## 5 Advanced Reinforced Graphene Nanoplatelet-Based Bio-Nanocomposites
### Graphene Nanoplatelets Reinforced Polyseters
It was observed that 5 wt % concentrations of the large GnPs augmented E\({}_{\text{g}}\) by 24%, while the small nanoflakes increased the elastic modulus by 10% at the same concentration. The obtained biocomposites were also electrically conductive, showing a lower percolation threshold for the large GnPs (7 wt % filler loading) compared with the small (13 wt % GnPs concentration). Other works compare the performance of graphene platelets and graphene oxide inside PLA. For example, [PERSON] and coauthors [178] reinforced thin films of PLA biopolymer with either GnPs or GO. They used solution processing procedures to fabricate the biopolymers. Both nanoflakes had an optimized load identified at about 0.4 wt % (see Figure 17). In these conditions, GnPs increased E\({}_{\text{g}}\) by 156% and yield strength by 129%. GO produced similar improvements. Additionally, permeability to nitrogen and oxygen diminished three and four times in films loaded with GO or GnP, respectively. Similar results were achieved by [PERSON] et al. in this work [179], but by employing melt blending as the production method. In this work [184] [PERSON] et al. also tested the biocompatibility of reinforced PLA-GnPs and PLA-GO composite materials, finding that low concentrations of graphene-based filler  
Figure 16: PLA-GnPs-ciprofloxacin composites and their antimicrobial release. Agar diffusion tests were performed with the purpose of investigating if the incorporation of ciprofloxacin inside the PLA specimens was conferring antimicrobial activity to the manufactured films. As bacterium, [PERSON] and coauthors selected _M. luteus_. Both pristine PLA and PLA/GnP displayed no antibacterial properties. In contrast, large bacterial growth inhibition halos were detected near both films, including ciprofloxacin. The presence of GnP led to a reduction of the inhibition zone; therefore, nanoflakes influenced not only the mechanical properties (see text), but also the ciprofloxacin release of the films. Reprinted with permission from Composite part B: Engineering 109, 138–146. Copyright 2017 Elsevier. can be safely incorporated, improving their mechanical properties. More details on graphene-based material biocompatibility can be found in another paper [185] by [PERSON] and coworker. Polycaprolactone (PCL), another heavily employed bio-polyester, was coupled with GnPs to enhance its mechanical properties. [PERSON] et al. [180] modified GnPs in water with poly(sodium 4-styrenesulfonate), and compounded such dispersion with PCL. At the best GnP concentration (0.5 wt %), they were able to enhance both the Young modulus and the elongation at a break of approximately the 12%. At 1 wt % GnPs loadings, agglomeration started and the tensile strength and elongation at break reduced considerably. The addition of GnPs augmented notably also the crystallization kinetics. Indeed, only 0.05 wt % nanoflake inclusion triggered a nearly 6 times improvement in crystallization rate. PLA and Mater-bi\({}^{\text{(\textregistered)}}\) (a blend of PCL and starch) were reinforced with GnPs in our recent work [65]. These two bio-polyesters were mixed with various types of few layer graphene (FLG) and commercially available GnPs. Free standing biocomposites were manufactured by solvent casting and hot-pressing. Exhaustive mechanical measurements were conducted in order to study the effect of FLGs and GnPs thickness and lateral size on the elastic modulus of both polymers. For comparison purposes, other 2D and 3D nanoscale fillers like iron oxides (see Figure 18), clay, and carbon black were used. Under solvent casting conditions (randomly oriented nanoflakes in the polymer matrix), FLG and GnPs did not perform better compared to other model fillers in increasing the elastic modulus of Mater-bi\({}^{\text{(\textregistered)}}\). On the other hand, both FLGs and large and thick commercially available GnPs increased the elastic moduli of PLA biocomposites more than other 2D and 3D fillers.