Introduction

Natural, safe, green, and environmental protection are the current development trends of cosmetics in the present world. Plant extracts, especially herbal extracts, are rapidly being developed in the cosmetics industry due to their natural sources, diverse biological activities, and high safety1,2,3,4. Among numerous plant extracts, essential oils are widely used in modern skincare products because of their complex active ingredients, natural fragrances, and ease of transdermal absorption5. An increasing number of studies are exploring more plant essential oils that can be used for skin care. For instance, Eman et al.6. discovered that frankincense essential oil could restored the antioxidant capacity (SOD and CAT) and prohibited inflammatory markers (IL6, NFκB p65) in UVB-irradiated rats via downregulation of MAPK (pERK, pJNK, and pp38) and PI3K/AKT signaling pathways, alongside upregulating TGF-β expression. Mentha piperita essential oil has been found to have inhibitory effects on Staphylococcus aureus, Propionibacterium acnes, and Streptococcus pyogenes, making it a good source of natural antibacterial substances for the development of acne products7,8,9. S. H. Kim10 isolated bornyl acetate and nezukol fractionated from Cryptomeria japonica essential oil. It was found that they had a strong ability to inhibit tyrosinase activity and were considered as potential natural whitening compounds. Additionally, essential oils form Chrysanthemum boreale Makino, geranium, Curcuma longa L., calendula and Origanum vulgare L. can also play roles in whitening, anti-aging, and antibacterial effects11,12,13,14.

Dried ginger (Zingiberis Rhizoma) is the rhizome of Zingiber officinale Rosc15. It has various pharmacological effects such as antibacterial, analgesic, antioxidant, and anti-inflammatory activities16,17. Importantly, in the skin beauty and care prescriptions recorded in traditional Chinese medicine prescription classics, dried ginger has proved to be a more commonly used medicine18. Dried ginger essential oil (DGEO) is one of the main active components of dried ginger. It not only endows dried ginger with special aromatic flavor19, but also in the previous studies of our group, DGEO was found to have antioxidant and whitening effects20. However, certain factors such as poor water solubility, high volatility, and poor stability21 have limited the use and development of DGEO. Therefore, it is very important to improve its solubility and stability.

β-cyclodextrin (β-CD) is a cyclic oligosaccharide. It both have non-polar cavities and hydrophilic surface22. Due to its structural feature, the cavity of β-CD can capture essential oil without denaturing its natural compounds23,24. And improve the stability, solubility, and transdermal absorption of the active ingredients25,26. Therefore, we assume that the inclusion of DGEO with β-CD can improve the stability, water solubility and skin’s absorption of DGEO.

In recent years, electrospinning technology has attracted widely attention for its high efficiency and low cost. The idea of applying electrospinning technology in the cosmetics industry has been proposed27. Through direct spinning of organic polymers and active ingredients by electrospinning, the active ingredients are fibrillated to form nanofiber masks28,29. This preparation process is green and safe, contains no moisture, and does not add any preservatives, fragrances, or other substances. It can also retain the activity of the ingredients30,31. There are a few reports on the preparation of nanofiber facial masks with plant essential oils by electrospinning technology, which holds great potential in the field of cosmetics.

Inspired by these, we propose to use β-CD improve the stability of DGEO, and develop a nanofiber mask with DGEO by electrospinning technology. In this paper, we firstly verify anti-bacterial and anti-aging effects of DGEO. And DGEO is coated with β-cyclodextrin (DGEO-β-CD) to improve its stability. A nanofiber facial mask containing DGEO-β-CD is prepared by electrospinning. And the structures, hydrophilicity and wettability are characterized. Further, we use red blood cell hemolysis test and chick embryo chorioallantoic membrane (CAM) test to evaluate the safety of the nanofiber facial mask. This study is the first to combine electrospinning and cyclodextrin inclusion technology for the preparation of nanofiber facial mask with natural herbal essential oils, which can enrich the types of facial mask in the market and providing new ideas for the development of innovative products of herbs extracts.

