Medical Design Briefs - April 2021 - 35

4D Bioengineering Materials Bend,
Curve Like Natural Tissue
The materials change
shape over time in
response to stimuli.
University of Illinois,
Champaign, IL
Tissue engineering has long depended
on geometrically static scaffolds seeded
with cells in the lab to create new tissues
and even organs. The scaffolding material - usually a biodegradable polymer
structure - is supplied with cells and the
cells, if supplied with the right nutrients,
then develop into tissue as the underlying
scaffold biodegrades. But this model
ignores the extraordinarily dynamic morphological processes that underlie the
natural development of tissues.
Now, researchers at the University of
Illinois Chicago have developed new 4D
hydrogels - 3D materials that have the
ability to change shape over time in
response to stimuli - that can morph
multiple times in a preprogrammed or
on-demand manner in response to external trigger signals.
In a new Advanced Science study, the
UIC researchers, led by Eben Alsberg,
show that these new materials may be
used to help develop tissues that more
closely resemble their natural counterparts, which are subject to forces that
drive movement during their formation.
" The hydrogels can be programmed or
induced to undergo multiple control-

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lable shape changes over time. This strategy creates experimental conditions to
partially mimic or stimulate the continuous different shape changes that developing or healing tissues undergo, and it may
let us study morphogenesis and also help
us engineer tissue architectures that
more closely resemble native tissues, " says
Alsberg, the Richard and Loan Hill
Professor of Biomedical Engineering and
corresponding author on the paper.
The novel material is made up of different hydrogels that swell or shrink at
different rates and extents in response to
water or the concentration of calcium.
By creating complex layering patterns,
the researchers can guide the conglomerate material to bend one way or another as the layers swell and/or shrink.
" We can change the shape of these
materials by adjusting, for example, the
amount of calcium present, " says
Alsberg, who also is professor of orthopedics, pharmacology, and mechanical
and industrial engineering at UIC.
In their experiments, the researchers
were able to cause the hydrogel to form
into pockets similar in shape to alveoli,
the tiny sac-like structures in the lung
where gas exchange takes place.
Not only are Alsberg's hydrogels able
to change their architecture multiple
times, but they also are highly cytocompatible, which means they can have
incorporated cells and the cells remain
alive - something that many existing
4D materials are unable to do.

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Stimulus 1

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4D hydrogel-based materials can undergo multiple conformational shape changes in response to
environmental cues. (Credit: Aixiang Ding)

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Medical Design Briefs - April 2021

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