Research Terms
This 3D printing support material allows for liquid ink-printed silicone structures to have features as small as 8 microns. Silicone is a highly useful material due to its high thermal stability and resistance to weathering, ozone, moisture, and UV radiation. However, soft silicone remains a challenging material to use in additive manufacturing or 3D printing. The most effective support medium available for 3D printing liquid silicone consists of hydrocarbon-based jammed microgels, but these microgels are difficult to formulate. Additionally, the destabilizing interfacial forces between the silicone ink and the microgels in the support medium can lead to the disintegration of more intricate details on the printed silicone structure over time.
Researchers at the University of Florida have developed a 3D medium that uses droplets of water and glycerol emulsified in silicone oil to support silicone prints with ultra-low interfacial tension. The support medium enables silicone 3D prints with smaller, more intricate features, which have applications for personalized implants, lab-on-a-chip devices, tissue/organ-on-a-chip devices, point-of-care devices, biological machines, and other medical devices.
Emulsion-based support material that facilitates 3D printing silicone structures that have finer details
The support material is a packed inverse emulsion in which emulsion droplets containing a mixture of water and glycerol are the dispersed phase, and silicone oil is the continuous phase. The relative proportions of water and glycerol match how fast light travels through the silicone oil, thus making the material optically clear. The mixture of water, glycerol, and silicone oil can have a wide range of different material properties that are easier to tune than those of hydrocarbon-based microgels. Using silicone oil as the continuous phase creates an environment that has ultra-low interfacial tension with deposited silicone-based inks. This prevents the breakup of small printed features, enabling constructs to have features as small as 8 microns in diameter, which is 10 times finer than previously achieved with hydrocarbon-based microgel support systems.
These nanoparticles release pesticides into the plant only upon contact with elevated concentrations of sugars or elevated pH levels found in the phloem. Citrus greening disease is one of the most serious citrus plant diseases in the world. There is no cure once a tree is infected, and the disease has put the future of America’s citrus crops at risk. Plants naturally have significantly elevated concentrations of sugar and pH in their phloem tissue, which is the main channel for moving sucralose and other metabolic products, as well as pesticides, from the leaves to the rest of the plant. Although pH-responsive materials have been extensively studied in the realm of medicine, few studies have applied such delivery methods within agriculture, despite the urgent need for specific delivery of pesticides and nutrients. Because only a small portion of their active compounds ever reach their targeted sites, pesticides frequently fail to kill harmful pathogens. Researchers at the University of Florida have created polymer nanoparticles that encapsulate pesticides and nutrients needed to combat plant disease, including citrus greening, and will only release these active compounds when elevated concentrations of sugar and pH are present in phloem tissue. This will enhance efficiency of agricultural fertilizers, nutrients, pesticides, antibiotics, and more.
Nanoparticles that release pesticides only upon contact with elevated concentrations of sugars or elevated pH levels in phloem tissue.
Polymer nanoparticles will include a monomer with water-solubility that is dependent on the presence or absence of sugars and/or pH. The nanoparticles comprise both the responsive monomers units and additional hydrophilic units. Their sugar-responsive nature derives from boronic acid-containing polymers. Upon binding sugars to hydrophobic boronic acid units, the units become hydrophilic, thereby disrupting the amphiphilicity that allowed nanoparticle formation to originally occur and leading to release of hydrophobic compounds. The application method can be via injection or spraying.
These charge-neutral microgels allow for 3D cell culture and printing. Bioprinting, or placement of biological samples into 3D support media, models cellular morphology, heterogeneity, and genetic profiles in a more accurate and reproducible fashion than traditional 2D cultures. Available 3D cell culture strategies involve the seeding and adhesion of cells into polymer scaffolds with subsequent perfusion of growth media. However, these systems present several limitations, such as limited cell migration, lack of time-effectiveness and optical access for microscopy, and polymer scaffolds restricting the cell environment. Additionally, cell viability is limited to a few days due to the accumulation of cellular waste, leading to localized cytotoxic environments and cell death. It is necessary to devise 3D growth media that allows for improved perfusion.
Researchers at the University of Florida have developed smooth, spherical charge-neutral microgels suitable for 3D cell culture and printing. They can also be used in perfusion bioreactors. The microgels’ spherical shapes enable easier perfusion of materials and make the microgel more absorbent than currently available options.
