Tag Archives: #3Dprinting

Researchers Advance 3D Printing to Aid Tissue Replacement (Bio Engineering)

Professor Arda Gozen looks to a future someday in which doctors can hit a button to print out a scaffold on their 3-D printers and create custom-made replacement skin, cartilage, or other tissue for their patients.

Gozen, George and Joan Berry associate professor in the Washington State University School of Mechanical and Materials Engineering, and a team of researchers have developed a unique scaffolding material for engineered tissues that can be fine-tuned for the tricky business of growing natural tissue. They report on their research in the journal, Bioprinting. The team also includes researchers from WSU’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering as well as from the University of Texas-San Antonio (UTSA), Morehouse College, and University of Rochester. The lead author is Mahmoud Amr, who received his PhD at UTSA.

In recent decades, researchers have been working to use biological material in 3D printing to create tissue or organs for patients recovering from injury or disease. Using 3D printing, or additive manufacturing, makes it possible to print complex, porous, and personalized structures and could allow doctors someday to print out tissue for a patient’s particular body and needs. To create biological structures, biological materials known as “bioinks” are dispensed out of a nozzle and deposited layer-by-layer, creating complex “scaffolds” for real biological material and providing a nice place for cells to grow.

Nature, however, has so far been more complicated than researchers can keep up with. Real biological cells like to grow on a scaffold that approaches their own properties. So, for instance, a skin cell wants to grow on a scaffold that feels like skin while a muscle cell will only develop on a scaffold that feels like muscle.

Closeup of a 3D-printed nose
A 3D-printed scaffold of a nose. © WSU

“The success of this method in manufacturing functional tissues relies heavily on how well the fabricated structures mimic the native tissues,” Gozen said. “If you want to grow cells and turn them into functional tissue, you need to match the mechanical environment of the native tissue.”

The way that researchers have traditionally varied their scaffolds was to simply remove trusses to make them softer or stiffer – a method that is too simple to address all the needed complexity in tissue engineering.

“We don’t have a lot of knobs to turn,” Gozen said. “You need more degrees of freedom – to create something softer or harder without changing the structure.”

The team of researchers developed a new bioink material that allows for customizing properties to closer approach what cells might need. The ingredients for their scaffold include gelatin, gum Arabic, and sodium alginate, which are all common thickening agents used in many processed foods.

Similar to the way a thick rope is made of braided strands, the researchers used three separate chemical processes to tie their three ingredients together into one scaffold material for printing.

Playing with the separate chemical processes then provides a way to finely tune the mechanical properties of the material, allowing them to make a softer or stiffer final scaffold.

“That gives you the capability of tuning the properties without changing the scaffold design and gives you an additional degree of freedom that we are seeking.”

Closeup of a 3D printer printing tissue
3D printing of a tissue scaffold. © WSU

By adjusting the chemical bonds between the rope strands, they didn’t change the material significantly, and it was amenable for growing cartilage cells.

The work is still in its early stages, and the researchers would like to figure out how to more precisely tune the process and final material. They might look at varying the composition of their three materials or printing at different temperatures, for instance.

Trying to imitate the vast complexity of natural tissue remains a challenge. Even a simple millimeter-sized piece of cartilage on the knee for instance, has three separate and distinct layers, each with different mechanical properties and functions.

“You’re not assembling Legos here. It’s always about replicating nature that works with the body,” Gozen said. “You can make living structures, but they look nothing like the native tissue. Precision is key because there is no single mechanical property target for a single piece of tissue.”

The research was funded by the National Science Foundation.

Featured image: closeup of Arda Gozen © WSU


Reference: Mahmoud Amr, India Dykes, Michele Counts, Joshua Kernan, Alia Mallah, Juana Mendenhall, Bernard Van Wie, Nehal Abu-Lail, B. Arda Gozen, 3D printed, mechanically tunable, composite sodium alginate, gelatin and Gum Arabic (SA-GEL-GA) scaffolds, Bioprinting, Volume 22, 2021, e00133, ISSN 2405-8866, https://doi.org/10.1016/j.bprint.2021.e00133. (https://www.sciencedirect.com/science/article/pii/S2405886621000063)


Provided by Washington State University

New Frontier For 3D Printing: Developed Soft Materials That Repair Themselves (Material Science)

The scientific community is concentrating many studies on the multiple applications of hydrogels , polymeric materials containing large quantities of water, potentially capable of reproducing the characteristics of biological tissues. This aspect is of particular importance in the field of regenerative medicine , which has long recognized and is using the potential of these materials. In order to be effectively used to replace organic tissues, hydrogels must meet two fundamental requirements: they must have a high geometric complexity and be able to self-repair themselves following damage, just like living tissues.

