Academic literature on the topic 'Tissue engineering. Articular cartilage'

Articular cartilage is a connective tissue structure that is found in anatomical areas that are important for the movement of the human body. Osteoarthritis is the ailment that most often affects the articular cartilage. Due to its poor intrinsic healing capacity, damage to the articular cartilage is highly detrimental and at present the reconstructive options for its repair are limited. Tissue engineering and the science of nanobiomaterials are two lines of research that together can contribute to the restoration of damaged tissue. The science of nanobiomaterials focuses on the development of different nanoscale structures that can be used as carriers of drugs / cells to treat and repair damaged tissues such as articular cartilage. This review article is an overview of the composition of articular cartilage, the causes and treatments of osteoarthritis, with a special emphasis on nanomaterials as carriers of drugs and cells, which reduce inflammation, promote the activation of biochemical factors and ultimately contribute to the total restoration of articular cartilage.

Tissue engineering is a new approach for articular cartilage repair. The aim of the present article was to review the current status of cartilage tissue engineering researches. The scaffold materials used for cartilage tissue engineering, the in vitro, in vivo studies and the clinical trials were all reviewed. Our researches about in vitro cartilage tissue engineering with new type bioactive scaffold and preliminary animal studies results will also be described. The scaffold was tricopolymer made from gelatin, hyaluronan and chondroitin. Chondrocytes seeded in tricopolymer showed in vitro engineered cartilage formation. The engineered cartilage constructs were implanted into knee joints of miniature pigs for animal study.

Structural organization of articular cartilage is rooted in the arrangement of mesenchymal stem cells (MSCs) into morphologically distinct zones during embryogenesis as a result of spatiotemporal gradients in biochemical, mechanical, and cellular factors that direct the formation of stratified structure of articular cartilage. These gradients are central to the function of cartilage as an articulating surface. Strategies that mimic zonal organization of articular cartilage are more likely to create an engineered tissue with more effective clinical outcome. The objective of this work was to measure the expression of human MSCs encapsulated in engineered gels that simulate stiffness of the superficial, middle and calcified zones of articular cartilage supplemented with zone specific growth factors. Size of the encapsulated cells increased from the gel simulating superficial zone to those simulating middle and calcified zones. Glycosaminoglycans (GAG) content progressively increased from the gel simulating superficial zone to those simulating middle and calcified zones. Human MSCs in the gel simulating the superficial zone showed up-regulation of Sox-9 and SZP whereas those in the calcified gel showed up-regulation of ALP. Results demonstrate that a developmental approach can potentially regenerate the zonal structure of articular cartilage.

