A method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials and its application

Abstract

A method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials and their applications are disclosed. The method includes the following steps: preparing Cu₂S nanoparticles via hydrothermal synthesis using copper sulfate pentahydrate (CuSO₄·5H₂O) and thiourea (CH₄N₂S) as raw materials; and preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction (Cu₂S-CeO₂) nanomaterials using Cu₂S nanoparticles and Ce(NO₃)₃·6H₂O as raw materials. This invention enhances antibacterial efficiency and antioxidant activity in the treatment of periodontitis through the synergistic effect of the cuprous sulfide (Cu₂S) and cerium oxide (CeO₂) heterojunction. This invention achieves dual functions of light-controlled antibacterial and antioxidant effects: efficiently catalyzing reactive oxygen species to kill periodontal pathogens under near-infrared light irradiation, and scavenging excess free radicals and alleviating oxidative stress when not under light irradiation.

Description

Technical Field

[0001] This invention relates to the field of biomedical materials, and in particular to a method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials and their applications. Background Technology

[0002] Periodontitis is a chronic inflammatory disease caused by an imbalance of oral flora, which leads to the destruction of the supporting tissues of the teeth. Traditional treatments aim to control infection, reduce inflammation, and promote tissue repair.

[0003] Traditional treatments that inhibit pathogenic bacteria include: For example, the literature "Ambati, M., Rani, K., Reddy, P., Suryaprasanna, J., Dasari, R., & Gireddy, H. (2017). Evaluation of oxidative stress in chronic periodontitis patients following systemic antioxidant supplementation: A clinical and biochemical study. Journal of Natural Science, Biology and Medicine, 8(1), 99." proposes supragingival scaling and subgingival curettage, which physically remove local irritants such as plaque and tartar, thereby reducing the number of bacteria in the oral cavity and disrupting their living environment to treat periodontitis. In addition, local or systemic use of antibacterial drugs can effectively inhibit periodontal pathogens, thus achieving therapeutic effects. Commonly used antibacterial drugs include metronidazole and tetracyclines. However, long-term use of antibacterial drugs may lead to bacterial resistance and dysbiosis, thereby causing other diseases. For example, the literature "Krishnaswami, V., Sugumaran, A., Jacob Raja, SA, Packiaraj, I., Muruppel, AM, & Somaraj, V. (2024). Light activated drug delivery platform for dental applications - current technologies and future perspectives. Lasers in Dental Science, 8(1)." provides a method using photodynamic therapy, an emerging antibacterial method that uses photosensitizers to combine with light of a specific wavelength to generate reactive oxygen species (ROS), thereby killing bacteria.

[0004] While these traditional treatments can achieve the goal of treating periodontitis, their effectiveness is limited, specifically in terms of insufficient antibacterial efficiency and limited antioxidant activity. Summary of the Invention

[0005] This invention provides a method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials and their applications, in order to overcome the shortcomings of the prior art and solve the problems of insufficient antibacterial efficiency and limited antioxidant activity of nanoenzyme materials in the treatment of periodontitis.

[0006] In order to achieve the objectives of this invention, the following technologies are proposed:

[0007] One approach provides a method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials, including the following steps:

[0008] Cu2S nanoparticles were prepared by hydrothermal synthesis using copper sulfate pentahydrate (CuSO4·5H2O) and thiourea (CH4N2S) as raw materials.

[0009] The preparation of cuprous sulfide-cerium oxide nanoenzyme heterojunction (Cu2S-CeO2) nanomaterials was carried out using Cu2S nanoparticles and Ce(NO3)3·6H2O as raw materials.

[0010] Furthermore, when preparing Cu2S nanoparticles via hydrothermal synthesis using copper sulfate pentahydrate (CuSO4·5H2O) and thiourea (CH4N2S) as raw materials, the following steps are performed:

[0011] Step 01: Dissolve copper sulfate pentahydrate (CuSO4·5H2O) and thiourea (CH4N2S) in deionized water;

[0012] Step 02: Add the mixture obtained in Step 01 into a hydrothermal reactor and react at 180°C for 24 hours;

[0013] Step 03: Centrifuge and filter the precipitate obtained in step 02, and wash the precipitate with deionized water.

[0014] Step 04: The precipitate obtained in step 03 is placed in a vacuum drying oven and dried at 60°C to obtain Cu2S nanoparticles.

[0015] Furthermore, the preparation of cuprous sulfide-cerium oxide nanoenzyme heterojunction (Cu2S-CeO2) nanomaterials using Cu2S nanoparticles and Ce(NO3)3·6H2O as raw materials is carried out through the following steps:

[0016] Step 05: Mix Cu2S nanoparticles and Ce(NO3)3·6H2O, and add the mixture to sodium hydroxide solution. Stir and react at 25°C for 22 hours.

