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International Journal of Bioprinting 3D printing and 3D-printed electronics in smart drug delivery devices

devices which contains or are designed to be used with material also causes the initial printed design to have a
electronics as well as 3D printing fabrication of electronics lower mechanical strength and be less able to hold its shape.
that are used in smart drug delivery devices. Thus, crosslinking of the printed design immediately after
printing could help to retain the shape.
2. Applying 3D printing to smart drug Vat-based 3D printing involves the use of selective
delivery devices with electronics curing of a vat of liquid crosslinkable material for the

2.1. 3D printing fabrication of the product. In most vat-based printing, a
Three-dimensional (3D) printing is a fabrication technique printing platform is lowered into the vat to the desired
which uses layer-by-layer deposition to fabricate the final printing thickness. Light in the desired printing pattern
product. The 3D printing techniques used in smart drug or lasers are then shown across the surface crosslinking
delivery devices can be classified into three main categories the material forming the design. The platform is then
based on the method of deposition. These categories are raised to allow for the liquid material to fill the void for
extrusion-based, droplet-based, and vat-based 3D printing. the printing of the next layer. This process is repeated
until the final product is formed . Examples of vat-based
[32]
In extrusion-based 3D printing, mechanical force is printing include stereolithography, digital light processing,
used to extrude material out through a nozzle. Different and two-photon polymerization (TPP) [33,34] . In TPP, the
methods can be used to provide the necessary mechanical material is cured only at the focal point of a high-power
force to extrude the material such as pneumatics, screw- pulse laser. This allows for the fabrication of products with
based, or mechanical pistons [25,26] . For extrusion-based nanometer-scale resolution . However, the drawback
[35]
3D printing, materials which exhibit shear thinning of TPP is the scalability of the process for printing larger
properties are preferred. Shear thinning materials undergo objects. For vat-based 3D printing, the optical properties of
a decrease in viscosity under high shear forces. At the the printing material will affect the interaction between the
extrusion nozzle, where the material experiences high material and lasers and change the degree of crosslinking
shear forces, the material will have a decreased viscosity of the material .
[36]
allowing for easy extrusion. After being extruded, the
high shear force is removed and the increase in viscosity The 3D printing methods described above are mainly
of the material allows for it to retain the printed shape . applied to the fabrication of the non-electronic parts of the
[27]
Alternatively, heat can be used to soften the printing smart drug delivery devices. The applications of the 3D
material. The heat can be applied at the nozzle or in the printing methods used for the direct fabrication of printed
cartridge housing the printing material. When the material electronics are different. A more detailed description and
leaves the nozzle, the heat is removed and the material examples of the 3D printing methods used for 3D-printed
hardens, holding the printed shape . electronics will be given in subsequent chapter.
[28]
For droplet-based printing, micro-droplets of the 2.1.1. Benefits of using 3D printing
printing or binding material are jetted onto a substrate or The use of 3D printing for the fabrication of products confers
material powder bed forming each layer of the product. several advantages. One such advantage is that the product
Examples of droplet-based 3D printing include microvalve, can be highly customizable. As the printing materials used
[29]
acoustic wave jetting, thermal, and piezoelectric inkjet . in 3D printing can be deposited or crosslinked on demand,
For binder-based droplet 3D printing, binding material it allows for free-form designs. Thus, the design of the
is dropped onto a powder bed of the desired printing product can be customized or tailored to individuals. 3D
material. After the desired pattern is formed on the layer, printing also allows for the fabrication of designs which are
another layer of powder is deposited on top and the hard or impossible to fabricate using traditional fabrication
process is repeated . In material-based droplet-based methods. Due to the layer-by-layer fabrication process of 3D
[30]
printing, droplets of the printing material are deposited printing, 3D printing can be used to fabricate certain unique
and subsequently crosslinked. This can be achieved designs which cannot be done by traditional fabrication due
through deposition of the printing material into a pool of to design restrictions . The fabrication of unique designs
[37]
crosslinking material or the crosslinking can be achieved also applies the internal designs of products, known as the
after deposition through methods such as UV crosslinking. infill. By customizing the infill of a printed item, different
The use of micro-droplets to form the final product allows infill designs can be fabricated. Different infill designs can
[31]
for a higher resolution of the printing design . However, affect different properties of the printed item such as weight,
due to the need for a lower viscosity in order to form the mechanical strength, diffusion rate, and density . Using
[38]
droplets, the types of material which can be printed using 3D printing to fabricate the product also greatly reduces the
this method are limited. The lower viscosity of the printing amount of material waste. Traditional fabrication methods

Volume 9 Issue 4 (2023) 146 https://doi.org/10.18063/ijb.725