[EN] Articular cartilage is a tissue that consists of chondrocytes surrounded by a dense extracellular matrix (ECM). The ECM is mainly composed of type II collagen and proteoglycans. The main function of articular cartilage is to provide a lubricated surface for articulation. Articular cartilage damage is common and may lead to osteoarthritis. Articular cartilage does not have blood vessels, nerves or lymphatic vessels and therefore has limited capacity for intrinsic healing and repair. Tissue engineering (TE) is a powerful approach for healing degenerated cartilage. TE uses three-dimensional (3D) scaffolds as cellular culture supports. The scaffold provides a structure that facilitates chondrocyte adhesion and expansion while maintaining a chondrocytic phenotype and limiting dedifferentiation, which is a problem in two-dimensional (2D) systems. Cell attachment to the scaffolds depends on the physical and chemical characteristics of their surface (morphology, rigidity, equilibrium water content, surface tension, hydrophilicity, presence of electric charges). The primary aim of this thesis was to study the influence of different kinds of biomaterials on the response of chondrocytes to in vitro culture. 3D scaffold constructs must have an interconnected porous structure in order to allow cell development through the network, to maintain their differentiated function, as well as to allow the entry and exit of nutrients and metabolic waste removal. Therefore, the effect of the hydrophilicity and pore architecture of the scaffolds was studied. A series of polymer and copolymer networks with varying hydrophilicity was synthesised and biologically tested in monolayer culture. Cell viability, proliferation and aggrecan expression were quantified. When human chondrocytes were cultured on polymer substrates in which the hydrophilic groups were homogeneously distributed, adhesion, proliferation and viability decreased with the content of hydrophilic groups. Nevertheless, copolymers in which hydrophilic and hydrophobic domains alternate showed better results than the corresponding homopolymers. Biostable and biodegradable scaffolds with different hydrophilicity and porosity were synthesised using a template of sintered microspheres of controlled size. This technique allows the interconnectivity between pores and their size to be controlled. Periodic and regular pore architectures and reproducible structures were obtained. The mechanical behaviour of the porous samples was significantly different from that of the bulk material of the same composition. Cells fully colonised the scaffolds when the pores' size and their interconnection were sufficiently large. Another objective was to assess the chondrogenic redifferentiation in a biodegradable 3D scaffold of polycaprolactone (PCL) of human autologous chondrocytes previously expanded in monolayer. This study demonstrated that chondrocytes cultured in PCL scaffolds without fetal bovine serum (FBS) efficiently redifferentiated, expressing a chondrocytic phenotype characterised by their ability to synthesise cartilage-specific ECM proteins. The influence that pore connectivity and hydrophilicity of caprolactone-based scaffolds has on the chondrocyte adhesion to the pore walls, proliferation and composition of the ECM produced was studied. The number of cells inside polycaprolactone scaffolds increased as porosity was increased. A minimum of around 70% porosity was necessary for this scaffold architecture to allow seeding and viability of the cells within. The results suggested that some of the cells inside the scaffold adhered to the pore walls and kept the dedifferentiated phenotype, while others redifferentiated. In conclusion, the findings of this thesis provide valuable insight into the field of cartilage regeneration using TE techniques. The studies carried out shed light on the right composition, porosity and hydrophilicity of the scaffolds to be used for optimal cartilage production.
[ES] El cartílago articular es un tejido compuesto por condrocitos rodeados por una densa matriz extracelular (MEC). La MEC se compone principalmente de colágeno tipo II y de proteoglicanos. La función principal del cartílago articular es proporcionar una superficie lubricada para las articulaciones. Las lesiones en el cartílago articular son comunes y pueden derivar a osteoartritis. El cartílago articular no tiene vasos sanguíneos, nervios o vasos linfáticos y, por tanto, tiene una capacidad limitada de auto-reparación. La ingeniería tisular (IT) es un área prometedora en la regeneración de cartílago. En la IT se utilizan "andamiajes" (scaffolds) tridimensionales (3D) como soportes para el cultivo celular y tisular. Los scaffolds proporcionan una estructura que facilita la adhesión y la expansión de los condrocitos, manteniendo un fenotipo condrocítico limitando su desdiferenciación; que es el mayor problema en los sistemas bidimensionales (2D). La adhesión celular a los scaffolds depende de las características físicas y químicas de su superficie (morfología, rigidez, contenido de agua en equilibrio, tensión superficial, hidrofilicidad, presencia de cargas eléctricas). El objetivo general de esta tesis fue estudiar la influencia de diferentes tipos de biomateriales en la respuesta de los condrocitos en cultivo in vitro. Los scaffolds deben tener una estructura porosa interconectada para permitir el desarrollo celular a través de toda la estructura 3D, potenciando que los condrocitos mantengan su fenotipo, así como permitiendo entrada de nutrientes y eliminación de desechos metabólicos. Se estudió el efecto de la hidrofilicidad y de la arquitectura de poro. Se cuantificó la viabilidad celular, la proliferación y la expresión de agrecano. Cuando los condrocitos humanos se cultivaron en sustratos poliméricos donde los grupos hidrófilos se distribuyeron de manera homogénea, la adhesión, la proliferación y la viabilidad disminuyó con el contenido de grupos hidrófilo. Sin embargo, los copolímeros en los que los dominios hidrófilos e hidrófobos se alternaban mostraron mejores resultados que los homopolímeros correspondientes. Se sintetizaron series de scaffolds bioestables y series biodegradables con diferente hidrofilicidad y porosidad utilizando plantillas de microesferas sinterizadas. Se obtuvieron arquitecturas de poros regulares y reproducibles. Las células colonizaron el scaffold en su totalidad cuando los poros y la interconexión entre ellos era lo suficientemente grande. Se evaluó la rediferenciación condrogénica de condrocitos autólogos humanos, previamente expandidos en monocapa, sembrados en un scaffold biodegradable de policaprolactona (PCL). Se demostró que los condrocitos cultivados en scaffolds de PCL con medio sin suero bovino fetal (FBS), se rediferenciaban de manera eficiente; expresando un fenotipo condrocítico, caracterizado por su capacidad de sintetizar proteínas de la MEC específicas de cartílago hialino. Se estudió la influencia de la hidrofilicidad y la conectividad de los poros de los scaffolds de caprolactona sobre la adhesión de los condrocitos a las paredes de los poros, su capacidad proliferativa y la composición de MEC sintetizada. Se observó que un mínimo de 70% de porosidad era necesario para permitir la siembra de los condrocitos en el scaffold y su posterior viabilidad. El número de células aumentaba a medida que aumentaba la porosidad del scaffold. Los resultados sugieren que parte de las células que se adherían a las paredes internas de los poros mantenían el fenotipo desdiferenciado de condrocitos cultivados en monocapa, mientras que otros se rediferenciaban. En conclusión, los resultados de esta tesis aportan un avance en el campo de la regeneración de cartílago articular utilizando técnicas de IT. Los estudios realizados proporcionan directrices sobre la composición, la porosidad y la hidrofilicidad más adecuada para l
[CAT] El cartílag articular és un teixit format per condròcits envoltats per una densa matriu extracel·lular (MEC). La MEC es compon principalment de col·lagen tipus II i de proteoglicans. La funció principal del cartílag articular és proporcionar una superfície lubricada a les articulacions. Les lesions en el cartílag articular són comuns i poden derivar en osteoartritis. El cartílag articular no té vasos sanguinis, nervis ni vasos limfàtics i, per tant, té una capacitat limitada d'auto-reparació. L'enginyeria tissular (IT) és una àrea prometedora en la regeneració del cartílag. A la IT s'utilitzen "bastiments" (scaffolds) tridimensionals (3D) com a suports per al cultiu cel·lular i tissular. Els scaffolds proporcionen una estructura que facilita l'adhesió i l'expansió dels condròcits, mantenint un fenotip condrocític limitant la seua desdiferenciació; que és el major problema en els sistemes bidimensionals (2D). L'adhesió cel·lular als scaffolds depèn de les característiques físiques i químiques de la superfície (morfologia, rigidesa, contingut d'aigua en equilibri, tensió superficial, hidrofilicitat i presència de càrregues elèctriques). L'objectiu general d'aquesta tesi va ser estudiar la influència de diferents tipus de biomaterials en la resposta dels condròcits en cultiu in vitro. Els scaffolds han de tindre una estructura porosa interconnectada per a permetre el desenvolupament cel·lular a través de tota l'estructura 3D, potenciant que els condròcits mantinguen el seu fenotip així com permetent l'entrada de nutrients i l'eliminació de productes metabòlics. S'ha estudiat l'efecte de la hidrofilicitat i de l'arquitectura de porus dels scaffolds. Es va quantificar la viabilitat cel·lular, la proliferació i l'expressió de agrecà. Quan els condròcits humans es van cultivar en substrats polimèrics en els quals els grups hidròfils es van distribuir de manera homogènia, l'adhesió, la proliferació i la viabilitat van disminuir amb el contingut de grups hidròfils. No obstant això, els copolímers en els quals els dominis hidròfils i hidròfobs s'alternaven van mostrar millors resultats que els homopolímers corresponents. Es van sintetitzar sèries de scaffolds bioestables i sèries biodegradables amb diferent hidrofilicitat i porositat utilitzant plantilles de microesferes sinteritzades. Es van obtindre arquitectures de porus regulars i reproduïbles. Les cèl·lules van colonitzar el scaffold en la seua totalitat quan els porus i la interconnexió entre ells era suficientment gran. Es van avaluar la rediferenciació condrogènica de condròcits autòlegs humans, prèviament expandits en monocapa, en un scaffold biodegradable de policaprolactona (PCL). Es va demostrar que els condròcits cultivats en scaffolds de PCL sense sèrum boví fetal (FBS) es rediferenciaven de manera eficient, expressant un fenotip condrocític caracteritzat per la seua capacitat de sintetitzar proteïnes de la MEC específiques de cartílag hialí. També es va estudiar la influència de la hidrofilicitat i la connectivitat dels porus dels scaffolds de caprolactona sobre l'adhesió dels condròcits a les parets dels porus, la seua capacitat proliferativa i la composició de MEC sintetitzada. Es va observar que un mínim del 70% de porositat sembla ser necessari per permetre la sembra dels condròcits i la seua posterior viabilitat en el scaffold. El nombre de cèl·lules augmentava a mesura que augmentava la porositat del scaffold. Els resultats suggereixen que part de les cèl·lules que s'adherien a les parets internes dels porus mantenien el fenotip desdiferenciat de condròcits cultivats en monocapa, mentre que altres es rediferenciaven. En conclusió, els resultats d'aquesta tesi proporcionen informació valuosa en el camp de la regeneració de cartílag utilitzant tècniques d'IT. Els estudis realitzats proporcionen directrius sobre la composició, la porositat i la hidrofilicitat m
Pérez Olmedilla, M. (2015). Tissue engineering techniques to regenerate articular cartilage using polymeric scaffolds [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/58987
TESIS

