polycaprolactone as a potential drug delivery system for the chemotherapy against cervical cancer

Journal Pre-proof pH-sensitive core-shell electrospun nanofibers based on polyvinyl alcohol/ polycaprolactone as a potential drug delivery system for the chemotherapy against cervical cancer Eryun Yan, Jinyu Jiang, Xiuying Yang, Liquan Fan, Yuwei Wang, Qinglong An, Zuoyuan Zhang, Borong Lu, Dianyu Wang, Deqing Zhang PII:

S1773-2247(19)30985-2

DOI:

https://doi.org/10.1016/j.jddst.2019.101455

Reference:

JDDST 101455

To appear in:

Journal of Drug Delivery Science and Technology

Received Date: 6 July 2019 Revised Date:

12 November 2019

Accepted Date: 9 December 2019

Please cite this article as: E. Yan, J. Jiang, X. Yang, L. Fan, Y. Wang, Q. An, Z. Zhang, B. Lu, D. Wang, D. Zhang, pH-sensitive core-shell electrospun nanofibers based on polyvinyl alcohol/polycaprolactone as a potential drug delivery system for the chemotherapy against cervical cancer, Journal of Drug Delivery Science and Technology (2020), doi: https://doi.org/10.1016/j.jddst.2019.101455. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

The as-prepared DOX loaded PVA/PCL core-shell nanofibers showed sustained and pH-responsive release of the drug. Additionally, with the change of the shell layer’s thickness, the release rate of DOX was also different.

pH-sensitive core-shell electrospun nanofibers based on polyvinyl alcohol/polycaprolactone as a potential drug delivery system for the chemotherapy against cervical cancer Eryun Yan*, Jinyu Jiang, Xiuying Yang, Liquan Fan, Yuwei Wang, Qinglong An, Zuoyuan Zhang, Borong Lu, Dianyu Wang and Deqing Zhang* College of Materials Science and Engineering, Heilongjiang Provincial Key Laboratory of Polymeric Composite Materials, Qiqihar University, Qiqihar 161006, P. R. China Corresponding author. Tel.: +86-452-2738223; fax: +86-452-2738350. E-mail address: [email protected] (E.Y. Yan) and [email protected] (D.Q. Zhang)

Abstract pH-sensitive polyvinyl alcohol/polycaprolactone (PVA/PCL) core-shell nanofibers were successfully fabricated by coaxial electrospinning method, in which PVA and PCL formed the core and shell layers, respectively. The core-shell microstructure of the fibers was certified by transmission electron microscopy (TEM). With the change of the feed ratio between PVA and PCL, there was little difference on the surface morphology of the fibers. FT-IR results indicated that there was no chemical interaction between PVA and PCL in the fibers. The as-prepared fibers can be used as a carrier for anticancer agent doxorubicin (DOX), which showed sustained and pH-responsive release of the drug. In addition, the DOX loaded fibers presented excellent performance against cervical cancer Hela cells. Such pH-sensitive

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nanofibers, which can degrade effectively in either acidic or neutral condition, have great potential for application in biomedical related fields. Keywords: Polyvinyl alcohol; Polycaprolactone; Electrospinning; Chemotherapy

1. Introduction Drug Delivery System (DDS) refers to a technical system that comprehensively regulates the distribution of drugs in living organisms in space, time and dosage [1]. Drug controlled release is one of the main purposes for drug delivery and an important topic in the field of biomedical research [1-5]. It is the use of controlled release materials as the drug delivery system, allowing the drug to be released slowly and continuously in the human body and maintaining an effective drug concentration for a long period. No need for frequent administration, it can not only maintain the efficacy of the drug, but also avoid the burst release, while reduce the side effects of the drug [6-9]. The most important component of the system is the drug-loaded entity, the carrier. A drug carrier is a system that changes the way a drug enters the body and the distribution of the drug in the body, while controlling the rate of drug release and delivering the drug to the targeted organ. An ideal drug carrier should have the following characteristics, such as stable physical and chemical properties, good biodegradability, biocompatibility and extremely low toxicity, and high drug-loading properties. This is also the overall trend in the development of drug carriers [10-13]. In recent years, the focus of drug delivery systems has been on transmission efficiency and low toxic side effects, and thus environmentally sensitive drug delivery

