Study reveals novel technique for handling molecules

Like trading companies, biological systems pick up freight items (in the form of small molecules), transport them from place to place and release them at their proper destination.

These processes are critical for activities ranging from photosynthesis in plants to neuronal signaling in the human brain. The efficient capture, transport and release of molecules is also vital for the maintenance of equilibrium, essential to all living things.

In research appearing in the current issue of the journal Nature Chemistry, Ximin He and her colleagues describe a method capable of mimicking nature’s ability to sort, capture, transport and release molecules. The technique sets the stage for continuous and efficient manipulation of a broad range of molecules of relevance to human and environmental health.

Professor He is a researcher at Arizona State University’s Biodesign Institute, where she recently joined the Center for Molecular Design and Biomimetics.

Material world

Much of He’s research, the current project included, centers around the design of energy-efficient, environmentally-responsive materials and devices capable of reacting to environmental cues, adapting their behaviors and exhibiting self-regulation. Such biomimetic materials have broad implications in diverse fields, ranging from biotechnology and biomedicine to chemical engineering and environmental cleanup.

“Biological systems use feedback as a crucial component to provide efficient performance. Yet, the use of feedback has not been exploited to a sufficient extent in the design of new material systems,” He said. “We must learn how to engineer responsiveness to environmental changes and the ability to perform important functions into the framework of new materials. In this research, the components are integrated to enable adaptive functionality and encompass feedback.”

The highly interdisciplinary research combines chemistry, materials science and mechanical engineering, in addition to biology.

This figure illustrates hydrogel-aptamer capture and release. In the current study, changes in solution pH cause the hydrogel to either swell or contract. High pH produces a swollen state, causing slender probes or aptamers (seen in blue) to extend, like the claws of a kitten. When the pH of the hydrogel is reduced and the environment becomes acidic, the hydrogel contracts, causing the aptamer probes to relax, pulling away the bound molecules (orange and yellow), which are released and free to re-circulate. Photo by: The Biodesign Institute at Arizona State University
This figure illustrates hydrogel-aptamer capture and release. In the current study, changes in solution pH cause the hydrogel to either swell or contract. High pH produces a swollen state, causing slender probes or aptamers (seen in blue) to extend, like the claws of a kitten. When the pH of the hydrogel is reduced and the environment becomes acidic, the hydrogel contracts, causing the aptamer probes to relax, pulling away the bound molecules (orange and yellow), which are released and free to re-circulate.
Photo by: The Biodesign Institute at Arizona State University

Recipes of nature

Continuous self-monitoring and self-regulation are hallmarks of living systems, which seamlessly convert chemical to mechanical energy and vice versa, subtly adjusting their state as environmental conditions change. Transformations of chemical and mechanical energy are essential for organismic self-regulation and survival, and are responsible for things like muscle contraction.

Researchers would like to create synthetic materials that can copy this behavior, but the task has been challenging. Typically, synthetic materials operate in only one direction, either transforming chemical to mechanical energy or the reverse, and tend to be responsive only to certain chemicals.

In contrast, the method described in the new study offers great versatility, permitting the capture, transport and release of specific molecules. The approach described could be used for sustained-release drug delivery systems, new generations of ultra-sensitive diagnostics and chemical sensing devices.

In addition to applications in biomedicine, the new method could be used to create an energy-efficient means of removing waste from the environment, capturing valuable minerals, performing desalination of sea water or trawling for hazardous substances like radioactive nuclides or heavy metals in rivers and streams.

Unlike most existing methods, the new technique can operate autonomously, mimicking the self-regulatory nature of living systems without the need for conventional external energy sources like laser, infrared, magnetic or electric fields.

Sifting for molecules

At the heart of the new system is a substance known as a hydrogel, a highly absorbent polymer that can mimic certain properties of living tissue.

Some hydrogels – referred to as ‘Smart Gels’ – can sense subtle changes in their surroundings, including alterations of temperature, pH or metabolite concentration. In response, the hydrogel may expand or contract, and in the process, cause the binding or release specified target molecules under proper conditions (see Figure 1).

Findings

The new technique offers a significant advance over conventional methods of sorting biomolecules, which typically involve molecular modification, numerous experimental steps and energy input from external sources.

The reversible nature of the capture, transport and release system allows for multiple recycling of biomolecules and high rates of target recovery. The use of complementary responsive materials permits the system to be custom designed to meet a broad range of needs.

In addition to her appointment at the Biodesign Institute, Ximin He is an assistant professor of materials science and engineering and graduate faculty of chemical engineering at the School for Engineering of Matter, Transport and Energy, one of ASU’s Ira A. Fulton Schools of Engineering.

The research is sponsored by the Department of Energy, Basic Energy Science Division, Biomolecular Materials Program.

Richard Harth, Richard.Harth@asu.edu
The Biodesign Institute

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