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International Journal of Bioprinting Applications of 3D printing in aging

or healthcare applications. Next, health conditions that deposition with a focused thermal energy source (e.g., laser
are associated with aging are closely examined according or plasma arc). This process is now only used for metals.
to human body systems with a strong focus on the Currently, the 3D printing methods that are commonly
applications of 3D printing in these areas, including the used in the biomedical field include material extrusion,
creation of in vitro models, synthesis of therapeutics, and vat photopolymerization, and material jetting, which are
fabrication of rehabilitation and assistive devices (Figure 1). described in detail in Table 1.
Although 3D printing may not be directly used for
addressing the aging issues of these human systems, it 3. Applications of 3D printing in medical
is used to improve conditions in these systems that are conditions associated with aging
associated with aging. This review also includes some
applications for general tissue engineering, but applicable 3.1. Nervous system
for addressing human aging problems. Some of the 3D By 2040, the World Health Organization (WHO) forecast
printing applications are not exclusively for aging-related that due to the aging of the population, neurodevelopmental
conditions, but also used for other purposes. In the end, disorder (NDD) will overtake cancer as the second most
[53]
the opportunities, challenges, and prospects of 3D printing deadly human disease . Aging is an important risk factor
in the field of aging are discussed. for NDD, such as Alzheimer’s disease (AD), Parkinson’s
disease (PD), amyotrophic lateral sclerosis (ALS), and
Huntington’s disease (HD). Frustratingly, almost all these
2. 3D printing methods commonly diseases have no effective cures available today. Studies
used in aging show that the incidence of AD, PD, and ALS is significantly

In 2009, ASTM International Technical Committee F42 positively correlated with age [54-57] . Aging causes multiple
on AM classified AM (which is used interchangeably unfavorable changes in the organism, which lead to a
with 3D printing in this article) into seven processes, progressive loss of synapses and inflammatory response in
[3]
including material extrusion, material jetting, binder the nervous system, and finally to neuronal death . These
jetting, vat photopolymerization, sheet lamination, powder phenomena are observed in cells of neural tissues where
bed fusion, and directed energy deposition . Material degenerative lesions occur, but the sequence and intensity
[24]
extrusion is a method in which the ink is extruded from of their occurrence vary.
a nozzle and selectively deposited according to the desired 3.1.1. Alzheimer’s disease
pattern. Compared with other 3D printing methods, it has According to the latest statistics released by the Alzheimer’s
the advantages of low printing cost, broad applicability to Association International, by 2030, 75 million people
many material systems, simple and convenient operation, are anticipated to have dementia globally . The clinical
[58]
and fast printing speed. One of the more precise 3D printing manifestations of AD are mainly cognitive dysfunction
methods is material jetting, which prints by ejecting liquid and memory impairment, and the main pathological
droplets into desired patterns that are subsequently cured features are the formation of senile plaques by extracellular
by UV or other means. Vat photopolymerization is an β-like amyloid deposition in the brain and intracellular tau
AM method that uses photo-activated polymerization to protein hyperphosphorylation, leading to the formation
selectively cure liquid photopolymer in a vat layer by layer of intracellular fiber. There are many hypotheses about
into 3D structures. It has the benefits of high processing the pathogenesis of AD, such as amyloid β protein (Aβ)
accuracy and smooth surface. Binder jetting creates 3D toxicity, tau protein hyperphosphorylation, cholinergic
structures by spraying adhesive onto a powder bed to nervous system damage, gene mutation, vascular
selectively bind powder materials into desired 3D structures. factors, oxidative stress, neuroinflammatory response,
Postprocessing is often required to permanently set the mitochondrial dysfunction, autophagy disorder, insulin
shape of printed parts. The principle of sheet lamination is signaling abnormalities, and intestinal flora imbalance [59-64] .
that the material sheets are cut by laser, and then bonded
or welded together to form a solid block. Sheet lamination 3.1.2. Parkinson’s disease
printing technology is available in materials other than After AD, PD is the second most prevalent
[65]
sheet metal and even in almost any other material that can neurodegenerative disease . As a result of the inability
be curled, such as paper. Powder bed fusion does not use to modulate motor activities, PD is characterized by
adhesives to bind the powders together. Instead, a high- resting tremor, motor bradykinesia, stiffness, and other
energy beam, such as a laser beam or electron beam, is symptoms that compromise the quality of life and finally
directly imparted on the power bed to selectively sinter result in severe disability. PD is primarily due to the loss of
or melt powder primers into solid parts layer by layer. In nigrostriatal dopaminergic neuron, resulting in a significant
the directed energy deposition, the material melts during decline in the dopamine levels in the striatum. Studies

Volume 9 Issue 4 (2023) 235 https://doi.org/10.18063/ijb.732