Abstract
Engineering scaffolds to augment the repair of hard-to-soft multitissue musculoskeletal tissue units, such as bone-tendon, to simultaneously support tissue healing and functional movement has had limited success. Overcoming this challenge will require not only precise spatial control of bone- and tendon-like biomechanical properties, but also consideration of the resultant biomechanical cues, as well as the embedded biochemical cues imparted by these scaffolds. Here, we report on the effects of a spatially engineered combination of stiffness and growth factor (GF) cues to control bone-tendon-like differentiation in vitro and tissue formation in vivo. This was achieved using mechanically graded, bone- and tendon-like QHM polyurethane (QHM: Q: Quadrol; H: hexamethylene diisocyanate; M: methacrylic anhydride) scaffolds selectively biopatterned with osteogenic bone morphogenetic protein-2 (BMP-2) and tenogenic fibroblast growth factor-2 (FGF-2). First, material characterization, including porosity, surface roughness, contact angle, and microindentation measurements, was performed. Second, in vitro studies demonstrated that increased material stiffness promoted GF-mediated osteoblast differentiation and reduced tenocyte differentiation. Sustained GF exposure masked this stiffness effect. Third, in vivo studies involving subcutaneous implantation of mechanically graded and biochemically patterned QHM scaffolds (composed of these bone- and tendon-promoting GFs biopatterned on biphasic bone and tendon biomechanically mimicking regions) in mice demonstrated spatial control of bone- and tendon-like tissue formation. Altogether, these data provide new insights for future engineering of scaffolds to augment hard-to-soft multitissue repair.
Highlights
Musculoskeletal tissue units are composed of different tissues and cell types that are organized in a functionally graded, spatially specific manner to mediate musculoskeletal tissue attachment and joint movement
While prior studies have already investigated the effects of material stiffness on cell differentiation, they were largely based on microscale measurements[4,13]
We aimed to study whether a similar phenomenon occurred with solid-phase biochemical cues interacting with biomechanical cues
Summary
Musculoskeletal tissue units are composed of different tissues and cell types that are organized in a functionally graded, spatially specific manner to mediate musculoskeletal tissue attachment and joint movement. For the repair of hard-to-soft multitissue units, there have been numerous investigations and advancements in the development of biomechanically or biochemically graded scaffolds in recent years These include but are not limited to utilizing various biomaterials (synthetic, natural or combinatorial) fabricated via either multiphasic- or gradient-based approaches. Successful reports of multitissue healing using such graded scaffolds in vivo have been limited This is primarily due to the challenging dual requirements of achieving mechanical properties that closely approximate bonetendon tissues for sustaining shoulder loading and spatial patterning of multiple musculoskeletal phenotypes, including osteoblasts and tenocytes for repopulating tissue-resident cells[10,11,12]. An improved understanding of this effect will allow appropriate scaffold biomechanical cues to be engineered for promoting both biomechanical function and multitissue healing
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