An insect repellent and a method of making the same

Abstract

The application is a mosquito repellent, which comprises plant mosquito repellent essential oil, chemical repellent, polylactic acid-glycolic acid copolymer, and the polylactic acid-glycolic acid copolymer encapsulates the plant mosquito repellent essential oil and the chemical repellent. The mass ratio of the plant mosquito repellent essential oil, the chemical repellent and the polylactic acid-glycolic acid copolymer is 1:1:10. The application provides a high-efficiency and safe mosquito repellent composition based on microcapsule slow-release technology and a preparation method thereof, aiming at the technical bottleneck that the existing mosquito repellent is difficult to balance long-acting protection and use safety. The application constructs a microcapsule slow-release system with a core-shell structure by introducing polylactic acid-glycolic acid copolymer (PLGA) as a wall material, which significantly prolongs the effective protection time of active ingredients.

Description

Technical Field

[0001] This invention relates to the field of mosquito repellent, and more particularly to a mosquito repellent agent and its preparation method. Background Technology

[0002] Vector-borne infectious diseases are a group of serious threats to human health transmitted by mosquitoes and other vectors. Common types include dengue fever, malaria, and Zika virus disease. Mosquito bites not only cause local skin reactions but can also carry pathogens that lead to the spread and outbreak of diseases, placing enormous pressure on public health security. Especially in tropical and subtropical regions, and in hot and humid summer environments, mosquito activity is frequent, significantly increasing the risk of exposure for the population, making the development of effective and durable personal protective measures urgently needed.

[0003] Currently, commonly used mosquito repellents are mainly divided into chemically synthesized types (such as DEET and IR3535) and plant-derived types (such as citronella oil and lemon eucalyptus oil). While chemically synthesized repellents have good mosquito-repelling effects, they pose safety risks such as skin irritation, allergic reactions, and potential neurotoxicity with long-term use. Plant-derived repellents, although generally safer, have highly volatile active ingredients and short-lasting effects, requiring frequent reapplication and offering less convenience, making them unsuitable for the protective needs of high-intensity, long-term scenarios such as prolonged outdoor work, field training, and border patrols.

[0004] To address the aforementioned issues, researchers have proposed improvement solutions. For example, Chinese patent application CN122004254A (application number: CN202610156964.8, application date: February 4, 2026) discloses a highly effective and safe plant essential oil mosquito repellent and its preparation method. This patent proposes using peppermint essential oil and perilla essential oil as core components, supplemented with at least two of lemongrass essential oil, artemisia essential oil, cinnamon essential oil, and calamus essential oil, combined with an ethanol-water solution solvent and a specific emulsifier to form a stable nanoemulsion system. This solution, through the combination of compound essential oils and ultrasonic emulsification, achieves rapid onset of action within 0.5 hours and sustained repellency for 3 hours, with repellency rates exceeding 92%. Simultaneously, by de-irritating the cinnamon essential oil, skin irritation is reduced, balancing high mosquito repellency with safety.

[0005] However, existing technologies still have certain limitations: on the one hand, the duration of action of most plant-derived repellents is still insufficient to meet the needs of all-weather outdoor operations; on the other hand, the synergistic mechanism of different essential oil components is not yet clear, and the formulation design lacks systematic guidance, resulting in the need to improve the stability and consistency of products under different environmental conditions. In addition, the preparation processes of existing products vary in complexity, and some solutions rely on specific equipment or conditions, limiting their large-scale production and widespread application.

[0006] Therefore, how to further optimize the formulation and preparation process of plant essential oil repellents, while ensuring high mosquito repellency and good safety, to extend the duration of effectiveness, improve environmental adaptability, simplify the production process, and reduce costs, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In view of the above technical problems, the present invention provides a slow-release mosquito repellent microcapsule that uses polylactic acid-glycolic acid copolymer (PLGA) as a biodegradable carrier and adopts a W / O / W double emulsion-solvent evaporation method to achieve synergistic encapsulation of citronella oil and IR3535. A mosquito repellent, characterized in that it comprises plant-based mosquito repellent essential oil, a chemical repellent, and polylactic-co-glycolic acid copolymer (PLGA), wherein the PLGA encapsulates the plant-based mosquito repellent essential oil and the chemical repellent. The mass ratio of the plant-based mosquito repellent essential oil, the chemical repellent, and the PLGA is 1:1:10.

