PCL co-mingled nanofibrous mats prepared via dual-jet electrospinning

Accepted Manuscript Preparation, characterization and hydrolytic degradation of PLA/PCL co-mingled nanofibrous mats prepared via dual-jet electrospinning Roberto Scaffaro, Francesco Lopresti, Luigi Botta PII: DOI: Reference:

S0014-3057(17)31620-8 http://dx.doi.org/10.1016/j.eurpolymj.2017.09.016 EPJ 8066

To appear in:

European Polymer Journal

Received Date: Revised Date: Accepted Date:

26 June 2017 6 September 2017 10 September 2017

Please cite this article as: Scaffaro, R., Lopresti, F., Botta, L., Preparation, characterization and hydrolytic degradation of PLA/PCL co-mingled nanofibrous mats prepared via dual-jet electrospinning, European Polymer Journal (2017), doi: http://dx.doi.org/10.1016/j.eurpolymj.2017.09.016

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Preparation, characterization and hydrolytic degradation of PLA/PCL co-mingled nanofibrous mats prepared via dual-jet electrospinning Roberto Scaffaro *, Francesco Lopresti, Luigi Botta

University of Palermo, Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale, dei Materiali, UdR INSTM di Palermo, Viale delle Scienze Ed. 6, 90128 Palermo, Italy

*Corresponding author. Mail: [email protected]. Tel: +39.09123863723

Abstract PLA/PCL co-mingled nanofibrous mats were prepared via multi-jet electrospinning. The concentration of PLA and PCL in the co-mingled mats were controlled by changing the flow rate of the two polymer solutions. The amount of PLA and PCL in the co-mingled nanofibrous mats was monitored by UV-Vis measurements through a colored dye added to PLA and by FTIR-ATR analysis. Morphology and mechanical properties of the nanofibrous mats were respectively examined by scanning electron microscopy (SEM) and tensile tests. Water contact angles measurements were also carried out in order to investigate the wettability of the materials. Finally, the hydrolytic degradation of the mats in buffer solution at pH 4, pH 7 and pH 10 were studied up to 50 days. Keywords: Hydrolytic degradation; Co-electrospinning; Dual-jet electrospinning; Polymer degradation; Co-mingled nanomats; pH dependent degradation

1. Introduction

Electrospinning is a straightforward method of producing ultrafine fibers ranging from micro- to nano-meter range diameters and with controlled surface morphology [1–5]. Electrospun nanofibers membranes show large high specific surface, high porosity as well as tunable mechanical properties and topological features [4,6,7]. In this context, a wide ranges of electrospun polymers have been extensively studied for application in catalysis [8,9], oil spill remediation [10,11], food packaging [12,13], intelligence field [14–16], drug delivery [17–19] and tissue engineering [2,3,20,21]. One of the major challenge of this method remains preparing mats with tunable properties for target applications. In this regard, multi-jet approaches can be used to fabricate co-mingled nanofibrous mats with bi- or multi-component polymers presenting different properties such as degradation rate, mechanical properties, diffusivity and so on [3]. For instance, Ding et al. reported about the preparation of co-mingled biodegradable nanofibrous mats made of poly(vinyl alcohol) (PVA) and cellulose acetate (CA) via multi-jet electrospinning [22]. Gu et al., prepared PVA/PU co-mingled nanofiber mats by dual-jet electrospinning, finding the best process conditions by adopting design of orthogonal matrix design [23]. Among the several polymer used for advanced applications such as ethyl oleate [24] or polyurethane [25], acrylonitrile- butadiene-styrene [26] and polydimethylsiloxane [27], polylactic acid (PLA) and polycaprolactone (PCL) have been extensively investigated to fabricate electrospun fibers with desired properties for tissue engineering and drug delivery applications [2,4,28–30]. PLA is a semicrystalline thermoplastic polymer that presents a fragile behavior with relative high elastic modulus and low elongation [31–36]. On the other hand, PCL is a ductile polymer intensively used in biomedical applications [34,37–43] or for bioprocess intensification [44,45], characterized by low elastic modulus and high elongation [46].

