A comparison of human mesenchymal stem cell osteogenesis in poly(ethylene glycol) hydrogels as a function of MMP‐sensitive crosslinker and crosslink density in chemically defined medium

• Published in: Biotechnology and bioengineering 2019-06, Vol.116 (6), p.1523-1536
• Main Authors: Aziz, Aaron H., Bryant, Stephanie J.
• Format: Article
• Language: English
• Subjects: Alkaline phosphatase; Biocompatibility; Calcium; Cell spreading; Collagen; Cross-linking; Crosslinking; Degradability; Degradation; extracellular matrix (ECM); hydrogel; Hydrogels; Matrix metalloproteinases; matrix‐metalloproteinase (MMP); mesenchymal stem cell (MSCs); Mesenchyme; Metalloproteinase; Mineralization; Modulus of elasticity; Organic chemistry; Osteogenesis; Polyethylene glycol; Spreading; Stem cells; Time compression
• ISSN: 0006-3592; 1097-0290
• DOI: 10.1002/bit.26957

This study investigated osteogenesis of human mesenchymal stem cells encapsulated in matrix‐metalloproteinase (MMP)‐sensitive poly(ethylene glycol) (PEG) hydrogels in chemically defined medium (10 ng/ml bone morphogenic factor‐2). Thiol‐norbornene photoclick hydrogels were formed with CRGDS and crosslinkers of PEG dithiol (nondegradable), CVPLS‐LYSGC (P1) or CRGRIGF‐LRTDC (P2; dash indicates cleavage site) at two crosslink densities. Exogenous MMP‐2 degraded P1 and P2 hydrogels similarly. MMP‐14 degraded P1 hydrogels more rapidly than P2 hydrogels. Cell spreading was greatest in P1 low crosslinked hydrogels and to a lesser degree in P2 low crosslinked hydrogels, but not evident in nondegradable and high crosslinked MMP‐sensitive hydrogels. Early osteogenesis (Alkaline phosphatase [ALP] activity) was accelerated in hydrogels that facilitated cell spreading. Contrarily, late osteogenesis (mineralization) was independent of cell spreading. Mineralized matrix was present in P1 hydrogels, but only present in P2 high crosslinked hydrogels and not yet present in nondegradable hydrogels. Overall, the low crosslinked P1 hydrogels exhibited an accelerated early and late osteogenesis with the highest ALP activity (Day 7), greatest calcium content (Day 14), and greatest collagen content (Day 28), concomitant with increased compressive modulus over time. Collectively, this study demonstrates that in chemically defined medium, hydrogel degradability is critical to accelerating early osteogenesis, but other factors are important in late osteogenesis. This study demonstrated that hydrogel properties affected early and late stage osteogenesis of human mesenchymal stem cells encapsulated in matrix‐metalloproteinase (MMP)‐sensitive poly(ethylene glycol) (PEG) hydrogels cultured in chemically defined medium with 10 ng/ml bone morphogenic factor‐2 [BMP‐2]. Early osteogenesis as measured by alkaline phosphatase activity was dependent on cell‐mediated degradation and cell spreading, while late stage osteogenesis as measured by mineral deposits was independent of cell spreading. Overall, these findings suggest that hydrogel properties differentially regulate early and late stage osteogenesis.