Reinforcing Concrete Fabric Formwork with 3D Printed Plastics

In the recently published ‘Tailored flexibility: reinforcing concrete fabric formwork with 3D printed plastics,’ authors Jon Engholt and Dave Pigram create a construction system integrating robotics and new techniques. The study focused on concrete because of its flexibility, while pointing out that this material is still somewhat limited—thus explaining why flat forms are still so often used routinely while curved structures are avoided. Flexible materials offer great potential for improving the structure of buildings, however.

3D printing, accompanied by robotics capable of plastic extrusion, can outweigh some of the previous challenges often connected to fabric framework. This also includes benefits like added options for forms and surface qualities, with plastic working to reinforce material and performing as a design medium too. Concrete is usually cast in molds, and curves are typically considered hard to achieve, leaving users to turn to materials like timber; however, wood and milled foam generally result in significant amounts of waste.

a. Wall by Kenzo Unno (Copyright: Kenzo Unno) b. Facade by Miguel Fisac
(Copyright: Miguel Fisac Foundation) c. P_wall by Matsys Design (Copyright: Andrew Kudless).

“Fabric formwork addresses some of these issues as a sustainable alternative to traditional formwork, utilised as both a means to reduce material use in formwork and a means to realise more complex and structurally efficient forms,” state Engholt and Pigram, also pointing out that there have been strides made with CNC 3D knitting, although the techniques are still somewhat limited.

For this research, they performed numerous tests, including matching extrusion and fabric material, tuning the print technique, and then dealing with the composition of concrete. They also detoured to compare 3D plastic printing to that of fabric frameworks and ‘the logic of tensile shuttering.’ The set up for this experiment consisted of a large-scale plastic extruder mounted on a KUKA 7-axis robotic arm, using ABS. The authors tested numerous fabrics:

“The textural quality and resolution of the fabric presented one variable that suggests perfect conditions for mechanical adhesion of extrusion material by partly penetrating the fabric,” explained the researchers. “The coarse resolution of both tulle fabric and geotextile weaves suggested a sufficiently uneven surface for adhesion.

“However, due to the material composition of these fabrics (tulle made of polyester and geotextile of polypropylene), the chemical bonding properties appeared to be the primary means of adhesion, preventing the extrusion material to bond with the surfaces.”

During the cooling process, the researchers discovered that ABS shrank while cooling, causing warping, and transformation in fit. The problem continued further as printing went on, with the plastic becoming ‘irregularly warped.’ As they experimented with PLA, the researchers found that they were able to get shrinkage under control, but then experienced decreased tensile strength and even brittleness.

“These issues with material strength and shuttering flexibility suggest further studies into printing media with different mechanical properties,” stated the researchers.

Initial casting evaluated shuttering of fabric and plastic extrusion, along with the weight of the concrete. The authors stated that the toolpath generation approach was abandoned; however, they did note that the discrete part toolpath generation permitted structural considerations to become part of the process.

a. Printed shuttering in rigid frame b. Shuttering before demoulding c. Concrete cast.

“The limited strength of the plastic thus introduced two resolutions of support: An overall distribution of clamps and a finer-resolution mesh of printed material – both of which had a finite limit in scale to prevent collapse. Printing bespoke ‘pinch-mould’ details to block out the shuttering and locally create openings through the casts mainly relied on the rigidity of the two clamped sides rather than adhesion and tensile strength – and thus proved efficient.”

a. Printed shuttering b. Fabric shuttering with cast c. Concrete cast.

Because the plastic was so limited, the researchers found two new ‘resolutions of support’ in the distribution of clamps—plus, finer resolution mesh of printed material. Overall, they discovered ‘a vast space of possibilities’ with a small number of variables.

“The process thus affords a high complexity in material manifestation through a low complexity in formal operations and design. Since the flexibility of the tailored shuttering allows it to adapt and attach to non-flat geometries, the process suggests a combination with bespoke bent rebar reinforcement that might offer enough rigidity to avoid any additional formwork components,” concluded the authors.

3D printing encompasses numerous elements, beginning with hardware; however, the study of materials and resulting form is critical—and as the choices continue to expand, users can experiment widely, from the use of different thermoplastics to metal composites, and other alternative materials. 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.

Small selection of combinations of tile designs and pixel distributions

Intersections: a. Horizontal overlap b. Vertical overlap c. Crossing d. Clamp
opening.

