Homologous structure-function relationships between native fibrocartilage and tissue engineered from MSC-seeded nanofibrous scaffolds.

Understanding the interplay of composition, organization and mechanical function in load-bearing tissues is a prerequisite in the successful engineering of tissues to replace diseased ones. Mesenchymal stem cells (MSCs) seeded on electrospun scaffolds have been successfully used to generate organized tissues that mimic fibrocartilages such as the knee meniscus and the annulus fibrosus of the intervertebral disc. While matrix deposition has been observed in parallel with improved mechanical properties, how composition, organization, and mechanical function are related is not known.

High-throughput screening of a small molecule library for promoters and inhibitors of mesenchymal stem cell osteogenic differentiation.

The use of high-throughput screening (HTS) techniques has long been employed by the pharmaceutical industry to increase discovery rates for new drugs that could be useful for disease treatment, yet this technology has only been minimally applied in other applications such as in tissue regeneration. In this work, an assay for the osteogenic differentiation of human mesenchymal stem cells (hMSCs) was developed and used to screen a library of small molecules for their potential as either promoters or inhibitors of osteogenesis, based on levels of alkaline phosphatase activity and cellular viability. From a library of 1,040 molecules, 36 promoters, and 20 inhibitors were identified as hits based on statistical criteria.

Dynamic culture enhances stem cell infiltration and modulates extracellular matrix production on aligned electrospun nanofibrous scaffolds.

Electrospun nanofibrous scaffolds have become widely investigated for tissue engineering applications, owing to their ability to replicate the scale and organization of many fiber-reinforced soft tissues such as the knee meniscus, the annulus fibrosus of the intervertebral disc, tendon, and cartilage. However, due to their small pore size and dense packing of fibers, cellular ingress into electrospun scaffolds is limited. Progress in the application of electrospun scaffolds has therefore been hampered, as limited cell infiltration results in heterogeneous deposition of extracellular matrix and mechanical properties that remain below native benchmarks.

Maturation state-dependent alterations in meniscus integration: implications for scaffold design and tissue engineering.

The knee meniscus is a crucial component of the knee that functions to stabilize the joint, distribute load, and maintain congruency. Meniscus tears and degeneration are common, and natural healing is limited. Notably, few children present with meniscus injuries and other related fibrocartilaginous tissues heal regeneratively in immature animals and in the fetus.

Mechano-topographic modulation of stem cell nuclear shape on nanofibrous scaffolds.

Stem cells transit along a variety of lineage-specific routes towards differentiated phenotypes. These fate decisions are dependent not just on the soluble chemical cues that are encountered or enforced in vivo and in vitro, but also on physical cues from the cellular microenvironment. These physical cues can consist of both nano- and micro-scale topographical features, as well as mechanical inputs provided passively (from the base properties of the materials to which they adhere) or actively (from extrinsic applied mechanical deformations).

Duty Cycle of Deformational Loading Influences the Growth of Engineered Articular Cartilage.

This study examines how variations in the duty cycle (the duration of applied loading) of deformational loading can influence the mechanical properties of tissue engineered cartilage constructs over one month in bioreactor culture. Dynamic loading was carried out with three different duty cycles: 1 h on/1 h off for a total of 3 h loading/day, 3 h continuous loading, or 6 h of continuous loading per day, with all loading performed 5 days/week. All loaded groups showed significant increases in Young's modulus after one month (vs.

Changes in plasma hormone levels correlate with fledging in nestling Leach's storm-petrels.

Leach's storm-petrels accumulate large amounts of body mass throughout the nestling period. Approximately 4days before fledging, nestlings weigh 50-100% more than adults. In order to shed this excess mass, nestlings engage in behavioral anorexia, and leave the burrow when they are light enough to fly.

The influence of an aligned nanofibrous topography on human mesenchymal stem cell fibrochondrogenesis.

Fibrocartilaginous tissues serve critical load-bearing functions in numerous joints throughout the body. As these structures are often injured, there exists great demand for engineered tissue for repair or replacement. This study assessed the ability of human marrow-derived mesenchymal stem cells (MSCs) to elaborate a mechanically functional, fibrocartilaginous matrix in a nanofibrous microenvironment.

Evaluation of the complex transcriptional topography of mesenchymal stem cell chondrogenesis for cartilage tissue engineering.

