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Uncovering 3D bioprinting research trends: A keyword network mapping analysis

each keyword. table 3. Most frequent terminology for materials, biological
In order to identify trends of research on 3D bio- components, and applications in papers analysed from APY 2011
to 2016.
printing the APY of the keywords contained on the
Most frequent
network map was determined. This was obtained aPY keywords Material Biological application
component
by averaging the publication years of each article (Occurrences) (Occurrences) (Occurrences) Occurrences)
containing each keyword. Results showed that the APYs ‘PLGA’ ‘Bioengineered
ranged from 2002 to 2016. However, for co-occurrence 2011 ‘Cell Sheet’ (25) ‘Bone Marrow’ Construct’
(148)
(44)
analysis, APYs of only 2011 to 2016 were considered as (20)
the majority of keywords (67% of 1,759) were found in 2012 ‘Expression’ ‘Biopolymer’ ‘Progenitor Cell’ ‘Bone Tissue
Engineering’
these years. (212) (52) (60) (153)
Figure 2 shows the co-occurrence network maps ‘Treatment’ ‘Hydroxyapatite’ ‘Mesenchymal ‘Vascular
obtained for each APY from 2011 to 2016; again, the 2013 (235) (33) Stem Cells’ Network’
(188)
(69)
keywords are represented by nodes and are connected by ‘Bone ‘Bone
links. Number of keywords and links are shown in Table 2014 Regeneration’ ‘PLA’ ‘MSCs’ Regeneration’
(56)
(54)
2. (112) (112)
‘Spheroid’ ‘GelMA’ ‘Pluripotent ‘Cartilage
2015 Stem Cells’ Repair’
table 2. Number of keywords and links by average publication (127) (37) (31) (28)
year (APY) ‘Photocurable
2016 ‘Bioink’ Resin’ ‘IPSC’ ‘Organoid’
(18)
(24)
(230)
aPY Number of keywords Number of links (6)
1,825
2011 207 years (2015–2017). The results obtained indicated that
studies on treatment were primarily focused on cancer,
2012 279 4,231
regenerative medicine, and MSC analysis. The keyword
2013 303 4,386 ‘Treatment’ was also related to other keywords such
as ‘Osteochondral Defect’, ‘Implant’, ‘Medicine’, and
2014 203 1,233 ‘Bone Defect’. By contrast, ‘Bioink’, a fundamental
element in bioprinting, was mainly found in relation
2015 148 620 to multicellular spheroid deposition for guaranteeing
maximal cell density [17,19,29,30] as well as in relation to
2016 53 66
hydrogels (e.g., ‘gelation’ and ‘GelMA’ or ‘Gelatin
Methacryloyl’) and ‘Cell Sheet’ and ‘Printability’, which
The keywords for APY 2011 to 2016 were analysed are crucial factors in the fabrication of living tissue.
to determine which of them dominated the discussion Additionally, to identify the predominant keywords
of 3D bioprinting materials, applications, or methods in papers published in the last three years (2015–2017),
during these years. the APY 2016 was analysed; the identified terminology
Table 3 shows the results of the most frequent can be considered to reflect recent research efforts in
terminology for materials, biological elements, and bioprinting. The results showed that the keyword ‘Bioink’
applications for each of the APYs analysed (APY 2011– occurred most frequently (230 occurrences) followed
2016). The most frequent keyword was ‘Treatment’ with by ‘Organoid’ and ‘ADSC’ or ‘Adipose Tissue-Derived
235 occurrences in APY 2013. For materials, the most Stem Cells’ (24 occurrences each); ‘Cell Spheroid’ (19
frequent keyword was ‘PLA’ (Polylactic acid) with 56 occurrences); ‘GelMA’ (9 occurrences); and ‘Calcium
occurrences in APY 2014. For biological elements, the Ion’, ‘Concave Microwell’, and ‘Integrin Binding’ (7
most frequent keyword was ‘Mesenchymal Stem Cells’ occurrences each). Four of these keywords (‘GelMA’,
with 188 occurrences in APY 2013; furthermore, it was ‘Calcium Ion’, ‘Concave Microwell’, and ‘Integrin
found as ‘MSCs’ with 54 occurrences in APY 2014. For Binding’) are directly related to bioprinting with cell
applications, the most frequent keywords were ‘Bone spheroids for the retention of 3D cellular structures .
[30]
Tissue Engineering’ with 153 occurrences in APY 2012 In terms of applications, the most frequent keyword was
and ‘Bone Regeneration’ with 112 occurrences in APY ‘Drug Development’ (12 occurrences), which reflects
2014. one of the emerging applications of bioprinting [1,9,22] .
From a general perspective, from APY 2011 to 2016, Finally, a specific outlook of bioprinting trends was
the most frequent keywords were ‘Treatment’ (in APY developed by considering the following elements:
2013) and ‘Bioink’ (in APY 2016), indicating that these bioprinting techniques, cell sources, and tissue/organs.
terms have been widely researched for the past three For this task, a keyword analysis of previously identified

4 International Journal of Bioprinting (2018)–Volume 4, Issue 2