Programmed multimaterial assembly by synergized 3D printing and freeform laser induction

In nature, structural and functional materials often form programmed three-dimensional (3D) assembly to perform daily functions, inspiring researchers to engineer multifunctional 3D structures. Despite much progress, a general method to fabricate and assemble a broad range of materials into functional 3D objects remains limited. Herein, to bridge the gap, we demonstrate a freeform multimaterial assembly process (FMAP) by integrating 3D printing (fused filament fabrication (FFF), direct ink writing (DIW)) with freeform laser induction (FLI). 3D printing performs the 3D structural material assembly, while FLI fabricates the functional materials in predesigned 3D space by synergistic, programmed control. This paper showcases the versatility of FMAP in spatially fabricating various types of functional materials (metals, semiconductors) within 3D structures for applications in crossbar circuits for LED display, a strain sensor for multifunctional springs and haptic manipulators, a UV sensor, a 3D electromagnet as a magnetic encoder, capacitive sensors for human machine interface, and an integrated microfluidic reactor with a built-in Joule heater for nanomaterial synthesis. This success underscores the potential of FMAP to redefine 3D printing and FLI for programmed multimaterial assembly.


ISSUES
-Much of the introduction is written in a grandiose fashion as if this process can produce virtually any functional material; this is misleading.
-The main focus of the paper is the FMAP process, but many of the figures are just examples of things that can be produced by FMAP.Are these examples put together systematically?Or is it just random?

