Three-dimensional in vitro effects of compression and time in culture on aggregate modulus and on gene expression and protein content of collagen type II in murine chondrocytes

Pre-hypertrophic chondrogenic enhancer landscape of limb and axial skeleton development

Chondrocyte differentiation controls skeleton development and stature. Here we provide a comprehensive map of chondrocyte-specific enhancers and show that they provide a mechanistic framework through which non-coding genetic variants can influence skeletal development and human stature. Working with fetal chondrocytes isolated from mice bearing a Col2a1 fluorescent regulatory sensor, we identify 780 genes and 2'704 putative enhancers specifically active in chondrocytes using a combination of RNA-seq, ATAC-seq and H3K27ac ChIP-seq. Most of these enhancers (74%) show pan-chondrogenic activity, with smaller populations being restricted to limb (18%) or trunk (8%) chondrocytes only. Notably, genetic variations overlapping these enhancers better explain height differences than those overlapping non-chondrogenic enhancers. Finally, targeted deletions of identified enhancers at the Fgfr3, Col2a1, Hhip and, Nkx3-2 loci confirm their role in regulating cognate genes. This enhancer map provides a framework for understanding how genes and non-coding variations influence bone development and diseases.

Lineage-specific differences and regulatory networks governing human chondrocyte development

To address large gaps in our understanding of the molecular regulation of articular and growth plate cartilage development in humans, we used our directed differentiation approach to generate these distinct cartilage tissues from human embryonic stem cells. The resulting transcriptomic profiles of hESC-derived articular and growth plate chondrocytes were similar to fetal epiphyseal and growth plate chondrocytes, with respect to genes both known and previously unknown to cartilage biology. With the goal to characterize the regulatory landscapes accompanying these respective transcriptomes, we mapped chromatin accessibility in hESC-derived chondrocyte lineages, and mouse embryonic chondrocytes, using ATAC-sequencing. Integration of the expression dataset with the differentially accessible genomic regions revealed lineage-specific gene regulatory networks. We validated functional interactions of two transcription factors (TFs) (RUNX2 in growth plate chondrocytes and RELA in articular chondrocytes) with their predicted genomic targets. The maps we provide thus represent a framework for probing regulatory interactions governing chondrocyte differentiation. This work constitutes a substantial step towards comprehensive and comparative molecular characterizations of distinct chondrogenic lineages and sheds new light on human cartilage development and biology.

"Slow walk" mimetic tensile loading maintains human meniscus tissue resident progenitor cells homeostasis in photocrosslinked gelatin hydrogel

Meniscus, the cushion in knee joint, is a load-bearing tissue that transfers mechanical forces to extracellular matrix (ECM) and tissue resident cells. The mechanoresponse of human tissue resident stem/progenitor cells in meniscus (hMeSPCs) is significant to tissue homeostasis and regeneration but is not well understood. This study reports that a mild cyclic tensile loading regimen of ∼1800 loads/day on hMeSPCs seeded in 3-dimensional (3D) photocrosslinked gelatin methacryloyl (GelMA) hydrogel is critical in maintaining cellular homeostasis. Experimentally, a "slow walk" biomimetic cyclic loading regimen (10% tensile strain, 0.5 Hz, 1 h/day, up to 15 days) is applied to hMeSPCs encapsulated in GelMA hydrogel with a magnetic force-controlled loading actuator. The loading significantly increases cell differentiation and fibrocartilage-like ECM deposition without affecting cell viability. Transcriptomic analysis reveals 332 mechanoresponsive genes, clustered into cell senescence, mechanical sensitivity, and ECM dynamics, associated with interleukins, integrins, and collagens/matrix metalloproteinase pathways. The cell-GelMA constructs show active ECM remodeling, traced using a green fluorescence tagged (GFT)-GelMA hydrogel. Loading enhances nascent pericellular matrix production by the encapsulated hMeSPCs, which gradually compensates for the hydrogel loss in the cultures. These findings demonstrate the strong tissue-forming ability of hMeSPCs, and the importance of mechanical factors in maintaining meniscus homeostasis.