Current surgical approaches to treating damage to articular cartilage, a highly specialised connective tissue, are limited in their ability to regenerate functional hyaline tissue. This has provided a driving force for the development of patient-specific, tissue engineered treatments. To date the majority of in vitro studies have focussed on engineering relatively small-dimension constructs; however justification remains for the production of large pieces of cartilage tissue. The aim of this research was therefore to investigate the potential for tissue engineering large, high quality cartilage constructs using several different culture methodologies Both small 'pin' (6 mm diameter) and large 'plate' (15 x 10 mm) constructs were successfully produced using primary bovine articular chondrocytes, a poly(glycolic acid) scaffold material and various culture conditions; static, semi-static and a rotating wall vessel (RWV) cell culture system. Small pin constructs cultured under standard static and semi-static conditions demonstrated a biochemical composition similar to that previously reported in published studies. Plate constructs cultured under static and semi-static conditions demonstrated an increased sulphated GAG and collagen type II content over their small pin counterparts, with an architecture possessing numerous lacunae and some zonal organisation. The Synthecon™ rotating wall vessel (RWV) bioreactor did not provide a suitable environment to engineer large plate constructs in standard cell culture medium. Due to their weight the constructs 'tumbled', resulting in damaged tissue with a poor quality extra cellular matrix rich in fibrous collagen type I. The design of a lightweight PTFE scaffold retention frame and the development of a dextran-modified, increased viscosity culture medium permitted the support of large constructs even at low vessel rotational RPM. The use of high viscosity culture medium in all culture environments however was found to have a detrimental impact on tissue quality, reduced mass transfer resulting in far lower matrix accumulation. It was concluded that large cartilage constructs may be produced under standard semi-static conditions that demonstrate hyaline-like features but biological quality was sacrificed. It was also concluded that an increased viscosity culture medium can demonstrate rheological properties comparable to those of synovial fluid, however in conjunction with the low-shear RWV bioreactor does not provide an ideal environment for engineering large cartilage constructs. The hydrodynamic properties of the increased viscosity culture medium could prove beneficial for the tissue engineering of articular cartilage constructs under a different bioreactor configuration.

