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3D Printed Surfboard: Researchers Test Different Bio-Inspired Core Structures

Just as a New Zealand-based surfer was inspired by the humpback whale and the microgrooves of shark skin when creating his surfboard fins, so too was a team of international researchers inspired by the natural world in their structure study of an on-water sports board. In their recently published paper, “3D Printing On-Water Sports Boards with Bio-Inspired Core Designs,” they explain their work advancing the board by using 3D printing and different bio-inspired core structures, such as the honeycomb.

“Modeling and analyzing the sports equipment for injury prevention, reduction in cost, and performance enhancement have gained considerable attention in the sports engineering community. In this regard, the structure study of on-water sports board (surfboard, kiteboard, and skimboard) is vital due to its close relation with environmental and human health as well as performance and safety of the board,” the researchers wrote.

(a) A natural honeycomb structure; (b) the designed honeycomb core inspired by nature.

3D printing has often been used in the sports field, but in previous studies about 3D printed boards, researchers mainly focused on the geometry, only making small modifications to the equipment. This research team actually introduced different patterns to use as the board’s internal core structure. FDM technology and PLA materials were used to make the first sample board, featuring a uniform honeycomb structure that was created with the help of CATIA V5 software.

Most modern boards feature a sandwich structure, where a thin outer shell covers an inner core made of foam, which allows for increased buoyancy and stability, less weight, and improved bending resistance. These structures typically feature a top shell, the lightweight core, and a bottom shell, but this board merged the bottom shell with the core.

“A smaller scale version of a real on-water sports board was designed,” the researchers wrote. “The board had a 48 mm width and 144 mm length with a 357 mm radius curvature at two sides. A bottom curvature of 600 mm was considered, resulting in a model closer to the real one. The hexagonal honeycomb structure formed the core of the board, and was repeated across the specimen.”

The honeycombs were 3 mm wide, and patterned with 1 mm thick walls, while the bottom and top shells had thicknesses of 5 and 1.5 mm, respectively. The team used an XYZprinting da Vinci 1.0 Pro 3D printer to make the sample board with a uniform honeycomb structure.

(a) Two separate 3D printed parts of the board; (b) two parts glued together with strong adhesive.

Surfboard fractures frequently happen between the surfer’s feet, in the board’s middle section. Usually, this occurs because the lip of the wave impacts in the middle and rips it into two parts after the surfer falls into the water, or because the surfer’s feet get too close together and concentrate their body’s pressure in the middle.

“In both of these circumstances, an immense force acts upon the middle portion of the board, causing large bending stress that may result in breakage,” the researchers explained.

“As both of these breakages are caused by bending stresses, a mechanical three-point bending test could be employed to determine the strength of the board in such loading.”

The board with a uniform honeycomb structure core under three-point bending test.

The team tested the honeycomb board under 3-point loading, though they had to change the grippers for the test.

“The test with the strain rate of 0.001 s−1 was carried out at room temperature with an 80 mm distance between two supports. A displacement-controlled test was conducted to get a maximum deflection of 4 mm in the elastic range.”

I-shaped beam and the board with equivalent sections shown with orange lines.

In order to validate these results, and model the structure’s deformation under the test, the researchers developed a “geometrically linear analytical method,” using an equivalent I-shaped section with geometrical stiffness varied along the X-axis, to simulate the honeycomb structure. Then, a geometrically non-linear finite element method, based on ABAQUS software, simulated the boards with a variety of different core structures under the three-point bending test.

Boundary conditions of the finite element method model.

A bending test was simulated to validate the FEM model, and the team performed a mesh sensitivity analysis to make sure the numerical results were accurate. Then, they applied the same test to the sample board with the honeycomb core for a 4 mm maximum deflection. The maximum stress of ∼40 MPa, found in the middle of the board, was low enough to keep the board “in the desired elastic region.” For comparison, the PLA had a yield test level of 60 MPa.

Von Mises stress contour of the board with the uniform honeycomb core.

“The force–deflection curve for the experimental, geometrically non-linear numerical, and geometrically linear analytical results are plotted and compared to each other in Figure 13,” the researchers explained. “The preliminary conclusion drawn from this figure is the fact that the PLA board shows a linear elastic deformation up to 300 N force, beyond which the material yields, followed by plastic deformation that is manifested as a plateau after 500 N.”

Comparison of the experimental, numerical, and analytical load–deflection curves for the three-point bending test of the honeycomb and fully-filled boards.