Microgel-based medium for 3D cell culture and printing, allowing for easier perfusion of materials than currently available formulations
These microgels consist of charge-neutral particles, enabling 3D cell culture and printing. The development of the microgels involves emulsion polymerization, more specifically, an inverse emulsion reaction, resulting in spherical microparticles comprising cross-linked polymers with superior properties for 3D culture. The microgels are derived from monomers, including poly (ethylene glycol) methyl ether acrylate (PEGa), poly(ethylene glycol) diacrylate (PEGda), or acrylamides, N-alkylacrylamides, N,N-dialkylacrylamides, and (meth)acrylates. Packed spherical microgels create well-defined and large pores spaces, improving permeability by a factor of 10,000 compared to currently available formulations, and allowing for easier perfusion of materials.
These materials incorporate thermolytically labile groups into widely used glass-substitute polymers, allowing solvent and catalyst-free degradation of the polymer into a high-purity composition of its monomers. These materials can therefore be recycled into reusable monomers at the end of their life cycle. Poly(methyl methacrylate) (PMMA) is a glass substitute used to manufacture automobiles and aircraft. Industrial sources manufacture 4 million tons of PMMA annually but recycle only 10 percent of that amount . Conventional routes to recycle PMMA require high temperatures and result in impure, difficult-to-reuse products. An efficient process for recycling PMMA into a pure composition of its methyl methacrylate monomer at an industrial scale would therefore increase the sustainability of the polymer industry.
Researchers at the University of Florida have synthesized PMMA with thermolytically labile pendent or chain-end groups that can be used to induce catalyst-free degradation into methyl methacrylate monomers. This simple recycling process takes place at lower temperatures than conventional PMMA degradation requires.
Synthesis of PMMA with thermolytically labile phthalimide groups that drive degradation into highly pure methyl methacrylate monomer
Upon formation of the PMMA, a long chain of carbon-carbon single bonds forms, two for every methyl methacrylate monomer. Recycling PMMA into a fresh polymer requires degrading this carbon backbone in a controlled manner to generate products with a high purity of methyl methacrylate monomers, so that these monomers can be reused to form a fresh polymer. One path to destabilizing the PMMA backbone is to liberate some attached functional groups, creating radicals.
For these polymers, UF scientists have created materials that enable on-demand creation of radicals in the PMMA backbone, and therefore incorporate recycling into their design. The first material is a copolymer including a small fraction of monomers containing phthalimide groups that decorate the PMMA backbone, known as pendent groups. The phthalimide pendent groups are thermolytically labile, generating radicals at high temperatures and inducing backbone fragmentation and degradation.
Alternatively, the material can generate radicals via its chain-end groups. The material is then a homopolymer constructed only from identical methyl methacrylate monomers, but a thermolytically labile phthalimide group is still present at the α-end of the chain. As before, these chain-end groups generate radicals at high temperatures and cause the polymer to degrade into a high-purity composition of reusable monomers.
This process efficiently synthesizes pure, highly-conjugated cyclic polyacetylene in film, bulk, and soluble form, producing conductive cyclic polymers for many applications. A cyclic polymer binds together the chain ends of a linear polymer, dramatically changing its physical properties, often for industrial advantage. However, cyclic polymers are very difficult to synthesize. Linear polyacetylene is a known conductive polymer. Its cyclic counterpart, which would offer superior electrical conductivity, remains unavailable.
Researchers at the University of Florida have developed a catalytic process that synthesizes cyclic polyacetylene, a polymer with high electrical conductivity suitable for use in functional thin films. Functional polymer thin films benefit many energy applications due to their conductivity and processability, providing a better material alternative for separation membranes in fuel cells, electrodes in batteries, and various components in solar power systems.
Cyclic polyacetylene synthesis for creating low-cost, electrically conductive functional polymer thin films
This is the first synthesis of cyclic polyacetylene ever reported. Unlike the synthesis of linear polyacetylene, this cyclic polyacetylene synthesis is versatile to polymerization temperature ranging from -90 to 70 °C, producing exclusively trans polyacetylene as a high-quality polymer, with low crosslinking defects, less than 1 percent. A UF catalyst enables cyclic polymerization of acetylene to form trans-cyclic polyacetylene in film, powder, or soluble form.
