To promote the transition
of cell cultures from 2D to 3D, hydrogels
are needed to biomimic the extracellular matrix (ECM). One potential
material for this purpose is gellan gum (GG), a biocompatible and
mechanically tunable hydrogel. However, GG alone does not provide
attachment sites for cells to thrive in 3D. One option for biofunctionalization
is the introduction of gelatin, a derivative of the abundant ECM protein
collagen. Unfortunately, gelatin lacks cross-linking moieties, making
the production of self-standing hydrogels difficult under physiological
conditions. Here, we explore the functionalization of GG with gelatin
at biologically relevant concentrations using semiorthogonal, cytocompatible,
and facile chemistry based on hydrazone reaction. These hydrogels
exhibit mechanical behavior, especially elasticity, which resembles
the cardiac tissue. The use of optical projection tomography for 3D
cell microscopy demonstrates good cytocompatibility and elongation
of human fibroblasts (WI-38). In addition, human-induced pluripotent
stem cell-derived cardiomyocytes attach to the hydrogels and recover
their spontaneous beating in 24 h culture. Beating is studied using
in-house-built phase contrast video analysis software, and it is comparable
with the beating of control cardiomyocytes under regular culture conditions.
These hydrogels provide a promising platform to transition cardiac
tissue engineering and disease modeling from 2D to 3D.
This article proposes the coupling of the recombinant protein avidin to the polysaccharide gellan gum to create a modular hydrogel substrate for 3D cell culture and tissue engineering. Avidin is capable of binding biotin, and thus biotinylated compounds can be tethered to the polymer network to improve cell response. The avidin is successfully conjugated to gellan gum and remains functional as shown with fluorescence titration and electrophoresis (SDS-PAGE). Self-standing hydrogels were formed using bioamines and calcium chloride, yielding long-term stability and adequate stiffness for 3D cell culture, as confirmed with compression testing. Human fibroblasts were successfully cultured within the hydrogel treated with biotinylated RGD or biotinylated fibronectin. Moreover, human bone marrow stromal cells were cultured with hydrogel treated with biotinylated RGD over 3 weeks. We demonstrate a modular and inexpensive hydrogel scaffold for cell encapsulation that can be equipped with any desired biotinylated cell ligand to accommodate a wide range of cell types.
Gellan gum is a hydrogel with several applications in ultrasonic imaging, novel drug delivery, and tissue regeneration. As hydrogels are dynamic entities, their viscocelastic and therefore their acoustic properties change over time, which is of interest to monitor. To determine the speed of sound from brightness-mode images, however, rather large quantities of hydrogel are needed. In this study, we investigated torsion rheometry as a means to determine acoustic properties. Perceived speeds of sound were derived and computed from torsion rheometry measurements of gelating gellan gum mixed with spermidine trihydrochloride crosslinker. For comparison, brightness-mode ultrasonic images were recorded of the same material inside a phantom well. The rheometry data converged to a speed of sound within a standard devitation of the speed of sound measured from the brightness-mode images.We have shown that dynamic acoustic properties of gelating gellan gum can be simulated and experimentally determined using torsion rheometry.
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