Fabrication of aqueous-based dual drug loaded silk ﬁ broin electrospun nano ﬁ bers embedded with curcumin-loaded RSF nanospheres for drugs controlled release †

This paper presents a new nanofabrication method for dual drug loaded regenerated silk ﬁ broin (RSF) nano ﬁ bers, based on a simple, colloid-electrospinning technique. In this process, curcumin (CUR, hydrophobic drug), loaded in RSF nanospheres, and doxorubicin hydrochloride (DOX $ HCl, hydrophilic drug) were blended with aqueous-based RSF solutions to prepare the nano ﬁ bers embedded with CUR-loaded nanospheres in core and DOX $ HCl in shell. The dual drug loaded nano ﬁ bers showed smooth surfaces and relatively uniform diameters and dispersity. The encapsulation of CUR-loaded nanospheres and DOX $ HCl were con ﬁ rmed by electron and ﬂ uorescence microscopy. FTIR spectra and X-ray di ﬀ raction results indicated that presence of intermolecular hydrogen bonding between drug and RSF ﬁ bers and the drugs were presented in an amorphous state in the nano ﬁ bers. In vitro dissolution tests showed that CUR-loaded nanospheres/DOX $ HCl-loaded RSF core/shell nano ﬁ bers exhibited dual drug release pro ﬁ les and achieved a sustained release, furthermore, the amount of drug release in core or shell phase of nano ﬁ bers was tunable by controlling the drug-loaded content and crystal content of nano ﬁ bers with water-annealing process at di ﬀ erent temperature. The release kinetics study showed that the mechanism of drug release could be described by a Fickian model. This drug delivery system could be potentially used as local multi-drug delivery systems for treatment of several medical conditions, including breast cancer or skin cancer.


Introduction
Electrospun bers have been developed in drug delivery systems in the last number of decades due to high surface to volume ratio, porosity, and a structure that mimics the extracellular matrix (ECM) structure. 1,2Different active ingredients and polymers, both synthetic and natural, were explored as potential drug delivery systems for the treatment of various diseases, such as wound healing, 3 periodontal disease, 4 and cancer. 5Silk broin (SF), derived from Bombyx mori cocoons, is a protein polymer which has biocompatibility, slow biodegradation, superior mechanical properties making it a favorable matrix for the incorporation and delivery of therapeutic agents. 6][9] However, most of these nanobers have been produced directly by electrospinning SF mixtures with various therapeutic agents; the treatment efficacy of therapeutic agent is oen limited.1][12] Liu et al. incorporated dual growth factors into regenerated silk broin (RSF) electrospun nanober scaffolds and found that the scaffolds signicantly promoted nerve regeneration when it was implanted into mice. 13However, the fabrication of the multidrug loading nanobers is quite challenging task.It needs to consider the inuences of various factors, such as the solubility of drug, the volatility of solvent, the interactions between drug and polymer and suitable the electrospinning process.8][19] The colloidelectrospinning technique is more favorable than coaxial spinning, because a simple single-nozzle electrospinning process and easy blend nano-or microcapsules or small emulsion droplets in colloidal dispersion solution.][22] Curcumin (CUR), a potent bioactive agent, was found in turmeric exhibiting a variety of good properties like antioxidant, anti-inammatory, anticancer. 23,24But its clinical application is currently limited, due to its low bioavailability and poor solubility in aqueous media.Doxorubicin hydrochloride (DOX$HCl) is hydrophilic antitumor and anticancer drugs.It was found that the two drugs could achieve synergistic therapeutic effect in cancer therapy. 25,26n this paper, we developed a new and convenient method to prepare dual drug loaded silk broin electrospun nanobers embedded with CUR-loaded RSF nanospheres in all aqueous system.In brief, rstly, CUR, hydrophobic drug, was loaded in SF nanospheres by ethanol precipitation the self-assembly of silk protein, then the CUR-loaded SF nanospheres and DOX$HCl, hydrophilic drug, were blended with RSF aqueous solutions to produce nanobers through a colloidelectrospinning technique.The encapsulation of CUR-loaded nanospheres in core phase and DOX$HCl in shell phase of the nanobers were examined by electron and uorescence microscopy.By controlling the amount of drug-loaded and crystal content of RSF matrix, we achieved the purpose of control the dual drug release rate.And the drug release kinetics was further studied.
Preparation of pure regenerated silk broin (RSF) aqueous solution RSF aqueous solution was prepared using previously described procedure. 27Briey, cocoons of Bombyx mori were degummed twice with 0.5 wt% Na 2 CO 3 solution at 100 C for 30 min and washed with deionized water to remove the sericin.Aer drying at room temperature, the degummed bers were dissolved in a 9.3 mol L À1 LiBr solution at 40 C for 2 h.This solution was dialyzed in deionized water for 3 days with a cellulose semipermeable membrane (molecular weight cut off 14 000 AE 2000 Da), yield a solution about 2 wt%.Then, the solution was condensed to 20 wt% by forced airow at 15 C.

