Engineering human cell-based, functionally integrated osteochondral grafts by biological bonding of engineered cartilage tissues to bony scaffolds

Advances in Polysaccharides for Cartilage Tissue Engineering Repair: A Review

Cartilage repair has been a significant challenge in orthopedics that has not yet been fully resolved. Due to the absence of blood vessels and the almost cell-free nature of mature cartilage tissue, the limited ability to repair cartilage has resulted in significant socioeconomic pressures. Polysaccharide materials have recently been widely used for cartilage tissue repair due to their excellent cell loading, biocompatibility, and chemical modifiability. They also provide a suitable microenvironment for cartilage repair and regeneration. In this Review, we summarize the techniques used clinically for cartilage repair, focusing on polysaccharides, polysaccharides for cartilage repair, and the differences between these and other materials. In addition, we summarize the techniques of tissue engineering strategies for cartilage repair and provide an outlook on developing next-generation cartilage repair and regeneration materials from polysaccharides. This Review will provide theoretical guidance for developing polysaccharide-based cartilage repair and regeneration materials with clinical applications for cartilage tissue repair and regeneration.

Articular cartilage repair biomaterials: strategies and applications

Articular cartilage injury is a frequent worldwide disease, while effective treatment is urgently needed. Due to lack of blood vessels and nerves, the ability of cartilage to self-repair is limited. Despite the availability of various clinical treatments, unfavorable prognoses and complications remain prevalent. However, the advent of tissue engineering and regenerative medicine has generated considerable interests in using biomaterials for articular cartilage repair. Nevertheless, there remains a notable scarcity of comprehensive reviews that provide an in-depth exploration of the various strategies and applications. Herein, we present an overview of the primary biomaterials and bioactive substances from the tissue engineering perspective to repair articular cartilage. The strategies include regeneration, substitution, and immunization. We comprehensively delineate the influence of mechanically supportive scaffolds on cellular behavior, shedding light on emerging scaffold technologies, including stimuli-responsive smart scaffolds, 3D-printed scaffolds, and cartilage bionic scaffolds. Biologically active substances, including bioactive factors, stem cells, extracellular vesicles (EVs), and cartilage organoids, are elucidated for their roles in regulating the activity of chondrocytes. Furthermore, the composite bioactive scaffolds produced industrially to put into clinical use, are also explicitly presented. This review offers innovative solutions for treating articular cartilage ailments and emphasizes the potential of biomaterials for articular cartilage repair in clinical translation.

Translation of nanotechnology-based implants for orthopedic applications: current barriers and future perspective

The objective of bioimplant engineering is to develop biologically compatible materials for restoring, preserving, or altering damaged tissues and/or organ functions. The variety of substances used for orthopedic implant applications has been substantially influenced by modern material technology. Therefore, nanomaterials can mimic the surface properties of normal tissues, including surface chemistry, topography, energy, and wettability. Moreover, the new characteristics of nanomaterials promote their application in sustaining the progression of many tissues. The current review establishes a basis for nanotechnology-driven biomaterials by demonstrating the fundamental design problems that influence the success or failure of an orthopedic graft, cell adhesion, proliferation, antimicrobial/antibacterial activity, and differentiation. In this context, extensive research has been conducted on the nano-functionalization of biomaterial surfaces to enhance cell adhesion, differentiation, propagation, and implant population with potent antimicrobial activity. The possible nanomaterials applications (in terms of a functional nanocoating or a nanostructured surface) may resolve a variety of issues (such as bacterial adhesion and corrosion) associated with conventional metallic or non-metallic grafts, primarily for optimizing implant procedures. Future developments in orthopedic biomaterials, such as smart biomaterials, porous structures, and 3D implants, show promise for achieving the necessary characteristics and shape of a stimuli-responsive implant. Ultimately, the major barriers to the commercialization of nanotechnology-derived biomaterials are addressed to help overcome the limitations of current orthopedic biomaterials in terms of critical fundamental factors including cost of therapy, quality, pain relief, and implant life. Despite the recent success of nanotechnology, there are significant hurdles that must be overcome before nanomedicine may be applied to orthopedics. The objective of this review was to provide a thorough examination of recent advancements, their commercialization prospects, as well as the challenges and potential perspectives associated with them. This review aims to assist healthcare providers and researchers in extracting relevant data to develop translational research within the field. In addition, it will assist the readers in comprehending the scope and gaps of nanomedicine's applicability in the orthopedics field.

Recent development in multizonal scaffolds for osteochondral regeneration

Osteochondral (OC) repair is an extremely challenging topic due to the complex biphasic structure and poor intrinsic regenerative capability of natural osteochondral tissue. In contrast to the current surgical approaches which yield only short-term relief of symptoms, tissue engineering strategy has been shown more promising outcomes in treating OC defects since its emergence in the 1990s. In particular, the use of multizonal scaffolds (MZSs) that mimic the gradient transitions, from cartilage surface to the subchondral bone with either continuous or discontinuous compositions, structures, and properties of natural OC tissue, has been gaining momentum in recent years. Scrutinizing the latest developments in the field, this review offers a comprehensive summary of recent advances, current hurdles, and future perspectives of OC repair, particularly the use of MZSs including bilayered, trilayered, multilayered, and gradient scaffolds, by bringing together onerous demands of architecture designs, material selections, manufacturing techniques as well as the choices of growth factors and cells, each of which possesses its unique challenges and opportunities.

Osteochondral regenerative engineering: challenges, state-of-the-art and translational perspectives

Despite quantum leaps, the biomimetic regeneration of cartilage and osteochondral regeneration remains a major challenge, owing to the complex and hierarchical nature of compositional, structural and functional properties. In this review, an account of the prevailing challenges in biomimicking the gradients in porous microstructure, cells and extracellular matrix (ECM) orientation is presented. Further, the spatial arrangement of the cues in inducing vascularization in the subchondral bone region while maintaining the avascular nature of the adjacent cartilage layer is highlighted. With rapid advancement in biomaterials science, biofabrication tools and strategies, the state-of-the-art in osteochondral regeneration since the last decade has expansively elaborated. This includes conventional and additive manufacturing of synthetic/natural/ECM-based biomaterials, tissue-specific/mesenchymal/progenitor cells, growth factors and/or signaling biomolecules. Beyond the laboratory-based research and development, the underlying challenges in translational research are also provided in a dedicated section. A new generation of biomaterial-based acellular scaffold systems with uncompromised biocompatibility and osteochondral regenerative capability is necessary to bridge the clinical demand and commercial supply. Encompassing the basic elements of osteochondral research, this review is believed to serve as a standalone guide for early career researchers, in expanding the research horizon to improve the quality of life of osteoarthritic patients affordably.