[0017] Step 06: Centrifuge and filter the reaction product obtained in step 05 to obtain the reaction precipitate, and wash the obtained reaction precipitate with deionized water.

[0018] Step 07: The reaction precipitate obtained in step 05 is placed in a vacuum drying oven and dried at 60°C to obtain cuprous sulfide-cerium oxide nanoenzyme heterojunction (Cu2S-CeO2) nanomaterial.

[0019] Furthermore, the molar ratio of copper sulfate pentahydrate (CuSO4·5H2O) and thiourea (CH4N2S) in step 01 is 1:(0.5-1).

[0020] Furthermore, in step 03, when washing the obtained precipitate with deionized water, the volume of the deionized water is 5 to 10 times that of the precipitate.

[0021] Furthermore, in step 03, when centrifuging and filtering the precipitate, the centrifugation speed is 8000 rpm / min-16000 rpm / min, and the centrifugation time is 5 min-10 min.

[0022] Furthermore, in step 05, the molar ratio of Cu2S nanoparticles to cerium nitrate (Ce(NO3)3·6H2O) is 1:(0.5-3), and the molar concentration of the sodium hydroxide solution is 0.05-0.1M.

[0023] Furthermore, the stirring speed in step 05 is 500 rpm / min-1500 rpm / min.

[0024] Furthermore, in step 06, when centrifuging the reaction product, the centrifugation speed is 8000 rpm / min-16000 rpm / min, and the centrifugation time is 5 min-10 min.

[0025] On the other hand, an application of a cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial is provided. Specifically, the cuprous sulfide-cerium oxide nanoenzyme heterojunction (Cu2S-CeO2) nanomaterial prepared using the aforementioned method is used in the preparation of periodontitis treatment drugs. When the drug is applied to treat periodontitis, the cuprous sulfide-cerium oxide nanoenzyme heterojunction (Cu2S-CeO2) nanomaterial, through the Cu2S nanoparticles in the heterojunction irradiated by near-infrared 808 nm light, catalyzes the generation of hydroxyl radicals (.OH) and peroxide radicals (O2).- It kills periodontal pathogens by eliminating reactive oxygen species (including .OH, O2, etc.) and simultaneously removes reactive oxygen species (including .OH, O2, etc.) from oxidative stress through CeO2 nanoparticles in the heterojunction when not exposed to light. - (etc.) to achieve synergistic antibacterial and antioxidant functions.

[0026] The advantages of the above technical solution are:

[0027] This invention enhances antibacterial efficiency and antioxidant activity in the treatment of periodontitis through the synergistic effect of the heterojunction of cuprous sulfide (Cu2S) and cerium oxide (CeO2).

[0028] This invention achieves dual functions of light-controlled antibacterial and antioxidant: it efficiently catalyzes active oxygen to kill periodontal pathogens under near-infrared light irradiation, and removes excess free radicals and alleviates oxidative stress when not under light irradiation.

[0029] The material of this invention has a stable structure, excellent biocompatibility, and its performance can be optimized through parameter adjustment, providing an efficient and safe solution for the treatment of periodontitis and antioxidant-related diseases. Attached Figure Description

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0031] Figure 1 TEM images of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Examples 3 to 5 are shown.

[0032] Figure 2 The XRD patterns of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Examples 3 to 5 are shown.

[0033] Figure 3 The image shows the detection results of singlet oxygen and hydroxyl radical formation of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial prepared in Example 3 under 808nm light irradiation for 5 min.

[0034] Figure 4 Line graphs showing the antioxidant properties of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Examples 3 to 5 are presented. Detailed Implementation

[0035] A method for preparing cuprous sulfide-cerium oxide nanoenzyme heterostructure nanomaterials, the synthesis principle of which is as follows:

[0036] CuSO4·5H2O + CH4N2S → Cu2S↓ + NH4SCN + SO2↑

[0037] Cu2S + Ce(NO3)3·6H2O + NaOH → Cu2S- CeO2↓ + NaNO3 + H2O.