Preparation of single and dual drug loaded RSF electrospun solutions
CUR-loaded silk broin nanospheres were prepared by ethanol precipitation the self-assembly of silk protein method according to the literatures reported previously. 28The methods for detailed preparation are referred to Appendix ESI S1. † The preparation procedure of dual drug loaded RSF electrospun solution as follows: rst, the lyophilized CUR-loaded nanospheres were dispersed in a 0.1 M MES-Tris buffer solution at pH 6.0; doxorubicin hydrochloride (DOX$HCl) was fully dissolved in DI water; second, the suspension of CUR-loaded nanospheres and DOX$HCl solution were added simultaneously to a 20 wt% RSF aqueous solution at the weight ratio of CUR-loaded nanospheres to RSF 1 wt%, 3 wt% and 5 wt% and DOX$HCl to RSF 0.1 wt%, respectively; nal, the mixed solution was placed on a shaker for intensive mixing and sequentially concentrated to 33 wt% by airow as a dual drug loaded electrospun solution.A single drug loaded RSF electrospun solution was prepared using the same protocol, without adding DOX$HCl.

Electrospinning for single and dual drug loaded RSF nanobers
The electrospinning process is illustrated in Fig. 1.The dual drug loaded electrospun solution was transformed into a 10 mL syringe capped with a steel needle (ID ¼ 0.51 mm) as a spinneret.The electrospinning was performed by applying a voltage of 30 kV, a ow rate of 0.9 mL h À1 , and the distance between the tip of needle and the collector is 15 cm.The optimization of electrospinning parameters is referred to Appendix ESI S3. † All the electrospinning processes were carried out at around 23 AE 3 C and 45 AE 5% humidity.

Water-annealing of electrospun RSF nanobrous mats
Water-annealing process was applied to increase water-insoluble of electrospun nanobrous mats.The drug-loaded RSF nano-brous mats were peeled off from the aluminum foil and were cut into 2 cm Â 2 cm small pieces.Then the samples were placed in a vacuum oven, which a water-lled plate in the bottom chamber, at 45 and 60 C for 24 h at 90% RH.Finally, the samples were stored in a desiccator for characterization and drug release.

Characterization
The morphology of drug loaded nanobers was observed by using a Mira3 scanning electron microscopy (SEM) (TESCAN, Czech).Fiber diameters were measured using microstructure measurement soware.The average size of CUR-loaded nanospheres were measured from the nanospheres suspension by dynamic light scattering (DLS) using a Zetasizer Nano ZS90 particle size analyzer (Malvern, England).The encapsulation and distribution of CUR-loaded nanospheres and DOX$HCl in the nanobers were observed by using an Axio Scope A1 uorescence microscope (ZEISS, Germany).The embedded structure of CUR-loaded nanospheres was further characterized using a JEM-2010 high resolution transmission electron microscope (HRTEM) (JEOL, Japan).The contact angles of the electrospun nanobrous mats treated before and aer waterannealing at different temperature were measured on the JC2000D1 contact angle measuring instrument (Shanghai powereach, Chain).The average contact angles were obtained by measuring each sample three times.The interaction between drugs and RSF mats, and the structural changes of drugs-loaded electrospun nanobrous mats before and aer water-annealing, were collected on the TENSOR II Fourier-transform infrared spectrometer (Bruker, Germany) with a resolution of 4 cm À1 at the wave number range of 400-4000 cm À1 .The drug distribution in the nanobers and the structural changes of drugsloaded electrospun nanobrous mats before and aer waterannealing were obtained on a Y2000 X-ray diffraction (Dandong, China) with Cu Ka radiation in the 2q range of 5-50 at 30 kV and 100 mA, scanning speed of 3.6 min À1 .Calculation of the crystallinity (I (%)): I (%) ¼ (A i /A) Â 100% where: A i ¼ area of crystalline regions, A ¼ area of all crystalline and amorphous regions. 29The data analysis was carried out by the peak separation processing soware PeakFit v4.12.

