2022 Quarter 4
Vol. 8, No. 4

Increasing Adoption of
Photopolymer Additive
Manufacturing
Premiere PAMA Mini Mag for
3D Printing/Additive Manufacturing

Official Publication of RadTech International North America

Welcome to the first PAMA “mini” magazine!
PAMA was formed as a collaboration between the National Institutes of Standards andTechnology (NIST) and RadTech, a nonprofit trade association, as additive manufacturing(AM) begins to accelerate on its journey into the manufacturing supply chain. The shift fromadvanced prototyping toward the use of AM in the production of commercial and consumer
goods only has begun to gain traction. As AM hardware and materials become morecommonplace in industrial markets, we feel it is important that our industry begins to selfregulate to keep AM users (and their end customers) safe while at the same time developing
shared language, methodologies and testing standards that will enable customers to makewell-informed decisions when comparing different technologies.
PAMA doesn’t necessarily target specific industries, but instead is a multi-stakeholder
organization which spans across the length of the entire AM supply chain (i.e., chemical
producers, resin formulators, hardware OEMs, print shops, end-users/customers) and acrossmultiple industry verticals (aerospace, automotive, dental, medical device, construction materials, etc.). This is a uniquedifferentiator between PAMA and other classical industry organizations that are working to organize best practices targeting
one specific process or vertical.
As you will see in these pages, PAMA’s various technical committees are busy developing activities and on-boarding newmembers to help ensure we are targeting the right questions – and we are excited to have nearly 30 organizations alreadyrepresented in our group. We hope that you enjoy this mini-magazine, and we look forward to including you in our work
advancing the photopolymer additive manufacturing space!

David A. Walker, PhD
Executive Chairperson
Photopolymer Additive Manufacturing Alliance (PAMA)

Premiere
PAMA
Mini Mag

2 | UV+EB Technology • Quarter 4, 2022

uvebtechnology.com + radtech.org

PAMA COMMITTEES

Want to Get Involved in PAMA?
Read On.
T

he Photopolymer Additive Manufacturing Alliance (PAMA) is
a collaboration between the National Institutes of Standards andTechnology and RadTech, a 501-c-6 nonprofit trade association withover 500 members, dedicated to the advancement of ultraviolet andelectron beam technologies. PAMA is an alliance of industry, academic,
governmental and NGO organizations with the goal of bringing commonly
accepted standards and practices to the field of photopolymer additive
manufacturing (PAM). Through voluntary self-regulation and work incollaboration with government agencies, PAMA seeks to help ensure PAM
technologies are adopted in a safe and responsible manner.
The activities of PAMA are guided by a roadmap prepared by NIST,
developed to offer strategic guidance for PAM stakeholders and to fuelcollaboration among the PAM community to accelerate innovation. The roadmap is the final report of a workshop held in
October 2019 at the NIST in Boulder, Colorado, with input from research, industry and regulatory communities on the PAM
research and development agenda.

PAMA Executive Advisory Board
Chair and End User Board
Members

David A. Walker, PhD

Chair of the PAMA Board;
CEO & Founder, Prismatic
Manufacturing

Vince Anewenter

Director, Rapid Prototyping
Center Consortium,
Milwaukee School ofEngineering

uvebtechnology.com + radtech.org

Michelle Bockman

Chief Simplification andTransformation Officer,
Stanley Black & Decker, Inc.

Carl Dekker

President, Met-L-Flo, Inc.

UV+EB Technology • Quarter 4, 2022 | 3

PAMA COMMITTEES

Working Committees
Drive PAMA Activities
W

orking committees bring together stakeholders
throughout the PAM community to collaborate,
recommend and take action on specific areas within
PAMA’s range of interest.

Materials Characterization
Working Committee
The PAMA Materials
Characterization (MC)Committee serves theinterests of stakeholders
by ensuring that thenecessary measurement
infrastructure exists and isdisseminated to characterize
resins, processing, partresolution, part-performanceand additional materials
characteristics to ensure
customer needs are met.

Jason P. Killgore, PhD,
NIST

Mission: The mission
Chair of PAMA Materialsof this committee will
Characterization Committee
be accomplished with asignificant emphasis on outreach and education whereby
the MC committee will publish documents and videos toengage characterization experts in PAM and related fields
to ensure PAMA membership is aware of best practices
and emerging methods to advance practical and scientificunderstanding of PAM. The MC committee will also
perform stake-holder-suggested novel research studies todevelop new characterization in areas where existing tools
are inadequate.
Current Objectives:• Evaluating and disseminating best practices forworking curve measurements• Assessment of resin lifetime and influence on partfidelity and performance• Measuring essential resin parameters for the modelingcommunity

4 | UV+EB Technology • Quarter 4, 2022

Hardware Characterization
Working Committee
The PAMA Hardware
Characterization
Committee’s mission is toenable the transformativevalue of this technology
by enlisting PAMA
experts across industry,
academia and government
to understand current
limitations to PAMA
hardware and how thecommunity can overcome
these barriers. The
Callie I. Higgins, PhD,
committee also serves as a
NIST
pre-competitive epicenter
Chair of PAMA Hardwarefor open discussion
Characterization Committee
regarding current andfuture advancements across the PAMA field to develop
novel characterization instruments that readily can be
implemented into industry settings.
Mission: Photopolymer AM characterization has theunique opportunity to innovate on novel characterization
methods due to the complex, diverse nature of the potential
applications paces. As photopolymer AM is a founding
father of AM, this community has a wealth of experts withdeep understanding of this technology that, until now, has
yet to be tapped into sufficiently. The committee aims toprovide a conduit for researchers and industry professionals
alike to learn about current characterization advancements
and inform new research directions.
Current Objectives:• Identify hardware characterization parameters that arecommon throughout PAM and corresponding methods
for characterization• Educate the PAM community on current bestpractices for hardware characterization and listing ofspecifications• Proselytize utility of characterization techniques for
implementation across the industry• Support ongoing research efforts and collaborations in
PAMA hardware characterization through concerted
networking events and educational workshops
uvebtechnology.com + radtech.org

Environmental, Health and Safety
Working Committee
The PAMA Environmental,
Health & Safety (EHS)
Committee serves the needsof the broader Photopolymer
Additive Manufacturing
Alliance by focusing on
current and emerging issues
involving the safe, legal
and responsible use ofphotopolymer raw materials,
technology and equipmentin additive manufacturing
applications. Oversight ofthese critical ‘components’of the AM industrial space isessential to promote healthy,
robust and sustainablegrowth of the technology
while avoiding concerns
related to human health andthe environment.