MINOR ISSUES
-The poetic living organisms first sentence is out of place in this article.
-"the multimaterial 3D printing" -remove "the" -Long awkward sentence: "Despite these advancements, challenges persist in these techniques with lacking the versality in 61 assembling the functional materials within any predesigned locations of the 3D structures and the 62 genericity in broader material choices." -Confusing sentence: "For instance, the multi-nozzle DIW and FDM only extrude functional materials that must be blended with polymers with suitable properties" -FDM extrudes polymers.
-Characterizations is not a word.It is "Characterization." Reviewer #2 (Remarks to the Author): In this manuscript, Zheng et al develop a hybrid printing platform for fabricating functional devices.
Here, the authors integrated fused filament fabrication (FFF), direct ink writing (DIW), and direct laser writing (DLW) into a five-axis printing platform.In particular, DLW can convert some FFF printed materials into laser-induced graphene and DIW printed ink into functional materials.The authors then demonstrated multiple functional devices that can be directly printed by this new platform.The work is interesting and can be published in Nat.Comm.after the following comments are addressed.
• For the LIG, it was mentioned that layer thickness was about 0.1-0.3mm.Could the authors comment on how well the converted thickness can be controlled?
• In Fig. 1, was LED diode placed manually?In the current text, it sounds that the LED diode was also fabricated.
• For Fig. 2di, did the authors only convert part of the PC samples into LIG?If so, what were the dimension of PC samples (height, width, and length)?Also, what was the dimension of LIG (height, width, and length)?It might be helpful if the authors can also provide the stress-strain curve of printed PC sample.
• FDM is not the official name.Please change to fused filament fabrication (FFF).
• Multimaterial printing for functional applications has drawn significant research interests in recent years.It might be worth to mention some recent advances, such as Nature Communications 14 (1), 1251; Nature Communications 14 (1), 5519.Also, for hybrid printing, photonic curing was used to fabricate structures with conductive traces, for example, Additive Manufacturing 29, 100819.
emitting diodes (LEDs). 10Embedded 3D printing has facilitated production of flexible sensors by embedding functional carbon grease within a polymer encapsulation. 11A multi-nozzle DIW printer with a rapid material switching capability has been developed to print diverse wax-based structures. 12Further advancement in a core-shell DIW nozzle has enabled assembled multimaterials, such as epoxy/silicone, into different 3D structures, including a sandwiches 13 and helices. 14Multi-axis fused filament fabrication (FFF) 15 and conformal DIW 16 can make conformal deposition of conductive filaments onto 3D curved surfaces.9 However, within the realm of multimaterial fabrication, these techniques still face challenges of lacking versatility in precisely placing functional materials within 3D structures and access to broader material options.For instance, the embedded 3D printing necessitates preparation of a mold for the structural materials. 11This necessity imposes constraints on the capability of achieving complex geometries, such as in hollow and freestanding features.In the case of coreshell 3D printing, although it can print objects with inner structures made from functional materials, the functional and structural materials are extruded simultaneously and continuously, so depositing the functional materials in predesigned locations, such as outer surface, is not achievable. 13,14esides the limitation in the complexity of printed structures, they often suffer from limited materials options.For instance, the multi-nozzle DIW extrude composite inks that contains both electrically conductive materials and polymers, 12,15 rendering the resulting materials with low electrical conductivity and low mechanical strength.DLP is quite limited to photosensitive resins. 17Moreover, the process for multimaterial printing requires switching between different vats while purging non-polymerized residual materials out of the vats, which results in inefficient materials utilization.All these challenges underscore the need for further innovation in the multimaterial fabrication methodologies with improved versatility in the structure complexity and broadened materials choices.Direct laser writing (DLW) has shown versatility in patterning various functional materials through induced photothermal or/and photochemical effects. 20It greatly expands the library of available materials ranging from laser-induced graphene (LIG), 21,22 to some metals, 23 metal oxides, 24 semiconductors, 25 and ceramics. 26A recent trend in DLW is to assemble these functional materials into 3D structures, 27,28 while this goal is largely limited by its capability in fabricating the functional materials on 2D planes.Recently, we introduced a freeform laser induction (FLI) method facilitated by a 5-axis laser processing platform.This method enables the direct fabrication of 3D conformable electronics on freeform surfaces. 29While this technique represents an advancement in DLW capabilities, spatially patterning functional materials within predesigned locations of 3D structures to create multifunctional objects remains a challenge.
Here, to tackle this challenge, we present a freeform multimaterial assembly process (FMAP) that synergistically marries advantages of three techniques-FLI, DIW, and FFF-to seamlessly assemble both structural and laser-processable functional materials into 3D engineered objects with complex geometries and multifunctionalities. FFF can construct structural components from commercially available thermoplastics such as polycarbonate (PC), polyethylene terephthalate glycol (PETG) and thermoplastic polyurethane (TPU), and polyvinylidene fluoride (PVDF), while FLI selectively converts the FFF-printed material into LIG in predesigned position in the 3D space.DIW can deposit precursors onto LIG electrodes for later laser-inducing other functional materials, e.g., silver, iron, cobalt, nickel, and copper oxides, to obtain LIG-based functional composites.With the advantages of FFF and FLI, the functional materials are either encapsulated inside the printed 3D objects or on their outside surfaces, thus forming integrated functioning 3D devices.They include a crossbar circuit for a light emitting diode (LED) array, strain sensors for an integrated multifunctional spring and a haptic manipulator, a UV sensor, a 3D electromagnet as a rotational encoder, a capacitive sensor for human machine interface (HMI), and an integrated microfluidic reactor with a built-in Joule heater for nanomaterial synthesis.The demonstrated methodology shows a series of advances.Firstly, it facilitates programmed assembly of both functional and structural materials into the integrated 3D devices by a single apparatus, thus eliminating the requirement of many processing steps in different apparatuses.Secondly, it augments the versatility by direct laser processing of different functional materials with negligible precursor waste streams.Thirdly, FLI decouples the synthesis of the functional materials from FFF and DIW, thus it can pattern them in any predesigned locations of the 3D structures.Overall, this methodology represents a step forward in the creation of integrated, multifunctional 3D objects with applications across electronics/sensors, HMI, robotics, and functional microfluids.'Nat.Commun.14, 5519 (2023).