[Source / Images: ‘Tailored Flexibility: Reinforcing concrete fabric formwork with 3D printed plastics’]

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Researchers Run Simulation Tests on Their 3D Printed CubeSat Before LEO Mission

A pair of researchers from Shantou University in China explored designing and manufacturing a CubeSat with 3D printing, which we have seen in the past. CubeSats, which are basically miniaturized satellites, offer plenty of advantages in space exploration, such as low cost, a short research cycle, and more lightweight construction, but conventional methods of manufacturing often negate these. Using 3D printing to make CubeSats can help achieve accurate details as well.

[Image: ESA]

The researchers, Zhiyong Chen and Nickolay Zosimovych, recently published a paper on their work titled “Mission Capability Assessment of 3D Printing Cubesats.”

“With the successful development of integrated technologies, many spacecraft subsystems have been continuously miniaturized, and CubeSats have gradually become the main executors of space science exploration missions,” they wrote.

The main task driving research paper is an LEO, or Low Earth Orbit, CubeSat mission, which would need to accelerate to a maximum of 5 g during launch.

“…the internal operating temperature range of the CubeSat is from 0 to 40 °C, external temperature from -80 to 100 °C,” the researchers explained.

During the design process, the duo took into account environmental factors, the received impact load during the launch process, and the surrounding environment once the CubeSat reached orbit. Once they determined the specific design parameters, ANSYS software was used to simulate, analyze, and verify the design’s feasibility.

PLA was used to make the mini satellite, which is obviously shaped like a cube. Each cube cell, called a unit, weighs approximately 1 kg, and has sides measuring 10 cm in length.

“The framework structure for a single CubeSat provides enough internal workspace for the hardware required to run the CubeSat. Although there are various CubeSat structure designs, several consistent design guidelines can be found by comparing these CubeSats,” the researchers wrote about the structure of their CubeSat.

These guidelines include:

  • a cube with a side length of 100 mm
  • 8.5 x 113.5 mm square columns placed at four parallel corners
  • usually made of aluminum for low cost, lightweight, easy machining

The CubeSat needs to be big enough to contain its power subsystem (secondary batteries and solar panels), in addition to the vitally important thermal subsystem, communication system for providing signal connections to ground stations back on Earth, ADCS, and CDH subsystems. It also consists of onboard antennae, radios, data circuit boards, a three-axis stability system, and autonomous navigation software.

“The adoption of this technology changes the concept of primary and secondary structure in the traditional design process, because the whole structure can be produced at the same time, which not only reduces the number of parts, reduces the need for screws and adhesion, but also improves the stability of the overall structure,” the pair wrote about using 3D printing to construct their CubeSat.

The mission overview for this 3D printed CubeSat explains that the device needs to complete performance tests on its camera payload for reliability evaluation, and test the effectiveness of any structures 3D printed “in an orbital environment.”

The Von mises stress diagram of the CubeSat structure.

In order to ensure that it’s ready to operate in LEO, the CubeSat’s structures was analyzed using ANSYS’ finite element analysis (FEA) software, and the researchers also performed a random vibration analysis, so that they can be certain it will hold up under the launch’s impact load.

“The CubeSat structure is validated by the numerical experiment. During launch process, CubeSat will be fixed inside the P-Pod, and the corresponding structural constraints should be added to the numerical model. In addition, the maximum acceleration impact during the launch process should also be considered. Static Structural module of ANSYS is used for calculation and analysis, the results show that the maximum stress of CubeSat Structure is 8.06 MPa, lower than the PLA yield strength of 40 Mpa,” the researchers explained.

Running in LEO, the 3D printed CubeSat will go through a 100°C temperature change, and the structure needs to be able to resist this, so the researchers also conducted a thermal shock test, which showed an acceptable thermal strain.

The thermal strain diagram of the CubeSat structure.

The team also conducted random vibration simulation experiments, so they could conform the structure of the 3D printed CubeSat to emission conditions. They simulated typical launch vibration characteristics, using NASA GEV qualification and acceptance as reference.

“The specific contents of the experiment include “Harmonic Response” and “Random Vibration”. Two identical harmonic response were performed before and after the random vibration test to assess the degree of structural degradation that may result from the launch load,” the researchers explained.

“This experiment helps us to evaluate the natural frequency of the structure, and the peak value indicates that the tested point (bottom panel) has reached the resonant frequency.”

Pre/Post Random Vibration test comparison between the curves of Harmonic Response.

As seen in the above figure, both the trend and peak points of the two curves are close to each other, which shows that there was no structural degradation after the vibration test, and that the structure itself conforms to launch stiffness specifications.