••

Consideration of material testing that will promote
acceptance of materials or to rebut poorly conductedstudies that bring unfair scrutiny of photopolymer raw
materials
Coordination with legal resources to promote andachieve industry goals where regulatory or nongovernmental entities oppose or obstruct fair and legal
commerce

Government Partnerships& Regulation Committee

Michael Gould, Rahn

Chair of Environmental,
Health and Safety Working
Committee

Mission: This mission
will be accomplished bycommunicating information
most relevant to health,safety and the environment
when it becomes available.
As information is collected
and shared, the principal
Jeremy Smith,goal of the committee is toNagaseSpecialty
achieve a steady state of
Co-Chair“self-regulation” whereinindustry participants are open
to suggestions and data which will guide best practices.
The goals are to promote emerging PAM technology, foster
innovation and avoid costly industry setbacks that may
occur due to misunderstanding of regulations, and to review
and scrutinize current practices in order to get broadest
agreement on best practices.
Objectives:• Collection and dissemination of emerging datathat will affect the labeling and classification ofphotopolymer raw materials, e.g., monomers,
oligomers, photoinitiators, stabilizers and additives• Discussion and clarification of current regulations
insofar as they affect critical materials in different
parts of the US or global market• Discussion of and/or crafting of guidelines for material
use protocols, particularly for FDA and ‘home
hobbyist’ applications outside of the industrial space
uvebtechnology.com + radtech.org

The PAMA Government
Collaborations Committee
explores the development
and application offederal, state and regional
government initiatives
supporting photopolymer
additive manufacturing(PAM) to advance or use thetechnology. The committee
also aims to understand theeffect of actions taken by
governmental organizations
on the industry production
and subsequent implications
for manufacturing
competitiveness throughan open forum with the
manufacturing community.

Dianne Poster, PhD, NIST
Chair of Government
Partnerships & Regulation
Committee

Mission: The committee isa collaborative collectionof organizations fromgovernment, industry
and academia sharing
information on initiatives
supporting or promoting
strategic research anddevelopment to advancePAM technology. The
Cameron Miller, PhD,
committee aims to encourageNIST
a dialogue about the
Co-Chair
government’s role and its
goals for PAM and to collect and disseminate information
on existing or newly developed standards and best practices,materials and engineering processes, and government
resources and assistance programs.
Objectives:• Review existing standards and best practices in PAM
and evaluate new needs• Review of government resources and assistanceprograms supporting PAM suppliers, equipment
page 6 u
UV+EB Technology • Quarter 4, 2022 | 5

PAMA COMMITTEESt page 5
manufacturers and end-users• Analyze the relationship between federal programs,
regional/state programs and private programs
supporting innovation in PAM• Plan for needed initiatives and alternative investment
opportunities in PAM• Identify opportunities for advancing PAM
technologies, investment approaches and international
collaborations

Market Research Working Committee
Understanding the current
state of the additive
manufacturing market isparamount for stakeholders
across the value chain to
make informed businessand research decisions.
Photopolymer Additive
Manufacturing (PAM)
technology represents aburgeoning sector of thisindustry. The PAMA Market
Research Committee aims togather data related to PAM– including materials, print
platforms, technologies andindustry applications – andreport this data in a succinct
and actionable form.

Mission: The committee is a collaborative collection oforganizations from industry, government and academia
focused on gathering information on PAM materials(e.g. volumes, prices, base chemistries, properties, etc.)
applications of use and industries involved. A main goalof the committee is to produce a reliable summary of
information focused on PAM, make this summary widely
available and, in doing so, encourage innovation, sales,
adoption and growth.
Objectives:• Creation of a survey to collect PAM materials usage
and industry application data
• Poll PAM stakeholders about futurist goals for
additive manufacturing and pitfalls on the horizon thatcollaborative action can avoid.
• Hold regular meetings to discuss market feedback,progress on the above and real-world examples of
PAM material utilization u

Stephanie Benight,
PhD, Tactile Materials
Solutions

Chair of Market ResearchWorking Committee

conference & expo
March 6-8, 2023 | San Diego, CA
6 | UV+EB Technology • Quarter 4, 2022

This event focuses on the BIG IDEAS
in the global space for UV+EB
technology and will include 3D
printing, additive manufacturing, UV
LED, printing, automotive, data-driven
materials and more. The BIG IDEAS
conference offers the industry aforum to discuss the future of UV andEB technologies while learning more
about the applications and sciencethat will enable developments two
years, five years and ten years down
the road.

bigideasconference.com
uvebtechnology.com + radtech.org

PAMA NEWS

Leading Groups Recognize Valuein PAMA MembershipWith PAMA activities kicking off less than one year ago,
PAMA is proud to have members from the following
organizations:
3D Systems
allnexAmeralabs
ArkemaDymax**
Henkel Corp
IGM Resins
Lawrence Livermore
National Laboratory
Met-L-Flo, Inc.
MicroTau
Mighty Buildings, Inc.
MIT
Miwon North America
Montana State University
NAGASE Specialty
Materials NA, LLC

Osaka Organic Chemical
Ind. Ltd **PrintFoam
Prismatic Manufacturing
Rahn
Rapid Prototyping
Consortium–MSOE
South Dakota School ofMines & Technology
Stanley X
TE Connectivity
University of Cincinnati
University of Denver
Vitro3D** Denotes PAMA Support as a Founding Member

RadTech and PAMA Support the US
Department of Energy’s Industrial Heat
Shot™: Ultraviolet Curing Included asa “Key Pathway”

RadTech, the association for UV+EB technologies, andPAMA, the Photopolymer Additive Manufacturing Alliance,
support the new US Department of Energy (DOE) Industrial
Heat Shot™ initiative. As excerpted from a late September
2022 US Department of Energy Release:“The DOE has launched Industrial Heat Shot™, a neweffort aimed at dramatically reducing the cost, energy use
and carbon emissions associated with the heat used inindustrial processes. This latest DOE Energy Earthshots
Initiative™ seeks to develop cost-competitive solutions forindustrial heat with at least 85% lower greenhouse gas
emissions by 2035.
The Industrial Heat Shot™ initiative includes as a “keypathway” to achieve targets:
Innovate low- or no-heat process technologies: Develop
new chemistry and emerging biotechnology processes toreduce heat demand, such as bio-based manufacturing,
electrolysis, ultraviolet curing and advanced separations.
uvebtechnology.com + radtech.org

