Study Unveils New Chemical Payload Bearing Polymer Ideal for Medical Implants

Caltech scientists have developed a new kind of polymer that can carry a chemical payload as part of its molecular structure and release it in response to mechanical stress. The chemical system they have developed could one day be used to create medical implants that can release drugs into the body when triggered by something like ultrasound waves, they say.

Set of Polymer Chains Bonded to the Payload System

The new material consists of a set of polymer chains bonded to the payload system, creating a mechanically sensitive unit called a mechanophore. A so-called cascade reaction ejects the payload from the polymer. In simple terms, force applied to the polymer causes weak bonds in the mechanophore to rupture, spitting out an unstable intermediate molecule that promptly breaks down to release the attached payload.

Release of Coumarin Dye

In their paper, the authors demonstrate the release of a coumarin dye, an organic molecule with useful properties, but they say the polymer could be tailored to release a variety of molecules, including those with therapeutic qualities.

Releasing Drugs on Command

A material that can release drugs on command could be used to provide more precise treatment of some medical conditions, for example, a cancer therapy could deliver a drug directly to the intended target.

"The generality of this new platform is unique in that it allows, in principle, the mechanically triggered release of a wide range of cargo molecules," Robb says.

New System Can Be Used for Triggered Depolymerization

The system Robb and his colleagues have developed could also be tweaked for other purposes. He says that it is possible to create a polymer that depolymerizes or completely breaks down into small molecules, when subjected to stress. Alternatively, a polymer could be tailored to release a reporter molecule to signal locations in a structure that are under stress and could lead to a structural failure.

"We are actively working on expanding the design in a number of directions, to evaluate the scope of cargo release and for triggered depolymerization, which is particularly promising for stress amplification since it allows a single triggering event to generate many small molecules through a domino reaction," Robb says.

Source: Caltech

Toray creates world’s first porous carbon fiber with a nanosized continuous pore structure

Using this fiber as a support layer could lighten advanced membranes used in greenhouse gas separation and hydrogen production and make them more compact, thereby enhancing performance.

The company will keep pushing ahead with R&D for this new material to foster carbon recycling, collaborating with other entities in developing applications to sustainably tap hydrogen energy and shrink environmental footprints.

Absorption- and adsorption-based facilities conventionally separate carbon dioxide, biogas, hydrogen, and other gases. The issue with such setups, however, is that they are large and consume a lot of energy, resulting in heavy carbon dioxide emissions. Gas separation methods employing membranes have thus attracted considerable attention. But despite ongoing research, no membranes have yet combined satisfactory gas separation performance and durability.

Toray’s new material is chemically stable because it comprises carbon, and offers outstanding gas permeability. The material employs thin, flexible fibers, so when it is used to support gas membranes a module can house many of them. Modules can thus be compact and light. Such support makes it possible to combine a range of gas separation layers.

Toray looks to contribute to the swift commercialization of advanced separation membranes that are vital to materializing eco-friendly natural gas and biogas purification and hydrogen production.Toray innovated its new material by combining its outstanding polymer technology with its market share-leading carbon fiber technologies and water treatment and other separation membrane technologies.

Harnessing its polymer technology enabled the company to create a porous carbon fiber with uniformly continuous pores and carbon. It is possible to set nano- through micro-level pore sizes for porous structures. Another possibility is to create a hollow fiber-shaped porous carbon fiber in the center of a fiber.Prospective applications leveraging the excellent adsorption of Toray’s new material include electrode materials and catalyst carriers (base substances for fixing other substances) in high-performance batteries.

Toray will open its R&D Innovation Center for the Future in December this year. The new facility will serve as a global headquarters for strategic innovations by engaging with academic institutions and key partners from diverse fields. The company will collaborate with several partners in efforts leveraging its new material in a drive to commercialize more advanced gas separation membranes.

Under the Toray Group Sustainability Vision, the company looks to keep developing technologies that help materialize low-carbon economies by 2050 by contributing to resolutions of environmental, resources, and energy issues.

Source:TORAY

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New Method to Synthesize Degradable Polymers for Medical Applications

MIT chemists have devised a way to synthesize polymers that can break down more readily in the body and in the environment.

Ring-opening Metathesis Polymerization

A chemical reaction called ring-opening metathesis polymerization, or ROMP, is handy for building novel polymers for various uses such as nanofabrication, high-performance resins, and delivering drugs or imaging agents. However, one downside to this synthesis method is that the resulting polymers do not naturally break down in natural environments, such as inside the body.

