- Power plants: Technologies for green fuel
- Environmental engineering, for stem cells
- Growing solar, at the speed of light (almost)
Power plants: Technologies for green fuel
California bay trees and clumps of Cladophora algae in the shallows of Madison’s Lake Mendota may not, at first glance, appear to have much in common. However, both species are seeding the future of biofuels research at UW-Madison.
Assistant Professor Brian Pfleger is working to turn sugars from biomass into hydrocarbon fuels. By inserting a gene from bay trees into E. coli, Pfleger is able to harness bacterial metabolism to convert sugars into free fatty acids. He can extract these fatty acids with hydrocarbons and pass the mixture over a catalyst, creating a form of diesel fuel that can be burned in current engines.
To optimize the expression of biosynthetic enzymes, Pfleger’s team takes a systems biology approach in studying the global picture of a cell’s DNA, RNA, proteins and metabolic processes. The researchers are using a variety of modeling and experimental techniques to understand how engineering a cell to create more fatty acids than it normally would affects enzyme production and overall cell viability.
“We’re applying engineering principles to biological systems,” Pfleger says. “If you build the right system, it theoretically should work. But it’s biology, so there’s always a question of the connections we don’t know or don’t understand yet.”
The many challenges of modeling and creating a working biological system means Pfleger collaborates extensively across campus, particularly with researchers in the Great Lakes Bioenergy Research Center. Some of these collaborations allow Pfleger to expand his work beyond molecular systems to more industrial biofuel issues.
Pfleger is part of a team studying the potential of Cladophora algae as a biomass source. Unlike terrestrial plants like corn stover or switchgrass, aquatic plants don’t have much lignin, the compound that makes breaking plants down to extract sugars difficult. Cladophora naturally produces a “beautiful” form of cellulose, says Pfleger, which can be easily decomposed and converted into fatty acids.
The team has received a grant from the Wisconsin Energy Independence Fund for pilot studies about the algae’s potential that will be published later in 2010.
Environmental engineering, for stem cells
Most stem cell researchers handle their samples very delicately. Associate Professor Sean Palecek prefers to pull them, add chemicals or pulse them with current.
Palecek is using embryonic and induced pluripotent stem cells to study how cells differentiate and how to guide that differentiation. Induced pluripotent stem cells are adult human cells that have been reverted back to an embryonic state via a method pioneered by renowned UW-Madison stem cell scientist James Thomson.
Cells in an embryonic state can divide an unlimited number of times and can differentiate into any type of cell in the body. These are special characteristics, as every other healthy cell in the body can make only a certain number of division.
Palecek is working to guide stem cell differentiation into endothelial (blood vessel) cells, epithelial (skin) cells and cardiomyocytes (heart cells). He places stem cells in various micro-environments to see which factors in those environments best facilitate cell growth. For example, endothelial cells have fluid flowing across them, so Palecek tests whether that fluid flow is necessary for the cells to develop. Epithelial cells develop well in a matrix and respond to particular chemical cues.
One of Palecek’s unique discoveries is that culturing stem cells in three-dimensional arrays stimulates cell-cell communication, significantly improving the yield of cardiomyocytes.
The variety of micro-environments means Palecek’s work encompasses a range of bioengineering issues. “We get pulled a lot into the mechanical side because the extracellular matrix that surrounds the cells ties into cell surface proteins,” he says. “The matrix allows the cells to attach to their environment and provides chemical signaling to the cells, so you can’t decouple mechanics from chemistry. We have to look at both.”
While producing whole human tissues and organs for medical treatment is a long way off, stem cell research also yields rare insight into early human development and produces tissues for pharmaceutical research to complement animal testing.
Growing solar, at the speed of light (almost)
Drawing on somewhat of an “old-school” crystal-growth method, Milton A. and J. Maude Shoemaker Professor Tom Kuech and graduate student Kevin Schulte are studying how rapid synthesis affects the chemistry and electrical properties of gallium arsenide. Their results could point the way to faster, less costly manufacturing processes for solar cell materials.
Most solar cells are made from silicon; however, gallium arsenide is a promising alternative as one component of multijunction, or “stacked,” solar cells, says Kuech. “The highest-efficiency solar cells consist of a solar cell of gallium arsenide, and then what you do is put another solar cell on top of that, and another one, and stack them — each one grabbing its own little bit of the solar spectrum,” he says.
The process for making gallium arsenide for solar cells is much like making transistors for cell phones and lasers for communications. Yet, particularly for solar cells, the process is costly and slow.
Working with researchers at the National Renewable Energy Lab, Kuech and Schulte are studying ways to synthesize materials for solar cells at rates that are orders of magnitude faster than the current methods, molecular beam epitaxy and metal-organic vapor phase epitaxy. Those processes require expensive equipment, within which researchers very slowly deposit atoms onto a wafer, and the atoms arrange themselves and continue to grow in the crystal form. Materials typically grow at the slow rate of a micron or two an hour.
Using a unique reactor they are building, Kuech and Schulte are investigating whether entirely different growth technology and material chemistry could accelerate the manufacturing process without sacrificing solar cell performance or introducing material defects. Their system takes advantage of an early-’80s semiconductor thin-film growth technique called hydride vapor phase epitaxy. While they are using gallium chloride and arsine for this research, Kuech and Schulte have shown they can grow gallium nitride materials at a rate of hundreds of microns an hour. It’s a system that could scale up from a batch process to a continuous manufacturing process, says Kuech. “So now you’re talking about time-on-tool that went from hours down to minutes,” he says.