Biomechanical Aspects of Osteochondral Regeneration: Implications and Strategies for Three-Dimensional Bioprinting

Osteoarthritis is among the most prevalent of musculoskeletal disorders in the world that causes joint pain, deformity, and limited range of movement. The resulting osteochondral defect can significantly decrease the patient's quality of life, but current treatment options have not demonstrated the capacity to fully regenerate the entire osteochondral microenvironment. Structurally, the osteochondral unit is a composite system composed of three layers-articular cartilage, calcified cartilage, and subchondral bone. Collectively these distinct layers contribute to the distinct biomechanical properties that maintain the health and aid in load transfer during joint articulation. The purpose of this review was to examine the role of the osteochondral interface in tissue engineering. Topics of discussion include the biomechanics of the osteochondral unit and an overview of various strategies for osteochondral interface tissue engineering, with a specific focus on three-dimensional bioprinting. The goal of this review was to elucidate the importance of the osteochondral interface and overview some strategies of developing an interface layer within tissue engineered scaffolds. Impact Statement This review provides an overview of interface tissue engineering for osteochondral regeneration. It offers a detailed investigation into the biomechanics of the osteochondral unit as it relates to tissue engineering, and highlights the strategies that have been utilized to develop the osteochondral interface within tissue engineering scaffolds.

Computational investigation of interface printing patterns within 3D printed multilayered scaffolds for osteochondral tissue engineering

Osteoarthritis is a highly prevalent rheumatic musculoskeletal disorder that commonly affects many joints. Repetitive joint overloading perpetuates the damage to the affected cartilage, which undermines the structural integrity of the osteochondral unit. Various tissue engineering strategies have been employed to design multiphasic osteochondral scaffolds that recapitulate layer-specific biomechanical properties, but the inability to fully satisfy mechanical demands within the joint has limited their success. Through computational modeling and extrusion-based bioprinting, we attempted to fabricate a biphasic osteochondral scaffold with improved shear properties and a mechanically strong interface. A 3D stationary solid mechanics model was developed to simulate the effect of lateral shear force on various thermoplastic polymer/hydrogel scaffolds with a patterned interface. Additionally, interfacial shear tests were performed on bioprinted polycaprolactone (PCL)/hydrogel interface scaffolds. The first simulation showed that the PCL/gelatin methacrylate (GelMA) and PCL/polyethylene glycol diacrylate (PEGDA) scaffolds interlocking hydrogel and PCL at interface in a 1:1 ratio possessed the largest average tensile (PCL/GelMA: 80.52 kPa; PCL/PEGDA: 79.75 kPa) and compressive stress (PCL/GelMA: 74.71 kPa; PCL/PEGDA: 73.83 kPa). Although there were significant differences in shear strength between PCL/GelMA and PCL/PEGDA scaffolds, no significant difference was observed among the treatment groups within both scaffold types. Lastly, the hypothetical simulations of potential biphasic 3D printed scaffolds showed that for every order of magnitude decrease in Young's modulus (E) of the soft bioink, all the scaffolds underwent an exponential increase in average displacement at the cartilage and interface layers. The following work provides valuable insights into the biomechanics of 3D printed osteochondral scaffolds, which will help inform future scaffold designs for enhanced regenerative outcomes.

New Insights into Cartilage Tissue Engineering: Improvement of Tissue-Scaffold Integration to Enhance Cartilage Regeneration

Distinctive characteristics of articular cartilage such as avascularity and low chondrocyte conversion rate present numerous challenges for orthopedists. Tissue engineering is a novel approach that ameliorates the regeneration process by exploiting the potential of cells, biodegradable materials, and growth factors. However, problems exist with the use of tissue-engineered construct, the most important of which is scaffold-cartilage integration. Recently, many attempts have been made to address this challenge via manipulation of cellular, material, and biomolecular composition of engineered tissue. Hence, in this review, we highlight strategies that facilitate cartilage-scaffold integration. Recent advances in where efficient integration between a scaffold and native cartilage could be achieved are emphasized, in addition to the positive aspects and remaining problems that will drive future research.

A Graded, Porous Composite of Natural Biopolymers and Octacalcium Phosphate Guides Osteochondral Differentiation of Stem Cells

Lesions involving the osteochondral unit are difficult to treat. Biomimetic scaffolds are previously shown as promising alternative. Such devices often lack multiple functional layers that mimic bone, cartilage, and the interface. In this study, multilayered scaffolds are developed based on the use of natural extracellular matrix (ECM)-like biopolymers. Particular attention is paid to obtain a complex matrix that mimics the native osteochondral transition. Porous, sponge-like chitosan-collagen-octacalcium phosphate (OCP) scaffolds are obtained. Collagen content increases while the amount of OCP particles decreases toward the cartilage layer. The scaffolds are bioactive as a mineral layer is deposited containing hydroxyapatite at the bony side. The scaffolds stimulate proliferation of human adipose-derived mesenchymal stem cells, but the degree of proliferation depends on the cell seeding density. The scaffolds give rise to a zone-specific gene expression. RUNX2, COL1A1, BGLAP, and SPP1 are upregulated in the bony layer of the scaffold. SOX9 is upregulated concomitant with COL2A1 expression in the cartilage zone. Mineralization in presence of the cells is prominent in the bone area with Ca and P steadily increasing over time. These results are encouraging for the fabrication of biomimetic scaffolds using ECM-like materials and featuring gradients that mimic native tissues and their interface.

Tissue Engineering: An Alternative to Repair Cartilage

Herein we review the state-of-the-art in tissue engineering for repair of articular cartilage. First, we describe the molecular, cellular, and histologic structure and function of endogenous cartilage, focusing on chondrocytes, collagens, extracellular matrix, and proteoglycans. We then explore in vitro cell culture on scaffolds, discussing the difficulties involved in maintaining or obtaining a chondrocytic phenotype. Next, we discuss the diverse compounds and designs used for these scaffolds, including natural and synthetic biomaterials and porous, fibrous, and multilayer architectures. We then report on the mechanical properties of different cell-loaded scaffolds, and the success of these scaffolds following in vivo implantation in small animals, in terms of generating tissue that structurally and functionally resembles native tissue. Last, we highlight future trends in this field. We conclude that despite major technical advances made over the past 15 years, and continually improving results in cartilage repair experiments in animals, the development of clinically useful implants for regeneration of articular cartilage remains a challenge

Combining multi-scale 3D printing technologies to engineer reinforced hydrogel-ceramic interfaces