Intrinsic and growth-mediated cell and matrix specialization during murine meniscus tissue assembly

The incredible mechanical strength and durability of mature fibrous tissues and their extremely limited turnover and regenerative capacity underscores the importance of proper matrix assembly during early postnatal growth. In tissues with composite extracellular matrix (ECM) structures, such as the adult knee meniscus, fibrous (Collagen-I rich), and cartilaginous (Collagen-II, proteoglycan-rich) matrix components are regionally segregated to the outer and inner portions of the tissue, respectively. While this spatial variation in composition is appreciated to be functionally important for resisting complex mechanical loads associated with gait, the establishment of these specialized zones is poorly understood. To address this issue, the following study tracked the growth of the murine meniscus from its embryonic formation through its first month of growth, encompassing the critical time-window during which animals begin to ambulate and weight bear. Using histological analysis, region specific high-throughput qPCR, and Col-1, and Col-2 fluorescent reporter mice, we found that matrix and cellular features defining specific tissue zones were already present at birth, before continuous weight-bearing had occurred. These differences in meniscus zones were further refined with postnatal growth and maturation, resulting in specialization of mature tissue regions. Taken together, this work establishes a detailed timeline of the concurrent spatiotemporal changes that occur at both the cellular and matrix level throughout meniscus maturation. The findings of this study provide a framework for investigating the reciprocal feedback between cells and their evolving microenvironments during assembly of a mechanically robust fibrocartilage tissue, thus providing insight into mechanisms of tissue degeneration and effective regenerative strategies.

Studies of surface grafted collagen and transforming growth factor β1 combined with cyclic stretching as a dual chemical and physical stimuli approach for rat adipose-derived stem cells (rADSCs) chondrogenesis differentiation

The adipose-derived stem cell has been used in various regenerative medicine research due to its multiple differentiation capabilities. Developing a stable and quick approach for the differentiation of stem cells is a critical issue in tissue regenerative field. In this investigation, rat adipose-derived stem cells (rADSCs) were seeded onto the type I collagen/transforming growth factor β1 (TGF-β1) immobilized polydimethylsiloxane (PDMS) substrate and then combined with short term dynamic stretching stimulation (intermittent or continuous stretching for 6 h) to induce the rADSCs chondrogenesis differentiation using the induction medium without growth factors added in vitro. Via regulating the extracellular chemical- and mechano-receptors of the cultured rADSCs, the chondrogenic differentiation was examined. After 72 h of static culture, proteoglycan secretion was noted on the surfaces modified by collagen with or without TGF-β1. After different stretching stimulations, significant proteoglycan secretion was noted on the surface modified by both collagen and collagen/TGF-β1, especially after the intermittent stretching culturing. Nonetheless, genetic expression of the chondrogenic markers: SOX-9, Col2a1, and aggrecan, instead, were dependent upon the surface grafted layer and the stretching mode utilized. These findings suggested that the surface chemical characteristics and external mechanical stimulation could synergistically affect the efficacy of chondrogenic differentiation of rADSCs.

Evolutionary Selection and Constraint on Human Knee Chondrocyte Regulation Impacts Osteoarthritis Risk

During human evolution, the knee adapted to the biomechanical demands of bipedalism by altering chondrocyte developmental programs. This adaptive process was likely not without deleterious consequences to health. Today, osteoarthritis occurs in 250 million people, with risk variants enriched in non-coding sequences near chondrocyte genes, loci that likely became optimized during knee evolution. We explore this relationship by epigenetically profiling joint chondrocytes, revealing ancient selection and recent constraint and drift on knee regulatory elements, which also overlap osteoarthritis variants that contribute to disease heritability by tending to modify constrained functional sequence. We propose a model whereby genetic violations to regulatory constraint, tolerated during knee development, lead to adult pathology. In support, we discover a causal enhancer variant (rs6060369) present in billions of people at a risk locus (GDF5-UQCC1), showing how it impacts mouse knee-shape and osteoarthritis. Overall, our methods link an evolutionarily novel aspect of human anatomy to its pathogenesis.

Studies of proliferation and chondrogenic differentiation of rat adipose stem cells using an anti-oxidative polyurethane scaffold combined with cyclic compression culture