Mesenchymal stem cells (MSCs) are a promising cell source for cartilage tissue engineering given their chondrogenic potential. This potential has yet to be fully realized, as the mechanical properties of MSC-based constructs are lower than those of chondrocyte-based constructs cultured identically. The aim of this study was to better understand the transcriptional underpinnings of this functional limitation.

Engineered disc-like angle-ply structures for intervertebral disc replacement.

Study Design: To develop a construction algorithm in which electrospun nanofibrous scaffolds are coupled with a biocompatible hydrogel to engineer a mesenchymal stem cell (MSC)-based disc replacement.

Objective: To engineer a disc-like angle-ply structure (DAPS) that replicates the multiscale architecture of the intervertebral disc.

Summary Of Background Data: Successful engineering of a replacement for the intervertebral disc requires replication of its mechanical function and anatomic form.

Long-term dynamic loading improves the mechanical properties of chondrogenic mesenchymal stem cell-laden hydrogel.

Mesenchymal stem cells (MSCs) are an attractive cell source for cartilage tissue engineering given their ability to undergo chondrogenesis in 3D culture systems. Mechanical forces play an important role in regulating both cartilage development and MSC chondrogenic gene expression, however, mechanical stimulation has yet to enhance the mechanical properties of engineered constructs. In this study, we applied long-term dynamic compression to MSC-seeded constructs and assessed whether varying pre-culture duration, loading regimens and inclusion of TGF-beta3 during loading would influence functional outcomes and these phenotypic transitions.

An anisotropic nanofiber/microsphere composite with controlled release of biomolecules for fibrous tissue engineering.

Aligned nanofibrous scaffolds can recapitulate the structural hierarchy of fiber-reinforced tissues of the musculoskeletal system. While these electrospun fibrous scaffolds provide physical cues that can direct tissue formation when seeded with cells, the ability to chemically guide a population of cells, without disrupting scaffold mechanical properties, would improve the maturation of such constructs and add additional functionality to the system both in vitro and in vivo. In this study, we developed a fabrication technique to entrap drug-delivering microspheres within nanofibrous scaffolds.

Mechanical design criteria for intervertebral disc tissue engineering.

Due to the inability of current clinical practices to restore function to degenerated intervertebral discs, the arena of disc tissue engineering has received substantial attention in recent years. Despite tremendous growth and progress in this field, translation to clinical implementation has been hindered by a lack of well-defined functional benchmarks. Because successful replacement of the disc is contingent upon replication of some or all of its complex mechanical behaviors, it is critically important that disc mechanics be well characterized in order to establish discrete functional goals for tissue engineering.

Nanofibrous biologic laminates replicate the form and function of the annulus fibrosus.

Successful engineering of load-bearing tissues requires recapitulation of their complex mechanical functions. Given the intimate relationship between function and form, biomimetic materials that replicate anatomic form are of great interest for tissue engineering applications. However, for complex tissues such as the annulus fibrosus, scaffolds have failed to capture their multi-scale structural hierarchy.

Biodegradable fibrous scaffolds with diverse properties by electrospinning candidates from a combinatorial macromer library.

The properties of electrospun fibrous scaffolds, including degradation, mechanics and cellular interactions, are important for their use in tissue engineering applications. Although some diversity has been obtained previously in fibrous scaffolds, optimization of scaffold properties relies on iterative techniques in both polymer synthesis and processing. Here, we electrospun candidates from a combinatorial library of biodegradable and photopolymerizable poly(beta-amino ester)s (PBAEs) to show that the diversity in properties found in this library is retained when processed into fibrous scaffolds.

Fabrication and modeling of dynamic multipolymer nanofibrous scaffolds.

Aligned nanofibrous scaffolds hold tremendous potential for the engineering of dense connective tissues. These biomimetic micropatterns direct organized cell-mediated matrix deposition and can be tuned to possess nonlinear and anisotropic mechanical properties. For these scaffolds to function in vivo, however, they must either recapitulate the full dynamic mechanical range of the native tissue upon implantation or must foster cell infiltration and matrix deposition so as to enable construct maturation to meet these criteria.

Mechanics and mechanobiology of mesenchymal stem cell-based engineered cartilage.