Multi-material 3D printing technologies that resolve features at different lengths down to the microscale open new avenues for regenerative medicine, particularly in the engineering of tissue interfaces. Herein, extrusion printing of a bone-biomimetic ceramic ink and melt electrowriting (MEW) of spatially organized polymeric microfibres are integrated for the biofabrication of an osteochondral plug, with a mechanically reinforced bone-to-cartilage interface. A printable physiological temperature-setting bioceramic, based on α-tricalcium phosphate, nanohydroxyapatite and a custom-synthesized biodegradable and crosslinkable poloxamer, was developed as bone support. The mild setting reaction of the bone ink enabled us to print directly within melt electrowritten polycaprolactone meshes, preserving their micro-architecture. Ceramic-integrated MEW meshes protruded into the cartilage region of the composite plug, and were embedded with mechanically soft gelatin-based hydrogels, laden with articular cartilage chondroprogenitor cells. Such interlocking design enhanced the hydrogel-to-ceramic adhesion strength >6.5-fold, compared with non-interlocking fibre architectures, enabling structural stability during handling and surgical implantation in osteochondral defects ex vivo. Furthermore, the MEW meshes endowed the chondral compartment with compressive properties approaching those of native cartilage (20-fold reinforcement versus pristine hydrogel). The osteal and chondral compartment supported osteogenesis and cartilage matrix deposition in vitro, and the neo-synthesized cartilage matrix further contributed to the mechanical reinforcement at the ceramic-hydrogel interface. This multi-material, multi-scale 3D printing approach provides a promising strategy for engineering advanced composite constructs for the regeneration of musculoskeletal and connective tissue interfaces.

Engineering a multiphasic, integrated graft with a biologically developed cartilage-bone interface for osteochondral defect repair

Tissue engineering is a promising approach to repair osteochondral defects, yet successful reconstruction of different layers in an integrated graft, especially the interface remains challenging. The multiphasic, functionally integrated tissue engineering graft described herein mimics the entire osteochondral tissue in terms of structure and composition at the cartilage, bone and cartilage-bone interface layer to repair osteochondral defects. In this manuscript, we report the fabrication of a multiphasic graft via bonding of a cartilaginous hydrogel and a sintered poly(lactic-co-glycolic acid) microsphere scaffold by an endogenous fibrotic cartilaginous extracellular matrix. We demonstrated that culturing chondrocytes within the alginate hydrogel conjugated to the poly(lactic-co-glycolic acid) scaffold allows for (i) gradient transition and integration from the cartilage layer to the subchondral bone layer as assessed by scanning electron microscopy, histology and biochemistry, and (ii) superior tissue repair efficacy in a rabbit knee defect model. Industrialization of the graft remains an unsolved challenge as after decellularization the tissue repair efficacy of the graft decreased. Taken together, the multiphasic osteochondral graft repaired the osteochondral defects successfully and has the potential to be applied clinically as an implant in orthopaedic surgery.

Additively Manufactured Multiphasic Bone-Ligament-Bone Scaffold for Scapholunate Interosseous Ligament Reconstruction

The scapholunate interosseous ligament (SLIL) is a frequently torn wrist ligament, and current surgical options for SLIL tears are suboptimal. This research aims to develop a novel multiphasic bone-ligament-bone scaffold (BLB) with a porous interface using 3D-printing and cell sheet technology for the reconstruction of the dorsal scapholunate interosseous ligament. The BLB comprises two bone compartments bridged by aligned polycaprolactone fibers mimicking the architecture of the native tissue. Mechanical testing of the BLBs shows their ability to withstand physiological forces. Combination of the BLB with human bone marrow mesenchymal stem cell sheet demonstrates that the harvesting did not compromise cell viability, while allowing homogeneous distribution in the ligament compartment. The BLBs are loaded with cell sheets and bone morphogenetic protein-2 in the ligament and bone compartment respectively prior to ectopic implantation into athymic rats. The histology demonstrates rapid tissue infiltration, high vascularization, and more importantly the maintenance of the compartmentalization as bone formation remains localized to the bone compartment despite the porous interface. The cells in the ligament compartment become preferentially aligned, and this proof-of-concept study demonstrates that the BLB can provide sufficient compartmentalization and fiber guiding properties necessary for the regeneration of the dorsal SLIL.

Preclinical safety study of a combined therapeutic bone wound dressing for osteoarticular regeneration

The extended life expectancy and the raise of accidental trauma call for an increase of osteoarticular surgical procedures. Arthroplasty, the main clinical option to treat osteoarticular lesions, has limitations and drawbacks. In this manuscript, we test the preclinical safety of the innovative implant ARTiCAR for the treatment of osteoarticular lesions. Thanks to the combination of two advanced therapy medicinal products, a polymeric nanofibrous bone wound dressing and bone marrow-derived mesenchymal stem cells, the ARTiCAR promotes both subchondral bone and cartilage regeneration. In this work, the ARTiCAR shows 1) the feasibility in treating osteochondral defects in a large animal model, 2) the possibility to monitor non-invasively the healing process and 3) the overall safety in two animal models under GLP preclinical standards. Our data indicate the preclinical safety of ARTiCAR according to the international regulatory guidelines; the ARTiCAR could therefore undergo phase I clinical trial.

Arthroplasty is the main clinical option for the treatment of osteoarticular lesions, but has limited efficacy. Here, the authors use a wound dressing with autologous mesenchymal stromal cells, functionalised for local BMP2 delivery, and show feasibility and safety in standardised preclinical tests in animal models, suggesting suitability for use in clinical trials.

Engineering of gradient osteochondral tissue: From nature to lab

The osteochondral tissue is an interface between two distinct tissues: articular cartilage and bone. These two tissues are significantly diverse with regard to their chemical compositions, mechanical properties, structure, electrical properties, and the amount of nutrient and oxygen consumption. Thus, transition from the surface of the articular cartilage to the subchondral bone needs to face several smooth gradients. These gradients are imperative to study to generate a scaffold suitable for the reconstruction of the cartilaginous and osseous layers of a defected osteochondral tissue, simultaneously. The aim of this review is to peruse the alternation of biochemical, biomechanical, structural, electrical, and metabolic properties of the osteochondral tissue moving from the surface of the articular cartilage to the subchondral bone. Moreover, this review also discusses currently developed approaches and ideal techniques with a focus on gradients present in the interface of the cartilage and bone. STATEMENT OF SIGNIFICANCE: The submitted review paper entitled as "Engineering of the gradient osteochondral tissue: from nature to lab" is a complete review with regard to the osteochondral tissue and transition of different properties between the cartilage and bone tissues. Moreover, previous studies on the osteochondral tissue engineering have been reviewed in this paper. This complete information can be a valuable and useful source for current and future researchers and scientists. Considering the scope of the submitted paper, Acta Biomaterialia would be a suitable journal for publishing this article.

