Translational Musculoskeletal Research Center

Philadelphia, PA, United States

Translational Musculoskeletal Research Center

Philadelphia, PA, United States

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Li Q.,Drexel University | Qu F.,University of Pennsylvania | Qu F.,Translational Musculoskeletal Research Center | Han B.,Drexel University | And 5 more authors.
Acta Biomaterialia | Year: 2017

To understand how the complex biomechanical functions of the meniscus are endowed by the nanostructure of its extracellular matrix (ECM), we studied the anisotropy and heterogeneity in the micromechanical properties of the meniscus ECM. We used atomic force microscopy (AFM) to quantify the time-dependent mechanical properties of juvenile bovine meniscus at deformation length scales corresponding to the diameters of collagen fibrils. At this scale, anisotropy in the elastic modulus of the circumferential fibers, the major ECM structural unit, can be attributed to differences in fibril deformation modes: uncrimping when normal to the fiber axis, and laterally constrained compression when parallel to the fiber axis. Heterogeneity among different structural units is mainly associated with their variations in microscale fiber orientation, while heterogeneity across anatomical zones is due to alterations in collagen fibril diameter and alignment at the nanoscale. Unlike the elastic modulus, the time-dependent properties are more homogeneous and isotropic throughout the ECM. These results enable a detailed understanding of the meniscus structure-mechanics at the nanoscale, and can serve as a benchmark for understanding meniscus biomechanical functions, documenting disease progression and designing tissue repair strategies. Statement of Significance: Meniscal damage is a common cause of joint injury, which can lead to the development of post-traumatic osteoarthritis among young adults. Restoration of meniscus function requires repairing its highly heterogeneous and complex extracellular matrix. Employing AFM, this study quantifies the anisotropic and heterogeneous features of the meniscus ECM structure and mechanics. The micromechanical properties are interpreted within the context of the collagen fibril nanostructure and its variation with tissue anatomical locations. These results provide a fundamental structure-mechanics knowledge benchmark, against which, repair and regeneration strategies can be developed and evaluated with respect to the specialized structural and functional complexity of the native tissue. © 2017 Acta Materialia Inc.


Mauck R.L.,University of Pennsylvania | Mauck R.L.,Translational Musculoskeletal Research Center | Burdick J.A.,University of Pennsylvania | Burdick J.A.,Translational Musculoskeletal Research Center
Annals of Biomedical Engineering | Year: 2015

When the field of tissue engineering first arose, scaffolds were conceived of as inert three-dimensional structures whose primary function was to support cellularity and tissue growth. Since then, advances in scaffold and biomaterial design have evolved to not only guide tissue formation, but also to interact dynamically with and manipulate the wound environment. At present, these efforts are being directed towards strategies that directly address limitations in endogenous wound repair, with the goal of reprogramming the local wound environment (and the cells within that locality) from a state that culminates in an inferior tissue repair into a state in which functional regeneration is achieved. This review will address this approach with a focus on recent advances in scaffold design towards the resolution of tears of the knee meniscus as a case example. The inherent limitations to endogenous repair will be discussed, as will specific examples of how biomaterials are being designed to overcome these limitations. Examples will include design of fibrous scaffolds that promote colonization by modulating local extracellular matrix density and delivering recruitment factors. Furthermore, we will discuss scaffolds that are themselves modulated by the wound environment to alter porosity and modulate therapeutic release through precise coordination of scaffold degradation. Finally, we will close with emerging concepts in local control of cell mechanics to improve interstitial cell migration and so advance repair. Overall, these examples will illustrate how emergent features within a biomaterial can be tuned to manipulate and harness the local tissue microenvironment in order to promote robust regeneration. © 2015, Biomedical Engineering Society.