The adipose stem cell is a potential candidate for the autologous chondrocytes repairing approach because of the abundance of fat in the animal body and its versatile differentiation capability. In this study, rat adipose stem cells (rASCs) were seeded into anti-oxidative N-acetylcysteine (NAC) grafted polyurethane (PU) scaffold and then combined with short dynamic compressive stimulation (24 h) to induce rASCs chondrogenesis differentiation in vitro. The inner pore surface of the PU scaffold was first modified via alginate and type I collagen to promote rASCs adherence. The modified layers crosslinked by genipin showed outstanding stability after ultrasonic treatment, indicating the modified layers were stable and can keep the cells adhesion well during dynamic compressive stimulation. After inner pore surface modification and 10 mM NAC grafting, the PU scaffold-A-C-G (graft 10 mM NAC) has shown the best proliferation efficiency with homogeneous cell distribution after 72hr static culture. After short term dynamic compressive stimulation, significant gene expression in chondrogenic markers, Sox-9, and Aggrecan, were noted in both PU scaffold-A-C-G and PU scaffold-A-C-G (graft 10 mM NAC). Considering the cell proliferation efficiency and gene expression, the anti-oxidative NAC grafted PU scaffold combined with short term dynamic compressive stimulation could be useful for cell culturing in stem cell therapy.

Dynamic Mechanical Compression of Chondrocytes for Tissue Engineering: A Critical Review

Articular cartilage functions to transmit and translate loads. In a classical structure-function relationship, the tissue resides in a dynamic mechanical environment that drives the formation of a highly organized tissue architecture suited to its biomechanical role. The dynamic mechanical environment includes multiaxial compressive and shear strains as well as hydrostatic and osmotic pressures. As the mechanical environment is known to modulate cell fate and influence tissue development toward a defined architecture in situ, dynamic mechanical loading has been hypothesized to induce the structure-function relationship during attempts at in vitro regeneration of articular cartilage. Researchers have designed increasingly sophisticated bioreactors with dynamic mechanical regimes, but the response of chondrocytes to dynamic compression and shear loading remains poorly characterized due to wide variation in study design, system variables, and outcome measurements. We assessed the literature pertaining to the use of dynamic compressive bioreactors for in vitro generation of cartilaginous tissue from primary and expanded chondrocytes. We used specific search terms to identify relevant publications from the PubMed database and manually sorted the data. It was very challenging to find consensus between studies because of species, age, cell source, and culture differences, coupled with the many loading regimes and the types of analyses used. Early studies that evaluated the response of primary bovine chondrocytes within hydrogels, and that employed dynamic single-axis compression with physiologic loading parameters, reported consistently favorable responses at the tissue level, with upregulation of biochemical synthesis and biomechanical properties. However, they rarely assessed the cellular response with gene expression or mechanotransduction pathway analyses. Later studies that employed increasingly sophisticated biomaterial-based systems, cells derived from different species, and complex loading regimes, did not necessarily corroborate prior positive results. These studies report positive results with respect to very specific conditions for cellular responses to dynamic load but fail to consistently achieve significant positive changes in relevant tissue engineering parameters, particularly collagen content and stiffness. There is a need for standardized methods and analyses of dynamic mechanical loading systems to guide the field of tissue engineering toward building cartilaginous implants that meet the goal of regenerating articular cartilage.

Gdf5 progenitors give rise to fibrocartilage cells that mineralize via hedgehog signaling to form the zonal enthesis

The sequence of events that leads to the formation of a functionally graded enthesis is not clearly defined. The current study demonstrates that clonal expansion of Gdf5 progenitors contributes to linear growth of the enthesis. Prior to mineralization, Col1+ cells in the enthesis appose Col2+ cells of the underlying primary cartilage. At the onset of enthesis mineralization, cells at the base of the enthesis express alkaline phosphatase, Indian hedgehog, and ColX as they mineralize. The mineralization front then extends towards the tendon midsubstance as cells above the front become encapsulated in mineralized fibrocartilage over time. The hedgehog (Hh) pathway regulates this process, as Hh-responsive Gli1+ cells within the developing enthesis mature from unmineralized to mineralized fibrochondrocytes in response to activated signaling. Hh signaling is required for mineralization, as tissue-specific deletion of its obligate transducer Smoothened in the developing tendon and enthesis cells leads to significant reductions in the apposition of mineralized fibrocartilage. Together, these findings provide a spatiotemporal map of events - from expansion of the embryonic progenitor pool to synthesis of the collagen template and finally mineralization of this template - that leads to the formation of the mature zonal enthesis. These results can inform future tendon-to-bone repair strategies to create a mechanically functional enthesis in which tendon collagen fibers are anchored to bone through mineralized fibrocartilage.