A Col I and BCP ceramic bi-layer scaffold implant promotes regeneration in osteochondral defects

Osteochondral defects occur in the superficial cartilage region, intermediate calcified cartilage, and subchondral bone. Due to the limited regenerative capacity and complex zonal structure, it is critically difficult to develop strategies for osteochondral defect repair that could meet clinical requirements. In this study, type I collagen (Col I) and BCP ceramics were used to fabricate a new bi-layer scaffold for regeneration in osteochondral defects. The in vitro studies showed that the bi-layer scaffold provided special functions for cell migration, proliferation and secretion due to the layered scaffold structure. The in vivo results demonstrated that the bi-layered scaffold could effectively promote the regeneration of both the cartilage and the subchondral bone, and the newly formed cartilage layer, with a similar structure and thickness to the natural cartilaginous layer, could seamlessly integrate with the surrounding natural cartilage and regenerate an interface layer to mimic the native osteochondral structure.

A new bi-layer scaffold composed of Col I and BCP ceramic was prepared to regenerate osteochondral defect. The result demonstrated the bi-layer scaffold could effectively promote the regeneration of both the cartilage and the subchondral bone layer.

Regulation of decellularized tissue remodeling via scaffold-mediated lentiviral delivery in anatomically-shaped osteochondral constructs

Cartilage-derived matrix (CDM) has emerged as a promising scaffold material for tissue engineering of cartilage and bone due to its native chondroinductive capacity and its ability to support endochondral ossification. Because it consists of native tissue, CDM can undergo cellular remodeling, which can promote integration with host tissue and enables it to be degraded and replaced by neotissue over time. However, enzymatic degradation of decellularized tissues can occur unpredictably and may not allow sufficient time for mechanically competent tissue to form, especially in the harsh inflammatory environment of a diseased joint. The goal of the current study was to engineer cartilage and bone constructs with the ability to inhibit aberrant inflammatory processes caused by the cytokine interleukin-1 (IL-1), through scaffold-mediated delivery of lentiviral particles containing a doxycycline-inducible IL-1 receptor antagonist (IL-1Ra) transgene on anatomically-shaped CDM constructs. Additionally, scaffold-mediated lentiviral gene delivery was used to facilitate spatial organization of simultaneous chondrogenic and osteogenic differentiation via site-specific transduction of a single mesenchymal stem cell (MSC) population to overexpress either chondrogenic, transforming growth factor-beta 3 (TGF-β3), or osteogenic, bone morphogenetic protein-2 (BMP-2), transgenes. Controlled induction of IL-1Ra expression protected CDM hemispheres from inflammation-mediated degradation, and supported robust bone and cartilage tissue formation even in the presence of IL-1. In the absence of inflammatory stimuli, controlled cellular remodeling was exploited as a mechanism for fusing concentric CDM hemispheres overexpressing BMP-2 and TGF-β3 into a single bi-layered osteochondral construct. Our findings demonstrate that site-specific delivery of inducible and tunable transgenes confers spatial and temporal control over both CDM scaffold remodeling and neotissue composition. Furthermore, these constructs provide a microphysiological in vitro joint organoid model with site-specific, tunable, and inducible protein delivery systems for examining the spatiotemporal response to pro-anabolic and/or inflammatory signaling across the osteochondral interface.

Tissue Mimicry in Morphology and Composition Promotes Hierarchical Matrix Remodeling of Invading Stem Cells in Osteochondral and Meniscus Scaffolds

An integral approach toward in situ tissue engineering through scaffolds that mimic tissue with regard to both tissue architecture and biochemical composition is presented. Monolithic osteochondral and meniscus scaffolds are prepared with tissue analog layered biochemical composition and perpendicularly oriented continuous micropores by a newly developed cryostructuring technology. These scaffolds enable rapid cell ingrowth and induce zonal-specific matrix synthesis of human multipotent mesenchymal stromal cells solely through their design without the need for supplementation of soluble factors such as growth factors.

Hierarchically structured seamless silk scaffolds for osteochondral interface tissue engineering

The osteochondral healthcare market is driven by the increasing demand for affordable and biomimetic scaffolds. To meet this demand, silk fibroin (SF) from Bombyx mori and Antheraea assamensis is used to fabricate a biphasic scaffold, with fiber-free and fiber-reinforced phases, stimulating cartilage and bone revival. The fabrication is a facile reproducible process using single polymer (SF), for both phases, designed in a continuous and integrated manner. Physicochemical and mechanical scaffold characterization, display interconnected pores with differential swelling and tunable degradation. The compressive modulus values, extend to 40 kPa and 25%, for tensile strain, at elongation. The scaffold support, for growth and proliferation of chondrocytes and osteoblasts, for respective cartilage and bone regeneration, is verified from in vitro assessment. Up-regulation of alkaline phosphatase (ALP) activity, extracellular matrix secretion and gene expression are significant; with acceptable in vitro immune response. Upon implantation in rabbit osteochondral defects for 8 weeks, the histological and micro-CT examinations show biphasic scaffolds significantly enhance regeneration of cartilage and subchondral bone tissues, as compared to monophasic scaffolds. The regenerated bone mineral density (BMD) ranges from 600-700 mg hydroxyapatite (HA) per cm³. The results, therefore, showcase the critically positive characteristics of in vitro ECM deposition, and in vivo regeneration of osteochondral tissue by this hierarchically structured biphasic scaffold.

The regenerative therapies of the ankle degeneration: a focus on multipotential mesenchymal stromal cells

The ankle degeneration ranging from focal osteochondral lesions to osteoarthritis can cause a total joint function loss. With rising life expectancy and activity of the patients, various regenerative therapies were introduced aiming to preserve the joint function via the induction of cartilage and bone repair. Here, biological events and mechanical changes of the ankle degeneration were discussed. The regenerative therapies were reviewed versus the standard surgical treatment. We especially focused on the use of mesenchymal (multipotential) stromal cells (MSCs) highlighting their dual functions of regeneration and cell modulation with an emphasis on the emerging MSC-based clinical studies. Being at an early step, more basic and clinical research is needed to optimize the applications of all ankle regenerative therapies including MSC-based methods.

A review on gradient hydrogel/fiber scaffolds for osteochondral regeneration

Osteochondral tissue regeneration is a complicated field due to the distinct properties and healing potential of osseous and chondral phases. In a natural osteochondral region, the composition, mechanics, and structure vary smoothly from bony to cartilaginous phase. Therefore, a homogeneous scaffold cannot satisfy the complexity of the osteochondral matrix. In essence, a natural extracellular matrix is composed of fibrous proteins elongated into a gelatinous background. A hydrogel/fiber scaffold possessing gradient in both phases would be of the utmost interest to imitate tissue arrangement of a native osteochondral interface. However, there are limited research works that exploit hydrogel/fiber scaffolds for osteochondral restoration. In the present review, currently used fibrous or gelatinous scaffolds for osteochondral damages are discussed. Moreover, superiority of using gradient hydrogel/fiber composites for osteochondral regeneration and practical approaches to develop those scaffolds is debated.