PCL has been widely used to increase the performance of PLA at room temperature by preparing PLA/PCL blends that present attractive synergic properties, referring to their mechanical and thermal behavior, [34,47,48] rheological properties [49,50] or degradation rates [51,52]. In this study, a series of PLA/PCL co-mingled nanofiber mats were prepared by dual-jet electrospinning. The relative amount of PLA and PCL were controlled by changing the flow rate of the two syringe pumps containing the polymeric solutions. The PLA:PCL weight ratio in the comingled mats was monitored UV-Vis measurements through a colored dye added to PLA nanofibrous mats and by FTIR-ATR analysis. Morphology and mechanical properties of the nanofibrous mats were examined by scanning electron microscopy (SEM) and tensile tests. Several studies reported that both PCL and PLA degradation rate are strongly pH dependent. In particular, it was found that their hydrolysis proceeds via mainly a surface erosion mechanism in alkaline solutions and homogeneously by mainly bulk erosion mechanism in acid environment [53,54]. However, to the best of our knowledge, hydrolysis of electrospun PCL/PLA co-mingled mats was not studied so far. In this work, the degradation rate of the PLA/PCL co-mingled nanofiber mats were evaluated up to 50 days in the same three different pH conditions i.e. pH 4, pH 7 and pH 10. Water contact angle (WCA) measurements were also carried out in order to investigate the wettability of the final membranes in contact with the same aqueous media.

2. Experimental section

2.1 Materials

In this work it was used a commercial grade of amorphous PLA (PLA 2002D, Natureworks®) [55]. PCL (Mw = 80 kDa), chloroform (TCM), acetone (Ac), dichloromethane (DCM), absolute ethanol (Et-OH) and the orange dye (Orange II sodium salt, dye content > 85%) were purchased by Sigma Aldrich. All the solvents were ACS grade (purity > 99%) and were used as received without any further purification. Water of double distilled quality (DDQW) was obtained from MilliQ Plus systems (Millipore, Germany). PLA and PCL were added (10 wt%) to 20 ml of TCM:Ac (2:1 vol) and DCM:EtOH (4:1) solutions respectively and completely dissolved by stirring overnight. The solvent mixtures were chosen in order to obtain a more stable electrospinning process and a more reproducible preparation of smooth and detached fibers [56,57]. The buffer solution at pH 4, pH 7 and pH 10 were purchased by Hanna Instruments Italia.

2.2 Preparation of PLA/PCL Co-mingled Nanofiber Mats by Dual-jet Electrospinning Figure 1 shows the schematics of the Dual-jet Electrospinning process.

Figure 1 - Schematics of the dual-jet electrospinning process adopted for the preparation of PLA/PCL co-mingled nanofiber mats

The PLA and PCL solutions were poured into two different 10-ml glass syringe fitted with a 19gauge stainless steel needle. A conventional electrospinning equipment (Linari EngineeringBiomedical Division, Italy) was used to prepare the nanofibers mats. The electrospinning was then performed using the following constant parameters: angle between the collector and each syringe, 45°; distance between the needle tips and the collector, 15 cm; supplied high voltage (HV), + 15 kV; temperature, 25 °C and relative humidity, 40%. It is expected that the distance between the tips of the syringes is the main parameter affecting the dispersive mixing of the fibers, which is likely to be affected more than the 3-dimensional nature of the electric field than the mechanical impingement of the jets due to their very low velocity. A preliminary study regarding the deposition rate of PCL and PLA at different flow rate was performed in order to determine the condition to prepare the co-mingled mats. In particular, 5 ml/h for PLA and 0.5 ml/h for PCL were chosen for the system presenting 75% of PLA and 25 % of PCL (3:1 wt.). Flow rates in the range 3 ml/h for PLA and 1 ml/h for PCL for the

system presenting 50% of PLA and 50% of PCL (1:1 wt.). Finally, flow rates of 1 ml/h for and 1.5 ml/h for PCL were chosen for the system 25% PLA and 75% PCL (1:3 wt.). For the neat PCL and PLA mats, a flow rate of 1 ml/h was chosen, as schematized in Table 1. Table 1 - System code of the mono-phasic and co-mingled electrospun mats and their corresponding PLA and PCL flow rates

