Scalable MSC-derived bone tissue modules: In vitro assessment of differentiation, matrix deposition, and compressive load bearing

摘要

Enhancements to the mechanical properties of modular designs for bone tissue engineering could increase their clinical applications. In this study, bone marrow mesenchymal stem cells (MSCs) and hydroxyapatite (HAP) microgranules were encapsulated in polyelectrolyte complex membranes composed of chondroitin 4-sulfate (C4S), carboxymethyl cellulose (CMC) and chitosan. Microcapsules were formed with and without HAP microgranules, and cultured in either osteoinduction medium (Osteo) or expansion medium (Exp) to produce four microcapsule conditions: Osteo, Osteo+HAP, Exp, and Exp +HAP. Microcapsules facilitated alkaline phosphatase secretion and deposition of bone specific proteins (osteocalcin and osteopontin) by encapsulated MSCs over 28 days of osteogenic culture. SEM and micro-CT analysis showed cell-deposited mineral covering the surfaces of the HAP microgranules and interior of the microcapsule membrane. The mineralized microcapsules could be combined and fused into cylindrical constructs (4 x 5 mm, W x H), and uniaxial compression tests confirmed that microcapsule mineralization greatly enhanced the yield stresses of Osteo and Osteo+HAP fused constructs (10.4 +/- 4.4 MPa and 6.4 +/- 2.8 MPa), compared to only HAP microgranules (Exp+HAP, 0.5 +/- 0.3 MPa). The C4S/C/Chitosan microcapsules provide a platform allowing pre-mineralization of microcapsules in vitro for later assembly of larger load-bearing constructs, or for use as an injectable bone regeneration strategy.