This catalyst selectively polymerizes the acetylene contained in ethylene gas, purifying streams more easily for the production of polyethylene. Analysts project the global polyethylene market to exceed $140 billion in value by 2026. Synthesizing polyethylene gas for its many industrial applications requires ethylene gas significantly free of acetylene, which most manufacturers remove by hydrogenating it into ethylene. This step requires excess ethylene and a catalyst to avoid hydrogenating the ethylene into ethane, but available catalysts have limited stability and selectivity.
Researchers at the University of Florida have developed a catalyst that polymerizes the acetylene in ethylene gas streams into solid cyclic polyacetylene without reacting with the ethylene. Removing acetylene via selective catalysis rather than hydrogenation enables more efficient purification and processing of ethylene gas streams in the production of polyethylene.
Catalytic removal of acetylene from ethylene gas for more efficient polyethylene manufacturing
Ethylene gas bubbles through a solution of this catalyst, polymerizing the acetylene without reacting with the ethylene. The catalytic solution converts acetylene into insoluble cyclic polyacetylene, which readily separates from the stream to purify ethylene gas for polyethylene production. Direct catalytic removal of acetylene replaces the standard hydrogenation reaction to facilitate more efficient processing and reduce energy required in polyethylene synthesis.
This magnetically-triggered drug delivery platform can deliver a wide array of nano-medicines to targeted cells in the body. Nanotechnology is a growing science that is useful in targeting and treating cancerous cells and other harmful agents. The global market for nanoparticles in life sciences is estimated at over $30 billion. While a variety of available nano-medicines allow for encapsulation and delivery of drugs, the mechanism for release is either passive or requires a response to environmental stimuli; most of these approaches do not allow for externally controlled drug release. These magnetically-triggered drug delivery vehicles would respond to an applied alternating magnetic field by releasing a drug, enabling an unprecedented level of control over the spatial and temporal distribution of a drug. This provides clinicians with alternatives to maximize drug efficacy while minimizing side effects.
Magnetically-triggered drug delivery platform for precise encapsulation and externally controlled, targeted delivery of therapeutics
University of Florida researchers have developed a magnetically-triggered drug delivery platform comprising magnetic nanoparticles coated with a biocompatible polymer and conjugated to therapeutic agents through a thermally labile bond. Upon application of an alternating magnetic field, the magnetic nanoparticles release thermal energy, breaking the bonds and actuating the release of the drug. In the absence of the magnetic field, the drug remains encapsulated in the biocompatible polymer shell. The design of these magnetically-triggered drug delivery vehicles is general enough to make this platform nanotechnology attractive for the delivery of a wide array of therapeutic agents, such as small molecule drugs, peptides, and genetic material. In addition, the vehicles could co-deliver multiple therapeutic agents.
This 3D bio-printed liver tissue model, which exhibits the functions of a human liver, tests for and predicts the liver toxicity of new drug therapies. Current approaches used in testing the potential liver toxicity in a compound during the drug development process are animal models and in vitro cell cultures. Animal models often fail to predict toxicity in humans, leading to costly clinical development failures, black box warnings, or withdrawal of drugs from the market. In vitro cultures lack the complexity of live tissue necessary for proper function and accurate responses. There is a critical need for technologies capable of predicting the toxicity of compounds while increasing the pace and lowering the costs of drug development.
Researchers at the University of Florida have developed a 3D bio-printed liver tissue model for toxicological investigations. The 3D-printed liver model has a function comparable to a human liver, accurately predicting the toxicity of drug compounds. It can also potentially be used for drug metabolism studies, identifying disease markers, assessing gene therapy vectors, screenings, and more.
Tests and predicts for liver toxicity of compounds found in drug therapies
This 3D bio-printed liver tissue model comprises a mixture of liver, hepatocyte cells, endothelial cells, extracellular matrix material, and a micro gel medium made from liver-specific culture. Growth media, containing either known toxic or potential therapeutic compounds, is infused into the liver tissue model to analyze compound toxicity. It will induce cellular toxicity or, alternatively, repair cells, allowing for analyzation of any changes to the model. This model also shows a stable production of albumin and urea levels and has a gene expression profile of typical human liver cells. Additionally, its enzymatic cell function is 70 to 80 percent of human liver cells.