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systems have received increasing attention. The drug delivery system not only can target the target site, promote drug absorption, but also can quantitatively release the drug in time to achieve an effective and safe therapeutic effect of the drug [14]. The pH-sensitive drug delivery system is one of the most widely studied environmentally sensitive drug delivery systems that regulates drug release through changes in the pH of the lesion. It is well known that the cancer cells themselves are acidic, and if infected, the infected site is also acidic. In tumors or inflamed tissues, the inflamed area is accompanied by hyperthermia and acidosis, which makes it possible to decompose certain drug carriers at a lower pH stimuli response, thereby releasing the drug. It is reported that a terpolymer composed of polystyrene, methyl ether and polyethylene glycol is coated with DOX, which is stable at pH 7.4, and the drug is rapidly released at pH 5 [16]. Hydroxyapatite loaded with metformin hydrochloride is easily degraded under acidic conditions, which is indeed a green, simple pH-responsive drug carrier material [16]. For the sodium diclofenac loaded layered composite based on halloysite and natural polymers, strong acidic conditions (pH = 3) prevent the drug release. In contrast, the drug is released at pH = 5.7 and 7.8 [17]. In a word, it is meaningful of constructing a drug carrier with pH sensitivity for tumor therapy and wound healing in clinic. In the present study, pH-sensitive PVA/PCL core-shell nanofibers were successfully fabricated by coaxial electrospinning method, in which PVA and PCL formed the core and shell layers, respectively. PVA is a water-soluble synthetic polymer with good cell compatibility and no obvious toxicity to cell growth, and it is widely used in

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medical biomaterials because of its spinnability [18]. PCL is a hydrophobic synthetic polymer material with excellent biodegradability and biocompatibility, which is firstly synthesized by the Carothers Group in the 1930s [19]. The as-prepared fibers, combining the outstanding properties of both polymers, can be used as a carrier for anticancer agent DOX, which showed pH-responsive release of the drug. More concretely, the release rate of DOX loaded under pH 4 is conspicuously higher than that under pH 7.4. This is desirable since human body fluid is neutral, while the tumor site or inflamed tissues is acidic. In addition, due to the pH-sensitive degradation of the polymers, the DOX loaded fibers presented perfect performance against cervical cancer Hela cells. It is anticipated that the pH-sensitive PVA/PCL nanofibers matrix may be of great application potential in chemotherapy of cervical cancer and other solid tumors.

2. Experimental 2.1. Materials PVA was supplied by Tokyo Chemical Industry Co., LTD (Tokyo, Japan); PCL was purchased from Shenzhen Guanghua Weiye Co., LTD; DOX was obtained from Targetmolecule Corp. (Boston, U.S.A). All the other chemicals were of analytical pure and used without further purification. Deionized (DI) water was used in all the experiments. 2.2. Formation of PVA/PCL core-shell nanofibers Typically, the preparation of PVA/PCL core-shell nanofibers was according to

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our previous study [20]. PVA solution (8 w/w%) was prepared by dissolving the polymer in distilled water via stirring at 60

for 2 h and 90

for 1 h, which was used

as the core-forming solution. PCL solution with a concentration of 12 w/w% was prepared by dissolving the polymer powder in 2,2,2-Trifluoroethanol via stirring for 3 h at room temperature, which was used as the shell-forming solution. The as-prepared core-shell nanofibers were fabricated using the electrospinning equipment installed with two coaxial injectors. The needle of the injector was connected to the emitting electrode of positive polarity and a collector with aluminum foil was connected to the negative polarity. A high voltage of 18 kV was applied to the droplet of the injected solutions. The needle tip was placed 15 cm away from the collector. The flow rate of PVA solution was fixed at 0.5 mL/h and that of the PCL solution was 0.5, 0.6 and 0.7 mL/h, respectively. That was, the flow ratio between core and shell solutions (PVA/PCL) was 0.5:0.5, 0.5:0.6 and 0.5:0.7. 2.3. Degradation of PVA/PCL core-shell fibers The degradation of the PVA/PCL core-shell fibers under acidic and neutral conditions was explored. For the core-shell fibers with flow ratio of 0.5:0.5, 10 identical core-shell fiber samples were weighed and placed in 10 centrifuge tubes containing 10 mL of pH=7.4 PBS (or pH=4 PBS), respectively, and they were allowed to stand under 37

in a constant temperature shaker. During this period, the samples

were withdrawn successively after the first day, and after every third day (4 days, 7 days, 10 days, and so forth). Each sample was dried in a vacuum oven at room temperature for 2 days and it was weighed to determine the mass change at each time