Polymer scaffold use has become commonplace in tissue engineering strategies. Scaffolds provide sturdy interfaces that securely anchor tissue engineered constructs to their designated locations. Researchers have used scaffolds to provide support to developing tissues as well as a growth template to aid the development of the desired phenotypic structure. In addition to using scaffolds for their mechanical support, scaffolds can be used as a diagnostic tool by attaching sensors. Strain gauge sensors have been attached to scaffolds to monitor compression and elongation. These polybutylterphalate (PBT) scaffolds were used in a cartilage tissue-engineering project for femoral cartilage repair. The aim of this project was to measure native cartilage pressure in normal canine stifle joints using strain gauge scaffolds. By using pressure sensitive films to confirm joint surface pressures determined with strain gauge measurements, "sensate" scaffolds were created to be able to provide in vivo joint loading measurements. An understanding of the in vivo pressures in the menisco-femoral joint space will facilitate the development of tissue engineered cartilage by determining chondrocyte mechanical triggers as well as helping define reasonable expectations for engineered articular cartilage tissue that is required for successful cartilage repair.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (p. 149-164).
Defects in articular cartilage exhibit little spontaneous healing response, in part due to the limited number of chondrocytes available to infiltrate the defect and the absence of a provisional fibrin scaffold to accommodate cell migration into the lesion. One variable related to tissue engineering strategies employing cell-seeded scaffolds to treat such defects is the amount of cartilage formed in the construct prior to implantation. The objectives of this thesis were to evaluate effects of scaffold cross-link density and bioreactor culture environment on chondrogenesis in cell-seeded type II collagen scaffolds in vitro, and to begin to test effects of implant compositional maturity (viz. glycosaminoglycan, GAG, content) on chondral defect repair. Scaffold cross-link density, a determinant of cell-mediated scaffold contraction and degradation, affected chondrogenesis; scaffolds of low cross-link density that experienced contraction exhibited greater cartilaginous tissue formation compared to highly cross-linked scaffolds that resisted contraction. In addition to tissue-level effects on histogenesis, cross-link density was found to direct phenotypic differentiation at the cellular level. When employing marrow-derived stem cells as an alternative to chondrocytes, scaffolds with lower cross-link densities (and thus less resistance to contraction and degradation) favored chondrocytic differentiation.
(cont.) In comparison to these findings, bioreactor culture of chondrocyte-seeded scaffolds demonstrated little benefit over static culture with respect to histogenesis within the first 2 weeks of culture. To begin to investigate effects of implant maturity on in vivo repair outcome, chondrocyte-seeded type II collagen scaffolds achieving 30% of the GAG content in native cartilage were implanted in chondral defects in a caprine model. Repair tissue evaluated at 15 weeks consisted primarily of fibrocartilage and small amounts of hyaline tissue. Implantation of the construct reduced fibrous tissue formation compared to controls, but did not significantly affect other outcome variables. Future animal investigations will evaluate effects of implanting constructs with GAG contents 50% and 75% of that in normal cartilage. An additional study evaluated a construct comprised of a non-cell-seeded type II collagen scaffold and a bone graft substitute for treating osteochondral defects in a goat model. These implants qualitatively improved bone formation, but did not significantly improve repair of cartilage compared to controls.
by Scott M. Vickers.
Ph.D.

