SCIENCE & TECHNOLOGY
from the SCENEs FROM THE ENVIRONMENTAL SCENE
SOME BIODEGRADABLE PLASTICS DON’T BIODEGRADE From bread bags to beverage bottles, many plastics now contain additives designed to make the materials biodegradable. But a new study shows that plastics with such additives do not break down in the environment faster than those without them (Environ. Sci. Technol. 2015, DOI: 10.1021/es504258u). Susan Selke and Rafael Auras of Michigan State University and colleagues prepared two plastic samples with three different additives that manufacturers claim help break down
FROM THE MATERIALS SCENE
ACS APPL. MATER. INTERFACES
CELLS CAN FERRY DRUGS IN DISKSHAPED PACKS Using an easy, inexpensive method, researchers have made tiny disk-shaped packs that can ride on cells to deliver drugs (ACS Appl. Mater. Interfaces 2015, DOI: 10.1021/acsami.5b00613). Carried by red or white blood cells, the biodegradable disks could slowly release drugs into the bloodstream or directly inside tumors, says Jingjiao Guan of Florida State University. Guan and his colleagues made a rubber stamp
long polymer chains into fragments that microbes can digest. The samples were films of a low-density polyethylene blend, which is used to make bags, and sheets of polyethylene terephthalate, which is used to make plastic water bottles. The researchers treated the plastics to mimic disposal in a compost pile, a landfill, and soil. After about six months of composting, a year and a half of landfill-like conditions, or three years of soil burial, samples with additives did not show significantly greater signs of microbial degradation than the samples without them. “Plastics with these additives don’t degrade under timescales we’d consider reasonable,” says David J. Tonjes of Stony Brook Uni-
with an array of microsized pillars and deposited four layers of materials on top: a biodegradable thermoplastic that can be loaded with drugs, a polyelectrolyte that adheres to cells, and two compounds sandwiched in the middle that link the thermoplastic to the polyelectrolyte. Pressing the stamp on a glass slide coated with polyvinyl alcohol (PVA) transfers four-layered disks from the pillars to the PVA, creating an array of 7-µm-wide, 220-nm-thick disks on the slide. The researchers then dissolved the PVA, releasing the disks into solution, and mixed them into a suspension of cultured human leukemia cells. Loaded with a fluorescent dye as a mock drug, the disks released 40% of their cargo by weight over seven days. A fluorescence micrograph shows cultured human leukemia cells (green) carrying microdisks (red) that can be loaded with drugs.
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APRIL 13, 2015
ENVIRON. SCI. TECHNOL.
A selection of stories from C&EN’s six online TOPICAL NEWS CHANNELS
After three years of burial in soil, polyethylene films containing additives designed to promote biodegradation (bottom row) did not decompose any faster than films without additives (top row).
versity, SUNY, who was not involved in the work.
FROM THE ANALYTICAL SCENE
MEASURING BACTERIAL DRUG UPTAKE By measuring tiny changes in the concentrations of drugs that remain outside bacterial cells, researchers can infer how much drug the cells have absorbed. The new method could be a simple, straightforward way to screen drug candidates for their ability to penetrate bacteria (Anal. Chem. 2015, DOI: 10.1021/ac504880r). Ying Zhou of AmberGen and her former colleagues at AstraZeneca devised a way to measure drug uptake using ultra-high-performance liquid chromatography paired with mass spectrometry. They mixed a drug and bacteria in both a nutrient solution at 37 °C and in a solution cooled to about –5 °C, a temperature low enough to prevent the bacteria from taking up the drug. After 30 to 60 minutes, the researchers drained off the cells and measured drug concentrations in the remaining liquid. They calculated how much drug was absorbed by the bacteria by comparing the difference between the cold and warm solutions. The team tested the method using two types of gram-negative bacteria and two different antibiotics at weak doses that wouldn’t kill the bacteria.