The development of these materials can now be easier and cheaper thanks to the use of 3D printing: the researchers of the MP4MNT (Materials and Processing for Micro and Nanotechnologies) team of the Department of Applied Science and Technology of the Politecnico , coordinated by Professor Fabrizio Pirri , have demonstrated for the first time the possibility of manufacturing hydrogels with complex architectures that can self-repair following a tear thanks to light-activated 3D printing . The research was published by the prestigious journal Nature Communication in an article entitled “3D-printed self-healing hydrogels via Digital Light Processing” ( DOI 10.1038 / s41467-021-22802-z)

Self-healing of complex geometries© Politecnico di Torino

In reality, hydrogels with self-healing or modelable properties in complex architectures through 3D printing had already been created in the laboratory, but in this case it is a solution that encompasses both characteristics, namely the complexity of the architecture and the ability to regenerate afterwards. of damage.

Furthermore, the hydrogel was made using materials available on the market, processed by a commercial printer , thus making the proposed approach extremely flexible and potentially applicable everywhere, with new development possibilities both in the biomedical field and in that of soft-robotics.

The research was developed as part of the HYDROPRINT3D doctoral project, funded by the Compagnia di San Paolo from the “Joint Projects with Top University” initiative and conducted by the doctoral student Matteo Caprioli , under the supervision of DISAT researcher Ignazio Roppolo , in collaboration with the research group of Professor Magdassi of the Hebrew University of Jerusalem (Israel).

“For several years – says Ignazio Roppolo – within the MP4MNT group a research unit has been created, coordinated by me and Dr. Annalisa Ch Japan, which is specifically concerned with developing new materials that can be processed through light-activated 3D printing. 3D printing is able to offer a synergistic effect between the design of the object and the intrinsic properties of the materials, allowing to obtain artifacts with unique characteristics. In our perspective, it is necessary to take advantage of this synergy to best develop the potential of 3D printing so that it can truly become an element present in our everyday life. And this study falls exactly in the wake of this philosophy ”.

This research represents a first step towards the development of highly complex devices that can exploit complex geometries and intrinsic self-repair properties in various fields. In particular, once the biocompatibility studies in progress at the Polytechnic Interdepartmental Polito BIO Med Lab have been refined , it will be possible to use these structures both for basic studies on cellular mechanisms and for applications in the field of regenerative medicine.


Reference: Caprioli, M., Roppolo, I., Chiappone, A. et al. 3D-printed self-healing hydrogels via Digital Light Processing. Nat Commun 12, 2462 (2021). https://doi.org/10.1038/s41467-021-22802-z


Provided by Politecnico Di Torino

Energy-saving Gas Turbines From the 3D Printer (Physics)

Neutrons “see” internal stress in components from additive manufacturing

3D printing has opened up a completely new range of possibilities. One example is the production of novel turbine buckets. However, the 3D printing process often induces internal stress in the components which can in the worst case lead to cracks. Now a research team has succeeded in using neutrons from the Technical University of Munich (TUM) research neutron source reactor for non-destructive detection of this internal stress – a key achievement for the improvement of the production processes.

Gas turbine buckets have to withstand extreme conditions: They are exposed to tremendous centrifugal forces under high pressure and at high temperatures. In order to further maximize energy yields, the buckets have to hold up to temperatures which are actually higher than the melting point of the material. This is made possible using hollow turbine buckets which are air-cooled from the inside.

These turbine buckets can be made using Laser Powder Bed Fusion, an additive manufacturing technology: Here the starter material in powder form is built up layer by layer by selective melting with a laser. Following the example of avian bones, intricate lattice structures inside the hollow turbine buckets provide the part with the necessary stability.