Once the team had validated the geometrically non-linear FEM model for the board with the honeycomb core structure, they simulated other patterns for the bottom shell’s core. Performing the three-point bending test with the geometrically non-linear FEM software package ABAQUS, while the board’s total volume was kept constant, helped them find the structure with the maximal bending resistance. The different structures they tested were:

  • Hexagonal-Rhomic (HR) Structure
  • Triangular Honeycomb Structure
  • Hexagonal Carbon Lattice
  • Pine Cone and Sunflower-Inspired Patterns
  • Spiderweb-Inspired Pattern
  • Functionally Graded (FG) Honeycomb Structure

“For all of the structures, the mesh convergence study was conducted and the appropriate number of elements for the FEM model was selected,” the researchers wrote. “Furthermore, the maximum stresses of all boards with various core structures were figured to have shown a maximum stress lower than the yield stress of the PLA material.”

(a) A pinecone with two 8-number and 13-number opposite directional spirals; (b) Sunflower with Fibonacci spiral; (c) Pinecone-inspired structure designed using Fibonacci spirals.

They found that the board with the FG honeycomb structure had the best bending performance – 31% better, in fact, than the board with the uniform honeycomb structure at 500 N force. This means that it can tolerate maximum forces, as opposed to an intermediate force like the rest of the structures.

“Due to the absence of similar designs and results in the literature, this paper is expected to advance the state of the art of on-water sports boards and provide designers with structures that could enhance the performance of sports equipment,” the researchers concluded.

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Slovakia: Experimenting with 3D Printed PLA Scaffolds for Bone Regeneration

Researchers from Slovakia are delving further into the uses of PLA in bioprinting, releasing their findings in the recently published, ‘3D printed Polylactid Acid based porous scaffold for bone tissue engineering: an in vitro study.’

The team created samples in the form of PLA scaffolds, assessing for both cytotoxicity and biocompatibility, with the ultimate goal of bone tissue engineering meant to assist in bone regeneration—one of the most challenging areas. Researchers have performed a wide range of different studies regarding bioprinting and bone regeneration, creating a variety of structures, scaffolds, and using different printing methods.

PLA has been used before, commonly, and while here the researchers use a commercially available type of PLA scaffolds, they separated samples into three different groups, each pre-treated with:

  • Complete culture medium
  • Bovine fetal serum
  • Human blood

Further, the research team analyzed periosteum-derived cells in terms of cytotoxicity and biocompatibility.

Properties of used material and properties of printing process

Scaffolds were created using FFF 3D printing (bq Witbox), with scaffold samples of 10 ´ 10 ´ 4 mm and porosity of 61%. Periosteum was taken from the proximal tibia of a 55-year-old female patient who was undergoing a knee replacement surgery. Her consent was given and the Ethical Committee of The University Hospital of Louis Pasteur in Košice approved the process.

“Subsequently, cells were collected by centrifugation at 150 ´ g for 7 min and seeded 25,000 cells/cm2 in a 25 cm2 culture flask (T25) containing Alpha-modified Minimal Essential Medium (Invitrogen, GIBCO®, USA) supplemented with 10% foetal bovine serum (FBS, Invitrogen, GIBCO®, USA) and 1% ATB,” explained the researchers.

“Non-adherent cells were removed after 5 days by changing the medium. Adherent cells were cultured under standard culture conditions at 37 °C in 5% CO2 humidified atmosphere and the medium was replaced every 2–3 days. Confluent cell layers were dissociated with 0.05% Trypsin-EDTA solution (Invitrogen, GIBCO®, USA) and the number and viability of cells was assessed by TC10™ Automated Cell Counter (Bio-Rad Laboratories). Periosteum – derived osteoprogenitor cells (PDO) from the third passage (P3) – were used for the flow cytometry analysis and co-cultivation with scaffold.”

The scaffolds were sterilized, and then separated into the three groups:

“First group was incubated within human serum, second in complete medium containing Alpha- -modified minimal essential medium supplemented with 10% FBS and 1% ATB, and third in 10% FBS.”

Printed scaffolds prepared by technology FFF, shown by Computed Industrial Tomography

Grafical outputs of scaffolds-internal structure of scaffold:
A) Top View (119%), B) Right view (167%)

Cells were measured four times and compared to the control group. The results yielded good biocompatibility; however, the researchers noted the best results in the scaffolds coated with human serum. This treatment also encouraged cell growth.

Proliferation of periosteum derived osteoprogenitors during co-cultivation with PLA scaffolds, measured after 1, 6, 11, and 14 days, respectively by CellTiter 96® AQueous One Solution Cell Proliferation Assay. Data represent mean ± SD value of four independent measures and value of p was p < 0.05 the first day of co-cultivation (*) or p < 0.01 in other days of co-culture (**)

“The distribution, adhesion and proliferation of human PDO on the native PLA scaffolds were also examined using SEM observation during two weeks of cultivation. The human PDOs showed good viability in the scaffolds, which were incubated for 48 hours in human serum, which was expressed by enhanced cellular spreading and proliferation and the pH of media, in which scaffolds and cells were co-cultivated, was 7.4 after 14 days. The pH reached the value of the one in human blood,” concluded the researchers.

