Page 332 - IJB-8-4

Three-Dimensional Printing Technologies for Drug Delivery Applications
Table 1. Characteristics and challenges of MJ
Characteristics Challenges
Method Droplets of ink are deposited from the nozzle into thin layers, In some cases, MJ needs support structure .
[14]
then cured with cooling air and in the presence of high-energy It is necessary to perform a post-processing for
light, such as ultraviolet (UV) . removing the support structure .
[10]
[15]
The droplet flight path, droplet impact, and surface wetting can
change the geometry of the product .
[11]
MJ can tune the drug composition during the printing process .
[12]
MJ can work with thermal or piezoelectric nozzle .
[13]
Material MJ works with melted polymers and waxes, UV curable resins, The viscosity can affect the optimization
solutions, suspensions, and complex multicomponent fluids . requirement .
[12]
[11]
MJ used waxes as the first materials . The materials are photosensitive (e.g., sensitive
[10]
This process can use photosensitive polymers but requires to daylight), and the mechanical properties
further processing to remove the photoinitiator . degrade over time .
[14]
[10]
This process can use multimaterials and full color .
[10]
Quality The quality and the curing method depend on material The final product has poor mechanical
properties . properties .
[10]
[14]
The final product has homogeneous mechanical and thermal
properties .
[14]
MJ: Material jetting, UV: Ultraviolet
Table 2. Characteristics and challenges of binder jetting (BJ)
Characteristics Challenges
Method Droplets of liquid binder bind the particles of the powder Pre-processing of the powdered materials is
bed layer [10-12] . necessary to ensure proper distribution of the
The drug can be found in the ink or in the powder bed . particle size and flow capacity of the powder for
[10]
BJ is a simple, versatile, low-cost and high-speed process uniform filling of the power bed .
[16]
that provides the personalized drug delivery system as Clogging of the print head can occur during printing
well as customizing the composition and properties of of non-homogeneous binder solutions [11,16] .
drug-eluting implants [11,16] . The porosity of products is poorly controllable .
[16]
The physicochemical properties of the dosage forms, and One risk in the process is the inconsistency or less
the drug-release profiles could be adjusted using different homogeneity between the layers, which can be
polymers and/or ratios between the bulk material, API (s), controlled by mediating the temperature and drying
binding agents, and other excipients . time between layers or jetting rate [11,16] .
[16]
Material The process works with ambient temperature that is The availability of suitable non-toxic solvents to
suitable for thermolabile drugs and excipients . increase the capacity of the binder solution is limited .
[16]
[16]
Quality BJ has lower printing resolution and poorer surface This could be improved by the additional
quality that can result in imprecise printing and post-processing .
[16]
low dimensional tolerance, compared to other AM
processes [11,16] .
2.2. Material extrusion (1) HME
Arguably the most recognized process of 3D printing, HME ejects semi-molten material from the nozzle tip;
extrusion-based technologies can be defined as the however, it additionally incorporates heated screws,
process in which material is selectively dispensed which melt, mix and eject the polymer from the
through a nozzle or orifice . Extrusion-based printing nozzle . This technique is regularly used for gels and
[16]
[9]
can be split into three key categories: hot melt extrusion pastes containing APIs at room or elevated temperatures,
(HME), filament extrusion, and syringe extrusion. allowing for solid dispersions to be printed . Where
[7]
In all three techniques, the material undergoes a filament extrusion requires impregnation of the filament
change in physical state between ejection from the with an API prior to printing, HME offers the addition
nozzle and solidification upon the substrate either by of the API in the melting stage, whereby it either melts
cooling or solvent evaporation, with printing processes alongside the polymer, dissolves within it, or disperses
(Figure 3) [10,12] . across the polymer mix .
[17]
324 International Journal of Bioprinting (2022)–Volume 8, Issue 4