Continuous Digital Light Processing
(cDLP): Highly Accurate Additive
Manufacturing of Tissue Engineering
Bone Scaffolds
Student: Alexander Guillen
CHE 722
10/21/2021
Goal & Motivation
Significance & Background
Approach
OUTLINE
Methods
Results
Summary & Conclusions
My Personal Evaluation
Goal: To fabricate resorbable polymer scaffolds via cDLP for cranial repair.
Motivation: Use of Additive Manufacturing (ASTM F2792-10) technology to render fully
or partially resorptive implants to fit patient-specific defect sites.
Significance and
Background

Significance: Highly accurate rendering of the external
and internal geometry of bone tissue engineering
scaffold effects fit at the defect site, loading of internal
pore spaces with cells, bioreactor-delivered nutrient and
growth factor circulation, and scaffold resorption.

Background: The current standard of care is to use
non-resorbable materials for intra or pre-operatively
prepared cranial implants.

Alternatively, operative procedures with resorbable
tissue engineering implants necessitate the render of
polymer scaffolds with 50 μm or less in accuracy.

To achieve this type of accuracy, cDLP is available.
Study: Development of a bioactive implant for repair and potential
healing of cranial defects.
Approach
(photopolymer)

The production of tissue engineering scaffolds via cDLP has
focused on resorbable polymers (light polymerizable
polymers).

A photopolymer or light-activated resin changes its properties
(structural and chemical) when exposed to light.

PPF – Poly (propylene fumarate)
 Controllable mechanical properties
 Tunable degradation
 Biocompatibility
(A schematic depicting polyaddition reactions that occur between PPF and
DEF. )
Approach
(Continuous Digital
Light Processing)

cDLP-based systems render
parts by projecting an image
through a clear basement plate
into a tray containing the resin,
curing at the bottom surface.

The parts attach to a build
platform which moves upward,
away form the basement plate,
after each layer is projected.
3D printing with light
https://www.youtube.com/watch?v=jcwYFBeetH0&t=35s
Methods

The scaffolds were fabricated using PPF, titanium dioxide as a dye, Irgacure as an
initiator, and diethyl fumarate as a solvent.

The resin contained between 1:1 and 2:1 weight ratio of PFF to DEF and between 0.52.0 wt% photoinitiator.

DEF monomer was incorporated into the scaffold to reduce rigidity (highly viscous polymer).


cDLP based system are susceptible to layer-setup issues.
The primary function of the dye is to attenuate light so that as much energy as it is needed can
be deposited in a layer of calibrated thickness.
Methods

The relationship between depth
of polymerization and exposure
in cDLP was determined for
each resin via a calibration
procedure consisting of six
steps.
Results

It was determined that a 2 wt%
titanium dioxide concentration
with 2 wt% BAPO and a 60 s
exposure time would yield an
average depth of polymerization
equal to 133.3 μm.

These settings could therefore
be used to build in 50 μm layers
with 83.3 μm of overcuring.
Results

They also observed a lateral spreading of
polymerization beyond the intended layer.

This area increased most quickly at higher
concentrations of TiO2,especially with
increased light input.

An extra step to the normal curing test
calibration was added. They measured cured
layer thickness in the X, Y, and Z dimension.
Results

They also printed a ‘plate and post’ scaffold
design.

Their first iteration consisted of 2-plate
scaffolds


It was useful to decrease the thickness of the
burn-in patch (first layer of a print job).
After rendering the 2-plate scaffolds, a full 11plate scaffolds was printed.

They found an incomplete build and a membrane
of polymerized material had formed on the
basement plate.
Summary and Conclusion

They developed an approach to fabricate resorbable polymer scaffolds via cDLP for
cranial repair.

They were confident that scaffold rendering resolution will continue to increase with
further iterations of cDLP devices.

Finally, there is a great need to produce and optimize materials in scaffold tissue
engineering.

Resorption kinetics and toxicity limit the list of light-polymerizable polymers that can
be used for rendering scaffolds.
My Personal Evaluation

Overall, an interesting and well-needed research study in the field of tissue engineering
scaffolds.

Collaboration with other countries – the same calibration study was performed using a
different dye by researchers in Taiwan.

Time constraint: 16 hour build cycle.

Personally, I am hesitant to recommend this product to be allowed for use in humans,
yet.