System Code

PLA wt.%

PCL wt.%

PLA flow rate

PCL flow rate

PLA

100

0

5 ml/h

0

PLA:PCL 3:1

75

25

5 ml/h

0.5 ml/h

PLA:PCL 1:1

50

50

2.5 ml/h

1 ml/h

PLA:PCL 1:3

25

75

1 ml/h

2 ml/h

PCL

0

100

0

2 ml/h

The nanofibers obtained were collected on a grounded rotary drum (diameter = 40 mm, speed = 5 rpm) wrapped in an aluminum foil in order to obtain membranes of approximately 100 µm thickness. The collected PLA/PCL nanofibrous co-mingled mats were subsequently dried for at least 1 day under fume hood in order to remove any residual solvent. In order to grant the uniformity of the co-mingled mats, the samples were taken along 3 cm in the center of the cylindrical collector. Only for the samples used for UV-Vis measurements, an orange dye (0.5 wt.% with respect to PLA) was added to PLA solution (PLA-dye).

2.3 FT-IR/ATR analysis The chemical surface properties of the samples were assessed by spectroscopic analysis. FTIR/ATR analysis was carried out by using a Perkin-Elmer FT-IR/NIR Spectrum 400 spectrophotometer, the spectra were recorded in the range 4000–400 cm−1.

2.4 UV-Vis analysis

A series of PLA-dye mats at the same thickness (100 µm) containing 0.5 wt%, 0.25 wt% and 0.125 wt% of the orange dye was used to obtain a calibration curve correlating the absorbance peak intensity and the dye amount by using a spectrophotometer UVPC 2401 (Shimadzu Corporation). In the concentration range here investigated, the calibration curve was found to be a line. The maximum absorbance peak of the PLA-dye electrospun mats was detected at 520 nm and this value was subtracted to the absorbance of PLA mats 100 µm thick. Successively, the calibration line was used to correlate the UV absorption (at 520 nm) to the amount of dye in the co-mingled mats. Since the amount of dye in PLA was known (0.5 wt%), it was possible to deduce the amount of PLA in the mats. The difference in weight was of PCL. 2.5 Morphological analysis The samples (4 x 4 mm) were attached on an aluminum stub using an adhesive carbon tape and then sputter coated with gold (Sputtering Scancoat Six, Edwards) for 90 s under argon atmosphere before imaging to avoid electrostatic discharge during the test. The morphology of the nanofiber mats were evaluated by scanning electron microscopy, (Phenom ProX, Phenom-World).

2.6 Fibers diameter determination

Fiber diameter distribution was determined using an image processing software [58]. The plugin (DiameterJ) is able to analyze an image obtained by SEM and to find the diameter of nanofibers at every pixel along a fiber axis. The software produces a histogram of these diameters and summarizes statistics such as mean fiber diameter [59].

2.7 Wettability determination Static contact angles were measured on all the samples by using buffer solution at pH 4, pH 7 and pH 10 as fluids with an FTA 1000 (First Ten Ångstroms, UK) instrument. More in detail, 4 μL of buffer solution were dropped on the fiber mats. Images of the water on the surface were taken at a

time of 10 seconds. At least 7 spots of each composite nanofiber mat were tested and the average value was taken. The maximum scattering observed was ± 4%.