“As the primary performer of today’s space exploration missions, the CubeSat design considers orbit, payload, thermal balance, subsystem layout, and mission requirements. In this research, a CubeSat design for performing LEO tasks was proposed, including power budget, mass distribution, and ground testing, and the CubeSat structure for manufacturing was combined with 3D printing technology,” the researchers concluded.

“The results show that the CubeSat can withstand the launch loads without structural damage and can meet the launch stiffness specification.”

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Improved FDM 3D Printing with Lignin Biocomposites

In the recently published ‘Lignin: A Biopolymer from Forestry Biomass for Biocomposites and 3D Printing,’ international researchers Mihaela Tanase-Opedal, Eduardo Espinosa, Alejandro Rodríguez, and Gary Chinga-Carrasco explore a very specific area of materials related to biopolymers.

As composites are used more often these days to improve existing materials—especially in 3D printing—alternative materials like wood are being experimented with also. Fiber-based biocomposites and lignin can be better options than petrochemical-based products. For this study, the authors gleaned lignin from spruce trees being reduced to pulp. They used the material to create composite filaments, printing sample dogbones to test mechanical properties.

Natural-fiber biocomposites offer the following:

  • Affordability
  • Good mechanical properties
  • No emission of toxins
  • Light weight

PLA is a popular polymer used in 3D printing, and as the authors remind us, it is actually a biopolymer—featuring good mechanical properties, biodegradability, easy melt-processability, and much more; however, it is also not always cost-effective or suitable for every project. As a composite, however, PLA becomes more versatile.

“Each year, over 50 million tons of lignin are produced worldwide as a side product from biorefineries, of which 98% are burned to generate energy. Only 2% of the lignin has been used for other purposes, mainly in applications such as dispersants, adhesives, and fillers,” state the researchers.

“Without modification, lignin can be directly incorporated into a polymeric matrix, such as UV-light stabilizer, antioxidant, flame retardant, plasticizer, and flow enhancer to reduce production cost, reduce plastic, and potentially improve material properties.”

As 3D printing brings so many advantages forth to industrial users, with the ability to create affordable and complex structures, as well as leaving behind less waste and energy usage, materials like lignin are attractive for use when mixed with other polymers. For this study, the researchers focused on PLA/soda lignin biocomposite filament for 3D printing.

“A motivation for selecting soda lignin is that it is sulphur-free. Soda lignin was thus expected to reduce the typical smell that is experienced when melt-processing biocompounds containing kraft lignin or lignosulfonates,” stated the researchers.

Samples were assessed for:

  • Mechanical (tensile testing)
  • Thermal (TGA, DSC analysis)
  • Morphological (SEM)
  • X-ray diffraction
  • Antioxidant properties

An original Prusa i3 MK3S was used in FDM 3D printing of the dogbone samples, with a length of 63mm and width of 3mm. Three sets were printed, as well as a phone case. The biocomposite demonstrated an increase in mechanical properties when temperatures were increased, with elastic modulus decreasing by 25% to 32%. Lignin offered an improvement in ductility, but a decrease in plasticity.

Mechanical properties of PLA and PLA/Lignin biocomposites.

 

Stress−strain curves for the different biocomposites

Antioxidant properties were also confirmed, showing that 3D printed samples with lignin had even more antioxidant capability than PLA, meaning there is the potential for use for other applications such as food packaging.

“The suitability of the PLA/lignin biocomposite filament for 3D printing was also tested, by printing a smartphone protective case,” stated the researchers. “The printing process revealed a good performance of the lignin-containing filament, and a functional protective case was effectively 3D printed. PLA/Lignin filaments are a plausible option for lignin utilization with potential in, e.g., rapid prototyping and consumer products. It is worth to mention that the typical smell from some lignins was not detected during the extrusion of the filaments or during the printing process, which is an additional advantage of using soda lignin in PLA biomaterials.

“Biocomposites exhibited good extrudability and flowability with no observable agglomeration of the lignin. This suggests that lignin-containing biocomposites are plausible alternatives for 3D printing applications.”

3D printing of a smartphone protective case with PLA/lignin biocomposite filament

The use of composites today is a growing trend due to the ability to improve prototypes and parts, from glass composites to copper metal to particle reinforced nanocomposites. 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 – ‘Lignin: A Biopolymer from Forestry Biomass for Biocomposites and 3D Printing’]

 

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Romanian researchers develop 3D printed Geneva drives for advanced mechanisms

Researchers from Politehnica of Bucharest University, Romania, have explored the behaviors of 3D printed gear mechanisms otherwise known as geneva systems. According to the study, published in IOP Conference Series: Materials Science and Engineering, such systems are of great practical importance in applications including weaving looms, precision measurement instruments, automated packaging and printing machinery. Thus, various FFF/FDM materials have […]

Researchers Study Behavior of 3D Printed Geneva Mechanisms

A Geneva drive is a gear that will turn a continuous rotation mechanism into an intermittent rotary motion mechanism by adding a driven wheel to the gear with multiple slots. It then advances a single 90° step each time the drive wheel rotates. Named for its frequent use in Swiss-made watches, it’s still used today in things like movie projectors, and even in 3D printed applications such as novelty items and drug delivery systems.