“The obtained PLA porous scaffolds favored attachment periosteum derived progenitors and proliferation, furthermore, cells penetrated into the scaffold through the interstitial pores, which was meaningful for cytocompatibility evaluation. New strategies, such as poly-therapy by using scaffolds, healing promotion factors and stem cells, and finally three-dimensional printings, are in their preliminary stages, but may offer new exciting alternatives in the near future.”

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 printed Polylactid Acid based porous scaffold for bone tissue engineering: an in vitro study’]

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Climate Disrupted: The Problem(s) with PLA

While our ecosystem is collapsing, we are at the very least fortunate to witness the rise of a potentially more sustainable form of manufacturing coinciding with the rise of potentially more sustainable materials. In the next few articles, we will cover both the new materials that are emerging for use with 3D printing, as well as the ways that 3D printing might contribute to a climate disrupted world.

As discussed in a previous story, oil majors are hoping to shift to petrochemicals as the world attempts to replace fossil fuels with renewable energy. Due to the historic role these conglomerates have played in our ongoing ecological collapse as well as the basic need to move away from fossil fuels altogether, industrial society might instead aim to supplant petro-based polymers with polymers derived from other natural sources.

In this series, we’ll discuss biopolymers that could become prominent feedstock in additive manufacturing (AM), as well as some that are already being used in 3D printing. One of them is so important, however, that it’s worth spending an entire article on the topic. Naturally, we have start to with polylactic acid (PLA).

Where Does PLA Come from?

PLA is the most popular material for desktop 3D printers, largely due to the fact that it is easy to process and has decent durability. Many 3D printer operators also believe PLA to be safe since it is derived from natural materials. PLA is made from natural sugars, which can be derived from corn starch, sugarcane, as well as cassava roots, chips or starch. In part due to the massive corn subsidies in the U.S., the most widely available brand of PLA is the corn-based Ingeo from NatureWorks, jointly owned by Cargill, the largest privately owned company in the U.S., and the Thai state-owned oil and gas business PTT Public Company Limited. The second-largest PLA manufacturer is Corbion, which manufactures Luminy brand PLA from sugarcane.

Ingeo comes from a specific breed of corn known as grade #2 yellow dent corn (or “field corn”), grown for industrial purposes such as livestock feed, sweetener, ethanol, starch for adhesives and other materials, and Ingeo. PLA is made only from the kernels of the corn, which are milled before the starch is extracted and converted from glucose to dextrose. Microorganisms ferment the dextrose into lactic acid, which is then converted into lactide and formed into long polymer chains using ring-opening polymerization to create PLA.

How Sustainable is PLA?

Instinct might tell us that PLA is more sustainable than petro-based plastics because they are not derived from petroleum or natural gas, but from biomass. Therefore, supplanting petroplastics with PLA could reduce the 1 percent of U.S. greenhouse gas (GHG) emissions associated with plastic production. In fact, a 2017 study determined that doing so would reduce GHG emissions by 25 percent and that, by powering plastic production facilities (PLA or not) with renewable energy, emissions could be cut by 50 to 75 percent.

However, there are other factors to consider related to PLA that should be taken into account, many of which are associated with the crops used to make PLA. PLA releases fewer GHGs from outgassing as it degrades in the environment when compared to petro-plastics; however, the fertilizers and pesticides used to grow the plants that make up PLA in the first place could release more pollutants. This could be reduced by switching to organic, non-genetically modified crops. In the meantime, NatureWorks gives its customers the option of purchasing non-GMO Ingeo, but the default product uses GMO plants, which are correlated with higher pesticide usage.

Moreover, fertilizers used to grow PLA feedstock are responsible for a large amount of GHG emissions. Nitrous oxide, a byproduct of low-cost, nitrogen-based fertilizers, is 310-times more potent than carbon dioxide. A competing bioplastic manufacturer calculated that, “if Natureworks was at full capacity in production it would create 56 [terra grams] of carbon dioxide equivalent more than all of the landfills combined in the United States…”

Image courtesy of Filabot.

PLA is also considered compostable and recyclable, but it such a categorization is misleading due to the fact that it can only be composted in an industrial compositing facility. Only one-quarter of the 113 total such facilities in the U.S. accept residential waste. In other words, not only is PLA not compostable in one’s backyard, but it is even difficult to compost via municipal waste collection in the U.S.

An industrial composting facility. Image courtesy of BioCycle.