[0008] The plant-based mosquito repellent essential oil is one or more of lemon eucalyptus oil, citronella oil, and lavender essential oil.

[0009] The chemical repellent is one or more of DEET, N, or picaridin.

[0010] A method for preparing a mosquito repellent is as follows: S1: Colostrum preparation; S2: Preparation of double emulsion; S3: Solvent evaporation and microsphere curing; S4: Freeze-drying process.

[0011] The specific method for preparing the colostrum is as follows: Weigh 10 mg PLGA, 1 mg citronella oil, and 1 mg DEET, place them in a 5 mL centrifuge tube, add 1 mL dichloromethane, and sonicate to fully dissolve them to obtain the organic phase. Then add 50 μL of distilled water as the inner aqueous phase, and use an ultrasonic cell disruptor at 50% power for continuous sonication for 30 s to form a white, turbid W / O colostrum.

[0012] The specific method for preparing the re-emulsion is as follows: 2 mL of 1% sodium cholate solution is added to another centrifuge tube as the external aqueous phase. The above-mentioned proemulsion is transferred to it using a pipette to form a layered oil-water two-phase system. The system is then placed in an ultrasonic cell disruptor and sonicated for 1 min at 65% power and pulse mode (1 s on, 1 s off) to obtain the W / O / W re-emulsion.

[0013] The specific method for solvent evaporation and microsphere solidification is as follows: 20 mL of 0.5% sodium cholate solution is placed in a beaker and then placed on a magnetic stirrer. While stirring at 800 rpm, the double emulsion is slowly added to the external aqueous phase, and stirring is continued at room temperature for 30 min. As dichloromethane evaporates, the solution gradually changes from turbid to clear.

[0014] The specific method for the freeze-drying process is as follows: The obtained solution is transferred to a vacuum drying oven and vacuum-treated at room temperature for 10 min to further remove residual dichloromethane. Then, it is centrifuged at 12,000 rpm for 30 min, and the supernatant is discarded. The precipitate is resuspended in 10 mL of distilled water and washed, and then freeze-dried for 48 h to obtain PLGA-encapsulated citronella oil-DEET microcapsules.

[0015] The beneficial effects of this invention are as follows:

[0016] To address the technical bottleneck of existing mosquito repellents in simultaneously providing long-lasting protection and ensuring safety, this invention provides a highly efficient and safe mosquito repellent composition based on microencapsulation sustained-release technology and its preparation method. Compared to existing technologies, this invention offers the following advantages: First, by introducing polylactic acid-glycolic acid copolymer (PLGA) as the wall material, the present invention constructs a core-shell structured microcapsule sustained-release system, which significantly prolongs the effective protection time of the active ingredient.

[0017] PLGA, as a biodegradable polymer material, possesses excellent film-forming properties and controlled-release characteristics. This invention utilizes PLGA to encapsulate mosquito-repellent active ingredients within microcapsules, forming a uniform and dense sustained-release reservoir on the skin surface, thereby achieving precise control over the release rate of the active ingredients. Experimental results show that mosquito repellent products using this invention's technology provide effective protection for over 48 hours, significantly superior to commercially available ester-based repellents (approximately 6 hours) and simple plant essential oil products (approximately 1.5-2.5 hours), successfully overcoming the application bottleneck of existing plant-derived repellents' short protection time and the need for frequent reapplication.

[0018] Second, while extending the protection time, the present invention significantly reduces the skin irritation and potential toxicity of the active ingredients.

[0019] Through the physical isolation provided by PLGA microcapsules, the direct contact between the mosquito-repellent active ingredients and the skin is significantly reduced, effectively minimizing the risks of skin irritation, allergic reactions, and neurotoxicity that chemical repellents may cause. Simultaneously, the sustained-release properties of the microcapsules allow for a more gradual and controllable release of the active ingredient into the skin per unit time, avoiding the safety hazards associated with single high-concentration exposure. The product of this invention has undergone skin irritation testing, with results showing no or mild irritation, making it suitable for a wide range of users, including those with sensitive skin.

[0020] Third, this invention achieves synergistic effects of sustained release, reduces the frequency of use, and improves user experience and compliance.

