Posted on

4DTexture: Holistic Computational Design for 3D Surfaces

Researchers from both the US and China are taking digital fabrication and texture in materials to the next level, releasing the findings of their study in the recently published ‘4D Texture: A Shape-Changing Fabrication Method for 3D Surfaces with Texture.’

4D printing is growing as an area of interest for many researchers, but like 3D printing—and even more so—there is still enormously uncharted territory. Users are able to move beyond the constraints of 3D printing to meet pressing needs for more complex projects like creating new metastructures, surfaces, and new materials and techniques. 4D printing offers more to users innovating beyond the 3D, seeking to fabricate more complex geometries too.

In this study, the authors introduce a new design approach called 4DTexture which they describe as a ‘holistic computational design and fabrication method, leveraging the state-of-the-art 4D printing process to make 3D surfaces with texture.’

Time and material consumption comparison between conventional printing and 4DTexture method.

Shape-changing principle: the textured structure can be printed without a support structure, which can transform into a 3D textured shape after heat triggering.

While the benefits of 3D printing are and continue to be vast for industrial users, 4D printing opens up new areas for fabrication that usually cannot be explored through conventional technology either. The new technique created in this study allows for actuators to be made with vertical texture structures—later to be turned into more complicated forms. The system runs on Rhino with Grasshopper, comprised of the following for preview and customization:

  • Texture element
  • Arrangement
  • Tendency and transformation type

The workflow: users can (a) design the element of texture and (b) the shape of actuator, define the transformation type and (c) the arrange type of the texture, (d) set the tendency of the texture, then (e) generate the g-code file which can be printed by an FDM printer, finally users can obtain (f) the printed flat piece which can be heat triggered into (g) the target 3D shape.

Experiments were performed on textured structures as the researchers built up a ‘library’ consisting of shapes like hemispheres, pyramids, and hemicylinders. The program offers tools so that parameters can be customized; for example, designers can use offered 4D morphing mechanisms from previous projects or modify the settings if needed. Once the actuator shapes are set, textures can be arranged. Height and size can be chosen, and users can also move textures.

PLA was used with a MakerBot Replicator 2X as the researchers printed sample textures using the defaults for the hardware, producing self-rising, self-coiling, and self-bending objects.

Transformation types: (a) self-rise (b) self-coil and (c) self-bend.

“The transformation mechanism can be controlled by the printing direction, which has been embedded into our system to simulate the behavior,” stated the researchers.

Just as 3D printing has allowed for a variety of different forays into fashion, 4D printing has too, bringing all the benefits of materials that can morph and shift as needed. In this study, the researchers fabricated fashion accessories, a modular toy, a haptic handle, and 3D fasteners.

Fashion design: (a) The flat printed piece; (b) The decorative scenario.

Customized haptic handle: (a) The flat printed piece; (b) The usage scenario.

3D fasteners: (a) The flat printed piece; (b, c) The usage scenario.

“We hope such a system can expand the design opportunity of 4D printing technology with a hobbyist FDM printer,” concluded the researchers. “In the future, we plan to implement a systematic material experiment for improving transformation accuracy and fine-tune the parametric setting with Grasshopper to make the design tool more user-friendly. We also found that the texture structure can serve as a constrained layer which needs further investigation.”

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

The post 4DTexture: Holistic Computational Design for 3D Surfaces appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

University of Auckland: Growth-Induced Bending of 3D Printed Samples Based on PET-RAFT Polymerization

4D printed objects are 3D printed objects made with smart materials that respond to environmental stimuli, like liquid and heat, or return to an original form after deformation. Researchers from the University of Auckland published a paper regarding 3D printing and growth-induced bending based on photo electron/energy transfer reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization.

By adding reversible deactivation radical polymerization (RDRP) constituents to a 3D printed structure to create “living” materials, which keep polymerizing on-demand, allows structures to be built with post-production functionality and modularity. But, as the Auckland team states, “this forms only half of the solution.”

RAFT processes have been used as a controlled polymerization technique to help with self-assembling macromolecules and block copolymerization. They previously demonstrated photo-RAFT polymerization 3D printing under several visible wavelengths, showing that a facile surface modification “could be performed on the samples after printing with a range of different monomers.”

Graphical abstract

“For this work, we further optimized the PET-RAFT 3D printing formulation and demonstrated the 3D printability using a commercial DLP 3D printer with standard 405nm light sources,” they wrote. “We also explore the 4D post-production modification capabilities of the 3D printed object using green light (λmax = 532 nm).”

The PET-RAFT recipe they used, below, adds a tertiary amine and the photo redox catalyst EY, the latter of which “is raised to an excited state (EY*) under irradiation where it then has several pathways to release its energy.” This is useful for 3D printing, since it’s a desirable “oxygen tolerant pathway.”

(A) Chemical structures of Eosin Y (EY), 2-(butylthiocarbonothioylthio) propanoic acid (BTPA), poly (ethylene glycol) diacrylate (PEGDA, average Mn = 250 g/mol), N, N-dimethylacrylamide (DMAm), and triethanolamine (TEtOHA). (B) Proposed combined PET-RAFT mechanism showing tertiary amine pathway by Qiao, Boyer, and Nomeir15, 23-25 (C) Reaction scheme for PET-RAFT polymerization of our 3D printing resin. (D) Schematic of a standard DLP 3D printer.