[0038] The principle of a cuprous sulfide-cerium oxide nanoenzyme heterostructure nanomaterial in the treatment of periodontitis is as follows:

[0039] Firstly, the principle behind its antibacterial properties is as follows:

[0040] H2O2→OH

[0041] O2→O2 -

[0042] Secondly, the principle of its antioxidant properties is as follows:

[0043] O2 - →O2↑

[0044] OH→H2O

[0045] Example 1: Preparation method of the first cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial

[0046] Using 0.4 g copper sulfate pentahydrate (CuSO4·5H2O) and 0.25 g thiourea (CH4N2S) as raw materials, they were dissolved in 100 mL of deionized water and then added to a 200 mL hydrothermal reactor. The reaction was carried out at 180 °C for 24 hours. After centrifugation at 8000 rpm / min for 10 min, the mixture was dried in a vacuum drying oven at 60 °C to obtain Cu2S nanoparticles. Subsequently, the synthesized Cu2S nanozyme and cerium nitrate (Ce(NO3)3·6H2O) were added to 40 mL of 0.05 M NaOH solution at a molar ratio of 1:0.5. The mixture was stirred in air at 25 °C at 500 rpm / min for 22 hours, washed several times with pure water, centrifuged at 8000 rpm / min for 10 min, and then dried in a vacuum drying oven at 60 °C to obtain the final product.

[0047] Example 2: Preparation method of the second type of cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial

[0048] Using 0.20 g of copper sulfate pentahydrate (CuSO4·5H2O) and 0.15 g of thiourea (CH4N2S) as raw materials, they were dissolved in 100 mL of deionized water and then added to a 200 mL hydrothermal reactor. The reaction was carried out at 180 °C for 24 hours. After centrifugation at 12000 rpm / min for 10 min, the mixture was dried in a vacuum drying oven at 60 °C to obtain Cu2S nanoparticles. Subsequently, the synthesized Cu2S nanozyme and cerium nitrate (Ce(NO3)3·6H2O) were added to 20 mL of 0.05 M NaOH solution at a 1:1 molar ratio. The mixture was stirred in air at 25 °C at 800 rpm / min for 22 hours, washed several times with pure water, centrifuged at 12000 rpm / min, and then dried in a vacuum drying oven at 60 °C to obtain the final product.

[0049] Example 3: Preparation method of the third type of cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial

[0050] Using 0.3 g of copper sulfate pentahydrate (CuSO4·5H2O) and 0.15 g of thiourea (CH4N2S) as raw materials, they were dissolved in 100 mL of deionized water and then added to a 200 mL hydrothermal reactor. The reaction was carried out at 180 °C for 24 hours. After centrifugation at 9000 rpm / min for 10 min, the mixture was dried in a vacuum drying oven at 60 °C to obtain Cu2S nanoparticles. Subsequently, the synthesized Cu2S nanozyme and cerium nitrate (Ce(NO3)3·6H2O) were added to 30 mL of 0.075 M NaOH solution at a molar ratio of 1:2. The mixture was stirred in air at 25 °C at 1000 rpm / min for 22 hours, washed several times with pure water, centrifuged at 9000 rpm / min, and then dried in a vacuum drying oven at 60 °C to obtain the final product.

[0051] Example 4: Preparation method of the fourth type of cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial

[0052] Using 0.30 g of copper sulfate pentahydrate (CuSO4·5H2O) and 0.30 g of thiourea (CH4N2S) as raw materials, they were dissolved in 100 mL of deionized water and then added to a 200 mL hydrothermal reactor. The reaction was carried out at 180 °C for 24 hours. After centrifugation at 16000 rpm / min for 5 min, the mixture was dried in a vacuum drying oven at 60 °C to obtain Cu2S nanoparticles. Subsequently, the synthesized Cu2S nanozyme and cerium nitrate (Ce(NO3)3·6H2O) were added to 20 mL of 0.05 M NaOH solution at a molar ratio of 1:2.5. The mixture was stirred in air at 25 °C at 1200 rpm / min for 22 hours, washed several times with pure water, centrifuged at 16000 rpm / min, and then dried in a vacuum drying oven at 60 °C to obtain the final product.

[0053] Example 5: Preparation method of the fifth type of cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial

[0054] Using 0.30 g of copper sulfate pentahydrate (CuSO4·5H2O) and 0.30 g of thiourea (CH4N2S) as raw materials, they were dissolved in 100 mL of deionized water and then added to a 200 mL hydrothermal reactor. The reaction was carried out at 180 °C for 24 hours. After centrifugation at 10000 rpm / min for 8 min, the mixture was dried in a vacuum drying oven at 60 °C to obtain Cu2S nanoparticles. Subsequently, the synthesized Cu2S nanozyme and cerium nitrate (Ce(NO3)3·6H2O) were added to 20 mL of 0.05 M NaOH solution at a molar ratio of 1:3. The mixture was stirred in air at 25 °C at 1500 rpm / min for 22 hours, washed several times with pure water, centrifuged at 10000 rpm / min, and then dried in a vacuum drying oven at 60 °C to obtain the final product.