In vitro drug release
The release studies for all nanobrous mat samples with the weight of 200 mg were immersed in the beakers containing 100 mL of release medium.The release medium was a mixture of phosphate buffer saline (PBS, pH 7.4) and ethanol (i.e. 5 : 5 v/ v ratio) as a more hydrophobic component.The solutions with samples were shaken at 100 rpm on a DKZ-2 orbital rotator (YIHENG, China) at 37 C.At predetermined time points, 4 mL of this solution was taken out, and 4 mL fresh buffer solution was added to maintain the same total solution volume.The concentration of CUR and DOX$HCl were measured by using a SQ-2800 UV-spectrophotometer (UNICO, China) at 425 nm and 500 nm, respectively.The cumulative percentage of drug release was determined from a standard calibration curve.All release studies were carried out in triplicate, and results were reported as mean AE S.D.

Analysis of drug release modelling
In order to understand drug-release mechanisms of drugloaded nanobers, the drug release proles were analyzed with the following Korsmeyer-Peppas eqn (1): where M t and M N are the cumulative amount of drug released at time t and innite time, respectively.k is constant specic to the drug delivery system, t is the release time, and n is the release exponent. 30The values of k and n can be obtained from a linear t to the plot of log(M t /M 0 ) vs. log t.

Results and discussion
The characterization of CUR-loaded nanospheres The morphology and drug loading of CUR-loaded nanospheres were observed by scanning electron microscopy (SEM) and uorescence microscope.The size of CUR-loaded nanospheres was measured by dynamic light scattering (DLS).
Results are presented in Fig. 2. The CUR-loaded nanospheres were spherical granules with a relative smooth surface; the hydrophobic CUR was loaded in the core of RSF nanospheres by hydrophobic interaction with the hydrophobic segments of silk broin.The average diameter of the CUR-loaded nanospheres were 273.3 AE 2 nm.The encapsulation efficiency and drug loading of CUR in CUR-loaded nanospheres were 40.3% and 1.2% (Appendix ESI S2 †).

The morphology analysis of drug loaded RSF nanobers
In the next step, the CUR-loaded nanospheres and DOX$HCl were mixed with RSF solution for the preparation of drugloaded nanobers.The morphology of drug-loaded nano-bers was observed by SEM and results are presented in Fig. 3.
The SEM images with the overall views of the bers showed relatively smooth and uniform nanobers.The average diameter of single drug loaded bers embedded with 3 wt% CUR-loaded nanospheres was 1224 nm (Fig. 3A(a)).Moreover, the average diameter of dual drug loaded bers, which embedded 1 wt%, 3 wt%, 5 wt% CUR-loaded nanospheres and added 0.1 wt% DOX$HCl, were 982, 987 and 1297 nm respectively (Fig. 3B(b), C(c) and D(d)).With increasing CURloaded nanospheres content, the ber diameter and distribution became larger and broader.Note that in all cases the ber diameters were at least three times larger than those of CUR-loaded nanospheres.In addition, compared Fig. 3A(a) with Fig. 3C(c), it can be found that the incorporation of DOX$HCl in the ber makes the ber diameters smaller.The possible reason is that adding DOX$HCl in the solution decreased the pH value of dual drug-loaded solution and promoted the evaporation of water from the solutions, which resulted in the decrease of ber diameter. 