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Lopez de Armentia, et al.
1. Introduction To achieve the advantages that nanomaterials offer,
it is important to obtain a good dispersion within the
Additive manufacturing (AM) is a promising and matrix materials. Many methods have been investigated
versatile technology for the fabrication of customized to improve the graphene-based nanomaterials (GBN)
structures in terms of design. Since its invention in the dispersion within the matrix materials and reduce the
late 1980s, different types of 3D printers have been incidence of agglomerate formation. To achieve a good
developed. Printers based on vat photopolymerizations dispersion, it is important to pay particular attention to
(stereolithography [SLA] and digital light projection
[DLP]) were the first commercially available printers . the methods used for stirring and dispersion, and also
[1]
The difference between SLA and DLP relates primarily chemical functionalization of the GBN.
In terms of stirring and dispersion, techniques such
to the light source. SLA technology uses a light from a as sonication using a soniprobe [27,28] or bath , high-
[29]
single laser beam of ultraviolet (UV) light, that forms shear mixing , high-speed disk , and calendaring
[30]
[31]
the layer point-by-point by changing the orientation of processes [32,33] have been commonly applied. When the
optical elements such as mirrors or lenses. However, in
the case of DLP printers, the entire layer is cured at the resin viscosity is too high, then ultrasonic or mechanical
same time using an array of mirrors that project UV light mixing cannot be applied successfully; therefore, it is
to the pattern of the printed cross-section . necessary to reduce the resin viscosity. For this purpose,
[2]
[28]
In particular, the biomedical engineering field needs different solvents have been used, for example, THF ,
[29]
[35]
to have the ability to fabricate customized structures at acetone [27,34] , isopropanol , and water . To improve
relatively low-volume levels. Therefore, AM is ideal for GBN dispersion, chemical functionalization such as
[34]
[28]
such applications. Furthermore, AM offers the potential polymer grafting , self-assembly functionalization ,
for accurate control of geometry and dimensions, which and the use of dispersants [35,36] have also successfully
is vital for the biomedical engineering field. Among the applied.
different technologies, SLA offers some advantages: At present, GBN has been introduced to AM
(i) it presents the highest accuracy, (ii) SLA-created technology with respect to the fabrication of SLA
structures can have smooth surfaces, and (iii) the printed constructs. In terms of biomedical engineering
materials used in SLA technology can be easily sterilized applications, GBN have been reported to offer
by UV. At present, SLA is already used in biomedical enhanced mechanical properties [21,37-39] , promote cell
[22]
engineering applications, such as in dentistry [3,4] , soft differentiation , and increase hydrophilicity and
[40]
tissue-engineering [5,6] , hard tissue-engineering [7,8] , subsequently improve cell adhesion .
delivery device fabrication [9,10] , and biopharmaceutical However, with respect to SLA and DLP techniques,
manufacture [11,12] . there is currently a lack of knowledge about the influence
Recently, there is an increasing interest in the of GBNs on the polymerization reaction, but some issues
[41]
improvement of commercially available photocurable relating to delamination and a reduction in maximum
[42]
resins to modify the electrical [13-17] , mechanical [15,18-21] , curable thickness per scan have been reported when
biological , and/or polymerization properties and GBNs were incorporated into photocurable resins. With
[22]
[23]
adapt these properties toward emerging biomedical the addition of nanomaterials into the resin, a competition
engineering applications. A promising way to modify and takes place in terms of light absorption between the
tailor the properties of the photocurable resin could be photoinitiator and nanomaterial. Usually, this competition
through the dispersion of nanomaterials within the resin. leads to a less effective UV polymerization process.
One of the most interesting nanomaterials that Nanomaterials may influence the UV polymerization
is currently receiving significant research attention reaction due to changes in optical properties, which
is graphene (G), which demonstrates high surface results in variations in absorbance or transmittance of
area, superior mechanical properties, thermal and the resin [17,19] . They also can act as light scattering and
electrical conductivity, excellent intrinsic carrier shielding center . Besides, the polymerization reaction
[43]
mobility, and barrier properties among other interesting may be affected by the nanomaterial [44,45] if they act as
qualities [24,25] . The main limitation of G is its difficulty chain transfer agent, thereby inhibiting polymer chain
to be manufactured at scale and its tendency to form growth , or as free radical scavengers that reduce the
[39]
agglomerates when being dispersed within a solution [26] . extent of polymerization reaction [46,47] .These effects
In general, other G-based nanomaterials, such as make studying the influence of nanomaterials especially
graphene oxide (GO) or graphite nanoplatelets (GoxNP), important, specifically their effect on the polymerization
present lower properties than G (in terms of mechanical reaction of photocurable resins and in the context of
or electrical properties), but they demonstrate the ability efficacious 3D printing, as these modifications can affect
to be manufactured at scale and they present better printability and the practicality of a particular 3D printing
dispersibility. technique. These effect depends on many factors, for

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