The Industrial Heat Shot™ will support the overarchingstrategy detailed in DOE’s “Industrial Decarbonization
Roadmap.” The Roadmap emphasizes the urgency of deep
decarbonization across the industrial sector and presents astaged research, development and demonstration (RD&D)
agenda for industry and government that will deliver thetechnologies needed to dramatically reduce emissions,increase American manufacturing competitiveness andcreate high-quality jobs.
As part of DOE’s commitment to building a decarbonizedindustrial sector of the future, the US is joining theIndustrial Deep Decarbonization Initiative. Coordinatedby UNIDO, this Clean Energy Ministerial global coalition
is designed to stimulate demand for low-carbon industrial
technologies.
The Industrial Heat Shot™ is an all-hands-on-deck effort
across DOE to address the critical technical barriers to
the development and widespread implementation of thecost-competitive, innovative technologies we need to fully
decarbonize our economy and overcome the climate crisis.
To learn more, read the Industrial Heat Shot™ fact sheet
and visit the Energy Earthshots Initiative homepage.”
RadTech and PAMA jointly plan to establish a task force tooffer feedback to the DOE on the execution of the Industrial
Heat Shot™ and participate in a DOE webinar that will
provide more information on opportunities for collaborationand information-sharing. RadTech and PAMA members
who would like to join our working group should contact
Gary Cohen at gary@radtech.org.

PAMA Partnering with RadTech to Develop
BIG IDEAS!
PAMA is a full partner in thedevelopment of RadTech’s
biennial BIG IDEAS
for UV+EB Technology
Conference, set for March 6-8,
2023, at the Wyndham Bayside
in San Diego, California. The
event focuses on the BIG IDEAS in the global space for
UV/EB technology and will include 3D printing, additive
manufacturing, UV LED, printing, automotive, datadriven materials and more. As a partner, PAMA members
are working to develop presentations and sessions for the
event to advance photopolymer additive manufacturing
technologies. The BIG IDEAS conference offers a forum forindustry to discuss the future of UV and EB technologies,
informing the development of the science and application ofphotopolymers to enable tech advancement two years, five
years and 10 years down the road. Learn more at https://bigideasconference.com/. u
UV+EB Technology • Quarter 4, 2022 | 7

RADLAUNCH SPOTLIGHTS

RadLaunch Spotlights
PAM Applications
R

adLaunch, a unique idea accelerator for UV/EB start-ups, students
and innovators, presented its 2022 class at RadTech 2022, in Orlando,
Florida. “RadLaunch serves as critical support to companies working in
the UV/EB space as they take their first steps on the long and challenging
road to commercialization,” said Mike Idacavage, co-chair of RadLaunch.
“Many companies that have an excellent idea and perhaps early positivelab results are missing the contacts and network that will take them past
the concept phase. One of the most valuable things that RadLaunch offers
is an introduction to member companies, such as material and equipment
suppliers and end users, that can furnish support and guidance.”
The RadTech RadLaunch 2022 award winners honored in Florida arefeatured here. Applications for the 2023 RadLaunch class now are being
accepted at www.radlaunch.org.

Camila Uzcategui, PhD,
CEO and Co-Founder, Vitro3D

Volumetric 3D-Printed Dental Aligners: Vitro3D

Making dental aligners at the point of care offers faster treatment andbetter patient outcomes using a novel and easy-to-use volumetric 3D
printing method. The dental aligner market is the biggest user of UV-based
3D printing/additive manufacturing. However, current manufacturing of
3D-printed dental molds to thermoform aligners is slow, wasteful andinefficient. This solution uses a new volumetric 3D-printing method which
is more sustainable, 100x faster and produces more accurate aligners for
improved patient outcomes. Ultraviolet (UV) photopolymerization is at
the core of the technology being developed by Vitro3D. By making useof the rapid reactions that take place during exposure to UV energy, alongwith the wide variety of UV photocurable materials available, Vitro3D
is leading the development work on the next generation of additive
manufacturing – volumetric printing. Potentially, all current suppliers ofortho aligners would benefit from the successful commercialization of thistechnology.

Johnny Hergert, PhD, CTO,
Founder and Materials Scientist, Vitro3D

Custom Bolus for Radiation Therapy:
BC Cancer Agency, Centre for the North

Centre for the North is working on a modern process for fabricating
tissue replacement (bolus) used during radiation therapy. A bolus is used
to modify a patient’s radiation treatment for cancers close to the skin,ensuring the tumor receives the correct dose. The historical method is
to manually cut out plastic, silicone, wax or other proprietary tissueequivalent materials onto a patient to conform with the planned treatment
field. While Centre for the North successfully has been using FDM 3Dprinters to produce a better bolus than legacy methods, these printersrequire a considerable amount of labor and skill. Ultraviolet (UV) SLA 3D
printers are easier to understand and operate than FDM printers and havethe potential to speed up the process, while creating a bolus that is easier toclean and sterilize for radiation therapy patients in BC.
8 | UV+EB Technology • Quarter 4, 2022

Nathan Smela,
BC Cancer Agency
uvebtechnology.com + radtech.org

Whytneigh R. Duffie, PhD Candidate in Chemical
and Biological Engineering, South Dakota
School of Mines & Technology

Special Academic Award: Disappearing 4D
Advanced Materials
Submitted by South Dakota School of Mines &Technology’s Whytneigh R. Duffie, PhD candidate in
Chemical and Biological Engineering, and Travis W.
Walker, associate professor in Chemical and BiologicalEngineering, this novel chemical technology platform
provides sustainable, biocompatible and high-resolution

photocurable resins that enable controlled and predictabledisappearing (biodegradability) of materials, while also
retaining mechanical integrity of the material. Potential
applications include opportunities for precision castingof parts that are difficult to machine; end-of-life disposalof a part or device (e.g., drone, sensor) to prevent reverse
engineering of sensitive technology; transient sensors;advanced reactor design; self-healing, sacrificial coatings;
and medical devices (e.g., fracture fixation, tissue sealants,
drug delivery). A key value proposition identified bypotential customers with the Department of Defense is theUV curing of disappearing resins with a 3D printer – thisincreases material and combat readiness, shortens the supply
chain and reduces costs associated with transportationand end-of-life disposal. UV serves as the source ofpolymerization, ensuring high-resolution and highefficiency manufacturing. UV offers the ability for custom
manufacturing on-demand via 3D printing to provide timeefficient and cost-savings processing that would not be
possible otherwise. u

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UV+EB Technology • Quarter 4, 2022 | 9

