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6 Inkjet and Binder Jet Printing in Pharmaceuticals 209
was successfully extended to a custom pilot scale binder jetting machine dubbed
HuskeyJet (Integrity Industrial Inkjet Integration, Inc., USA), which includes a
moving sled with powder feed bed and powder build bed beneath three fixed print
head assemblies (Chang et al.
2021).
Since approval of SPRITAM, in 2021–2022 additional binder jetting research
has been published using similar orodispersible compositions of levetiracetam as
a starting point, and expanding upon popular AM themes. The work includes
prototyping of multicolor cartoon-shaped levetiracetam tablets in scalable sizes for
personalized pediatric dosing using a ProJet CJP 660Pro (Wang et al.
2021). Also,
using self-developed apparatus, three region concentric cylindrical tablets were
prototyped including pyridoxine jetted into the nested intermediate region in order to
model personalized combination therapy with levetiracetam (Hong et al.
2021). As
a potential guide to personalized dosing, a physiologically based pharmacokinetic
(PBPK) model was developed for binder jetted instantly dissolving levetiracetam
tablets in Chinese children (Li et al.
2022). This model included key inputs from in
vivo bioequivalence data of prototype tablets versus SPRITAM in beagles, the drug
attributes, and PBPK modeling and simulation results for Chinese adults.
There is also an example of binder jetting work at the University of Texas
at Austin, the birthplace of selective laser sintering (SLS). In 2022, low-dose
deposition of three model antiviral drugs was shown using two-apparatus process:
(1) binder jetting of drug-free flat, modular concentric cylindrical tablet “blanks”
using ProJet 360 (3D Systems, USA) and non-pharmaceutical powder; and (2)
controlled deposition of model compounds onto respective sections of the tablet
blanks using Bio X
heads (Lu et al.
®
bioprinter (Cellink, USA) configured with syringe pump print
2022).
Beyond apparatus, there has been increased interest in evaluating suitable
materials. This includes support from excipient vendors seeking to demonstrate
suitability of their product lines for use in binder jetting and AM more generally. In
2019, swallow tablets having high loading of caffeine (70% w/w) were prototyped
on a VX200 printer (Voxeljet AG, Germany) in the course of evaluating four grades
of hydroxypropyl cellulose as solid binder (30% w/w) using a solute-free print
fluid (Infanger et al.
2019). There is also renewed interest in lactose, one of the
most widely used binder jetting excipients for over two decades. In 2021, twentyseven excipient powders were evaluated for powder flow, wetting, and mechanical
print properties in binder jetting using a ProJet CJP 460 Plus 3D printer (3D
Systems, USA), focusing on lactose, microcrystalline cellulose, and copovidone
(Antic et al.
2021). Also, lactose and pregelatinized starch orally disintegrating
tablets were prototyped incorporating low levels (10% w/w) of acetaminophen
or diclofenac sodium as model compounds using the PBP Next printer (TNO,
Eindhoven, The Netherlands) equipped with solenoid microvalve print head, similar
to some of Therics’ systems (van den Heuvel et al.
2021). The ingredients, use
levels, and printing parameters in this work align well with prior references (Yoo et
al.
2002; Lee et al. 2003). In 2022, follow-on work with the lactose/starch system
utilized wider ranges for drug concentration (5%–50% w/w) and total mass (50 to
210 T. G. West and J. Yoo
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500 mg) in immediate release tablet prototypes as an effective demonstration of
dose adjustment ranges relevant to early clinical trials (van den Heuvel et al.
2022).
In 2022, hydrophobic model drug clotrimazole was co-spray dried with
hydrophilic excipients to aid prototyping of fast disintegrating tablets (50 mg), along
with parallel prototyping of low-dose quinapril hydrochloride fast disintegrating
tablets (3 mg), each using a Spectrum Z510 printer (3D Systems, USA), and
an effective generalized formulation workflow for binder jetting was proposed
(Kozakiewicz-Latała et al.
2022). Such co-processing of hydrophobic drugs with
hydrophilic excipients is recognized in conventional formulation practice and has
been used with binder jetting as well (Jacob et al.
2016a). Additional publications
in 2022 explored the influence of formulation and process factors of binder jetting
via multistage DOE for screening and optimization. This includes prototyping of
model drug ketoprofen using a custom PicoJet 220 apparatus (Spectra Laboratories,
Slovenia), including recycling of unprinted powder (Kreft et al.
