Biological materials are materials that are produced by living organisms, such as, blood, bone, proteins, muscle, and other organic material. Biomaterials, on the other hand, are materials that are created specifically to be used for biological applications. These applications can include bone replacement, skin replacement, membranes for dialysis, artificial limbs, etc. Examples of biomaterials include metals, ceramics, glass, and polymers. These biomaterials can be found in things such as contact lenses, pacemakers, heart valves, orthopedic devices, and much more.
Bio-based materials are materials that are derived from living organisms but are repurposed for other applications. One example of a bio-based material would be enzymes mass-produced by microbes to be used in the synthesis of drugs. Biomimetic materials are materials that are physically or chemically similar to materials produced by living organisms. Biologically derived materials have numerous applications in biomedical fields and beyond. Yet, the properties of these materials are difficult to alter because the natural biosynthetic mechanisms are difficult to elucidate, imitate, or adjust. Thus, many bio-derived materials are isolated from natural tissues, or substitutes are recombinantly produced and then modified ex vivo.
Structural biomaterials, as the name implies, have as their primary function physical support and structure. Structural biomaterials are sometimes referred to as inert biomaterials. An example of a structural biomaterial would be a titanium steel implant with a ball and socket being used as a hip replacement. Functional biomaterials (also known as active biomaterials) have a non-structural application as their primary function. An example of a functional biomaterial would be membranes used during dialysis to filter impurities from blood.
The structural materials that are currently used in our human-built environments wear out due to age and damage, and have limited ability to respond to changes in their immediate surroundings. In contrast, living biological materials like bone, skin, bark, and coral, have attributes that provide advantages over the non-living materials people build with – they can be grown where needed, self-repair when damaged, and respond to changes in their surroundings.
Biological systems in nature assemble living materials that are autonomously patterned, can self-repair and can sense and respond to their environment; however, engineering materials typically cannot (grown engineering materials are not entirely new, e.g. wood, but they are rendered inert during the manufacturing process, so they exhibit few of their components’ original biological advantages).
The inclusion of living materials in human-built environments could offer significant benefits. Unfortunately, scientists and engineers are unable to easily control the size and shape of living materials in ways that would make them useful for construction.
A major shift in this paradigm is being driven by the maturing field of synthetic biology, which is innovating a ‘tool box’ of methods to tune biomolecules and biosynthetic mechanisms in vivo. Thus, application of the synthetic biology ‘tool box’ to bio-derived materials heralds a new era where bio-derived materials are replicated, mimicked, and modified with engineered biosynthesis.
Biomedically relevant structural polymers produced by microbes can be improved or modified with synthetic biology. These biomaterials fall into two broad classes—ribosomally synthesized proteins and non-ribosomally synthesized polymers.
Ribosomal protein-based structural biomaterials largely consist of polypeptides that comprise or mimic the extracellular matrix (ECM). These include ECM proteins such as collagen, laminin, fibronectin, and elastin, which are currently sourced from tissue or in low-yield recombinant fermentations. For example, collagen has historically been low-yield, and has only recently been produced in tobacco plants in quantities sufficient for the production of collagen-based medical devices.
The limited availability of ECM proteins has led to sourcing of ECM protein mimics from non-mammals. These include recombinant bacterial collagen-like proteins, silk from arthropods, and the insect elastomer resilin. These ECM analogs can be produced in microbial fermentation systems with recombinant DNA. In particular, silk fibroin is a protein with remarkable mechanical properties, inspiring its extensive use as a structural biomaterial.
Non-ribosomally synthesized structural polymers are naturally produced in several microorganisms and have garnered interest for biomedical applications, and more broadly as bioplastics and biofuels. These include exopolysaccharides, polyesters, and other heteropolymers. Exopolysaccharides are structural biopolymers made from sugars which are either synthesized extracellularly or secreted by microorganisms. The assembly mechanisms allow for the formation of high-molecular weight polysaccharides with a variety of properties, including branched or linear structures and homomeric or heteromeric composition.
While many polysaccharides are used as structural materials, bacterial cellulose and hyaluronic acid in particular have drawn recent attention. Bacterial cellulose has broad applications in electronics, acoustics, and medicine due to its regular nanostructure and high purity. Each of non-ribosomal polymers has a unique biosynthetic mechanism and utility as structural biomaterials.
Application of synthetic biology to structural material production
Synthetic biology involves engineering microbes like bacteria to program them to behave in certain ways. For example, bacteria can be engineered to glow when they detect certain molecules and can be turned into tiny factories to produce chemicals. Innovations in the synthetic biology have produced tools that can design, predict, and control complex biological processes—removing the historical barriers to designing materials in vivo. Future advances might include the construction of new biological parts and brain-computer interfaces. Synthetic biology has potential to provide on-demand bio-production of novel drugs, new materials, food, fuels, sensors and coatings whatever suits the military’s needs, according to DARPA.