Materials and methods

Materials and chemicals

All chemicals were analytical grade and used without further purification. Citric acid monohydrate, sodium citrate dihydrate and β-CD were purchased from Chengdu Colon Chemical Co., LTD. Cellulase was purchased from Shanghai Yien Chemical Technology Co., LTD. DPPH, ABTS, tyrosinase, L-tyrosine, arbutin, L-ascorbic acid, etc. were purchased from Shanghai Maclin Biochemical Technology Co., LTD. D-galactose was purchased from Chengdu Cloma Biotechnology Co., LTD. BCA protein concentration detection kit was purchased from Langeco Technology Co., LTD. TNF-α and MMP1 Test kits were purchased from Wuhan Eliret Biotechnology Co., LTD. Polyvinyl alcohol 1788 and hyaluronic acid were purchased from Chengdu Maclin Biotechnology Co., LTD. Fresh sterile defibrillated sheep blood was purchased from Beijing solarbio science & technology Co., LTD. Vitin Hair Removal Cream was commercially available hair removal cream purchased in a local pharmacy.

Evaluation of the skin care efficacy of DGEO

Our group has studied the extraction method of DGEO before. In this study, we extracted DGEO based on the enzymatic hydrolysis from previous study, and further explored the anti-bacterial and anti-aging effects of DGEO.

Antimicrobial activity of DGEO

Staphylococcus aureus and Propionibacterium acnes bacteria were used to evaluate the antibacterial effect of DGEO. The Staphylococcus aureus and Propionibacterium acnes bacteria were diluted with sterile PBS solution to 106 CFU/mL. The bacterial diluent was applied evenly on LB solid medium in the 37 ℃ constant temperature incubator (DNP-9052 thermostatic incubator, Jinghong Experimental Equipment Co., LTD, Shanghai, China) for cultivating 24 h. Then took pictures with camera to measure the determination of diameter of inhibition zone (DIZ) by Cross Patch method.

LB liquid mediums which containing 0.125 to 8 mg/mL final concentration of DGEO was prepared and placed in the test tubes. 100 µL bacterial suspension was added in LB liquid mediums. Put the test tubes in a shaking table (WD-9405 A decolorizing shaker, Liuyi Instrument Factory, Beijing, China) at 37 °C and 180 r/min for 24 h cultivating and observe the growth of bacteria. In the group without obvious turbidity, the corresponding DGEO concentration was minimum inhibitory concentration (MIC) value. In all the groups without obvious turbidity, took 50 µL of bacterial suspension and applied on the surface of LB liquid mediums, respectively. They were incubated at the same temperature for 24 h. The corresponding DGEO concentration in the group without bacterial growth was minimum bactericidal concentration (MBC) value.

Anti-aging activity of DGEO

All experimental protocols involving live animals were approved by the Ethics Committee of the School of Pharmacy, Chengdu University of Traditional Chinese Medicine. The in vivo experiments were conducted in accordance with guidelines approved by the Animal Ethics Committee for Care and Use of Laboratory Animals of the Chengdu University of Traditional Chinese Medicine.

Healthy female SPF Kunming mice were purchased from Beijing SPF Biotechnology Co., LTD. (Production license: SYXK (Beijing) 2019-0010). Skin aging mice were mainly induced by subcutaneous injection of 10% D-galactose and continuous modeling irradiation with ultraviolet (UV) lamp (UVA-340LAMP, Chuangu Lighting Technology Co., LTD, Dongguan, Guangdong, China)32. Twenty-four female KM mice were randomly divided into 4 groups: normal group (NG), model group (MG), low-dose DGEO group (DGEO-L) and high-dose DGEO group (DGEO-H), with 6 mice in each group (n = 6). All groups were treated with hair removal. Except for the normal group, the other three groups were given daily subcutaneous injection of 10% D-galactose (10 µL/g) on the neck and back. After the injection, 40 min of UV irradiation was performed. The light source was about 40 cm from the vertical height of the mice. The irradiation was performed every other day, and the modeling continued for 42 days. If acute inflammatory manifestations such as skin blisters, erosion and exudation occurred during UV irradiation, the irradiation should be suspended for 2 to 3 days. And then continued after the symptoms improved33.

Appropriate amount of skin was cut into pieces, and homogenized with tissue grinding instrument (KZ-III-F high speed low temperature tissue grinding instrument, Xavier, Wuhan, China) in 9 volumes of cold normal saline at 4℃ to get the 10% skin tissue homogenate. The skin tissue was centrifuged at 3000 g for 20 min at 4 1 C. The total supernatant was used for TNF-α and MMP-1 assays. All of the biochemical assays mentioned above were carried out following the manufacturer’s protocols of the corresponding ELISA kits (Eliret, Wuhan, China).