References
Also, the first sentence of abstract has been updated as 'In nature, structural and functional materials often form programmed three-dimensional (3D) assembly to perform daily functions, which has inspired researchers to replicate this principle to engineer these multimaterials into 3D multifunctional structures.' 2. The main focus of the paper is the FMAP process, but many of the figures are just examples of things that can be produced by FMAP.
Response: we appreciate the reviewer's insightful comment.Indeed, the primary focus of our paper is the FMAP process.To illustrate the process, systemic studies on the capabilities of the process must be done And we added the following sentence in Page 9 of the manuscript: 'The laser induction resolution is illustrated in Fig. 2c, where a conductive LIG strip with a width of ~200 µm can effectively power a LED.Fig. S6   Accordingly, we have added the following discussion in Page 9 of the manuscript: 'This observation agrees well with the result shown in Fig. S3, where the electrical resistance in the zaxis direction is dramatically increased when the layer height exceeds 0.15 mm.Fig. S4 shows that a slower scan rate results in a smaller sheet resistance, reaching the smallest value of 98.2 Ω/sq at 100 mm/min.The relationship between the LIG thickness and laser power is revealed in Fig. S5.It shows that as the laser power rises, the LIG thickness increases.The laser induction resolution is illustrated in Fig. 2c, where a conductive LIG trace with a width of 200 µm can effectively power an LED.'  Accordingly, we added the following sentences in Page 10 of the manuscript: 'Furthermore, tensile testing was performed on specimens embedded with LIG.The LIG dimensions were varied while keeping laser power and printing layer height constant.Fig. S7 shows that as the LIG thickness and width increases, respectively, both the tensile strength and fracture strain decrease.' Finally, to better illustrate the actuation accuracy of the platform, we added new information about the actuation system.In brief, we utilized two stepper motors with harmonic reducers with a reduction ratio of 1:30 to offer higher torque and smoother operation compared to direct-drive systems for the rotational axis, two additional stepper motors for driving Z-axis, and a belt system for driving X and Y axes.These motors were actuated by DRV8825 at 1/32 micro-stepping.To achieve even higher accuracy, we can use DMT542T     42 However, its operation is limited to room temperature, restricting the range of materials that can be synthesized.An embedded heating electrode for in-situ Joule heating could overcome this limitation. 43Herein, we demonstrate the use of FMAP to one-step fabricate an integrated microfluidic reactor with a LIG electrode embedded 0.6 mm underneath the channels as a Joule heater (Fig. 5a-b).Two precursors for ZIF-8 synthesis were fed into the…' Moreover, we have revised the discussion section to highlight the advantages of FMAP in fabricating the demonstrated applications, as well as its limitations along with proposed measures for improvement in future.'FMAP enables the fabrication and assembly of diverse functional and structural materials into a 3D engineered object.The functional materials encompass laser-processable materials like LIG, metals, and metal oxides.As a concept of demonstration, various applications including crossbar LED circuits, capacitive sensor-based touchpads and sliders for HMI, and a UV sensor, are fabricated and tested.Moreover, a LIG strain sensor-embedded spring, gripper for haptic grasping, and micro 3D electromagnets, were realized.Further expanding the application area, a microfluidic reactor featuring Joule heating was demonstrated.The sensors within these prints consistently exhibit attributes of high linearity, accuracy, and rapid response.Overall, FMAP offers advantages for programmed assembly of both functional and structural materials into 3D engineered objects.Despite the enormous potential in 3D electronic manufacturing, there remain several improvements in the FMAP to be addressed in future.The first one lies in its processing rate.The current setup requires FLI, DIW, and FFF processes to be operated separately.To enhance efficiency, end-effectors of these processes can be equipped to different robotic manipulators to perform simultaneous, collaborative work to improve the processing rate.Secondly, although the current laser can achieve ~100 μm linewidth meeting the requirement for most printed wearable electronics, higher resolution can be attained by upgrading the laser system.Last but not the least, while the current work focuses on functional materials for electronic applications, future research includes extending this FMAP to fields such as robotic fabrication, and incorporating other processes, such as aerosol printing, 45 to this FMAP to further expanding the materials options.'

MINOR ISSUES -The poetic living organisms first sentence is out of place in this article.
We thank the reviewer for this suggestion, the first sentence of the introduction has been revised to 'Assembly of multimaterials into structural and functional components is ubiquitous in nature, inspiring researchers to explore new design principles and fabrication methodologies for creating engineered three-dimensional (3D) structures with multifunctionalities. 1,2 ' The first sentence of the abstract part has been revised to 'In nature, structural and functional materials often form programmed three-dimensional (3D) assembly to perform daily functions, which has inspired researchers to replicate this principle to engineer these multimaterials into 3D multifunctional structures.' -"the multimaterial 3D printing" -remove "the" We thank the reviewer for such detailed comments."the" was removed from the sentence.
-Long awkward sentence: "Despite these advancements, challenges persist in these techniques with lacking the versality in 61 assembling the functional materials within any predesigned locations of the 3D structures and the 62 genericity in broader material choices."We thank the reviewer for pointing this out, the sentence has been revised to 'these techniques still face challenges of lacking versatility in precisely placing functional materials within 3D structures and access to broader material options.' -Confusing sentence: "For instance, the multi-nozzle DIW and FDM only extrude functional materials that must be blended with polymers with suitable properties" -FDM extrudes polymers.
We Thank the reviewer for pointing this out, the 'FDM' part has been removed and the sentence has been updated as 'For instance, the multi-nozzle DIW extrude composite inks that contains both electrically conductive materials and polymers, 12,15 rendering the resulting materials with low electrical conductivity and low mechanical strength.'-Characterizations is not a word.It is "Characterization." We thank the reviewer for pointing this out, the 'Characterizations' in both the caption of Fig. 2