Manufacturing process creates internal stress in the material

“Complex components with such intricate structures would be impossible to make using conventional manufacturing methods like casting or milling,” says Dr. Tobias Fritsch of the German Federal Institute for Materials Research and Testing (BAM).

Using the remote control Dr. Tobias Fritsch brings the lattice structure into the correct measuring position in the residual stress diffractometer STRESS-SPEC at the Research Neutron Source Heinz Maier-Leibnitz of the Technical University of Munich. © Dr. Michael Hofmann

But the laser’s highly localized heat input and the rapid cooling of the melt pool lead to residual stress in the material. Manufacturers usually eliminate such stress in a downstream heat-treatment step, which however takes time and thus costs money.

Unfortunately, these stresses can also damage the components as early as during the production process and up until post-processing takes place. “The stress can result in deformations and in the worst cases lead to cracks,” says Tobias Fritsch. 

Therefore, he investigated a gas turbine component for internal stress using neutrons from the Research Neutron Source Heinz Maier-Leibnitz (FRM II). The component was made using additive production processes by gas turbine manufacturer Siemens Energy.

Post-processing intentionally omitted

For the neutron experiment at the FRM II, Siemens Energy printed a lattice structure only a few millimeters in size using a nickel-chrome alloy typical of those used for gas turbine components. The usual heat-treatment after production was intentionally omitted. 

“We wanted to see whether or not we could use neutrons to detect internal stresses in this complex component,” explains Tobias Fritsch. He had already gained experience with neutron measurements at the Berlin research reactor BER II, which however was shut down in late 2019. 

“We are very glad to be able to make measurements in the Heinz Maier-Leibnitz Zentrum in Garching; with the equipment provided by STRESS-SPEC we were even able to resolve internal stress in lattice structures as intricate and complex as these,” the physicist says.

Even distribution of heat during printing

Now that the team has succeeded in detecting the internal stress within the component, the next step is to reduce this destructive stress. “We know that we have to modify the production process parameters and thus the way in which the component is built up during printing,” says Fritsch. Here the crucial factor is the heat input over time when building up the individual layers. “The more localized the heat application is during the melting process, the more internal stress results.” 

For as long as the printer’s laser is aimed at a given point, the heat of the point rises relative to adjacent areas. This results in temperature gradients that lead to irregularities in the atomic lattice. 

“So we have to distribute the heat as evenly as possible during the printing process,” says Fritsch. In the future the group will research the situation with new components and modified printing parameters. The team is already working together with Siemens to plan new measurements with the TUM neutron source in Garching. 

Featured image: 3D image of the examined lattice structure as measured with the aid of computed tomography. Image: Tobias Fritsch / BAM


Publications:

On the determination of residual stresses in additively manufactured lattice structures
Tobias Fritsch, Maximilian Sprengel, Alexander Evans, Lena Farahbod-Sternahl, Romeo Saliwan-Neumann, Michael Hofmann and Giovanni Bruno
Journal of Applied Crystallography, 2021, 54, 228–236 – DOI: 10.1107/S1600576720015344


Provided by Technical University of Munich

3D Printing Polymers (Material Science)

The material yields soft, elastic objects that feel like human tissue

Researchers in the labs of Christopher Bates, an assistant professor of materials at UC Santa Barbara, and Michael Chabinyc, a professor of materials and chair of the department, have teamed to develop the first 3D-printable “bottlebrush” elastomer. The new material results in printed objects that have unusual softness and elasticity — mechanical properties that closely resemble those of human tissue.

Conventional elastomers, i.e. rubbers, are stiffer than many biological tissues. That’s due to the size and shape of their constituent polymers, which are long, linear molecules that easily entangle like cooked spaghetti. In contrast, bottlebrush polymers have additional polymers attached to the linear backbone, leading to a structure more akin to a bottle brush you might find in your kitchen. The bottlebrush polymer structure imparts the ability to form extremely soft elastomers.

The ability to 3D-print bottlebrush elastomers makes it possible to leverage these unique mechanical properties in applications that require careful control over the dimensions of objects ranging from biomimetic tissue to high-sensitivity electronic devices, such as touch pads, sensors and actuators.