Fisher M.B.,University of Pennsylvania | Fisher M.B.,Translational Musculoskeletal Research Center | Henning E.A.,University of Pennsylvania | Henning E.A.,Translational Musculoskeletal Research Center | And 7 more authors.
Biomaterials | Year: 2014

Given the limitations of current surgical approaches to treat articular cartilage injuries, tissue engineering (TE) approaches have been aggressively pursued. Despite reproduction of key mechanical attributes of native tissue, the ability of TE cartilage constructs to integrate with native tissue must also be optimized for clinical success. In this paper, we propose a "trajectory-based" tissue engineering (TB-TE) approach, based on the hypothesis that time-dependent increases in construct maturation in-vitro prior to implantation (i.e. positive rates) may provide a reliable predictor of in-vivo success. As an example TE system, we utilized hyaluronic acid hydrogels laden with mesenchymal stem cells. We first modeled the maturation of these constructs in-vitro to capture time-dependent changes. We then performed a sensitivity analysis of the model to optimize the timing and amount of data collection. Finally, we showed that integration to cartilage in-vitro is not correlated to the maturation state of TE constructs, but rather their maturation rate, providing a proof-of-concept for the use of TB-TE to enhance treatment outcomes following cartilage injury. This new approach challenges the traditional TE paradigm of matching only native state parameters of maturity and emphasizes the importance of also establishing an in-vitro trajectory in constructs in order to improve the chance of in-vivo success. © 2013 Elsevier Ltd.


Martin J.T.,University of Pennsylvania | Martin J.T.,Translational Musculoskeletal Research Center | Milby A.H.,University of Pennsylvania | Milby A.H.,Translational Musculoskeletal Research Center | And 10 more authors.
Acta Biomaterialia | Year: 2014

Intervertebral disc degeneration has been implicated in the etiology of low back pain; however, the current surgical strategies for treating symptomatic disc disease are limited. A variety of materials have been developed to replace disc components, including the nucleus pulposus (NP), the annulus fibrosus (AF) and their combination into disc-like engineered constructs. We have previously shown that layers of electrospun poly(ε-caprolactone) scaffold, mimicking the hierarchical organization of the native AF, can achieve functional parity with native tissue. Likewise, we have combined these structures with cell-seeded hydrogels (as an NP replacement) to form disc-like angle-ply structures (DAPS). The objective of this study was to develop a model for the evaluation of DAPS in vivo. Through a series of studies, we developed a surgical approach to replace the rat caudal disc with an acellular DAPS and then stabilized the motion segment via external fixation. We then optimized cell infiltration into DAPS by including sacrificial poly(ethylene oxide) layers interspersed throughout the angle-ply structure. Our findings illustrate that DAPS are stable in the caudal spine, are infiltrated by cells from the peri-implant space and that infiltration is expedited by providing additional routes for cell migration. These findings establish a new in vivo platform in which to evaluate and optimize the design of functional disc replacements. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Lieberthal J.,University of Pennsylvania | Sambamurthy N.,University of Pennsylvania | Scanzello C.R.,University of Pennsylvania | Scanzello C.R.,Translational Musculoskeletal Research Center
Osteoarthritis and Cartilage | Year: 2015

Inflammation is a variable feature of osteoarthritis (OA), associated with joint symptoms and progression of disease. Signs of inflammation can be observed in joint fluids and tissues from patients with joint injuries at risk for development of post-traumatic osteoarthritis (PTOA). Furthermore, inflammatory mechanisms are hypothesized to contribute to the risk of OA development and progression after injury. Animal models of PTOA have been instrumental in understanding factors and mechanisms involved in chronic progressive cartilage degradation observed after a predisposing injury. Specific aspects of inflammation observed in humans, including cytokine and chemokine production, synovial reaction, cellular infiltration and inflammatory pathway activation, are also observed in models of PTOA. Many of these models are now being utilized to understand the impact of post-injury inflammatory response on PTOA development and progression, including risk of progressive cartilage degeneration and development of chronic symptoms post-injury. As evidenced from these models, a vigorous inflammatory response occurs very early after joint injury but is then sustained at a lower level at the later phases. This early inflammatory response contributes to the development of PTOA features including cartilage erosion and is potentially modifiable, but specific mediators may also play a role in tissue repair. Although the optimal approach and timing of anti-inflammatory interventions after joint injury are yet to be determined, this body of work should provide hope for the future of disease modification tin PTOA. © 2015 Osteoarthritis Research Society International.