2022). Likewise
prototyping of model drugs ibuprofen and paracetamol (acetaminophen) was
conducted within a Quality by Design (QBD) framework using Easy3DP-M300
printer (EasyMade, China), with optimization of paracetamol (30%w/w) tablets
(Wang et al.
2022).
Additional compound AM approaches have been demonstrated. In 2017–2018,
University of California Los Angeles (UCLA) demonstrated a sequential approach
of binder jetting, infiltration, coating, and material jetting of drug-containing
photocurable bioinks,(Acosta-Vélez et al.
2017, 2018a, b) bringing full circle one
of the earliest researchers in pharmaceutical binder jetting from M.I.T (Wu et al.
1996). The UCLA work created stackable, drug-free tablet segments using calcium
sulfate modeling powder on a ProJet 660 printer (3D Systems). After infiltration and
coating the segments, a piezoelectric dispenser (MicroFab, Plano TX) and controller
(Microdrop, Norderstedt, Germany) delivered the bioinks. The hydrophilic bioink
was based on hyaluronic acid norbornene, poly(ethylene glycol) dithiol, phosphate
buffered saline, and Eosin Y. The hydrophobic bioink was based on poly(ethylene
glycol) diacrylate, polyethylene glycol, Eosin Y, and mPEG amine. The drugs
studied include ropinirole, ibuprofen, naproxen, spironolactone, and lisinopril.
6.3 Regulatory “Firsts” for Binder Jetting
6.3.1 Perspective and Context for AM
The establishment of a cogent regulatory strategy is pivotal in commercializing any
new technology for medical use.
discussion of this topic. While some proponents of AM have suggested that entirely
3
Authors note that a complete review of regulatory pathways is beyond the scope of this chapter.
Some basic information on certain regulatory pathways is provided in order to illustrate the use
of binder jetting technology in certain marketed products. This chapter should not be construed as
regulatory or legal advice.
3
Since the advent of AM, there has been substantial
6 Inkjet and Binder Jet Printing in Pharmaceuticals 211
new regulatory pathways were required simply to accommodate new technology,
that supposition has proven incorrect. As the binder jetting examples in this section
demonstrate, the existing regulatory frameworks in the U.S. (at a minimum) are
flexible enough to encompass AM-based products, and have already been applied
to marketing authorization of several products. This view has also been echoed
in publications by current and former FDA staff relating to medical devices (Di
Prima et al.
type of science-based and risk-based approaches used in the development, review,
and marketing authorization of products made by traditional techniques can also be
applied to products made by AM.
Although this chapter and textbook are focused on pharmaceuticals, the vast
majority of authorized FDA-regulated AM products are medical devices. Moreover,
the first FDA authorizations for products made using binder jetting were medical
devices. And so it is instructive to consider this usage briefly ahead of discussing
pharmaceuticals.
At a general level, a regulatory strategy must contemplate the type of product
to be made, the applicable laws governing its approval, the center at FDA (or
equivalent agency) responsible for reviewing the applicant’s submission(s), and any
regulatory guidance provided by that center. Applicants should seek experienced
and competent regulatory and legal advice in the correct area of specialty from the
earliest stages of product development.
The examples that follow have a few key attributes in common. Firstly, they
each used an equivalence-based regulatory pathway involving comparison of the
new product candidate to a previously approved reference product in order to
help establish the new product’s safety and efficacy. Secondly, they each involved
deployment of binder jetting in centralized manufacturing plants having equipment
and batch sizes sufficiently scaled to make specialized products in their respective fields. These attributes allowed for relatively compact clinical development
requirements while maximizing the similarity to traditional manufacturing schema.
Accordingly, each regulatory dialogue could better isolate the topics unique to the
deployment of binder jetting or to the specific product candidates. Moreover, with
these early regulatory precedents in place, future products can be envisioned that
require more extensive clinical programs or involve more complex manufacturing
deployments than the ones described below, provided that the new programs
generate commensurate data under an appropriately selected regulatory framework.