Derivation of chondrocyte and osteoblast reporter mouse embryonic stem cell lines

With the establishment of methods that provide evidence for the generation of chondrocyte and osteoblast cell types from ESCs, there is a need for reagents that will enable their further characterization. Here we report on the derivation of chondrocyte and osteoblast reporter ESCs from previously generated and characterized transgenic mouse lines, Collagen type 2 alpha 1(Col2a1)-ECFP, Bone Sialoprotein (BSP)-Topaz, and BSP-Topaz/Dentin Matrix Protein 1 (DMP1)-Cherry dual reporter mice. Col2a1-ECFP is highly expressed in chondrocytes, while BSP-Topaz and DMP1-Cherry are highly expressed in osteoblasts and osteocytes, respectively. These new skeletal reporter mouse ESC lines will serve as valuable reagents to investigate the functionality of ESC derived chondrocyte and osteoblast cell types.

Mechanostimulation changes the catabolic phenotype of human dedifferentiated osteoarthritic chondrocytes

PURPOSE

The treatment of cartilage defects with matrix-embedded autologous chondrocytes is a promising method to support the repair process and to foster reconstitution of full functionality of the joint.

METHODS

Human osteoarthritic chondrocytes were harvest from nine different patients (mean ± SD age 68 ± 8 years) who underwent total knee replacement. The chondrocytes were embedded after a precultivation phase into a collagen I hydrogel. Mid-term intermitted mechanostimulation on matrix-embedded dedifferentiated human osteoarthritic chondrocytes was performed by intermittently applying a cyclic sinusoid compression regime for 4 days (cycles of 1 h of sinusoidal stimulation (1 Hz) and 4 h of break; maximum compression 2.5%). Stimulated (Flex) and non-stimulated (No Flex) cell matrix constructs were analysed concerning the expression of genes involved in tissue metabolism, the content of sulphated glycosaminoglycans (sGAG) and the morphology of the chondrocytes.

RESULTS

Gene expression analysis showed a high significant increase in collagen type II expression (p < 0.001), a significant increase in aggrecan expression (p < 0.04) and a high significant decrease in MMP-13 expression (p < 0.001) under stimulation condition compared with unstimulated controls. No significant changes were found in the gene expression rate of MMP-3. This positive effect of the mechanostimulation was confirmed by the analyses of sGAG. Mechanically stimulated cell-matrix constructs had nearly tripled sGAG content than the non-stimulated control (p < 0.002). In addition, histological examination showed that morphology of chondrocytes was altered from a spindle-shaped to a chondrocyte-characteristic rounded phenotype.

CONCLUSION

Mid-term intermitted mechanical stimulation in vitro has the potential to improve the cell quality of cell matrix constructs prepared from dedifferentiated osteoarthritic chondrocytes. This observation may extend the inclusion criteria for matrix-assisted autologous chondrocyte implantation (MACI) and confirms the importance of moderate dynamic compression in clinical rehabilitation after MACI.

Discriminating multiplexed GFP reporters in primary articular chondrocyte cultures using image cytometry

Flow cytometry has become a standard tool for defining a heterogeneous cell population based on surface expressed epitopes or GFP reporters that reflect cell types or cellular differentiation. The introduction of image cytometry raised the possibility of adaptation to discriminate GFP reporters used to appreciate cell heterogeneity within the skeletal lineages. The optical filters and LEDs were optimized for the reporters used in transgenic mice expressing various fluorescent proteins. In addition, the need for compensation between eGFP and surrounding reporters due to optical cross-talk was eliminated by selecting the appropriate excitation and emission filters. Bone marrow or articular cartilage cell cultures from GFP and RFP reporter mouse lines were established to demonstrate the equivalency in functionalities of image to flow cytometry analysis. To examine the ability for monitoring primary cell differentiation, articular chondrocyte cell cultures were established from mice that were single or doubly transgenic (Dkk3eGFP and Col2A1GFPcyan), which identify the progression of superficial small articular cell to a mature chondrocyte. The instrument was able to rapidly and accurately discriminate cells that were Dkk3eGFP only, Dkk3eGFP/Col2A1GFPcyan, and Col2A1GFP, which provides a useful tool for studying the impact of culture conditions on lineage expansion and differentiation.