A team of researchers from the Politehnica of Bucharest University in Romania published a paper, titled “Study behavior of Geneva mechanism using 3D printing technology,” where they considered the use of a variety of materials and technologies for developing, and studying the behavior of, these gears.

The abstract states, “In this paper the authors considered external Geneva mechanism. The design and machining of a conventional Geneva mechanism are generally well known, but there are some particularities, if we consider 3D printing technologies. Conventional, Geneva mechanisms are used to low-speed applications, or to those in which noise and vibration are of no importance. Using PLA+Copper or ABS materials noise and vibrations are reduced considerably. Also, the entire mechanism has a reduced weight. There were considered different fill factors for 3D printed parts. The experimental setup allows fast changing of mechanism parts. This research aims the study of behaviour of 3D Printed machine elements like: springs, bearings, clutches gears, bellows, diaphragms, bushes, brakes, sliders, etc developed by authors.”

A Geneva mechanism is a type of indexing mechanism with a fairly simple design – just a driving crank and wheel, with straight slots. This is known as a Maltese Cross mechanism. Conventional Geneva mechanisms are used for more low-speed applications, where the amount of vibration or noise made doesn’t matter.

The researchers 3D printed five Geneva mechanisms – each with five Maltese crosses and five driving cranks with pins – out of five different materials:

  • Plexiglass
  • PLA
  • ABS
  • PLA + copper
  • PLA + bronze

“The Geneva mechanism translates continuous motion to intermittent motion through the driving wheel whose crank pin is shown in figure 1,” the researchers explained. “It drives the Geneva wheel as it slides into and out of the slot of the Geneva wheel. It thus advances it – one step at a time when engaged. The driver wheel usually consists of both the crank and a raised circular blocking disk that locks the Geneva wheel in position between steps to avoid excessive vibration while rotating.”

Each cross had six slots, but a Matlab environment was used to develop a theoretical study that considered different Geneva mechanisms with z = 3, 4 and 6 slots; you can see these results in Figure 2.

Figure 2. Geneva mechanisms position and speed characteristics with different number of slots

The team also created experimental setups for five mechanisms so they could “determine cinematic parameters of Geneva mechanisms.” They used reflective sensors to find the time between two successive slots.

Figure 3. Operating mode of optical reflective sensors

“When the slot of the Maltese cross is in front of the reflective sensor the reflected beam is interrupted,” the researchers wrote. “Then, the cross is rotating with an angle of 60°. The cross passes in front of the reflective sensor and the time is recorded until the next (successive) slot is reached. When the cross is in front of the reflective sensor the beam is reflected.”

Figure 5. CAD models of Maltese cross

Different angular rotation speeds for the driver crank were also tested for the paper, in order to study the Geneva mechanisms’ cinematic and dynamic behaviors.

The experimental setups with Geneva mechanisms are connected to PC through a USB interface.

Figure 6. Experimental setups PLA (left) and PLEXI (right)

“The models obtained are used as demonstration stands used in didactic applications,” the researchers concluded. “Of the five investigated materials, ABS and PLA + Copper have been proved to have properties and characteristics close to mechanical engineering applications and these results are demonstrated by graphs. ABS also has the advantage of lighter weight, which makes it suitable for applications where low mass is needed. It can also be concluded that the angular speed of the drive element is inversely proportional to the difference between the angular speeds of the Malta crosses.”

Co-authors of the paper are D. RizescuD. BesneaC.I. Rizescu, and E. Moraru.

Figure 7. Geneva mechanisms from different materials: a) PMMA b) PLA c) ABS d) PLA + copper e) PLA + bronze

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Kenyan and Zimbabwean Researchers Study 3D Printed Polymer/PLA on Fabric

Researchers from Kenya and Zimbabwe are tackling more complex 3D printing adhesion and material topics in their recently published, ‘Use of regression to study the effect of fabric parameters on the adhesion of 3D printed PLA polymer onto woven fabrics.’ Familiar with the benefits of 3D printing, and its potential for use with a wide range of materials and fabrics, authors Nonsikelelo Sheron Mpofu, Josphat Igadwa Mwasiagi, Londiwe C. Nkiwane, and David Njuguna experiment further with polylactic acid (PLA) polymer onto a variety of fabrics, including cotton, polyester, and acrylic.