In their previous research, they used a 3D printing resin that was much slower to polymerize, and produced brittle objects. This time, they made several changes to the resin, such as replacing the RAFT agent CDTPA with BTPA and adjusting monomer composition.

“The development of an optimized 3D printing resin formula for use in a commercial DLP printer (λmax = 405nm, 101.86µW/cm2) was the first step in this research. Thus, several criteria were used to determine the quality of the optimized resin; the optimized resin must be able to hold its form in 60 seconds or less exposure time, the printed objects must have a good layer to layer resolution and binding, must be an accurate representation of the CAD model, and the resin must be stable enough to be reusable for consecutive runs,” the team explained.

They kept these criteria in mind while creating and testing new resin recipes with Photo Differential Scanning Calorimetry (Photo-DSC) and a 400-500 nm light source range.

“A monomer to RAFT agent ratio of 500:1 was chosen as a balance between a faster build speed, and a high enough RAFT concentration to perform post-production modifications,” they said. “For the first step in optimization we decided to compare two asymmetric RAFT agents, CDTPA and BTPA.”

Photo-DSC plot showing resin composition of [BTPA]: [PEGDA]: [EY]: [TEtOHA] = 1:500:0.01:20 (blue), [BTPA]: [PEGDA]: [DMAm]: [EY]: [TEtOHA] = 1:350:150:0.01:20 (green), [BTPA]: [PEGDA]: [DMAm]: [EY]: [TEtOHA] = 1:150:350:0.01:20 (red), [CDTPA]: [PEGDA]: [EY]: [TEOHA] = 1:500:0.01:20 (black), and [CDTPA]:[PEGDA]:[EY]:[TEA] = 1:200:0.01:2 (orange) form our previous PET-RAFT work, were compared to find an optimum new resin formula. The effects of different RAFT agent and comonomer ratio are noticeable on the maximum heat flow and the peak position of tmax.

The first formula, [BTPA]: [PEGDA]: [EY]: [TEtOHA] = 1:500:0.01:20, had a limited inhibition period, while [CDTPA]: [PEGDA]: [EY]: [TEtOHA] = 1:500:0.01:20 had a longer one.

“These results help to demonstrate the increase in polymerization rate that can be achieved by using BTPA in place of CDTPA,” they noted.

Because of its high glass transition temperature, DMAm was added as a comonomer in [PEGDA]: [DMAm] = 70:30 and 30:70 ratios. This slowed the polymerization rate for the resin formulas [BTPA]: [PEGDA]: [DMAm]: [EY]: [TEtOHA] = 1:350:150:0.01:20 and [BTPA]: [PEGDA]: [DMAm]: [EY]: [TEtOHA] = 1:150:350:0.01:20, but it was still faster than the CDTPA formulation. The researchers used this formulation to 3D print samples for dynamic mechanical analysis (DMA) and 4D post-production modification.

UV-Vis absorption spectra; (A) EB under 405nm (397.45µW/cm2) exposure for; initial (black), 10 (red), 20 (blue), 30 (magenta) and 40 minutes (olive). (B) EY under 405nm exposure for; initial, 10, 20, 30 and 40 minutes.

It’s important that photocatalysts don’t have issues like photobleaching or photodegradation during a photocatalytic process. Above, you can see a comparison in absorbance loss between organic photocatalysts EY and Erythrosin B (EB), “using their absorbance curves after different periods of 405 nm light irradiation.”

“Both showed a noticeable gradual decrease in UV absorbance which could likely be due to irreversible photodegradation, given that the effect remains after the sample has been stored overnight in a dark environment and measured again,” the team explained.

After longer periods of time, the EB solution started changing color, but this didn’t happen with the EY formulation, which is why the team kept it in their 3D-RAFT resin composition. A photostable catalyst, like EY, makes it possible for the 3D printing process to continue undisturbed.

The 3D printed samples that underwent DMA analysis were:

  • optimized RAFT resin before and after post-production modification
  • non-3D printed DMA sample by PET-RAFT polymerization in bulk
  • 3D printed free radical polymerization (FRP) control sample

The first type were 3D printed with a 30 µm thickness, a 60 second attachment time, and 30 seconds of exposure per each of the 53 layers. The second was fabricated with the same optimized formula “but polymerized in bulk using an external mold and a conventional 405nm lamp external,” while the FRP samples were printed with the same monomer composition and parameters but used a “conventional photoinitiator, phenylbis (2, 4, 6-trimethylbenzoyl) phosphine oxide (TPO).”

DMA plot showing (black) storage modulus (E’) and (black dashed) Tan δ from 3D printed DMA sample by normal FRP of resin formula [PEGDA]: [DMAm]: [TPO] = 350:150 and 2wt% TPO; (blue) the E’ and (blue dashed) Tan δ from 3D-RAFT printed DMA sample using resin formula [BTPA] :[PEGDA]: [DMAm]: [EY]: [TEtOHA] = 1:350:150:0.01:20; (green) the E’ and (green dashed) Tan δ from the post-print modified DMA sample; lastly (red) the E’ and (red dashed) Tan δ from the non-3D printed DMA sample prepared by normal PET-RAFT polymerization in bulk.

A temperature ramp (2˚C/min) was performed in order to find the storage modulus (E’) and glass transition temperature (Tg) of the samples, and there was a major change “in the E’ to 80 MPa and Tg to 15˚C” when the samples were compared to ones that weren’t 3D printed but instead polymerized in a mold.