APPLICATION

3D Printing for Boli inCancer Radiation Treatment:
FDM or MSLA?
By Liz Stevens, writer, UV+EB TechnologyAt BC Cancer – Prince George (Centre for the North), in
Prince George, BC, Canada, researchers are conducting
a comparison study of two additive manufacturing methods
for creating the boli used during radiation treatments. If apatient needs treatment for cancer that is near the surface ofthe skin, it often is necessary to fabricate an anatomicallycustomized, form-fitting bolus – a tissue-replacement mass
– that is placed on the patient to optimize how the radiation
plane strikes and penetrates the target area. Historically,materials such as plastic, silicone and wax, or commercial
replacement tissue, have been used. With these methods,
however, achieving a custom fit with an optimal shape has
been problematic, time-consuming and can yield boli thatare difficult to sterilize.
In their study, BC Cancer researchers are comparing fused
deposition modeling (FDM) and masked stereolithography(MSLA) to see which method/technology/material
combination will produce the best boli in an efficient,affordable and manageable way. UV+EB Technology talked
with Nathan Smela, radiation therapy service technologist,to learn about BC Cancer’s study, which earned a RadTech2022 RadLaunch Award.
For either FDM or MSLA production of a bolus, thebeginning steps are the same. “A CT scan is taken whena patient is first admitted,” said Smela. “We then plan aradiotherapy treatment in our treatment planning software.
The specs for the bolus automatically are generated
and prescribed in that software. We extract the bolus
prescription and convert the 3D mesh object that it describes
into a STL file (the file format for 3D printing) and use
another application to smooth the mesh.”
For the printing step, said Smela, the group already had
experience with FDM 3D printing. “But while BC Cancer– Prince George has been successfully using FDM printing
on an open-air bed with polylactic acid (PLA) filament toproduce a better bolus than legacy methods,” he said, “adrawback of FDM it that it requires a considerable amount

10 | UV+EB Technology • Quarter 4, 2022

of labor and skill.”
The various consumergrade FDM printers that
Smela et al have usedhave a steep learning
curve. “Operating andmaintaining a FDM
printer require significant
training,” said Smela. Operators must learn to calibrate
filament rolls and do this for each and every roll, which
requires temperature towers and stringing tests.
“The user also needs to ensure a consistent first layer,”
he continued, “and must avoid filament loading issues,
watch for temperature probe issues and check for needed
maintenance on belts and bearings.” And all of this,Smela emphasized, doesn’t include the important tests
needed to finetune an FDM printer to its full potential, likecalibrating pressure advance, extrusion width tests, testing
for acceleration/jerk settings or performing updates to thefirmware and slicing software.
Ultraviolet (405 nm) MSLA printers that work with a vatof liquid material are easier to understand and operate thana FDM printer, according to Smela. They also can offer
about twice the print speed of an FDM printer and can beused to create a bolus that is easier to clean and sterilize forradiation therapy patients.
“FDM’s printing speed is volumetric,” Smela added,“meaning that if you double the number of objects to be
produced during a single print run, you at least double theprint time. With MSLA, the print time is based only on
the longest dimension of any or all objects, regardless ofthe cubic volume of the object or multiple objects.” In thiscase, two objects can be printed in the same time as one
object, shaving off valuable print time that Smela can use
for making test prints to find the best orientation for printing
a bolus.

uvebtechnology.com + radtech.org

For this study, Smela iscomparing two consumer-grade
3D printers, a $1,200 (CAD)
consumer FDM printer vs. a$1,600 (CAD) consumer MSLA
printer. While the costs of theprinters themselves and theirparts/maintenance consumables
are comparable, MSLA-printed
objects require more postprocessing (wash and cure, andsterilization), which calls for
additional hardware.
The ability to easily disinfector sterilize a bolus is importantsince cancer therapy patients
may have compromised
BC Cancer – Prince George (Centre for the North)immune systems or may have
– Prince George and this study, economy carried special
communicable illnesses. FDM printing of boli is far fromweight. “We are operating on a very tight budget,” Smela
ideal, hygienically-speaking. The process takes place insaid. “The members involved with the study volunteer
open air, and an object made from heated filament is a great
their time to ensure that we have enough budget to fully
host environment for pathogens.
test FDM vs. MSLA printing.” That leads the group to becreative with its MSLA post-processing equipment because“In order to print quickly on a FDM printer,” said Smela,
the preferred cleaning and curing system is beyond the“we have to use large layer heights, but this leaves big
study’s budget. To make do, Smela is using an ultrasoniccavities for microorganisms to thrive in. There also are tinycleaner and a UV LED lamp with a solar-powered turngaps internally in an FDM-produced object – more places
table.
for microorganisms to colonize.” To address this problem,
Smela wraps each bolus in plastic wrap and routinely cleans
Smela hopes this study will empower innovation in
it with disinfectant. “An MSLA-produced resin bolus, onradiation treatment. “We would like to see this study guidethe other hand,” Smela said, “can be printed with a smaller
and justify the use of UV polymers in radiation treatment at
layer height. It also should have a completely filled interior,the clinical level,” he said. “We would like to show that amaking disinfection faster and easier. And with MSLA
3D printer could pay for itself for a single purpose, knowing
printing, there also are sterilizable resin options.”
that success in a first use will spur people to consider whatelse can be achieved with 3D printing.”
Using 3D printing for medical use calls for careful attention
to the type of filament or resin used. “The best patient bolus
The group looks forward to seeing this technology growmaterial,” said Smela, “would be biocompatible, easy tobeyond merely being an intriguing technology, to becoming
print, nearly equivalent to water for radiation occlusion,a multi-purpose tool in search of the next problem to solve.
have no odor, be antiviral/antibacterial or sterilizable, and“Given these printers’ relatively low cost,” said Smela,
be inexpensive. A super-soft material would be ideal – with
“we hope to show that they are easy enough to use, thus
a shore hardness in the 00 or 000 range – but the peelingencouraging other treatment centers to try out the process
forces of the MSLA process would make material that softthemselves.”
exceptionally difficult to handle and therefore is out of
scope for this project.” For FDM printing, PLA (polylactic
RadTech applauds BC Cancer’s exploration and evaluationacid) filament was used. Comparable biocompatible, rigidof FDM and MSLA 3D printing, where the features andconsumer-grade MSLA resin roughly is triple the cost of
benefits of UV can play a part in improving radiation
FDM filament, and this introduces another data point –treatment for cancer patients. umaterial cost – to evaluate during the study.
Cost of materials, as well as cost of hardware and software,always is an important factor to consider when choosing
between methods and technologies but, for BC Cancer
uvebtechnology.com + radtech.org