As a result, PLA in the U.S. tends to end up in landfills, with researchers unable to determine the exact natural decomposition rate but estimating between 100 and 1,000 years. As it decomposes, it releases methane, a gas 23 times more potent than carbon dioxide.

We should also note the amount of water required to make PLA, which is about 2.5-times less than is needed to produce Styrofoam but 38 percent more than polypropylene and 10 percent more than PET. If we look at total water usage throughout production, some estimates state that around 50 Kg of water is needed for one kilogram of PLA. This is probably higher than you imagined but is still significantly lower than the 700 Kg needed for one kilogram of Polyamide 66. If we look at the water footprint of bioplastics one researcher found that PLA compares well to almost all bioplastics in that regard.

We might consider the amount of land that PLA feedstock requires. The Plastic Pollution Coalition projected that, to meet global demand for bioplastics by 2019, 3.4 million acres of land (bigger than Belgium, the Netherlands and Denmark combined), would be required. In a climate-disrupted world with a rising population, where agricultural yields are shrinking as a result of volatile weather, increased drought, and more pests, land for bioplastics will be competing with land used for food production.

This is then linked to how land by PLA manufacturing agro-businesses is used. Putting aside its issues that aren’t directly tied to the climate crisis—such as its human rights abuses, child trafficking and land grabs—Cargill has been heavily involved in deforestation to make room for the production of its crops, such as soy, palm oil and cocoa.

For all of these reasons, we will have to thoughtfully consider the role that we want plastics, petro-based or otherwise, to play in a society constrained by climate disruption. In the next section of this series, we will consider more of these bioplastics with the hope of overcoming some of the issues associated with desktop 3D printing’s favorite plastic, PLA.

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Exploring the Spongy Properties of Foaming PLA @CNC_Kitchen

In this episode of CNC Kitchen, Stefan does some experimenting with Colorfabb Light-Weight PLA filament.

LW-PLA is a type of PLA filament that creates microscopic bubbles in the material during the printing process. This can lower the density of your prints by almost 60%. Stefan tests for printability and strength of the LW-PLA at different degrees of foaming to determine which applications this material might be useful for.

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Seoul: Assessing Infill Densities for Better 3D Printing of Models in Radiation Therapy

In the recently published Radiological Characteristics of Materials Used in 3-Dimensional Printing with Various Infill Densities,’ researchers from the Veterans Health Service Medical Center in Seoul, Korea are assessing new materials for 3D printing.

With a focus on how infill densities affect 3D printing techniques, the research team considered a wide variety of materials, evaluated by examining their Hounsfield units—a measurement commonly used in the radiology field to measure radio density.

In this study, the researchers are even more specifically concerned with radiation oncology and the fabrication of improved compensators—tools that help target the exact areas where radiation is to be delivered to tumors. The key is to kill the tumor while preventing as much of the surrounding organs as possible from being exposed to radiation.

The technology of 3D printing offers great results in the medical field today by way of 3D printed medical models, devices like implants, prosthetics, and more, and a variety of guides. Here, metal compensators are fabricated after being completely customized to the patient’s shape, refining the uniformity of dosage—and offering an improvement over conventional methods.

3D printed models may also be used to target the radiation at the skin’s surface. The researchers point out that many efforts have been made so far to create better quality assurance in radiation therapy too by making phantoms, derived from CD data converted into 3D printing files.

While 3D printers play an obvious and enormous role in digital fabrication, the science of materials is one of great study today and of critical importance in making medical models and devices.

Specifications for 3-dimensional printer

Printing settings in Z-Suite program to select the infill density values.

Six different materials were assessed regarding the effects of infill density with a Zortrax M300 Plus:

  • ABS
  • ULTRAT
  • HIPS
  • PETG
  • PLA
  • FLEX

Physical characteristics of materials used in 3-dimensional printing

With Z-suite software designed for the Zortrax printer, the researchers could print with various infill densities, allowing them to make a variety of samples: 4×4×2 cm rectangles made from HIPS and PLA

For the study experiments, samples were created as follows:

“… six printing materials, each at an infill density of 60%. ABS, ULTRAT, HIPS, PETG, PLA, and FLEX had HU values of −535±12, −557±10, −542±7, −508±20, −530±25, and −633±15, respectively. The HU values were similar regardless of the specific density of the materials.”

Hounsfield unit (HU) values of materials used in 3-dimensional printing with infill density of 60%

Correlations between Hounsfield unit (HUs) and infill density values for high impact polystyrene (HIPS) and polylactic acid (PLA) are plotted with dashed lines, respectively. Polynomial fitting curves for these correlations for HIPS and PLA are plotted with solid lines, respectively.

