Tissue-to-tissue interfaces are commonly present in all tissues exhibiting structural, biological and
chemical gradients serving a wide range of physiological functions. These interfaces are responsible for
mediation of load transfer between two adjacent tissues. They are also important structures in
sustaining the cellular communications to retain tissue’s functional integration and homeostasis. [1] All
cells have the capacity to sense and respond to physical and chemical stimulus and when cultured in
three-dimensional (3D) environments they tend to perform their function better than in two-dimensional
(2D) environments. Spatial and temporal 3D gradient hydrogels better resemble the natural environment
of cells in mimicking their extracellular matrix. [2] In this study we hypothesize that differential functional
properties can be engineered by modulation of macromolecule gradients in a cell seeded threedimensional
hydrogel system. Specifically, differential paracrine secretory profiles can be engineered
using human Bone Marrow Stem Cells (hBMSC’s). Hence, the specific objectives of this study are to:
assemble the macromolecular gradient hydrogels to evaluate the suitablity for hBMSC’s encapsulation
by cellular viability and biofunctionality by assessing the paracrine secretion of hBMSC’s over time. The
gradient hydrogels solutions were prepared by blend of macromolecules in one solution such as
hyaluronic (HA) acid and collagen (Col) at different ratios. The gradient hydrogels were fabricated into
cylindrical silicon moulds with higher ratio solutions assembled at the bottom of the mould and adding
the two solutions consecutively on top of each other. The labelling of the macromolecules was
performed to confirm the gradient through fluorescence microscopy. Additionally, AFM was conducted
to assess the gradient hydrogels stiffness. Gradient hydrogels characterization was performed by HA
and Col degradation assay, degree of crosslinking and stability. hBMSC’s at P3 were encapsulated into
each batch solution at 106 cells/ml solution and gradient hydrogels were produced as previously
described. The hBMSC’s were observed under confocal microscopy to assess viability by Live/Dead®
staining. Cellular behaviour concerning proliferation and matrix deposition was also performed.
Secretory cytokine measurement for pro-inflammatory and angiogenesis factors was carried out using
ELISA. At genomic level, qPCR was carried out. The 3D gradient hydrogels platform made of different
macromolecules showed to be a suitable environment for hBMSC’s. The hBMSC’s gradient hydrogels
supported high cell survival and exhibited biofunctionality. Besides, the 3D gradient hydrogels
demonstrated differentially secretion of pro-inflammatory and angiogenic factors by the encapsulated
hBMSC’s.
References:
1. Mikos, AG. et al., Engineering complex tissues. Tissue Engineering 12,3307, 2006
2. Phillips, JE. et al., Proc Natl Acad Sci USA, 26:12170-5, 2008