Selectively Cross-Linked Tetra-PEG Hydrogels Provide Control over Mechanical Strength with Minimal Impact on Diffusivity.
ACS Biomater Sci Eng 2021;
7:4293-4304. [PMID:
34151570 PMCID:
PMC7611660 DOI:
10.1021/acsbiomaterials.0c01723]
[Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
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Synthetic hydrogels
formed from poly(ethylene glycol) (PEG) are
widely used to study how cells interact with their extracellular matrix.
These in vivo-like 3D environments provide a basis
for tissue engineering and cell therapies but also for research into
fundamental biological questions and disease modeling. The physical
properties of PEG hydrogels can be modulated to provide mechanical
cues to encapsulated cells; however, the impact of changing hydrogel
stiffness on the diffusivity of solutes to and from encapsulated cells
has received only limited attention. This is particularly true in
selectively cross-linked “tetra-PEG” hydrogels, whose
design limits network inhomogeneities. Here, we used a combination
of theoretical calculations, predictive modeling, and experimental
measurements of hydrogel swelling, rheological behavior, and diffusion
kinetics to characterize tetra-PEG hydrogels’ permissiveness
to the diffusion of molecules of biologically relevant size as we
changed polymer concentration, and thus hydrogel mechanical strength.
Our models predict that hydrogel mesh size has little effect on the
diffusivity of model molecules and instead predicts that diffusion
rates are more highly dependent on solute size. Indeed, our model
predicts that changes in hydrogel mesh size only begin to have a non-negligible
impact on the concentration of a solute that diffuses out of hydrogels
for the smallest mesh sizes and largest diffusing solutes. Experimental
measurements characterizing the diffusion of fluorescein isothiocyanate
(FITC)-labeled dextran molecules of known size aligned well with modeling
predictions and suggest that doubling the polymer concentration from
2.5% (w/v) to 5% produces stiffer gels with faster gelling kinetics
without affecting the diffusivity of solutes of biologically relevant
size but that 10% hydrogels can slow their diffusion. Our findings
provide confidence that the stiffness of tetra-PEG hydrogels can be
modulated over a physiological range without significantly impacting
the transport rates of solutes to and from encapsulated cells.
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