**3. Characterization of GOnPs-polymer composite electrospun scaffold meshes**

Electrospun GO-polymer (like PCL, PLGA or PVA) composite scaffolds showed enhancement of conductivity (*σ*) dielectric constant (*ε*) with their threshold values around 0.85 and 0.75wt% of GOnPs , respectively , for the case of GO-PCL (**Figure 1**) and GO-PLGA.

**Figure 2a** showed the well dispersed GOnPs solution, spin-coated GO film and sheet (prepared from pure GOnPs water solution). **Figure 2b** showed the characteristic GO peak appearing at 2*θ* = 11.1°, corresponding to a lattice *d*-spacing of 0.78 nm. For the GO-PCL or GO-PLGA meshes, an XRD peak (**Figure 2c**) appeared at 21.65° representing the crystalline phase of the polymer with no peak for GO around 2*θ* = 11.1°. The absence of GO peak was also reported earlier in case of GO-PVA composite [17] which indicated disappearance of the regular and periodic structure of graphene oxide, the formation of fully exfoliated structures, and the homogeneous distribution of GOnPs in the polymer matrix [18].

**Figure 1.** Dependence of (a) effective dielectric constant (*ε*) and (b) conductivity (*σ*) of the GO-PCL composite on GO concentration *f*GO.

**Figure 2.** (a) Well dispersed GO-PCL solution (1), a free standing bendable tin GO sheet composed of GOnPs prepared by solution casting (2) which can be dispersed in water and spin coated GO sheet on cover glass (3) produced from GO solution. (b) The X-ray diffraction patterns of GO and pristine graphite powder, (c) GO-PCL and PCL, respectively.

The SEM micrograph of a GO sheet surface shown in **Figure 3a** indicated uniformly rough surface morphology. Inset of **Figure 3a** also presented FESEM micrograph showing the surface morphology of thin GO sheet which indicated wrinkles stacked in multiple GOnPs layers which favoured cell proliferation.

**Figure 3b** represented the SEM micrograph of the electrospun fibrous meshes and the selected area electron diffraction (SAED) pattern (inset of **Figure 3b**) with (average fibre diameter of 490 ±125 nm and porosity ~80–85%. **Figure 3c** presented the FESEM micrograph showing morphology of the broken edge of a GO sheet and inset of **Figure 3c** showed the HR TEM image of a single layer of the GOnPs film.

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earlier in case of GO-PVA composite [17] which indicated disappearance of the regular and periodic structure of graphene oxide, the formation of fully exfoliated structures, and the

**Figure 1.** Dependence of (a) effective dielectric constant (*ε*) and (b) conductivity (*σ*) of the GO-PCL composite on GO

**Figure 2.** (a) Well dispersed GO-PCL solution (1), a free standing bendable tin GO sheet composed of GOnPs prepared by solution casting (2) which can be dispersed in water and spin coated GO sheet on cover glass (3) produced from GO solution. (b) The X-ray diffraction patterns of GO and pristine graphite powder, (c) GO-PCL and PCL, respectively.

The SEM micrograph of a GO sheet surface shown in **Figure 3a** indicated uniformly rough surface morphology. Inset of **Figure 3a** also presented FESEM micrograph showing the surface morphology of thin GO sheet which indicated wrinkles stacked in multiple GOnPs layers

**Figure 3b** represented the SEM micrograph of the electrospun fibrous meshes and the selected area electron diffraction (SAED) pattern (inset of **Figure 3b**) with (average fibre diameter of 490 ±125 nm and porosity ~80–85%. **Figure 3c** presented the FESEM micrograph showing morphology of the broken edge of a GO sheet and inset of **Figure 3c** showed the HR TEM

homogeneous distribution of GOnPs in the polymer matrix [18].

224 Umbilical Cord Blood Banking for Clinical Application and Regenerative Medicine

concentration *f*GO.

which favoured cell proliferation.

image of a single layer of the GOnPs film.

**Figure 3.** (a) SEM micrograph showing surface morphology of thin GO sheet (inset shows the FESEM micrographs of a particular portion the surface). (b) SEM micrograph of the GO-PCL electrospun meshes (inset shows the HRTEM image of GO present in GO-PCL along with the selected area electron diffraction (SAED) image). (c) FESEM micrographs of a broken edge of thin GO sheet (inset shows the HRTEM image of a single layer GO film). (d) FTIR spectra of GO sheets and pristine graphite powder (inset) distinguishing the behaviour of graphene and graphite powder. In GO intense bond around 3438 cm−1 corresponding to O–H band of CO–H is observed [6].

Raman is the vibration spectroscopic technique used to characterize GOnPs and identify the presence of GO in GO-PCL composite. Raman spectra of GO sheet as shown in **Figure 4a**, indicated the characteristic feature of GO peaks at frequencies around 1345 and 1597 cm−1, respectively, for the G and D band usually assigned to the E2g phonon of Csp2 atoms and a phonon breathing mode of symmetry A1g.Far infra-red (FTIR) spectra of GO and pristine graphite powder were shown in **Figure 4b**. The intense band at 3438 cm−1 is attributed to the O–H band of CO–H. The band at 1639 cm−1 is associated with the stretching of the C═O bond of carbonyl and carboxyl group.

**Figure 4.** (a) Raman spectra of GO and GO-PCL composite meshes. (b) FTIR spectra of PCL and GO-PCL mesh distinguishing the behaviour of the two spectra. The spectra of GO-PCL if different from those of PCL and GO indicating strong coupling of GO and the PCL polymer. GO-PCL showed absorption bands at 1727 cm−1 indicating carbonyl stretching [20].

