One step closer to "design on demand" scaffolds for tissue regeneration

The structure of cross-linked polymeric gels is very similar to that of soft tissues, which is why understanding this material is so essential, according to Kelly Schultz, an assistant professor in the Department of Chemical and Biomolecular Engineering at Lehigh University.

Schultz was part of a special session of the annual meeting of the AIChE (American Institute of Chemical Engineering) in Pittsburgh last month, where she was invited to present the work of her lab to determine how the Increasing polymer concentrations in solution altered the structure of the crosslinked gels. . The title of the session was "Future AIChE Newspapers: New Directions in Chemical Engineering Research".

Schultz's presentation is based on an article she invited by participating in the first edition of AIChE's "Future Issues," designed to highlight the work of early-career researchers . The paper, co-authored by his former doctoral student Matthew Wehrman, and four Lehigh students, is titled "Rheological Properties and Structure of Step-and-Chain Growth Gels Concentrated Above Concentration Overlap."

"The increase in polymer concentration allows them to interact," Schultz said. "These interactions can alter the structure of the material and even potentially weaken it."

Through experiments, she and her team discovered that the structure of the cross-linked polymer gels was independent of the concentration until a limit was reached, called the overlap concentration, at which the polymers began to interact. . After this limit, the structure is again independent of the concentration.

The group's central finding is that more polymers do not necessarily mean that the gel will be more elastic or stiffer.

"It was unexpected," says Schultz. "We thought that there would be a gradual change in the structure of the scaffold, but there is a gradual change when these interactions become high enough."

The identification of this feature could be of particular importance for industrial applications, as the team's work shows that these crosslinked polymeric gel structures can be obtained with a smaller amount of polymer.

"In other words," says Schultz, "you can achieve the desired result with the least amount of hardware possible."

Schultz's work on this topic is new because of the way his team has examined scaffolds with high polymer concentrations – or with polymer interactions. Most studies, she says, remain under the overlap concentration so that polymer interactions do not complicate gelation.

"With this work, chemical engineers can begin to understand how polymer interactions alter gel structure and how to access these structures at relatively low polymer concentrations," says Schultz.

The team used a technique called microrheology of Multiple Particle Tracking (MPT) to measure the gelation of these polymer hydrogel scaffolds. This technique uses video microscopy to capture the thermal motion of embedded probe particles. From the thermal movement, they can determine the properties of the material. By combining MPT and an analysis technique, the time-hardening superposition, they were able to determine the gel time and material structure at the gel point, when the first sample covering the network is formed.

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More information:
Matthew D. Wehrman et al. The rheological properties and structure of step and chain growth gels concentrated above the overlap concentration, AIChE Journal (2017). DOI: 10.1002 / aic.16062