Indiana University-Purdue University Indianapolis (IUPUI) / Dynamic changes to the extracellular matrix (ECM) impact many cell fate pro-
cesses. The ECM can experience changes in sti ness as well as changes in composi-
tion in response to injury, development, and diseases. To better understand the role
that these dynamic processes have on the cells residing within the environment, re-
searchers have turned towards 4-dimensional (4D) hydrogel designs. These 4D hydro-
gels re-capitulate not only 3-dimensional (3D) matrix architectures, but also temporal
changes in the physicochemical properties. The goal of this thesis was to design a
unify chemistry (i.e., Sortase A (SrtA)-mediated transpeptidation) for dynamic tun-
ing hydrogel sti ness and the presence of bioactive ligands. The rst objective was
to establish a tunable and cytocompatible enzymatic scheme for softening cell-laden
hydrogels. Brie
y, the e ects of SrtA-mediated matrix cleavage were investigated us-
ing poly(ethylene glycol) (PEG)-peptide hydrogels crosslinked by SrtA-sensitive and
insensitive peptides. Initially, the e ects of various parameters with respect to cat-
alytic reactions of SrtA were characterized rheologically, including enzyme and sub-
strate concentrations, macromer content, peptide composition, and treatment time.
Gel moduli pre- and post-enzyme treatment were measured to verify SrtA-mediated
hydrogel softening. The cytocompatibility of SrtA-mediated gel softening system was
investigated using human mesenchymal stem cell (hMSC). Upon treatment with SrtA
and an oligoglycine substrate, encapsulated hMSCs exhibited extensive spreading in
comparison to those within statically sti matrices. The second objective was to es-
tablish a reversible ligand exchange system utilizing SrtA-mediated transpeptidation.
SrtA-sensitive pendant ligands were immobilized within PEG hydrogels, which were treated with SrtA and an oligoglycine substrate to a ord tunable removal of the pen-
dant ligand. Through measurement of the liberated pendant peptide concentration,
it was found that higher concentrations of SrtA or extending treatment times led
to higher ligand removal e ciency. Finally, the e ect of peptide ligand removal on
cell behaviors were evaluated using NIH 3T3 broblasts. Fibroblasts were culture
both on and within hydrogels containing SrtA-cleavable cell adhesion peptide. After
treatment, both conditions led to a decrease in broblast spreading in comparison
to non-treated gels. Overall, the utility of SrtA as versatile agent for controlling the
mechanical properties and the presence of biologically active components within a
hydrogel system was demonstrated. These systems could be further explored with natural-based materials to better mimic the physiological environment experienced
by cells.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/18925 |
| Date | 05 1900 |
| Creators | Moore, Dustin M. |
| Contributors | Lin, Chien-Chi, Xie, Dong, Li, Jiliang |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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