Introduction: ECM-based materials are attractive for tissue engineering strategies because they can potentially aid in stem cell recruitment, cell infiltration, and cell differentiation without supplementing with additional biological factors.[1] Although it is a relatively new biomaterial, cartilage ECM has shown potential to be chondroinductive,[2] although in general, hydrogels composed of natural materials are often mechanically inferior to synthetic materials, which may not be ideal for load-bearing tissue applications.[3] Therefore, we endeavored to create a hydrogel composed of entirely native cartilage ECM that was mechanically similar to native cartilage tissue and would promote chondrogenesis.
Methods: Porcine cartilage was decellularized, solubilized, methacrylated and UV photocrosslinked to create methacrylated solubilized decellularized cartilage (MeSDCC) gels. Methacrylated gelatin (GelMA) was used as a control. Rat bone marrow stem cells were encapsulated in these networks and the constructs were cultured in vitro for 6 weeks, where chondrogenic gene expression, the compressive modulus (linear region of stress-strain curve), swelling, and histology were analyzed.
Results and Discussion: One day after crosslinking, the compressive modulus of the 20% MeSDCC gels was 1069.6 ± 147.5 kPa (Fig. 1), which is similar to that reported for native cartilage tissue.
Figure 1. Compressive Modulus of crosslinked hydrogels after 1 day and 6 weeks of culture. Data reported as mean + standard deviation (n=5); * significantly different from 10% GelMA at same time point (p<0.05), #significantly different from 10% MeSDCC at same time point (p<0.05), &p<0.05 for specified comparison, @significantly different from same group at first time point (p<0.05), -not tested.
Furthermore, when we compared the stress strain profiles of our 20% MeSDCC gels with native porcine cartilage, the stress strain profile of the 20% MeSDCC gels fell within the 95% confidence interval range of native porcine cartilage until the 20% MeSDCC gels fractured at 7.5% strain. Additionally, MeSDCC gels significantly upregulated chondrogenic genes compared to GelMA at day 1 and supported matrix synthesis as observed with Safrinin-O/Fast Green and H&E staining.
Conclusion: Overall, because these gels are approaching the mechanics of native cartilage tissue and because they are supporting matrix synthesis and chondrogenic gene expression, MeSDCC hydrogels may be promising materials for cartilage tissue engineering applications, although future improvements will be necessary for fracture performance. Additionally, future work will evaluate how these gels perform in vivo.
NIH S10 RR024664; NSF Graduate Research Fellowship (E.B.); NSF Major Research Instrumentation Grant (0320648); Kansas Bioscience Authority Rising Star Award (M.D.); NIH R01 DE022472 (C.B.)
References:
[1] Burdick, J.A., et al., Acellular biomaterials: an evolving alternative to cell-based therapies. Sci Transl Med, 2013. 5(176): p. 176ps4.
[2] Sutherland, A.J., et al., The bioactivity of cartilage extracellular matrix in articular cartilage regeneration. Advanced healthcare materials, 2015. 4(1): p. 29-39.
[3] Tatman, P.D., et al., Multi-scale Biofabrication of Articular Cartilage: Bioinspired and Biomimetic Approaches. Tissue Engineering, 2015(ja).