“This layer-by-layer construction appeared to play a major role in the E’ at room temperature of the overall sample,” the team noted. “Each layer in the 3D printed sample received equal light irradiation (apart from attachment layer where specified), whereas in the bulk samples light had to penetrate through the entire thickness of the resin.”

Samples printed with RAFT resin had methyl methacrylate (MMA) monomer inserted post-production “in a growth medium devoid of solvent,” and DMA was used to analyze the effect of this modification on the prints’ mechanical properties, as well as “the relative effect on E’ and Tg of the sample.”

“The E’ at room temperature of the sample had decreased to 100 MPa but the Tg remained constant at about 19˚C,” they explained. “These limited changes can largely be attributed to the fact that BTPA is an asymmetric RAFT agent, all the growth being surface focused thus limiting the mechanical effects on the 3D printed RAFT sample.”

A1) CAD model for shapes upon 3 × 3 cm base. A2) Corresponding 3D-RAFT objects printed using DLP 3D printer. B1) Kiwi bird CAD model upon tiered base. B2) Corresponding 3D-RAFT printed object.

Once they determined the optimal RAFT 3D printing resin, the researchers designed CAD models for the objects they would print. They arranged different shapes, like triangles and Kiwi birds, on top of square and hexagonal base plates and circular coins, in order to see how the PET-RAFT resin formulation could handle features like corners and curves.

“These objects generally represented an accurate 3D print of the corresponding CAD model, confirming that the current 3D-RAFT resin was capable of printing 3D objects using a 405nm DLP 3D printer (λmax = 405 nm, 101.86µW/cm2),” they noted.

“Objects printed with 3D-RAFT also displayed an actual build speed of 2286 µm/hr (calculated from the actual height of printed objects over the full print time) consistent with that of the theoretical build speed, which is significantly faster than our previous PET-RAFT resin formula…”

Only limited shrinkage occurred on these prints, and after being washed for two days each in ethanol, THF, and DMSO, the team did not note a visible loss in yellow “arising from the trithiocarbonate group of the RAFT agent.” The 3D-RAFT resin was also reusable over more than ten prints.

“Having demonstrated that we could reliably print objects using our new RAFT resin, we endeavoured to demonstrate that these objects had retained their desired “living” behavior and could undergo post-production modification,” the team wrote.

They immersed half of a 3D-RAFT printed strip in a growth medium containing [BA]: [EY]: [TEtOHA] = 500:0.01:20 in DMSO. Then, a green 532 nm LED light was directed onto one of its faces, and after 15 minutes, “the strip showed moderate curvature.” They could see the strip was bending considerably after 15 more minutes, and it was also much softer, with the irradiated face paler than the other, and the growth medium was cloudier.

Optical images and graphical representations of growth-induced bending process. (A) The initial 3D-RAFT printed strip. (B) 3D-RAFT strip after 15 minutes monodirectional green light irradiation (532nm, 58.72µW/cm2) in a growth medium of DMSO and BA. (C) The same strip after 30 minutes monodirectional green light irradiation in the same growth medium. (D) Reaction scheme for the photo-catalyzed insertion of BA monomer under green light irradiation.

They next performed some control experiments. First, they tried the same thing with an FRP printed strip and a [PEGDA]: [DMAm] = 350:150 and 2wt% TPO growth medium, but this did not bend. A 3D-RAFT printed strip was left to soak in the original growth medium, without any light irradiation, for 24 hours, “to ensure that the bending was coming from growth rather than an alternate stimulus such as solvent swelling,” and saw no changes. Finally, they tried the same original process to return the bent 3D-RAFT strip back to its original form by shining the green light at it from the opposite direction. While it ultimately worked, it took three hours of irradiation to bend the strip back, which “indicates the unfavorability of introducing stress on the opposing side of the strip by our current methods.”

“To the best of our knowledge, this is the first demonstration of the growth of new material into the surface of an existing 3D printed object using RAFT polymerization to induce a bending response,” they concluded.

“In summary, we have further developed a 3D printable RAFT resin formula with an improved build speed up to 2286 µm/hr and demonstrated its ability to undergo 4D post-production transformation. We first demonstrated a facile method for growth induced bending of 3D-RAFT printed strips which opens an alternative pathway for movement and modification of these printed objects.”

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

The post University of Auckland: Growth-Induced Bending of 3D Printed Samples Based on PET-RAFT Polymerization appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

What Does the Future Hold for 3D & 4D Printing? Reviewing Current Processes & Ongoing Potential

Researchers come together to review both 3D and 4D printing, as well as exploring its ongoing potential in ‘Recent 3D and 4D intelligent printing technologies: a comparative review and future perspective.’

While both technologies offer great opportunity for industrial users to make and maintain functional parts and prototypes, 3D and 4D printing are a source of fascination around the world due to the ability to innovate at will, cutting out the middleman, and making new objects with new materials that may not have been possible previously.

The brief overview of relevant 3D printing methods

In the 4D realm, we see the progress being made from materials that may be less flexible to those that are able to shift with their environment—and according to the user’s needs. The authors not only delve further into fundamentals and development (especially in the evolution from 3D to 4D) but also perform comparative analysis regarding both forms of digital fabrication.