27e structures characterization of drug loaded RSF nanobers The structures of drug-loaded RSF nanobers embedded with CUR-loaded nanospheres were observed by TEM and uorescence microscope (Fig. 4).The CUR-loaded nanospheres were embedded in the nanober (Fig. 4A), the green uoresce came from CUR-loaded nanospheres and red uoresce came from DOX$HCl.Fig. 4B shows uorescent image of single drug loaded nanobers embedded with CUR-loaded nanospheres, it indicates that CUR-loaded nanospheres were encapsulated in nanobers.Fig. 4C and D shows dual drug loaded nanobers composited with DOX$HCl and CURloaded nanospheres at the same position of nanober mats.
It is conrm that DOX$HCl shell phase (4C) and CUR-loaded nanospheres core phase (4D) were dispersed and encapsulated in nanobers respectively.
The contact angle of drug loaded RSF nanobrous mats before and aer water-annealing The size of the contact angle is an effective method for evaluation of hydrophilic and hydrophobic materials.Aer waterannealing, the water-insoluble and strength of RSF nano-brous mats were enhanced. 31The hydrophobic properties changes of RSF nanobrous mats could reect conformation changed from the macroscopic.The results are showed in Fig. 5. Before the treatment, the contact angle was 79.0 , aer water-annealing, the contact angle increases from 106.5 to 111 with the treatment temperature increasing from 45 to 60 C.  Compared with Fig. 6A(a-c), it was found that there were several drug related weak peaks in Fig. 6A(d and e), the characteristic peaks of CUR were detected in 1278 and 1116 cm À1 (Fig. 6A(d)), suggesting that CUR-loaded nanospheres existed in RSF nanobers; the characteristic peaks of CUR and DOX$HCl were detected in 1725, 1283, 1116 and 1073 cm À1 (Fig. 6A(e)), indicating that CUR/DOX$HCl were effective loaded in RSF nanobers.In addition, there was a broad peak at 3433 cm À1 in Fig. 6A(d and e), which was a shi to the lower band of the stretching vibration of OH bands of CUR and DOX$HCl at 3505 and 3508 cm À1 , meanwhile, in the ngerprint regions, the small peaks at 872 and 760 cm À1 of DOX$HCl almost disappeared from the spectra of drug loaded nanobers, indicating that the presence of intermolecular hydrogen bonding between drugs and RSF matrix.
Fig. 6B is the FTIR spectra of drug loaded RSF nanobrous mats before and aer water-annealing with different temperature.Before the treatment (Fig. 6B(a)), the RSF nanobrous mats showed peaks around 1650 cm À1 (amide I) and 1542 cm À1 (amide II), indicating the RSF nanobrous mats were dominated by random coil conformation.Aer water-annealing at temperature of 45 and 60 C, the peak of amide I at 1650 cm À1 basically unchanged, but the peak of amide II at 1542 cm À1 was  Table 1 The contents of the amorphous and the crystalline of RSF nanofibers before and after water-annealing at different temperature a The angle of structure gradually shied to 1525 cm À1 , reecting a transition of random coil conformation to b-sheet conformation.The results of conformation transformation good agree with the observation of the contact angle.