[0021] Traditional plant-based essential oil repellents are highly volatile and have a short duration of effectiveness, requiring users to reapply every 1-2 hours. This significantly impacts their usability in prolonged exposure scenarios such as outdoor work, field training, and border patrols. This invention, utilizing PLGA microencapsulation technology, extends the effective protection time to a single application covering the entire working period, drastically reducing the need for reapplication. This not only reduces the user's workload but also ensures the continuity and reliability of the protective effect, providing a more durable and safer solution for breaking the transmission chain of mosquito-borne infectious diseases.

[0022] In summary, this invention overcomes the technical bias of existing mosquito repellent products that struggle to achieve both high-efficiency mosquito repellency and long-lasting safety. Through the innovative design of the PLGA microcapsule sustained-release system, it achieves a breakthrough improvement in protection time and simultaneous improvement in safety, providing a green, efficient, and sustainable new approach to personal protection for the prevention and control of vector-borne infectious diseases. Attached Figure Description

[0023] Figure 1 SEM image of PLGA encapsulated with citronella oil and DEET microcapsules; Figure 2 The particle size and zeta potential of PLGA-encapsulated citronella oil and DEET microcapsules; A represents the particle size of PLGA-encapsulated citronella oil and DEET microcapsules; B represents the zeta potential of PLGA-encapsulated citronella oil and DEET microcapsules. Figure 3 XRD patterns of PLGA (A) and PLGA-encapsulated citronella oil and DEET microcapsules (B); A is the XRD pattern of PLGA (A); B is the XRD pattern of PLGA-encapsulated citronella oil and DEET microcapsules (B); Figure 4 Infrared spectra of PLGA (red) and PLGA encapsulated with citronella oil and DEET microcapsules (black); Figure 5 TG (black) and FTG (red) curves for PLGA encapsulated with citronella oil and DEET microcapsules; Figure 6 To improve the room temperature stability of PLGA-encapsulated citronella oil and DEET microcapsules; A represents the appearance at different times; B represents the change in particle size; C represents the change in pH value; and D represents the change in encapsulation efficiency. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Example 1

[0026] Experimental Procedure for Encapsulating Citronella Oil and DEET Microcapsules with PLGA

[0027] Plant-based mosquito repellent essential oils use citronella oil, while chemical repellents use DEET. 1. Colostrum preparation Weigh 10 mg PLGA, 1 mg citronella oil, and 1 mg DEET, place them in a 5 mL centrifuge tube, add 1 mL dichloromethane, and sonicate to dissolve completely to obtain the organic phase. Then add 50 μL of distilled water as the inner aqueous phase, and sonicate continuously for 30 s using an ultrasonic cell disruptor at 50% power to form a white, turbid W / O colostrum.

[0028] 2. Preparation of double emulsion Add 2 mL of 1% sodium cholate solution to another centrifuge tube as the external aqueous phase, and transfer the above-mentioned colostrum into it using a pipette to form a layered oil-water two-phase system. Place this system in an ultrasonic cell disruptor and sonicate for 1 min at 65% power and pulse mode (1 s on, 1 s off) to obtain a W / O / W re-emulsion.

[0029] 3. Solvent evaporation and microsphere curing Measure 20 mL of 0.5% sodium cholate solution into a beaker and place it on a magnetic stirrer. While stirring at 800 rpm, slowly add the double emulsion to the aqueous phase and continue stirring at room temperature for 30 min. As the dichloromethane evaporates, the solution gradually changes from cloudy to clear.

[0030] 4. Post-processing and freeze-drying

[0031] The resulting solution was transferred to a vacuum drying oven and treated under vacuum at room temperature for 10 min to further remove residual dichloromethane. Then, it was centrifuged at 12,000 rpm for 30 min, and the supernatant was discarded. The precipitate was resuspended in 10 mL of distilled water, washed, and then freeze-dried for 48 h to obtain PLGA-encapsulated citronella oil-DEET microcapsules.

[0032] Example 2

[0033] The only difference from Example 1 is that it consists of the following parts by weight of raw materials: The plant-based mosquito repellent essential oil is made from lemon eucalyptus oil, and the chemical repellent is made from DEET. The ingredients are 1 part lemon eucalyptus oil, 1 part DEET, and 10 parts PLGA.

