Osteochondral tissue engineering using biphasic silk re-enforced 3D printed scaffolds

Osteochondral tissue damage is a serious concern, with even small levels of cartilage damage increasing an individual’s risk of suffering from joint discomfort or pain, with some instances even leading to osteoarthritis. Cartilage damage is often seen as a result of traumatic injury from sports or work. Currently, one of the most common treatments for osteoarthritis is joint replacement; however, this is not an optimal treatment because the replacements and procedure itself are highly invasive and the joint replacement has a limited lifespan. Therefore, especially with younger and more active patients, an earlier intervention is needed to repair the initial cartilage damage and its underlying subchondral bone. 3D printing is an exciting scaffold development method for tissue regeneration, especially within personalised medicine. However, many 3D printing techniques rely on creating a lattice structure, which often demonstrates poor cell bridging between filaments due to its large pore size, reducing regenerative capacity as cells are unable to efficiently remodel the scaffold. To tackle this issue a novel biphasic silk reinforced 3D printed scaffold was developed. This biphasic scaffold consisted of a 3D printed poly(ethylene glycol)-terephthalate-poly(butylene-terephthalate) (PEGT/PBT) lattice, infilled with a cast and freeze dried porous silk scaffold (derived from Bombyx mori silk fibroin), which continued on to a seamless silk top layer. Compression testing showed that scaffolds had a compressive modulus, ultimate compressive strength and fatigue resistance that would allow for their theoretical survival during implantation and joint articulation without stress-shielding mechanosensitive cells. Fluorescent microscopy showed biphasic scaffolds could support human bone marrow stromal cell (hBMSC) attachment and spreading after 24 hours of seeding. Scaffolds were able to successfully support cell growth for three weeks under chondrogenic conditions, and six weeks under osteogenic conditions. Histological analysis also demonstrated scaffolds allowed for osteogenic or chondrogenic differentiation of seeded hBMSCs. Histological analysis revealed, however, that scaffolds failed to create osteochondral like tissue in vitro within osteochondral culture conditions. By combining two different and unique materials, this biphasic scaffold possesses the mechanical and structural advantages of PEGT/PBT with the biocompatibility and cell supporting characteristics of silk, with none of the individual materials’ disadvantages. However, future experimentation is needed to improve the osteochondral conductivity of the biphasic scaffold.