Macroporous Hydrogels Upregulate Osteogenic Signal Expression and Promote Bone Regeneration

Abstract

The objective of this work was to investigate the effects of macroporous hydrogel architecture on the osteogenic signal expression and differentiation of human mesenchymal stem cells (hMSCs). In particular, we have proposed a tissue engineering approach for orbital bone repair based on a cyclic acetal biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). The EHD monomer and PEGDA polymer may be fabricated into macroporous EH-PEG hydrogels by radical polymerization and subsequent porogen leaching, a novel technique for hydrophilic gels. We hypothesized that EH-PEG hydrogel macroporosity facilitates intercellular signaling among hMSCs. To investigate this phenomenon, hMSCs were loaded into EH-PEG hydrogels with varying pore size and porosity. The viability of hMSCs, the expression of bone morphogenetic protein-2 (BMP-2), BMP receptor type 1A, and BMP receptor type 2 by hMSCs, and the differentiation of hMSCs were then assessed. Results demonstrate that macroporous EH-PEG hydrogels support hMSCs and that this macroporous environment promotes a dramatic increase in BMP-2 expression by hMSCs. This upregulation of BMP-2 expression is associated by a more rapid hMSC differentiation, as measured by alkaline phosphatase expression. Altering hMSC interactions with the EH-PEG hydrogel surface, by the addition of fibronectin, did not appear to augment BMP-2 expression. We therefore speculate that EH-PEG hydrogel macroporosity facilitates autocrine and paracrine signaling by localizing endogenously expressed factors within the hydrogel's pores and thus promotes hMSC osteoblastic differentiation and bone regeneration.

Stereolithographic Bone Scaffold Design Parameters: Osteogenic Differentiation and Signal Expression

“…21 Using an EH-PEG hydrogel fabricated from poly(ethylene glycol)-diacrylate (PEG-DA) and 5-ethyl-5-(hydroxymethyl)-b,b-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD), the effect of pore size and porosity on the BMP-2 signaling of human MSCs was investigated in scaffolds with pore sizes of 100 and 250 mm. 45 In this study, BMP-2 signaling was upregulated in the scaffolds with 250 mm pore size when compared with those with 100 mm pore size with the same porosity on days 4, 8, and 12. This indicates that pore size has an effect on BMP-2 signal expression.…”

“…35,40 Finally, pore size and porosity affect in vivo and in vitro cell signaling, which in turn affects osteoblastic differentiation of MSCs and the production of ECM proteins. 35,[41][42][43][44][45] Not only must the optimal bone tissue engineering scaffold support the growth and osteogenesis of a seeded cell population, it must also support osteoconduction and vascularization from the surrounding tissue. 46,47 Both osteoconduction and vascularization are influenced by scaffold pore size, porosity, and interconnectivity of pores.…”

Development of a Dynamic Stem Cell Culture Platform for Mesenchymal Stem Cell Adhesion and Evaluation

“…23 Hydrogels were tested at two concentrations: soft (5% w/v PEGDA) or stiff (20% w/v PEGDA). Solutions containing 5.0 or 20.0 mg PEGDA/100 μL water were used to vary stiffness.…”

“…16,23 hMSCs were expanded on tissue culture polystyrene flasks with medium changes every 3 days according to the manufacturer’s specifications. hMSCs at passage 4 were used for all experiments.…”

Fabrication of Cell-Laden Macroporous Biodegradable Hydrogels with Tunable Porosities and Pore Sizes

“…4,6,7 A number of fabrication techniques have been developed to generate pores within hydrogels for tissue engineering applications, including electrospinning, 8,9 gas foaming, [10][11][12][13] freeze-thaw, 14,15 phase separation, [16][17][18][19] and salt leaching. [20][21][22] However, the majority of these techniques for generating macroporous hydrogels often involve cytotoxic procedures or chemicals that undermine a key advantage hydrogels have over other traditional tissue engineering scaffolds: the ability to encapsulate viable cells with a homogeneous distribution within the 3D scaffold during fabrication. 4,23 Subsequent cell seeding in such scaffolds may lead to low seeding efficiency and a heterogeneous cell distribution, particularly without proper pore interconnectivity.…”