Cote A.J.,University of Pennsylvania | McLeod C.M.,University of Pennsylvania | McLeod C.M.,Translational Musculoskeletal Research Center | Farrell M.J.,University of Pennsylvania | And 5 more authors.
Nature Communications | Year: 2016

Mesenchymal stem cells (MSCs) display substantial cell-to-cell heterogeneity, complicating their use in regenerative medicine. However, conventional bulk assays mask this variability. Here we show that both chondrocytes and chondrogenically induced MSCs exhibit substantial mRNA expression heterogeneity. Single-molecule RNA FISH to measure mRNA expression of differentiation markers in single cells reveals that sister cell pairs have high levels of mRNA variability, suggesting that marker expression is not heritable. Surprisingly, this variability does not correlate with cell-to-cell differences in cartilage-like matrix production. Transcriptome-wide analysis suggests that no combination of markers can predict functional potential. De-differentiating chondrocytes also show a disconnect between mRNA expression of the cartilage marker aggrecan and cartilage-like matrix accumulation. Altogether, these quantitative analyses suggest that sorting subpopulations based on these markers would only marginally enrich the progenitor population for 'superior' MSCs. Our results suggest that instantaneous mRNA abundance of canonical markers is tenuously linked to the chondrogenic phenotype at the single-cell level.


Driscoll T.P.,University of Pennsylvania | Cosgrove B.D.,University of Pennsylvania | Heo S.-J.,University of Pennsylvania | Shurden Z.E.,University of Pennsylvania | And 2 more authors.
Biophysical Journal | Year: 2015

Mechanical forces transduced to cells through the extracellular matrix are critical regulators of tissue development, growth, and homeostasis, and can play important roles in directing stem cell differentiation. In addition to force-sensing mechanisms that reside at the cell surface, there is growing evidence that forces transmitted through the cytoskeleton and to the nuclear envelope are important for mechanosensing, including activation of the Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) pathway. Moreover, nuclear shape, mechanics, and deformability change with differentiation state and have been likewise implicated in force sensing and differentiation. However, the significance of force transfer to the nucleus through the mechanosensing cytoskeletal machinery in the regulation of mesenchymal stem cell mechanobiologic response remains unclear. Here we report that actomyosin-generated cytoskeletal tension regulates nuclear shape and force transmission through the cytoskeleton and demonstrate the differential short- and long-term response of mesenchymal stem cells to dynamic tensile loading based on the contractility state, the patency of the actin cytoskeleton, and the connections it makes with the nucleus. Specifically, we show that while some mechanoactive signaling pathways (e.g., ERK signaling) can be activated in the absence of nuclear strain transfer, cytoskeletal strain transfer to the nucleus is essential for activation of the YAP/TAZ pathway with stretch. © 2015 Biophysical Society.


Farrell M.J.,University of Pennsylvania | Farrell M.J.,Translational Musculoskeletal Research Center | Shin J.I.,University of Pennsylvania | Smith L.J.,University of Pennsylvania | And 3 more authors.
Osteoarthritis and Cartilage | Year: 2015