Current strategies for integrative cartilage repair

Osteoarthritis (OA) is a degenerative joint condition characterized by painful cartilage lesions that impair joint mobility. Current treatments such as lavage, microfracture, and osteochondral implantation fail to integrate newly formed tissue with host tissues and establish a stable transition to subchondral bone. Similarly, tissue-engineered grafts that facilitate cartilage and bone regeneration are challenged by how to integrate the graft seamlessly with surrounding host cartilage and/or bone. This review centers on current approaches to promote cartilage graft integration. It begins with an overview of articular cartilage structure and function, as well as degenerative changes to this relationship attributed to aging, disease, and trauma. A discussion of the current progress in integrative cartilage repair follows, focusing on graft or scaffold design strategies targeting cartilage-cartilage and/or cartilage-bone integration. It is emphasized that integrative repair is required to ensure long-term success of the cartilage graft and preserve the integrity of the newly engineered articular cartilage. Studies involving the use of enzymes, choice of cell source, biomaterial selection, growth factor incorporation, and stratified versus gradient scaffolds are therefore highlighted. Moreover, models that accurately evaluate the ability of cartilage grafts to enhance tissue integrity and prevent ectopic calcification are also discussed. A summary and future directions section concludes the review.

Ectopic models for endochondral ossification: comparing pellet and alginate bead culture methods

Key aspects of native endochondral bone development and fracture healing can be mimicked in mesenchymal stem cells (MSCs) through standard in vitro chondrogenic induction. Exploiting this phenomenon has recently emerged as an attractive technique to engineer bone tissue, however, relatively little is known about the best conditions for doing so. The objective of the present study was to compare the bone-forming capacity and angiogenic induction of hypertrophic cell constructs containing human adipose-derived stem cells (hASCs) primed for chondrogenesis in two different culture systems: high-density pellets and alginate bead hydrogels. The hASC constructs were subjected to 4 weeks of identical chondrogenic induction in vitro, encapsulated in an agarose carrier, and then implanted subcutaneously in immune-compromised mice for 8 weeks to evaluate their endochondral potential. At the time of implantation, both pellets and beads expressed aggrecan and type II collagen, as well as alkaline phosphatase (ALP) and type X collagen. Interestingly, ASCs in pellets formed a matrix containing higher glycosaminoglycan and collagen contents than that in beads, and ALP activity per cell was higher in pellets. However, after 8 weeks in vivo, pellets and beads induced an equivalent volume of mineralized tissue and a comparable level of vascularization. Although osteocalcin and osteopontin-positive osteogenic tissue and new vascular growth was found within both types of constructs, all appeared to be better distributed throughout the hydrogel beads. The results of this ectopic model indicate that hydrogel culture may be an attractive alternative to cell pellets for bone tissue engineering via the endochondral pathway. Copyright © 2016 John Wiley & Sons, Ltd.

Nanoengineered biomaterials for repair and regeneration of orthopedic tissue interfaces

Orthopedic interface tissue engineering aims to mimic the structure and function of soft-to-hard tissue junctions, particularly bone-ligament, bone-tendon, and bone-cartilage interfaces. A range of engineering approaches has been proposed to mimic the gradient architecture, physical properties and chemical characteristics of interface tissues using conventional polymeric biomaterials. Recent developments in nanomaterials and nanofabrication technologies introduce a range of synthesis and fabrication tools to effectively engineer the structure and function of native tissue interfaces. In this review, we will focus on nanoengineered strategies used to replicate the structural and functional aspects of native biological tissues for engineering bone-cartilage, bone-ligament, and bone-tendon interfaces. This review will also highlight some of the emerging applications and future potential of nanomaterials and fabrication technologies in engineering tissue interfaces.

STATEMENT OF SIGNIFICANCE

A major challenge in engineering interfaces is to control the physical and structural characteristics of an artificial environment. The use of nanomaterials and nanoengineered strategies allow for greater control over the changes in structure and function at molecular and nanometer length scale. This review focuses on advanced nanomaterials and nanofabrication approaches developed to emulate bone-cartilage, bone-ligament, and bone-tendon interface regions. Some of the emerging nanoengineered biomaterials proposed to mimic tissue interfaces are also highlighted.

Multi-layered collagen-based scaffolds for osteochondral defect repair in rabbits

INTRODUCTION

Identification of a suitable treatment for osteochondral repair presents a major challenge due to existing limitations and an urgent clinical need remains for an off-the-shelf, low cost, one-step approach. A biomimetic approach, where the biomaterial itself encourages cellular infiltration from the underlying bone marrow and provides physical and chemical cues to direct these cells to regenerate the damaged tissue, provides a potential solution. To meet this need, a multi-layer collagen-based osteochondral defect repair scaffold has been developed in our group.

AIM

The objective of this study was to assess the in vivo response to this scaffold and determine its ability to direct regenerative responses in each layer in order to repair osteochondral tissue in a critical-sized defect in a rabbit knee.

METHODS

Multi-layer scaffolds, consisting of a bone layer composed of type I collagen (bovine source) and hydroxyapatite (HA), an intermediate layer composed of type I and type II collagen and HA; and a superficial layer composed of type I and type II collagen (porcine source) and hyaluronic acid (HyA), were implanted into critical size (3 × 5 mm) osteochondral defects created in the medial femoral condyle of the knee joint of New Zealand white rabbits and compared to an empty control group. Repair was assessed macroscopically, histologically and using micro-CT analysis at 12 weeks post implantation.

RESULTS

Analysis of repair tissue demonstrated an enhanced macroscopic appearance in the multi-layer scaffold group compared to the empty group. In addition, diffuse host cellular infiltration in the scaffold group resulted in tissue regeneration with a zonal organisation, with repair of the subchondral bone, formation of an overlying cartilaginous layer and evidence of an intermediate tidemark.

CONCLUSION

These results demonstrate the potential of this biomimetic multi-layered scaffold to support and guide the host reparative response in the treatment of osteochondral defects.

STATEMENT OF SIGNIFICANCE

Osteochondral defects, involving cartilage and the underlying subchondral bone, frequently occur in young active patients due to disease or injury. While some treatment options are available, success is limited and patients often eventually require joint replacement. To address this clinical need, a multi-layer collagen-based osteochondral defect repair scaffold designed to direct host-stem cell mediated tissue formation within each region, has been developed in our group. The present study investigates the in vivo response to this scaffold in a critical-sized defect in a rabbit knee. Results shows the scaffolds ability to guide the host reparative response leading to tissue regeneration with a zonal organisation, repair of the subchondral bone, formation of an overlying cartilaginous layer and evidence of an intermediate tidemark.