2.8 Mechanical properties Tensile mechanical measurements were carried out by using a dynamometer (Instron model 3365) on rectangular shaped specimens (10×90 mm) cut off from films. The tests were performed at a crosshead speed of 1 mm min-1 for 2 minutes and 50 mm min-1 thereafter until fracture occurred. The distance between the jaws was 20 mm, whereas the thickness was measured before each measurement was taken. The representative nominal stress-strain curves were reported for each material. The nominal stress was calculated as the ratio of the tensile force to the initial perpendicular cross section of the sample while the strain was evaluated as the ratio between the change in laws distance and the initial jaws distance. The elastic modulus was calculated from the initial part of the slope from nominal stress–strain curves. Seven samples were tested for each material and the average values of the mechanical parameters and standard deviations were reported.

2.9 Hydrolysis The hydrolysis of the electrospun mats (10 mm x 40 mm x 100 µm) was performed in 10 ml of buffer solutions (pH 4.0, pH 7 and pH 10) at 37 °C up to 50 days. At fixed times, i.e. 4, 21, 50 days, the electrospun mats were washed thoroughly with distilled water at room temperature, followed by drying under chemical hood for 1 day. After drying, the samples were weighed (mdry).

2.10 Intrinsic viscosity

The intrinsic viscosity [η] was measured by means of a iVisc Capillary Viscometer LMV 830 (Lauda Proline PV 15, Lauda-Königshofen, Germany) instrument equipped with a Ubbelohde (K = 0.009676) capillary viscometer in an oil bath thermostated at 35 °C for PLA and 30 °C for PCL [60,61]. In order to prepare the solution at the concentration of 0.1 wt%, each material was dissolved in THF under stirring at ambient temperature for 1 hour. Flow time measurements were performed in triplicate for each sample until the standard deviation was below 0.5 s. The intrinsic viscosity, [η], values was calculated according to Solomon-Ciuta by Eqn. (1) [62]: (1) where c is the concentration of the polymer solution, ηsp and ηrel are, respectively, specific and relative viscosity. The solution viscosity of each sample was obtained by averaging 5 flow measurements. The viscosimetric molecular weight (Mv) was calculated using the Mark-Houwink’s equation (Eqn. (2)): (2) The parameter values of the Mark-Houwink constants, α and K, depend upon the specific polymersolvent system. For PLA-THF, K =1.74·10–4 and α = 0.736 [60]; for PCL-THF, K = 1.396·10–4 and a = 0.786 [61].

3

Results and discussion

3.1 Determination of electrospinning conditions and verification of the relative PLA/PCL weight ratio in electrospun co-mingled nanofibrous mats The relative flow rates of PLA and PCL solutions selected to prepare PLA/PCL co-mingled nanofiber mats via dual-jet electrospinning were chosen by evaluating the thickness of PCL and of PLA electrospun mats for 60 minutes using a single-jet electrospinning.

Figure 2 – Thickness of PCL and PLA after 60 minutes of electrospinning as a function of the flow rates

Since the apparent density of the mats did not change significantly during the process, the results showed in Fig. 2, demonstrated that the flow rate of the polymeric solution strongly affect the electrospun thickness, keeping constant the other process parameters. In particular, it can be observed an increasing thickness deposition upon increasing the flow rates for both the polymers and that at the same deposition time, PLA shows smaller thickness if compared to PCL. More in detail, to achieve the same 80 µm thickness it is necessary to apply a flow rate approximately 2.5 times higher. The different deposition rate of the two systems can be ascribed to the partial losses of PLA solution deposed out of the target collector. Based on these results the PLA/PCL co-mingled electrospun mats were prepared as schematized materials and method section (see Table 1).

In order to verify that the relative amount of PLA and PCL in the co-mingled electrospun mats corresponded to the designed ones, UV-Vis measurements were carried out on PLA-dye/PCL mats. The absorbance measured as a function of the designed PLA wt. fraction is shown in Fig. 3. The analysis revealed that the absorbance of the co-mingled system linearly increase upon increasing the amount of PLA-dye. As the dye was added only to the PLA phase, this result demonstrates that the PLA content in the co-mingled mats grows as expected. These results permitted us to conclude that the amount of PLA in the co-mingled system can be finely tuned by controlling the relative flow rates of PLA and PCL during dual jet electrospinning process.

