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Three-Dimensional Printing Technologies for Drug Delivery Applications
Table 7. Characteristics and challenges of digital light processing (DLP)
Characteristics Challenges
Method DLP uses UV light and micro-mirror device for projected digital light The post-curing steps may result in
into the vat of photopolymer . a loss of drug loaded and imprecise
[20]
The projector system can be bottom-up or top-bottom . dosing .
[21]
[12]
This process is faster in printing time and more efficient as well as The residual resin can represent a
allows operating at a wider range of wavelengths, compared to SLA . toxicity risk .
[11]
[22]
DLP can work with customized resin reservoirs and small volumes of
photoreactive polymers .
[22]
Material DLP uses photoreactive and photocurable materials . This process only works with
[12]
The medicine can be loaded directly into the liquid prepolymer photoreactive and photocurable
solution, depending on its solubility . materials .
[12]
[12]
DLP uses standard and castable resins .
[14]
Quality Like the others processes of vat photopolymerization, DLP prints with
high resolution .
[21]
Carbon 3D (US) has several Carbon Digital Light Synthesis printers
and the resolution are 25, 50 or 100 μm [18,23] .
Table 8. Characteristics and challenges of selective laser sintering (SLS)
Characteristics Challenges
Method The powder bed is controlled by a leveling system that moves in from The printing speed of SLS is limited to
one part to another. Then, a focused laser beam scans selectively, 1–5 cm/h approximately, which impacts the
which heats the powder just below the melting temperature [10,16] . time of production .
[16]
Only a few researchers work with this process in pharmaceutical SLS produces significant powder waste after
field . printing process .
[16]
[16]
The printing product does not need supporting structures
because the unsintered powder provides all the necessary
support [14] .
Material Drug delivery device worked with nylon, polyamide, PLLA, and SLS works with high levels of energy;
PCL as the polymeric base material for customized porosity and therefore, there are few pharmaceutical
microstructures . excipients and API that can resist these
[16]
temperatures [10,16] .
Quality The porosity of the drug delivery device could be controlled On the final structure, a post-treatment
by varying the powder bed temperature, the length between the is required due to non-sintered powder
dense walls and the SLS laser power . residue [11,16] .
[16]
The sPro EOS P 396 printer from 3D Systems (US) and EOS
(Germany), has a layer thickness of 100 μm and can achieve a
resolution of 500 μm .
[18]

3. Materials for 3D printing in
pharmaceutical manufacturing
There are a wide range of polymeric, glass, and hydrogel
materials which have been explored to act as drug-
eluting devices, many of which exhibit biodegradable
characteristics that allow for single administration into
the body .
[11]
3.1. Polymers
Polymers can be divided into those which are
Figure 5. Powder bed fusion. biodegradable and those which are not. Biodegradable

328 International Journal of Bioprinting (2022)–Volume 8, Issue 4