base film;

(2) grafting: putting the activated base membrane into an aqueous solution containing a hydrophilic high molecular compound, introducing nitrogen for 5-10 min to remove oxygen, and irradiating the surface of one side of the activated base membrane soaked in the aqueous solution for 5-10 h by using an ultraviolet lamp;

(3) cleaning: transferring the base film treated in the step (2) into deionized water for soaking for 12-48 h, replacing the deionized water for three times during soaking, and washing away unreacted compounds on the surface of the base film;

(4) compounding: transferring the base membrane treated in the step (3) into a clamp, sequentially adding raw materials of hydrogel into a mold in the clamp, and synthesizing and growing the hydrogel on the surface of one side of the activated base membrane grafted with the hydrophilic macromolecules to be compounded with the base membrane;

(5) and (3) post-treatment: taking out the base film after the hydrogel is cured, coating pressure-sensitive adhesive on the blank area around the hydrogel on the base film, pasting isolation paper on the back of the base film, and sealing and packaging to obtain the composite dressing.

2. The composite dressing of claim 1, wherein the polytetrafluoroethylene film is expanded and biaxially oriented, and the average pore diameter of the pore structure of the polytetrafluoroethylene film is less than 0.5 μm.

3. The composite dressing of claim 1, wherein the polytetrafluoroethylene film has a porosity of greater than 90% and a thickness of 20-500 μm.

4. The composite dressing of claim 1, wherein the hydrogel comprises a PVA hydrogel, a hydroxyethyl methacrylate hydrogel, a polymethacrylic acid hydrogel, or a polyethylene glycol diacrylate hydrogel.

5. The composite dressing of claim 1, wherein the hydrophilic polymer compound comprises acrylamide, methylene acrylamide, acrylic acid, methacrylic acid, vinyl pyrrolidone, or methacrylate compounds.

6. The composite dressing of claim 1, wherein the concentration of the hydrophilic polymer compound in the aqueous solution of the hydrophilic polymer compound in step (2) is 0.2-5 mol/L.

7. The composite dressing of claim 1, wherein the hydrogel is prepared from one or more monomers selected from acrylamide, methylene acrylamide, acrylic acid, methacrylic acid, and hydroxyethyl methacrylate; or the raw material for preparing the hydrogel is one or more of a plurality of high molecular compounds of hyaluronic acid, polyvinyl alcohol or polyethylene glycol diacrylate.

8. The composite dressing of claim 1, wherein the hydrogel is synthesized from small molecule monomers by free radical reaction under the action of a cross-linking agent and an initiator.

9. The composite dressing of claim 1, wherein the hydrogel is prepared by physical or chemical crosslinking of a polymer compound.