Purpose-To examine mesenchymal stem cell (MSC) labeling with micrometer-sized iron oxide particles (MPIOs) for magnetic resonance imaging (MRI) based tracking, and its application to monitoring articular cartilage regeneration. Methods-RabbitMSCs were labeled using commercial MPIOs. In vitro MRI was performed with gradient echo (GRE) and spin echo (SE) sequences at 3 tesla, and quantitatively characterized using line profile and region of interest analysis. Ex vivo MRI of hydrogel-encapsulated labeled MSCs implanted within a bovine knee was performed with spoiled GRE (SPGR) and T 1ρ sequences. Fluorescence microscopy, labeling efficiency, and chondrogenesis of MPIO-labeled cells were also examined.Results-MPIO-labeling results in efficient contrast uptake, and signal loss that can be visualized and quantitatively characterized via MRI. SPGR imaging of implanted cells results in ex vivo detection within native tissue, and T 1ρ imaging is unaffected by the presence of labeled cells immediately following implantation. MPIO labeling does not affect quantitative glycosaminoglycan production during chondrogenesis, but iron aggregation hinders extracellular matrix visualization. This aggregation may result from excess unincorporated particles following labeling, and is an issue that necessitates further investigation.Conclusion-This study demonstrates the promise of MPIO labeling for monitoring cartilage regeneration, and highlights its potential in the development of cell-based tissue engineering strategies.

Objective The development of osteoarthritis following traumatic anterior cruciate ligament (ACL) injury is well established. However, few reliable indicators of early osteoarthritic changes have been established, which has limited the development of effective therapies. T1ρ and T2 mapping techniques have the ability to provide highly accurate and quantitative measurements of articular cartilage degeneration in vivo. Relating these cartilaginous changes to high-resolution bone-densitometric evaluations of the late-stage osteoarthritic bone is crucial in elucidating the mechanisms of development of traumatic osteoarthritis (OA) and potential therapies for early- or late-stage intervention. Methods Twelve rabbits were monitored with in vivo magnetic resonance imaging (MRI) scans following ACL transection surgery with a contralateral leg sham operation. Six of the rabbits were treated with oral doxycycline for the duration of the experiment. At 12 weeks, the excised knees from three animals from each group (n=6 overall) were subjected to micro-computed tomography (CT) analysis. Results Consistent with previous studies, initial elevations in T1ρ and T2 values in ACL-transected animals were observed with relative normalization towards values see in sham-operated legs over the 12-week study. This biphasic pattern could hold diagnostic potential to differentiate osteoarthritic cartilage by tracking the relative proportions of T1ρ and T2 values as they rise with inflammation then fall as collagen and proteoglycan loss leads to further dehydration. The addition of doxycycline resulted in inconclusive, yet potentially interesting, cartilaginous changes in several compartments of the rabbit legs. Micro-CT studies demonstrated decreased bone densitometrics in ACL-transected knees. Correlation studies suggest that the cartilaginous changes may be associated with some aspects of bony change and the development of OA. Conclusion We conclude that there are definite relationships between cartilaginous changes as seen on MRI and late-stage microstructural bony changes after traumatic ACL injury in rabbits. In addition, doxycycline may show promise in mitigating early-stage cartilage damage that may serve to lessen late-stage osteoarthritic changes. This study demonstrates the ability to track OA progression and therapeutic efficacy with imaging modalities in vivo.

In specialized capillary beds such as the kidney glomerulus, the sheet-like structure of the basement membrane in conjunction with opposing monolayers of endothelium and epithelium form the functioning filtration unit of the kidney. Using a novel cross-linking method on a collagen substrate, we have created a novel hydrogel scaffold to substitute for the basement membrane. Using a simple casting method to create thin films of the hydrogel scaffold (1–5μm), the scaffolds were suitable for long-term static culture, and supported cell attachment and long term cell viability similar to a standard type I collagen substrate. Bulk diffusion and protein permeability of the hydrogel scaffold were evaluated, in addition to its use in a perfusion chamber where it withstood hydraulic pressures typical for glomerular capillaries. This system thus provided a suitable cell substrate for the co-culture of renal epithelial podocytes and endothelial cells in a device that replicates the geometry of the in vivo juxtaposition of the two cell types in relation to their basement membrane.