Synthesis and characterization of DGEO-β-CD inclusion complex (DGEO/βCD-IC)

Preparation of DGEO/βCD-IC

DGEO/βCD-IC was prepared by follows: weighed a certain amount of β-CD in pure water, and heated and stirred the solution until it was completely dissolved. The ethanol solution of DGEO was diluted with 10 times the amount of anhydrous ethanol, and was slowly dropped into the β-CD solution. After full reaction and mixing, it was cooled to room temperature, and refrigerated at 4 ℃ overnight. Centrifuging the mixed solution (8000 rpm, 10 min, 4℃) with high speed refrigerated centrifuge (D3024R desktop high speed refrigerated centrifuge, SCILOGEX, USA). Then put the bottom precipitate in the oven (DZF-6050 vacuum drying chamber, Yiheng Scientific Instrument Co., LTD, Shanghai, China) at 50 ℃, and grinding the dried bottom precipitate to obtain a creamy white powder inclusion complex.

In order to improve the yield of DGEO/βCD-IC, the factors such as core wall ratio (mass ratio of DGEO to β-CD), reaction temperature and reaction time were investigated through single factor experiment and orthogonal experiment. And we used the comprehensive score of clathrate yield and inclusion rate as the evaluation index. The ultraviolet-visible spectrophotometer (UV-6100 double beam ultraviolet-visible spectrophotometer Shanghai Mapada Instrument Co., LTD) was used to measure the absorbance of DGEO at 202 nm to determine the mass of the inclusive DGEO (Fig. 2A). And the absorption curve of DGEO was established. The absorption curve had a good linear relationship (R2 = 0.9935) in the concentration of 5 ~ 40 µg/ml (Fig. 2B). The comprehensive score was calculated according to the inclusion rate weighting coefficient 0.7 and the clathrate yield weighting coefficient 0.3. The formula can be seen as follows34:

$$\:\text{C}\text{l}\text{a}\text{t}\text{h}\text{r}\text{a}\text{t}\text{e}\:\text{y}\text{i}\text{e}\text{l}\text{d}=\frac{{\text{M}}_{clathrate\:compound}}{{\text{M}}_{\beta\:-CD}+{\text{M}}_{DGEO}}$$
(1)
$${\text{Inclusion~rate}}\frac{{\text{m}}}{{\text{M}}} \times 100\%$$
(2)

In the formula: m represents the amount of inclusive DGEO; M represents the amount of DGEO oil added.

Structural properties analysis of DGEO/βCD-IC

Scanning electron microscope (SEM)

The β-CD, physical mixture and DGEO/βCD-IC samples were treated with conductive adhesive and gold spray coating, the scanning image differences of the three samples were compared by SEM (Sigma 300 scanning electron microscope, ZEISS, Germany), and analyzed the morphological changes of β-CD before and after formation of inclusion complex.

Fourier transform infrared spectroscopy (FTIR)

The FTIR spectra of DGEO, β-CD, physical mixture and DGEO/βCD-IC were recorded using Nicolet iS20 FTIR spectrometer (Thermo Scientific Nicolet, USA). The scanning wave number range was 400–4000 cm−1, the resolution ratio was 4 cm−1, and the scanning time was 32 times.

X-ray diffraction (XRD)

XRD was performed by using Ultma IV X-ray diffractometer (Rigaku, Japan). The physicochemical properties of β-CD, physical mixture and DGEO/βCD-IC were analyzed in the range of 3 ~ 60°, Cu/Kα radiation conditions were 45 kV, 30 mA, scanning rate was 5°min−1, and the diffraction patterns were obtained and analyzed.

Thermogravimetric analysis (TGA)

The β-CD, the physical mixture and the optimized DGEO/βCD-IC were analyzed by tga 2 TGA (Mettler, Switzerland). 5 mg samples were placed in the crucible of the thermogritty analyzer. 99.99% nitrogen was used as dynamic gas at a flow rate of 100mL·h−1. The heating rate was 20 °C·min−1, and the temperature range was between 30 and 500 °C.

Synthesis of nanofiber facial mask loaded with the DGEO/βCD-IC

The polyvinyl alcohol 1788 (PVA) was dissolved in pure water and heated until completely dissolved to obtain an 8% (w/v) PVA solution. A certain amount of hyaluronic acid (HA) was dissolved in the PVA solution to prepare PVA-HA solution, and stirred it at room temperature for 5 h. Then the DGEO was dissolved in the PVA-HA solution at 2 mg/mL. The DGEO/βCD-IC were dissolved at 2, 3 and 4 mg/mL respectively and stirred for 2 h. Finally, the solutions we prepared were ultrasonically defoamed for 15 min to obtain uniform PVA, PVA-HA, PVA-HA-DGEO, PVA-HA-DGEO /βCD-IC-2, PVA-HA-DGEO/βCD-IC3, PVA-HA-DGEO/βCD-IC-4 electrospinning solutions28.