XRD analysis
X-ray diffraction was used to further conrm FTIR observations, and the results are given in Fig. 7.The presence of many distinct peaks at 10-30 in the XRD patterns (Fig. 7A) was results of raw DOX$HCl and CUR, which showed that the DOX$HCl and CUR were crystalline. 37,38 was narrow, and the peaks at 12.2 (silk I) and at 24.3 (silk II) appeared, reecting a transition of amorphous structure to silk I and silk II structure.The contents of the amorphous and crystalline of these RSF nanobers were calculated through peak separation by Peak Fit v 4.12 soware, the results shows in Table 1.
Before the treatment, the content of amorphous of drugloaded RSF nanobers was 92.4%.Aer the treatment, the contents of crystalline silk II of that were increased from 25.87 to 31.89%, and the content of crystalline silk I of that were increased from 8.11 to 10.16%.Water-annealing treatment could induced a structure transition of RSF nanobers from amorphous to silk II structure, but the silk I structure were still existed in RSF nanobers at the processes condition of this paper, which good agreed with the previous FTIR results.

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Drug release study Fig. 8A shows the release proles of CUR from CUR-loaded RSF nanospheres, RSF nanobers embedded with CUR-loaded nanospheres, CUR-loaded RSF nanospheres/DOX$HCl-loaded core/shell RSF nanobers RSF in release medium (PBS/ ethanol ¼ 5 : 5 (v/v)) at 37 C, respectively.It can be seen that there was relatively slow release process for RSF nanobers embedded with CUR-loaded nanospheres and CUR-loaded RSF nanospheres/DOX$HCl-loaded core/shell RSF nanobers compared to that of CUR-loaded RSF nanospheres in the rst several hours.Aer the release process of 36 h, it was found that CUR release rate, RSF nanobers embedded with CUR-loaded nanospheres and CUR-loaded RSF nanospheres/DOX$HClloaded core/shell RSF nanobers, was 41.99% and 34.43% respectively, whereas the CUR release rate of CUR-loaded RSF nanospheres was up to 74.66%.In the case of drug loaded RSF nanobers, apart from the barrier of the core layer, the CUR molecules had to permeate across the shell barrier of RSF nanobers to arrive at the release medium.So the drug release rate is down to 41.99% and 34.43%, respectively.This conrms that the RSF nanobrous mats could provide a slow, long term release for a drug.
Fig. 8B shows the CUR release proles of RSF nanobers embedded with 3% CUR-loaded nanospheres and 3% CURloaded RSF nanospheres/0.1% DOX$HCl-loaded core/shell RSF nanobers in release medium of PBS/ethanol ¼ 5 : 5 (v/v) at 37 C.In the early stage (2 h) of drug release, the release rate of CUR in the dual drug loaded core/shell nanobers was faster than that of the single-drug loaded ones, which may be due to the thinning of the ber diameter aer the loading of DOX$HCl (the average diameter of dual-drug loaded core/shell bers was 987 nm and single-drug loaded bers was 1224 nm).Thus, it has a large specic surface area and could contact with the outside medium adequately, and the diffusion of drug molecules into the medium was faster.In the mid and later stage of drug release, the release rate of CUR in the dual drug loaded nanobers was slower than that of CUR in the single-drug loaded ones, and reached at 31.40% and 39.03% respectively.This may be due to the fact that dual drug loaded nanobers has relatively higher drug density than that of the single-drug loaded ones and thus reduce the diffusion velocity of the water molecules to enter the bers.These results suggested that the release behavior of CUR from dual drug loaded bers might be affected by the ber diameter and drug density. 39n order to understand the effect of crystal content of RSF nanobers on drug release, we tested the drug release behavior of single and dual drug loaded RSF nanobers treated with water-annealing at different temperature and the drug release proles are illustrated in Fig. 8C and D. It can be seen that (Fig. 8C) the release level of DOX from 5% CUR-loaded nanospheres/0.1% DOX$HCl-loaded RSF core/shell nanobers was higher than the release level of CUR from the same one.This is because DOX$HCl was loaded in shell layer of nano-bers and CUR was loaded in nanospheres which were embedded in core layer of nanobers.During the release process of the drug, the diffusion front of DOX was across the shell layer of RSF nano-bers to the release medium, while the diffusion front of CUR had to migrate through the coating layer of nanosphere to the shell layer of RSF nanobers, and then into the release medium.Meanwhile, from the point of view of the rst layer barrier of drug diffusion, the concentration gradient of DOX between the shell layer of RSF nanobers and the unsaturated release medium was higher than that of CUR between the coating layer of nanosphere and the shell layer of RSF nanobers.So the release rate of DOX was higher than that of CUR.
Compared Fig. 8C with Fig. 8D, it can be found that the release proles of CUR from nanobers followed the similar trend, whether it's from a single drug or dual drug nanobers.That is, the release rate of drug from nanobers treated at 45 C was relatively faster than that of drug from RSF nanobers treated at 60 C.This was because nanobers treated at 45 C contained low crystal content (25.87% silk II, 8.11% silk I, schematic diagram in Fig. 9B), while nanobers treated at 60 C contained high crystal content (31.89% silk II, 10.16% silk I, schematic diagram in Fig. 9C).When drug loaded nanobers was submerged in release medium, water molecules penetrated into RSF bers, RSF matrix was swollen the drug was diffusion from nanobers.The crystalline region of RSF matrix could limit the swelling ratio of the matrix and the diffusion rate of drug from nanobers, thus the presence of low crystal content in nanobers allowed greater water permeation and leaded to relatively higher release rate of drug.The schematic diagram of drug diffusion from nanobers is showed in Fig. 9.By controlling the content of drug loaded and crystal content, we can achieve the purpose of control the dual drug release rate.

Study on the release mechanism
In order to study drug-release mechanisms, we tted the drug release prole in Fig. 8C.The values of release coefficient k, diffusional exponent n, and correlation coefficient R 2 are summarized in Table 2.The R 2 value indicates that the Korsmeyer-Peppas model is best suited for the release kinetics.Research shows that the release exponent of thin lm, cylinder and sphere is 0.5, 0.45 and 0.43 according to Fickian diffusion mechanism, respectively. 40For the drug-loaded nanobers, the n value was within the limiting value of 0.45 in all the cases, the release exponent is a clear indication that Fickian model could be the principal release mechanism for drug.