From the inception of 3D printing in the 80’s via Chuck Hull to its emergence in the mainstream and now integration into many fields—from robotics to tissue engineering, electronics, and more—the authors follow 3D printing, pointing out correctly that it is currently ‘still in the active stage of industrial innovation.’ Designers and engineers are able to take advantage of a wide variety of benefits—even including applications like fashion and jewelry.

Schematic illustration of 1D, 2D, 3D, and 4D concepts

General schematic overview of 3D printing technology with solid, liquid and power-based patterns (a) FDM; (b) SLS; (c) SLA (Sources: https://www.custompartnet.com)

While advantages such as affordability, accessibility, and greater efficiency in production are being enjoyed by many, there are still challenges regarding materials in applications like soft robotics and aerospace. With the ability to shift form while under pressure from temperature or moisture, 4D printed smart materials avail the user of greater flexibility and versatility.

“Compared  to  3D  printing,  4D  printing  updates  the  concept  of  change  in  the  printed  configuration  over  time,  which  relies  on  environmental  stimuli.  Therefore,  4D  printed  structures  should  be  fully  preprogrammed  using  time-dependent  deformations  of  products,” state the authors.

4D printing relies on:

  • Suitable hardware
  • Stimulus-responsive material
  • Stimuli
  • Interactive mechanisms
  • Mathematical modeling

SWOT analysis of a). 3D printing technology; b). 4D printing technology.

Smart materials and the ability to deform and then return to their natural shape mean that 4D printing is suitable for not only for robotics but also self-repairing of materials like hydrogels, piping, and other materials which may be related to reusability and recycling.

The illustration of shapeshifting by self-folding using water absorption materials: (a) 1D to 3D41; (b) 2D to 3D41

While one of the obstacles in 3D printing is the general need to fabricate items with only one material, 4D printing is beginning to emerge as a forerunner in applications like the medical and engineering fields.

3D printed models in the medical area (a) 3D printed heart; (b) 3D printed skull (Source: https://3dprintingindustry.com/news; sketchucation.com)

3D printing is still becoming increasingly popular, however, for use in the military field, creating weaponry and allowing for better maintenance of parts. 3D printed models are improving treatment for patients and can be used as extremely helpful pre-planning devices for surgery. Various hardware has also been created for extrusion of food like chocolate and pancake batter.

As for 4D printing, the authors expect that it will be used to create more advanced smart materials that can transform environmentally as users require, offer ‘self-controllable functions,’ expand longevity in products, and promote greater complexity in structures.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘Recent 3D and 4D intelligent printing technologies: a comparative review and future perspective’]

The post What Does the Future Hold for 3D & 4D Printing? Reviewing Current Processes & Ongoing Potential appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

Ulsan National Institute of Science and Technology (UNIST): Multicolor 4D Printing of Shape-Memory Polymers

Researchers from Ulsan National Institute of Science and Technology (UNIST) take 3D printing to the next level, releasing findings from their study in the recently published ‘Multicolor 4D printing of shape-memory polymers for light-induced selective heating and remote actuation.’

While the miracles of 3D printing continue to abound, 4D printing allows users to work with materials that respond to their environment, deforming accordingly—and then reverting to their initial, natural shapes. In this study, the authors 4D print multicolor shape-memory polymers (SMPs) and demonstrate how light absorption and subsequent heating of the material cause remote actuation.

Previous studies have tended to focus on how SMPs deform in the presence of heat or moisture, but here light is used as a powerful force in causing stimuli-responsive changes. Selective heating was allowed due to choices in color of light, also resulting in color-dependent structural transformations.

“4D printing can allow the complex geometries of multicolor composites with predesigned responses,” stated the authors. “In addition, SMPs can be reused multiple times by conducting thermomechanical programming again. Therefore, multicolor 4D printing of SMPs can offer unique merits for light-induced structural changes and remote actuation.”

For the study, the authors created a light-activating structure measuring L = 40 mm, w = 5.5 mm, t = 2 mm, a = 0.4 mm, and made of three materials:

  • Yellow (Veroyellow)
  • Blue (Verocyan)
  • Sky-blue matrix (Tango +)

A 3D printed light-activating structure. (a) Schematic for the multicolor SMP structure. (b) Side view of the structure. (c) Thermomechanical programming and bending behavior (the dotted line in the figure is an eye guide).

Light was able to reach both the yellow and blue fibers due to strategic positioning of the fibers. After 3D printing and post-processing, the structure was bent downward, reverting to its initial shape after being exposed to blue light. Through continued experimentation with color dependent selective heating, the researchers realized that they could manipulate actuation through sequences of light.

Bending behavior of the multicolor sample. A thermomechanically programmed structure bends to a n-shape under red illumination. After bending, the structure can recover to an initial flat state with blue illumination. In case of illuminating blue light first, the structure bends to a U-shape. It can also recover to the initial state with red-light illumination. (a) is the schematic for dual-step actuation, while (b) is the experimental result.

“Applying red light later caused the entire structure to retain its initial flat state. However, when the structure was heated in hot water (instead of selective heating with colored light), the change in shape of our sample was insignificant (data is not shown here). In the hot water, both blue and yellow SMPs recovered at the same rate, and the entire structure shrank to its original length but remained flat (i.e., no shape change occurred),” stated the researchers.

“The rise in temperature due to direct blue-light absorption was significantly smaller than that due to heat transfer. Thus, it shows that the dominant factor causing the temperature increase in the blue fibers at the lower layer was the heat transferred from the yellow fibers at the top layer.”