Objective: Tissue engineering approaches for cartilage repair have focused on the use of mesenchymal stem cells (MSCs). For clinical success, MSCs must survive and produce extracellular matrix in the physiological context of the synovial joint, where low nutrient conditions engendered by avascularity, nutrient utilization, and waste production prevail. This study sought to delineate the role of microenvironmental stressors on MSC viability and functional capacity in three dimensional (3D) culture. Design: We evaluated the impact of glucose and oxygen deprivation on the functional maturation of 3D MSC-laden agarose constructs. Since MSC isolation procedures result in a heterogeneous cell population, we also utilized micro-pellet culture to investigate whether clonal subpopulations respond to these microenvironmental stressors in a distinct fashion. Results: MSC health and the functional maturation of 3D constructs were compromised by both glucose and oxygen deprivation. Importantly, glucose deprivation severely limited viability, and so compromised the functional maturation of 3D constructs to the greatest extent. The observation that not all cells died suggested there exists heterogeneity in the response of MSC populations to metabolic stressors. Population heterogeneity was confirmed through a series of studies utilizing clonally derived subpopulations, with a spectrum of matrix production and cell survival observed under conditions of metabolic stress. Conclusions: Our findings show that glucose deprivation has a significant impact on functional maturation, and that some MSC subpopulations are more resilient to metabolic challenge than others. These findings suggest that pre-selection of subpopulations that are resilient to metabolic challenge may improve invivo outcomes. © 2014 Osteoarthritis Research Society International.


Kim D.H.,University of Pennsylvania | Kim D.H.,Translational Musculoskeletal Research Center | Martin J.T.,University of Pennsylvania | Martin J.T.,Translational Musculoskeletal Research Center | And 5 more authors.
Acta Biomaterialia | Year: 2015

Degradation of the nucleus pulposus (NP) is an early hallmark of intervertebral disc degeneration. The capacity for endogenous regeneration in the NP is limited due to the low cellularity and poor nutrient and vascular supply. Towards restoring the NP, a number of biomaterials have been explored for cell delivery. These materials must support the NP cell phenotype while promoting the elaboration of an NP-like extracellular matrix in the shortest possible time. Our previous work with chondrocytes and mesenchymal stem cells demonstrated that hydrogels based on hyaluronic acid (HA) are effective at promoting matrix production and the development of functional material properties. However, this material has not been evaluated in the context of NP cells. Therefore, to test this material for NP regeneration, bovine NP cells were encapsulated in 1% w/vol HA hydrogels at either a low seeding density (20 × 106 cells ml-1) or a high seeding density (60 × 106 cells ml-1), and constructs were cultured over an 8 week period. These NP cell-laden HA hydrogels showed functional matrix accumulation, with increasing matrix content and mechanical properties with time in culture at both seeding densities. Furthermore, encapsulated cells showed NP-specific gene expression profiles that were significantly higher than expanded NP cells prior to encapsulation, suggesting a restoration of phenotype. Interestingly, these levels were higher at the lower seeding density compared to the higher seeding density. These findings support the use of HA-based hydrogels for NP tissue engineering and cellular therapies directed at restoration or replacement of the endogenous NP. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Gorth D.J.,University of Pennsylvania | Gorth D.J.,Translational Musculoskeletal Research Center | Lothstein K.E.,University of Pennsylvania | Lothstein K.E.,Translational Musculoskeletal Research Center | And 11 more authors.
Journal of Orthopaedic Research | Year: 2015

Degeneration of the intervertebral discs is strongly implicated as a cause of low back pain. Since current treatments for discogenic low back pain show poor long-term efficacy, a number of new biological strategies are being pursued. For such therapies to succeed, it is critical that they be validated in conditions that mimic the unique biochemical microenvironment of the nucleus pulposus (NP), which include low oxygen tension. Therefore, the objective of this study was to investigate the effects of oxygen tension on NP cell functional extracellular matrix elaboration in 3D culture. Bovine NP cells were encapsulated in agarose constructs and cultured for 14 or 42 days in either 20% or 2% oxygen in defined media containing transforming growth factor beta-3. At each time point, extracellular matrix composition, biomechanics, and mRNA expression of key phenotypic markers were evaluated. Results showed that while bulk mechanics and composition were largely independent of oxygen level, low oxygen promoted improved restoration of the NP phenotype, higher mRNA expression of extracellular matrix and NP specific markers, and more uniform matrix elaboration. These findings indicate that culture under physiological oxygen levels is an important consideration for successful development of cell and growth factor-based regenerative strategies for the disc. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

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