Tissue engineered repair of articular cartilage has now become a clinical reality with techniques for cell culture having advanced from laboratory experimentation to clinical application. Despite the advances in the use of this technology in clinical applications, the basic cell culture techniques for autologous chondrocytes are still based on primitive in-vitro monolayer culture methods. Articular chondrocytes are known to undergo fibroblastic change in monolayer culture as this is not their normal state in-vivo. They are more likely to maintain their phenotype when cultured in three dimensional environments. In this state they become spherical in shape and synthesise normal cartilage matrix products. Various substances are being presently investigated with the aim of designing a suitable material that is biocompatible, biodegradable and suitable for implantation. The major problem of culturing cells in three dimensional scaffolds is the limitation posed by the biomaterial on nutrient diffusion to cells deep within the scaffold. In order for this technology to succeed in clinical practice there is a important need to develop solutions to overcome these diffusional restraints. The use of dynamic culture devices which can, not only stimulate chondrocytes, but also maintain their original characteristics are investigated in this project. This thesis tests the hypothesis that culture within a dynamic culture device ie a rotating wall vessel bioreactor or roller bottles, enhances proliferation and cartilage-specific matrix synthesis by chondrocytes seeded in a three dimensional construct. The long term survival of chondrocytes in hydrogel matrices is also examined and cell cultures in dynamic devices are compared with traditional static culture systems. Biochemical, histological and immunostain data is presented an the possibility of using human cells is also explored.