Then the spinning solutions were prepared into a facial mask by the electrospinning device (TL-Pro-BM high pressure electrostatic spinning machine, Tongli Micro Nano Technology Co., LTD, Shenzhen China). The relevant parameters were as follows: using the NO.20 needle, with 300r/min rotate speed, 18 kV spinning voltage, 0.4mL/h feed rate, and 15 cm receiving distance.

Characterization of nanofiber facial mask

SEM

Each group of nanofiber mask was cut into a certain size. And the sample was scanned and photographed by SEM with 20,000 times after sprayed. Image J software was used to measure 50 times of each sample to determine the average nanofiber diameter of each sample. The Origin software was used to analyze the diameter distribution of nanofiber and calculate the average diameter.

FTIR

The FTIR spectra of PVA, PVA-HA, PVA-HA-DGEO and PVA-HA-DGEO/βCD-IC nanofiber facial masks were performed by Nicolet iS20 FTIR spectrometer with wavelength range of 4000–600 cm−1.

Contact angle

The contact angle was used to evaluate hydrophilicity of nanofiber facial mask. The prepared nanofiber mask was made into a 1 cm× 3 cm strip-type sample, and the contact angle between the mask and the water drop was observed by the seat drop method.

Moisturizing efficacy of nanofiber facial mask

According to QB/ T4256-2011 “Guidelines for Evaluation of Moisturizing Effect of Cosmetics” to investigate the skin moisturizing ability of nanofiber mask35,36,37. A total of 10 female participant (20–25 years old) were recruited for this study. All experimental protocols involving human participants were approved by the Ethics Committee of the School of Pharmacy, Chengdu University of Traditional Chinese Medicine. We confirm that informed consent was obtained from all participants, and all experiments were performed in accordance with relevant guidelines and regulations.

We marked a test area of 3 cm×3 cm on the inner side of the subject’s arm. The interval between each test area shall be no less than 1 cm. A skin tester (M-6601 Skin tester, Fuhengtong Technology Co., LTD, Shenzhen, China) was used to measure the skin water content before applying the nanofiber facial mask. The nanofiber facial mask samples were applied to the test area after appropriate amount of pure water was sprayed. The skin water content of the test area was measured after 20 min, and each group of samples was tested 10 times.

Safety evaluation of nanofiber facial mask

Red blood cell hemolysis test

Fresh sterile defibrillated sheep blood was centrifuged to obtain the supernatant liquid. The supernatant liquid was diluted with PBS buffer to prepare erythrocyte suspension.

PVA/HA/DGEO-βCD-IC-4 nanofiber facial mask was dissolved in PBS to obtain 20 mg/mL mask solution. Then the mask solution was diluted with 1.15, 1.25, 1.35 and 1.5 times, respectively to obtain samples of different concentrations. The different concentration of sample solution and red blood cell suspension were mixed at 1:1 volume ratio (500 µL: 500 µL). After full reaction by vibration centrifugation, the absorbance value was determined at 560 nm by Spectra Max iD3 multifunctional enzyme marker (Meigu Molecular Instrument, Shanghai, Chian). Each group of samples was tested 3 times. PBS was used as self-hemolysis group and 100 mg/L SDS solution was used as total hemolysis group.

The formula for calculating HR of hemolysis rate is as follows:

$$\:\text{H}\text{R}=\frac{\text{A}1-\text{A}2}{\text{A}3-\text{A}2}\times\:100\text{\%}$$
(3)

Among them, A1, A2 and A3 are the absorbance values of test sample group, self-hemolysis group and total hemolysis group at 560 nm, respectively.

Chick embryo CAM test

The nanofiber facial mask was dissolved in PBS to obtain 10 mg/mL mask solution. 0.3mL positive control (1% sodium dodecyl sulfate solution), negative control (0.9% NaCl solution) and mask solution were directly dropped on the surface of CAM of chicken embryo, and stayed for 3 min. After that, gently cleaned the CAM surface with normal saline and poured out the liquid. The degree of bleeding, coagulation and hemolysis of blood vessels was observed by M205FA stereo microscope (Leica Microsystems, Germany) immediately. Each group tested 6 times in parallel.