Chris Bates Photo Credit: COURTESY IMAGE

Two postdoctoral researchers — Renxuan Xie and Sanjoy Mukherjee — played key roles in developing the new material. Their findings were published in the journal Science Advances.

Xie’s and Mukherjee’s key discovery involves the self-assembly of bottlebrush polymers at the nanometer length scale, which causes a solid-to-liquid transition in response to applied pressure. This material is categorized as a yield-stress fluid, meaning it begins as a semi-soft solid that holds its shape, like butter or toothpaste, but when sufficient pressure is applied, it liquefies and can be squeezed through a syringe. The team exploits this property to create inks in a 3D-printing process called direct ink writing (DIW).

The researchers can tune the material to flow under various amounts of pressure to match the desired processing conditions. “For instance, maybe you want the polymer to hold its shape under a different level of stress, such as when vibration is present,” says Xie. “Our material can hold its shape for hours. That’s important, because if the material sags during printing, the printed part will have poor structural stability.”

Once the object is printed, UV light is shined onto it to activate crosslinkers that Mukherjee synthesized and included as a part of the ink formulation. The crosslinkers can link up nearby bottlebrush polymers, resulting in a super-soft elastomer. At that point, the material becomes a permanent solid — it will no longer liquefy under pressure — and exhibits extraordinary properties.

Michael Chabinyc Photo Credit: UC Santa Barbara

“We start with long polymers that are not crosslinked,” said Xie. “That allows them to flow like a fluid. But, after you shine the light on them, the small molecules between the polymer chains react and are linked together into a network, so you have a solid, an elastomer that, when stretched, will return to its original shape.”

The softness of a material is measured in terms of its modulus, and for most elastomers, it is rather high, meaning their stiffness and elasticity are similar to those of a rubber band. “The modulus of our material is a thousand times smaller than that of a rubber band,” Xie notes. “It is super-soft — it feels very much like human tissue — and very stretchy. It can stretch about three to four times its length.”

An Accidental Ink

Mukherjee discovered the material by accident, while trying to develop a material for a different project, one that would increase the amount of charge that can be stored by an actuator. When the elastomer came to Xie for characterization, he knew immediately that it was special. “I could see right away that it was different, because it could hold its shape so well,” he recalled.

“When we saw this really well-defined yield stress, it dawned on everyone collectively that we could 3D-print it,” Bates said, “and that would be cool, because none of the 3D-printable materials we know of have this super-soft property.”

Bottlebrush polymers have been around for more than twenty years. But, Bates said, “The field has exploded in the past ten years thanks to advances in synthetic chemistry that provide exquisite control over the size and shape of these unique molecules.

“These super-soft elastomers might be applicable as implants,” he added. “You may be able to reduce inflammation and rejection by the body if the mechanical properties of an implant match native tissue.”

Another important element of the new material is that it is pure polymer, Chabinyc noted.

“There’s no water or other solvent in them to artificially make them softer,” he said.

To understand the importance of having no water in the polymer, it’s helpful to think of Jell-O, which is mostly water and can hold its shape, but only as long as the water remains inside. “If the water went away, then you’d just have a shapeless pile of material,” said Chabinyc. “With a conventional polymer, you must figure out how to keep the right amount of water in it to maintain its structure, but this new material is all solid, so it will never change.”

Moreover, the new material can be 3D-printed and processed without solvent, which is also unusual. “People often add solvent to liquify a solid so that it can be squeezed out of a nozzle,” said Xie, “but if you add solvent, it has to evaporate after printing causing the object to change its shape or crack.”

Mukherjee added, “We wanted the material and the printing process to be as clean and as easy as possible, so we played a chemistry trick with solubility and self-assembly, which enabled the solvent-free process. The fact that we don’t use solvent is a tremendous advantage.”

