Page 36 - IJB-9-2

International Journal of Bioprinting Scaffolds printed with light sheet stereolithography

medical applications [1,2] . For instance, scaffolds are require high-resolution capabilities, limiting the scaling-up
highly porous structures as they consist of void spaces possibilities of technology. Investigations on the pore size
within the material. Due to their high porosity, scaffolds have shown a positive impact on cellular behavior for
exhibit high permeability, which allows blood vessel pore size that ranges from ≈ 20 μm to 150 μm [25,27] , from
ingrowth, nutrient diffusion, oxygen transport, and waste which it was pointed out that an average pore size of 100
removal [2-5] . In addition, the properly selected fabrication μm may work as a promising size . Although the ideas
[27]
materials [6-8] , pore size, and distribution promote the of producing large size items with high precision have not
adhesion, proliferation, and differentiation of cells [9,10] been integrated in the fabrication of bioengineered wound
and influence the mechanical properties of scaffolds for dressing, the achieved progress in tissue engineering allows
its target applications [4,5,11] . Their structural properties and for targeting specific scaffold’s designs and fabrication
fabrication technologies are of great research interest in strategies to pave the way on the fabrication of this type of
today’s tissue engineering. scaffolds as requested by medical specialists.
Bioengineered wound dressing is one of the applications Many available commercial bioengineered wound
where scaffolds have been widely implemented in research dressings result from technologies such as freeze-dry and
[28]
and industry [12-14] . Wound dressings are used to protect the electrospinning . Both technologies allow for centimeter-
[29]
tissue injury site from further mechanical and microbial scale scaffold fabrication with highly porous characteristics.
stress, and maintain proper moisture and temperature at However, these technologies are constrained in their
[15]
the wound bed . In medical field, the benefits introduced ability to control the pore size and distribution, leading
by bioengineered wound dressings have contributed to limited pore distributions with large size deviations
[25]
to an accelerated and improved healing process of the (40 – 150 μm in the same fabrication process) and low pore
injured tissue , including optimal management and cost interconnectivity (tubular or superficial) [25,26,29,30] . The latter
[8]
reduction of wound treatments in the health system [16-19] . is recognized as the key feature for the permeability and
However, the large surface-to-volume ratio characteristics migration properties of the scaffolds.
of wound tissues make the fabrication of engineered On the other hand, three-dimensional (3D) bioprinting
scaffolds a complex technological challenge [20-22] . The first has emerged as a fabrication technique, which is highly
reason is the need of large size wound dressings. In daily accepted, in the field of tissue engineering due to its free-
cases, the wounds, for example, ulcers and burns, can form 3D fabrication framework, high resolution, and
extend from a few millimeters up to a great extension of the
human body. Particularly, investigations on burn wound variety of biocompatible materials. Bioprinting allows
for complex pore patterning, high repeatability, and
dressings reported a minimum average area of 872 cm² of interconnectivity in engineered scaffolds [9,31-33] . At present,
a functionalized wound dressing used in a sample group extrusion - and jetting -based bioprinting play a
[34]
[35]
of 50 patients , requiring multiple applications of wound major role in tissue substitute fabrication because of their
[23]
dressing substitute. Furthermore, medical specialists have capabilities to construct cell-laden scaffolds and control
pointed out the importance of large size wound dressings cell density, location, and model geometries. Among
by quoting that a wound dressing size between 50 × 50 mm²
to 400 × 400 mm² is preferred by medical practitioners , 3D bioprinting methods, both material extrusion and
[24]
suggesting that new fabrication approaches must be material jetting methods possess the most versatile and
developed to reduce the cost of such large bioengineered low-cost configurations to construct cell-laden scaffolds
wound dressings. The second reason lies in the fine struts of multiple cells and soft materials (bioinks), making
.
these technologies attractive options to researchers
[34,35]
that provide the scaffold’s structure with the properties to Nevertheless, inability to fabricate sub-micron structures,
closely mimic the native tissue microenvironment. The their dependence on nozzles, and mechanical translational
pores within the scaffold consist of void space within the
material, and its physical characteristics, such as size, stages hinder bioprinting techniques in rapid fabricating
geometry, or interconnectivity, are determined by choosing of large size substitutes with fine structures that mimic the
the strut position and orientation (in other works, the native tissue microenvironment.
word “filament” or “fiber” is used to refer to strut, the Among the 3D bioprinting technologies, vat
[11]
[25]
structuring element of the scaffold). Many studies have photopolymerization (VP)-based bioprinting is currently
shown that the pores in a scaffold not only promote the the only technique that can fabricate with the highest
migration of nutrients, oxygen, and cells but also influence resolution and precision [36,37] . VP techniques use light
the physical properties of the scaffolds, such as mechanical radiation to harden a liquid material locally using
properties , absorption , and permeability [3,5] . Thus, in polymerization. By steering a laser beam or projecting a
[26]
[5]
terms of fabrication, the pores in an engineered scaffold two-dimensional (2D) image on the liquid material, a 3D
Volume 9 Issue 2 (2023) 28 https://doi.org/10.18063/ijb.v9i2.650