[0034] Example 3

[0035] The only difference from Example 1 is that it consists of the following parts by weight of raw materials: The plant-based mosquito repellent essential oil is a combination of citronella oil and lavender essential oil, and the chemical repellent is a combination of DEET and picaridin. The ingredients are 1 part plant-based mosquito repellent essential oil, 1 part chemical repellent, and 10 parts PLGA.

[0036] Example 4

[0037] Experimental results of PLGA encapsulating citronella oil and DEET microcapsules

[0038] 1. Scanning Electron Microscopy (SEM) Analysis: The morphology of the microcapsules was observed using a Nova NanoSEM 430 with an accelerating voltage of 15 kV. Representative SEM images were captured at 20000× magnification. The results showed that the PLGA-encapsulated citronellol-DEET microcapsules had uniform particle size and good sphericity, indicating that the target microcapsules were successfully prepared.

[0039] 2. Particle size and Zeta potential: The hydrodynamic diameter and Zeta potential of the microcapsules were determined using a Zetasizer Nano ZS dynamic light scattering (DLS) instrument.

[0040] The results showed that the average particle size of the prepared microcapsules was about 224 nm, with a uniform particle size distribution, which is consistent with the characteristics of nanoparticles; the zeta potential was -27.6 mV, indicating that the colloidal system has good physical stability.

[0041] 3. X-ray diffraction (XRD) analysis: XRD tests were performed on a MiniFlex 600 diffractometer.

[0042] Pure PLGA exhibited broad, diffuse diffraction peaks in the range of 2θ ≈ 18°–22°, indicating that it is an amorphous polymer. No sharp crystalline diffraction peaks were observed, consistent with the characteristics of PLGA reported in the literature. After encapsulation with citronella oil and DEET, the XRD pattern maintained a broad peak morphology, with no new sharp diffraction peaks appearing. Furthermore, the intensity of the original amorphous peaks decreased slightly, and the peak shape broadened slightly. This suggests that citronella oil and DEET are completely dispersed at the molecular level or in an amorphous state and embedded within the amorphous framework of PLGA, without forming an independent crystalline phase. The composite microcapsules maintain the amorphous structure, which is beneficial for the uniform encapsulation of the active ingredients and subsequent controlled release.

[0043] 4. Fourier transform infrared spectroscopy (FTIR) analysis: The chemical composition of PLGA-encapsulated citronella oil and DEET microcapsules was characterized using FTIR spectroscopy.

[0044] Compared to pure PLGA, the C=O stretching vibration peak near 1750 cm⁻¹ showed a slight shift or change in shape, indicating a slight influence of the active ingredient incorporation on the ester environment. Multiple absorption peaks appeared in the C–H bending vibration region of 1500–1300 cm⁻¹, suggesting the superposition of characteristic functional groups from citronella oil or IR3535. The C–O–C and C–O–H stretching vibrations in 1300–1000 cm⁻¹ showed a slight increase in intensity, further supporting the contribution of additional C–O bonds in the complex. The fingerprint region of 800–400 cm⁻¹ showed subtle changes but still maintained the PLGA backbone structure. In summary, the characteristic peaks of citronella oil and IR3535 were superimposed on the PLGA spectrum without disrupting the PLGA backbone, confirming the successful encapsulation of the two active ingredients within the microcapsules.

[0045] 5. Thermogravimetric analysis (TGA): The thermal degradation behavior of microcapsules is analyzed by TGA.

[0046] The TG curves show that the initial thermogravimetric temperature of the microcapsules is approximately 200–220 °C, corresponding to the thermal degradation range of the PLGA backbone; the DTG curves show the maximum weight loss rate peak at approximately 310 °C. The slight weight loss observed in the 100–200 °C range may be attributed to the volatilization or low-temperature thermal decomposition of some citronella oil or IR3535, indicating that the thermal stability of the active ingredients themselves is lower than that of PLGA. Microencapsulation can effectively improve the thermal stability of citronella oil and IR3535. The residual mass of the sample at 500 °C is less than 10%, indicating that the system mainly consists of biodegradable organic components with almost no high-temperature stable inorganic residues.

[0047] 6. Storage stability study: The microcapsules were kept at room temperature for 28 days to observe the changes in physical appearance, particle size, pH value and encapsulation efficiency.

[0048] The results showed that the appearance of the microcapsules did not change significantly within 28 days, the particle size remained within a controllable range, the pH value fluctuated within ±0.5, and the encapsulation efficiency remained above 95%. This indicates that the microcapsule system has good physicochemical stability under room temperature storage conditions.