Osteochondral scaffold combined with aligned nanofibrous scaffolds for cartilage regeneration

Osteochondral defect repair poses a significant challenge in its reconstruction as the damage is presented in both articular cartilage and the underlying subchondral bone. Thus we present a osteochondral scaffold for articular cartilage repair.

Generation and characterization of osteochondral grafts with human nasal chondrocytes

We investigated whether nasal chondrocytes (NC) can be used to generate composite constructs with properties necessary for the repair of osteochondral (OC) lesions, namely maturation, integration and capacity to recover from inflammatory burst. OC grafts were fabricated by combining engineered cartilage tissues (generated by culturing NC or articular chondrocytes - AC - onto Chondro-Gide® matrices) with devitalized spongiosa cylinders (Tutobone®). OC tissues were then exposed to IL-1β for three days and cultured for additional 2 weeks in the absence of IL-1β. Cartilage maturation extent was assessed (immune) histologically, biochemically and by delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) while cartilage/bone integration was assessed using a peel-off mechanical test. The use of NC as compared to AC allowed for more efficient cartilage matrix accumulation and superior integration of the cartilage/bone layers. dGEMRIC and biochemical analyzes of the OC constructs showed a reduced glycosaminoglycan (GAG) contents upon IL-1β administration. Cartilaginous matrix contents and integration forces returned to baseline up on withdrawal of IL-1β. By having a cartilage layer well developed and strongly integrated to the subchondral layer, OC tissues generated with NC may successfully engraft in an inflammatory post-surgery joint environment.

Engineering complex orthopaedic tissues via strategic biomimicry

The primary current challenge in regenerative engineering resides in the simultaneous formation of more than one type of tissue, as well as their functional assembly into complex tissues or organ systems. Tissue-tissue synchrony is especially important in the musculoskeletal system, wherein overall organ function is enabled by the seamless integration of bone with soft tissues such as ligament, tendon, or cartilage, as well as the integration of muscle with tendon. Therefore, in lieu of a traditional single-tissue system (e.g., bone, ligament), composite tissue scaffold designs for the regeneration of functional connective tissue units (e.g., bone-ligament-bone) are being actively investigated. Closely related is the effort to re-establish tissue-tissue interfaces, which is essential for joining these tissue building blocks and facilitating host integration. Much of the research at the forefront of the field has centered on bioinspired stratified or gradient scaffold designs which aim to recapitulate the structural and compositional inhomogeneity inherent across distinct tissue regions. As such, given the complexity of these musculoskeletal tissue units, the key question is how to identify the most relevant parameters for recapitulating the native structure-function relationships in the scaffold design. Therefore, the focus of this review, in addition to presenting the state-of-the-art in complex scaffold design, is to explore how strategic biomimicry can be applied in engineering tissue connectivity. The objective of strategic biomimicry is to avoid over-engineering by establishing what needs to be learned from nature and defining the essential matrix characteristics that must be reproduced in scaffold design. Application of this engineering strategy for the regeneration of the most common musculoskeletal tissue units (e.g., bone-ligament-bone, muscle-tendon-bone, cartilage-bone) will be discussed in this review. It is anticipated that these exciting efforts will enable integrative and functional repair of soft tissue injuries, and moreover, lay the foundation for the development of composite tissue systems and ultimately, total limb or joint regeneration.

The effect of interface microstructure on interfacial shear strength for osteochondral scaffolds based on biomimetic design and 3D printing

Interface integration between chondral phase and osseous phase is crucial in engineered osteochondral scaffolds. However, the integration was poorly understood and commonly failed to meet the need of osteochondral scaffolds. In this paper, a biphasic polyethylene glycol (PEG)/β-tricalcium phosphate (β-TCP) scaffold with enhanced interfacial integration was developed. The chondral phase was a PEG hydrogel. The osseous phase was a β-TCP ceramic scaffold. The PEG hydrogel was directly cured on the ceramic interface layer by layer to fabricate osteochondral scaffolds by 3D printing technology. Meanwhile, a series of interface structure were designed with different interface pore area percentages (0/10/20/30/40/50/60%), and interfacial shear test was applied for interface structure optimization (n=6 samples/group). The interfacial shear strength of 30% pore area group was nearly three folds improved compared with that of 0% pore area percentage group, and more than fifty folds improved compared with that of traditional integration (5.91±0.59 kPa). In conclusion, the biomimetic PEG/β-TCP scaffolds with interface structure enhanced integration show promising potential application for osteochondral tissue engineering.

Scaffold-based regeneration of skeletal tissues to meet clinical challenges

The management and reconstruction of damaged or diseased skeletal tissues have remained a significant global healthcare challenge. The limited efficacy of conventional treatment strategies for large bone, cartilage and osteochondral defects has inspired the development of scaffold-based tissue engineering solutions, with the aim of achieving complete biological and functional restoration of the affected tissue in the presence of a supporting matrix. Nevertheless, significant regulatory hurdles have rendered the clinical translation of novel scaffold designs to be an inefficient process, mainly due to the difficulties of arriving at a simple, reproducible and effective solution that does not rely on the incorporation of cells and/or bioactive molecules. In the context of the current clinical situation and recent research advances, this review will discuss scaffold-based strategies for the regeneration of skeletal tissues, with focus on the contribution of bioactive ceramic scaffolds and silk fibroin, and combinations thereof, towards the development of clinically viable solutions.

90° Peel off Tests of Tissue Engineered Osteochondral Constructs: A New Method to Determine the Osteochondral Integration

One promising treatment of localized osteochondral defects in the knee joint may be the implantation of in vitro tissue-engineered osteochondral constructs. A crucial aspect of this kind of osteochondral construct is the bonding between the bone-scaffold and scaffold-based chondral layer. Here, a 90° peel off test is proposed as an appropriate method to measure the integration of cartilage to bone in osteochondral constructs for different primary methods of bonding the cartilage scaffold to the bone scaffold, with and without seeded chondroblasts. The method was developed and then tested on tissue-engineered constructs. The force/displacement data obtained allow determination of both the maximum force and the total energy required to separate the two layers. The tests showed good reproducibility and good discrimination between measurements as a function of seeding times. Average maximum peel-off forces varied between 10 mN for fibrin glue only to 575 mN for constructs with cells after four weeks of incubation. Linear regression of the area under the curve (AUC) as a function of maximum force shows a high correlation between the two parameters with R2 = 0.97. The main limitation of the test is that the data provide only a modest ability to decide how uniform the bond is over the area between the two layers.

One-step surgery with multipotent stem cells for the treatment of large full-thickness chondral defects of the knee

BACKGROUND

Chondral lesions in athletically active patients cause considerable morbidity, and treatment with existing cell-based therapies can be challenging. Bone marrow has been shown as a possible source of multipotent stem cells (MSCs) with chondrogenic potential and is easy to harvest during the same surgical procedure.