(a) The measured temperature change of the multicolor structure. The yellow solid line is the temperature of yellow SMP fibers, whereas the blue dashed line indicates the temperature of blue SMP fibers obtained from heat transfer simulations. The red solid line is the measured temperature of blue SMP fibers in a control sample that contains blue SMP fibers only. (b) Results of solid-mechanics simulations. The color bar indicates the total displacement measured from the bottom plane.

Bent structures reverted to a flat shape due to heat being transferred while illuminated; however, this type of heat transfer occurred after the light was turned off also, evidenced by slight relaxing afterward. The researchers attributed this action to residual heat in the structure, allowing for relaxation in the form. To prevent this, they considered adding a thermal insulating layer.

Their final sample included a hinged structure meant for experimentation with multistep actuation. The team used colored SMP fibers in the hinges, manipulating deformation through colors. Rapid transformation occurred as they focused the LED light onto the structure with a focal lens.

Multicolor hinged structure for multistep actuation. (a) Schematic for the multicolor hinged structure. (b) Example of multistep actuation. This hinged structure can transform into different 3D shapes depending on the color of light and duration of illumination.

“SMPs can be reused by conducting thermomechanical programming again and their response temperatures can be adjusted via material synthesis or by dynamic mixing during 3D printing. Moreover, 4D printing can enable the fabrication of complex, multicolor geometries for tailored responses. Therefore, multicolor 4D printing of SMP composites have unique merits for light-induced structural changes and remote actuation,” concluded the researchers.

(a) Storage modulus and (b) Loss tangent obtained with dynamic mechanical analysis (DMA) measurements.

4D printing continues to gain traction with users around the world, particularly researchers, investigating nanoscale 4D printing, customized printing for metastructures, 4D printing in optics, and more.

[Source / Images: ‘Multicolor 4D printing of shape-memory polymers for light-induced selective heating and remote actuation’]

The post Ulsan National Institute of Science and Technology (UNIST): Multicolor 4D Printing of Shape-Memory Polymers appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

Zhejiang researchers develop modular 4D printed assembly

Researchers in China have presented a study on a modular method of 4D printing that aims to overcome the geometrical limitations of the process.  The advantage of 4D printing, based on a digitally controlled 2D-to-3D transformation, is that it forgoes the layer-by-layer fabrication process of 3D printing, resulting in a faster production method. However, the […]
Posted on

4D Printed Structures to Impact Many Industries in the Future

Researchers from Libya are doing more than just delving past the limits of 3D printing and into 4D printing—they are investigating a full revolution in digital fabrication where structures can change over time as their environment transforms.

With their findings recently released in ‘4D Printing Technology: A Revolution Across Manufacturing,’ the authors define 4D printing as ‘the use of the 3D printing in the creation of objects which alter/change their shape when they are removed from the 3D printing. The aim is that objects made self-assemble when being exposed to heat, air or water, this is caused by chemical reactions due to the materials utilized in the manufacturing processes.’

4D printing offers benefits due to the versatility available as shapes adjust to heat or moisture, for example, offering properties and functionality suitable for many applications today. Commonly referred to as smart materials, 4D structures are created through mathematical modeling.

The differences between 3D printing technology and 4D printing technology

The bases of the 4D printing

A variety of different materials can be used in 4D printing, to include:

  • Thermo-responsive
  • Moisture-responsive
  • Photo-responsive
  • Electro-responsive
  • Magneto-responsive

Classes of materials that can respond to various types of stimulus including heat, electricity, moisture, light, and magnetic field.[12]

Smart materials show ongoing potential for use in applications like medicine, with the use of 4D printed implants able to deform in size as patients grow; for example, such a device was responsible for saving the life of a child in 2015, solving respiratory problems and adapting as the child grew—eventually dissolving.

“At present, the use of 4D printing technology in ultrasound scans allows, for example, to know more precisely the structural and functional development of the nervous system of the fetus. In the future, vascular endoprosthesis (stents) or other 4D parts that react to body heat and expand to adapt to the patient, may be able to be printed,” explained the researchers.

a: 4D-printed heart and b: 4D-printed skull

Clothing and footwear may continue to feel the positive impacts of 4D printing too, offering incredible customization for the wearer, who is able to experience a new level of comfort as items completely adapt to their form.

“The USA military is testing, for example, uniforms that change color depending on the environment, or that regulate perspiration depending on the environment temperature or the soldier’s pulse. 4D printed shoes will also be able to adapt to movement, impact, atmospheric pressure, and temperature.”

a: 4D-printed t-shirts and b: 4D-printed shoe

As organizations like NASA continue using 3D printing for items like rocket engines, robots, and a wide range of sophisticated projects, they are also reaching to 4D printing for features like metallic fabrics that could be used to offer greater insulation for astronauts. Smart materials able to deform quickly are also being tested for use in automobile airbags.

a: 4D-printed plane and b: 4D-printed car.

“Smart printing can be applied to many fields from simple changes of shape to bio printing for organisms,” concluded the researchers. “Using multi-material 3D printing technology and smart materials, 4D printing has been improved. 4D printing provides a feasible method to fabricate compact deployable products structures. Smart materials used are the cornerstone for 4D printing technology. This new technology will reduce the energy expenditure resource and consumption in the industry.”