We used the end point scoring (ES) method to judge the results, and scores were given by: no/light irritation, ES ≤ 12; moderate irritation, 12< ES<16; severe irritation, ES ≥ 16. The average of ES scores is calculated as follows:

\({\text{ES = (sum of bleeding, coagulation, and hemolysis observed in 6 chicken embryos)/3}}{\text{.}}\)

Results

The antimicrobial and anti-aging efiicacy of DGEO

DGEO can inhibited strains

The quantitative analysis of DIZ, MIC and MBC of Staphylococcus aureus and Propionibacterium acnes strains affected by DGEO were shown in (Fig. 1A–C). DGEO had inhibitory effects on both tested strains, but it showed different range of MIC and MBC values to the two tested strains. Propionibacterium acnes showed higher sensitivity to DGEO than Staphylococcus aureus did. The MIC and MBC values of Propionibacterium acnes were 2 mg/mL and 4 mg/mL, respectively. And the MIC and MBC values of Staphylococcus aureus were 4 mg/mL and 8 mg/mL, respectively.

DGEO alleviated the skin aging caused by UV irradiation

As we can see from the (Fig. 1D–F). The normal group of mice had smooth, good elasticity skin. There were no erythema and wrinkles, and the skin epidermis of mice was thin and intact. After 42 days of modeling, compared with the normal group, the skin of the model group was rough, dull and with poor elasticity. And the skin had erythema and deeply coarse wrinkles. The epidermis was orange peel and leather like appearance. The epidermis was obviously thickened (P < 0.01).

Compared with the model group, the skin status with DGEO intervened groups were improved to varying degrees. In the DGEO-L group, there were only a few erythema and fine wrinkles, while the skin of the DGEO-H group was significantly smoother and fewer wrinkles. But both DGEO-L and DGEO-H groups could significantly reduce the epidermal thickness of mice with aging skin (P < 0.05, P < 0.01).

The content determination result (Fig. 1G–H) showed that compared with normal group, the TNF-α and MMP-1 contents in model group were significantly increased (P < 0.05). Compared with the model group, both DGEO-L and DGEO-H groups could significantly reduced the levels of TNF-α and MMP-1 contents (P < 0.01).

Fig. 1
figure 1

Synthesis and characterization of DGEO/βCD-IC. (A) DIZ of DGEO; (B) Determination of MIC of DGEO; (C) Determination of MBC of DGEO; (D) Effect of DGEO on general skin condition of skin aging model mice; (E) HE staining of mouse skin tissue (200×); (F) Analysis of skin thickness (n = 5); (G) TNF-α factor levels in mice (n = 6); (H)MMP-1 factor levels in mice (n = 6). Compared with the normal group, #P < 0.05, ##P < 0.01; Compared with the model group, **P < 0.01.

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The optimum preparation condition and characterization of DGEO/βCD-IC

From the single factor experiments, we obtained the optimal core-wall ratio was 1:4, reaction temperature was 40℃, and reaction time was 90 min (Fig. 2C). On this basis, orthogonal test was conducted, and the optimum preparation condition was core-wall ratio 1:4, reaction temperature 40 ℃, reaction time 60 min. And the optimum process was prepared in 3 parallel batches. The comprehensive scores were 81.20, 82.51 and 81.60, respectively.

The SEM result showed that DGEO/βCD-IC distributed more evenly. It can be seen from Fig. 2D, β-CD is irregular block with large particles, flat surface, tight structure. In the physical mixture, DGEO is adsorbed on the surface of β-CD in the form of a milky opaque substance. And DGEO/βCD-ID particles are smaller, tend to be uniform in size, and have strong cohesion. The surface morphology of DGEO/βCD-ID is clearly different from that of the physical mixture, suggesting that β-CD and DGEO combine to form a new complex.