This polymer offers potent heat protection and retains its shape during use while having the ability to be molded during manufacturing, reprocessing, and recycling. Conventional heat-shielding materials consist of brittle polymers that burn down to an insulating layer of char under high temperatures. The hardness of such polymers is useful for shielding but complicates manufacturers’ ability to mold or recycle them. With the growing need for robust thermal shielding materials in aerospace, defense, and electronic applications, it is important to consider re-processability and ease of manufacturing.
Researchers at the University of Florida have developed a dynamic polymer with mutable inter-chain links that allow it to access a shapeable state during manufacture and a shielding state for heat protection. Furthermore, this material contains a remarkable amount of inorganic filler, so it can form a large, insulating char layer when burned.
Heat-shielding material for extreme temperature applications that is straightforward to manufacture, mold, and recycle
Polymers are composed of long molecular chains that interact through a combination of physical and chemical forces, including covalent inter-chain linkages, such as crosslinks. These linkages restrict the mobility of chains relative to one another, which significantly influences the mechanical properties of the material. Crosslinking typically enhances rigidity and thermal stability, making such polymers suitable for applications like heat shielding. However, for processes such as reshaping or recycling, materials with greater malleability are desired.
This innovation introduces a dynamic polymer, classified as a vitrimer, combining the desirable traits of rigidity and malleability. Vitrimers feature dynamic covalent bonds capable of bond exchange reactions under specific conditions, enabling reprocessing or reshaping without compromising their structural integrity.
To further enhance its performance, this material is reinforced with polyhedral oligomeric silsesquioxane (POSS), a cage-like inorganic molecule. The incorporation of POSS improves thermal stability and contributes to the integrity and expansion of the insulating char layer formed during combustion. This char layer provides enhanced heat shielding and fire resistance. Researchers at UF successfully synthesized and characterized several dynamic polymer systems reinforced with POSS, demonstrating their potential for advanced applications requiring a combination of thermal stability, mechanical robustness, and recyclability.
This ultrahigh molecular weight (UHMW) adhesive polymer derives its enhanced cohesive strength, creep resistance, and thermal stability from the tangles that naturally form among its long molecular chains. Polymers such as poly(methyl acrylate) consist of exceptionally long strands of repeating units. The more repeating units in a single spaghetti-like strand, the higher the molecular weight of the polymer, with strands weighing in at several million times the weight of a single hydrogen classified as UHMW polymers. Although tangles feature in many polymers, in non-UHMW polymers, entanglement produces only weak physical linkages between strands. This results in a material that is not cohesive enough for applications as a pressure-sensitive adhesive, as found in products such as stickers and tape that are applied simply by pressing down. Chemists typically compensate for weak physical linkages by inducing the different strands to form chemical bonds (cross-links) with each other, linking the various strands more tightly. However, this solution hinders the polymer’s ability to stick to other surfaces (adhesion) even as it boosts its ability to stick to itself (cohesion). A pressure-sensitive adhesive with strong cohesion without cross-links should have better mechanical properties, including a closer balance between cohesion and adhesion. Moreover, by relying on transient entanglements between chains instead of permanent cross-links, these adhesives can be readily debonded to promote the recyclability of electronic wastes.
Researchers at the University of Florida have developed adhesives from UHMW polymers whose hefty molecular weights make them harder to pull apart when entangled, enhancing their cohesion without resorting to cross-links. They also observed that increasing the molecular weights of these materials promoted many desirable mechanical properties, such as creep resistance and toughness.
Pressure-sensitive adhesive with enhanced mechanical and thermal properties without requiring cross-linkers
Commercial adhesive polymers such as those in Sticky Notes and labels can form bonds when pressed down but also should be judged according to their ability to avoid sliding (shear resistance), ability to retain shape over long times (creep resistance), and ability to stay intact at high temperatures (thermal stability). Finally, they should not leave behind a residue when peeled away (cohesive failure), necessitating strong cohesion within the molecules making up the adhesive. The structure of the polymer, including physical entanglement of the chains and chemical cross-links between them, underpins cohesion and other desirable properties. This technology bolsters the contribution of the entangled chains to cohesion by increasing the molecular weight of the chains up to the ultra-high molecular weight (UHMW) regime. To access UHMW materials, light-mediated reversible deactivation is employed to synthesize the polymers. This method not only simplifies production by minimizing steps but also enhances cohesive strength and thermal stability by doing away with the need for cross-linkers.