Reviewer 2
In this manuscript, Zheng et al develop a hybrid printing platform for fabricating functional devices.Here, the authors integrated fused filament fabrication (FFF), direct ink writing (DIW), and direct laser writing (DLW) into a five-axis printing platform.In particular, DLW can convert some FFF printed materials into laser-induced graphene and DIW printed ink into functional materials.The authors then demonstrated multiple functional devices that can be directly printed by this new platform.The work is interesting and can be published in Nat.Comm.after the following comments are addressed.
Response: we thank the reviewer for the positive assessment of our work.
For the LIG, it was mentioned that layer thickness was about 0.1-0.3mm.Could the authors comment on how well the converted thickness can be controlled?
Response: we thank the reviewer for this question, additional experiment has been done to address this issue.
We first studied how the scan rate of the laser affects the sheet resistance of the LIG (Fig. S4).It suggests that a slower scan rate results in a smaller resistance, reaching the smallest value of 98.2 Ω/sq at 100 mm/min.Considering the trade-off with the increased fabrication time as the decreased scan rate, we chose a scan rate of 300 mm/min, resulting in 163.9 Ω/sq, for LIG patterning on PC.Accordingly, we added the following discussion in Page 9 of the manuscript 'This observation agrees well with the result shown in Fig. S3, where the sheet resistance in the z-axis direction is dramatically increased when the layer height exceeds 0.15 mm.Fig. S4 shows that a slower scan rate results in a smaller sheet resistance, reaching the smallest value of 98.2 Ω/sq at 100 mm/min.
The relationship between the LIG thickness and laser power is revealed in Fig. S5.It shows that as the laser power rises, the LIG thickness increases.The laser induction resolution is illustrated in Fig. 2c, where a conductive LIG electrode with a width of 200 µm can effectively power an LED.' In Fig. 1, was LED diode placed manually?In the current text, it sounds that the LED diode was also fabricated.
Response: we thank the reviewer for this question.Yes, the LED diode was assembled manually.To avoid confusion, we have updated the related sentences in Page 10 of the manuscript.'Fig.1d displays the fabricated wireless LED, with a cross-section view illustrating the distribution of the conductive LIG/Ag electrode inside the PC structure.Note that the LED diode was manually integrated with the FMAP-fabricated coil.'For Fig. 2d-i, did the authors only convert part of the PC samples into LIG?If so, what were the dimension of PC samples (height, width, and length)?Also, what was the dimension of LIG (height, width, and length)?It might be helpful if the authors can also provide the stress-strain curve of printed PC sample.
Response: we thank the reviewer for this question.Yes, only part of the PC was converted to LIG.The corresponding description in Page 10 has been updated as 'Tensile testing specimens (dimensions: 25 mm × 3 mm × 1 mm) with embedded LIG in the center (dimensions: 25 mm × 2mm × 0.4 mm) were produced by our FMAP.The PC was printed with the layer heights of 0.1-0.2mm.Fig. 2d-i shows that their tensile strengths all exceed 35 MPa, which is compatible to pure PC specimens, indicating well-maintained mechanical properties even if the PC is partially converted to LIG.' We have included the stress-strain curve of the printed PC samples into Fig.2d-i   Accordingly, we added the following sentences in Page 10 of the manuscript: 'Furthermore, tensile testing was performed on specimens embedded with LIG.The LIG dimensions were varied while keeping laser power and printing layer height constant.Fig. S7 shows that as the LIG thickness and width increases, respectively, both the tensile strength and fracture strain decrease.'FDM is not the official name.Please change to fused filament fabrication (FFF).
Response: we thank the reviewer for the suggestion.All 33 'FDM' and 'fused deposition modeling' in both manuscript and supporting information have been corrected to 'FFF' and 'fused filament fabrication', respectively.And the 'FDM' in Fig. 1c and Fig. S1 has also been corrected.Multimaterial printing for functional applications has drawn significant research interests in recent years.It might be worth to mention some recent advances, such as Nature Communications 14 (1), 1251; Nature Communications 14 (1), 5519.Also, for hybrid printing, photonic curing was used to fabricate structures with conductive traces, for example, Additive Manufacturing 29, 100819.