PLA/cotton structure, a before cutting out the fabric parts around the composite and b prepared for loading on the tensile tester for adhesion tests

FDM 3D printing in textiles, while previously extended to the creation of fabric-polymer structures has given researchers challenge, mainly in adhesion due to surface texture. Improvement of such issues could open the door to a much wider range of fabric-polymer combinations. In this research, the scientists created 15 fabric samples, customized using SolidWorks, sliced with Cura, and then 3D printed with PLA. The team then tested the samples for the following:

  • Fabric areal density according to ASTM D3776.
  • Fabric ends/inch according to ASTM D3775.
  • Fabric picks/inch according to ASTM D3775.
  • Warp and weft count according to ASTM D1059-01.
  • Fabric thickness according ASTM D1777.
  • Fibre type according to American Association of Textile Chemists and Colourists (AATCC) 20.

Assessments were based on how texture felt to the human hand, whether smooth or rough, hard or smooth, stiff or limp. A panel of students was chosen to test the surfaces with their eyes covered to ensure judgment based purely on texture and not visuals. They were asked to grade the fabric on a scale on one to five, with one being smoothest and five being roughest.

The researchers noted average scores for the samples, documenting a clear effect on adhesion force. As all the properties being examined (fabric areal density, warp, and weft count, fabric thickness and fabric roughness) were increased, adhesion force increased too—with the opposite being noted for the ends/inch and picks/inch which were negatively correlated to adhesion force.

Adhesion test on the Testometric Micro 500 model tensile tester

“Considering the fiber types used to manufacture the fabrics (acrylic, cotton, polyester/cotton blend and polyester), tests showed that the acrylic based fabrics displayed the highest adhesion force to PLA with polyester based fabrics showing the lowest adhesion force,” concluded the researchers.

While 3D printing and additive manufacturing processes have already offered enormous contributions to nearly every industry, refining the technology has become critical for many users—on all levels—from studying typical problems and making improvements in construction printing to experimenting with ultrasonic vibration, and creating other new filaments, along with using 3D printing materials in fashion, often as additional applications for accessories and items like handbags too.

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Effect of fiber type on adhesion force

PLA/cotton structure, a before cutting out the fabric parts around the composite and b prepared for loading on the tensile tester for adhesion tests

[Source / Images: ‘Use of regression to study the effect of fabric parameters on the adhesion of 3D printed PLA polymer onto woven fabrics’]

 

 

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3D Printed Cellular Fingers Offer Material Balance Required for Modern Robotics

In ‘Toward a Smart Compliant Robotic Gripper Equipped with 3D-Designed Cellular Fingers,’ authors Manpreet Kaur and Woo Soo Kim delve into the world of combining 3D printing and robotics. Their recently published paper focuses on the design of a robotic structure with deformable cellular structures that are easy to fabricate.

The conventional metal robot or robotic components are increasingly being upstaged by softer materials that offer more versatility for industrial applications. Not only that, many of these new materials are able to morph to their environment, affected by environments such as temperature or moisture. Kaur and Kim remind us that many of these innovations are originally inspired by nature, such as the movement of and the frictional properties of the snake.

Design and fabrication of multi‐material auxetic structure: A) 2D sketch of the re‐entrant honeycomb unit cell with defined parameters. B) Schematic demonstration of filament extrusion–based multi‐material 3D printing. C) Different designs of auxetic unit cells with two important parameters, α (the ratio of length of vertical strut h by re‐entrant strut l) and θ (the re‐entrant angle), defined in the sketch (A). D) The CAD image of the 3D re‐entrant honeycomb structure made by joining two 2D structures at 90°. The single tone gray color indicates the usage of a single material that is a TPU‐based flexible material. E) A dual‐material‐based auxetic unit cell where the re‐entrant struts (red) made of flexible material and the vertical struts (gray) made of rigid material. F) Different designs of dual‐material‐based auxetic unit cell, where the joints (gray) are made of flexible material and the rest of the portion of the struts (blue) are printed with the combination of both flexible and rigid material with equal proportion.

In creating soft robotics, however, there is the challenge of finding a balance between flexibility and structural stiffness and incorporating electronics which usually consist of a variety of different bulky systems. The cellular finger noted in this research can be made with embedded sensors in the fingertips, allowing for a significant gripping force of 16N, and the ability to pick up numerous objects—and acting as an example of more complex architectures for better functionality and performance overall.