UV+EB Technology • Quarter 4, 2022 | 11

ANHYDRIDE RESINS

Additive Manufacturing of Novel
Surface-Eroding, Non-Swelling
Anhydride Resins
Whytneigh R. Duffie; Kevin D. Barz; Tsvetanka S. Filipova; Katrina J. Donovan; Timothy M. Brenza; and Travis
W. Walker, South Dakota School of Mines & Technology

Several groups have studied the application of watersoluble resin formulations for 3D printing of materials4,
with a common concern being the swelling of the polymer
matrix during the dissolution process. In this work, asynthesis protocol was developed to produce uniquesurface eroding methacrylic-anhydride-based oligomers
that later react to form crosslinked networks during the
3D-printing process. Chemical degradation leads to surface
erosion of the crosslinked network after 3D printing, which
provides ample opportunity for a wide array of applications
where swelling of the polymer matrix has previously
been a significant drawback in the functionality of watersusceptible 3D-printed parts.

eroding, anhydride-based formulations via 3D digital lightprocessing (DLP). Hydrolysis of the anhydride bondsin the presence of water yields the diacid monomer andpoly(methacrylic acid) via a surface-erosion mechanism.1
Surface erosion occurs when chemical degradation andsubsequent mass loss is limited to the outermost layer of thecrosslinked product (Figure 1).

Introduction

Methods and materials

Bulk erosion occurs when chemical degradation and massloss occur throughout the entire volume of the material(Figure 1). Surface erosion leads to higher retention of
mechanical properties, less water uptake and swelling, and amore controlled degradation rate.3

Development of 3D printable thermosets that chemically
Photopolymer resin(s) were prepared with novel synthesizeddegrade in the presence of water in a controlled, predictive
methacrylated-anhydride-based oligomers, reactive diluentsmanner has been postulated as a novel strategy to engineer
and photoinitiators. The synthesized oligomers werea number of advanced composites, including biomaterials
characterized using FTIR for functional group confirmation(e.g., drug delivery, fracture fixation, tissue sealants),(16 scans), 1HNMR for structural confirmation anddisposable single-use medical devices, and advanced
determination of molecular weight (300MHz, 1024 scans,transient sensor technologies.1,2Previous efforts to incorporate
surface-eroding oligomers into
resin formulations have beenfurther limited by the commercial
availability of surface-eroding
constituents that are suitable foruse in light-based 3D printing.
Incorporation of the surfaceeroding oligomers into novel
resin formulations enables
high-resolution, 3D-printable,
acrylic-based resins thatchemically degrade in thepresence of water. Multiple
avenues have been identified fordevelopment that allow for local
Figure 1. Surface erosion (top) vs. bulk erosion (bottom) as related to the degree ofphotopolymerization of surfacedegradation over time.
12 | UV+EB Technology • Quarter 4, 2022

uvebtechnology.com + radtech.org

printer (Figure 2, left). Printed samples were dried with alint-free towel and cured in a B9Creations UV cure unit.
Degradation studies of formulations containing a reactive
diluent with equivalent weight percentages of three different
oligomers were performed in triplicate using PBS buffer
solution at a fixed agitation of 60 RPM and a temperatureof 37° C. After the degraded samples were allowed to drycompletely, the disks were massed to calculate the rate ofdegradation of the disks.

Figure 2. Image of an Anycubic Photon LCD printer(left), and the modified Anycubic Photon LCD printer(right).

CDCl3), 13CNMR for structural confirmation (300MHz,
8192 scans, CDCl3) and Dept-135 NMR for confirmation ofpeak assignments (300MHz, 8192 scans, CDCl3).
Crosslinked cylindrical disks (15 mm diameter and 1.85mm height) were produced using an Anycubic Photon LCD

An Anycubic Photon printer was modified in this work tominimize the volume that is required for printing novel
formulations to less than 1 mL (Figure 2, right). The
modifications to the Anycubic Photon printer included a vat
insert with a new area for loading the film, an additionalpart that was added to the original build plate to serve as the
new build area, a 3D-printed sensor piece and an upper-limit
switch with 3D-printed housing. The vat insert included atapered cylindrical cavity at a reduced volume. The cavity
that was created to hold the liquid resin included a slighttapering of the inner channel to create turbulence as well asa mixing effect given the dynamics of the printing process.
The vat insert was secured with epoxy adhesive around theedges to avoid issues of the build plate lifting the insert
page 14 u

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UV+EB Technology • Quarter 4, 2022 | 13

ANHYDRIDE RESINSt page 13
during the printing process. Empty cavities were createdon the bottom side of the vat insert to reduce the overall
weight of the part. The FEP film insert with a smaller area
was created with the same general idea as the originalvat. The maximum volume that the new vat can hold isapproximately 5 mL. Resin is added and removed from thevat using a disposable pipette.
A cylinder was attached to the original build plate using a
set screw, and it can be removed at any time with the correct
tool. The current cylinder has a diameter of approximately
25.25 mm, and a height of approximately 35.90 mm. The
3D-printed sensor piece has the same shape as the original
metal piece that was provided with the Photon; however, thenew piece is longer to accommodate for the length of thecylinder that was added to the build plate. The sensor length(55 mm) was chosen to allow for the (z = 0) position to be
set slightly lower than the home position without the sensor
piece ramming into the bottom of the printer.

Results and discussion

To date, the novel synthesis route has enabled the inventionof three previously unobtainable oligomers. Percent yields
for all synthesized oligomers were over 70%, and oligomers
that were chosen for further evaluation were limited to an‘n’ value of two, where ‘n’ represents the average repeatof the anhydride oligomer. These lower-molecular-weightstarting materials, available in both solid and liquid statesat room temperature, allow for a wide array of applications,
including 3D DLP (Figure 3).

Figure 3. Methacrylated-anhydride-based oligomers
available commercially and as a result of the novel
synthesis protocol.

