#shape memory polymers

Super-adhesive patches can adapt to different motions for enhanced skin interaction

A research team affiliated with UNIST has unveiled an ultra-strong adhesive patch platform that adheres effectively to rough skin surfaces and shows remarkable motion adaptiveness during dynamic body movements, all while offering irritation-free removal on demand. The key to this technology lies in the surface adaptability inspired by barnacles and armadillo carapaces, which feature a tessellated structure that balances rigidity and flexibility. The team, led by Professor Hoon Eui Jeong from the Department of Mechanical Engineering and Professor Jae Joon Kim from the Department of Electrical Engineering at UNIST, along with researchers from the National Institute of Ecology (NIE), has introduced a highly adhesive, detachable, and stretchable skin patch, known as the Motion Adaptive Tessellation Patch.

Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a smart, reusable adhesive more than ten times stronger than a gecko's feet adhesion, pointing the way for development of reusable superglue and grippers capable of holding heavy weights across rough and smooth surfaces. The NTU research team, led by Professor K Jimmy Hsia, found a way to maximise the adhesion of the smart adhesives by using shape-memory polymers, which can stick and detach easily when needed simply by heating them. Writing last month in the scientific journal National Science Review, the team details their breakthrough in adhesion by designing the shape-memory polymer material in the shape of hair-like fibrils.

Swift 4-D printing with shape-memory polymers

Shape-memory polymers or shape-shifting materials are smart materials that have gained significant attention within materials science and biomedical engineering in recent years to build smart structures and devices. Digital light processing is a vat photopolymerization–based method with significantly faster technology to print a complete layer in a single step to create smart materials. Fahad Alam and a team of scientists in electrical and computer engineering, and nuclear engineering at the King Abdullah University of Science and Technology, Saudi Arabia developed a facile and fast method to 3D print shape-memory polymer-based smart structures with a digital light printing 3D printer and custom resin. They combined a liquid crystal (a material that can change its shape with temperature) with resin, to introduce shape-memory properties to directly 3D print thermoresponsive structures—while avoiding the complexity of resin preparation. The team printed the structures with different geometries and measured the shape-memory response. The shape-memory polymers can be conveniently prepared for use as smart tools, toys, and meta-materials.

High-energy shape memory polymer could someday help robots flex their muscles

When stretched or deformed, shape memory polymers return to their original shapes after heat or light is applied. These materials show great promise for soft robotics, smart biomedical devices and deployable space structures, but until now they haven't been able to store enough energy. Now, researchers reporting in ACS Central Science have developed a shape memory polymer that stores almost six times more energy than previous versions.

Shape memory polymers alternate between an original, undeformed state and a secondary, deformed state. The deformed state is created by stretching the polymer and is held in place by molecular changes, such as dynamic bonding networks or strain-induced crystallization, that are reversed with heat or light. The polymer then returns to its original state through the release of stored entropic energy. But it's been challenging for scientists to make these polymers perform energy-intensive tasks. Zhenan Bao and colleagues wanted to develop a new type of shape memory polymer that stretches into a stable, highly elongated state, allowing it to release large amounts of energy when returning to its original state.

New method to produce composites with 'shape memory'

Skoltech researchers have investigated a promising type of composite material in terms of their shape memory behavior—how they resume their original shape following deformation if exposed to the right temperature or other conditions. The materials studied were glass fiber-reinforced epoxy-based flat laminates, produced with a technique called pultrusion. While it has considerable potential for manufacturing composites with shape memory for electronics, biomedicine, and more, the method's application to such materials is examined for the first time in the Skoltech-led study reported in Composites Part A: Applied Science and Manufacturing.

Shape memory polymers, or SMPs, are materials that can recover their initial shape under external stimuli such as temperature, light, moisture, acidity, electricity, or electromagnetic field. They are widely used in the aerospace, biomedical, and automotive industries, as well as in 4D printing, temperature sensors, and electronic devices.

SMPs are often reinforced with carbon, basalt, or glass fibers, resulting in composite materials with superior properties. A number of techniques are used for SMP composite manufacturing, most of them fairly well-studied. Surprisingly, until now there have been no studies on the shape memory effect in composites produced by pultrusion—the most efficient composite manufacturing process available. It is a fast, versatile, and low-waste technology that could potentially yield new types of shape memory structural components with unique combinations of geometries and mechanical properties, impossible to produce with other methods.

Research team extends 4-D printing to nanophotonics

The Singapore University of Technology and Design (SUTD) and its research collaborators have successfully demonstrated the four-dimensional (4-D) printing of shape memory polymers in submicron dimensions which are comparable to the wavelength of visible light. This novel development has allowed researchers to now explore new applications in the field of nanophotonics.

4-D printing enables 3-D printed structures to change its configurations over time and is used in a wide variety of fields such as soft robotics, flexible electronics, and medical devices.

Different materials such as hydrogels, liquid crystal elastomers and magnetic nanoparticles embedded resists along with corresponding printing methods like Direct Ink Writing (DIW), Polyjet, Digital Light Processing (DLP) lithography and Stereolithography (SLA) have been developed for 4-D printing. However, the material and patterning challenges inherent to these methods limit the resolution of 4-D printing to ~10 μm at best.

Plasmon-coupled gold nanoparticles useful for thermal history sensing

Researchers have demonstrated that stretching shape-memory polymers embedded with clusters of gold nanoparticles alters their plasmon-coupling, giving rise to desirable optical properties. One potential application for the material is a sensor that relies on optical properties to track an object or environment's thermal history.   

At issue is a stretchable polymer embedded with gold nanospheres. If the material is heated and stretched, followed by cooling to room temperature, the material will hold its stretched shape indefinitely. Once reheated to 120 degrees Celsius, the material returns to its original shape.

But what's really interesting is that the gold nanospheres are not perfectly dispersed in the polymer. Instead, they form clusters, in which their surface plasmon resonances are coupled. These plasmon-coupled nanoparticles have optical properties that shift depending on how close they are to each other, which changes when stretching alters the shape of the composite.

Tiny magnetic particles enable new material to bend, twist, and grab

A team of researchers from the Georgia Institute of Technology and The Ohio State University has developed a soft polymer material, called magnetic shape memory polymer, that uses magnetic fields to transform into a variety of shapes. The material could enable a range of new applications from antennas that change frequencies on the fly to gripper arms for delicate or heavy objects.

The material is a mixture of three different ingredients, all with unique characteristics: two types of magnetic particles, one for inductive heat and one with strong magnetic attraction, and shape-memory polymers to help lock various shape changes into place.

"This is the first material that combines the strengths of all of these individual components into a single system capable of rapid and reprogrammable shape changes that are lockable and reversible," said Jerry Qi, a professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech.

The research, which was reported Dec. 9 in the journal Advanced Materials, was sponsored by the National Foundation of Science, the Air Force Office of Scientific Research, and the Department of Energy.