Electrospun Fibers from Biopolymers

Keywords

Electrospinning • Polylactic acid • Polyethylene glycol • Polytrimethylene terephthalate • Artificial wool • PHBV • Implant

Synthetic biopolymers such as PLA, PEG, and PHBV that are considered to be suitable for medical applications have been made into electrospun structures. Unique crimped and bicomponent nanofibers were produced from high shrinkage polyethylene terephthalate (PET) and polytrimethylene terephthalate (PTT). The polymers were separately dissolved and electrospun into the same collector from different sources and with opposite charges. Such an arrangement led to the attraction between the oppositely charged polymers and formation of twisted fibers. Such twisted fibers were also produced from polyurethane and polyacrylonitrile and termed as artificial wool [12Li]. Figure 60.1a-d shows SEM images of the twisted fibers obtained with an average diameter of about 800 nm [12Li].

Poly(D, L-lactide-co-glycolide) (PLGA) was electrospun into fibers with diameters ranging from 500 to 800 nm and the scaffold was found to have favorable cell-matrix interactions [02Li]. Scaffolds obtained had strength of 19-23 MPa, elongation of 20-120 %, and modulus of 130-323 MPa, similar to that of skin. Composite nanofibers consisting of poly(ethylene oxide), hydrated iron, and sodium alginate were prepared for multifunctional applications

[12Moo]. Matrices containing fibers with diameters ranging from 159 to 475 nm had ultimate tensile strength of about 32 MPa. Addition of hydrated ion provided the scaffolds ability for bacterial decontamination, and the presence of sodium alginate provided antimicrobial properties [12Moo].

Similar to PLA, PHBV is a synthetic biopolymer considered to be biocompatible and suitable for medical and other applications. Considerable attempts have been made to develop electrospun structures from PHBV. Electrospun fibers from PHBV with coral-like surface microstructure were developed by Yang

et al. [13Yan]. PHBV with a molecular weight of 1,000,000 was dissolved in

© Springer-Verlag Berlin Heidelberg 2015 297

N. Reddy, Y. Yang, Innovative Biofibers from Renewable Resources,

DOI 10.1007/978-3-662-45136-6_60

Fig. 60.1 SEM images of electrospun “artificial wool” bicomponent 14 % HSPET and 13 % PAN fibers obtained using TFA/DCM (a) and PAN in DMF (b). Fibers obtained using PU in DMF (c) and PAN in DMF (d) consisted of 13 % PU and 11 % PAN [12Li]

Fig. 60.2 SEM image of PHBV nanofibers produced at 25 °C (a), 30 °C (b), and 35 °C (c)

chloroform (4-16 wt%) and fibers were electrospun by varying the voltage, dis­tance between collector and needle, and extrusion rates. SEM images in Fig. 60.2 depict the beaded and coral-like surface of the fibers. Increasing the temperature decreased the number of beads as seen in Fig. 60.2. Cytotoxicity assays showed that the fibers were biocompatible and promoted cell attachment and proliferation [13Yan]. Defect-free electrospun PHBV fibers were developed for tissue engineer­ing using dichloromethane and dimethylformamide as the solvents [11Kup]. Fibers developed had average diameter of 724 ± 91 nm and used as substrates to culture human skin fibroblast cells. Proliferation of cells on the PHBV fibers was similar to that of polystyrene control whereas gene expression of collagen I and elastin was significantly upregulated and collagen II was downregulated on PHBV fibers after 14 days of culture. The addition of angiogenis factor (R-Spondin 1) to the PHBV

Fig. 60.3 Images of the reduction in wound contracture after implantation of the PHBV fibrous scaffolds. A1 and A2 are images after 1 week and 2 weeks of negative control, respectively. B1 and B2 are images after 1 week and 2 weeks of positive control, respectively. C1 and C2, 1 and 2 are images obtained after implanting the scaffolds after weeks of PHBV fibers; D1 and D2 are weeks after R. spondin and E1 and E2 are 1 and 2 weeks after using PHBV fibers containing R. spondin [11Kup]

fibers considerably increased wound contracture as seen in Fig. 60.3. As seen in the figure, significantly higher wound healing was obtained after 7 days for the PHBV fibers with and without R. spondin, but the difference was insignificant after 14 days of culture.

Table 60.1 Properties of PHBV and PHBV-g-PVP electrospun fibers [llKha] Substrate AH (J/g) % Crystallinity Pore diameter (pm) Porosity (%) Fiber diameter (pm) Contact angle (°) PHBV 68.4 51.3 4.72 68.7 301 112.8 PHBV-g — PVP (2.5) 14.3 10.8 2.67 66.4 312 113.7 PHBV-g — PVP (7.0) 12.7 9.9 2.43 66.3 371 114.6 PHBV-g — PVP (9.0) 11.0 8.3 3.94 67.6 432 109.8 PHBV-g — PVP (10.5) 10.8 8.1 3.25 67.2 448 113.1

PHBV was grafted with poly(N-vinylpyrrolidone) groups and electrospun into fibers for potential drug delivery applications [12Wan]. Grafted PHBV was dissolved (4 %) in chloroform and electrospun into fibers. Later, drugs were loaded onto the fibers and the release behavior was studied. SEM pictures revealed bead — free fibers with surface morphology that did not change after the drugs were released from the fibers. The percentage of drug released from the fibers was found to increase with increasing graft %. Some of the properties of the electrospun fibers obtained are given in Table 60.1.

