Synergistic Action of Growth Factors and Dynamic Loading for Articular Cartilage Tissue Engineering

Abstract

It has previously been demonstrated that dynamic deformational loading of chondrocyte-seeded agarose hydrogels over the course of 1 month can increase construct mechanical and biochemical properties relative to free-swelling controls. The present study examines the manner in which two mediators of matrix biosynthesis, the growth factors TGF-beta1 and IGF-I, interact with applied dynamic deformational loading. Under free-swelling conditions in control medium (C), the [proteoglycan content][collagen content][equilibrium aggregate modulus] of cell-laden (10 x 10(6) cells/mL) 2% agarose constructs reached a peak of [0.54% wet weight (ww)][0.16% ww][13.4 kPa]c, whereas the addition of TGF-beta1 or IGF-I to the control medium led to significantly higher peaks of [1.18% ww][0.97% ww][23.6 kPa](C-TGF) and [1.00% ww][0.63% ww][19.3 kPa](C-IGF), respectively, by day 28 or 35 (p<0.01). Under dynamic loading in control medium (L), the measured parameters were [1.10% ww][0.52% ww][24.5 kPa]L, and with the addition of TGF-beta1 or IGF-I to the control medium these further increased to [1.49% ww][1.07% ww][50.5 kPa](L-TGF) and [1.48% ww][0.81% ww][46.2 kPa](L-IGF), respectively (p<0.05). Immunohistochemical staining revealed that type II collagen accumulated primarily in the pericellular area under free-swelling conditions, but spanned the entire tissue in dynamically loaded constructs. Applied in concert, dynamic deformational loading and TGF-beta1 or IGF-I increased the aggregate modulus of engineered constructs by 277 or 245%, respectively, an increase greater than the sum of either stimulus applied alone. These results support the hypothesis that the combination of chemical and mechanical promoters of matrix biosynthesis can optimize the growth of tissue-engineered cartilage constructs.

The Local Matrix Distribution and the Functional Development of Tissue Engineered Cartilage, a Finite Element Study

“…18 A prerequisite for clinical use is that a cultured cartilage construct meets, or has the capacity to adapt to, in-vivo functional requirements. 8 The construct's mechanical properties can be modulated by adjusting the parameters that define the culture environment, such as scaffold material, 25 hydrodynamic conditions, 36,59 mechanical loading, 5,37,39 addition of growthfactors, 37,44 cell seeding density and nutrition. 40 Although it has been shown that mechanical properties which approach those of natural cartilage can be obtained after long term culture, 17 there is still a lack of control over the functional development of tissue engineered constructs.…”

“…Patterns of matrix deposition around individual cells in agarose have been quantified and observed to spread outwards in time. 5,37,47 It has been hypothesized that mechanical functionality arises when contact occurs between zones of matrix associated with individual cells. 5,37,40,47 In addition it has been speculated that one of the mechanisms by which dynamic loading could contribute to improved mechanical functionality is the dispersion of matrix constituents by compression induced fluid flow, leading to a local matrix redistribution.…”

“…5,37,47 It has been hypothesized that mechanical functionality arises when contact occurs between zones of matrix associated with individual cells. 5,37,40,47 In addition it has been speculated that one of the mechanisms by which dynamic loading could contribute to improved mechanical functionality is the dispersion of matrix constituents by compression induced fluid flow, leading to a local matrix redistribution. 37,46 The main question is whether assessment of tissue functionality from the main ECM constituents requires in the first place additional information about the local matrix distribution from histology, or complementary global measurements of molecular organization.…”

“…5,37,40,47 In addition it has been speculated that one of the mechanisms by which dynamic loading could contribute to improved mechanical functionality is the dispersion of matrix constituents by compression induced fluid flow, leading to a local matrix redistribution. 37,46 The main question is whether assessment of tissue functionality from the main ECM constituents requires in the first place additional information about the local matrix distribution from histology, or complementary global measurements of molecular organization. Therefore the objective of this study is to determine whether the local distribution of newly synthesized extracellular matrix contributes to the evolution of the global mechanical properties of tissue engineered cartilage constructs, in particular the aggregate modulus Ha and hydraulic permeability K .…”

“…To answer these questions a computational approach is particularly useful, since it enables to distinguish matrix distribution from other important factors that affect functionality, such as for example in the case of dynamic compression, an increase in the amount of matrix synthesized and the production of more link molecules. 7,14,32,37 …”