Oligomers existing in the solid state at room temperatureare suitable materials for DLP upon dissolution in lightsensitive liquid crosslinking agents. Thus, solid-stateoligomers that are loaded at specific weight fractions into
the crosslinking agent undergo co-polymerization upon
exposure to light with the addition of a photoinitiator.
Several groups have demonstrated the successful
14 | UV+EB Technology • Quarter 4, 2022

Figure 4. Mass loss versus time of three resin
formulations, where the size of R1 < R2 < R3.

copolymerization of solid-liquid mixtures by utilizing
methacrylated sebacic anhydride, which is available
via a single-stage synthesis route, and loading it into
commercially available methacrylic anhydride.2,3 Whilemethacrylic anhydride is the only commercially available
liquid bi-functional anhydride, literature suggests thatwhen choosing homopolymerization of liquid methacrylic
anhydride, limitations exist that are a result of limited
radical diffusion. The long timeframes that are needed tocrosslink the material at small volumes are unsuitable formost applications. While the addition of methacrylated
sebacic anhydride was found to improve these exposure
limitations, the increase in hydrophobicity of the
backbone composition and decrease in crosslink density
led to decreased erosion rates and decreased mechanicalperformance of the material.3 Thus, constituents that aresuitable for loading into methacrylic anhydride are bothpromising and worthy of investigation for applications that
require increased erosion rates and improved mechanicalperformance. The additional availability of the products
from the novel oligomeric synthesis allows the opportunity
to further establish a trend of faster degradation rates
and increased mechanical integrity as the length between
methacrylated-anhydride functional groups decreases.
Disks that were 3D printed exhibited linear rates ofdegradation and shrinkage along only the surface, basedon the observation of surface cracking. These results
indicate that the crosslinked products were, in fact, surface
degrading. The degradation studies suggested that, at
a constant value of ‘n,’ a decrease in the length of theR-group in the formulation resulted in an increase in therate of mass loss (Figure 4). In other words, the rate ofdegradation was found to increase as the hydrophilicity
page 16 u
uvebtechnology.com + radtech.org

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ANHYDRIDE RESINSt page 14of the R-group increased, as found in the literature.2,3Controlled degradation rates provide the opportunity forcommercialization in countless applications.

Next steps

By utilizing novel methacrylated-anhydride oligomers
that are available solely through an innovative synthesis
route, formulation development has shown great promisein providing expanded physical properties of degradable
thermoset materials that are suitable for 3D printing. Given
that the materials are surface eroding, it is hypothesized
in future experiments that the modulus with respect to thethickness of a sample will exhibit very little change overmost of the material lifetime. Toward the end of the material
lifetime, the thickness of the sample approaches the sameorder of magnitude as the thickness of the erosion zone on
the outer surface of the material. In this case, the modulus
with respect to the thickness of the sample rapidly will
decline.
Standard characterization techniques provide limited
information about the degradation kinetics and mechanismof erosion. Therefore, a frugal microfluidic device has beendeveloped to further access the kinetics and mechanism of
surface-eroding polymer degradation (Figure 5). Liquid
is introduced into the channel at a constant flow rate andtemperature.
Polymer degradation can be assessed readily via image
analysis by evaluating the erosion over time with respect tomaterial formulation, polymerization conditions and sample
environments. In-depth analysis of the degradation rates

By utilizing novel
methacrylated-anhydride
oligomers that are available
solely through an innovativesynthesis route, formulation
development has shown
great promise in providing
expanded physical propertiesof degradable thermoset
materials that are suitable for
3D printing.
16 | UV+EB Technology • Quarter 4, 2022

Figure 5. Preliminary data of a surface eroding polymer
material resulting from the frugal microfluidic device.

and erosion mechanisms with the novel and adaptable flow
apparatus can be coupled with previously explored methodsof analysis to give insight into the complex mechanismsthat take place during erosion. An increase in the number ofcrosslinks or in the hydrophobicity of the backbone should
result in a decreased rate of degradation.

Acknowledgements

The authors would like to thank the South Dakota Boardof Regents Competitive Research Grant and the NSF
EPSCoR 2DBest Graduate Student seed grant for funding.
This material is based upon work that was supported by the
National Science Foundation Research Traineeship program
under award number 1828462. The authors also would liketo thank Christen V. Gauker and Jacob P. Fyffe for theirassistance, as well as B9Creations, LLC for its support ofthe project overall. Two invention disclosures have been
submitted in relation to this work, with a provisional patentapplication being finalized. u
References
1. Kristi S Anseth and Deborah J Quick. Polymerizationsof multifunctional anhydride monomers to form highly
crosslinked degradable networks. Macromolecular Rapid
Communications, 22(8):564–572, 2001.
2. Andrew W Watkins and Kristi S Anseth. Copolymerizationof photocrosslinkable anhydride monomers for use as abiodegradable bone cement. Journal of Biomaterials Science,
Polymer Edition, 14(3):267–278, 2003.
3. Jennifer S Young, Kelly D Gonzales, and Kristi S Anseth.
Photopolymers in orthopedics: characterization of novel
crosslinked polyanhydrides. Biomaterials, 21(11):1181–1188,
2000.
4. Robert Liska, Florian Schwager, Christine Maier,
Rafael Cano‐Vives, and Jürgen Stampfl. Water‐soluble
photopolymers for rapid prototyping of cellular materials.
Journal of applied polymer science, 97(6):2286–2298, 2005.
uvebtechnology.com + radtech.org

RADIOMETRYRadiometry: Variations
in Consistency Across
3D-Printer Models
By Paul Snowwhite, Katie Snowwhite and Hunter Peczynski, 7D Innovators, LLC
Editor’s Introduction: The authors created an experiment
to better understand why 3D printers created by various
manufacturers perform differently even when using thesame print settings or why a print fail occurs after multiple
successful prints. Variables initially considered included
material, cure source and printer calibration, but what
emerged were concerns about consistent radiometry
data across the width of the print platform. With better
understanding of 3D printers, the ability to develop highquality materials will be enhanced.

and clear electrodes. When a field is applied, the crystal
molecules align and, depending on the orientation of thepolarizers, light can pass or it is blocked. An array of UV
LED panels is used as a cure source, only allowing UV
to pass through where resin needs to be cured, reducing
the need for galvanometers or mirrors and simplifying theprinting process. LCD-based printers have a print qualitythat depends on the LCD density. The more pixels a display
has, the better the quality of the print. LCD printers arescalable in a way DLP printers are not.

