Tuning Polymer Hydrophilicity to Regulate Gel Mechanics and Encapsulated Cell Morphology

Abstract

Mechanically tunable hydrogels are attractive platforms for 3D cell culture, as hydrogel stiffness plays an important role in cell behavior. Traditionally, hydrogel stiffness has been controlled through altering either the polymer concentration or the stoichiometry between crosslinker reactive groups. Here, an alternative strategy based upon tuning the hydrophilicity of an elastin-like protein (ELP) is presented. ELPs undergo a phase transition that leads to protein aggregation at increasing temperatures. It is hypothesized that increasing this transition temperature through bioconjugation with azide-containing molecules of increasing hydrophilicity will allow direct control of the resulting gel stiffness by making the crosslinking groups more accessible. These azide-modified ELPs are crosslinked into hydrogels with bicyclononyne-modified hyaluronic acid (HA-BCN) using bioorthogonal, click chemistry, resulting in hydrogels with tunable storage moduli (100-1000 Pa). Human mesenchymal stromal cells (hMSCs), human umbilical vein endothelial cells (HUVECs), and human neural progenitor cells (hNPCs) are all observed to alter their cell morphology when encapsulated within hydrogels of varying stiffness. Taken together, the use of protein hydrophilicity as a lever to tune hydrogel mechanical properties is demonstrated. These hydrogels have tunable moduli over a stiffness range relevant to soft tissues, support the viability of encapsulated cells, and modify cell spreading as a consequence of gel stiffness.

Elastin‐like protein hydrogels with controllable stress relaxation rate and stiffness modulate endothelial cell function

“…The CH vibrations were coherently driven by two laser beams overlapped in time and space, generated by a picosecond‐pulsed laser system consisting of a 1031 nm fiber laser and an optical parametric oscillator (OPO) tunable between 690–960 nm (APE picoEmerald S, 2 ps pulse length, 80 MHz repetition rate, and 10 cm −1 bandwidth). We have previously observed protein‐specific stretching modes of CH 3 for ELP in the range 2930–2940 cm −1 , and to address this vibration the OPO wavelength was set to 791 nm 11,18,22–25 . The CARS signal depends quadratically on the number density of the probed vibrational group, providing contrast for regions dense in ELP polymer without the need for external labels or other disruptive sample preparations.…”

Layer-by-Layer siRNA Particle Assemblies for Localized Delivery of siRNA to Epithelial Cells through Surface-Mediated Particle Uptake

“…Development of materials conducive to directing cell behavior through local gene transfer in a spatiotemporally defined manner is critical to many tissue engineering and regenerative medicine applications. To achieve complex tissue organization and appropriate regrowth, attempts involve replicating key features of the extracellular matrix. , Gene delivery from extracellular matrix-like materials can then be used to direct cell fate . While the incorporation of a genetic material can be a powerful approach, its applicability is hampered by exonucleases which degrade them if they are unprotected in the extracellular space.…”

Tunable Mesoscopic Collagen Island Architectures Modulate Stem Cell Behavior

“…[44,45] Much of the literature has shown that global stiffness is able to modulate differentiation behavior. [10,46,47] However, bulk stiffness values are measured at a scale much larger than what cells are able to sense. In addition, local stiffness profiles do not necessarily correlate with global stiffness.…”