In this review, we outline seminal and recent work highlighting the potential of mesenchymal stem cells (MSCs) in producing cartilage-like tissue equivalents. Specific focus is placed on the mechanical properties of engineered MSC-based cartilage and how these properties relate to that of engineered cartilage based on primary chondrocytes and to native tissue properties. We discuss current limitations and/or concerns that must be addressed for the clinical realization of MSC-based cartilage therapeutics, and provide some insight into potential underpinnings for the observed deviations from chondrocyte-based engineered constructs.

New directions in nanofibrous scaffolds for soft tissue engineering and regeneration.

This review focuses on the role of nanostructure and nanoscale materials for tissue engineering applications. We detail a scaffold production method (electrospinning) for the production of nanofiber-based scaffolds that can approximate many critical features of the normal cellular microenvironment, and so foster and direct tissue formation. Further, we describe new and emerging methods to increase the applicability of these scaffolds for in vitro and in vivo application.

The influence of degradation characteristics of hyaluronic acid hydrogels on in vitro neocartilage formation by mesenchymal stem cells.

The potential of mesenchymal stem cells (MSCs) as a viable cell source for cartilage repair hinges on the development of engineered scaffolds that support adequate cartilage tissue formation. Evolving networks (hydrogels with mesh sizes that change over time due to crosslink degradation) may provide the control needed to enhance overall tissue formation when compared to static scaffolds. In this study, MSCs were photoencapsulated in combinations of hydrolytically and enzymatically degradable hyaluronic acid (HA) hydrogels to investigate the tunability of these hydrogels and the influence of network evolution on neocartilage formation.

Transient exposure to transforming growth factor beta 3 improves the mechanical properties of mesenchymal stem cell-laden cartilage constructs in a density-dependent manner.

Mesenchymal stem cells (MSCs) are an attractive cell source for cartilage tissue engineering and regenerative medicine. However, the use of these cells has been limited by their reduced ability to form functional tissue compared to chondrocytes when placed in three-dimensional culture systems. To optimize MSC functional chondrogenesis, we examined the effects of increasing seeding density and transient application of transforming growth factor beta 3 (TGF-beta3), two factors previously shown to improve growth of chondrocyte-based constructs.

Meniscus tissue engineering on the nanoscale: from basic principles to clinical application.

The meniscus is a fibrocartilaginous tissue uniquely adapted to enable load transmission in the knee. Although the meniscus was once considered a useless remnant of joint formation, removal of all or part of the meniscus initiates osteoarthritis. Surgical repair methods focus on fragment stabilization or biologic enhancement of healing.

Engineering on the straight and narrow: the mechanics of nanofibrous assemblies for fiber-reinforced tissue regeneration.

Tissue engineering of fibrous tissues of the musculoskeletal system represents a considerable challenge because of the complex architecture and mechanical properties of the component structures. Natural healing processes in these dense tissues are limited as a result of the mechanically challenging environment of the damaged tissue and the hypocellularity and avascular nature of the extracellular matrix. When healing does occur, the ordered structure of the native tissue is replaced with a disorganized fibrous scar with inferior mechanical properties, engendering sites that are prone to re-injury.

Differential maturation and structure-function relationships in mesenchymal stem cell- and chondrocyte-seeded hydrogels.

Degenerative disease and damage to articular cartilage represents a growing concern in the aging population. New strategies for engineering cartilage have employed mesenchymal stem cells (MSCs) as a cell source. However, recent work has suggested that chondrocytes (CHs) produce extracellular matrix (ECM) with superior mechanical properties than MSCs do.

ISSLS prize winner: integrating theoretical and experimental methods for functional tissue engineering of the annulus fibrosus.

Study Design: Integrating theoretical and experimental approaches for annulus fibrosus (AF) functional tissue engineering.

Objective: Apply a hyperelastic constitutive model to characterize the evolution of engineered AF via scalar model parameters. Validate the model and predict the response of engineered constructs to physiologic loading scenarios.

High-throughput screening for modulators of mesenchymal stem cell chondrogenesis.

Mesenchymal stem cells (MSCs) are an attractive cell source for regenerative medicine and the study of skeletal development. Despite considerable interest in MSC chondrogenesis, the signal transduction and molecular mechanisms underlying this process remain largely undefined. To explore the signaling topology regulating chondrogenic differentiation, as well as to discover novel modulators, we developed and validated a high-throughput screening (HTS) assay for MSC chondrogenesis.