“Stretching‐dominated cellular solids, such as octet, octahedral, and so on, show higher initial yield strength compared with bending‐dominated foamed materials, which is due to their different layout of structural components and makes them better alternatives for lightweight structural applications. One such unique spatially arranged structure produces a negative Poisson’s ratio (NPR); these are called auxetics. Like other types of mechanical metamaterials, the NPR of auxetics is generally a direct consequence of the topology, where the joints rotate to move the structure,” state the researchers.

Characterization of 3D printed auxetic structures: A) Compressed samples from the design with α = 1.5 and θ = −20°. Three different material distributions in the unit cell (single, dual 1, and dual 2 designs) are studied. Images were captured for each sample at 0%, 20%, and 40% strains. B) Stress–strain graph of three samples with different combinations of α = 1.5, 2 and θ = −20°, −30 ° for designs (single, dual 1, and dual 2). The legends read as “a” for alpha, “t” for theta, and S, D1, D2 for single, dual 1, and dual 2, respectively. C) Finite element analysis (FEA) simulation analysis of compressed auxetic unit cell to study the different stress distributions in the elastic region for the three different designs. The color code is kept constant and is defined next to each image. The corresponding elastic curves from experiment and simulation are compared for each case. D) The cellular finger is designed using the rigid stretching‐dominated octet structure for the main body and using chosen auxetic structure (α = 1.5 and θ = −20°) with dual 2 designs for the joints.

NPR materials are also able to deform and show ‘compliant-bending behavior.’ In this research project, Kaur and Kim used honeycomb structures—again, inspired by nature—examining their ability to absorb energy and bend. These re-entrant structures are more easily translated to the 3D realm and allowed the authors to experiment regarding parameters and resulting cell properties. The end goal was to achieve deformity, along with suitable durability and energy efficiency.

With the use of porous cellular materials meant to meet the balance of both softness and flexibility and the need for firmness also, the researchers were able to roll their knowledge of materials, manufacturing, and robotics into one—along with 3D printing and the use of triple materials. The robotic gripper finger was made up of the following lightweight parts:

  • Three octet segments
  • Two auxetic joints (mimicking human bones and joints)
  • Integrated pressure sensor on the fingertip

The following materials were used for 3D printing the single, dual 1, and dual 2 designs: SemiFlex, PLA, and carbon fiber reinforced PLA (CFRPLA). The porosity level allowed for the sought-after balance in a lightweight structure as well as offering the proper rigidity for various gripping functions. The overall design was also responsible for the system of fingers able to deform as needed, in tune with objects and their specific shapes—while the fingertip sensors monitoring the environment.

Mechanical properties of the samples from compression test

“Our architectured robotic finger is a starting point of cellular design concept. Therefore, there is a lot of room for further research in this topic. Design of other mechanical metamaterials has lots of opportunities, so other lattice structures can be investigated to tune additional mechanical deformation functionality in the robotic finger,” concluded the researchers.

“The optimization of sensor design and addition of other sensors can also be investigated to achieve its ubiquitous performance. This compliant robotic design with metamaterial body can prove to enhance the functionality and durability of robotic bodies for prosthetic or industrial applications, thus developing new generation of robotic systems with better performance and greater adaptability in a variety of tasks.”

Robotics and 3D printing are paired up often these days, in projects ranging from uses in furniture manufacturing to soft robotics, 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.

Auxetic unit cell designs based on different α and θ parameters

[Source / Images: ‘Toward a Smart Compliant Robotic Gripper Equipped with 3D-Designed Cellular Fingers’]

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University of Nottingham: 3D Printed PG/PLA Composites for Repairing Fractures

In ‘Mechanical properties and in vitro degradation behavior of additively manufactured phosphate glass particles/fibers reinforced polyactide,’ authors Lizhe He, Jiahui Zhong, Chenkai Zhu, and Xiaoling Liu explore a new level of material for 3D printing with phosphate glass/polylactide (PG/PLA) composites for use in medical applications such as fabrication of customized bone fixation plates for repairing fractures.

While bone regeneration is an area of great interest in 3D printing and additive manufacturing, so is the more common element of healing breaks, as researchers continue to look for better ways to improve the process—often accompanied by a range of bone fixation plates, screws, pins, and rods. Materials are key, along with integrity in design. Implants must be biocompatible, but the process is seamless when they are biodegradable too, thus eliminating the need for surgery.