Figure 3 – UV-Vis measurements for the PLA-dye/PCL co-mingled electrospun mats as a function of the PCL fraction. Insets) Pictures of the PLA-dye/PCL co-mingled electrospun mats as a function of PCL fraction.

3.2 Morphology and FTIR-ATR of the electrospun nanofiber mats The SEM images of the electrospun PLA, PCL, and of the PLA/PCL (1:1) co-mingled nanofiber mats are respectively presented in Figs. 4a-c.

Figure 4 - SEM images of a) PLA electrospun mats; b) PLA/PCL (1:1) co-mingled nanofiber mats; c) PCL electrospun mats. Scale bars are 80 µm; Diameter size distribution of a’) PLA electrospun mats; b’) PLA/PCL (1:1) co-mingled nanofiber mats; c’) PCL electrospun mats. The vertical orientation of the picture a) is at 45° with the axial direction of the collector b) and c) are at 0° with the axial direction of the collector.

The figures show that all the fibers are in the nanoscale, randomly oriented even if a slight, although not significant, orientation along the hoop direction in particular for the PLA and PLA/PCL (1:1) electrospun mats can be observed. Furthermore, it can be noticed that the fibers are characterized by a similar diameter size distribution, as quantitatively reported in Figs. 4a’-c’. More in detail, from Fig. 4a, it is possible to observe that the PLA fibers present a homogeneous diameter all over the surface. A similar feature was observed for the morphology of PCL fibers Figs. 4c,c’ and for PLA/PCL (1:1) co-mingled nanofiber mats Figs. 4b,b’.

Figure 5 – FTIR-ATR measurements of PLA, PCL and of the co-mingled electrospun mats

Table 2 - Peak band assignment for PLA [63] and PCL [64] Peak number

Assignment

-1

Wavenumber cm

REF [63]

PLA 1

-CH- strech

3000 (asym.); 2948 (sym.)

2

-C=O carbonil strech

1747

3

-CH bend

1456

4

-CH- asymmetric; symmetric deformation

1382; 1360

5

-CH- bend

1315-1300

6

-C-O- strech

1265

7

-C=O bend

1211

8,9,10

-C-O- strech

1180, 1129, 1083

11

-OH bend

1044

12

-CH rocking mode

955, 916

13

-C-C- strech crystalline phase

869

14

amorphous phase

755

3

3

[64]

PCL 15

-CH - strech

2949 (asym.)

16

-CH - strech

2865 (sym.)

17

-C=O carbonil strech

1727

18

C–O and C–C stretching in the crystalline phase

1293

19

-C-O- strech

1240 (asym.)

20

-C-O- strech

1190 (sym.)

21

C–O and C–C stretching in the crystalline

1157

2

2

phase

In order to confirm that the surfaces observed with SEM mats are composed by both PCL and PLA forming a really uniform co-mingled system, FTIR-ATR measurements were carried out on neat PLA and PCL mats and on PLA/PCL mats (Fig. 5). The FTIR-ATR spectra of PLA and PCL, show their typical bands, as listed in Table 2 [63,64]. As expected, since the co-mingled mats are a microscopic physical mixture of non-interactive fibers, the FTIR-ATR spectrum showed bands that are typical of both PCL and PLA. In particular, pointing attention on the PLA/PCL (3:1) co-mingled system, it is possible to observe both the carbonyl stretch (1747 cm-1 for PLA and 1727 cm-1 for PCL) while in the other two co-mingled systems, the results showed a peak at 1727 cm-1 and a shoulder at 1747 cm-1. Furthermore, it can be observed that the intensity of the band depend on the amount of PLA and PCL in the co-mingled electrospun mats. The test also prove that the system is a really uniform co-mingled system in the as in the portion analyzed there are no zones with a single phase concentration