Deformation of the C–O bans is observed at the band present at 1070 cm−1. FTIR spectra (**Figure 4b**) of GO-PCL showed absorption bands at 1727 cm−1 indicating carbonyl stretching. The bands appearing at 1295 and 1240 cm−1 represented the C–O and C–C stretching bonds [19]. The bands at 1239 and 1175 cm−1 were comparable with the asymmetric C–O–C stretching bonds indicating characteristic absorption [6] of PCL and strong interaction between GOnPs and polymer matrises.

**Figure 5** indicates electrospun GO-PCL composite meshes which degrade up to ~16% in PBS (phosphate buffer saline) solution whereas electrospun PCL meshes degrade ~9% after 30 days of time interval. GO-PCL composite mesh showed optimized degradability rate that is suitable for cellular growth. Hydrophilicity of the GO sheet and GO-PCL composites were measured by contact angle measurement. Wetting (CAw) and dewetting (CAdw) contact angles of thin GO sheet and GO-PCL mesh films are shown in **Figure 5** (inset). In case of thin GO sheets, CAw was found to be around ~58.7° with hysteresis (CAw−CAdw) of ~4° which might be a measure of the solid-liquid interaction [6, 20].

**Figure 5.** *In-vitro* degradation pattern of electrospun PCL and GO-PCL composite scaffolds in PBS(phosphate-buffer solution) for 30 days. Inset shows contact angle analysis (in degrees) representing both advancing (wetting) and receding (dewetting) water sessile drop on GO sheets, GO-PCL and PCL meshes. Error bars present standard deviation.

The stress-strain curves of GO sheets and GO-PCL meshes were shown in **Figure 6**. The tensile strength of PCL (~1.88 ± 0.25 MPa) was found to increase significantly with addition of GO (~4.8 ± 0.25 MPa). The tensile strength is also known to increase with increasing GO concentration. Favourable mechanical property supported GO-PCL and GO-PLGA meshes for tissue engineering applications.

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Deformation of the C–O bans is observed at the band present at 1070 cm−1. FTIR spectra (**Figure 4b**) of GO-PCL showed absorption bands at 1727 cm−1 indicating carbonyl stretching. The bands appearing at 1295 and 1240 cm−1 represented the C–O and C–C stretching bonds [19]. The bands at 1239 and 1175 cm−1 were comparable with the asymmetric C–O–C stretching bonds indicating characteristic absorption [6] of PCL and strong interaction be-

**Figure 5** indicates electrospun GO-PCL composite meshes which degrade up to ~16% in PBS (phosphate buffer saline) solution whereas electrospun PCL meshes degrade ~9% after 30 days of time interval. GO-PCL composite mesh showed optimized degradability rate that is suitable for cellular growth. Hydrophilicity of the GO sheet and GO-PCL composites were measured by contact angle measurement. Wetting (CAw) and dewetting (CAdw) contact angles of thin GO sheet and GO-PCL mesh films are shown in **Figure 5** (inset). In case of thin GO sheets, CAw was found to be around ~58.7° with hysteresis (CAw−CAdw) of ~4° which might be a measure

**Figure 5.** *In-vitro* degradation pattern of electrospun PCL and GO-PCL composite scaffolds in PBS(phosphate-buffer solution) for 30 days. Inset shows contact angle analysis (in degrees) representing both advancing (wetting) and receding (dewetting) water sessile drop on GO sheets, GO-PCL and PCL meshes. Error bars present standard deviation.

The stress-strain curves of GO sheets and GO-PCL meshes were shown in **Figure 6**. The tensile strength of PCL (~1.88 ± 0.25 MPa) was found to increase significantly with addition of GO (~4.8 ± 0.25 MPa). The tensile strength is also known to increase with increasing GO concentration. Favourable mechanical property supported GO-PCL and GO-PLGA meshes for tissue

tween GOnPs and polymer matrises.

226 Umbilical Cord Blood Banking for Clinical Application and Regenerative Medicine

of the solid-liquid interaction [6, 20].

engineering applications.

**Figure 6.** The stress-strain curve of the GO sheet and GO-PCL meshes carried out at RT with GO concentration within the non-toxic limit (~20 μg/ml) [6].

As shown in **Figure 7**, GO added PCL (GO-PCL composite) exhibited appreciably large increase of both *ε* (~300 for GO-PCL and only ~25 for PCL) and *σ* (>2 orders of magnitude higher in GO-PCL compared to that of GO sheet). Similar enhancement of *σ* and *ε* was also observed in GO-polyvinyl alcohol (PVA) and other GO-polymer composites [6, 17].

**Figure 7.** (a) Room temperature (RT) dielectric constant (*ε*) and (b) conductivity (*σ*) data of GO-PCL meshes before (0 days) and after immersion in PBS solution for up to 7 days. RT *ε* (c) and *σ* (d) data of PCL meshes before (indicated by the 0 days) and after immersion in PBS solution (all measurements were performed 1 kHz).

Similar conductivity and dielectric constant behaviour (shown in **Figure 7**) was also observed in case of GOnPs-PLGA meshes soaked in PBS solution. In this case, enhancement of conductivity is little lower than those of GOnPs-PCL scaffold meshes indicating little lower biocompatibility of the GOnPs-PLGA composite.
