(770g) Multi-Compartment Collagen-Glycosaminoglycan Scaffolds for Tendon-Bone Interfacial Tissue Engineering

Tendon and ligament injuries are exceedingly common with over 32 million occurrences annually in the United States and associated costs of $30 billion [1]. Current surgical and tissue engineering approaches have had limited success, particularly when dealing with injuries at the tendon-bone interface (TBI). Failure rates for TBI repairs are as high as 94% [2]. This is largely due to the inability of available repair strategies to recapitulate the spatially-graded microstructural, mechanical, and chemical properties of the native interfacial tissue. Collagen-glycosaminolgycan (CG) scaffolds have previously been used as regenerative templates for soft tissues such as dermis [3] and more recently have been applied to bone and osteochondral defects [4]. This work details the development of a potential strategy to improve TBI injury outcomes through the application of CG scaffolds containing distinct tendinous and osseous compartments joined by a continuous interface mimicking native TBI physiology.

Multi-compartment CG scaffolds were fabricated using a previously described liquid-phase co-synthesis method [4]. Briefly, a suspension of type I collagen, chondroitin sulfate, and calcium salts (osseous compartment) was layered on top of a suspension of type I collagen and chondroitin sulfate (tendinous compartment) and allowed to interdiffuse. The suspensions were then freeze-dried in a thermally mismatched mold to promote directional solidification and the formation of aligned pore tracks to mimic the native microstructure of tendon [5]. SEM analysis demonstrated that pores were aligned in the longitudinal plane of the tendinous compartment but more isotropic in the osseous compartment. Additionally, SEM showed a continuous network of CG content at the osseous-tendinous interface. MicroCT and mechanical testing are being used to further characterize the microstructural and mechanical properties of the scaffolds. Multi-compartment CG scaffolds have been shown to support tenocyte, osteoblast, and human mesenchymal stem cell (hMSC) viability for up to three weeks of in vitro culture. Histology (H&E and Alizarin Red) will be used to assess the distribution of hMSCs and mineral content respectively. The alignment of hMSCs within the tendinous compartment will be measured from H&E stained histology sections using the OrientationJ plugin within ImageJ. Ongoing work is assessing the differential effects of scaffold pore size (controlled by final freezing temperature), osseous compartment mineral content, and soluble factor presentation on hMSC number, metabolic activity, soluble collagen synthesis, and expression of tendon (collagen I and III, COMP, tenomodulin, scleraxis) and bone (collagen I, ALP, osteocalcin, bone sialoprotein) markers.

References

1. Butler D.L. et al. J Orthop Res, 2008. 26(1): p. 1-9.
2. Galatz L.M. et al. J Bone Joint Surg Am, 2004. 86-A(2): p. 219-24.
3. Harley B.A.C. and L.J. Gibson. Chemical Engineering Journal, 2008. 137(1): p. 102-121.
4. Harley B.A. et al. J Biomed Mater Res A, 2010. 92(3): p. 1078-93.
5. Caliari S.R. and B.A.C. Harley. Biomaterials, in press.