2016) and to drug products (Norman et al. 2017). In short, the same
6.3.2 2003–2004: Early Medical Device Clearances Based on Binder
Jetting
In 2003, Therics Inc. obtained FDA clearance for the TheriRidge Block (510(k)
Summary K023998
a sterile implantable device made by binder jetting, and likely one of the earliest
FDA actions related to an AM product for use within the body. TheriRidge Block
was a synthetic bone graft substitute for dental use consisting of hydroxyapatite, a
2003). This timing is presumably the first FDA clearance for
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calcium phosphate-based bioceramic similar to the mineral portion of natural bone
tissue. Binder jetting was used to create the overall shape, macroscopic channels,
and microporosity features of the implant that were designed to encourage tissue
growth onto and into the device. It was manufactured as rectangular blocks available
in three standardized, preset sizes. The blocks could then be modified manually by
the surgeon to fit the unique surgical site of each patient (e.g., by drilling or shaving
excess material). Hydroxyapatite is considered osteoconductive and nonresorbable,
so the device would be expected to integrate with the patient’s own native bone
without being replaced by it. Synthetic bone graft substitutes like this are used as an
alternative to actual tissue from the same patient (autograft), tissue from a human
donor (allograft), or nonhuman tissue (xenograft). Some preclinical data related to
TheriRidge development have been published more recently (Fiorellini et al.
2018).
TheriRidge was cleared via 510(k) premarket notification procedure. This procedure allows for authorization of certain devices based on a showing of substantial
equivalence to an earlier legally marketed device, referred to as a predicate device.
A determination of substantial equivalence means that the new device is considered
as safe and effective as the predicate (FDA Website
n.d.-a). Eligibility for the 510(k)
pathway is determined based on the level of regulatory controls needed to assure the
safety and effectiveness of the device, as established in FDA’s device classifications
(FDA Website
n.d.-b).
As noted in FDA’s 510(k) Summary,(510(k) Summary K023998 2003)the
showing of substantial equivalence for TheriRidge was substantiated by the same
intended use and indications, the same or similar principles of operation and
technological characteristics, and equivalent performance to the predicate device in
an appropriate animal model. This is based on original preclinical data comparing
TheriRidge to ProOsteon
®
200 in a canine model according to the indication,
showing similar results in handling characteristics, wound healing, implant stability,
and presence of healthy tissue growth proximal to the implants. It also includes
summary comparative physical and chemical characteristics between the devices.
Using a similar approach, Therics Inc. obtained FDA clearance for two additional devices made using binder jetting technology. TheriFil Bone Void Filler
(subsequently renamed TheriLok) was cleared later in 2003,(FDA 510(k) Summary
K031040
Summary K040134
2003) and TheriLink Bone Void Filler was cleared in 2004,(FDA 510(k)
2004) each via 510(k) pathway. These two clearances expanded
Therics’ body of work to a different device classification, different label indications,
different choice of predicate devices, different part design and geometry, and a
different material composition. Each was comprised of a different bioceramic, betatricalcium phosphate, as these two devices were aimed at broader orthopedic use
and were designed to resorb during healing of the bony defect site and to be
replaced with native bone. Due to timing and similarities in the products, TheriFil
was available to serve as one of the predicate devices for the later submission of
TheriLink.
6 Inkjet and Binder Jet Printing in Pharmaceuticals 213
6.3.2.1 Relevance to Pharmaceuticals
How do these medical device examples relate to pharmaceuticals? At a high level,
they show how products made by binder jetting may be conceptualized, cast into
an appropriate regulatory framework, and then developed and manufactured in
accordance with the applicable requirements. The same generalized approach can
be used within the respective framework for pharmaceuticals.
6.3.3 2015: First Pharmaceutical Product Approval Based
on Binder Jetting
In July of 2015, Aprecia Pharmaceuticals obtained FDA approval for SPRITAM
(levetiracetam) tablets for oral suspension,(FDA Approval Letter for NDA 207958
2015) the first pharmaceutical product approval worldwide that uses AM, specif-
ically binder jetting, in the manufacturing process. The product launched in 2016
and has been marketed to date.
SPRITAM is a nonsterile solid oral dosage form containing the established
anti-epilepsy drug levetiracetam in a new orodispersible format. The architectural
control of binder jetting, combined with novel formulation, enables the product to
contain high concentration and high-dose loading of drug while retaining the ability
to disintegrate directly in the mouth in seconds when taken with a sip of liquid.
