## 2 Overview of the Conventional Techniques for Graphene-Added Biomaterials  
At present, the preparation of graphene-added materials are mainly developed through melt blending [37], electrospinninging [38], solvent-assisted casting technique [39; 40; 41], in situ polymerization [42; 43], layer-by-layer assembly [44; 45], freeze-drying [46]. Unfortunately, the full potential of using graphene in a polymer matrix is not reached due to its aggregation. Moreover, the absence of active groups on the graphene surface weakens the forces between the polymer matrix and graphene; hence, phase separation occurs. Melt processing was embraced by the industry for obvious reasons: it is cost-effective, simple and facilitates large scale production for a wide range of affordable products. The process consists in melting the polymer pellets and mixing them with fillers and additives by applying a high shear force for homogeneity. Clearly, the uselessness of using solvents to disperse the filler into the polymer matrix is an advantage for environmental and safety reasons since organic solvents are toxic. Though, the downsides of this technique are: (i) the poor dispersion of the filler in the polymer matrix, specifically in higher filler loadings due to the high viscosity of the mixture [47; 48], (ii) requires high temperature to ensure the homogeneity of the mixture, which can cause occasional degradation of the polymer, and (iii) works preferentially with thermoplastics (polyethene, polypropylene, polyethene terephthalate, polyvinylchloride, polyamides, polycarbonates, polyurethanes and silicones). In terms of medical applications, the first option is the use of biopolymers as matrices, as they can replace parts of soft and hard tissue and their degradation products are not immunogenic. Secondly, the environmental problems related to fossil-based polymers moved the attention to the synthesis of polymers starting from raw materials that can be obtained from renewable resources (e.g., starch, glucose, cellulose resulting from bacterial fermentation). Such an example is poly(butylene succinate), which exhibits mechanical and thermal properties comparable with polyethene and polypropylene. [PERSON] et al. [49] reported the melt blending of poly(butylene succinate) with graphene nanoplatelets in a concentration from 0.5 to 6.0 wt%. Importantly, graphene nanoplatelets were found to increase the thermal conductivity during melt blending of poly(butylene succinate), which facilitate the reduction of the processing parameters, i.e., temperature and time, and thus the thermal degradation of the thermoplastic biopolymer can be prevented. The melt processing technology is inappropriate for many biopolymers currently used in tissue engineering, such as proteins or other natural polymers. Apart from that, the complexity of the final shapes is reduced, and, most importantly, the high processing temperature hinders the survival of the embedded cells. Solution blending is another extensive method for the preparation of graphene/polymer composites, mainly due to its accessibility. The process consists of the dispersion of graphene in an organic solvent under sonication, followed by the addition of the polymer, and, finally, removing the solvent. In this process, an important issue is the difficulty of uniformly dispersing graphene in the polymer solution. To overcome this, scientists have several choices: the addition of complex dispersing agents [50], graphene functionalization [51] or synthesis of chemically reduced GO (r-GO) in the presence of NaCl, which acts as a flocculant and simplifies the redispersion of r-GO aggregates in organic media [52]. However, the most important shortcoming of the solvent blending method relates exactly to the use of organic solvents, which are adsorbed between the graphene layers and cannot be completely removed, even at high temperatures [53]. In the end, this affects the performances of the final composites.