PURPOSE

To investigate the clinical outcome in a group of active patients with large full-thickness chondral defects of the knee treated with 1-step surgery using bone marrow-derived MSCs and a second-generation matrix.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

From January 2007 to February 2010, 25 patients (average age, 46.5 years) with symptomatic large chondral defects of the knee (International Cartilage Repair Society grade 4) who underwent cartilage transplantation with MSCs and a collagen type I/III matrix were followed up for a minimum of 3 years. The average lesion size was 8.3 cm(2). Coexisting injuries were treated during the same surgical procedure in 18 patients. All patients underwent a standard postoperative rehabilitation program. Preoperative and postoperative evaluations at 1-year, 2-year, and final follow-up included radiographs, magnetic resonance imaging (MRI), and visual analog scale (VAS) for pain, International Knee Documentation Committee (IKDC), Knee injury and Osteoarthritis Outcome Score (KOOS), Lysholm, Marx, and Tegner scores. Seven patients underwent second-look arthroscopic surgery, with 4 consenting to a tissue biopsy.

RESULTS

No patients were lost at final follow-up. The average preoperative values for the evaluated scores were significantly improved at final follow-up (P < .001): VAS, 5.4 ± 0.37 to 0.48 ± 0.19; IKDC subjective, 37.92 ± 4.52 to 81.73 ± 2.42; KOOS pain, 61.04 ± 3.95 to 93.32 ± 1.92; KOOS symptoms, 55.64 ± 3.23 to 89.32 ± 2.32; KOOS activities of daily living, 63.96 ± 4.48 to 91.20 ± 2.74; KOOS sports, 34.20 ± 5.04 to 80.00 ± 3.92; KOOS quality of life, 32.20 ± 4.43 to 83.04 ± 3.37; Lysholm, 46.36 ± 2.25 to 86.52 ± 2.73; Marx, 3.00 ± 0.79 to 9.04 ± 0.79; and Tegner, 2.12 ± 0.32 to 5.64 ± 0.26. Patients younger than 45 years of age and those with smaller or single lesions showed better outcomes. The MRI scans showed good stability of the implant and complete filling of the defect in 80% of patients, and hyaline-like cartilage was found in the histological analysis of the biopsied tissue. No adverse reactions or postoperative complications were noted.

CONCLUSION

The treatment of large chondral defects with MSCs is an effective procedure and can be performed routinely in clinical practice. Moreover, it can be achieved with 1-step surgery, avoiding a previous surgical procedure to harvest cartilage and subsequent chondrocyte cultivation.

Tissue engineering stratified scaffolds for articular cartilage and subchondral bone defects repair

Due to their good biocompatibility and mechanical integrity, tissue engineering scaffolds have become a principal method of repair and regeneration of osteochondral defects. To improve their intrinsic properties, control their degenerative times, and enhance their cell adhesion and differentiation, numerous scaffold architectures and formation methods have been developed and tested, but the ideal scaffold design is still controversial. Moreover, scaffold fixation has a significant influence on repair and regeneration after implantation. The authors analyzed relative studies to address the latest scaffold designs, including biphasic scaffold, multilayered scaffold, and continuous nonstratified scaffold, and this article compares their advantages and disadvantages. In addition, the authors introduce a novel modified method for scaffold fixation known as magnetic fixation. Both stratified and nonstratified scaffolds can repair osteochondral defects, but continuous nonstratified scaffolds are more biomimetic compared with the native osteochondral structures, and they lead to a better regeneration of hyaline-like cartilage and structured bone tissue. Therefore, the authors suggest continuous nonstratified scaffolds are an effective option for treating osteochondral defects.

The impact of compact layer in biphasic scaffold on osteochondral tissue engineering

The structure of an osteochondral biphasic scaffold is required to mimic native tissue, which owns a calcified layer associated with mechanical and separation function. The two phases of biphasic scaffold should possess efficient integration to provide chondrocytes and osteocytes with an independent living environment. In this study, a novel biphasic scaffold composed of a bony phase, chondral phase and compact layer was developed. The compact layer-free biphasic scaffold taken as control group was also fabricated. The purpose of current study was to evaluate the impact of the compact layer in the biphasic scaffold. Bony and chondral phases were seeded with autogeneic osteoblast- or chondrocyte-induced bone marrow stromal cells (BMSCs), respectively. The biphasic scaffolds-cells constructs were then implanted into osteochondral defects of rabbits’ knees, and the regenerated osteochondral tissue was evaluated at 3 and 6 months after surgery. Anti-tensile and anti-shear properties of the compact layer-containing biphasic scaffold were significantly higher than those of the compact layer-free biphasic scaffold in vitro. Furthermore, in vivo studies revealed superior macroscopic scores, glycosaminoglycan (GAG) and collagen content, micro tomograph imaging results, and histological properties of regenerated tissue in the compact layer-containing biphasic scaffold compared to the control group. These results indicated that the compact layer could significantly enhance the biomechanical properties of biphasic scaffold in vitro and regeneration of osteochondral tissue in vivo, and thus represented a promising approach to osteochondral tissue engineering.

Unlike bone, cartilage regeneration remains elusive

Articular cartilage was predicted to be one of the first tissues to successfully be regenerated, but this proved incorrect. In contrast, bone (but also vasculature and cardiac tissues) has seen numerous successful reparative approaches, despite consisting of multiple cell and tissue types and, thus, possessing more complex design requirements. Here, we use bone-regeneration successes to highlight cartilage-regeneration challenges: such as selecting appropriate cell sources and scaffolds, creating biomechanically suitable tissues, and integrating to native tissue. We also discuss technologies that can address the hurdles of engineering a tissue possessing mechanical properties that are unmatched in human-made materials and functioning in environments unfavorable to neotissue growth.

Osteochondral tissue engineering: scaffolds, stem cells and applications

Osteochondral tissue engineering has shown an increasing development to provide suitable strategies for the regeneration of damaged cartilage and underlying subchondral bone tissue. For reasons of the limitation in the capacity of articular cartilage to self-repair, it is essential to develop approaches based on suitable scaffolds made of appropriate engineered biomaterials. The combination of biodegradable polymers and bioactive ceramics in a variety of composite structures is promising in this area, whereby the fabrication methods, associated cells and signalling factors determine the success of the strategies. The objective of this review is to present and discuss approaches being proposed in osteochondral tissue engineering, which are focused on the application of various materials forming bilayered composite scaffolds, including polymers and ceramics, discussing the variety of scaffold designs and fabrication methods being developed. Additionally, cell sources and biological protein incorporation methods are discussed, addressing their interaction with scaffolds and highlighting the potential for creating a new generation of bilayered composite scaffolds that can mimic the native interfacial tissue properties, and are able to adapt to the biological environment.

