German RepRap Introduces New L320 3D Printer for Liquid Additive Manufacturing

First introduced on the AM trade show circuit in 2017, the unique Liquid Additive Manufacturing (LAM) 3D printing process by industrial 3D printer manufacturer German RepRap works somewhat like FDM, as each layer is extruded and then cross-linked through thermal curing. This can create parts that have very interesting mechanical properties which could allow for many new applications in 3D printing.

The company’s LAM technology, developed in partnership with Dow Corning, works with materials that are not melted and then solidified again, as with FFF 3D printing. Instead, the process uses a liquid material, like German RepRap’s customizable polyurethane-based plastic, which is then vulcanized under heat exposure; this is what fully cross-links the individual deposited layers so they are firmly connected.

What also makes LAM such a unique AM process is that it allows for the industrial 3D printing of liquid or high viscosity material, such as Liquid Silicone Rubber (LSR). The company claims that LAM 3D printing can make components with nearly the same properties as injection molded parts, which could prove useful in developing new customer groups that need a more economical method of manufacturing. Especially in flexible materials, this process could see many exciting applications in the medical or footwear arena. Silicone has excellent properties and many firms are very familiar with using it.

German RepRap L320

This fall, German RepRap presented its LAM process at formnext 2018, along with its first production-ready LAM 3D printer, the L280. The company has been working to further develop the technology for industry use, and is now introducing its new L320 LAM 3D printer, which is an “extremely stable” system, according to German RepRap, that has been “adapted to the high demands of industrial continuous operation.”

With a 250 x 320 x 150 mm build platform and weighing in at approximately 350 kg (without the cartridge system), the L320 features a touchscreen display for intuitive operation, industrial rollers and stand for easy handling, and volumetric extrusion with a lift and sunk system. The printer uses Simplify3D software, and its new printhead technology allows for precise metering and mixing ratios. The nozzle itself would seem to be one by German firm Viscotec but this was not disclosed.

Thermal crosslinking

LAM technology makes it possible to influence the application direction, in turn influencing layer-level vulcanization as well. The polymers used in this process have a better molecular structure, as base materials, rather than processed ones, are used. Because insights from 3D printed prototype models can be directly transferred to injection molding, customers benefit from a reduced time-to-market, and the design freedom afforded by 3D printing makes it possible to use cross, lattice, or honeycomb structures to fill parts for better optimization of customized products.

“A high-temperature halogen lamp releases activation energy to accelerate complete crosslinking, at the molecular level. This fine-tuned reaction, in both small and large objects, is ensured by the driving speed of the lamp,” German RepRap explains on its website. “Due to this thermal cross-linking, the printing time is considerably reduced, at the same time the printing result, especially also in terms of time savings, sets new standards.”

Through extensive testing and pilot applications, the company says that it has proven the reliability of its new L320 3D printer in achieving precise, continuous operation. The printer also features sound safety technology, which monitors the curing process, and the system also registers and displays any deviations; if there are any serious irregularities, the print job will automatically stop.

To request test prints, or to talk about purchasing the L320 for individual use, email info@germanreprap.com. Commercial users who require high reliability and availability can also get a maintenance contract and professional on-site service from trained German RepRap technicians. This service includes hardware and software training, in addition to maintenance and repair of the L320 itself.

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[Images: German RepRap]

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Colombian Researchers Study Potential for SIS-Based Photocrosslinking in Bioinks

(a) Preparation of the 0.5% (w/v) riboflavin (RF) bioink and (b) its successful extrusion through a 21 G needle. (c) Filament formation during extrusion of the bioink through a 21 G needle. (d) Presumed photo-mediated crosslinking reaction thought to be occurring in the proposed bioinks.

Colombian researchers performed a recent study, outlined in ‘Formulation and Characterization of a SIS-Based Photocrosslinkable Bioink,’ explaining the possible value in crosslinking to create better materials for 3D printing cells. Here, they are using small intestinal submucosa (SIS) with photocrosslinked reactions to manipulate the gelation process, despite some expected challenges.

While the use of natural materials is always preferable, the researchers point out that they can also be difficult to work with due to lack of strength and stability. In the end that leads to inferior printability and further challenge.

“An avenue through which to overcome these issues is to mix them with synthetic polymers such as polyethylene glycol (PEG), polylactic acid (PLA), and polycaprolactone (PCL), which have demonstrated their ability to alter the mechanical response upon blending,” state the researchers. “Additionally, they have been proven able to shorten degradation rates, though at the expense of decreasing their biocompatibility.”

The authors also began to study decellularized extracellular matrices (dECMs) further, as they have the potential to copy the natural cellular environment. dECMs include the following proteins:

  • Collagen
  • Elastin
  • Laminin
  • Glycosaminoglycans
  • Proteoglycans
  • Growth factors

dECMs are not always stable though, and that presents challenges in bioprinting:

“Despite these obstacles, several research groups worldwide have attempted the development of bioinks based on dECMs,” state the researchers. “For inducing gelation, these studies have incorporated thermally-induced or photocrosslinking mechanisms, as well as a combination of the two.”