Articular cartilage is a resilient and load bearing material that provides diarthrodial joints with excellent friction, lubrication and wear characteristics required for continuous motion. However, articular cartilage has a poor regenerative capacity and its degeneration is a common cause of morbidity in terms of loss of joint function and osteoarthritis, frequently resulting in the need for total knee replacement. Articular cartilage has a distinct zonal architecture with biochemical and cellular variations existing from the surface zone to the deeper calcified layers. Thus, the development of the tissue must be stringently controlled, both spatially and temporally in order for the complex structure to be established. Importantly, the surface zone is believed to be responsible for the appositional growth of articular cartilage during development and this growth is believed to be driven by a population of slow cycling progenitor cells within the surface zone itself. The focus of this thesis is the isolation and characterisation of articular cartilage progenitor cells together with an exploration of the cells capabilities in potential cartilage repair therapies. The cells were identified on the basis of differential adhesion assays and colony forming ability. Subsequent experiments were carried out to show the differential expression of various cell surface markers eg Notch 1 receptors and the role of the onco-foetal form of fibronectin, known as fibronectin-EDA on the modulation of cell behaviour. In terms of the potential of the cells for use in tissue engineering, a promising feature of the cells is the discovery that enriched populations of the cells can undergo extensive expansion in simple monolayer cultures and yet retain their ability to undergo chondrogenic differentiation. This property may enable the use of the cells in commercial cartilage repair and/or tissue engineering strategies.

Articular cartilage is an anisotropic tissue composed of compositional and functional layers. One clinical approach to the regeneration of articular cartilage defects incorporates a porous polymer scaffold to support and direct cartilage formation in full‐thickness defects. These scaffolds are regularly isotropic in structure, unlike the tissue they aim to regenerate. A number of scaffold production techniques were combined to produce porous anisotropic scaffolds with zonally‐biomimetic microarchitecture and mechanical properties. The final scaffold design featured a combination of an electrospun fibrous superficial zone, isotropic foam intermediate zone and directionally frozen deep zone. The zonal scaffold microenvironments influenced cellular distribution, gene expression, and extracellular matrix deposition in vitro without requiring chemical modification or culture under dynamic loading. The scaffold development work culminated in a porcine in vivo study, currently on‐going. Initial data from the 3‐month preliminary surgical trial suggests full cellular infiltration of acellular scaffolds, no immunological response, and improved articular surface morphologies relative to empty defect controls. Variations on the polymer poly(ϵ‐caprolactone) (PCL) were investigated for use in osteochondral tissue engineering applications. The incorporation of alternate monomers was found to modify the biological and mechanical properties of the resulting materials and scaffolds. The work contained within this thesis has expanded the field of anisotropic scaffold design, with implications for articular cartilage engineering. The combination of electrospun fibres and anisotropic foams for scaffold engineering was the first in the field when published. The design of the third‐generation scaffold is new to the field, as is the order‐of‐magnitude increase in stiffness in a porous polymer scaffold while maintaining interconnectivity and polymer composition. The observation of differentially aligned ECM within a single multi‐layer scaffold without zonally distinct materials or surface functionalisation is also believed to be the first in the field.