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘4D Printing Technology: A Revolution Across Manufacturing’]

 

The post 4D Printed Structures to Impact Many Industries in the Future appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

FDM 4D Printing: Energy Absorbing Tunable Meta-Sandwiches Created

International researchers are taking advantage of the next level beyond 3D printing to produce novel materials and structures, as outlined in the recently published ‘Reversible energy absorbing meta-sandwiches by FDM 4D printing.’

With a focus on reversible energy absorption applications, the authors fabricate ‘meta-sandwiches,’ developed from hyper-elastic polymers and elasto-plastic shape memory polymers.

Harkening to natural energy absorbers such as bones, teeth, hooves, and more, the scientists strive to create stable structures for use in cars and planes, make protective packaging, sports equipment, and more.

“The principle of energy absorption in meta-materials and lattice-based structures provides the capability to convert kinetic energy into other types of energies through elastic and/or plastic deformations, mechanical instability and structural collapse,” explain the authors.

In recent work, plastic deformation in metal and plastics has been the route for energy absorption, using alloys like nickel-titanium (NiTi), or combining amorphous polymers and flexible elastomers. With 3D printing, however, scientists have been able to experiment with metamaterials and lattice-based structures with success in energy absorption.

Auxetic meta-sandwiches are evidence of a conceptual design made up of soft hyper-elastic polymers and elasto-plastic hard SMPs, accentuated with cold programming—and ultimately, the authors expect to see these concepts offer new benefits in the design process of reversible energy dissipation devices.

As smart materials that can deform and then return to their initial shape, SMPs were used here at room temperature ‘lower than their glass transition temperature.’ The researchers then heated it above transition temperature range until it reverted to its normal state.

SMP cold programming: (a) thermomechanical procedure, (b) stress-strain temperature diagram.

“The dissipated energy through the plastic deformation of SMPs, revealed as a hysteresis loop, is considered as the energy absorption mechanism in this work,” explain the researchers. “The SME is also considered to introduce recoverable energy absorbers.”

The researchers used a 3DGence Double P255 (with dual interchangeable hotends for dual-material printing) for 4D printing their sample lattice-based energy absorbers.

DMA measurement result on the 3D printed SMP in terms of storage
modulus (Es) and tan (?).

(a) Single unit cell and auxetic geometry, (b) lattice schematic

Evaluating the metastructures (both experimentally and numerically) showed that the designs offered the required non-linear stiffness and dissipating energy. Their experiments showed:

  • Existence of the hysteresis loop
  • Physics of snap-through instability
  • Elasto-plasticity

“Comparison studies revealed that the main aspects of meta-sandwiches were well simulated in capturing yield stress, plateau during plastic deformation growth, unloading path and hysteresis area. It was also experimentally shown that the deformation and the dissipation processes are reversible opening an avenue for the design and implementation of recoverable energy dissipation devices for impact protection and shock mitigation applications,” concluded the researchers.

“Due to the absence of similar concept and results in the specialized literature, this paper is likely to advance the state-of-the-art 4D printing tunable metasandwiches with reversible energy absorption features.”

SMP meta-structure: (a)-(g) experimental and computational configuration, (h) force-displacement path for loading-unloading and thermal shape recovery (free strain recovery by thermal loading is represented by the red dash-dotted line), (i) dissipated and absorbed energies.

4D printing is one of the most exciting new areas to be inspired by 3D printing; and while it espouses much of the same technological processes, this is an area that seems even closer to magic, allowing for the use of exceptional metamaterials, magnetic actuators, composite materials, and more.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘Reversible energy absorbing meta-sandwiches by FDM 4D printing’]

The post FDM 4D Printing: Energy Absorbing Tunable Meta-Sandwiches Created appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

4D Printing in Singapore: Researchers Pair Compliant Mechanisms with Chitosan Biopolymers

Researchers continue to reach from the 3D realm to the next level, seeking to master the comprehensive fabrication of 4D structures. Now, a team of scientists from Singapore is exploring new ways to create flexible, programmable passive actuators, outlining their findings in the recently published ‘3D Printing of Compliant Passively Actuated 4D Structures.’

For this study, the research team paired compliant mechanisms (CM) with water-responsive chitosan biopolymers. With CM, the scientists were able to take advantage of benefits such as:

  • No hysteresis
  • Compactness
  • Ease of fabrication
  • Simplicity
  • Light weight
  • High reliability
  • Frictionless, wear-free motion

CMs are beneficial today in applications such as:

  • Implants
  • Soft robotics
  • Building structures
  • Space research
  • Micro-engineering

Previous work of chitosan based passive actuator with revolute joints

And while there is a long list of ‘pros’, CMs still offer a host of issues researchers, manufacturers, and industrial users must surpass in terms of both design and fabrication. With additive manufacturing being used in CM manufacturing, the goal is to provide the mechanical force required to spur on movement and possible deformation of the compliant part, which may respond to temperature, light, and moisture. Such products are categorized as 4D or ‘smart materials’ as they are able to respond to their environment accordingly.

Materials such as chitosan, an extremely common polymer, have been used more often with 3D printing, in examples like bioprinting neural tissue. Materials bordering on the 4D have been tested and used many times also with soft robotics, reinforced composites, and more.

Initially, a single design was created for the actuator nodes, with a ‘truss-inspired cantilever fitted with hygroscopic chitosan films.’ Chitosan biopolymers allow for the necessary deformation in this project design, as well as many applications today like textiles, cosmetics, agriculture, bioprinting, and more.