Featured image: From left: the unlinked polymer ink, infrared light being applied to activate the crosslinks, and the final product — a super-soft, super-elastic crosslinked Elastomer. Photo Credit: Isabelle Chabinyc


Reference: Renxuan Xie, Sanjoy Mukherjee, Adam E. Levi, Veronica G. Reynolds, Hengbin Wang, Michael L. Chabinyc, Christopher M. Bates, “Room temperature 3D printing of super-soft and solvent-free elastomers”, Science Advances 13 Nov 2020: Vol. 6, no. 46, eabc6900 DOI: 10.1126/sciadv.abc6900


Provided by UC Santa Barbara

Researchers Prepare Tailored and Wearable Sensor by 3D Printed UV-curable Sacrificial Mold

Three-dimensional (3D) printing techniques have the ability to fabricate wearable sensors with customized and complex designs compared with conventional processes. The vat photopolymerization 3D printing technique exhibits better printing resolution, faster printing speed, and is capable of fabricating a refined structure. Due to the lack of highly conductive photocurable resins, it is difficult to prepare sensors through vat photopolymerization 3D printing technique.

Process to develop PFSS © Peng et al.

In a study published in Adv. Funct. Mater., the research group led by Prof. WU Lixin from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences developed porous flexible strain sensors (PFSS) with high stretchability and an excellent recoverability. 

The researchers first synthesized a bifunctional monomer hydrolyzably hindered urea acrylate to create a crosslinked polymer network, preventing the dissolution of printed parts in the uncured resin. 3D printed scaffolds can be hydrolyzed in hot water, which provides an attractive option for sacrificial molds. 

They then cast polyurethane/carbon nanotubes composites in molds to prepare flexible sensors as the PFSS. This PFSS exhibited a good pressure sensitivity (0.111 kPa-1) at the low compressive strain.  

The resistance response signals were stable after 100 cycles of 60% mechanical loads with high cycle repeatability and stability. 

Besides, the researchers demonstrated the practical applications of PFSS for in situ human motion detection including gait analysis and finger motion, proving it a promising material for smart wearable device preparation.  

This study showed that the sacrificial molding process has great potential for user-specific stretchable wearable devices.

Reference: Peng, S., Wang, Z., Lin, J., Miao, J.‐T., Zheng, L., Yang, Z., Weng, Z., Wu, L., Tailored and Highly Stretchable Sensor Prepared by Crosslinking an Enhanced 3D Printed UV‐Curable Sacrificial Mold. Adv. Funct. Mater. 2020, 2008729. https://onlinelibrary.wiley.com/doi/10.1002/adfm.202008729 https://doi.org/10.1002/adfm.202008729

Provided by Chinese Academy of Sciences

Researchers Develop New Combined Process For 3D Printing (Chemistry)

Chemists at Martin Luther University Halle-Wittenberg (MLU) have developed a way to integrate liquids directly into materials during the 3D printing process. This allows, for example, active medical agents to be incorporated into pharmaceutical products or luminous liquids to be integrated into materials, which allow monitoring of damage. The study was published in “Advanced Materials Technologies”.

Inside the 3-D-printed material (right) a lattice structure (left) contains the added liquids. © Harald Rupp / Uni Halle

3D printing is now widely used for a range of applications. Generally, however, the method is limited to materials which are liquefied through heat and become solid after printing. If the finished product is to contain liquid components, these are usually added afterwards. This is time-consuming and costly. “The future lies in more complex methods that combine several production steps,” says Professor Wolfgang Binder from the Institute of Chemistry at MLU. “That is why we were looking for a way to integrate liquids directly into the material during the printing process.”

To this endeavour, Binder and his colleague Harald Rupp combined common 3D printing processes with traditional printing methods such as those used in inkjet or laser printers. Liquids are added drop by drop at the desired location during the extrusion of the basic material. This allows them to be integrated directly and into the material in a targeted manner.

The chemists have been able to show that their method works through two examples. First, they integrated an active liquid substance into a biodegradable material. “We were able to prove that the active ingredient was not affected by the printing process and remained active,” explains Binder. In the pharmaceutical industry, such materials are used as drug depots which can be slowly broken down by the body. They can be used after operations, for example, to prevent inflammation. This new process could facilitate their production.

Secondly, the scientists integrated a luminous liquid into a plastic material. When the material becomes damaged, the liquid leaks out and indicates where the damage has occurred. “You could imprint something like this into a small part of a product that is exposed to particularly high levels of stress,” says Binder. For example, in parts of cars or aircraft that are under a lot of strain. According to Binder, damage to plastic materials has so far been difficult to detect – unlike damage to metals, where X-rays can expose micro-cracks. The new approach could therefore increase safety.