The concept of cartilage functional tissue engineering (FTE) has promoted the use of physiologic loading bioreactor systems to cultivate engineered tissues with load-bearing properties [1]. Prior studies have demonstrated that culturing agarose constructs seeded with primary bovine chondrocytes from immature joints, and subjected to dynamic deformation, produced equilibrium compressive properties and proteoglycan content matching the native tissue [2]. In the process of translating these results to an adult canine animal model, it was found that protocols previously successful with immature bovine primary chondrocytes did not produce the same successful outcome when using adult canine primary chondrocytes [3]. The objective of this study was to assess the efficacy of a modified FTE protocol using adult (canine) chondrocyte-seeded hydrogel constructs and applied dynamic loading.

Damage to articular cartilage is a common condition affecting the joints of millions of people. This is a major problem considering the poor regenerative capacity of adult articular cartilage and the disability and pain that accompanies these injuries [13]. There exists a range of options that have been applied in clinical practice, with variable degrees of success, for repair of focal lesions and damage of the articular surface, including tissue adhesives [1,6,11,12,18], enzymatic treatments [8] and laser solder welding [21], autograft cell/tissue transfer via osteoperiosteal grafts [17], osteochondral grafts (mosaicplasty) [10] and Carticel [4,5]. The poor healing capacity of articular cartilage [13], potential for donor site pain and morbidity in autograft procedures, risk of disease transmission in allograft procedures, and the limited longevity of arthroplasty systems (i.e., ∼15 years for a total knee arthroplasty), has generated considerable research efforts to develop cell-based therapies for articular cartilage repair and replacement.

Articular cartilage has a poor capacity for repair. Of the many procedures available to the orthopaedic surgeon, osteochondral grafting is the only technique which reliably produces hyaline cartilage within a defect.1 Bone marrow derived mesenchymal stem cells (MSCs) are an interesting alternative to harvesting cartilage grafts for chondrocytes as they also have the ability to produce cartilaginous tissues in vitro. This suggests that if tissue engineering strategies could be used to develop cartilaginous grafts with mechanical properties approaching that of normal articular cartilage, then hyaline tissue could be regenerated. Of concern with such approaches are reports that the mechanical properties of cartilaginous tissues engineered using MSCs are inferior to that engineered using chondrocytes derived from articular cartilage, although recent studies have demonstrated that adult equine MSCs produce a cartilaginous tissue mechanically superior to that derived using animal-matched adult chondrocytes.2

Under physiological conditions of loading, articular cartilage is subjected to both compressive strains, normal to the articular surface, and tensile strains, tangential to the articular surface. Previous studies have shown that articular cartilage exhibits a much higher modulus in tension than compression. Theoretical analyses have suggested that this tension-compression nonlinearity enhances the magnitude of interstitial fluid pressurization during loading in unconfined compression, above a theoretical threshold of 33% of the average applied stress. The first hypothesis of this experimental study is that the peak fluid load support in unconfined compression is significantly greater than the 33% theoretical limit predicted for porous permeable tissues modeled with equal moduli in tension and compression [1]. The second hypothesis is that the peak fluid load support is higher at the articular surface side of the tissue samples than near the deep zone, because the disparity between the tensile and compressive moduli is greater at the surface zone.

Articular cartilage and surrounding soft tissues in the knee are important to normal joint function. However, disease, trauma, and progressive degeneration can alter the function of the joint, often changing the distributions of tissue deformation through the tissues of the knee [1], and lead to advanced osteoarthritis [2]. Knowledge of the mechanical properties of the soft tissues in the knee is important to characterize both normal and damaged joints. Additionally, the ability to restore the strain distribution of damaged regions to accepted normal values could be used as a measure of success of a tissue engineering solution. Noninvasive imaging technologies, such as magnetic resonance imaging (MRI), can be used to study normal tissue, detect tissue damage, and monitor both degeneration and the progress of repair treatments.