Values of HIPS and PLA were evaluated, with the scientists considering also how long it took to 3D print each material at a specific infill density, as follows:

  • Average printing time of 32 minutes with infill density of 10%
  • Average printing time of 12 hours and 45 minutes with infill density of 100%

“Considering that the volume of each prepared cube was 32 m3, a printing time of 12 hours and 45 minutes could be considered quite wasteful. Using 100% infill density should therefore be carefully considered while manufacturing patient-specific human phantoms,” concluded the researchers.

“The results suggest that using optimized infill densities will help improve the quality of radiation therapy by producing customized instruments for each field of radiation therapy.”

(a) High impact polystyrene material with infill density values from 10% to 100% and (b) computed tomography (CT) images in coronal view obtained by the Brilliance CT Big Bore™.

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.

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Australian Researchers 3D Printing Tactile Sensors with TPU and PLA Composites

In the recently published ‘An Ultrasensitive 3D Printed Tactile Sensor for Soft Robotics,’ Australian researchers Saeb Mousavi, David Howard, Chun Wang, and Shuying Wu create a new method for production of piezo-resistive tactile sensors for soft robotics, using FDM 3D printing with thermoplastic polyurethane (TPU) and a polylactic acid-graphene (PLA-G) composite.

Fabrication of tactile sensors via 3D printing are receiving increasingly more attention due to the benefits offered—from greater affordability overall to increased speed in production, and the ability to use multiple materials, including graphene. Due to ‘superior surface area’ and high conductivity, graphene shows great promise as a material for tactile sensing. Thermoplastics are accessible and affordable, and easy to print. No post-processing is required, and stronger bonding occurs for embedded networks due to greater hardness in the graphite.

For this study, the researchers used polylactic acidgraphene (PLA-G) conductive polymer composite (CPC) as a piezoresistive sensing material for 3D printing tactile sensors. They 3D printed a stretchable sensor, testing performance by assessing the bending angle and wide pressure range. While the sample the researchers created for this study was basic, it shows promise for the ability to 3D print and use more complex geometries later as the material is sensitive to the differences in pressure and bending.

“The ability to integrate structural and sensing materials into one printed part gives several advantages and bypasses some of the limitations of conventional fabrication methods,” state the researchers. “This sensor can easily be integrated or attached to soft robotic actuators for acquiring tactile information.”

Because PLA is not flexible, they created the PLA-G composite to work as a layer sandwiched between the TPU (here, the research team used Ninjaflex), with no ‘debonding’ noted.

3D printed sensor. PLA-G is sandwiched between two layers of TPU. At the two ends, PLA-G is designed to be exposed to facilitate wire bonding.

“The sensor was glued at two ends on an aluminum hinge to test its sensitivity to confined bending. During each experiment, the hinge was bended to a certain degree and returned to its original state rapidly,” explained the researchers. “By measuring the initial gauge length and the radius of curvature, the corresponding strain (ε) induced in the sensor for each bending angle was calculated (ε = ΔL/L0), and the gauge factor (GF) was calculated subsequently (GF = (ΔR/R0)/ε).”

Bending angle detection results. The sensor was fixed at two ends on a hinge. The gauge factor (GF) was calculated by calculating the induced strain in each bending cycle.

The researchers used a load cell to apply contact pressure on the sensor as they evaluated its ability to detect pressure. Three different applied pressures were used during the experiments.

Contact pressure detection results. The inset shows the result for the smallest detectable pressure (292 Pa).

“The thermoplastic filaments facilitate the process, because no curing or post-processing is required. Furthermore, this sensor can be printed or attached on any surface (e.g. on soft actuators) and can give accurate and reliable tactile feedback. The ability to sense contact pressure and bending angle is crucial for a soft actuator and this sensor proved to be a very good candidate to develop such robotic actuators in future,” concluded the researchers.

Soft robotics continue to progress for a wide range of industrial applications, accompanied by 3D printing, whether creating new frameworks, metamaterials to work with robotics, or 4D concepts.

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: ‘An Ultrasensitive 3D Printed Tactile Sensor for Soft Robotics’]

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New Method for Circular Chemical Recycling of PLA

In existing mechanical recycling processes, plastic items are chopped into fine pieces, melted and extruded into new plastic feedstock, which causes them to degrade in quality. Recycled virgin plastic is often used for lower grade applications, including park benches, water pipes, and traffic cones. For that reason, scientists from the Universities of Bath and Birmingham are researching a method of chemical recycling that breaks polymers like PLA and PETG into their base molecules.

The paper, published in ChemSusChem, describes how McKeown et al., sought about developing a viable method of chemically recycling PLA plastic into its constituent chemical components. Using a complex made up of zinc as a catalyst, the team successfully performed the break up of PLA and the formation of lactic acid, the basis for PLA plastic. The researchers employed several zinc complexes for dissolving PLA samples, with the most active complex consuming the PLA completely within 30 minutes.