The materials were tested for suitable mechanical properties as well as in vitro degradation behavior after creating models designed with PTC Creo Parametric, which were then imported into Simplify3D and the PG/PLA composites were 3D printed on an Ultimaker 2+. With the ability to fabricate complex geometries, the researchers could also control the level of porosity for bioprinting and tissue engineering purposes.

“Comparisons were made with PLA, and PLA reinforced with different loadings of PG particles (PGPs) as well as composites with reinforcements of different geometries [PGPs or milled phosphate glass fibers (PGFs)].”

The aim was to evaluate the AM composites as fracture fixation plates. A three-point bending test was performed, along with in vitro degradation for examining the strength and hydroscopy of the composites. There was a pH value check, along with dynamic mechanical analysis, and fiber length and laser particle size analysis. Both microscopy and statistical analysis were performed also.

Initial flexural properties of the FDM fabricated PLA, PGP/PLA, and PGF/PLA composites. Error bars represent standard deviation. Significance was marked with: * (p < 0.05, n = 5), ** (p < 0.01, n = 5) in black (strength) and red (modulus).

In continuing to compare with PLA specimens, the authors noted the following:

  • Improved flexural modulus
  • Reduced flexural strength
  • Reduced strain at break
  • Intensified effects with increased PGP loading

Typical stress–strain curves of the three‐point bending test of the FDM fabricated PLA, PGP/PLA, and PGF/PLA composites.

“Embrittlement and strength reduction are associated with of stress concentration and low interfacial strength. It is likely here that the stress concentration effect was augmented by the incorporation of particulate with sharp corners. With increased filler loading, stress concentration sites also increased and led to more pronounced strength reduction and the same effect on strain at failure,” noted the authors.

Here, the average fiber length was 54 μm, and median and mode of fiber length were even lower. In comparison to authentic cortical bones, the PGF 10 composite was noted by the researchers to be ‘a close approximation,’ although flexural modulus was found to be considerably lower.

“Stiffness matching is recognized as the ‘gold standard’ for bone fixation implants, as fixation implants with such mechanical properties are strong and stiff enough for the load‐bearing activities without leading to ‘stress shielding.’ As such, it is probably necessary to consider the use of higher/longer fiber loading for this type of application,” stated the researchers.

Continuous PGF/PLA composites are more ‘suitable,’ according to the authors, in regard to load-bearing fixation—a feature connected with continuous fibers leading to stiffness. The flexural modulus of these materials, however, was reduced by ~80% after 28 days of degradation. The PGF 10 composites lost ~30% of initial flexural modulus after a degradation period of 56 days. The rapid flexural modulus could have been a result of the fiber ends being exposed in degradation media.

“Based on the consideration of both the initial mechanical properties and the facility to produce composites with desired geometries straightforwardly, the additive manufacturing of PG/PLA composites exhibits good potential in the making of patient‐specific fixation implants for bone that has low demand for load‐bearing, for example, zygoma, ankle, and maxilla,” concluded the researchers.

“These bones have been previously reported to be successfully restored using PLA‐based biodegradable fixation devices. Compared to PLA alone, it was demonstrated that the incorporation of PGF enhanced the flexural modulus of implants. It is also anticipated that the degradation of PGF releases magnesium, calcium, and phosphate to upregulate bone regrowth. Moreover, the FDM process allows fixation implants with customized geometries to be built directly and may remove the need for contouring of implants for anatomic fit during the operation.”

A serious interest in 3D printing today translates into a serious interest in materials—and most likely composites too, as they are able to add significant strength and improved properties to prototypes and parts, including that of polymers, bioprinting applications, and metals like titanium. 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.

SEM images of polished/pristine fractured surfaces of virgin PLA (a,b); PGP 10 (c,d); PGP 20 (e,f); and PGF 10 (g,h) composites

SEM images of pristine fractured surfaces of PLA (a,b); PGP 10 (c,d); PGP 20 (e,f); and PGF 10 (g,h) degraded at 37 °C in PBS for 28/56 days.

SEM images showing the fusion of PGPs (a) and PGFs (b) into excrescences, captured on Day 56.

[Source / Images: ‘Mechanical properties and in vitro degradation behavior of additively manufactured phosphate glass particles/fibers reinforced polyactide‘]

The post University of Nottingham: 3D Printed PG/PLA Composites for Repairing Fractures appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

H and H 3D plastics launch new industrial sized filament spools

U.S based filament manufacturer H and H 3D Plastics is launching a new line of industrial sized spools to facilitate the growth of large format 3D printing. “If you’re producing a 3D print which takes 48 hours or more – and many of our clients already are – you simply don’t want to keep switching […]

PLA Derivatives Suitable for 3D Printing Biomedical Devices

In ‘Differential thermal analysis of the antibacterial effect of PLA-based materials planned for 3D printing,’ authors P. Maroti, B. Kocsis, A. Ferencz, M. Nyitrai, and D. Lorinczy explore the opportunities biomedical applications offer to research and medicine, along with the importance of evaluating materials used in creating devices.