Blends of PHBV (Mw of 680,000) were also made with poly(e-caprolactone) (Mw of 80,000) and electrospun into matrices for culturing bone cells [11Kha]. The polymers were dissolved in a mixture of chloroform/dimethylformamide and the solution electrospun at various conditions. Among the various conditions studied, a l0 % solution of PHBV/PCL provided smooth fibers that promoted the attachment, proliferation, and differentiation of preosteoblastic cells. Some of the properties of the fibers are given in Table 60.2.

PHBV was also blended with poly(ethylene oxide) and the microstructural, mechanical, and thermal properties of the electrospun fibers were studied [13Bia]. Fibers obtained had diameters between 0.5 and 2.6 pm and were heavily dependent on the ratio of the blend. In terms of structure, separate crystalline phases with interdispersed amorphous phases were seen and the mechanical properties of the blend fibers (Table 60.3) were in between that of the two neat polymers [l3Bia]. In a similar study, PHB and PHB blends with PEO were electrospun into fibers with various amounts of chlorhexidine, an antimicrobial agent, and the potential of using the matrices for controlled release applications was investigated [l4Fer]. Inclusion of l % chlorhexidine resulted in high antimicrobial activity with 100 and 99.69 % reduction in colony-forming units for Escherichia coli and Staphylococcus aureus, respectively. Figure 60.4 shows the zones of inhibition of

Table 60.2 Properties of PHBV and PCL blend fibers at various ratios of PCL in the blend Sample Fiber diameter (pm) Thickness (pm) Water contact angle (°) Strength (MPa) Modulus (MPa) Elongation (%) 4 % PCL/PHBV 0.44 ± 0.09 93 ±7 121 ±2 0.98 ± 0.06 162.1 ±4.6 1.4 ±0.2 6 % PCL/PHBV 0.51 ±0.03 98 ±3 117 ± 1 1.21 ±0.38 145.6 ±3.7 2.3 ±0.6 8 % PCL/PHBV 0.58 ±0.02 109 ±4 106 ±3 1.58 ± 0.17 139.2 ±3.8 2.8 ±0.4 10 % PCL/PHBV 0.77 ± 0.02 117 ± 5 85 ±2 1.84 ±0.09 112.3 ±1.9 4.3 ±0.7 12 % PCL/PHBV 1.08 ±0.06 113 ± 6 90 ±1 1.87 ±0.11 108.8 ±2.2 4.5 ±0.5 14 % PCL/PHBV 1.79 ±0.05 110 ± 5 99 ±1 1.95 ±0.26 102.7 ±2.6 4.9 ±0.2 12 % PCL 0.96 ± 0.04 121 ±2 103 ±1 2.41 ±0.36 82.4 ±5.6 5.7 ±0.8 14 % PHBV 2.19 ±0.07 92 ±4 115 ± 3 1.79 ±0.13 126.7 ±7.1 3.8 ±0.3

Table 60.3 Tensile properties of electrospun fibers produced from the neat and blended PHBV and PEO Sample Modulus (MPa) Strength (MPa) Elongation (%) PHBV 80 ± 15 1.8 ± 0.2 30 ± 20 PHBV/PEO 80/20 40 ± 10 0.8 ± 0.2 25 ± 10 PHBV/PEO 70/30 30 ± 4 0.4 ± 0.1 30 ± 2 PHBV/PEO 50/50 50 ± 10 0.4 ± 0.2 10 ± 5 PEO 4 ± 2 0.20 ± 0.03 15 ± 4

Fig. 60.4 Digital images showing the zone of inhibition of the PHB/PEO blend membranes against E. coli (a) and S. aureus (b) at three different levels of the antimicrobial agent [14Fer]

Table 60.4 Mechanical properties of the neat PHB and PHB/PEO blend fibers containing different levels of the antimicrobial agent chlorhexidine [14Fer] Sample Modulus (MPa) Strength (MPa) Elongation (%) PHB 54 ± 5 0.95 ± 0.3 10 ± 3 PHB/PEO, 0 % 38 ± 15 0.87 ± 0.2 30 ± 6 PHB/PEO, 1 % 93 ± 15 1.91 ± 0.4 10 ± 3 PHB/PEO, 5 % 97 ± 9 1.49 ± 0.3 23 ± 4

the blend membranes against E. coli and S. aureus at three different concentrations of chlorhexidine. Mechanical properties of the fiber matrices showed considerable increase in strength and modulus but decrease in elongation after the addition of the antimicrobial agent as seen in Table 60.4. It was supposed that chlorhexidine acted as filler and had excellent interfacial adhesion resulting in increased mechanical properties [14Fer].

References

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Part VII

Fibers from Biotechnology