Page 196 - IJB-9-6

International Journal of Bioprinting Attractiveness of 4D printing in medical field

methods and providing novel research and development (i) Printing methods: This considers the manufacturing
(R&D) areas . Through 3D printing, also called additive process established within additive manufacturing
[1]
manufacturing, it is also possible to fabricate complex technology, which fabricates products layer by layer
geometries by printing materials through a layer-by- using a wide variety of materials . Use of smart
[9]
layer method using computer-aided controls, facilitating materials in 3D printing processes allows printed
a faster development of novel ideas. This technology structures to be responsive to stimuli, and with time
has gained huge attention in the medical field because added as a new dimension for 3D-printed models,
of its capacity to offer cost-effective, customized, 4D printing is conceptualized . Techniques such as
[10]
and personalized solutions such as medical devices, material extrusion, vat photopolymerization, powder
medicine, and equipment . However, 3D printing faces bed fusion, and material jetting are the most used to
[2]
challenges in certain applications such as regenerative print 4D objects . Material extrusion is subdivided
[11]
medicine and tissue engineering because of its static into fused deposition modeling (FDM) and direct
structures. Due to these limitations, four-dimensional ink writing (DIW). Vat photopolymerization is
(4D) printing technology has emerged and rapidly gained subdivided into stereolithography (SLA) and digital
the attention of researchers because of its capability to light processing (DLP) . While powder bed fusion
[12]
fabricate dynamic structures and novel applications process comprises selective laser sintering (SLS)
in the medical field. 4D printing is a revolutionary and selective laser melting (SLM), material jetting
technology that uses 3D printing methods and smart method includes inkjet printing (IJP) . The chosen
[13]
materials to produce dynamic structures capable of self- technique depends on both the material to be used as
transforming in response to a given stimulus, improving well as the desired properties or functions of the final
their performance and functions . 4D printing involves structure. The printing method can also be chosen
[3]
time as an additional dimension, representing the change to facilitate and/or enhance the shape-memory
of shape over time due to a variation in its environment . functionality of the construct .
[4]
[14]
According to the literature, the design of 4D-printed (ii) Materials: The benefits of 4D printing come from
structures considers mainly the correlation of five the materials that make this technique possible; the
factors: (i) printing methods, (ii) external stimuli, (iii) quality of the final 4D-printed product depends
materials, (iv) mathematical models, and (v) interaction strongly on them. In the literature, these materials
mechanisms [5,6] . are called stimuli-responsive materials (SRMs) ,
[15]
The medical field has benefited from technological and they play an important role in receiving,
advances in these design factors; however, no research transmitting, and processing the applied stimulus .
[14]
has studied the existent technological tendencies of A desirable characteristic of these materials is their
the design factors and applications in this field. For this ability to deform into a temporary state and return
aim, competitive technology intelligence (CTI) helps to to their original form by changing the stimulus.
identify technological trends. CTI is a process utilized The main subcategories of SRMs identified are
to ethically gather and analyze information from legal temperature-responsive materials, pH-responsive
sources to ultimately produce intelligence and support a materials, moisture-responsive materials, electric
decision-making process regarding R&D . Several CTI and field-responsive materials, light-responsive
[7]
methodologies have been developed, among which the materials, acoustic-responsive materials, and
eight-step methodology proposed by Rodriguez-Salvador multiple responsive materials. Some of these, such
and Castillo-Valdez is used . In this context, the purpose as alginate-based pH-sensitive materials, hybrid
[8]
of this study is to reveal technological advances in design hydrogel-polyaniline materials, graphene-based
factors and applications of 4D printing in the medical field nanomaterials, magnetically responsive materials,
using a CTI methodology, with the aim of supporting the etc., have great potential to be used in bioinks for 4D
decision-making process of researchers, academics, and bioprinting .
[16]
companies regarding the direction of their efforts in R&D There are other types of materials such as shape change
and innovation.
material (SCM), shape memory materials (SMMs),
2. 4D printing design factors liquid crystal elastomers (LCE), and hydrogels.
SMMs are driven by shape memory effect (SME),
As mentioned above, the five main design factors of which means they are capable of returning to their
4D printing are: (i) printing methods, (ii) materials, initial shape after a temporary deformation when the
(iii) external stimuli, (iv) mathematical models, and appropriate stimulus is applied again (Figure 1a);
[17]
[5]
(v) interaction mechanisms . most of the time the stimulus is heat. Several SMMs
Volume 9 Issue 6 (2023) 188 https://doi.org/10.36922/ijb.1112