The FTIR spectra of β-CD, DGEO, physical mixture and DGEO/βCD-ID were showed in (Fig. 2E). The characteristic peaks of β-CD were 3385.04 cm− 1 (–OH), 2926.07 cm− 1(CH3), 1157.31 cm− 1(C–O), 1028.83 cm− 1(C–O–C) and 1652.62 cm− 1(H–O–H). The characteristic absorption peaks of DGEO were at 2960.78 cm− 1 (–CH3), 2919.41 cm− 1 and 2858.07 cm− 1 (–CH2). Physical mixture’s characteristic absorption peaks were at 3382.80 cm− 1 (–OH), 2926.73 cm− 1 (–CH3) and 1654.56 cm− 1 (H–O–H), which was almost identical with those of β-CD. And it had the common absorption peaks of DGEO and β-CD. And in the FTIR spectra of DGEO/βCD-IC. The peaks of DGEO disappeared at 2858.07, 2960.78 and 1446.60 cm− 1, which indicating that DGEO and β-CD have strong physical crosslinking. It can be inferred that the inclusion complex was successfully formed between DGEO and β-CD.

From the Fig. 2F of XRD, we could see that there was almost no significant difference between physical mixture and β-CD in the XRD patterns, indicating that there was no new phase has been created. And by comparison, the XRD pattern of DGEO/βCD-IC was obviously different from that of β-CD and physical mixture. At the same time, when DGEO combined with β-CD, β-CD crystal diffraction peaks mostly disappeared, which indicated that the addition of DGEO caused the rearrangement of molecular structure of β-CD.

TGA result was shown in (Fig. 2G). β-CD underwent two significant thermal degradations. However, the physical mixture and DGEO/βCD-IC had only one significant degradation process, and both showed a slow and stable degradation state before the thermal degradation of β-CD. In the whole thermal degradation process, the water loss rate of DGEO/βCD-IC was always lower than that of the physical mixture. It indicated that DGEO/βCD-IC has better thermal stability.

Fig. 2
figure 2

Synthesis and characterization of DGEO/βCD-IC. (A) UV-vis absorption spectrum of DGEO; (B) Standard curve of DGEO; (C) Single factor experiment results of preparation of DGEO/βCD-IC; (D) Scanning electron microscope images of β-CD, the physical mixture and the DGEO/βCD-IC at 500×magnification; (E) FTIR spectra of β-CD, DGEO, the physical mixture, DGEO/βCD-IC; (F) X-ray diffraction patterns of β-CD, physical mixture, and the DGEO/βCD-IC; (G) Thermogravimetric curves of β-CD, physical mixture and the DGEO/βCD-IC.

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Micro- structure of nanofiber facial mask

The SEM images were shown in (Fig. 3A). The results showed that the nanofiber facial mask was composed of a large number of randomly oriented nanofibers in a three-dimensional network structure. The diameters were 155.76 ± 22.96, 109.94 ± 17.57, 69.86 ± 19.99, 92.16 ± 23.26, 107.02 ± 18.04 and 94.22 ± 21.77 nm, respectively.

Fig. 3
figure 3

Characterization and safety of nanofiber facial mask. (A) SEM image and diameter distribution; (B) Infrared spectrum; (C) Static water contact angle; (D) Hemolysis rate of red blood cells; (E) Hemolysis rate of CAM.

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The FTIR analysis of the nanofiber facial mask was showed in (Fig. 3B). We can see that all samples had similar FTIR spectra (displacement change is ± 5 cm− 1).

The hydrophilic and moisturizing effect of nanofiber facial mask

The average contact angles of the PVA, PVA-HA, PVA-HA-DGEO, PVA-HA-DGEO /βCD-IC-2, PVA-HA-DGEO/βCD-IC-3, PVA-HA-DGEO/βCD-IC-4 nanofiber facial mask at 150ms were 59.52, 50.79, 53.23, 44.74, 56.90 and 61.67°, respectively (Fig. 3C). The results indicated that the nanofiber facial mask had good wetting ability.

The result of moisturizing property could be seen in (Table 1). Before the experiment, the average skin water content tested was about 24%. The use of PVA nanofiber facial mask did not significantly improve skin water content. After the addition of HA, the average water content of the skin surface had been improved to about 44% extent. Compared with PVA/HA groups, the water content of the PVA-HA-DGEO nanofiber facial mask decreased a little and the average water content was about 35%. The average water content of PVA-HA-DGEO/βCD-IC-2, PVA-HA-DGEO/βCD-IC-3, PVA-HA-DGEO /βCD-IC-4 nanofiber facial mask was about 44, 46, 43%.

In vitro safety evaluation of nanofiber facial mask

Red blood cell hemolysis and CAM of chicken embryo experiments were taken for evaluating the facial mask’s stimulation to eyes38. The red blood cell hemolysis results showed that nanofiber facial mask with the highest supplemental amount of DGEO only caused 4.71% red blood cell hemolysis rate (Fig. 3D).

