Date of Award

2015

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Ehsan Jabbarzadeh

Abstract

Current methods of treating critical size bone defects (CSDs) include autografts and allografts, however both present major limitations including donor-site morbidity, risk of disease transmission, and immune-rejection. Tissue engineering provides a promising alternative to circumvent these shortcomings through the use of stem cells, three dimensional (3D) scaffolds, and growth factors. Cells receive signals from their microenvironment that determine cell phenotype, and a combination of physical cues and chemical factors is thought to have the most profound influence on stem cell behavior. A major focus of tissue engineering strategies is scaffold design to recapitulate in vivo microenvironmental architecture to direct stem cell lineage commitment. In combination with relevant microenvironment design, the success of bone tissue engineering strategies critically depends on the rapid formation of a mature vascular network in the scaffolds after implantation. However, conventional approaches fail to consider the role of the host response in regulating tissue ingrowth and extent of vascularization. The work presented here focuses on i) designing an osteomimetic 3D substrate to guide human embryonic stem cell (hESC) differentiation towards bone lineage, and ii) investigating the ability of the polyphenol resveratrol to harness the potential of the inflammatory response to enhance angiogenesis and osseointegration in 3D scaffolds for bone repair.

The osteomimetic scaffold with native bone extracellular matrix (ECM) components successfully directed the osteogenic differentiation of hESCs. A microsphere-sintering technique was used to fabricate poly(lactic-co-glycolic acid) .

(PLGA) scaffolds with optimum mechanical properties, and human osteoblasts (hOBs) were seeded on these scaffolds to deposit bone ECM. This was followed by a decellularization step leaving the mineralized matrix intact. hESCs were seeded on the osteomimetic substrates in the presence of osteogenic growth medium, and osteogenicity was determined according to calcium content, osteocalcin expression, and bone marker gene regulation. The results from this study demonstrate the potential of PLGA scaffolds with native bone ECM components to direct osteogenic differentiation of hESCs and induce bone formation.

Engineered resveratrol nanoparticle-incorporated PLGA scaffolds enabled the concurrent (i) mediation of inflammatory (M1) to wound healing (M2) macrophage differentiation, (ii) natural release of angiogenic factors by M2 macrophages and (iii) enhanced osteogenic differentiation of human mesenchymal stem cells (hMSCs). To this end, we mapped the time-dependent response of macrophage gene expression as well as hMSC osteogenic differentiation to varying doses of resveratrol. Our results delineate the potential to synergistically control angiogenic factor secretion and downstream osteogenic signaling pathways by “dialing” the appropriate degree of resveratrol release from nanoparticle-incorporated PLGA scaffolds.

Rights

© 2015, Katherine Elizabeth Rutledge

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