[0049] Example 5

[0050] Release rate of mosquito repellent active ingredients

[0051] Microspheres were dispersed in ethyl acetate, and an in vitro release experiment was conducted at 37 °C. Samples were taken periodically to measure the absorbance of the mosquito-repellent active substances in the release medium, and the cumulative release rate at each time point was calculated. The cumulative release rates of PLGA-encapsulated citronella oil and DEET microcapsules at 10 h, 24 h, 48 h, 72 h, and 96 h were 37.70%, 53.84%, 89.72%, 100%, and 100%, respectively, indicating that the microcapsules can achieve continuous release for 48–72 h.

[0052] Example 6

[0053] Mosquito repellency tests were conducted according to GB / T 13917.9-2009. A total of 16 personnel were tested, and the duration of release was measured by applying the above-mentioned mosquito repellent composition (application amount 1.5 μL / cm²). The test results are shown in Table 1. Comparative Example 1 is Liushen Floral Water; Comparative Example 2 is Longrich Mosquito Repellent; Comparative Document 3 is Artemisia argyi mosquito repellent. Continuous release time Example 1 72 h Example 2 48 h Example 3 50 h Comparative Example 1 6.0 h Comparative Example 2 6.3 h Comparative Example 3 2.0 h The foregoing has shown and described the basic principles, main features, and advantages of the present invention. The various components mentioned in this invention are common technologies in the existing field. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A mosquito repellent, characterized in that... The product comprises plant-based mosquito repellent essential oil, chemical repellent, and polylactic acid-glycolic acid copolymer, wherein the polylactic acid-glycolic acid copolymer encapsulates the plant-based mosquito repellent essential oil and the chemical repellent. The mass ratio of the plant-based mosquito repellent essential oil, the chemical repellent, and the polylactic acid-glycolic acid copolymer is 1:1:

10.

2. A mosquito repellent according to claim 1, characterized in that... The plant-based mosquito repellent essential oil is one or more of lemon eucalyptus oil, citronella oil, and lavender essential oil.

3. A mosquito repellent according to claim 1, characterized in that... The chemical repellent is one or more of DEET, N, or picaridin.

4. A mosquito repellent according to claim 1, characterized in that... Its preparation method is as follows: S1: Colostrum preparation; S2: Preparation of double emulsion; S3: Solvent evaporation and microsphere curing; S4: Freeze-drying process. Plant-based mosquito repellent essential oils and chemical repellents.

5. A mosquito repellent according to claim 1, characterized in that... The specific method for preparing the colostrum is as follows: weigh polylactic acid-glycolic acid copolymer (PLGA), plant-based mosquito repellent essential oil, and chemical repellent, place them in a centrifuge tube, add dichloromethane, and sonicate to fully dissolve them to obtain an organic phase; then add distilled water as the inner aqueous phase, and use an ultrasonic cell disruptor to continuously sonicate at 50% power to form a white, turbid W / O colostrum.

6. A mosquito repellent according to claim 1, characterized in that... The specific method for preparing the double emulsion is as follows: Add a 1% sodium cholate solution as the external aqueous phase to another centrifuge tube, and transfer the above-mentioned primary emulsion into it using a pipette. A layered oil-water two-phase system is formed. The system is placed in an ultrasonic cell disruptor and sonicated for 1 minute at 65% power in pulse mode (1 second on, 1 second off) to obtain a W / O / W re-emulsion.

7. A mosquito repellent according to claim 1, characterized in that... The specific method for solvent evaporation and microsphere solidification is as follows: A 0.5% sodium cholate solution is measured and placed in a beaker, which is then placed on a magnetic stirrer. While stirring, the emulsion is slowly added to the external aqueous phase, and stirring continues at room temperature. As dichloromethane evaporates, the solution gradually changes from turbid to clear.

8. A mosquito repellent according to claim 1, characterized in that... The specific method of the freeze-drying process is as follows: the obtained solution is transferred to a vacuum drying oven and vacuum-treated at room temperature to further remove residual dichloromethane; then centrifuged, the supernatant is discarded, the precipitate is resuspended and washed with distilled water, and then freeze-dried to obtain the plant-based mosquito repellent essential oil-chemical repellent loaded with PLGA.

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