Reconstruction of iliac crest with bovine cancellous allograft after bone graft harvest for symphysis pubis arthrodesis

PURPOSE

The aim of this study was to evaluate the safety and efficiency, as well as the incorporation characteristics of a specific type of xenograft used for iliac crest defects post-harvesting tri-cortical iliac crest bone graft.

METHODS

Sixteen patients diagnosed with chronic anterior pelvic pain were operated for pubic symphysis fusion. The tri-cortical graft harvested from the iliac crest was inserted into the pubic symphysis and compressed with a reconstruction plate. The defect in the iliac crest was filled with a block of cancellous bovine substitute (Tutobone®). The length of iliac crest defect, time to fusion of pubic symphysis, time to incorporation of the graft and complications were recorded. The postoperative pain and patients' satisfaction were evaluated.

RESULTS

The median age of patients was 36.5 years (range 27-75). Fusion was obtained in 15 patients (94 %). The median time to fusion was four months (range three to seven). The length of the iliac crest bone defect ranged from 40 to 70 mm. Integration of the bovine substitute was achieved in 15 patients (94 %) over a median period of three months (range two to six). The postoperative median pain score was 2 (range 1-5). Twelve patients (75 %) reported good satisfaction. No major complications or allergic reactions were observed.

CONCLUSIONS

The xenograft used in this study provided a safe and effective method of reconstruction of iliac crest donor site defects. It has satisfactory incorporation, high biocompatibility and no signs of inflammatory reactions. This new technique is simple and easily reproducible in routine clinical practice.

Anular delamination strength of human lumbar intervertebral disc

INTRODUCTION

Progression of intervertebral disc (IVD) herniation does not occur exclusively in a linear manner through the anulus fibrosus (AF), but can migrate circumferentially due to localized AF delamination. Consequently, resistance to delamination is an important factor in determining risk of herniation progression. The inter-lamellar matrix located between the AF layers is responsible for resisting this delamination; however, its mechanical properties are largely unknown. This study aimed to determine the mechanical properties of the inter-lamellar matrix in human AF samples via a peel test.

MATERIALS AND METHODS

Seventeen human IVDs (degeneration grades of 2-3) were obtained from six lumbar spines. From these 17 discs, 53 tissue samples were obtained from the superficial and deep regions of the anterior and posterior AF. Samples were dissected into a 'T' configuration to facilitate a T-peel test (or 180-degree peel test) by initiating delamination between the two middle AF layers.

RESULTS

Peel strength was found to be 33 % higher in tissues obtained from the superficial AF region as compared with the deep region (p = 0.047).

CONCLUSION

This finding may indicate a higher resistance to delamination in the superficial AF, and as a result, delamination and herniation progression may occur more readily in the deeper layers of the AF.

Continuous gradients of material composition and growth factors for effective regeneration of the osteochondral interface

Most contemporary biomaterial designs for osteochondral regeneration utilize monolithic, biphasic, or even multiphasic constructs. We have introduced a microsphere-based approach to create a continuous gradient in both material composition and encapsulated growth factors. The gradients were fabricated by filling a cylindrical mold with opposing gradients of two different types of poly(D,L-lactic-co-glycolic acid) microspheres. The chondrogenic microspheres were loaded with transforming growth factor-β1, whereas the osteogenic microspheres contained bone morphogenetic protein-2 with or without nanophase hydroxyapatite. The gradient scaffolds (material gradient only, signal gradient only, or material/signal gradient combination) or blank control scaffolds were implanted in 3.5 mm-diameter defects in rabbit knees for 6 or 12 weeks. This is the first in vivo evaluation of these novel gradient scaffolds in the knee. The gross morphology, MRI, and histology indicated that the greatest extent of regeneration was achieved when both signal and material gradients were included together. This combination resulted in complete bone ingrowth, with an overlying cartilage layer with high glycosaminoglycan content, appropriate thickness, and integration with the surrounding cartilage and underlying bone. The results suggest that osteochondral regeneration may benefit from biomaterials that integrate a continuous gradient in both material composition and encapsulated growth factors.

One-Step Cartilage Repair with Bone Marrow Aspirate Concentrated Cells and Collagen Matrix in Full-Thickness Knee Cartilage Lesions: Results at 2-Year Follow-up

OBJECTIVE

The purpose of our study was to determine the effectiveness of cartilage repair utilizing 1-step surgery with bone marrow aspirate concentrate (BMAC) and a collagen I/III matrix (Chondro-Gide, Geistlich, Wolhusen, Switzerland).

MATERIALS AND METHODS

We prospectively followed up for 2 years 15 patients (mean age, 48 years) who were operated for grade IV cartilage lesions of the knee. Six of the patients had multiple chondral lesions; the average size of the lesions was 9.2 cm(2). All patients underwent a mini-arthrotomy and concomitant transplantation with BMAC covered with the collagen matrix. Coexisting pathologies were treated before or during the same surgery. X-rays and MRI were collected preoperatively and at 1 and 2 years' follow-up. Visual analog scale (VAS), International Knee Documentation Committee (IKDC), Knee injury and Osteoarthritis Outcome Score (KOOS), Lysholm, Marx, SF-36 (physical/mental), and Tegner scores were collected preoperatively and at 6, 12, and 24 months' follow-up. Four patients gave their consent for second-look arthroscopy and 3 of them for a concomitant biopsy.

RESULTS

Patients showed significant improvement in all scores at final follow-up (P < 0.005). Patients presenting single lesions and patients with small lesions showed higher improvement. MRI showed coverage of the lesion with hyaline-like tissue in all patients in accordance with clinical results. Hyaline-like histological findings were also reported for all the specimens analyzed. No adverse reactions or postoperative complications were noted.

CONCLUSION

This study showed that 1-step surgery with BMAC and collagen I/III matrix could be a viable technique in the treatment of grade IV knee chondral lesions.

Biomedical use of isothermal microcalorimeters

Isothermal microcalorimetry is becoming widely used for monitoring biological activities in vitro. Microcalorimeters are now able to measure heat production rates of less than a microwatt. As a result, metabolism and growth of relatively small numbers of cultured bacteria, protozoans, human cells and even small animals can be monitored continuously and extremely accurately at any chosen temperature. Dynamic effects on these organisms of changes in the culture environment—or of additions to it—are easily assessed over periods from hours to days. In addition microcalorimetry is a non-destructive method that does not require much sample preparation. It is also completely passive and thus allows subsequent evaluations of any kind on the undisturbed sample. In this review, we present a basic description of current microcalorimetry instruments and an overview of their use for various biomedical applications. These include detecting infections, evaluating effects of pharmaceutical or antimicrobial agents on cells, monitoring growth of cells harvested for tissue eingineering, and assessing medical and surgical device material physico-chemical stability and cellular biocompatibility.