The production of energy-rich fats by microalgae may provide a sustainable, renewable energy source that can help combat climate change. However, microalgae, which are engineered to produce lipids rapidly, typically grow slowly themselves, making it difficult to increase overall yield.
UCLA bioengineers have developed a new type of petri dish in the form of microscopic, permeable particles that can significantly speed up research and development (R&D) schedules for biological products, such as fatty acids for biofuels. Dubbed PicoShells, the porous picoliter (trillionths of a liter) hydrogel particles can allow more than a million individual cells to be subdivided, cultured in production-relevant environments, and selected based on growth and biomass accumulation characteristics using standard cell processing equipment.
Proceedings of the National Academy of Sciences recently published a study describing how PicoShells work and their potential applications.
PicoShells consist of a hollow inner cavity in which cells are encapsulated and a porous outer shell that allows continuous solution exchange with the external environment, allowing nutrients, cell-communicating molecules, and cytotoxic cellular byproducts to be freely transported in and out of the inner cavity. The shell also keeps the small groups of growing cells enclosed, allowing researchers to study and compare their behavior – what they do, how fast they grow, what they produce – with that of other groups in different PicoShells.
This new class of laboratory tools allows researchers to grow live, single-celled microorganisms – including algae, fungi and bacteria – under the same industrial production conditions as e.g. B. in a bioreactor filled with waste water or an open-air cultivation pond.
“PicoShells are like very small net balloons. The growing cells within them are effectively fenced off, but not sealed off,” said study leader Dino Di Carlo, UCLA Armond and Elena Hairapetian Professor of Engineering and Medicine at the UCLA Samueli School of Engineering. “With this new tool, we can now study the individual behavior of millions of living cells in the respective environment. This could shorten the timeframe from R&D to commercial production of organic products from a few years to a few months. PicoShells could also be a valuable tool for basic biology studies.”
The permeability of PicoShells can bring the lab into the industrial environment and allow testing in a segregated area of a work facility. Growth can be faster and well-functioning cell strains can be identified and selected for further screening.
According to the researchers, another benefit of this new tool is that it automates the analysis of millions of PicoShells, since they are also compatible with standard laboratory equipment used for large-scale cell processing.
Huge groups of cells, up to 10 million in a day, can be sorted and organized according to specific characteristics. Ongoing analysis could lead to ideal sets of cells — those that already perform well in the environment with the right temperature, nutrient composition, and other properties that could be used in mass production — in just a few days, rather than the several months that use lasts would current technologies.
The shells can be engineered to rupture when the cells inside have divided and outgrown their maximum volume. These free cells are still viable and can be recaptured for further research or further selection. Researchers can also fabricate dishes with chemical groups that break down when exposed to biocompatible reagents, allowing for a versatile approach to release selected cells.
“If we want to focus on algae that are best at producing biofuels, we can use PicoShells to organize, grow, and process millions of individual algal cells,” said lead author Mark van Zee, a graduate student in bioengineering at UCLA Samueli. “And we can do that in machines sorting them with fluorescent labels that light up to show fuel levels.”
Currently, culturing and comparing such microorganisms is mainly done using traditional laboratory tools such as microtiter plates—cardboard boxes containing several dozen small test-tube-like volumes. However, these methods are slow and it is difficult to quantify their effectiveness as it can take weeks or months to grow large colonies for studies. Other approaches, such as water-in-oil droplet emulsions, can be used to analyze cells in smaller volumes, but surrounding oils prevent the free exchange of medium into the water droplets. Even cells or microorganisms that perform well in laboratory conditions may not perform as well when placed in industrial settings such as bioreactors or outdoor culture. For this reason, cell strains developed in the laboratory often do not show the same beneficial properties when transferred to industrial production.
Microtiter plates are also limited in the number of experiments that can be performed, leading to a great deal of trial and error to find cell strains that work well enough for mass production.
The researchers demonstrated the new tool by growing algae and yeast colonies and comparing their growth and viability to other colonies grown in water-in-oil emulsions. In the algae, the team found that PicoShell colonies quickly accumulated biomass, while algae in water-in-oil emulsions did not grow at all. Similar results were found in their yeast experiments. By selecting the best-growing algae in PicoShells, the researchers were able to increase chlorophyll biomass production by 8% after just a single cycle.
The authors said PicoShells could provide a faster alternative for developing new strains of algae and yeast, leading to improved biofuels, plastics, carbon capture materials, and even food products and alcoholic beverages. Further refinements of the technology, such as coating the shells with antibodies, could also lead to the development of new types of protein-based drugs.
Di Carlo, van Zee and study co-author Joseph de Rutte Ph.D. ’20, a former member of Di Carlo’s research group, is named as the inventor in a patent application filed by the UCLA Technology Development Group.
The other UCLA authors on the paper are Rose Rumyan, Cayden Williamson, Trevor Burnes, Andrew Sonico Eugenio, Sara Badih, Dong-Hyun Lee, and Maani Archang. Randor Radakovits of Synthetic Genomics of San Diego is also an author.
The study was supported by the Presidential Early Career Award for Scientists and Engineers and a planning award from the California NanoSystems Institute (CNSI) at UCLA.
Di Carlo holds faculty appointments in bioengineering and mechanical and aerospace engineering at UCLA Samueli. He is a member of CNSI and the Jonsson Comprehensive Cancer Center at UCLA.