Background of 3D Printing

A common problem with LEDs is that they start to dimas they come to the end of their lifespan, which is unlike
traditional light bulbs that burn out all at once. Each LED
will age differently due to manufacturing (high-quality
LEDs can have a long lifespan and fairly predictable
degradation over time), and there are thousands of LEDs
within a singular array. Small imperfections in the LEDchip semiconductor crystals can cause the LED to begin
page 18 uIn the industry of additive manufacturing, 3D printers
vary not only in the material used for printing – whether
they print resin, filament or even cement – but also in how
things get printed, with differences in positioning or curing
sources. Three types of resin 3D printers are addressedin this article: stereolithography (SLA), digital light
projector (DLP) and liquid crystal display (LCD). SLA,DLP and LCD printers (Image 1) use a process called vat
polymerization to cure the resin into layers by using a resintank and a certain type of light source.
SLA started to be commercialized in the mid-1980s anduses a laser beam to selectively cure layers of resin on
the bottom of the resin tank that then adhere to a print
platform. The laser works by using galvanometers, which
are little mirrors under the resin tank, to guide the laser
to the precise position that needs to be cured. In DLP 3D
printing, a digital light projector is used to cure the layer ofresin simultaneously, using the color black or no light at all
to get precise layers. LCD printers use light emitting diodes(LEDs) that shine through LCD panels to cure the current
layer of resin. LCD printers are the focus here.

LCD Printers with LED Light Sources

Liquid Crystal Display (LCD) printers have become apopular option for 3D printing as they provide a highquality product while also being cost effective. LCD 3D
printers take advantage of the light-modulating propertiesof liquid crystals when placed between crossed polarizers
uvebtechnology.com + radtech.org

Image 1. Schematic of SLA, DLP and LCD printers.

UV+EB Technology • Quarter 4, 2022 | 17

RADIOMETRYt page 17
losing brightness. LEDs let out a small amount of heat whenturned on and improper cooling can increase the rate ofdecay.
According to online reference ledlights.org, “The term
degradation in connection with LED lighting describes thedecrease in luminous flux over the course of a lifetime. The
luminous flux slowly decreases due to material changes inthe LED chip and clouding of the optics. Degradation istherefore an aging process in which an LED lamp loses its
brightness over time and slowly becomes darker.”

Printer Consistency Issues and Observations

When 3D printing, there are many parameters that need tobe met for a successful print to take place. Print failures
can occur due to incorrect settings, support placement orequipment that needs calibration. Through their use of 3D
printers, the authors have seen how important it is to include
radiometry in the conversation about print issues.
When printing, failures have been observed on printers that
had been consistently printing, were calibrated, had beencleaned, had correctly inputted settings and were using aknown material. Sometimes these print fails were minor –such as a deformed support or an unlevel surface that wasable to be sanded smooth – however, other times it would
be a complete failure, with no model attached to the print
platform or half the model missing. After a while, with thesefailures seemingly coming out of nowhere, it was time tobegin investigating and learning more about the 3D printers
being used.
It was observed that lifting and uneven models mostly wereprinted if they took up a majority of the print platform or
were placed close to the edges. The starship in Image 2 is a

Table 1. Radiometer precision testing.

good example of what it looks like when the print is lifting.
This print took up most of the print platform horizontally,
and the edges of the print lift more as it gets closer to theedges of the platform.
Some 3D printer manufacturers offer replacement screensand instructional videos for their printers due to theseinconsistency issues. Other 3D printing companies don’t
offer a replacement option. While it’s understandable thatcompanies don’t want untrained users trying to do theirown printer repairs and (possibly) worsening the problem,
acknowledging the problem and addressing it would be ideal.

Purpose of Experiment

One of the reasons this experiment was designed is because
the authors started to notice that a print would fail on one
printer, but it would print perfectly when tried on a different
printer from the same manufacturer with the same printsettings. In looking for the cause of this inconsistency,
variables such as material, cure source and printercalibration were reviewed. In the past, there had been issues
with prints peeling up at the edges, but those were attributed
to not having a high-enough bottom exposure level. As more
research into 3D printers was done, the authors learned that
LED-curing arrays begin to dim, which causes them not towork at 100% power consistently or can cause inconsistencyof cure over the whole screen.

Image 2. This starship shows lifting at the edges of theprint.

18 | UV+EB Technology • Quarter 4, 2022

Overall, the main reason for this experiment was to do more
research to better understand the printers, find out why there
are inconsistencies in print quality and explain the reasons
uvebtechnology.com + radtech.org

To understand any variations that might occur, multiple
spots across a printer’s surface were measured – centerand edges. The middle measurement for every printer was
taken at the center of the screen, a fixed point. For left andright measurements, the size of the printer’s screen had tobe considered. To get these measurements, the probe wasplaced so that the outside edge of the probe aligned with theedge of the screen while being along the same horizontal
line of the center measurement. This was done for both theleft and right measurements.
Table 2. Commercial cost range of tested printers.

The precision of the radiometer also was evaluated to ensure
accuracy. Several experiments were done to understand thevariation with respect to measurement. These were doneby measuring printers in the same spot 180 times between
three different printers with the radiometer cycled on andoff without moving the probe (Table 1). As can be seen, theradiometer’s measurements are extremely consistent withlow variability. It also is important to note that all printerstested were within the specification per the manufacturer at
the time testing was performed.
For the experiments performed, several printers wereused. As the commercial cost range data show in Table 2,
some printers tested were on the lower end and some on
the higher end. The printers varied in how they allowed
radiometry testing as well; some give measurement
internally, but most don’t, and some have an option to test
the array’s power without an actual measurement produced.

Table 3. Manufacturer A.

for a print fail after multiple successful prints when there are
no obvious reasons for failure. Material developers need tounderstand these things to develop materials at the highest
quality possible for this industry.

Procedure and Equipment
A UV meter (radiometer) was used to measure the output
of curing sources in the operation of 3D printers from avariety of manufacturers. The first step was making sure theradiometer was on and in the correct parameters (uW/cm^2)for this experiment. While wearing proper PPE, the display
was turned on or the print was started, depending on theprinter. Then, the probe was placed on the printer’s screen
to take a measurement of the UV output, running the probe
for five seconds and recording the data. The process thenwas repeated and, depending on which measurements werebeing taken, the probe was kept in the same spot for more
readings or moved to another spot on the printer’s screen
and data was recorded. The spot size of the probe was 1 cm
in diameter. The average of three measurements was used to
get the data reported for each particular printer.
uvebtechnology.com + radtech.org

The point of this experiment was not to evaluate which
printer or manufacturer had the best printer, but to create
discussion about radiometry and 3D printing. Letters havebeen assigned to the printers within this experiment, and theprinters have been categorized by cost in ranges to give a
scope of understanding for readers.

Challenge in Measuring Energy Outputs

When beginning the testing for this experiment, it wasobserved that some manufacturers allow users to check the
exposure levels and/or display an image that allows users
to check the quality of the LED. With a few printers, it wasnecessary to start a print with a long exposure time and tricksome safety features before being able to check the energy
output. Three printer manufacturers have safety features orare designed in a way that do not allow users to check theirenergy output. With these challenges, the total energy output
for individual printer manufacturers is not being comparedacross manufacturers.

