Long-term dynamic loading improves the mechanical properties of chondrogenic mesenchymal stem cell-laden hydrogel

Abstract

Mesenchymal stem cells (MSCs) are an attractive cell source for cartilage tissue engineering given their ability to undergo chondrogenesis in 3D culture systems. Mechanical forces play an important role in regulating both cartilage development and MSC chondrogenic gene expression, however, mechanical stimulation has yet to enhance the mechanical properties of engineered constructs. In this study, we applied long-term dynamic compression to MSC-seeded constructs and assessed whether varying pre-culture duration, loading regimens and inclusion of TGF-β3 during loading would influence functional outcomes and these phenotypic transitions. Loading initiated before chondrogenesis decreased functional maturation, although chondrogenic gene expression increased. In contrast, loading initiated after chondrogenesis and matrix elaboration further improved the mechanical properties of MSC-based constructs, but only when TGF-β3 levels were maintained and under specific loading parameters. Although matrix quantity was not affected by dynamic compression, matrix distribution, assessed histologically and by FT-IRIS analysis, was significantly improved on the micro-(pericellular) and macro-(construct expanse) scales. Further, whole genome expression profiling revealed marked shifts in the molecular topography with dynamic loading. These results demonstrate, for the first time, that dynamic compressive loading initiated after a sufficient period of chondroinduction and with sustained TGF-β exposure enhances matrix distribution and the mechanical properties of MSCseeded constructs.

Cartilage Matrix Formation by Bovine Mesenchymal Stem Cells in Three-dimensional Culture Is Age-dependent

“…Likewise, bovine MSCs show a sharp decrease with age in cartilage matrix-forming capacity that is more severe than reported for human MSCs in this same format [5]. Overall, at each age, and under ideal conditions (absence of TGF for chondrocytes, presence of TGF for MSCs), bovine chondrocytes in pellet culture produce more GAG and collagen than MSCs, consistent with our previous findings [17,22,33]. Taken together, when considering an autologous cellbased tissue engineering strategy for cartilage repair, age must be an important consideration.…”

Expansion in the presence of FGF-2 enhances the functional development of cartilaginous tissues engineered using infrapatellar fat pad derived MSCs

“…Therefore identifying expansion and differentiation conditions that promote a more chondrogenic phenotype is critical to enhancing their utility for cartilage tissue engineering applications. Differentiation conditions that have been shown to promote the chondrogenic potential of MSCs include a low oxygen (5%) microenvironment (Khan et al 2007;Buckley et al 2010a;Meyer et al 2010), various combinations of growth factors (Mastrogiacomo et al 2001;Sakimura et al 2006;Hennig et al 2007;Diekman et al 2010;Buxton et al 2011) and mechanical signals (Huang et al 2005;Mauck et al 2007;Huang et al 2010a;Huang et al 2010b;Kelly and Jacobs 2010;Li et al 2010; Thorpe et al 2010;Haugh et al 2011). …”

Unravelling the Role of Mechanical Stimuli in Regulating Cell Fate During Osteochondral Defect Repair

“…The objective of this study was thus to improve the predictive capacity of the model by including a series of rules whereby the local mechanical environment affected the fate of cartilage. Based on the findings of a number of in vitro studies which have shown that mechanical loading can either prevent hypertrophy and endochondral ossification of cartilage [12][13][14][15][16] , or promote the formation of fibrocartilage 18,19 , it was hypothesised that the fate of the cartilage that forms within an osteochondral defect depends on both oxygen availability and the local mechanical environment. It was postulated that hypertrophy was supressed by appropriate magnitudes of local strain, while fibrocartilage formed in regions where the local strain was excessively high.…”

“…In general it has been shown that active loading applied at an early stage leads to the formation of fibrous tissue and fibrocartilage, while continuous passive motion has been shown to result in the formation of hyaline cartilage 7,8,11 . A number of in vitro studies, where the levels of mechanical stimulation can be carefully controlled using bioreactor systems, have also demonstrated how compressive loading can regulate chondrogenesis of MSCs [12][13][14][15][16] . For example, Thorpe et al 17 showed that dynamic compressive loading of chondrogenically primed MSCs led to the upregulation of chondrogenic markers and also inhibited terminal differentiation and mineralisation.…”