.
Figure S6| Resolution of laser induced materials on various substrates.(a) A photograph showing a LIG strip with a 218 µm linewidth induced from lignin on a PETG substrate.(b) A photograph showing a LIG strip with a 235 µm linewidth induced from a PVDF substrate, (c) A photograph showing a LIG/Ag composite strip with a 247 µm linewidth induced from PC and Ag precursor.(d) A photograph showing an Ag strip with a 104 µm linewidth induced from an Ag precursor film on a PC substrate when the laser was defocused at -1.5 mm.Scale bar: 200 µm.
Figure S4| Sheet resistance of LIG as a function of the laser scan rates.The LIG was induced from PC which was printed by FFF at a 0.15 mm layer height.

Fig.
Fig.S7ashows a schematic of LIG distribution within a printed PC sample with thickness of 1 mm and width of 3 mm for tensile testing.Fig.S7b-cshows that as the LIG thickness and width increases, respectively, both the tensile strength and fracture strain decrease.Nevertheless, if we keep the thickness with 0.15 mm or width of 0.1 mm, the tensile strength and fracture stain can be compatible to the pure PC without LIG.

Figure
Figure S7| Tensile testing was conducted on PC samples featuring different dimensions of embedded LIG.(a) A schematic illustrates the structure of a tensile testing specimen with LIG embeded inside.(b) Stress-strain curves of PC specimens with varied thicknessed LIG.(c) Stressstrain curves of PC specimens with varied widthed LIG.

Response:
We thank the reviewer for the question.The examples were presented intentionally.To improve the understanding, herein, we explain them in a logical way as follows.Fig.3focuses on functional materials used as conductive electrodes, showcasing applications related to PCBs.We chose this application because, compared to traditional PCB fabrication methods that involve etching, our FMAP's material utilization rate is close to 100%.This efficiency stems from the minimal waste of substrate material printed by FFF.Moreover, the laser can directly convert the substrate material into conductive electrodes.Therefore, Fig.3shows examples of a cross-bar circuit for LED display and self-capacitance sensors on both rigid and flexible substrates for human-machine interfaces.Accordingly, we have updated the description of Fig.3in Page 12: 'Fig.3showcasesfunctional materials used as conductive electrodes for PCBs.Examples of a cross-bar circuit for LED display and self-capacitance sensors on both rigid and flexible substrates for HMI were demonstrated to show the potential of FMAP in fabricating integrated 3D electronic devices.It shows that compared to traditional PCB fabrication processes that involve chemical etching, our FMAP simplifies the procedures with material utilization of ~100%.'Also, to further strengthen this logic in presentation, we have upgraded the previous example shown in Fig.3aby designing a PCB that integrates both a microchip controller and a LED array.Fig.3aand the corresponding video (Movie S5) for this demonstration were updated.Correspondingly, we updated Fig.S11for depicting the fabrication steps.

Figure 3| FabricationFig
Figure 3| Fabrication of a crossbar circuit for LED array and self-capacitance touch input device by FMAP.(a-i) Schematic showing the equivalent circuit of the crossbar LED array and its onboard microchip controller.(a-ii) Exploded view showing the layer-by-layer electrode structure of the crossbar circuit for a LED array.(a-iii) A photograph of the crossbar LED array and its onboard microchip on PC with LIG/Ag as the electrode.(a-iv) Photographs showing the

