Author: Shalini Saxena

The advent of plastics has given humanity a prominent materials footprint on the world. Plastics provide lots of benefits, such as convenience and low cost, but proper recycling or disposal of plastics is an ongoing challenge.

Most conventional plastics do not undergo appreciable biological degradation. Plastic that is not properly disposed of ends up in the environment, where it breaks down into smaller and smaller pieces. In the ocean, plastic often ends up in fragments less than five millimeters in size.

This microplastic debris can be ingested by marine biota, and it affects life both physically and chemically. But little is known about the overall effect of plastic pollution on marine animals or the mechanisms that would drive any effects. In a recent investigation published in Science, researchers from Sweden explored the influence of plastic microparticles on the development and survival of a fairly typical fish.

Customizable, wearable electronics open the door to things like heart-monitoring t-shirts and health-tracking bracelets. But placing the needed wiring in a complex 3D architecture has been hard to do cheaply. Existing approaches are limited by material requirements and, in the case of 3D writing, slow printing speeds. Recently, a research team at Harvard University developed a new method to rapidly 3D print free-standing, highly conductive, ductile metallic wires.

The new method combines 3D printing with focused infrared lasers that quickly anneal the printed nanoparticles into the desired architecture. The result is a wire with an electrical conductivity that approaches that of bulk silver.

3D printed conductive wires

The new 3D printing approach starts like a standard inkjet: concentrated silver nanoparticle inks are printed through a glass nozzle. The ink is then rapidly annealed by a focused infrared beam trailing the print stream by 100µm. This laser annealing process increases the density of the nanoparticles, transforming them into a shiny silver wire. The researchers demonstrated its ability to print an array of silver wires with diameters ranging from the sub-micron up to 20µm through variation of a few key printing parameters.

Our skin provides a protective barrier against things like extreme temperatures, toxins, microorganisms, radiation, and mechanical force. But as skin ages, it becomes weaker, more sensitive, and less able to repair itself. Aging also results in things we don't like, such as the formation of wrinkles or sagging skin.

Many individuals spend a great deal of time and money trying to restore their skin’s youthful appearance, but what if there was a simpler way? In an investigation recently published in Nature Materials, a team of scientists have developed a synthetic skin that can be worn invisibly, restoring both the mechanical and aesthetic characteristics of normal, youthful skin.

Complex design criteria

Though the skin may seem like a simple organ, development of a synthetic skin isn’t as easy as it sounds. The material needs to be formulated so that it can be easily spread across the skin and then adhere to it. It also needs to be biocompatible, preventing skin irritation or sensitization. The synthetic skin would have to be breathable yet protect against the environment—and it can't be toxic itself.

Most of us are by now aware of the harmful effect greenhouse gas emissions exert through rising global temperatures. As temperatures go up, glaciers melt and ocean levels rise. Climate change also exacerbates water scarcity worldwide.

Water scarcity significantly impacts agricultural productivity and food scarcity. These impacts will be felt the most in arid regions, where agriculture depends on irrigation, which represents humanity's largest diversion of freshwater.

For the most part, we think of rising levels of carbon dioxide as an environmental problem. But atmospheric CO₂ can also boost agricultural productivity by helping plants grow. How do these potential issues balance out? In an investigation recently published in Nature Climate Change, scientists have looked into the global implications of carbon dioxide's ability to enhance agricultural productivity.

Heat engines are able to turn the thermal energy of a material into force and motion. Since the industrial revolution, they've been essential for the development of modern machines and industrial plants.

Heat engines require a heat source and a colder heat sink. Mechanical motion is generated through the movement of a material from the higher temperature heat source to a lower temperature heat sink. Typical heat engines are large, containing a lot of fluid—usually on the order of 10²⁴ fluid particles.

In the 1950s, leading scientists suggested that heat engines could operate at the atomic-level. Over the past decade, scientists and engineers have worked to miniaturize the heat engine. Their efforts resulted in the development of microscale heat engines, but the atomic-level heat engine remained elusive.

Semiconductors are integral to modern electronics. Currently, they're made by etching features into silicon, but researchers are constantly exploring new fabrication approaches that balance cost, energy efficiency, electronic capabilities, and mechanical properties.