The combined process is also conceivable for many other areas of application, says the chemist. The team soon plans to use the method to print parts of batteries. “Larger quantities cannot be produced in the laboratory with our setup,” Binder explains. In order to produce industrial quantities, the process must be further developed outside the university.

The research was supported by the Leistungszentrum “System- und Biotechnologie”, the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) and by the EU as part of the “Horizon 2020” programme.

References: Rupp, H., Binder, W.H. 3D Printing of Core-Shell Capsule Composites for Post-Reactive and Damage Sensing Applications. Advanced Materials Technologies (2020). doi: 10.1002/admt.202000509 https://onlinelibrary.wiley.com/doi/10.1002/admt.202000509

Provided by Martin-Luther-Universität Halle-Wittenberg

This 3D Printer Doesn’t Gloss Over The Details (Engineering)

A new system enables realistic variations in glossiness across a 3D-printed surface; the advance could aid fine art reproduction and the design of prosthetics.

Shape, color, and gloss.

Those are an object’s three most salient visual features. Currently, 3D printers can reproduce shape and color reasonably well. Gloss, however, remains a challenge. That’s because 3D printing hardware isn’t designed to deal with the different viscosities of the varnishes that lend surfaces a glossy or matte look.

In this image, the left side shows traditional 3D printing, which doesn’t have varying reflectivity. The right side shows the new improvements, where one can choose which surfaces are glossy and which are matte. Credits: Courtesy of the researchers

MIT researcher Michael Foshey and his colleagues may have a solution. They’ve developed a combined hardware and software printing system that uses off-the-shelf varnishes to finish objects with realistic, spatially varying gloss patterns. Foshey calls the advance “a chapter in the book of how to do high-fidelity appearance reproduction using a 3D printer.”

He envisions a range of applications for the technology. It might be used to faithfully reproduce fine art, allowing near-flawless replicas to be distributed to museums without access to originals. It might also help create more realistic-looking prosthetics. Foshey hopes the advance represents a step toward visually perfect 3D printing, “where you could almost not tell the difference between the object and the reproduction.”

Foshey, a mechanical engineer in the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL), will present the paper at next month’s SIGGRAPH Asia conference, along with lead author Michal Piovarči of the University of Lugano in Switzerland. Co-authors include MIT’s Wojciech Matusik, Vahid Babaei of the Max Planck Institute, Szymon Rusinkiewicz of Princeton University, and Piotr Didyk of the University of Lugano.

Glossiness is simply a measure of how much light is reflected from a surface. A high gloss surface is reflective, like a mirror. A low gloss, or matte, surface is unreflective, like concrete. Varnishes that lend a glossy finish tend to be less viscous and to dry into a smooth surface. Varnishes that lend a matte finish are more viscous — closer to honey than water. They contain large polymers that, when dried, protrude randomly from the surface and absorb light. “You have a bunch of these particles popping out of the surface, which gives you that roughness,” says Foshey.

Typical 3D printers can’t handle the high-viscosity varnishes necessary to vary the reflectivity of a surface. Researcher Michael Foshey (CSAIL) and colleagues have developed a new 3D printer to solve this problem. Credits: Courtesy of the researchers

But those polymers pose a dilemma for 3D printers, whose skinny fluid channels and nozzles aren’t built for honey. “They’re very small, and they can get clogged easily,” says Foshey.

The state-of-the-art way to reproduce a surface with spatially varying gloss is labor-intensive: The object is initially printed with high gloss and with support structures covering the spots where a matte finish is ultimately desired. Then the support material is removed to lend roughness to the final surface. “There’s no way of instructing the printer to produce a matte finish in one area, or a glossy finish in another,” says Foshey. So, his team devised one.

They designed a printer with large nozzles and the ability to deposit varnish droplets of varying sizes. The varnish is stored in the printer’s pressurized reservoir, and a needle valve opens and closes to release varnish droplets onto the printing surface. A variety of droplet sizes is achieved by controlling factors like the reservoir pressure and the speed of the needle valve’s movements. The more varnish released, the larger the droplet deposited. The same goes for the speed of the droplet’s release. “The faster it goes, the more it spreads out once it impacts the surface,” says Foshey. “So we essentially vary all these parameters to get the droplet size we want.”

