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Zhang, et al.
features to the products. The medical models have laser assisted printing, selective laser melting
fine shape and physical property for simulating (SLM), and selective laser sintering (SLS). The
human body. Additionally, favorable structures DLP and laser assisted printing methods apply
can be integrated into implants to promote tissue photopolymerization reactions. During the process
regeneration. Besides, artificial tissues and organs of SLM and SLS, material powders are melted
are built with precise bionic structure and high and reshaped at the high temperature created by
cell viability. Last but not least, customized drug laser. These 3D printing platforms have significant
delivery system can provide a nuanced solution differences in printing mechanism, speed, material
to controlled release, accurate drug dosages, and selection, and resolution [12,13] . Table 1 compares
minimally invasive delivery [6-10] . the DLP printing with other 3D techniques used in
This review introduces the DLP-based 3D the medical field.
printing technology and its applications in medical DLP-based 3D printing technology comes
field. The principle and characteristics of DLP from the image projection technology developed
[5]
printing technology are introduced. Then, the main by Texas Instruments in the 1980s . This
applications demonstrate the influence of DLP- method uses a set of chipsets based on optical
based 3D printing to medicine (Figure 1). Finally, micro-electromechanical technology to process
this review culminates with the limitations of working light sources to photosensitive materials
existing techniques and future research directions. (Figure 1). The main functional part is a digital
micro mirror device (DMD) which consists of a
2 DLP-based 3D printing group of micron-sized, controllable mirrors. The

2.1 DLP-based 3D printing technology mirrors rotate to control the path of light and then
project it onto the photosensitive resin during
The concept of 3D printing is first described working. The ordinary arrays have a large number
in 1986 by Charles . The method, named of mirrors, from nearly a million mirrors to more
[11]
stereolithography, sequentially print many layers than 2 million. On the other hand, the pixel
by ultraviolet light to create 3D structures. With the spacing of the micromirror is only a few microns
development of additive manufacturing technology or a dozen microns. The resolution of the DLP-
and material science, various 3D printing methods based 3D printing depends on the projection plane
have emerged. There are two common types of 3D adjusted by DMD and lens. Thus, the DLP printing
printing methods: The nozzle-based and the light- technique has a relatively high resolution, which
based 3D printing. The nozzle-based 3D printing is usually at the micron scale . Furthermore, the
[12]
includes extrusion printing and inkjet printing. In printing conditions are mild for cells. In general,
these printing methods, the printed materials are the printing process without high temperature,
extruded or jetted and deposited onto the platform. pressure, and shear stress caused by the nozzle is
The light-based 3D printing includes DLP printing, suitable for printing living tissues or organs with

Table 1. Comparison of various 3D printing methods in the medical field [12,14,15] .
Properties Materials Printing process Resolution Speed Cell
(μm) viability
Nozzle based printing
Extrusion Thermoplastic polymer Serial (line by line) 50 Slow (μm/s) 40-80%
Inkjet Thermoplastic polymer Serial (drop by drop) 50 Medium (mm/s) ＞85%
Light based printing
DLP Photosensitive polymer Continue Plane (layer by layer) 6 Fast (mm³/s) 85-95%
Laser assisted Photosensitive polymer Serial (dot by dot) ~1 Medium (mm/s) ＞85%
SLM/SLS Metals and alloys powder, Serial (dot by dot) 80 slow (μm/s) —
ceramic and polymer

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