3.2 Mechanical properties Figure 6 shows the representative nominal stress-strain curves of the tensile tests carried out on neat PLA and PCL mats and on the PLA/PCL electrospun co-mingled mats. The vertical line indicates the strain level of the crosshead speed increment. PLA presents the typical nominal stress-strain curve of a fragile material with relative high elastic modulus (E) and low elongation (ε). On the contrary, PCL electrospun mats appears ductile with high εb and low E. The PLA/PCL hybrid mats showed an intermediate behavior, affected by the PLA:PCL weight ratio. In particular, on increasing the amount of PCL, the mas showed and higher elongation (ε) and reducing the Young’s Modulus (E) as shown in Figure 7.

Figure 6 – Nominal stress-strain curves of electrospun PCL, PLA and co-mingled mats

Figure 7 - Young modulus and elongation of the PLA/PCL electrospun hybrid mats as a function of PCL fraction

These results highlighted that the mechanical performances can be tuned by controlling the amount of PCL and PLA in the nanofibrous hybrid mats.

Hydrolytic degradation The hydrolytic degradation behavior of the electrospun mats was evaluated in different buffered medium (i.e. pH 4, pH 7 and pH 10) up to 50 days. The weight loss of electrospun mats at 37 °C as a function of time, are shown in Fig. 8a-c. The electrospun mats start to lose mass only after 50 days at pH 7 and pH 4 while, at pH 10, the phenomenon is observed starting at day 21. Hydrolytic tests demonstrated that pH significantly affect the weight loss in fact all the materials are more subjected to weight loss at pH 10 while seem to be less damaged at pH 7. In particular, at pH 7, PCL seems to be the most sensitive material losing approximately 11 % of the initial weight after 50 days. After the same time, a negligible weight loss was detected for PLA while the weight loss of the co-mingled systems decrease upon increasing the PLA fraction. A similar behavior was observed for system degraded at pH 4. More in detail, at pH 4, PCL is the most sensitive material losing approximately 16 % of its original weight after 50 days. On the contrary, PLA seems to be less affected at this condition losing only 1.5 % of its weight after 50 days. Similarly, to the systems at pH 7, the weight loss of the co-mingled mats decrease upon increasing the PLA fraction. On the other hand, at pH 10 the trend is completely different, as PLA seem to be the most sensitive material losing more than 75 % of the initial weight after 50 days. In this case, PCL result as the less sensitive material, losing approximately 18 % of its initial weight after 50 days. In this case, the weight loss of the co-mingled systems showed the opposite trend, decreasing upon increasing the PCL content. The extent and mechanism of hydrolysis are determined by the amount, presence and location of water molecules. Thus, the polymers’ chemical composition, hydrophobicity, size and design all play an important role in this interaction with water [65]. The differences in the degradation

behavior at different pH can be correlated with the effect of pH on hydrophilicity. The polymers at alkaline pH (pH 10) keeps its non-polar (hydrophobic) character, probably because hydroxyl ions are entrapped by the ester groups on the film surface, which lowers theirs absorption capacity. As a result, water cannot penetrate the sample and the weight loss can only be produced by superficial degradation. However, at acid pH (pH 4) the electrospun mats change from hydrophobic to hydrophilic in character during the stay in the degradation solution [53].

Figure 8 – Weigth loss of electrospun PLA, PCL and of the co-mingled mats as a function of time in the different buffered medium: a) at pH 4; b) at pH 7 and c) at pH 10

This phenomenon was confirmed by water contact angles analysis. The results, showed in Figure 9, highlighted that for both PCL and PLA the increment of pH increased their hydrophobic character.