Data and Analysis

The experiment began by looking at data from Manufacturer
A. Testing was performed on a total of 12 printers from
Manufacturer A, ranging in age from one month to 12 months
page 20 u
UV+EB Technology • Quarter 4, 2022 | 19

RADIOMETRYt page 19

Table 4. Manufacturer B.

Table 6. Manufacturer D.

Manufacturer C is the only machine that does calibration of
its own LED sources internally. However, the data displayedin Table 5 was a measurement taken with the authors’radiometer as per the method listed above to maintainconsistency with the rest of the collected data. The printeris impressive with respect to the precision of irradiance, as
shown through the data in the table.

Table 5. Manufacturer C.

and in use from ~10 hours to ~200 hours. When looking at
Manufacturer A and the data reported for these printers, it
is important to note that the assigned printer number is not
significant to the age of a particular printer or amount oftime used. The assigned numbers are purely for distinction
between printers of this manufacturer within the lab.
Manufacturer A’s printers show a range of variation acrossthe print platform (Table 3). A correlation study for exposure
vs. print issues has not been done, and faster chemistries will
be more robust with respect to this error. However, based onsome calculations for this system, less than 2% is expected
to be great, less than 5% to be acceptable, 5 to 10% could
possibly start causing issues and >10% probably results inprint issues. These percentages may vary due to differencesin formulas and printers; however, these calculations could
be applied to other manufacturers. For these 12 printers, sixor seven of them could have significant print issues acrossthe surface. The variation also is very high from printer toprinter, so if it could be very challenging to reproduce amethod over these printers.
Looking at the data produced by Manufacturer B’s printers(Table 4), it can be seen that an older model had more issues
with consistent prints as it aged. Due to this, a new one
was purchased. The older printer meets the manufacturer’s
specifications (although the specifications do not take into
account the changing output of the LEDs as aging occurs),
and the new printer is fairly consistent with prints. The dataclearly show the new printer has significantly less variation
than the old printer (by greater than a factor of three) acrossthe print surface and an even higher difference in irradiance.
20 | UV+EB Technology • Quarter 4, 2022

As great example of “you don’t always get what you payfor,” Manufacturer D produces a very expensive printer, andits consistency across the build platform is poor (Table 6).
One of the largest printing surfaces comes from
Manufacturer E. This printer was less than a month oldwith minimal hours printed on it at the time of testing. The
data (Table 7) illustrates the difficulty with making a large
print, and the variation will make it challenging to use thewhole surface, especially as the printer ages. Although thevariation was within an acceptable range at the time of
measurement (less than one month old and fewer than five
hours of use), will the variation worse as the machine ages?
Manufacturer F’s printer is relatively new, and it is ok outof the box with respect to irradiance over the entire surfaceof the printer (Table 8). Similar to E, concern is present thatvariation will worsen as the equipment ages. And finally,
Manufacturer G – one of the older printers in the lab at over
15 months of age with pre-2020 technology – provides datameasurements (Table 9) showing what was expected withrespect to the variability due to its age.

Conclusion

In conclusion, when selecting a 3D printer, it is importantto understand the machine’s light source output quality
and how the source might age in the future. This study has
shown that the most expensive 3D printers don’t guarantee
a curing source that is the best option – according to thedata, money doesn’t necessarily buy quality when it comesto prints.
Having consistent radiometry across the entirety of thescreen is important, but also difficult to achieve due topage 22 uuvebtechnology.com + radtech.org

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Table 7. Manufacturer E.

Table 9. Manufacturer G.

user could use to perform testing themselves also is a good
option.

Table 8. Manufacturer F.

structural differences or age of curing sources. As seen in
the data on printers from Manufacturer A, seven of them
have significant differences between the middle and edges
on the screens.
Understanding the radiometry also can make a differencein print quality and success. The worst-case scenario isthat failed prints occur with a failing curing source, but adegraded LED source also might be causing printed models
to have different conversion levels if printed on different
parts of the print platform – or even a singular model tohave different conversion on different areas of its surface if
it spans across a print platform. Uneven curing across theentire print also can cause added stress and embrittlement
when undergoing post-cure.
After performing this study, some recommendations andguidelines have resulted for people looking to purchase a
new 3D printer or create a method for a material. Whensetting up a method that is consistent for a material on a
3D printer, it’s important to take into account the lowest
cure settings that work for the material (not the average orhighest) as not all print platforms give good results acrossthe surface.
Manufacturer C, which had the best consistency data, wasthe only printer tested that had internal radiometry metrics.
Therefore, it would follow that printer manufacturers whosemachines have an internal option to check the radiometry
would be recommended. However, simply having a printerthat includes a display, internal test or calibration that a
22 | UV+EB Technology • Quarter 4, 2022

This is the authors’ first in-depth look into the radiometryof the 3D printers to which they have access, and the entire
study has been found to be very interesting. Throughout theexperiment, questions have arisen that could be the focus of
future investigation. These include the following:• If a printer is producing good prints but there isvariation across the surface of the printer, how does
post-cure affect the material’s properties?
• Do material physical properties change with the 10%
difference in light, or does post cure bring all printed
models to the same state?
• The authors’ lab has done work on the effects ofover-curing and under-curing materials during
development, with negative results experienced whena material becomes over-cured and has embrittlement.
Could this be happening to parts if a post process is
optimized for prints that have been exposed to lessenergy from a particular printer?
• What is the correlation between the LED source’s age
and how many hours it has been used to print? uResources
Ledlights.org. 2022. Do LED Lights Dim Over Time? [online]
Available at: <http://www.ledlights.org/FAQ/Do-LED-Lights-DimOver-Time.html> [Accessed 25 March 2022].
LampHQ. 2022. LED Brightness Degradation: Do LED Lights
Dim with Age? - LampHQ. [online]
Available at: <https://lamphq.com/led-degradation/> [Accessed 25
March 2022].
Creality.com. 2022. The Basic Introductory Guide of Resin 3D
Printers. [online] Available at: <https://www.creality.com/blogdetail/the-basic-introductory-guide-of-resin-3d-printers>[Accessed 24 March 2022].
ELEGOO Official. 2022. Types of 3d Printers: SLA vs DLP vs
LCD vs FDM. [online] Available at: <https://www.elegoo.com/
blogs/learn/types-of-3d-printers> [Accessed 24 March 2022].

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