Synthetic biology methods can control the biosynthesis of each of the materials described above, including gene expression, protein function, metabolism, secretion, and extracellular assembly. The majority of these methods focus on engineering gene expression—transcription, translation, and posttranslational modifications. Additionally, metabolic engineering and protein engineering methods have been applied to alter metabolism, secretion, and extracellular assembly.
This has led to the emergence of a relatively new research field: Engineered Living Materials (ELMs). This is a novel class of materials that exploit the properties of living organisms. DARPA has even launched an Engineered Living Materials program seeking to “revolutionize military logistics and construction in remote, austere, high-risk, and/or post-disaster environments by developing living biomaterials that combine the structural properties of traditional building materials with attributes of living systems, including the ability to rapidly grow in situ, self-repair, and adapt to the environment.”
Ultimately, ELMs could lead to a future where diverse materials could be grown at home or in local production facilities, using biology rather than resource-intensive centralized manufacturing.
Synthetic biology allows synthesis of new materials that mimic natural tissues and materials with no natural analog. One of the first examples is the use of metabolic engineering to synthesize new cellulose-chitin heteropolysaccharides in bacteria
Radical route produces non-natural polymers inside cells
UK researchers have made non-natural polymers inside living cells for the first time using free radical chemistry. The technique offers a unique way to merge synthetic materials with biology to control cell behaviour, which could lead to widespread applications including new therapies for cancer and other diseases.
Free radicals are usually associated with disease and aging due to their role in oxidative stress on cells, proteins and DNA. To limit this damage, cells produce specific molecules including antioxidants that round up free radicals. It would be expected, then, that generating radicals in cells to make new polymers simply wouldn’t work.
‘No one has ever shown that free radical chemistry can take place inside cells – indeed dogma has been that the cellular defences would prevent this,’ says Mark Bradley whose lab conducted the work at the University of Edinburgh, UK. ‘We show that this is not the case and we can make a variety of polymers via free radical polymerisation methods.’
Bradley and his colleagues attempted the seemingly impossible because of their understanding of radical scavenging mechanisms inside cells. This suggested to them that free radical scavengers such as glutathione – a potent antioxidant in living cells – would not react fast enough to quench the necessary radicals required for polymerisation and offer a unique way to alter and control cells.
Convinced it was possible, the researchers developed their polymerisation technique by first finding a way to generate free radicals inside cells. They did this by introducing a cell-friendly photoinitiator molecule into human cell cultures, which produces free radicals when illuminated by UV light. Next, the team introduced various biocompatible monomers to the human cell cultures too.
With the cells taking up both the photoinitiator and monomers, the researchers could then use UV light to trigger the production of free radicals inside cells. These subsequently reacted with the double-bonded monomer building blocks in a chain reaction that produced different polymers inside cells depending on the monomers used. Some polymers became fluorescent once made, while others became nanoparticles or altered the way cells moved and behaved.
‘The work represents a significant step forward in our ability to merge abiotic materials with the biotic world inside of cells,’ comments Frankie Rawson who investigates bioelectronics to control cells at the University of Nottingham, UK. ‘What really excites me is the plethora of applications this approach could have based on the assembly of active materials inside cells, from treating disease to bioelectronic systems comprising conductive polymers.’
Bradley now wants to find out if polymers inside cells alter their longevity and whether tumour cells could be killed by generating certain polymers inside cells. ‘The possibilities are now enormous,’ Bradley says. ‘It opens up the scope of carrying out new chemistries inside cells – opening perhaps a whole new area of chemical biology.’
Scientists Take Big Step Towards Producing Novel Polymers In Living Cells reported in Nov 2018
A team of Yale chemists is one step closer to using the ribosome — the cell’s protein-making factory — to create designer polymers, including stronger and more flexible materials and life-saving drugs. The ribosome has a surprising capacity to insert the novel building blocks of polymers at the beginning of a protein sequence, the researchers report in the journal ACS Central Science.
“This paper reports that the ribosome can begin protein synthesis with molecules like those found in Kevlar or the precursors to important antibiotics,” said Alanna Schepartz, co-corresponding author of the study, Sterling Professor of Chemistry, and professor of molecular, cellular, and developmental biology.