Though PLA is often described as biodegradable and compostable, it is only biodegradable in industrial composting facilities and not in backyard composters. Moreover, it is not easily recycled in traditional recycling facilities and usually ends up in landfills.

The research team was able to derive different constituent materials depending on the exact nature of the zinc complex. When combined with ethanol as a solvent, for instance, the zinc complex was able to form alkyl lactates, which are considered “green” solvents and, therefore, a useful and potentially sustainable result of PLA recycling. In addition to PLA, the researchers were able to run small tests on the recycling of PET, the plastic used to make water bottles, using the same process.

While chemical recycling has been demonstrated in the past, the researchers consider the zinc complexes used in this study to be more environmentally friendly than catalysts used in previous methods of chemical recycling. The team was also able to perform the recycling at lower temperatures, which means less energy was used. The scale at which the recycling was carried out was very small, but the University of Birmingham team is exploring ways to scale the system up to produce larger quantities of starting chemicals.

Compared to fossil fuel used for transportation, electricity and industrial applications, plastics represent a small, but still significant portion of industrialized society’s carbon footprint. Finding the global numbers is a bit more difficult, but the production of plastics makes up 1 percent of U.S. greenhouse gas (GHG) emissions and 3 percent of the country’s primary energy use. Moreover, the Center for International Environmental Law points out that, as polymers are often made using the byproducts of fossil fuel extraction, “the two product chains [plastics and fossil fuels] are intimately linked.”

If society wants to maintain any semblance of its current industrial and consumer form, it will be necessary to ditch the petro-plastics, leaving industrialized society in need of alternatives. This means recycling the plastics we do have and finding other sources for our polymers. For the moment, the dominant form of polymer not derived from fossil fuels is polylactic acid (PLA), primarily derived from the sugar in corn starch and sugarcane, as well as cassava roots, chips or starch.

A 2017 study suggested that by using PLA as a replacement for plastics derived from fossil fuels, GHG emissions could be cut by 25 percent. Using renewable energy sources to power PLA production could reduce emissions even further. However, switching to PLA alone is not enough to completely drop its ecological impact. The material must be disposed of and recycled properly.

PLA releases GHGs as it degrades, though fewer than its petro-based counterparts, and, according to a 2010 study, it may release more pollutants due to the fertilizers and pesticides used to grow the crops that serve as the basis for PLA. NatureWorks, the largest supplier of PLA, allows partners to purchase Ingeo made without genetically modified (GM) crops. However, the use of GM plants is the default practice and, because GM plants have high pesticide resistance, they are typically linked to increased pesticide usage.

The actual growing of the feedstock for PLA also results in its own significant GHG emissions with the nitrous oxide used in low-cost fertilizers 310 times as powerful in terms of its effect on the atmosphere than CO2 and 15 times more powerful than methane. According to one calculation the use of these fertilizers in NatureWorks products results in the emission of “56 Tg of carbon dioxide equivalent, more than all of the landfills combined in the United States according to the US Gas and Sinks.”

In other words, the sort of circular economy envisioned by the Bath and Birmingham scientists is needed more than one might even imagine. Of course, it’s important to remember that, even in such a scenario, this process is not a zero-sum game. It still requires extra material and energy inputs to recycle the plastic, which have to come from somewhere.

In this case, zinc is the major material input, though at very small quantities. Though the U.S. has its own share of zinc reserves, it imported nearly as much refined zinc as the amount of raw zinc that it produced in 2018. Other industrialized countries, like every country in Europe except for Sweden, have no zinc reserves of their own and must rely on imports entirely, which means shipping, which means more emissions.

This may sound like needless nitpicking but given the fact that our ecosystem is collapsing due in no small part to global society’s near-total reliance on fossil fuels, it is completely necessary to consider every material input and output when embarking on new technological endeavors. Such an accounting probably should have been employed form the beginning, but you live and you learn, right?

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Stabilizing Electrospun Nanofiber Mats Through 3D Printing

In the recently published ‘Stabilization of Electrospun Nanofiber Mats Used for Filters by 3D Printing,’ international researchers explore the technology of electrospinning in detail, attempting to refine production of nanofiber mats used in applications requiring large areas of material like medical wound dressing, biotechnological procedures, and catalyzers.

Nanofiber mats may require added stability, often possible through the following:

  • Heat pressing
  • Ultrasonic welding of several other mats
  • Coating of mats
  • Laminating
  • Crosslinking fibers
  • Embedding nanofiber mats into textile composites

As the study of mechanical properties and improvement thereof continues to be a central focus in 3D printing, research like this also targets better ways to increase stability. For this study, samples were evaluated on a simple Orcabot XXL FDM 3D printer, using PLA as the material.