Making Polymers More Degradable

The MIT research team has come up with a way to make those polymers more degradable by adding a novel type of building block to the backbone of the polymer. This new building block, or monomer, forms chemical bonds that can be broken down by weak acids, bases, and ions such as fluoride.

“We believe that this is the first general way to produce ROMP polymers with facile degradability under biologically relevant conditions,” says Jeremiah Johnson, an associate professor of chemistry at MIT and the senior author of the study. “The nice part is that it works using the standard ROMP workflow; you just need to sprinkle in the new monomer, making it very convenient.”

This building block could be incorporated into polymers for a wide variety of uses, including not only medical applications but also synthesis of industrial polymers that would break down more rapidly after use, the researchers say.

Non-degradability: The Issue at Hand

The most common building blocks of ROMP-generated polymers are molecules called norbornenes, which contain a ring structure that can be easily opened and strung together to form polymers. Molecules such as drugs or imaging agents can be added to norbornenes before the polymerization occurs.

Johnson’s lab has used this synthesis approach to create polymers with many different structures, including linear polymers, bottlebrush polymers, and star-shaped polymers. These novel materials could be used for delivering many cancer drugs at once or carrying imaging agents for magnetic resonance imaging (MRI) and other types of imaging.

“It’s a very robust and powerful polymerization reaction,” Johnson says. “But one of the big downsides is that the backbone of the polymers produced entirely consists of carbon-carbon bonds, and as a result, the polymers are not readily degradable. That’s always been something we’ve kept in the backs of our minds when thinking about making polymers for the biomaterials space.”

Smaller Polymers, Easy Degradation

To circumvent that issue, Johnson’s lab has focused on developing small polymers, on the order of about 10 nanometers in diameter, which could be cleared from the body more easily than larger particles. Other chemists have tried to make the polymers degradable by using building blocks other than norbornenes, but these building blocks don’t polymerize as efficiently. It’s also more difficult to attach drugs or other molecules to them, and they often require harsh conditions to degrade.

“We prefer to continue to use norbornene as the molecule that enables us to polymerize these complex monomers,” Johnson says. “The dream has been to identify another type of monomer and add it as a co-monomer into a polymerization that already uses norbornene.”

The New Possible Solution

The researchers came upon a possible solution through work Shieh was doing on another project. He was looking for new ways to trigger drug release from polymers, when he synthesized a ring-containing molecule that is like norbornene but contains an oxygen-silicon-oxygen bond. The researchers discovered that this kind of ring, called a silyl ether, can also be opened and polymerized with the ROMP reaction, leading to polymers with oxygen-silicon-oxygen bonds that degrade more easily. Thus, instead of using it for drug release, the researchers decided to try to incorporate it into the polymer backbone to make it degradable.

They found that by simply adding the silyl-ether monomer in a 1:1 ratio with norbornene monomers, they could create similar polymer structures to what they have previously made, with the new monomer incorporated fairly uniformly throughout the backbone. But now, when exposed to a slightly acidic pH, around 6.5, the polymer chain begins to break apart.

“It’s quite simple,” Johnson says. “It’s a monomer we can add to widely used polymers to make them degradable. But as simple as that is, examples of such an approach are surprisingly rare.”

Faster Breakdown

In tests in mice, the researchers found that during the first week or two, the degradable polymers showed the same distribution through the body as the original polymers, but they began to break down soon after that. After six weeks, the concentrations of the new polymers in the body were between three and 10 times less than the concentrations of the original polymers, depending on the exact chemical composition of the silyl-ether monomers that the researchers used.

The findings suggest that adding this monomer to polymers for drug delivery or imaging could help them get cleared from the body more quickly.

Tuning the Breakdown of ROMP-based Polymers

“We are excited about the prospect of using this technology to precisely tune the breakdown of ROMP-based polymers in biological tissues, which we believe could be leveraged to control biodistribution, drug release kinetics, and many other features,” Johnson says.

The researchers have also started working on adding the new monomers to industrial resins, such as plastics or adhesives. They believe it would be economically feasible to incorporate these monomers into the manufacturing processes of industrial polymers, to make them more degradable, and they are working with Millipore-Sigma to commercialize this family of monomers and make them available for research.

Source: MIT

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