Conclusions
In the present work, dual polarities drugs, curcumin (CUR, hydrophobic drug, loading in nanospheres) and doxorubicin hydrochloride (DOX$HCl, hydrophilic drug) were fabricated in aqueous-based regenerated silk broin nanobers with a simple, colloid-electrospinning technique.The content of CUR-loaded nanospheres affected the ber diameter and distribution of drug loaded nanober.TEM and uorescence microscope conrmed CUR-loaded nanospheres core phase and DOX$HCl shell phase were dispersed and encapsulated in nanobers.FTIR spectra demonstrated that RSF nanobers had good compatibility with CUR and DOX$HCl as a result of hydrogen bonds forming.XRD tests veried that dual drug components in the nanobers were presented in an amorphous state and the crystal content of RSF nanobers could be tuned by water-annealing process at different temperature.In vitro dissolution tests showed that CUR-loaded nanospheres/ DOX$HCl-loaded RSF core/shell nanobers exhibited dual drug release proles and achieved a sustained release, while the amount of drug release in core or shell phase of nanobers was tunable by controlling the drug-loaded content and crystal content of nanobers.The release kinetics study showed that the mechanism of drug release belonged to Fickian model.This drug delivery system gives the possibility to fabricate multi-drug delivery systems that needs to be achieve synergistic effect and seems to be a promising candidates for use in tissue engineering and regenerative medicine.

Fig. 2
Fig. 2 SEM image, fluorescence image and DLS image of CUR-loaded nanospheres.

Fig. 3
Fig. 3 The morphology and the diameter distribution of drug loaded RSF fibers: (A and a) RSF nanofibers embedded with 3 wt% CUR-loaded nanospheres, (B and b) RSF nanofibers embedded with 1 wt% CURloaded nanospheres in core and 0.1% DOX$HCl in shell, (C and c) RSF nanofibers embedded with 3 wt% CUR-loaded nanospheres in core and 0.1% DOX$HCl in shell (D and d) RSF nanofibers embedded with 5 wt% CUR-loaded nanospheres in core and 0.1% DOX$HCl in shell.

Fig. 4 Fig. 5
Fig. 4 TEM image and fluorescence images of drug loaded RSF nanofibers embedded with CUR-loaded nanospheres: (A) TEM image of RSF nanofibers embedded with CUR-loaded nanospheres; (B) fluorescence image of single drug loaded nanofibers embedded with CUR-loaded nanospheres; (C and D) fluorescence images of dual drug loaded nanofibers embedded with CUR-loaded nanospheres in core and DOX$HCl in shell at the same position of nanofiber mats, respectively.

Fig. 7
Fig. 7 The XRD of samples: (A) DOX$HCl (a) and CUR (b); (B) dual drug loaded RSF nanofibers before and after water-annealing at different temperature: (a) untreatment (b) treatment at 45 C (c) treatment at 60 C.
Fig. 7B(b), the dual drug loaded RSF nanobers showed broad humps pattern, absence of any distinct diffraction peaks, indicating that CUR and DOX$HCl were encapsulated in amorphous forms in the bers.Aer water-annealing at temperature of 45 and 60 C, the patterns of the dual drug loaded RSF bers cannot be seen the related characteristic diffraction peaks of CUR and DOX$HCl, but just can be seen the related silk I and silk II characteristic peaks of RSF nanobers.With the temperature increased from 45 to 60 C, the central peak at 20.6 (silk II)

Fig. 8
Fig. 8 The release profiles of drug loaded RSF nanofibrous mats: (A) the release of CUR from CUR-loaded RSF nanospheres, RSF nanofibers embedded with CUR-loaded nanospheres, and RSF nanofibers embedded with CUR-loaded nanospheres in core and DOX$HCl in shell, respectively; (B) the release of CUR from 3% CUR-loaded nanospheres RSF nanofibers and 3% CUR-loaded RSF nanospheres/0.1% DOX$HClloaded core/shell RSF nanofibers treated with water-annealing at temperature of 45 C; (C) the release of CUR and DOX from 5% CUR-loaded RSF nanospheres/0.1% DOX$HCl-loaded core/shell RSF nanofibers treated with water-annealing at temperature of 45 and 60 C, (D) the release of CUR from 3% CUR-loaded nanospheres RSF nanofibers treated with water-annealing at temperature of 45 and 60 C, respectively.

Fig. 9
Fig. 9 Schematic diagram of drug release simulation: (A) schematic diagram of CUR and DOX$HCl from untreatment sample (B) schematic diagram of CUR and DOX$HCl from low content of silk II crystal (C) schematic diagram of CUR and DOX$HCl from high content of silk II crystal.

Table 2
Parameters obtained by fitting the drug release profile of dual drug loaded RSF nanofibers treated with water-annealing at different temperature Open Access Article.Published on 15 December 2017.Downloaded on 12/18/2019 10:34:03 PM.This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.