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point. The procedure of the degradation test for the other two kinds of core-shell fibers was same as mentioned above. The degradation experiment was repeated for three times. 2.4. Preparation of DOX-loaded core-shell fibers and drug release study DOX was chosen to be the model drug. The DOX-loaded PVA/PCL nanofibers were prepared by coaxial electrospinning, and the preparation process was provided in Scheme 1. The mass ratio of DOX to PVA was 1:100. A certain amount of DOX-loaded PVA/PCL nanofibers was immersed in 5 mL of pH=7.4 PBS (or pH=4 PBS), and it was shaken under 37 °C in a constant temperature shaker. At appropriate intervals, the released solution was taken out and an equal amount of PBS was added. Then the amount of the released drug was analyzed at 480 nm using UV-vis spectroscopy. Based on the drawn standard curve of DOX at 480 nm, the cumulative drug release amount was calculated. The drug release experiment was repeated for three times. 2.5. In vitro cell culture for SEM measurement Hela cells were cultured onto slides with the DOX-loaded PVA/PCL core-shell nanofibers in a culture dish in RPMI-1640 medium (Gibco) supplemented with 10% fetal bovine serum (FBS, Hyclone, Logan, UT), streptomycin at 100 μg mL-1, penicillin at 100 IU mL-1 and 4 mM mL-1 glutamine at 37 °C in a humidified 5% CO2 containing atmosphere. After cultured for determined time, the slides with cell monolayers were taken out of the medium, washed with ice-cold PBS and distilled water, and fixed with fresh 1.25 wt% GA solution for 5 min. Then, the fixative was

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removed, and fresh GA solution was added to fix the cells for another 10 min. In succession, The slides were washed with ice-cold PBS or distilled water alternatively for three times. At last, the medium was removed and the slides were dried in the air. After fixing and drying, the samples were sputtered with gold and observed using SEM. 2.6. Characterization The surface morphology of the PVA/PCL core-shell nanofibers with different flow ratios was taken on an S-4300 SEM (Hitachi, Japan) at a voltage of 20 kV with working distance of 16.1 mm. The nanofiber sample was made conductive by spraying a thin layer of gold prior to observation. The average diameter and diameter distribution for each fiber sample was determined by measuring the diameters of at least 50 randomly selected fibers. A copper grid was fixed on the aluminum foil to receive a very thin layer of nanofibers, then the inner structure of the core-shell nanofibers was observed by H-7650 TEM (Hitachi, Japan) at a working voltage of 100 kV with working distance of 15 mm. To investigate the chemical interaction between PVA and PCL in the fibers, the FT-IR (PerkinElmer, USA) spectrum of the nanofibers with the flow ratio of 0.5:0.5 was conducted. The contact angle was tested for confirming the hydrophilicity of the nanofibrous membrane, which was carried out on a JY-82B device made in China.

3. Results and discussion 3.1. Morphology and inner structure of the PVA/PCL core-shell nanofibers

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PVA/PCL core-shell nanofibers were successfully fabricated by coaxial electrospinning. The morphology of the fibers was characterized by SEM, shown in Fig. 1. In the procedure of electrospinning, the flow rate of PVA solution was fixed at 0.5 mL/h, and that of the PCL solution gradually increased from 0.5, 0.6 to 0.7 mL/h. In general, with the change of the feed ratio between PVA and PCL, there was little difference on the morphology of the fibers. All the as-prepared nanofibers oriented randomly on the substrate and a measure of adhesion among the fibers existed. Thus, with the increase of the shell flow rate, the diameter of fibers was largely increased, which can be obviously observed from Fig. 1A, B and C. It can be deduced that the shell flow rate played an important role in adjusting the size of the core-shell nanofibers. In addition, seen from the graphs of the fiber diameter distribution (Fig. 1a, b and c), all the three samples showed wide distribution of fibers’ size. The percentage of fibers with large size for the PVA/PCL fibers (flow ratio of 0.5: 0.7) was more than that of the fiber samples (flow ratio of 0.5: 0.5 and 0.5: 0.6). The inner structures of the three PVA/PCL fiber samples (flow ratio of 0.5:0.5, 0.5:0.6 and 0.5:0.7) were characterized by TEM, shown in Fig. 2. The core layer and the shell layer of the fibers were clearly observed, indicating that the core-shell structure of the PVA/PCL fibers was successfully constructed. When the shell flow rate was different, the microstructure of the fibers have not changed except for the thickness of the shell. As can be seen from Fig. 2, the diameters of all the three kinds of fibers were approximately 200 nm, but as the shell flow rate increased, the shell thickness became larger and larger (the shell thicknesses of Fig. 2A, 2B and 2C were