“Despite the crosslinking strategy implemented, the achieved mechanical stability has been observed to still not be sufficient, thereby requiring the use of synthetic materials as structural improvement supports.”

Shear stress profiles of the bioinks at different nozzle diameters and extrusion pressures: (a) 10 kPa, (b) 20 kPa, and (c) 60 kPa.

UV light has been used previously to increase the bioink stiffness in photocrosslinking, and for this study the authors experimented with the SIS dECM-based materials, using riboflavin (RF) as a photoinitiator. Visible light was used for the photocrosslinking. The research team created four different types of bioinks, with successful printability.

“Our experiments suggest that a successful extrusion can be accomplished while the pressure is maintained in the range 25–45 kPa,” stated the researchers.

(a–c) Viscosity and shear rate as a function of time, measured at different points of the nozzle tip geometry (center, middle, and wall). Structural parameter for the three extrusion nozzles studied with diameters of (d) 0.21 mm, (e) 0.25 mm, and (f) 0.41 mm.

They also went on to state that these bioinks demonstrate strong mechanical properties that could ensure success in bioprinting endeavors—following in line with previous research studies where crosslinking resulted in excellent printability parameters, as well as offering better integrity in shape.

“Further in silico experiments allowed us to calculate a stability parameter that provided conceptual evidence for the aggregation of collagen in times as short as 5 s,” concluded the researchers. “Finally, rheology tests allowed us to recover power law parameters for CFD simulations that confirmed shear stress values low enough to maintain high cell viability levels.

“Future work will be focused on reformulating the bioink with the aid of synthetic polymers and/or thermal processing such that collagen fibers remain in an extended state and are readily accessible to the photoinitiated molecules.”

The study of materials in 3D printing has become a vast realm, and a necessary one for those dedicated to such progressive fabrication techniques. It is also a very serious area of study for scientists engaged in seeking out the best ways to grow tissue in the lab, with the potential for making serious impacts in medicine.

Researchers around the world are on an intense journey to perfect bioprinting, and eventually, reach the pinnacle of success in fabricating human organs. The challenge today, as tissue engineering results in a variety of different implants, is to keep cells alive to serve their function in bioprinting. This means seeking out the best bioprinted structures to build, bio-inks, printers, and techniques. Find out more about photocrosslinkable inks 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.

[Source / Images: ‘Formulation and Characterization of a SIS-Based Photocrosslinkable Bioink’]

Bioprinting 101: Part 2 Hydrogels

 

 

hydrogels

Simple Hydrogel

A hydrogel is a macromolecular polymer gel constructed of a network of crosslinked polymer chains. Hydrogels are synthesized from hydrophilic monomers by either chain or step growth, along with a functional crosslinker to promote network formation. A net-like structure along with void imperfections enhance the hydrogel’s ability to absorb large amounts of water via hydrogen bonding. As a result, hydrogels are self-healing in nature. They also develop firm yet have great elastic mechanical properties. Self-healing refers to the spontaneous formation of new bonds when old bonds are broken within a material. The ability to self-heal is very attractive to bio-printing and systems related to the body. Human biology is a system based on reproductive and self-healing components, thus the need for self-healing agents and materials is paramount.

The chemical structure of a hydrogel allows for a variety of chemical reactions to occur. Depending on their composition, they are responsive to various stimuli including heating, pH, light, and other chemical agents. The important property to understand within a hydrogel is the ability to capture water while simultaneously maintaining its chemical bonding structure and therefore its three-dimensional structure.

Engineered Hydrogel

The stability of a three-dimensional structure is important for 3D printing. The main usage of hydrogels within bioprinting are as scaffolds within tissue engineering. Tissue engineering is defined as a combination of materials, engineering, and cells to improve or replace biological organs. This needs finding proper types of cells and culturing them in a suitable scaffold under appropriate conditions. Hydrogels are an appealing scaffold material because their structures are similar to the extracellular matrix of many tissues, they can often be processed under relatively mild conditions, and they may be delivered in a minimally invasive manner.


Synthetic Hydrogel Scaffold

In terms of bio-engineering, scaffold creation with hydrogels can be done through two methods: natural derivation or synthetic derivation. For a 3D bio-printing enthusiast, it is beneficial to have a synthetic method. These methods are easy to control in terms of chemistry and structure. This allows for manipulable properties. Synthetic bio-engineering is the most probable route for anything 3D bio-printing related within a home setting. It is easier to experiment within this context. It is also easier to create specific skin properties for different areas of the body with easily manipulable synthetic hydrogels.

In summary, the benefits of hydrogels and 3D bio-printing are tremendous in terms of easily engineer-able materials within synthetic methods. This allows for a variety of uses for hydrogel materials. Within the context of materials it is optimal and gives us a lot of flexibility on its own. We will discuss in our next article different 3D bio-printing setups. This will also allow us to understand hydrogels in the context of a machine and why they are beneficial, as well as some limitations that need to be understood.

This article is part of a series Bioprinting 101 which hopes to teach people how to bioprint in the home, the first article is here.