From the results of CAM of chicken embryo experiment (Fig. 3E), we could know that the negative control group had no effect on CAM vascular network and ES value was 0. In positive control, there was obvious hemolysis and coagulation, and ES value was 16. The evaluation results of six kinds of nanofiber facial masks showed that there was no hemolysis, which indicated that none of the 6 nanofiber masks had eye irritation.

Table 1 Skin moisture content.
Full size table

Discussion

In this paper, DGEO’s antibacterial and anti-aging effects were investigated. Staphylococcus aureus39is the main cause of human skin bacterial infection and Propionibacterium acne is closely related to acne. They would affect the skin’s ability to self-clean, moisturize and acne treatment40,41. The multi-function results shows that the DGEO has the ability to inhibit Staphylococcus aureus and Propionibacterium acnes. And its MIC are 4 and 2 mg·mL−1, respectively. DGEO can obviously improve the skin condition of senescent mice and inhibit UV-induced epidermal thickening. Study42 has shown that under long-term UV irradiation, the expression level of TNF-α in the skin can be significantly increased. And then activating ROS by the P38-MAPK signaling pathway to promote the aging of human dermal fibroblasts. In addition, matrix metalloproteinases (MMPs) participate in the downstream pathway of ROS induced collagen degradation. In aging skin, reactive oxygen species increase the transcription of MMP gene through a series of cascade reactions, resulting in the imbalance of MMPs in the skin. Thus, accelerating the degradation of collagen in the skin and exacerbating skin aging43.

In our research, we discovered that DGEO could reduce the inflammatory response of mice with aging skin model by down-regulating the expression level of TNF-α and the production of MMP-1. It may relate to the anti-inflammatory effect and inhibiting collagen degradation, which needs further research. Combine with our previous studies, we investigated the antioxidant and anti-tyrosinase activities of DGEO in vitro. It found that DGEO had clear effects on DPPH and ABTS free radicals. The IC50 was 12.10 mg/mL and 2.834 mg/mL, respectively. In addition, DGEO had a strong inhibitory ability to tyrosinase, and its IC50 was 0.868 7 mg/mL. This indicates that DGEO has antioxidant effects for inhibiting DPPH and ABTS and skin brightening effects for inhibiting tyrosinase, and has the potential to be developed into skin care products.

β-CD can improve the stability of components, improve bioavailability, increase antioxidant activity, and promotes skin permeability44,45,46. We chose orthogonal test to select the optimum preparation technology of DGEO/βCD-IC. The optimum inclusion conditions are as follows: mass ratio of DGEO to β-CD is 1:4, reaction temperature is 40 ℃ and reaction time is 60 min. Under these conditions, the average inclusion rate is 84.75%, the average clathrate yield was 74.82% and the average composite score is 81.77. It showed that the inclusion process has good repeatability and stability. Among these three factors, the core wall ratio has the greatest effect on the results, followed by the reaction time and the reaction temperature. In order to further verify the inclusion compounds, it was characterized by SEM, FTIR, XRD and TGA. The results shows that the particle distribution of DGEO/βCD-IC is uniform. The infrared absorption peak changes obviously, which indicates that the crystal structure changes, and a new phase is produced. The thermal stability of DGEO/βCD-IC is significantly improved and the degradation process is slower than that of the physical mixture. It shows that the effective package of β-CD improves the stability of DGEO. The results shows that the DGEO/βCD-IC could not only effectively improve the stability of DGEO, but also facilitate the further development of DGEO cosmetics.

PVA is a non-toxic, hydrophilic, biodegradable, and low-cost spinnable biomedical material47. At the same time, as a natural glycosaminoglycan, HA has rich carboxylic and hydroxyl functional groups. It has high solubility in water and could effectively capture water to form gels28. What’s more, some studies have indicated that when HA was in mixture with other compounds, there is hopeful to have an anti-aging effect though its moisturizing48,49. In this study, PVA, PVA-HA, PVA-HA-DGEO and PVA-HA-DGEO/βCD nanofiber facial masks were successfully prepared by electrospinning.