Evolving strategies in mechanobiology to more effectively treat damaged musculoskeletal tissues

In this paper, we had four primary objectives. (1) We reviewed a brief history of the Lissner award and the individual for whom it is named, H.R. Lissner. We examined the type (musculoskeletal, cardiovascular, and other) and scale (organism to molecular) of research performed by prior Lissner awardees using a hierarchical paradigm adopted at the 2007 Biomechanics Summit of the US National Committee on Biomechanics. (2) We compared the research conducted by the Lissner award winners working in the musculoskeletal (MS) field with the evolution of our MS research and showed similar trends in scale over the past 35 years. (3) We discussed our evolving mechanobiology strategies for treating musculoskeletal injuries by accounting for clinical, biomechanical, and biological considerations. These strategies included studies to determine the function of the anterior cruciate ligament and its graft replacements as well as novel methods to enhance soft tissue healing using tissue engineering, functional tissue engineering, and, more recently, fundamental tissue engineering approaches. (4) We concluded with thoughts about future directions, suggesting grand challenges still facing bioengineers as well as the immense opportunities for young investigators working in musculoskeletal research. Hopefully, these retrospective and prospective analyses will be useful as the ASME Bioengineering Division charts future research directions.

Dual reporter approaches for identification of Cre efficacy and astrocyte heterogeneity

Gene inactivation reporters are powerful tools to circumvent limitations of the widely used Cre/loxP system of conditional mutagenesis. With new conditional transgenic mouse lines expressing the enhanced cyan fluorescent protein (ECFP) instead of connexin43 (Cx43) after Cre-mediated recombination, we demonstrate dual reporter approaches to simultaneously examine astrocyte subpopulations expressing different connexins, identify compensatory up-regulation within gene families, and quantify Cre-mediated deletion at the allelic level. Analysis of a newly generated Cx43 knock-in ECFP mouse revealed an unexpected heterogeneity of Cx43-expressing astrocytes across brain areas.

A 3D system for culturing human articular chondrocytes in synovial fluid

Cartilage destruction is a central pathological feature of osteoarthritis, a leading cause of disability in the US. Cartilage in the adult does not regenerate very efficiently in vivo; and as a result, osteoarthritis leads to irreversible cartilage loss and is accompanied by chronic pain and immobility (1,2). Cartilage tissue engineering offers promising potential to regenerate and restore tissue function. This technology typically involves seeding chondrocytes into natural or synthetic scaffolds and culturing the resulting 3D construct in a balanced medium over a period of time with a goal of engineering a biochemically and biomechanically mature tissue that can be transplanted into a defect site in vivo (3-6). Achieving an optimal condition for chondrocyte growth and matrix deposition is essential for the success of cartilage tissue engineering. In the native joint cavity, cartilage at the articular surface of the bone is bathed in synovial fluid. This clear and viscous fluid provides nutrients to the avascular articular cartilage and contains growth factors, cytokines and enzymes that are important for chondrocyte metabolism (7,8). Furthermore, synovial fluid facilitates low-friction movement between cartilaginous surfaces mainly through secreting two key components, hyaluronan and lubricin (9 10). In contrast, tissue engineered cartilage is most often cultured in artificial media. While these media are likely able to provide more defined conditions for studying chondrocyte metabolism, synovial fluid most accurately reflects the natural environment of which articular chondrocytes reside in. Indeed, synovial fluid has the advantage of being easy to obtain and store, and can often be regularly replenished by the body. Several groups have supplemented the culture medium with synovial fluid in growing human, bovine, rabbit and dog chondrocytes, but mostly used only low levels of synovial fluid (below 20%) (11-25). While chicken, horse and human chondrocytes have been cultured in the medium with higher percentage of synovial fluid, these culture systems were two-dimensional (26-28). Here we present our method of culturing human articular chondrocytes in a 3D system with a high percentage of synovial fluid (up to 100%) over a period of 21 days. In doing so, we overcame a major hurdle presented by the high viscosity of the synovial fluid. This system provides the possibility of studying human chondrocytes in synovial fluid in a 3D setting, which can be further combined with two other important factors (oxygen tension and mechanical loading) (29,30) that constitute the natural environment for cartilage to mimic the natural milieu for cartilage growth. Furthermore, This system may also be used for assaying synovial fluid activity on chondrocytes and provide a platform for developing cartilage regeneration technologies and therapeutic options for arthritis.

Isolation and characterization of murine mandibular condylar cartilage cell populations

OBJECTIVES

The mandibular condylar cartilage is a heterogeneous tissue containing cells at various stages of chondrocyte maturation organized into 4 zones: superficial, polymorphic, flattened, and hypertrophic. The goal of this study was to use transgenic mice containing chondrocyte maturation markers fused to fluorescent protein transgenes to isolate and characterize homogenous cell populations of the mandibular condylar cartilage.