These attributes are the basis of Aprecia’s platform formulations grouped under the
ZipDose
available in conventional immediate release and extended release tablets that must
be swallowed intact. Oral solutions are also available, but they are less portable and
require measurement at every dosing. While individualization is a common theme
for AM, SPRITAM represents the scaled use of binder jetting to tailor dosage form
properties useful to segments of patients versus individual patients—specifically,
patients that are unable to swallow large tablets intact on a regular basis for a longterm therapy. These dosage form properties are also unaddressed by legacy orally
disintegrating tablet (ODT) technologies, which are predominantly used for dose
loading under 30 mg, and rarely used on tablet strengths above 100 mg. In contrast,
SPRITAM is provided in four fixed strengths matching those well-established in
clinical use of levetiracetam: 250, 500, 750, and 1000 mg.
special type of NDA for which some of the information relied upon for approval is
provided by studies not conducted by or for the applicant, or for which the applicant
has not obtained a right of reference. This information may include reliance on
FDA’s prior findings of safety and/or efficacy for one or more listed drug(s) based
on shared characteristics or conditions of use and is substantiated by submission
of appropriate original bridging data (e.g., biostudy data) comparing the product
candidate to the listed drug(s). Generally, the applicant must provide sufficient data
or scientific justification to address any differences from the listed drug(s) that are
referenced by the new application (FDA Guidance for Industry
®
technology name. The active ingredient, levetiracetam, was previously
SPRITAM was approved as a 505(b)(2) New Drug Application (NDA). This is a
2019).
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The 505(b)(2) NDA for SPRITAM relied on FDA’s prior findings of safety
and efficacy for KEPPRA levetiracetam film-coated tablet (UCB) (FDA Review
Summaries for NDA 207958
2015). Differences from the listed drug include dosage
form, composition, appearance, disintegration, and the method of administration.
For bridging purposes, the NDA included original comparative bioavailability data
establishing bioequivalence to the listed drug. Food effect data were provided by
an additional arm of this study. A second biostudy demonstrated that administration
without water (i.e., contrary to label instructions) would not adversely affect the
pharmacokinetics of the product. A supplement to the NDA clarified the dosage
form designation, recognizing the differences in product attributes and methods of
administration vis-à-vis conventional tablets and ODTs (FDA Supplement Approval
Letter for NDA 207958/S-002
2016).
6.3.3.1 Significance of First Pharmaceutical Product Approval
This approval provides several foundational reference points for future work. Firstly,
it is an example of binder jetting use explicitly under a pharmaceutical regulatory
submission and approval. Secondly, in connection with that approval it requires
binder jetting operations in compliance with pharmaceutical cGMPs, including
registration and inspection of a centralized site. Thirdly, it substantiates the continued progression of binder jetting technology from an early prototyping tool to a
direct manufacturing technology (in this instance, using novel scaled equipment).
In addition, it demonstrates commercialization of a differentiated dosage form type
having capabilities that were not attainable with prior technologies.
Finally, it exemplifies a strategic approach that may be generalized to: (i) other
types of novel dosage forms; (ii) drug applications having different clinical scope;
(iii) other types of AM applied to pharmaceuticals; and (iv) other types or other
jurisdictions of pharmaceutical regulation having different formal requirements or
procedures.
6.4 Principles of Binder Jetting
6.4.1 Binder Jetting in Context with Other Early AM
As binder jetting technology entered the scene, other AM techniques were
already in use for layer-by-layer construction of parts, primarily stereolithography
(ISO/ASTM: vat polymerization), selective laser sintering (ISO/ASTM: powder
bed fusion), and fused deposition modeling (ISO/ASTM: material extrusion).
Stereolithography applies directed light energy in order to cure liquid resin by
photothermal process. Selective laser sintering applies light energy to directly bond
powders through thermally induced solid state diffusion. Fused deposition modeling
uses a nozzle for directed placement of molten material by extrusion. Each of these
processes is additive in the sense that objects are built up incrementally, step by step,
within a build zone of no material or of unbound material. This additive approach is
opposite to that of subtractive processes such as machining, which remove material
6 Inkjet and Binder Jet Printing in Pharmaceuticals 215
by cutting, drilling, abrading, and the like from simpler pre-formed shapes in order
to form more complex final objects. In context with predecessor AM techniques, the
advent of binder jetting provided a new low-energy process that is still capable of
working with powders as the main input material, and essentially a wider selection
of powders.
Binder jetting’s mechanisms for connecting and solidifying material differ
from those of other AM processes, leading to certain advantages. One forming
mechanism uses the jetted liquid to deliver and leave behind a further solid material
that adheres to and bridges between powder particles. Another mechanism uses
the jetted liquid to dissolve some of the powder material, allowing the dissolved
material to precipitate and create interconnections between powder particles. These
mechanisms can be used alone or in combination. Drying conditions for the parts
can be chosen based on the thermal stability of the materials used to make the parts.