As they began working to create four compliant designs, researchers used cotton gauze to strengthen the chitosan, structuring it into thin pieces of film with a specific solution that is filtered, degassed, and then cast into molds. They put the films through another washing and drying cycle and then began experimenting with their designs, on a mission to make strides in achieving suitable and programmable shape deformation.  In their prototype, the researchers used an ‘intuitive physical’ concept as they investigated several different CM designs to meet the necessary range of motion in a variety of shapes, layer thickness, and more.

The flexure must be compliant enough to deflect 9.34 mm under the load from a
50gm test weight in order to achieve the targeted shape change

Several ‘springy’ designs were developed to spread the load for each flexure, along with allowing for better control with programmable bending in the system. Strength was evaluated also with a load test, and static non-linear structural FEM analysis.

Different springy-derivative flexural designs (a) CMD 1 (b) CMD 2 (c) CMD 3 (d) CMD 4

FEA simulation for four different CM designs (a, b, e & f) Maximum stress (c, d, g & h) Maximum deflection

3D printing of the research project’s actuator was performed on a Stratasys Fortus 450mc FDM 3D printer, using ASA—a propriety model material by Stratasys that is similar to ABS. The team spent 4.5 hours printing the part, and then it was placed in a solution to assist in removal of support materials. In testing, the researchers noted good performance from the actuator, with no signs of mechanical failure at all; however, there were still ‘significant variations from the expected results.’

3D printing of the actuator (a) Sliced model of the actuator before printing (b) Print results of CM Design 3

“The average total deformation between the two states of the actuator was calculated to be 71.2mm, measured by changes in height of the cantilevering end of the actuator. This 71.2 mm represents nearly one-third of the total actuator length, which points to the ability of the CM to accommodate a relatively large range of motion. The expected deformation from 2D simulation was 95.6mm, and so evidently the chitosan did not expand to their 12.8 % capacity as expected,” concluded the researchers.

“It is possible that even though the films lose much of their stiffness when saturated, that there was still insufficient driving force to cause significant mechanical strain of the films. One potential workaround would be to implement another tensile element to the assembly that, when added on top of the assembly’s self-weight, could encourage the full elongation of the chitosan films.”

Comparison of (a) Simulated curve of dry and wet state (b) Physical results of dry and wet state curvature

Comparison of curvature over three cycles (a) Dry state (b) Wet state

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘3D Printing of Compliant Passively Actuated 4D Structures’]

 

The post 4D Printing in Singapore: Researchers Pair Compliant Mechanisms with Chitosan Biopolymers appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

4D Printing in China: Shape Memory Polymers and Continuous Carbon Fiber

Researchers have been looking further into the benefits of shape memory polymers (SMPs) with the addition of raw materials in the form of continuous carbon fiber (CCF). Authors Xinxin Shen, Baoxian Jia, Hanxing Zhao, Xing Yang, and Zhengxian Liu have studied mechanical properties in composite samples, along with performance—outlining details in the recently published ‘Study on 3D printing process of continuous carbon fiber reinforced shape memory polymer composites.’

SMPs are a ‘hotspot in academic research’ today as scientists embrace a growing fascination with materials that can deform and return to their natural state as required by users. Refining SMPs continues also, especially with materials like carbon fibers for overcoming challenges regarding strength and stiffness. While continuous fibers have been shown to be more effective than short fibers, the authors point out that forming processes are complex, and better ways are needed for creating continuous carbon fiber-reinforced composites. Here, they turn to FDM 3D printing as a solution:

“The composite 3D printer was mainly composed of motion platform, printing nozzle, fiber feeding mechanism and control system,” stated the researchers. “Compared with conventional printers, the nozzle of this printer can feed resin and fiber from two channels simultaneously and extrude them from the same nozzle.”

Printing principle of continuous carbon fiber reinforced SMP composites.

“In addition, the fiber feeding mechanism was designed to continuously feed the fiber at a suitable speed by adjusting the rotating speed of the stepping motor to avoid breakage of the fiber during printing.”

Four ply angles of carbon fibers, (a) 0° (b) 90° (c) 0° /90° (d) ±45°.

In using orthogonal experimental design, the authors studied influences such as:

  • Printing temperature
  • Printing speed
  • Scanning pitch
  • Ply angle

Partial printed specimens with different process parameters.

In examining issues with mechanical properties further, the researchers found that the ply angle of carbon factors was a key factor. As they varied ply angles, changes in tensile strength and modulus of the specimens resulted, showing tension along the fibers at 0 degrees, but at 90 degrees it was perpendicular, opening the potential for problems with adhesion.

The study also showed that mechanical properties were more suitable at about 200℃, with excessive printing speed affecting ‘impregnation’ of fibers and resin. The authors also noted little effect on SMPs due to changes in fiber content.

SEM of fracture cross section of specimens under different temperatures

“The rapid manufacture of shape memory carbon fiber composites has potential use in the field of aerospace,” concluded the researchers.

While researchers, engineers, designers, and users around the world still may have yet to scratch the surface of the potential of 3D printing, many are delving further into the next level with materials that are able to morph to their environments, from soft actuators to 4D printing with wood composites, to exceptional new metamaterials.

Find out more about carbon fiber and SMPs here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Shape memory performance test with different fiber contents.