METHODS

Fluorescent reporter expression in the mandibular condylar cartilage of transgenic mice containing the 3.6-kb fragment of the rat collagen type 1 promoter fused to a topaz-fluorescent protein (Col3.6-tpz), collagen type 2 promoter fused to a cyan-fluorescent protein (Col2-cyan), and/or collagen type 10 promoter fused to cherry-fluorescent protein (Col10-cherry) was examined. Mandibular condylar cartilage cells were analyzed by fluorescence-activated cell sorting (FACS) and either used for gene expression analysis or plated in cell cultures and exposed to adipogenic, osteogenic, or chondrogenic conditions. To determine cell fate, transgenic mice containing the Col3.6-cre recombinase were bred with cre reporter mice.

RESULTS

Localization and analysis of gene expression revealed that Col3.6-tpz-positive cells corresponded to the polymorphic/flattened zones and Col2-cyan-positive cells corresponded to the flattened/hypertrophic zones of the mandibular condylar cartilage. Mandibular condylar cartilage FACS-sorted Col3.6-tpz-positive cells have the potential to differentiate into bone, cartilage, and fat. Cell fate mapping revealed that Col3.6 cells are precursors of some of the hypertrophic chondrocytes in the mandibular condylar cartilage.

CONCLUSION

Col3.6-tpz cells represent an earlier stage of the mandibular condylar cartilage maturation pathway.

Generation and characterization of Col10a1-mcherry reporter mice

We report here on the generation of a new fluorescent protein reporter transgenic mouse line, Col10a1-mCherry, which can be used as a tool to study chondrocyte biology and pathology. Collagen, Type X, alpha 1 (Col10a1) is highly expressed in hypertrophic chondrocytes and commonly used as a gene marker for this cell population. The Col10a1-mCherry reporter line was generated using a bacterial recombination strategy with the mouse BAC clone RP23-192A7. To aid in the characterization of this animal model, we intercrossed Col10a1-mCherry mice with Collagen, Type II, alpha 1 (Col2a1) enhanced cyan fluorescent protein (ECFP) reporter mice and characterized the expression of both chondrocyte reporters during embryonic skeletal development from days E10.5 to E17.5. Additionally, at postnatal day 0, Col10a1-mCherry reporter expression was compared to endogenous Col10a1 mRNA expression in long bones and revealed that mCherry fluorescence extended past the Col10a1 expression domain. However, in situ hybridization for mCherry was consistent with the zone of Col10a1 mRNA expression, indicating that the persistent detection of mCherry fluorescence was a result of the long protein half life of mCherry in conjunction with a very rapid phase of skeletal growth and not due to aberrant transcriptional regulation. Taking advantage of the continued fluorescence of hypertrophic chondrocytes at the chondro-osseus junction, we intercrossed Col10a1-mCherry mice with two different Collagen, Type 1, alpha 1, (Col1a1) osteoblast reporter mice, pOBCol3.6-Topaz and pOBCol2.3-Emerald to investigate the possibility that hypertrophic chondrocytes transdifferentiate into osteoblasts. Evaluation of long bones at birth suggests that residual hypertrophic chondrocytes and osteoblasts in the trabecular zone exist as two completely distinct cell populations. genesis 49:410-418, 2011.

A novel bioreactor for the dynamic stimulation and mechanical evaluation of multiple tissue-engineered constructs

Systematic advancements in the field of musculoskeletal tissue engineering require clear communication about the mechanical environments that promote functional tissue growth. To support the rapid discovery of effective mechanostimulation protocols, this study developed and validated a mechanoactive transduction and evaluation bioreactor (MATE). The MATE provides independent and consistent mechanical loading of six specimens with minimal hardware. The six individual chambers accurately applied static and dynamic loads (1 and 10 Hz) in unconfined compression from 0.1 to 10 N. The material properties of poly(ethylene glycol) diacrylate hydrogels and bovine cartilage were measured by the bioreactor, and these values were within 10% of the values obtained from a standard single-chamber material testing system. The bioreactor was able to detect a 1-day 12% reduction (2 kPa) in equilibrium modulus after collagenase was added to six collagenase sensitive poly(ethylene glycol) diacrylate hydrogels (p = 0.03). By integrating dynamic stimulation and mechanical evaluation into a single batch-testing research platform, the MATE can efficiently map the biomechanical development of tissue-engineered constructs during long-term culture.