Because a wide range of substances can be formed into flowable powders, and the
drying conditions for binder jetting can be tailored to a chosen powder’s needs,
binder jetting can be used with the most diverse range of feedstocks among AM
processes. Indeed, across industries binder jetting has been applied to forming parts
from metals, ceramics, minerals, polymers, sugars, starches, and other categories
of organic or inorganic solids. This type of versatility is particularly attractive for
pharmaceutical applications given the varied physicochemical properties of drug
substances and excipients.
6.4.2 Process Overview
Binder jetting forms objects using selective deposition of liquid onto thin layers of
powder, repeated sequentially layer by layer to join the powder together. Hence,
there are a minimum of two material inputs: at least one powder and at least one
liquid. The powder provides the majority of an assembled part’s final structure and
composition. The liquid is used to determine the location and effectuate the extent
of binding of the powder, while also contributing minor ingredients to the final part.
The powder may be a single ingredient, dry blend, granulate, or other formulated
particulate form, provided that the particle size and flow are suitable to allow
consistent feeding and spreading. The liquid is typically a solvent blend, solution,
or suspension, formulated for fluid properties amenable to selective deposition, e.g.,
via inkjet print head.
From a part design perspective, binder jetting is loosely analogous to desktop
printing of paper documents. The powder represents the “paper,” and the liquid
represents the “ink.” The assembled part is similar to a stack of pages in a paper
document. Each layer of a finished part can have a similar or different design, just
as the printed pattern can differ on each page of a paper document. Unlike a paper
document, the layers bind together in the final binder jetted parts, and the unprinted
zones remain as loose powder.
During binder jetting, an initial quantity of powder is fed and spread into the
empty working zone to serve as a foundation layer. The part assembly sequence
216 T. G. West and J. Yoo
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Raw
Materials
Fig. 6.1 Generalized process flow diagram for binder jetting of pharmaceuticals
Process
Intermediates
Liquid
Preparation
Powder
Preparation
Formation of Bulk
Unit Doses
Binder Jetting Drying
Harvesting &
Dedusting
Filling of
Packaged Units
Primary
Packaging
commences next, spreading a thin layer of powder and selectively depositing
a pattern of liquid for each respective 2D “slice” of the part according to a
predetermined design. The materials for each layer of the part are assembled atop
the previously deposited layers, building the overall 3D part vertically from bottom
to top. This spatially arranged combination of powder and liquid is defined in part
by the spacing between the droplets on Cartesian coordinate axes, i.e., the drop
spacing (dX), the line spacing (dY), and the layer thickness (dZ). After binder
jetting is complete, the parts are dried and separated from the loose unbound powder
(“harvesting”), dedusted, and then packaged. The loose unbound powder is fed back
into the binder jetting process. Depending on the chosen process design, this powder
may be re-fed alone or in combination with fresh feed powder.
A generalized process flow diagram is shown in Fig. 6.1. Most of the unit
operations are similar to those of conventional pharmaceutical processing (white
background). The liquid preparation may include mixing of solid and liquid
ingredients to form a solution or suspension, as appropriate. The powder preparation
may be dry blending, granulation, or other particle engineering upstream of binder
jetting as appropriate to the overall product design. The new unit operations
(highlighted) are binder jetting itself and harvesting/dedusting arising from binder
jetting. In between, the parts are typically actively dried, e.g., using convective tray
dryer. Harvesting may be performed with rotary or vibratory shaking over screens,
and dedusting with compressed air. For binder jetted products that are less rugged
than conventional tablets, primary packaging is usually in unit dose blisters.
Compared to other AM, binder jetting is distinguished in its ability to position
spatially certain minor ingredients within the nascent part structure via one or more
printing fluids, each having a respective composition. Also, since binder jetting is
a wet powder-based process, it is generally preferable that the unprinted powder
surrounding the wet parts remains in place until the parts are dry enough to have
sufficient mechanical integrity for handling. The timing of this differs by material
set, as do the drying conditions.
6 Inkjet and Binder Jet Printing in Pharmaceuticals 217
6.4.3 Example Machine Configurations
Viewed from its end state, the core concept of binder jetting is to arrange a 3D
pattern of liquid droplets spatially within an imaginary “3D grid” superimposed on
a porous powder bed. From a machine design standpoint, this can be carried out in
multiple ways.
Table 6.1 lists the models of binder jetting equipment used in the main references
cited
in this chapter for pharmaceutical work. The machines are labeled with a
letter-code grouping (A, B, C) to aid discussion and illustration of several key
points. As noted earlier, most are small-scale research models not intended to make
pharmaceutical products for human use.