Recently, scientists have demonstrated the ability to design and fabricate flexible, high-performance semiconductors out of colloidal nanocrystals. The approach allowed them to lay out the circuitry using simple solution processing, in which the components are put in place while suspended in a liquid. Solution processing is generally cheap and convenient, and it can be used to cover large areas at once.

Field effects

The specific type of device the researchers designed is called a field-effect transistor. In general, transistors are semiconductor devices used to amplify or switch electrical signals and power. Field-effect transistors use an electric field in a device called a gate to influence the conductivity of a nearby semiconductor.

Black carbon particles are composed of pure carbon, linked via several types of bonds. The particles are formed by the incomplete combustion of fossil fuels, biofuels, and biomass. When they're suspended in the atmosphere, these particles can mix with other aerosols, including organics and sulfates, and they can directly absorb sunlight. So once in the air, black carbon can both influence the climate and impact air quality.

Once suspended in the atmosphere, black carbon's warming effect can last days to weeks; it also absorbs a broad range of light. However, it is still unclear whether this absorption changes as the particles undergo chemical reactions in the atmosphere—changes that could have big implications for its influence on the climate.

Now, an international team of scientists developed an environmental chamber that allowed them to study the evolution of black carbon's properties in the atmosphere. They tested their new technique on pollution from cities in the US and China.

Diabetes is growing into a global public health crisis, one that places enormous economic burdens on many nations. Once thought of as a disease that typically strikes affluent adults, type 2 diabetes has quickly spread all over the world, indifferent to socioeconomic status or age.

Treatment of type 2 diabetes requires patients to control their blood sugar levels through a mix of dietary restrictions and medication. Unfortunately, following the progress of these efforts is not as easy as it sounds. Glucose-monitoring devices available on the market typically require the user to obtain a small blood sample that can be read to quantify the level of the sugar. A minimally or non-invasive alternative would probably help many patients stay on top of their health.

Recently, a team of scientists have designed a flexible glucose-monitoring device that conforms to the skin and is barely visible. The device contains an array of sensors that are patterned onto gold-doped graphene and connected by a gold mesh. This setup both improves the electrochemical activity of graphene and enhances the biochemical sensitivity of the system.

Plastics are everywhere. Once they get into the environment as trash, they stay there for years, decades, or even centuries. That's because most plastic is chemically inert and immune to the enzymatic processes involved in biodegradation. We've tried to curtail plastic pollution through recycling and by creating plastics that are biodegradable or compostable. But what about all the plastic litter that's already out there and could persist long after our grandchildren are gone?

Life may be coming to our aid. A team of scientists in Japan, led by Shosuke Yoshida of Kyoto University, has recently discovered a species of bacteria that can degrade a plastic called PET.

Identifying microbes that degrade PET

PET stands for polyethylene terephthalate, a plastic with good mechanical, barrier, and optical properties. Bottles for water and soft drinks are just a couple of PET's many, many uses. PET is a polyester compound with a high aromatic content, which makes it chemically inert. As a result, it is typically considered resistant to microbial degradation, although certain fungi grow on a mineral medium containing PET. Roughly 56 million tons of PET are produced each year, and a lot of that ends up in the environment.

Carbon dioxide (CO₂) is the most common greenhouse gas produced by the US. It enters the atmosphere through the burning of fossil fuels, solid wastes, wood, and certain manufacturing processes. The growing abundance of CO₂ in the atmosphere makes it an attractive feedstock for commodity synthesis, which could reduce the greenhouse gases in the atmosphere.

Though scientists have explored this concept before, few have had success due to the difficulty of breaking the carbon-oxygen bond and forming carbon-carbon bonds efficiently. The current approaches require high-energy reagents, which limit the reactions to low volumes, ultimately negating any environmental benefit of drawing down CO₂.

A team of scientists at Stanford recently published a successful route to using CO₂ to produce a highly desirable bio-based feedstock. This particular feedstock can be used to synthesize a renewable polymer that has the potential to replace a pervasive, fossil-fuel derived polymer, polyethylene terephthalate.