Articular cartilage has a poor healing capacity, and so, any damage to the joint surface often progresses to osteoarthritis (OA), a debilitating joint disease. For patients with symptomatic knee OA, total knee replacement (TKR) is by far the most common clinical solution. However, TKR is an invasive and end stage procedure, and there is a growing market for alternate treatments to restore the structure and function of articular cartilage to ideally prevent OA, or at least delay the time to TKR. While native tissue grafts can be easily press-fit in vivo, their supply is limited and autologous harvest can lead to pain, motivating tissue engineering (TE) strategies. To date, most of the work in the field of cartilage TE has focused on producing functional tissues, but has ignored the integration of these tissues in vivo, limiting the function and durability of cartilage repair. In this proposal, we seek to engineer cartilage tissues that permit endogenous marrow cell entry in vivo, and subsequently control the fate of these cells to enhance mineralized matrix deposition between the construct and underlying bone, ultimately improving construct anchorage. To permit marrow cell infiltration into our cartilage constructs, a novel magneto-patterning method will be implemented in Aim 1 to mimic the cell distribution of native cartilage in the engineered constructs. This high-to-low cell distribution will lead to a cell and matrix-sparse region at the bottom of the constructs, whereby a secondary cell source?the endogenous marrow cells, can infiltrate. We will create cell gradients in hydrogels using the aforementioned magneto- patterning approach, which eliminates the need for cell-bound magnetic tags, and instead transiently increases the magnetic susceptibility of the hydrogel precursor solution to manipulate cell position under a magnetic field. The magneto-patterned constructs will be cultured in vitro, and we will assess the depth-dependent matrix accumulation in these cartilage constructs via histological, biochemical, and mechanical measures. To promote cartilaginous and mineralized matrix interdigitation, we will exploit the force required to press-fit an engineered construct into a cartilage defect to locally deliver bone-promoting agents (BPAs) at the osteochondral interface. For this, in Aim 2, magneto-responsive press-activated microcapsules containing BPAs?Triiodothyronine and ?-glycerophosphate?will be patterned in the cell-sparse region of the engineered constructs. Within the cell laden constructs, the microcapsules will retain their contents throughout the pre-culture period, until they are press-activated upon in vivo implantation to ensure local `on demand' delivery of the BPAs. Finally, in Aim 3, the magneto-patterned constructs with opposing populations of mesenchymal stromal cells and press- activated microcapsules, will be implanted into a minipig trochlear cartilage defect model. Fluorochrome labeling, micro computed tomography, histology, and mechanical testing will elucidate the clinical efficacy of this cartilage repair treatment post-sacrifice. Overall, this work has the potential to advance this novel interface tissue engineering strategy, and specifically improve the state-of-the-art in cartilage repair.
Articular cartilage has a poor healing capacity, motivating tissue engineering strategies to replace damaged tissue and relieve pain. While the field has advanced to the stage where it is possible to grow functional cartilage tissue, integration of the neocartilage with underlying subchondral bone remains a significant issue that is critical for construct function and survival post-implantation. This proposal implements a novel magneto- patterning approach to engineer cartilage constructs that permit endogenous marrow cell entry upon implantation in vivo, and control the subsequent fate and matrix deposition of these marrow cells via local release of bone promoting agents at the osteochondral interface.