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51 nm, 64 nm and 85 nm, respectively). 3.2. Chemical structures analysis of the PVA/PCL core-shell nanofibers The chemical structures of the PVA/PCL core-shell fibers were investigated by FT-IR spectra and the results were presented in Fig. 3. Fig. 3A, B, and C are the FT-IR spectra of pure PCL nanofibers, pure PVA nanofibers, and the PVA/PCL core-shell fibers with the flow ratio of 0.5:0.5, respectively. For the pure PCL nanofibers (Fig. 3A), the sharp peaks observed at 2944 and 2867cm-1 could be assigned to asymmetric and symmetric stretching vibrations of methylene groups. The band corresponding to the carbonyl stretching vibrations in PCL can be seen at 1731 cm-1. The bands appeared at 1294, 1240 and 1174 cm-1 are the characteristic peaks of PCL, which are related to stretching vibrations of C-C and C-O, asymmetric and symmetric stretching vibrations of C-O-C, respectively [21]. For the pure PVA nanofibers (Fig. 3B), there is a strong absorption peak of O-H stretching vibration capable of forming hydrogen bonds in 3000-3500 cm-1. The band corresponding to asymmetric C-H stretching vibration occurs at 2936 cm-1. The sharp bands occurring at 1717 and 1570 cm-1 are due to the presence of carbonyl group. The other sharp band at 1091 cm-1 corresponds to C-O stretching of acetyl groups presented on the PVA backbone. The corresponding bending and wagging of CH2 vibrations are at 1425 and 1329 cm-1, respectively [22, 23]. In Fig. 3C, all the characteristic peaks belonging to PVA and PCL exist in the FT-IR spectrum of PVA/PCL core-shell fibers and no peak position changes was observed, revealing that there is no chemical interaction between PVA and PCL in the fibers.

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3.3. Contact angle tests The size of the water contact angle reflected the hydrophilicity or hydrophobicity of the materials. The contact angle of the as-prepared PVA/PCL core-shell fibers was tested, shown in Fig. 4. As can be seen, The contact angles of the fibers with different flow ratios (0.5: 0.5, 0.5: 0.6 and 0.5: 0.7) were 124.7°, 131.16°, and 137°, respectively. It was easy to be comprehend that since the fiber shell layer was a hydrophobic polymer PCL, the surface of all the fiber samples were hydrophobic. As the flow velocity of the shell was relatively low, it was possible that a small amount of PVA exposed on the surface, leading to the decrease of the water contact angle (Fig. 4A). When the flow rate of shell solution was high, the core of fibers was well protected, as a result, the water contact angle was increased. The apparent hydrophobicity of the fiber surface proved that there was almost no PVA on the fiber surface. In combination with TEM results, it can be indirectly proved that the obtained electrospun fiber was of core-shell structure. 3.4. Degradation performance of the PVA/PCL core-shell nanofibers To investigate the degradation performance of the PVA/PCL core-shell fibers, the as-prepared fibers were placed in acidic or neutral conditions, and the weight loss rate was assessed by weighing the fibers every 3 days up to 28 days, displayed in Fig. 5. As can be seen, the three kinds of PVA/PCL core-shell fibers degraded in a predictable pattern over the 28 days’ period. Whether it was under an acidic environment (pH=4) or a neutral environment (pH=7.4), with the increase of the fiber shell’s flow rate, the fibers’ degradation rate decreased. It was well known that PCL

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degraded slowly over the course of several months [24-25], whereas PVA degraded quickly since it was a hydrophilic polymer. Thus, with the increase of the shell’s flow rate, the amount of PCL in the fibers was bound to increase. As a result, the degradation rate of fibers decreased correspondingly. That was, the larger the shell’s flow rate, the thicker the fiber’s shell, the lower the degradation rate of the fibers and the weight loss rate. Moreover, the hydrophilic PVA was encapsulated by the hydrophobic PCL, inhibiting the dissolution of PVA, which was also in favor of lowering the degradation rate of fibers. In addition, for the same fiber sample, the degradation rate of the fibers in the acidic condition was conspicuously higher than that in the neutral condition. It was revealed that the pH value of the solution had a significant effect on the degradation of PVA/PCL core-shell fibers. 3.5. In vitro drug release profiles As was known, the tissue fluid and blood surrounding the normal tissues in the human body were neutral, while the intracellular organelles and tumor site were acidic. So in the present work, a common anticancer drug DOX was loaded into the core of the PVA/PCL core-shell nanofibers, and the release profiles of the drug was explored under pH=4 and pH=7.4 PBS to test their potential applications as a local drug delivery system. For the release profiles in acidic condition (Fig. 6A), a burst release of DOX was observed for all the three kinds of core-shell fibers. The slight burst phenomenon can be attributed to a little leakage of the PVA during the electrospinning process, resulting in that some of the core part exposed on the surface of the fibers. As a result,