In this study, researchers are specifically concerned with contamination risk and the purported antibacterial properties of PLA, along with PLA-HDT, a PLA-Ag nanocomposite, with DTA/TG. PLA and its derivatives have been attractive to researchers over time because of its natural plant-based origins and biodegradability. The researchers point out the need for sterilization in bioprinting practices, and especially for patients about to receive implants, with the most popular methods as follows:

  • Steam sterilization (at high pressure and * 130 C)
  • Dry sterilization (close to 200 C)
  • Sterilization with radioactive sources
  • Gas sterilization (mainly in ethylene oxide)

As research progressed, the team tested the antimicrobial properties of the materials, using the following:

  • Micrococcus luteus–Sarcina lutea ATCC 9341 – commonly found in human skin flora
  • Bacillus subtilis ATCC 6633 – bioassay organism for detecting antimicrobial agents
  • Staphylococcus aureus ATCC 25923
  • Escherichia coli ATCC 25922
  • Pseudomonas aeruginosa ATCC 15442

“The surfaces of media were continuously inoculated with test bacteria; the test disks containing presumably antimicrobial materials were placed on the inoculated surface of the media,” explained the authors. “After 24 h incubation at 37 C in a thermostat, the disks were removed and discarded.”

The disks remained clear of bacterial colonies—even for weeks, although they did note that in a few cases ‘contaminated colonies’ were found, most likely due to faulty removal of the test with forceps, which caused the bacteria to be shifted into the initial sample area.

Ultimately, this type of evaluation is critical in bioprinting and the use of devices. The authors point out that ‘indiscriminate use of antifungal agents’ has led to an increase in microorganisms tolerant to drugs used today; in fact, they report that other researchers recently detected an antibacterial and antioxidant activity of a PLA nano-silver composite.

Results of this research also showed that the PLA-Ag composite would be the best choice for 3D printed products used in surgeries due to superior thermal parameters, although they also recommend PLA-HDT as having the potential for biomedical applications too.

“The bacterial test result was very surprising for us because the usual halo (‘paraselene’) around the printed sample did not appear,” stated the authors.

PLA-based sample disks in different bacterium milieu: Symbols are: bacterial beds BS, Bacillus subtilis; SA, Staphylococcus aureus; EC, Escherichia coli; PS, Pseudomonas aeruginosa; SL, Sarcina lutea. Printed samples: 1—PLA “Model” (20% CaCO3), 2—PLA, 3—PLA-Ag, 4—PLA “Gypsum” (50% CaCO3), 5—PLA-HDT. Photographs were made 5 days after the removal of disks (row a, except of PLA), 8 days of removal (row b) and at 11th day (row c).

PLA samples in SL—Sarcina lutea bed. Upper left PLA-Ag, upper right PLA-HDT and bottom PLA disks: a in 5 days, b after 10 days, c after 15 days and d after 19 days of removing the plastic disks. The two neighbor Petri-disks differ from each other only in the percentage of print completeness

The researchers continue to stress the importance of sterilization but realize now that high temperatures should not be used for disinfection. They also recommend HDT-PLA and PLAAg as ‘promising materials’ for composites in heat-based sterilization.

 “The results showed that these composites, based on their thermal characteristics, can be suitable for 3D print biomedical devices such as orthoses, casts, medical models and also surgical guides; therefore, their further examination should be important, regarding mechanical characteristics and their possible antibacterial effect,” concluded the researchers.

Bioprinting is achieved today with many different materials, from chitosan-gelatin hydrogels to nanofiber coated tubular scaffolds and more. Find out more PLA and other variations in creating biomedical devices 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.

Heating and (spontaneous) cooling curves (inserts) for PLA base fiber: a with 10 °C min−1 and b with 40 °C min−1 heating rate. Solid lines: DTA average curves, dashed lines TG curves. Here and in all further figure too, the endotherm process is downward.

The melting (fusion) and cooling curves of PLA-HDT. In the case of 40 °C min−1 heating rate, there was no crystallization in the spontaneous cooling phase.

[Source / Images: ‘Differential thermal analysis of the antibacterial effect of PLA-based materials planned for 3D printing’]