Meanwhile, we used SEM, FTIR, contact angle and moisturizing efficacy to characterize the nanofiber facial masks. The SEM results shows that the nanofiber facial mask was composed of a large number of randomly oriented nanofibers in a three-dimensional network structure. The nanofibers made by electrospinning with simple PVA and PVA\HA solution are uniformly distributed and with no string of beads. After DGEO is added, it is not effectively encapsulated. The properties of nanofibers are unstable and a large number of spindle bodies appear. When DGEO is added in the form of clathrate compound, it could be effectively encapsulated in the nanofibers. And the nanofibers are uniformly distributed and no string of beads. The slight variation in fiber diameters may be related to the difference in the viscosity and conductivity of spinning solutions50. And FTIR results of nanofiber facial masks showed that a wide and deep absorption peaks at 3305 cm−1. It is attributed to the superimposed characteristic absorption peaks of O-H bond or N-H bond tensile vibrations. The peak at 2931 cm−1 is the stretching vibration of C-H bond of alkyl. And the absorption peak at 1249 cm−1 is mainly the C-H variable angle vibration of peptide bond. All samples have similar FTIR spectra, which means that the prepare process of nanofiber facial masks is just physical mixing, and no chemical reaction. It indicating that DGEO is confined in the fiber dressing by van der Waals forces.

With the better hydrophilicity of the mask has, it would have a faster rate of transdermal absorption. The hydrophilicity of the mask is related to the number of hydrophilic groups contained on the surface51. In order to characterize the wettability of nanofiber mask, the static contact angle was measured. The results shows that the nanofiber facial mask is hydrophilic. And due to the addition of a large number of polar groups in HA and PVA, the surface static contact Angle is reduced, and the hydrophilicity of the nanofiber mask is increased52,53. With the increase of lipophilic DGEO concentration, the hydrophilicity of nanofiber mask is affected to some extent. But on the whole, the PVA-HA-GEO/βCD nanofiber facial mask have good wettability. In addition, moisturizing property is one of the important indexes to evaluate the standard of facial mask54. The moisture property of the prepared nanofiber facial mask could be investigated through the moisture retention test. The results of moisturizing property shows that the prepared nanofiber facial mask has good hydrating and moisturizing ability. This may be due to HA is a highly hydrophilic substance55. After combined with PVA, the moisturizing effect was enhanced. This improves the tightness of the nanofiber facial mask, effectively inhibited the diffusion of water molecules.

More importantly, facial mask is applied directly to the skin, so it is necessary to keep safe to face and eyes. We use red blood cell hemolysis test and chicken embryo CAM test to evaluate the safety of nanofiber facial mask. And the results shows that the toxicity of nanofiber facial mask to red blood cells could be negligible. And it doesn’t have eye irritation in the concentration range of 4 mg/mL, which indicates our facial mask has good security.

Finally, this study shows the potential of DGEO as a natural, safe, and multi-functional Chinese herbal extract for the development of facial masks. In order to overcome its poor stability and high volatility, DGEO is prepared into DGEO/βCD-IC, and further successfully prepare into PVA-HA-DGEO/βCD nanofiber facial masks. In our research, we have verified that DGEO has multiple cosmetic effects, and the mechanism of DGEO delaying skin aging in mice is preliminary explored. But the mechanisms of other effects are unknow, which needed to be further investigated. And we evaluate the moisturizing effect and safety of the nanofiber facial mask. It is necessary to further evaluate more beauty and skin care efficacy of the nanofiber facial mask. In addition, it needs to develop more new technologies and methods suitable for natural herbs essential oil cosmetics, so as to realize the exquisite utilization of natural herbs.

Conclusion

In this study, DGEO’s antibacterial and anti-aging effects are verified. Combine with the skin brightening and antioxidant effects of the research group before, it shows that DGEO has a good beauty effect and has the potential to be developed into cosmetics. In order to improve the stability of DGEO, DGEO was complexed with β-CD to form a DGEO-β-CD-IC. This effectively improves the thermal stability of DGEO and slows down the rate of degradation of DGEO. For better application of DGEO, DGEO-β-CD nanofiber facial mask with smooth surface and compact structure were prepared by electrospinning technology. It has a uniform distribution and a diameter between 90 and 110 nm. And the preparation of the facial mask is a physical process without chemical reaction. The facial mask has good hydrophilicity and moisturizing efficacy. It can increase the skin water content by 47.82% on average. In addition, DGEO-β-CD nanofiber facial mask is found to be highly safe in the concentration range of 4 mg/mL. The above results indicate that DGEO is suitable for the development of facial mask. This not only enriches the types of facial masks, but also provides a reference for the application of herbal extracts in skin care products, and provides a reference for the high value-added utilization of DGEO in the field of cosmetics.