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DOX molecule in this position was quickly released. As the thickness of the fiber’s shell increased, the burst release of the drug was weakened to some extent. And that, except for the initial burst, on the whole, DOX was released gradually. Finally, a cumulative release of DOX can reach approximately 83%, 69% and 66% for the PVA/PCL core-shell fibers with the flow ratio of 0.5: 0.5, 0.5: 0.6 and 0.5: 0.7, respectively. Due to the coating of the outer layer with hydrophobic PCL, a barrier was formed between the drug and the release medium, which inhibited the diffusion of the drug into the medium. Especially, the larger the flow rate of shell, the more the amount of PCL. Therefore, the fibers with the largest flow rate of shell possessed the lowest amount of DOX released. It can be deduced that the thickness of the shell layer was a key factor in controlling the release rate of the loaded drug. The trend of the DOX release profiles in neutral condition (Fig. 6B) was similar to that in acidic condition. But, the cumulative release of DOX in pH=4 PBS was significantly higher than that in pH=7.4 PBS. It has been stated that the degradation rate of the fibers in the acidic condition was faster than that in the neutral condition. Hence, the rapid degradation of polymers under pH=4 even more favored the diffusion of DOX. The release profiles were carried out by the Korsmeyer-Peppas model. According to this model, the release data between 0 and 60% were successfully fitted by R%=ktn

(1)

Where R% is the percentage of drug released at time t, k is the kinetic constant and n is the release exponent that characterizes the release mechanism [26]. The fitting

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parameters are shown in Table 1. It can be seen that the DOX release curves of PVA/PCL core-shell fibers with the flow ratios of 0.5: 0.6 and 0.5: 0.7 under pH=7.4 were not fitted, since the DOX release amount was lower than 60%. The results indicated that the kinetic constant is significantly influenced by the thickness of PCL shell. The as-prepared fibers can be seen as cylinders. It has been reported that n has the limiting value of 0.45 for release from cylinders in Fickian release [27]. So, except for the delivery system of PVA/PCL (0.5:0.5, pH=4), all the others belonged to Fickian release. From the data obtained, it can be analyzed that the encapsulation of DOX into the core of nanofibers can greatly extend the release period of DOX. From the comparison of Fig. 6A and Fig. 6B, it can be seen that the release of DOX in the core-shell fibers was pH dependent. Additionally, the shell rate of fibers also played an important role in controlling the release of drug. As a pH-sensitive drug delivery system, the as-prepared co-axial nanofibrous were very useful in biomedical related fields, especially the treatment for the solid malignant tumors or inflammatory site. In fact, PVA/PCL based electrospun nanofibers have been extensively reported in previous study. Different from the system in our work, they focused on the applications of bone regeneration [28, 29], active wound dressings [30], skin substitutes [31]. 3.6. Preliminary study on the chemotherapy of cervical cancer To examine the DOX loaded PVA/PCL nanofibers in the biomedical applications, the cervical cancer Hela cells were grown onto the as-prepared fibers and the

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morphology change of the cells was tracked, as presented in Fig. 7. When the fibers with ratios of 0.5: 0.5, 0.5: 0.6 and 0.5: 0.7 were cultured with the cells for 1 day (Fig. A1, B1 and C1), the Hela cells maintained their normal morphology. And that, the shape of fibers can be clearly observed. This may be a consequence of the high surface area available for cell attachment due to the three-dimensional features and high surface area to volume ratio of the fibers. After seeding for 3 days (Fig. A2, B2 and C2), some of the cells’ state was largely changed. Their shape changed from fusiform to spherical, indicating the apoptosis of cells. The fibers disappeared from the images, revealing that degradation of the fibers happened. With the degradation of the polymers, DOX was released from the fibers, which was killing the cancer cells. After cultured for 7 days (Fig. A3, B3 and C3), the morphology of the cells can’t be identified, implying that the Hela cells were killed by the drug. It was noticed that with the change of the fibers’ flow ratio, there was no significant difference in cell morphology under the same culture time from the SEM images. In theory, the number of the apoptotic cells should be different, since the release rate of DOX was distinct (see Fig. 6). Herein, the quantitative analysis of the cells’ number was not conducted. In general, the results of the chemotherapy against cervical cancer were satisfactory. The core-shell structures of fibers had a positive effect on sustained release of the drug, which was desirable for further clinical applications. In addition, the as-prepared fibers degraded obviously in the physiological environment (after cultured for 3 days), which was promising for the tissue engineering applications. The

