Although 3D printing has steadily been gaining ground in O&P, the use of environmentally friendly, plant-based materials is still in its infancy in O&P. There are still bumps and hurdles along the way, as well as some environmental caveats to consider, in which eco-friendly gains in one way can be offset by environmental damage in another. Other issues exist, such as cost effectiveness and transference from research to practical clinical use. But technology has a history of overcoming challenges as it is refined and improved. Where human imagination goes, practical technology often follows.
Some strong possibilities for eco-friendly 3D printing materials include PHA (polyhydroxyalkanoate), PA11 (nylon polyamide 11, an eco-friendlier variation of Nylon PA12 for 3D printing), and PLA (polylactic acid).
PHA: No Current Use Found, Future Possibilities
Biodegradable plastics such as polyhydroxyalkanoates (PHAs) comprise a group of biodegradable linear polyesters that are naturally synthesized by bacteria that cause fermentation of sugar and lipids to store carbon and energy. The mechanical and biocompatibility of PHA can also be changed by blending, modifying the surface, or combining PHA with other polymers, enzymes, and inorganic materials, thus making it possible for a wider range of applications. PHA polymers are thermoplastic, becoming liquid at their melting point, are UV stable, and have low water permeability.
Although one 2015 research study recommended PHA for fabricating prosthetic limbs, it did not include 3D printing, and no other details about current uses for PHA for 3D printing or conventional fabrication were found. However, PHA may have a future application, since more than 150 different monomers can be combined within this family to give materials with extremely different properties, according to Bioplastics News.
PA11: Finding a Place in O&P
PA11 presents a “sustainable alternative to PA12,” in that it is produced from castor beans changed into an oil and transformed to a monomer before being polymerized into PA11, according to 3scomputers.com news, quoting Sculpteo, a French 3D printing service. Its makers market its pore and skin contact compatibility and robustness for medical 3D printing, including orthoses.
Sculpteo has collaborated with Swiss orthopedics specialist Daniel Robert Orthopedie to produce a novel eco-friendly orthosis.
By additive manufacturing the body-realigning wearable from Sculpteo’s bio-based PA11, the firms have managed to make it both sustainable to produce and tailorable to the needs of patients. In addition to “strengthening its position as a leader in 3D printing,” Sculpteo anticipates that the collaboration will “yield next-generation prosthetics and orthotics with life-changing potential.”
PLA: Playing a Role in O&P
PLA is a polymer derived from renewable biomass from fermented plant starch, such as corn, cassava, sugarcane, or sugar beet pulp, and is the primary raw material used in 3D printing. PLA is biodegradable under commercial composting conditions and will break down within twelve weeks, according to one source, making it a more environmentally friendly choice than traditional plastics, which can take centuries to decompose and end up creating harmful microplastics.
The PLA manufacturing process is also more environmentally friendly than that of traditional plastics made from fossil resources. According to research, carbon emissions associated with PLA production are 80 percent lower than that of traditional plastic. PLA can be recycled since it can be broken down to its original monomer by a thermal depolymerization process or by hydrolysis. The result is a purifiable monomer solution that can be reused for PLA production without loss of quality. However, the recycling infrastructure for PLA is small, chiefly since end markets for the recycled material have not yet been developed. Although recycling PLA might be a better option in the future, commercial composting as a preferred end-of-life option is currently recommended.
A 2021 research paper, “Development of an AFO with Dual-material Using an FDM Printer,” Otegen et al., details the development of a model using PLA and other materials. Eventually, PLA material was chosen to be printed in an FDM printer over ABS (acrylonitrile butadiene styrene) and PE (polyethylene) due to its nontoxicity and other material property behaviors, according to the authors.
An article by Emily Schmitt in the June 2021 issue of The O&P EDGE, “Materials Report: Polylactic Acid,” discusses a research study by Shahar et al., as well as other research and information. The study concluded that additive manufacturing produces AFOs with comparable strength as conventionally manufactured devices. Their study involved producing AFOs out of several materials using both thermoforming and 3D printing. PLA was the one material to only be 3D printed and not thermoformed, but it was noted that PLA has the highest tensile strength and lowest cost of the thermoplastics used, as well as minimal warping, making it the best material for additive manufacturing of AFOs.
In O&P, polylactic acid or composites of it are most often applied to the production of rigid or semirigid components of custom-fabricated upper- and lower-limb orthoses. “PLA comes in sheets and can be thermoformed as polypropylene often is, but academic literature supports that PLA orthoses are mainly being manufactured through 3D printing,” according to Schmitt.
4D Printing: Shape-shifting Technology
4D printing adds another way to print bioplastics for O&P. While 3D printing contains the instructions to print layers of material successively, 4D printing adds a precise geometric code to the process based on the angles and dimensions of the desired shape. The code gives the shape memory and instructions on how to move or adapt under certain environmental conditions, the AZO Materials website explains.