[Source / Image: ‘Study on 3D printing process of continuous carbon fiber reinforced shape memory polymer composites’]

 

The post 4D Printing in China: Shape Memory Polymers and Continuous Carbon Fiber appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Posted on

4D Printed Shape Memory Polymers Given Better Performance & Recyclability

Authors Ang Li, Adithya Challapalli, and Guoqiang Li explore a trend that continues to grow: 4D printing. Their findings are explained in the recently published “4D Printing of Recyclable Lightweight Architectures Using High Recovery Stress Shape Memory Polymer.” Here, the benefits of smart materials that can adapt to their environment are explored as the researchers consider challenges in 3D printing self-healing shape memory polymer (SMP) microlattices, and move forward to develop their own thermoset polymer offering the following features:

  • High strength
  • High recovery stress
  • Perfect shape recovery
  • Good recyclability
  • 3D printability with DLP

The ability to create lightweight structures is one of the greatest benefits of 3D printing, but users are continually looking for better ways to have it all, including good mechanical properties. This is especially important in advanced engineering applications where capabilities such as the following are in demand:

  • Shape memory
  • Recovery stress
  • Damage healing
  • Recyclability

Schematic of recyclable and shape memory microlattices using 3D-RSMP. (a) 3D printing (direct light printing (DLP) of advanced multifunctional microlattice structures using the 3D-RSMP. (b) Compression programming of the printed microlattice to a temporary shape and recovery to the original shape. (c) Recycling of the ball milled multifunctional microlattices under high pressure and high temperature. (d) The remolded specimen for mechanical tests.

3D printed shape memory polymers tend to offer better potential, offering higher speed in production, less energy consumption to produce, and less post-processing. Shape memory effect is usually improved too, in what is ultimately the process of 4D printing, bringing forth ‘stimuli-responsive self-evolving features’ which offer better performance for load-bearing parts and structures. Before this study, however, the researchers found a resource for SMPs with high stress output lacking. Creating a higher-performance SMP meant turning to thermosets and either DLP or SLA methods.

The research team created a specialized 3D-RSMP resin for universal DLP 3D printing, offering mechanical properties they believe to be as good as some of the ‘best commercial DLP resins without multifunctionality,’ with higher shape memory and better self-healing qualities. 3D structures were designed in SolidWorks and then 3D printed on the Asiga Pico 2, with 3D-RSMP resin with 0.15mm layer thickness. Samples were also tested for recycling, crushed and broken, and then ground up via ball milling. Afterward, the researchers added the particles to a steel mold, with pressure applied at 200 °C or 150 °C for 2 hours.

Recycling of the crushed microlattices. (a) A recycling process is described: broken and failed shape memory microlattices were crushed into powders via ball milling; a steel mold was used for recycling milled powders of 3D printed microlattice structures under varying conditions. A mechanical test was performed on the remolded rectangular specimen made of the milled powders. (b) Typical tensile stress vs. strain curves of the remolded rectangular specimens obtained under varying conditions ((200C12M2H represents molding at 200 °C and under 12MPa pressure for 2h; 150C12M2H represents molding at 150 °C and under 12MPa pressure for 2h; and 150C9M2H represents molding at 150 °C and under 9MPa pressure for 2h) with a loading rate=0.5mm/min at room temperature.

The 3D-RSMP product appears so far to be the only SMP that can be both 3D printed and recycled—with recovery stress larger than 10MPa. In terms of application, the researchers also found their cubic microlattice to have the highest mechanical strength ‘with comparable or even higher specific compressive strength than metallic microlattices and ceramic microlattices without shape memory effect.’

 “The results show that the cubic microlattice has mechanical strength comparable to or even greater than that of metallic microlattices, good SME, decent recovery stress, and recyclability, making it the first multifunctional lightweight architecture (MLA) for potential multifunctional lightweight load carrying structural applications,” concluded the researchers.

“Future work will be focusing on improving the recycling efficiency of the 3D-RSMP and the microlattice, and further optimizing the geometry through topological optimization or biomimicry in order to obtain microlattices with higher mechanical strength and shape memory effect for advanced structural and engineering applications.”

Mechanical properties of various microlattices upon compression. (a) Compressive strength vs. apparent density plots of various microlattices and foams. (b) Compressive modulus vs. apparent density plots of the three microlattices in this study.

 

While 3D printing is a source of fascination around the world, still, 4D printing takes fabrication to another magical level as researchers produce innovations like tunable metamaterials, multi-metals, and processes for other industrial applications.

Tree unit cell geometries have been drawn in Solidworks and then assembled to the corresponding microlattice structures. (Row 1: unit cells, from left to right: Octet unit cell (OCT UC); Kelvin unit cell (KVNUC); Cubic unit cell (CBC UC), Row 2: 3D printed microlattice structures, from left to right: Octet microlattice structure (OCT LTC), Kelvin microlattice structure (KVN LTC), and cubic microlattice structure (CBC LTC); Row 3: multi-length scale microlattices, from left to right: 1st order octet truss (1O OCT) and 2nd order octet truss (2O OCT)). (Te scale bar applies to all the five lattice structures).

[Source / Images: ‘4D Printing of Recyclable Lightweight Architectures Using High Recovery Stress Shape Memory Polymer’]

 

The post 4D Printed Shape Memory Polymers Given Better Performance & Recyclability appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.