Ribosomes string together amino acids into long polymer chains that fold into unique structures — the proteins found in every living cell. The sequence of amino acids required to make each protein is encoded genetically and decoded by the ribosome. Scientists like co-corresponding author Dieter Söll, Sterling Professor of Molecular Biophysics and Biochemistry and professor of chemistry, have spent decades figuring out how to introduce novel amino acids into proteins.
In this study, researchers went a step further and found that the ribosome itself can create bonds between amino acids and completely unrelated chemicals. “Our results were completely unexpected, as the ribosome certainly did not evolve to begin protein synthesis in this way,” Schepartz said.
These findings represent an important first step toward coaxing the ribosome to synthesize chains of unnatural polymers, say the researchers. Since the ribosome synthesizes polymers based on genetically encoded instructions, these unnatural polymers can be programmed in the same way that the cell programs protein synthesis, the authors note.
“One can imagine in the future using these tools to generate novel fabrics, such as those with the sheerness of nylon and strength of Kevlar, or new therapeutics,” said Schepartz. One molecule introduced to the ribosome is a precursor to valuable natural products, which already serve as the basis for several antibiotics and cholesterol-lowering drugs.
Making chemical polymers that possess a defined sequence and length from living cells is the mission of the Center for Genetically Encoded Materials (C-GEM), led by Schepartz. C-GEM brings together scientists with a broad range of expertise, including co-corresponding authors Söll and Scott Miller, the Irénée du Pont Professor of Chemistry and an expert in synthetic chemistry.
“This discovery is a direct result of the highly collaborative interdisciplinary environment of C-GEM,” Miller said. C-GEM is a National Science Foundation (NSF) Center for Chemical Innovation established at Yale in 2017. Co-workers on this project include Agilent Fellow Omer Ad, postdoctoral associates Kyle Hoffman and Andrew Cairns, and graduate student Aaron Featherston.
“This project, proposed to us in 2017, was considered high-risk yet high-reward,” said Carol Bessel, acting Division Director of NSF Chemistry. “It is great to see progress toward that reward as they work to harness biological chemistries, evolved over thousands of years, to design novel synthetic pathways for new or difficult-to-make molecules and polymers.”
US Army project makes key findings in ribosomal monomers research reported in Nov 2019
A research project funded by the US Army has made a breakthrough in the quest for a new class of high-performance materials and therapeutics for soldiers. Synthetic biologists at Northwestern University have created new substrates that could guide the manufacturing of new classes of synthetic polymers. Researchers developed a set of design rules that guide how ‘ribosomes can incorporate new kinds of monomers’. The findings could lead to the creation of advanced materials that could deliver capabilities for use by the army.
US Army Research Office polymer chemistry programme manager Dr Dawanne Poree said: “These findings are an exciting step forward to achieving sequence-defined synthetic polymers, which has been a grand challenge in the field of polymer chemistry. “The ability to harness and adapt cellular machinery to produce non-biological polymers would, in essence, bring synthetic materials into the realm of biological functions. This could render advanced, high-performance materials such as nanoelectronics, self-healing materials, and other materials of interest for the army.”
The new synthetic polymers could be used in applications such as developing electronics, advanced solar cells and nanofabrication, and personal protective gear for the soldiers, Poree added. In a statement, the US Army Research Laboratory said: “This project looked at how to re-engineer biological machinery to allow it to work with non-biological building blocks that would offer a route to creating synthetic polymers with the precision of biology.”
The team sought to expand the range of monomers used by the ribosome. The monomers need to be attached to Transfer ribonucleic acid (tRNAs). Researchers chose a new process called flexizyme for linking the monomers to the tRNAs. They created 37 monomers from a diverse repertoire of scaffolds. The project was carried out under the US Department of Defense’s Multidisciplinary University Research Initiatives programme.
Start-up uses CO2 to create bio-building blocks reported in Oct 2021
Cemvita Factory is putting microbes to work in reducing greenhouse gas emissions and producing bio-polymers used in the manufacturing of plastics. The Houston-based industrial biotechnology start-up, funded by an Occidental subsidiary and others, transforms carbon dioxide into “value-added products” using its synthetic biology conversion platform.
“Rather than use corn or sugar as feedstock and yeast for the fermentation process to make biofuels, Cemvita has genetically engineered microbes to use carbon dioxide as the feedstock to create valuable organic molecules.” The company has identified more than 30 critical molecules that can be made from carbon dioxide, according to Karimi. “Our focus is mostly on the building blocks of polymers and plastics since they will sequester the carbon in a longer timeframe as opposed to fuels, which will be burned and create emissions,” he said.
Ethylene is a hydrocarbon that is widely used in the chemical industry primarily as a precursor to polymers for use in durable, long-life products. It is also a naturally occurring plant hormone that facilitates the ripening of fruits. “Ripening is a naturally occurring chemical reaction that happens under ambient pressure and temperature inside the banana,” said Karimi.