Adult articular cartilage has a poor healing capacity, which has lead to intense research toward development of cell-based therapies for cartilage repair. The destruction of articular cartilage results in osteoarthritis (OA), which affects about 27 million Americans. In order to create functional tissue, it is essential to mimic the native environment by optimizing expansion protocols. Cell passaging and priming with chemical or physical factors are often necessary steps in cell-based strategies for regenerative medicine [1]. The ability to identify biomarkers that can act as predictors of cells with a high capacity to form functional engineered cartilage will permit optimization of protocols for cartilage tissue engineering using different cell sources. Recent investigations have shown that chondrocytes and synovium-derived stem cells (SDSCs) are promising cell sources for cartilage repair [2,3]. The analysis of gene expression and comparative proteomics, which defines the differences in expression of proteins among different biological states, provides a potentially powerful tool in this effort [4]. The aim of this study was to investigate the impact of growth factor priming in 2D canine chondrocytes and SDSCs cultures by identifying differentially regulated biomarkers, which can correlate to functional tissue elaboration in 3D.

The demand for tissue engineered articular cartilage for implantation in patients with osteoarthritis requires the development of stable and robust large scale production systems. This can be accomplished through the use of a bioreactor that applies mechanical loading and regulates nutrient transport to promote cell growth, cell differentiation and tissue production. In the present work we have developed a shear stress and perfusion bioreactor (SSPB) capable of providing multiple stimuli to facilitate large-scale production of tissue engineered cartilage.

The design of tissue-engineered constructs grown in vitro is a promising treatment strategy for degenerated cartilaginous tissues. Cartilaginous tissues such as articular cartilage and the annulus fibrosus are collagen fiber-reinforced composites that exhibit orthotropic behavior and highly asymmetric tensile-compressive responses. They also experience finite deformations in vivo. Successful integration with surrounding tissue upon implantation likely will require cartilage constructs to have similar structural and functional properties as native tissue. Reliable stress constitutive equations that accurately characterize the tissue’s mechanical properties must be developed to achieve this aim. Recent studies have successfully implemented bimodular theories for infinitesimal strains (Soltz et al., 2000; Wang et al., 2003); those models were based on the theory of Curnier et al. (1995).

This paper highlights the development of a multi-arm bioprinter (MABP) capable of concurrent deposition of multiple materials with independent dispensing parameters including deposition speed, material dispensing rate and frequency for functional zonal-stratified articular cartilage tissue fabrication. The MABP consists of two Cartesian robots mounted in parallel on the same mechanical frame. This platform is used for concurrent filament fabrication and cell spheroid deposition. A single-layer structure is fabricated and concurrently deposited with spheroids to validate this system. Preliminary results showed that the MABP was able to produce filaments and spheroids with well-defined geometry and high cell viability. The resulting filament width has a variation of +/-170 μm and the center-to-center filament distance was within 100 μm of the specified distance. This fabrication system is aimed to be further refined for printing structures with varying porosities to mimic the natural cartilage structure in order to produce functional tissue-engineered articular cartilage using cell spheroids containing cartilage progenitor cells (CPCs).

Articular cartilage has superior functions such as impact absorption and low friction, although their healing capacities are limited. It is one of potential options for the repair of articular cartilage to use cell-based therapies. We have been developing a novel tissue-engineering technique for the repair of cartilage which involves a stem cell-based self-assembled tissue (scSAT) derived from synovium. As the scSAT is a scaffold-free contrust composed of cells with their native extracellular matrix, it is free from concern regarding long-term immunological effects. The scSAT is expressed as tissue engineered construct (TEC) when it is used for cartilage repair. Previous studies indicated that the mechanical properties of cartilage-like tissues repaired using the scSAT were slightly inferiorer to those of normal cartilage. We have a hypothesis that the mechanical properties of the cartilage-like tissues are improved if the scSAT is subjected to an adequate compressive stimulation in vitro before implantation. The present study was conducted as a preliminary study to determine whether static compression improves the mechanical property of the scSAT for more advanced regenerative medicine to cartilage injuries and degeneration.