Applied osmotic loading for promoting development of engineered cartilage

Abstract

This study investigated the potential use of static osmotic loading as a cartilage tissue engineering strategy for growing clinically relevant grafts from either synovium-derived stem cells (SDSCs) or chondrocytes. Bovine SDSCs and chondrocytes were individually encapsulated in 2% w/v agarose and divided into chondrogenic media of osmolarities 300 (hypotonic), 330 (isotonic), and 400 (hypertonic, physiologic) mOsM for up to 7 weeks. The application of hypertonic media to constructs comprised of SDSCs or chondrocytes led to increased mechanical properties as compared to hypotonic (300 mOsM) or isotonic (330 mOsM) media (p<0.05). Constant exposure of SDSC-seeded constructs to 400 mOsM media from day 0 to day 49 yielded a Young’s modulus of 513±89 kPa and GAG content of 7.39±0.52% ww on day 49, well within the range of values of native, immature bovine cartilage. Primary chondrocyte-seeded constructs achieved almost as high a Young’s modulus, reaching 487±187 kPa and 6.77±0.54%ww (GAG) for the 400 mOsM condition (day 42). These findings suggest hypertonic loading as a straightforward strategy for 3D cultivation with significant benefits for cartilage tissue engineering strategies. In an effort to understand potential mechanisms responsible for the observed response, cell volume measurements in response to varying osmotic conditions were evaluated in relation to the Boyle–van’t Hoff (BVH) law. Results confirmed that chondrocytes behave as perfect osmometers; however SDSCs deviated from the BVH relation.

Analyzing the effects of mechanical and osmotic loading on glycosaminoglycan synthesis rate in cartilaginous tissues

“…1b. Thus, the value of parameter β for bovine NP cells is 0.62, which is close to the value (~0.6) for mesenchymal stem cells (Sampat et al, 2013). …”

“…Osmotic loading and mechanical loading have been shown to affect the synthesis of GAG in vitro in both explant and cell culture experiments [e.g., (Bush and Hall, 2001; Gray et al, 1988; Gray et al, 1989; Guilak et al, 1994; Johnson et al, 2014; Maroudas and Evans, 1974; O'Conor et al, 2014; Sampat et al, 2013; Schneiderman et al, 1986; Urban et al, 1993)]. For example, the extracellular osmolarity has been found to have a dose-dependent effect on GAG synthesis rate by isolated cells (Ishihara et al, 1997; Negoro et al, 2008); the cells in the NP explant exhibit a higher synthesis rate of GAG at the osmolarity level close to the in situ value (van Dijk et al, 2011; van Dijk et al, 2013); the GAG synthesis rate has been observed to decrease in osmotic loaded articular cartilages (Bayliss et al, 1986; Schneiderman et al, 1986); a static compression has been shown to suppress GAG synthesis in articular cartilage (Kim et al, 1994; Schneiderman et al, 1986), whereas the GAG synthesis rate in bovine tail disc was found to be elevated if the static loading is less than 5 kg (Ohshima et al, 1995).…”

Promoting increased mechanical properties of tissue engineered neocartilage via the application of hyperosmolarity and 4α-phorbol 12,13-didecanoate (4αPDD)

“…Additionally, 4αPDD and hyperosmolarity interacted to enhance collagen content over hyperosmolarity alone (Figure 2). Previous studies have not examined the interaction of 4αPDD and hyperosmolarity on functional neocartilage properties, though they have investigated these agents independently (O'Conor et al, 2014; Sampat et al, 2013). Overall, the results of this study support 4αPDD as critical in affecting enhanced neocartilage properties, with 4αPDD able to augment the effects of other agents.…”

Biomechanics and mechanobiology in functional tissue engineering

“…From these seminal studies, investigators have examined other types of physical stimuli such as combinations of different mechanical or physicochemical loading regimens that could even further improve construct qualities (Huang et al, 2012; Huey and Athanasiou, 2011; Jungreuthmayer et al, 2009; Meinel et al, 2004; Sampat et al, 2013; Schatti et al, 2011; Zhang et al, 2009). With further understanding of the role of the biomechanical microenvironment on cell behavior (Guilak et al, 2009; Reilly and Engler, 2010), other studies have examined the role of factors such as extracellular matrix topography or modulus within scaffolds as means of influencing local cellular responses (Dellatore et al, 2008; Gauvin et al, 2012; Guex et al, 2013; Kolambkar et al, 2014; Lim et al, 2011; Nii et al, 2013).…”