Figure 5
Figure5demonstrates an application that shows a 3D functioning microfluid for nanomaterial synthesis.The embedded LIG acts as a heating element, which can be manufactured in a single step with the microfluidic channel.In our previous study, we demonstrated a 3D printed microfluidic reactor for synthesizing zeolitic imidazolate framework (ZIF) NPs, achieving reduced reagent usage, faster reaction rates, and energy savings.However, its operation is limited to room temperature, constraining the range of materials that can be synthesized.Integrating micro-heater in the microfluid channels would open new door for nanomaterial synthesis.According, we have updated the description of Fig.5in Page 21: 'In our previous study, we demonstrated a 3D printed microfluidic reactor for synthesizing zeolitic imidazolate framework (ZIF) NPs with reduced reagent usage, fast reaction rate, and energy savings.42However, its operation is limited to room temperature, restricting the range of materials that can be synthesized.An embedded heating electrode for in-situ Joule heating could overcome this limitation.43Herein, and Author contributions are corrected.'Figure 2| Characterization.(a) SEM and EDS images of metals and metal oxides in LIG induced from various polymers: (i) LIG/Ag in PC; (ii) LIG/Ag in PETG; (iii) LIG/Fe in PC; (iv) LIG/Co in PC; (v) LIG/Ni in PC; (vi) LIG/CuO in PC.Scale bar: 20 µm….'And '…B.Z. designed and constructed the FMAP, and he conducted the structure/device fabrication and characterization.Y. X. contributed to material…'

Figure
Figure S4| Sheet resistance of LIG as a function of the laser scan rate.The LIG was induced from PC which was printed by FFF at a 0.15 mm layer height.

Figure
Figure S5| Relationship between laser power and the LIG thickness.(a) Photographs showing cross sections of 8 LIG samples made by different laser powers.(b) LIG thickness as a function of laser power.Scale bar: 500 μm.

Figure
Figure S3| Characterization on the LIG induced from PC printed with different layer heights.(a) Cross-sectional optical images of the LIG induced from PC printed with five different layer heights, a scan rate of 300mm/min and power of 2.5 W. Scale bar: 200 μm.(b) Change of the resistance of LIG in the z-axis direction vs. the layer height.Note: because of decreased .Accordingly, Fig.2has been revised as follows.

Figure
Figure S7| Tensile testing was conducted on PC samples featuring different dimensions of embedded LIG.(a) A schematic illustrates the structure of a tensile testing specimen with LIG embeded inside.(b) Stress-strain curves of PC specimens with varied thicknessed LIG.(c) Stressstrain curves of PC specimens with varied widthed LIG.

Figure
Figure 1| Schematic of FMAP and workflow of fabricating 3D devices by assembling structural and functional materials using FMAP.(a) Schematic showing FMAP and its actuation system.(b) Schematic of end effectors for FFF, DIW, and FLI.(c) Workflow of fabricating a 3D wireless LED circuit with LIG (induced from PC) and Ag electrodes.(d) Scheme and a photograph of the fabricated 3D wireless LED.(e) A photograph of a fabricated 3D wireless LED with LIG (induced from lignin) and Ag electrodes on a cloth.Scale bar: 10 mm.

Figure
Figure S1| Workflow of fabricating a wireless LED using FMAP.(a) Design and modeling of electrodes for a wireless LED and respective G-code generation.The coil and shell electrodes are modeled independently.Subsequently, the toolpaths for both the coil and shell are generated using a slicer tool, which are tailored to the specific requirements of FLI, DIW, and FFF.(b) Toolpaths for FFF, FLI, and DIW.To achieve precise positioning of the three end effectors, the toolpaths are integrated with their respective offset parameters.(c) Time-lapse images of the different fabrication steps for a wireless LED: (i) printing of a polycarbonate (PC) substrate; (ii) multilayer LIG/Ag electrodes are fabricated within the printed PC structure; (iii) conformal patterning of the LIG/Ag electrodes on the surface of the PC structure.Throughout this procedure, all actuators work synergistically to ensure that the laser beam remains perpendicular to the target 3D surface.'

at 1/128 micro- stepping in future. R5 Correspondingly, we have updated the method part: Design and Construction of FMAP Processing Apparatus:
The platform was built upon a Creality CR-10 V2 3D printer, with the X and Y motion mechanisms upgraded to linear rails driven by a belt.The Z axis is driven by two stepper motors.A customized rotational mechanism, consisting of two orthogonal NEMA17 stepper motors with harmonic reducers from robotdigg, was integrated.Motion control was achieved using an Arduino Mega 2560 and a Ramps 1.6+ board.Temperature control of the FFF hotend and build plate was managed by a separate Creality V2.2 control board.' https://www.omc-stepperonline.com/download/DM542T.pdfAre these examples put together systematically?Or is it just random?