[0055] like Figure 1 and Figure 2 TEM images and XRD patterns of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Examples 3 to 5 show that the Cu2S-CeO2 heterojunction materials prepared in Examples 3 to 5 have a uniform nanoparticle structure with a particle size distribution range of 500-800 nm, and a clear interfacial contact is formed between Cu2S and CeO2 nanoparticles, confirming the successful construction of the heterojunction. Figure 2In the XRD pattern, the diffraction peaks at 2θ = 29.2°, 31.8°, and 47.9° correspond to the (102), (103), and (110) crystal planes of Cu2S (PDF#06-0464), respectively, while the characteristic peaks at 28.5°, 47.5°, and 56.3° match the (111), (220), and (311) crystal planes of CeO2 (PDF#43-1002). The absence of impurity peaks indicates high crystallinity and good purity of the heterojunction. These structural features provide a fundamental basis for the material's photocatalytic antibacterial and antioxidant properties.

[0056] Antibacterial performance testing: *Porphyromonas gingivalis* and *Fusobacterium nucleatum* were used to evaluate the antibacterial activity of the materials. The antibacterial effect was investigated using the plating method. A nanozyme heterojunction solution was mixed with a bacterial suspension (600 μL, 1 × 10⁵ CFU mL⁻¹). The mixture was spread on LB (Luria Bertani) medium and incubated for 1 day. The colony count (CFU) was counted, and the inhibition rate was calculated according to the literature.

[0057] inhibition ratios = [(N0-N test )÷N0]×100%

[0058] Where N0 represents the number of colonies in the control group, N test This indicates the number of colonies in the Cu2S @ MSN - SCS group.

[0059] The antibacterial properties of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Examples 3 to 5 are shown in the table below:

[0060] The antibacterial properties of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Example 3 are shown in the table below:

[0061] ;

[0062] The antibacterial performance evaluation results showed that the Cu2S-CeO2 nanozyme heterojunction material prepared in this invention exhibited excellent antibacterial activity against *Porphyromonas gingivalis*. The antibacterial rate of Example 3 (Cu2S:CeO2=1:1) reached 98.5% when the material concentration was 100 μg / mL, significantly better than that of single components Cu2S (94.0%) and CeO2 (91.0%). This synergistic antibacterial effect mainly stems from the following mechanism: First, the electronic coupling at the heterojunction interface enhances the photocatalytic activity of the material, generating more hydroxyl radicals (.OH) and superoxide radicals (O2) under near-infrared light irradiation. - ( ) and other reactive oxygen species; secondly, the CeO2 component through its variable Ce 3+ / Ce4+ The redox pair continuously catalyzes the decomposition of hydrogen peroxide produced by bacterial metabolism, disrupting the bacterial redox balance. Most importantly, the heterojunction structure effectively inhibits the recombination of photogenerated electron-hole pairs, significantly improving quantum efficiency. Further experimental data show that, under a 1:1 molar ratio (Example 3), the material exhibits optimal antibacterial performance, which is closely related to its optimal electron transfer efficiency and maximum active site exposure area. This synergistic mechanism of "photocatalytic sterilization-chemokinetic therapy" demonstrates significant advantages in the treatment of periodontitis, providing an important reference for the development of novel antibacterial materials.

[0063] The content of Cu2S-catalyzed H2O2-generating .OH (hydroxyl radical) in the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials prepared in Examples 3 to 5 after illumination was detected by electron paramagnetic resonance (EPR) technology.

[0064] like Figure 3 As shown, the experimental results indicate that no obvious hydroxyl radical (.OH) signal was detected in the material under dark conditions. However, after irradiation with 808 nm near-infrared light (1.5 W / cm²) for 5 minutes, a typical .OH characteristic peak (1:2:2:1 quartet) was clearly observed in the EPR spectrum. This result conclusively confirms that the Cu₂S component in the heterojunction can efficiently catalyze the production of highly oxidizing .OH from H₂O₂ under light irradiation. This photoresponsive radical generation characteristic provides direct evidence for the antibacterial function of the material under near-infrared light irradiation, and also reveals its potential application value as a photodynamic therapy agent. Notably, the intensity change of the EPR signal is positively correlated with the irradiation time, indicating that the catalytic activity of the material can be precisely controlled by the irradiation parameters.