“We took the gene for the ethylene-forming enzyme from bananas and engineered it into our host micro-organism that uses carbon dioxide as a feedstock. “This engineered micro-organism is now turning carbon dioxide and water into bio-ethylene,” he explained. Cemvita Factory’s early economic assessment shows that the company can utilise 1.7 million tonnes of carbon dioxide from the flue gas of a co-generation power plant to produce 1 billion pounds of bio-ethylene per year.
Using living bacteria to design self-growing engineering materials reported in March 2021
Researchers at the University of Southern California have now reported progress in exploiting living bacteria and 3D-printed materials to grow bionic mineralized composites with ordered microstructures (Advanced Materials, “Growing Living Composites with Ordered Microstructures and Exceptional Mechanical Properties”). This paper provides an example of harnessing living bacteria to design self-growing materials and opens the door for a new class of engineering materials that can self-grow like living creatures.
“We have developed a strategy to manufacture bionic mineralized composites by harnessing bacteria-assisted mineralization within 3D-printed polymer scaffolds,” Qiming Wang, the Stephen Schrank Early Career Chair in Civil and Environmental Engineering and an assistant professor in the Department of Civil and Environmental Engineering at the University of Southern California, tells Nanowerk. “Compared to other existing methods, our bionic method can produce mineralized composites with high fractions of minerals and highly ordered mineral orientations.”
Wang and his team’s work focusses on mineralized composites. These are tough materials that widely exist in nature, such as teeth, pearl, nacre, and mantis shrimp club. To design mineralized composites with high fracture toughness, two requirements must be met: The mineral volume fraction should be high; and the mineral fibers should form microstructures with ordered orientations (such as the Bouligand structure).
“Nature’s growing method can fulfill both requirements,” says Wang. “However, existing engineering methods can only fulfill one requirement: either a high volume-fraction of minerals, or a complex architecture of mineral layout.”
The team’s new method can fulfill both requirements: the mineral volume fraction is relatively high (45-90%) and the mineral layout follows an ordered microstructure.
“Although bacteria-assisted mineralization has been previously used to heal cementitious materials, harnessing guided bacterial mineralization to design structural composites has not been explored,” Wang notes. This novel manufacturing strategy primarily relies on bacteria-assisted mineral growth within 3D-printed microporous lattice scaffolds.
The researchers work with specific bacteria (S. pasteurii) known for secreting the enzyme urease. When urease is exposed to urea and calcium ions, it produces calcium carbonate, a fundamental and strong mineral compound found in bones and teeth. By guiding the bacteria to grow calcium carbonate minerals, the researchers achieved ordered microstructures, which are similar to those in the natural mineralized composites.
“Because our new materials fulfill both requirements – a high volume-fraction of minerals as well as a complex mineral architecture – the mechanical property of our bionic materials are exceptional,” Wang points out. “They exhibit outstanding specific strength and fracture toughness that are comparable to natural composites, and exceptional energy absorption capability that is superior to both natural and artificial counterparts.”
These materials could find applications in areas that require high-performance structures such as aerospace panels and vehicle frames. The materials are relatively lightweight, also offering options for defense applications like body or vehicle armors. “An interesting vision is that these living materials still possess self-growing properties,” says Wang. “So for instance if we use them in a bridge, we can repair any damage by introducing bacteria to grow the affected structures back.”
Naval Research Office-led program to demonstrate biosynthetic materials in Dec 2021
The Naval Air Warfare Center Weapons Division intends to partner with a contractor that can create biosynthetic materials—developed in a lab and based on processes in living organisms—and then test how they hold up against fire, lasers and on drones.
For the latest pursuit detailed in this sources sought notice, officials aim to make and evaluate biosynthetic composite materials based on resveratrol, which is a compound produced by certain plants that defends against pathogens like bacteria. Resveratrol possesses a wide range of biological properties, among them antioxidant, cardioprotective, neuroprotective, anti-inflammatory and anticancer activities
In an attached statement of work, they confirm that, among other requirements, the chosen contractor would need to produce a biosynthetic resin and a man-sized drone with composite wings. The contractor would be expected to “conduct ground tests with the drone,” which would need to include fire-resistance testing and a laser strike simulation. Comparative laser tests with both a commercial epoxy composite and the resveratrol-based composite material would need to be completed.
“The contractor shall deliver a final report documenting composite fabrication, flight tests, laser strike simulations, fire resistance testing and the other requirements listed above,” officials wrote in the statement of work. “The final report will be delivered prior to October 1, 2022.”
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