3D printing with fused deposition modeling (FDM) technology on a polyacrylonitrile (PAN) nanofiber mat. The printing polymer PLA (here green) is delivered as a filament into the nozzle in a molten state and placed on the nanofiber mat.

During this research, the authors discovered that to 3D print on nanofiber mats with success, the distance between the nozzle and the nanofiber mat had to be controlled precisely:

“On the one hand, the nanofiber mat breaks at once if the distance is too small or the nozzle even touches the mat, which is opposite to 3D printing on woven, warp knitted, or weft knitted fabrics, where it can be advantageous in terms of adhesion for pressing the filament into the textile by printing “below” the textile surface,” stated the researchers. “On the other hand, if the distance is too large, the contact between both materials is lost, resulting in a very uneven surface.”

During testing, nanofiber mats were glued onto the printing bed, with varying degrees in temperature. They discovered that adhesion was ‘strongly supported’ at a temperature of 60 °C or higher, while advancing to 80 °C caused ‘severe problems.’

“Since heating the printing bed did not show any advantage, the results depicted here were gained with the printing bed at room temperature,” stated the researchers.

The team also noted that it would seem adhesion problems occur when the nozzle is set ‘slightly too high’ due to electrostatic repulsion between printing materials and the mat. Soaking and drying the sample in water or a soapy solution did support relaxation, however, leading the research team to deem such treatment advantageous and beneficial to any 3D printing with nanofiber mats.

3D printing squares of dimensions 40 mm × 40 mm on nanofiber mats previously dipped in soap water: (a) rough surface for a too large distance between nanofiber mat and printing nozzle; (b) 3D printed layer with uneven surface and even several not closed areas near the diagonal, i.e., along the longest lines, due to a too large distance between nozzle and nanofiber mat.

Confocal laser scanning microscope (CLSM) images of polyacrylonitrile (PAN) nanofiber mats: (a) pure PAN (electrospun with 80 kV), (b) pure PAN (electrospun with 80 kV) after printing on the other side of the nanofiber mat, (c) carbonized PAN (electrospun with 50 kV), and (d) carbonized PAN (electrospun with 50 kV) after printing on the other side of the nanofiber mat.

“Optical and chemical examinations revealed that the nanofiber mats were not measurably modified by the 3D printing process. Contact angle examinations did not show significant differences in hydrophilicity, comparing the pure nanofiber mat and the composite surface,” concluded the researchers.

“While in this first proof-of-principle, a full layer was 3D printed on the nanofiber mats, as the composites could be used in filter applications with the liquid flow parallel to them, future experiments have to be conducted to investigate the possibility to print open mesh-like structures on nanofiber mats to also enable utilization in filters through which the liquid flows.”

Researchers continue to study methods in electrospinning, from bone regeneration to bioprinting, wound repair, 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.

Electrospun nanofiber mat in Martindale abrasion test holder, (a) before the test, (b) after 10 cycles in dry state, and (c) after one cycle in wet state.

[Source / Images: ‘Stabilization of Electrospun Nanofiber Mats Used for Filters by 3D Printing’]

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3D Printing to Study Behavior of 3D Miura-Ori Column Structures

In the recently published ‘Study on the compressive behavior of Miura origami column structure,’ authors I.G.R. Permana, M. Rismalia, S.C. Hidajat, A.B. Nadiyanto, and F. Triawan explored the mechanical properties of Miura-origami patterns. Because their versatility—mainly in foldability—is a source of continued fascination, the researchers chose to study the mechanical behavior when 3D printed.

An ancient Japanese art that is both a source of fascination and reverence around the world, origami is becoming increasingly more popular in engineering applications due to its potential for design in aerospace, energy (such as solar panels), robotics, and more. Some research has also reviewed its potential for energy absorption devices like automotive crash boxes. And while there is little prior knowledge of how Miura-Ori structures function under compressive load, this study investigates the mechanical properties of column structures.

 “The Miura-Ori pattern is constructed with four repeating parallelograms panels which are arranged along the alternating mountain and valley folds as shown in figure 1. The size of each parallelogram for all specimens were kept constant where b = 11 mm and c = 8.66 mm. In this study, the Miura origami column was designed with three folding angle variation (θ = 70o , 90o , 110o ) and two thickness variation (t = 1 mm and 2 mm).”

The unit cell of Miura-Ori pattern.

Front (a) and isometric (b) view of Miura-Ori column structure.