[0065] Antioxidant performance testing, the test results are as follows Figure 4As shown, the antioxidant performance test results indicate that the Cu2S-CeO2 nanozyme heterojunction material prepared by this method exhibits excellent catalase-mimicking activity. Quantitative analysis was performed using a catalase assay kit, and the catalytic activity was evaluated by detecting the absorbance change of the red product at a wavelength of 520 nm. Experimental data show that when the molar ratio of Cu2S to CeO2 is 1:1 (Example 3), the material exhibits the best catalytic efficiency (2.4 μM / min / mg), which is 100% higher than that of pure Cu2S (1.2 μM / min / mg). This significant enhancement is mainly attributed to the electron transfer channels formed at the heterojunction interface, which effectively promote the catalytic reaction. Notably, when the CeO2 ratio increases to 1:3 (Example 4), the catalytic activity significantly decreases to 0.3 μM / min / mg. This may be because excess CeO2 covers the active sites on the Cu2S surface, hindering the catalytic reaction. Furthermore, at a Cu2S to CeO2 ratio of 1.5:1 (Example 5), the activity was 0.9 μM / min / mg, further confirming that 1:1 is the optimal component ratio. Particularly noteworthy is the material's unique photoresponsive properties: under near-infrared light irradiation, the Cu2S component selectively generates reactive oxygen species to exert antibacterial effects; while under dark conditions, the CeO2 component dominates free radical scavenging. This intelligent, responsive "antibacterial-antioxidant" dual-function synergistic mechanism allows its functional properties to be dynamically adjusted according to the actual needs of periodontitis treatment, demonstrating broad application prospects in the field of oral disease treatment.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials, characterized in that, Including the following steps: Cu2S nanoparticles were prepared by hydrothermal synthesis using copper sulfate pentahydrate CuSO4·5H2O and thiourea CH4N2S as raw materials. The preparation of Cu2S-CeO2, a heterojunction nanomaterial of cuprous sulfide-cerium oxide nanoenzyme, was carried out using Cu2S nanoparticles and Ce(NO3)3·6H2O as raw materials. The preparation of Cu2S nanoparticles via hydrothermal synthesis using copper sulfate pentahydrate (CuSO4·5H2O) and thiourea (CH4N2S) as raw materials involves the following steps: Step 01: Dissolve copper sulfate pentahydrate CuSO4·5H2O and thiourea CH4N2S in deionized water; Step 02: Add the mixture obtained in Step 01 into a hydrothermal reactor and react at 180°C for 24 hours; Step 03: Centrifuge and filter the precipitate obtained in step 02, and wash the precipitate with deionized water. Step 04: The precipitate obtained in step 03 is dried in a vacuum drying oven at 60°C to obtain Cu2S nanoparticles. The preparation of Cu2S-CeO2, a cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial, using Cu2S nanoparticles and Ce(NO3)3·6H2O as raw materials, involves the following steps: Step 05: Mix Cu2S nanoparticles and Ce(NO3)3·6H2O, and add the mixture to sodium hydroxide solution. Stir the mixture at 25°C for 22 hours. The molar ratio of Cu2S nanoparticles to cerium nitrate Ce(NO3)3·6H2O is 1:1, and the stirring speed is 500 rpm / min to 1500 rpm / min. Step 06: Centrifuge and filter the reaction product obtained in step 05 to obtain the reaction precipitate, and wash the obtained reaction precipitate with deionized water. Step 07: The reaction precipitate obtained in step 06 is placed in a vacuum drying oven and dried at 60°C to obtain the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial Cu2S-CeO2.

2. The method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials according to claim 1, characterized in that, In step 01, the molar ratio of copper sulfate pentahydrate CuSO4·5H2O and thiourea CH4N2S is 1:(0.5-1).

3. The method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials according to claim 1, characterized in that, In step 03, when washing the obtained precipitate with deionized water, the volume of the deionized water should be 5 to 10 times that of the precipitate.

4. The method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials according to claim 1, characterized in that, In step 03, when centrifuging and filtering the precipitate, the centrifugation speed is 8000 rpm / min-16000 rpm / min and the centrifugation time is 5 min-10 min.

5. The method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials according to claim 1, characterized in that, In step 05, the molar concentration of the sodium hydroxide solution is 0.05M-0.1M.

6. The method for preparing cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterials according to claim 1, characterized in that, In step 06, when centrifuging the reaction product, the centrifugation speed is 8000 rpm / min-16000 rpm / min, and the centrifugation time is 5 min-10 min.

7. An application of a cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial, characterized in that, The application of the cuprous sulfide-cerium oxide nanoenzyme heterojunction nanomaterial Cu2S-CeO2 prepared by the method described in claim 1 in the preparation of periodontitis treatment drugs.

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