Summary
Transforming growth factor beta (TGF-) has become one of the most widely utilized mediators to promote
cartilage growth in tissue engineering (TE) applications. Conventionally, for in vitro culture phases, TGF- is
supplemented in the culture medium with the expectation that it will readily diffuse into tissues and promote
the biosynthesis of a healthy cartilage ECM. However, a growing body of evidence brings to light a central
paradox with this conventional TGF- delivery strategy: physiologic TGF- doses exhibit limited penetration
into the tissue, giving rise to undesirable non-uniform growth, while the alternative use of higher,
supraphysiologic TGF- doses promotes the formation of cartilage with compromised tissue quality (e.g.,
fibrosis, hypertrophy, hyperplasia). In contrast to conventional TE TGF- delivery strategies, the natural
process of TGF- delivery in native cartilage occurs quite differently, where chondrocytes are surrounded by
large stores of TGF- that are sequestered in an inactive form, termed latent TGF- (LTGF-). Chondrocytes
activate LTGF- stores via integrins or secreted enzymes, leading to highly advantageous, need-based
activity throughout the tissue, which allows for essential ECM biosynthesis while avoiding the induction of
pathological tissue formation.
This proposal capitalizes on this native regulatory mechanism by creating a bio-inspired TE strategy,
whereby chondrogenic cells are encapsulated in a hydrogel scaffold conjugated with large stores of LTGF-,
akin to the native environment. This platform allows cells to endogenously activate these LTGF- stores,
giving rise to the highly beneficial delivery of uniform and moderated, near-physiologic TGF- doses to cells,
which promote biosynthetic enhancements in the absence of tissue quality limitations.
Further, a novel reaction-diffusion modeling framework is developed to predict the activity of TGF-
exposed to cells in constructs while accounting for the critical patient-specific chemical reactions applied to
TGF- in the tissue. These patient-specific models can guide optimal LTGF- design parameters, allowing for
optimal activity doses and giving rise to improved TE cartilage quality and mitigation of pathogenic off-target
desorption of TGF- from the construct.
In the current project, we examine the efficacy of this bio-inspired LTGF- scaffold platform by assessing:
1) the capability of reaction-diffusion models to optimize growth outcomes in patient-specific cell populations
(human chondrocytes and MSCs), 2) the capability of model-optimized LTGF- scaffolds to improve TE
cartilage performance in the hostile mechanochemical environment of the OA synovial joint through use of an
ex vivo synovial joint bioreactor, and 3) the capability of LTGF- scaffolds to improve TE cartilage performance
in an in vivo porcine focal defect model.