Tab le 6 .1 Models of binder jetting equipment used in selected references, grouped based on
machine attributes
Model(s) Make Purpose Refs Group
Various
Unspecified
TheriForm 1100
TheriForm 2100
Machine 0 (M0) Aprecia Pharmaceuticals
Unspecified Fochif
Unspecified Z-Corp (3D
Spectrum Z510 Z-Corp (3D
ProJet CJP
660Pro
ProJet 360 3D Systems Solid Models from
ProJet CJP 460
Plus
Massachusetts
Institute of
Technology
Therics Pharmaceuticals
Mechatronics
Systems)
Systems)
3D Systems Solid Models from
3D Systems Solid Models from
Materials Research Sachs et al. (1992), Cima et al.
and Tissue R&D
cGMP
Development &
Manufacturing
Solid Models from
CAD
Solid Models from
CAD
Solid Models from
CAD
CAD
CAD
CAD
(1994), Giordano et al. (1996),
u et al. (1996), Rowe et al.
W
(2000), Katstra et al. (2000),
we et al. (2002), Katstra
Ro
(2001)
Kumar et al. (1998), Yoo et al.
(1997), Lee et al. (2003),
Monkhouse
(2001), Rowe et al. (2000),
al.
Katstra
(2002), Wang et al. (2006),
Katstra
West and Bradbury (2019) B
Yu et al. (2009a, b, c, 2007)
Huang et al. (2007), Wu et al.
(2009)
(Shi et al. 2019) A
Kozakiewicz-Latała et al. (2022) A
Sen et al. (2020), Chang et al.
(2020), Wang et al. (2021),
Acosta-Vélez
Acosta-Vélez
Lu et al. (2022) A
Antic et al. (2021) A
et al. (1997), Lin et
et al. (2000), Rowe et al.
(2001)
et al. (2017),
et al. (2018a, b)
A
A
A
A
(continued)
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Tab le 6 .1 (continued)
Model(s) Make Purpose Refs Group
VX200 Vo x e l j e t Solid Models from
Unspecified,
using Epson
4720 piezo
PBP Next using
Lee microvalve
HuskeyJet Integrity
Unspecified,
using PicoJet
220
Easy3DP-M300 EasyMade Solid Models from
Beijing Institute
of
Pharmacology
and Toxicology
TNO Materials R&D van den Heuvel et al. (2021),
Industrial Inkjet
Integration
Spectra
Laboratories
CAD
Pharmaceuticals
Research
Materials R&D Chang et al. (2021) C
Materials R&D Kreft et al. (2022) A
CAD
Infanger et al. (2019) A
Hong et al. (2021) A
A
van den Heuvel et al. (2022)
Wang et al. (2022) A?
Group A. This group is based on the early M.I.T. machines and includes the
CAD modeling / prototyping equipment of Z-Corp (3D Systems) as well as the
GMP-oriented equipment of Therics. These machines are designed for X-Y motion
of print heads on an overhead gantry above a fixed build bed with Z-axis stage,
which serves as the working zone. Most use a feed bed with Z-axis stage adjacent
to the build bed to supply powder from below, transferring it from “bed to bed.” A
powder roller is typically attached to the X-Y (two-axis) gantry. This style of binder
jetting machine operates by an alternating sequence of material additions over a
single shared working zone: (1) translational movement of the powder spreader
(Y) to deposit a smooth new layer of powder and (2) reciprocating (raster mode)
movement of the print head (long X movement, short Y, long X, short Y, ...), line
by line, to address the printable area required for each layer of the part design. A
variation of this style, such as the Fochif Mechatronics system, Picojet D220 system,
and TNO system, uses an overhead powder doser instead of a feed bed to supply a
roller or spreader assembly. On the TNO system, the equivalent relative XY motion
is created using a moving build bed and stationary print head and roller. Information
is limited on the EasyMade system, which is perhaps in Group A.
Group B. This group includes the scaled “open bed” equipment (Z-Free) of
Aprecia,
exemplified by Machine 0. These machines are based on use of several
build beds moving uni-directionally along a continuous stadium-shaped path (i.e.,
oval having straight, parallel sides) beneath a fixed overhead powder feeder and a
fixed overhead print head. Multiple moving build beds allow for spatial separation
of the powder spreading and liquid printing steps, allowing each to run essentially
continuously and concurrently from start to finish of the print job. Powder feed is
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