3D printing samples for the research study with PLA, the authors examined variations with both angles in folding and wall thickness of prints. After that, they looked at the energy absorption capacity also. Specimens were comprised of three layers, with compression testing performed and data recorded afterward regarding load and displacement curve.

Specimen dimension.

The researchers discovered that they were able to make the structure stronger by increasing the folding angle of the pattern, realizing that while a low peak force was necessary for the best energy absorption, a high mean crushing force was also required.

“However, due to its geometric constraint, the result showed that the wider folding angle could reduce the energy absorption capacity of the structure,” concluded the researchers. “Finally, the structure with 2 mm wall thickness exhibits higher yield stress, compressive modulus, and energy absorption capacity compared to the 1 mm structure. As a future work, the development of finite element model (FEM) to understand comprehensively the behavior of Miura-Ori column structure will be done.”

Schematic diagram of the compression test.

You might be surprised to find out how often the Japanese inspiration of folding structures and patterns like origami and 3D printing cross paths, from fabrication of metamaterials resulting in a tunable Miura-ori tribe, to expandable structures for engineering applications to mechanisms for creating robots. 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.

Stress-strain curves of Miura-Ori column with 2 mm thickness

[Source / Images: ‘Study on the compressive behavior of Miura origami column structure]

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Silk Fibroin-Reinforced PLA to Make 3D Printed Interlocking Nail for Fracture Healing

A diaphyseal fracture is a common break that occurs along the shaft of a long bone, like the femur, and can be treated with interlocking nails, which are inserted in the bone and transfixed by screws at the ends. But these eventually need to be removed because of complications that can occur when the nails have been implanted for a long time, such as materials like stainless steel not providing a good biological environment for cells.

Researchers S. Pitjamit, K. Thunsiri, W. Nakkiew, and P. Pothacharoen from the Chiang Mai University in Thailand published a paper, titled “Preparation and characterization of silk fibroin from four different species of Thai-local silk cocoon for Bone implanted applications,” about their work using PLA, reinforced with locally sourced silk fibroin material, to 3D print a biocomposite interlocking nail.

Silk may look and feel soft, but the protein fiber is made of 75% biocompatible fibroin, a strong, insoluble material that has multiple applications in the medical field, including sutures, wound healing, and tissue engineering.

“Previous studies have proved that fibroin has good biological and mechanical properties such as biocompatibility, biodegradability, water permeability, non-cytotoxicity and the strength and resiliency of silk fibers,” the researchers wrote. “Silk fibers has an ultimate tensile strength 740 MPa while collagen and polylactic acid has an ultimate tensile strength only 0.9 to 7.4 and 28 to 50 MPa, respectively.”

The team chose four species of local Thai Bombyx mori silk cocoons from which to extract silk fibroin: Nangnoi Srisaket-I (NN), Nanglai (NL), Luang Saraburi (LS), and J108. They cut the cocoons into small pieces, which were then degummed, rinsed, and dried for 24 hours, before being dissolved in a solvent.

The resulting solution was soaked in DI water for three days, with the water changed daily, and then the dialyzed silk solution was filtered and frozen. Finally, in order to create sponges, the frozen solution was lyophilized (freeze-dried).

“After the extraction, fibroins of each silk cocoon species were characterized and compared the physical property by using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDS) and Fourier Transform Infrared Spectroscopy (FT-IR),” the researchers wrote. “Then, the biological test was performed on cell viability and cytotoxicity with human fetal osteoblast cell line.”

The researchers investigated the “conformations of fibroin protein in regenerated each silk scaffolds” using FTIR spectroscopy, and each species showed typical random coil structures and Beta-sheet structures. SEM and EDS tests showed that each of the silk fibroin species had interconnected pores, at an average size of 10-60 microns.

“As shown in Figure 4, silk fibroin weight percentage consist of Carbon (C), Nitrogen (N) and Oxygen (O) element only which symbolize the proteinaceous compounds originating from Silk Bombyx mori,” the team wrote.

Finally, an Alamar blue assay was performed on the four species of silk fibroin solutions, in order to observe cell viability and confirm that they weren’t toxic.

“The comparison of each silk species with control presented that cell viability percentage all scaffolds were not significantly the control (p-value> 0.05) as shown in Figure 5,” the researchers stated.

The results of this test showed that they all had non-cytotoxicity, which means they can be safely used in animal and human bodies.

“The best silk species from biological performance will be used to reinforce PLA interlocking nails using 3DP process in the future study,” the team concluded. “From the result, all of local silk cocoons species present non-cytotoxicity ability which can be used in human or animal body without endangerment. For future work, bio-composite filament for 3DP from silk fibroin reinforcing PLA will be tested and observed the other abilities such as cell proliferation ability, mechanical properties and printing morphology.”

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