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as-prepared DOX loaded PVA/PCL fibers owned wide application prospect in biomedical related fields.

4. Conclusion pH-sensitive PVA/PCL core-shell nanofibers were successfully prepared by the coaxial electrospinning technology. With the change of the feed ratio between PVA and PCL, there was little difference on the surface morphology of the fibers. TEM results indicated that the shell flow rate determined the thickness of the fiber’s shell. FT-IR analysis demonstrated that there was no chemical interaction between PVA and PCL. The PVA/PCL core-shell nanofibers can be degraded effectively in either acidic or neutral environment. Additionally, the resulting fibers can be used as a carrier for anticancer agent DOX, which showed sustained and pH-responsive release of the drug. And that, the drug loaded nanofibers were quite effective in prohibiting the Hela cells attachment and proliferation. In summary, the as-prepared co-axial nanofibrous may have a powerful potential to be a safe and environment friendly drug carrier against cervical cancer and other solid malignant tumors.

Acknowledgments The present study has been supported by The Fundamental Research Funds in Heilongjiang Provincial Universities (No: 135309339).

References

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Scheme 1. Schematic showing the preparation of DOX contained PVA/PCL core-shell nanofibers.µ

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Fig. 1. SEM images of the PVA/PCL core-shell nanofibers with flow ratios of 0.5: 0.5 (A), 0.5: 0.6 (B) and 0.5: 0.7 (C); the graphs of a, b and c show the fiber diameter distribution corresponding to A, B and C, respectively.

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Fig. 2. TEM images of the PVA/PCL core-shell nanofibers with flow ratios of 0.5: 0.5 (A), 0.5: 0.6 (B) and 0.5: 0.7 (C).

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Fig. 3. FT-IR spectra of PCL nanofibers (A), PVA nanofibers (B) and PVA/PCL core-shell nanofibers with flow ratio of 0.5: 0.5 (C).

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Fig. 4. Contact angle of the PVA/PCL core-shell nanofibers with flow ratios of 0.5: 0.5 (A), 0.5: 0.6 (B) and 0.5: 0.7 (C).

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Fig. 5. Degradation curves of the PVA/PCL core-shell nanofibers in pH=4 PBS (A) and in pH=7.4 (B).

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Fig. 6. Drug release profiles of the PVA/PCL core-shell nanofibers in pH=4 PBS (A) and in pH=7.4 (B).

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Table 1. Kinetic Parameters for DOX Release from the Korsmeyer−Peppas Model.

delivery system

k/h−n

n

PVA/PCL(0.5:0.5, pH=4)

0.43±0.02

0.48±0.06

PVA/PCL(0.5:0.6, pH=4)

0.45±0.03

0.43±0.08

PVA/PCL(0.5:0.7, pH=4)

0.20±0.02

0.27±0.03

PVA/PCL(0.5:0.5, pH=7.4)

0.39±0.03

0.24±0.05

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Fig. 7. SEM images of Hela cells grown onto the DOX loaded PVA/PCL core-shell nanofibers with flow ratio of 0.5: 0.5, 0.5: 0.6 and 0.5: 0.7 for 1 day (A1, B1 and C1), 3 days (A2, B2 and C2) and 7 days (A3, B3 and C3), respectively. The Hela cells were pointed by the arrow in the images.

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Conflict of interest There is no conflict of interest to be stated.

Author Statement

Eryun Yan: Conceptualization, Methodology; Jinyu Jiang: Data curation, Writing-Original draft preparation; Xiuying Yang: Visualization, Investigation; Liquan Fan: Supervision; Yuwei Wang: Software, Validation; Qinglong An: Investigation; Zuoyuan Zhang: Software; Borong Lu: Visualization; Dianyu Wang: Investigation; Deqing Zhang: Writing- Reviewing and Editing.