The printer achieves spatially varying gloss through halftoning. In this technique, discrete varnish droplets are arranged in patterns that, when viewed from a distance, appear like a continuous surface. “Our eyes actually do the mixing itself,” says Foshey. The printer uses just three off-the-shelf varnishes — one glossy, one matte, and one in between. By incorporating these varnishes into its preprogrammed halftoning pattern, the printer can yield continuous, spatially varying shades of glossiness across the printing surface.

Along with the hardware, Foshey’s team produced a software pipeline to control the printer’s output. First, the user indicates their desired gloss pattern on the surface to be printed. Next, the printer runs a calibration, trying various halftoning patterns of the three supplied varnishes. Based on the reflectance of those calibration patterns, the printer determines the proper halftoning pattern to use on the final print job to achieve the best possible reproduction. The researchers demonstrated their results on a variety of “2.5D” objects — mostly-flat printouts with textures that varied by half a centimeter in height. “They were impressive,” says Foshey. “They definitely have more of a feel of what you’re actually trying to reproduce.”

The team plans to continue developing the hardware for use on fully-3D objects. Didyk says “the system is designed in such a way that the future integration with commercial 3D printers is possible.”

This work was supported by the National Science Foundation and the European Research council.

References: “Towards Spatially Varying Gloss Reproduction for 3D Printing” https://gfx.cs.princeton.edu/pubs/Piovar%C4%8Di_2020_TSV/glossprint_sga20.pdf

Provided by MIT

3D-printed Glass Enhances Optical Design Flexibility (Optics / Computer)

Lawrence Livermore National Laboratory (LLNL) researchers have used multi-material 3D printing to create tailored gradient refractive index glass optics that could make for better military specialized eyewear and virtual reality goggles.

Artistic rendering of an aspirational future automated production process for custom GRIN optics, showing multi-material 3D printing of a tailored composition optic preform, conversion to glass via heat treatment, polishing and inspection of the final optics with refractive index gradients. Image by Jacob Long and Brian Chavez. ©LLNL

The new technique could achieve a variety of conventional and unconventional optical functions in a flat glass component (with no surface curvature), offering new optical design versatility in environmentally stable glass materials.

The team was able to tailor the gradient in the material compositions by actively controlling the ratio of two different glass-forming pastes or “inks” blended together inline using the direct ink writing (DIW) method of 3D printing. After the composition-varying optical preform is built using DIW, it is then densified to glass and can be finished using conventional optical polishing.

“The change in material composition leads to a change in refractive index once we convert it to glass,” said LLNL scientist Rebecca Dylla-Spears, lead author of a paper appearing today in Science Advances.

The project started in 2016 when the team began looking at ways that additive manufacturing could be used to advance optics and optical systems. Because additive manufacturing offers the ability to control both structure and composition, it provided a new path to manufacturing of gradient refractive index glass lenses.

Gradient refractive index (GRIN) optics provide an alternative to conventionally finished optics. GRIN optics contain a spatial gradient in material composition, which provides a gradient in the material refractive index — altering how light travels through the medium. A GRIN lens can have a flat surface figure yet still perform the same optical function as an equivalent conventional lens.

GRIN optics already exist in nature because of the evolution of eye lenses. Examples can be found in most species, where the change in refractive index across the eye lens is governed by the varying concentration of structural proteins.

An array of polished, 3D printed gradient refractive index lenses made of titania-doped silica glass. Grid squares are 1 millimeter on each side. ©LLNL

The ability to fully spatially control material composition and optical functionality provides new options for GRIN optic design. For example, multiple functionalities could be designed into a single optic, such as focusing combined with correction of common optical aberrations. In addition, it has been shown that the use of optics with combined surface curvature and gradients in refractive index has the potential to reduce the size and weight of optical systems.

By tailoring the index, a curved optic can be replaced with a flat surface, which could reduce finishing costs. Surface curvature also could be added to manipulate light using both bulk and surface effects.