Figure 9 – Wet contact angles measurements on electrospun PCL and PLA for the different buffered solution used as hydrolytic medium

The co-mingled mats degradation behavior are obviously affected by the presence of the two polymers in the same membrane. Their weight loss rate depend on the relative fraction of PLA and PCL indicating that the less sensitive polymer (i.e. PLA at pH 4 and pH 7; PCL at pH 10) are able to reduce the weight loss of the whole co-mingled mats. The results highlighted the possibility to tune the degradation rate of the electrospun mats by controlling the relative amount of PCL and PLA during the dual-jet electrospinning process. The changes in molecular weight of PCL and PLA for the three different degradation conditions, presented different behaviors (Fig. 10). In alkaline environment (pH 10), the viscosimetric

molecular weight of PCL and PLA remains unchanged even after 50 days;

Figure 10 – Viscosimetric molecular weight of neat electrospun PLA and PCL and of the same materials after 50 days of hydrolytic degradation in different buffered medium

On the other hand, at pH 4, the viscosimetric molecular weight was seen to move towards lower values for both the polymers. Similar behavior of the dependence of the molecular weight was also From a morphological point of view, before hydrolysis, all the films showed a homogeneous and smooth fibrous structure (Figs. 4a-c). After degradation, samples immersed in hydrolytic medium exhibit quite different morphologies after 50 days (Fig. 11). At pH 7 the morphology of PLA mats (left column) resulted without breakages but less weaved than the pristine system. A similar result was observed for the PCL system and for the PLA:PCL 1:1 co-mingled mats after 50 days in the same medium. More differences were observed for the systems exposed to pH 4. Fibers made of PCL (right column) presented a larger diameter if compared with the pristine mats, furthermore they are more irregular and with higher number of defects. On the contrary, PLA (left column) seems to be almost affected by the acid medium, presenting only few morphologic differences with the pristine system. The co-mingled system PLA:PCL 1:1 (middle column) present both the characteristic of the two systems. In fact, there are visible both large-diameter PCL fibers and the thinnest PLA fibers. The

increased diameter of PCL can be related to the bulk degradation observed at pH 4 and to its relative low Tg that can ease the swelling at hydrolytic temperature (37 °C) more than for the PLA. The alkaline medium (pH 10) affected the morphology of both PCL and PLA. PLA presented thinner and fractured fibers if compared with the pristine mats while PCL fibers resulted irregular and corrugated. The co-mingled system displayed both the features at the same time and the PCL and PLA fibers can be easily identified by the SEM image.

Figure 11 – SEM images of electrospun PLA, PCL and of the co-mingled system PLA:PCL 1:1 after 50 days in different buffered hydrolytic medium.

Conclusions

In this work, PLA/PCL nanofibrous co-mingled mats were prepared via dual-jet electrospinning. UV-Vis and FTIR-ATR measurements confirmed the effectiveness of this approach to modulate the relative amount of polymers in the co-mingled structure by tuning the respective flow rates during the process. Tensile tests confirmed that the Young modulus and the elongation of the electrospun mats depends on the composition and therefore can be tuned by controlling flow rates of PCL and PLA during dual-jet electrospinning. The hydrolytic degradation of the membranes in three different buffered medium (pH 4, pH 7 and pH 10), were monitored by following mass loss, morphology and viscosimetric molecular weight. The faster weight loss was observed at pH 10 for both PCL and PLA and for the co-mingled systems. However, in the alkaline medium, PLA was more sensitive than PCL displaying the highest weight loss (up to 75% after 50 days). These results, along with viscosimetric measurements, suggested a surface degradation at pH 10 and bulk degradation at pH 4 for both PCL and PLA. The morphology of the membranes after hydrolysis were consistent with the weight loss and viscosimetric measurements.

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Highlights 

PLA/PCL co-mingled nanofibrous mats were prepared via dual-jet electrospinning



The relative amount of polymers in the co-mingled mats can be finely modulated



The faster weight loss was observed at pH 10 for all the investigated systems



Hydrolytic tests revealed pH dependent mechanism of degradation