“4D printing relies on suitable hardware, stimulus-responsive material, stimuli, interactive mechanisms, and mathematical modeling,” writer Bridget O’Neal explains in her article, “What Does the Future Hold for 3D and 4D Printing? Reviewing Ongoing Processes and Future Potential” (3dprint.com, May 18, 2020, based on an industry conference). “…3D and 4D printing are a source of fascination around the world due to the ability to innovate at will, cutting out the middleman, and making new objects with new materials that may not have been possible previously.”
As an example, the University of Stuttgart and the University of Freiburg in Germany developed a new design method for 4D printing and created a wrist orthosis that contracts and forms to the wearer’s biology, according to an article on 3dprint.com by Assad Siddiqui (“4D Printed Splint Self-Tightens on Wearer’s Wrist,” August 11, 2021, based on a research article in Advanced Science).
The technology was inspired by the air potato, an invasive vine that lightly wraps around the trunk of a tree and releases stipules that create enough pressure to climb the tree. Structurally predetermined deformation occurs when individual cells and tissues absorb water molecules from the environment, and depending on their orientation, will cause a swelling or shrinking. “These passive-nastic movements in nature inspire promising designs in 4D printing and can be emulated through functional additive bilayers,” Siddiqui writes.
The material, a combination of wood filament and stimuli-responsive actuating material, causes the wrist orthosis to slowly adapt, form, and tighten around the user’s own anatomy, utilizing a complex structure of pocket mechanisms to apply pressure and tighten in desired areas.
The wrist orthosis can be printed on any standard fused filament fabrication (FFF) printer, thus making the technology easier for mass adoption, the author points out.
Caveats and Hope for Solutions
“The Truth about Bioplastics,” by Renee Cho, on the Columbia University website (December 13, 2017), describes both negative and positive aspects of bioplastics in general, although other than PLA, the article does not specifically mention any of the 3D printing options for O&P devices. Some takeaway points from the article are:
- Biodegradable plastic can be broken down completely into water, carbon dioxide, and compost by microorganisms under the right conditions. “Biodegradable” implies that the decomposition happens in weeks to months. Bioplastics that do not biodegrade that quickly are called “durable,” and some bioplastics made from biomass that cannot easily be broken down by microorganisms are considered non-biodegradable.
- Compostable plastic will biodegrade in a compost site. Microorganisms break it down into carbon dioxide, water, inorganic compounds, and biomass at the same rate as other organic materials in the compost pile, leaving no toxic residue.
- While bioplastics are generally considered to be more eco-friendly than traditional plastics, a 2010 study from the University of Pittsburgh found that was not necessarily true when the materials’ life cycles were taken into consideration.
- The study compared seven traditional plastics, four bioplastics, and one made from both fossil fuel and renewable sources. The researchers determined that bioplastics production resulted in greater amounts of pollutants due to the fertilizers and pesticides used in growing the crops and the chemical processing needed to turn organic material into plastic. The bioplastics also contributed more to ozone depletion than the traditional plastics and required extensive land use.
- Bioplastics do produce significantly fewer greenhouse gas emissions than traditional plastics over their lifetime. There is no net increase in carbon dioxide when they break down because the plants used to make bioplastics absorbed that same amount of carbon dioxide as they grew. A 2017 study determined that switching from traditional plastic to corn-based PLA would cut US greenhouse gas emissions by 25 percent. The study also concluded that if traditional plastics were produced using renewable energy sources, greenhouse gas emissions could be reduced 50 to 75 percent; however, bioplastics that might in the future be produced with renewable energy showed the most promise for substantially reducing greenhouse gas emissions.
- While the biodegradability of bioplastics is an advantage, most need high-temperature industrial composting facilities to break down. However, very few cities have the necessary infrastructure. As a result, bioplastics often end up in landfills where, deprived of oxygen, they may release methane, a greenhouse gas 23 times more potent than carbon dioxide.
- Bioplastics are also relatively expensive; PLA can be 20 to 50 percent more costly than comparable materials because of the complex process used to convert corn or sugarcane into the building blocks for PLA. However, prices are coming down as researchers and companies develop more efficient eco-friendly strategies to produce bioplastics.
- In 2017, it was hard to claim that bioplastics were more environmentally friendly than traditional plastics when all aspects of their life cycle were considered: land use, pesticides and herbicides, energy consumption, water use, greenhouse gas and methane emissions, biodegradability, recyclability, and more. But as researchers around the world work to develop greener varieties and more efficient production processes, bioplastics do hold promise to help lessen plastic pollution and reduce their carbon footprint.
Additionally, bacteria, fungi, waxworms (the larvae of the greater wax moth), mealworms, and even a mushroom are able to eat plastic without harming the organisms. Mealworms can eat plastics without impairing their nutritional value and safety as food for other organisms. One researcher was quoted as saying that if research can discover just how the waxworms’ gut processes the plastic, they might be able to design the ideal plastic biodegradation system. Although none of the information specifically mentioned types of bioplastics including those with possible use in O&P 3D printing, additional research may reveal more natural bioremediation options that are applicable.
An exciting future appears ahead for eco-friendly 3D printing.