The new technique also can save weight in optical systems. For example, it’s critical that optics used by soldiers in the field are light and portable.

“This is the first time we have combined two different glass materials by 3D printing and demonstrated their function as an optic. Although demonstrated for GRIN, the approach could be used to tailor other material or optical properties as well,” Dylla-Spears said.

Other Livermore researchers involved in the project include Timothy Yee, Koroush Sasan, Du Nguyen, Nikola Dudukovic, Jason Ortega, Michael Johnson, Oscar Herrera, Frederick Ryerson and Lana Wong. The Laboratory Directed Research and Development program funded the work.

Provided by LLNL

3D Bioprinted Heart Provides New Tool For Surgeons (Bioengineering / Engineering)

Professor of Biomedical Engineering Adam Feinberg and his team have created the first full-size 3D bioprinted human heart model using their Freeform Reversible Embedding of Suspended Hydrogels (FRESH) technique. Showcased in a recent video by American Chemical Society and created from MRI data using a specially built 3D printer, the model mimics the elasticity of cardiac tissue and sutures realistically. This milestone represents the culmination of two years of research, holding both immediate promise for surgeons and clinicians, as well as long term implications for the future of bioengineered organ research.

A 3D bioprinted heart model developed by Adam Feinberg and his team. ©Carnegie Mellon University College of Engineering

The FRESH technique of 3D bioprinting was invented in Feinberg’s lab to fill an unfilled demand for 3D printed soft polymers, which lack the rigidity to stand unsupported as in a normal print. FRESH 3D printing uses a needle to inject bioink into a bath of soft hydrogel, which supports the object as it prints. Once finished, a simple application of heat causes the hydrogel to melt away, leaving only the 3D bioprinted object.

While Feinberg’s lab has proven both the versatility and the fidelity of the FRESH technique, the major obstacle to achieving this milestone was printing a human heart at full scale. This necessitated the building of a new 3D printer custom made to hold a gel support bath large enough to print at the desired size, as well as minor software changes to maintain the speed and fidelity of the print.

A needle prints the alginate into a hydrogel bath, which is later melted away to leave the finished model. ©Carnegie Mellon University College of Engineering

Major hospitals often have facilities for 3D printing models of a patient’s body to help surgeons educate patients and plan for the actual procedure, however these tissues and organs can only be modeled in hard plastic or rubber. Feinberg’s team’s heart is made from a soft natural polymer called alginate, giving it properties similar to real cardiac tissue. For surgeons, this enables the creation of models that can cut, suture, and be manipulated in ways similar to a real heart. Feinberg’s immediate goal is to begin working with surgeons and clinicians to fine tune their technique and ensure it’s ready for the hospital setting.

“We can now build a model that not only allows for visual planning, but allows for physical practice,” says Feinberg. “The surgeon can manipulate it and have it actually respond like real tissue, so that when they get into the operating site they’ve got an additional layer of realistic practice in that setting.”

Modeling incorporates imaging data into the final 3D printed object. ©Carnegie Mellon University College of Engineering

This paper represents another important marker on the long path to bioengineering a functional human organ. Soft, biocompatible scaffolds like that created by Feinberg’s group may one day provide the structure onto which cells adhere and form an organ system, placing biomedicine one step closer to the ability to repair or replace full human organs.

“While major hurdles still exist in bioprinting a full-sized functional human heart, we are proud to help establish its foundational groundwork using the FRESH platform while showing immediate applications for realistic surgical simulation,” added Eman Mirdamadi, lead author on the publication.

Published in ACS Biomaterials Science and Engineering, the paper was co-authored by Feinberg’s students Joshua W. Tashman, Daniel J. Shiwarski, Rachelle N. Palchesko, and former student Eman Mirdamadi.

References: Eman Mirdamadi, Joshua W. Tashman, Daniel J. Shiwarski, Rachelle N. Palchesko, and Adam W. Feinberg, “FRESH 3D Bioprinting a Full-Size Model of the Human Heart”, ACS Biomater. Sci. Eng. 2020, 6, 11, 6453–6459. https://doi.org/10.1021/acsbiomaterials.0c01133

Provided by Carnegie Mellon University