Chondral Phase Research Articles

Osteochondral Regeneration With Anatomical Scaffold 3D-Printing-Design Considerations for Interface Integration.

There is a clinical need for osteochondral scaffolds with complex geometries for restoring articulating joint surfaces. To address that need, 3D-printing has enabled scaffolds to be created with anatomically shaped geometries and interconnected internal architectures, going beyond simple plug-shaped scaffolds that are limited to small, cylindrical, focal defects. A key challenge for restoring articulating joint surfaces with 3D-printed constructs is the mechanical loading environment, particularly to withstand delamination or mechanical failure. Although the mechanical performance of interfacial scaffolds is essential, interface strength testing has rarely been emphasized in prior studies with stratified scaffolds. In the pioneering studies where interface strength was assessed, varying methods were employed, which has made direct comparisons difficult. Therefore, the current review focused on 3D-printed scaffolds for osteochondral applications with an emphasis on interface integration and biomechanical evaluation. This 3D-printing focus included both multiphasic cylindrical scaffolds and anatomically shaped scaffolds. Combinations of different 3D-printing methods (e.g., fused deposition modeling, stereolithography, bioprinting with pneumatic extrusion of cell-laden hydrogels) have been employed in a handful of studies to integrate osteoinductive and chondroinductive regions into a single scaffold. Most 3D-printed multiphasic structures utilized either an interdigitating or a mechanical interlocking design to strengthen the construct interface and to prevent delamination during function. The most effective approach to combine phases may be to infill a robust 3D-printed osteal polymer with an interlocking chondral phase hydrogel. Mechanical interlocking is therefore recommended for scaling up multiphasic scaffold applications to larger anatomically shaped joint surface regeneration. For the evaluation of layer integration, the interface shear test is recommended to avoid artifacts or variability that may be associated with alternative approaches that require adhesives or mechanical grips. The 3D-printing literature with interfacial scaffolds provides a compelling foundation for continued work toward successful regeneration of injured or diseased osteochondral tissues in load-bearing joints such as the knee, hip, or temporomandibular joint.

Chitosan/Hyaluronan and Alginate-Nanohydroxyapatite Biphasic Scaffold as a Promising Matrix for Osteoarthritis Disorders.

Regenerative medicine offers new techniques for osteoarthritis (OA) disorders, especially while considering simultaneous chondral and subchondral regenerations. Chitosan and hyaluronan were chemically bound as the chondral phase and the osteogenic layer was prepared with alginate and nano-hydroxyapatite (nHAP). These scaffolds were fixed by fibrin glue as a biphasic scaffold and then examined. Scanning electron microscopy (SEM) confirmed the porosity of 61.45±4.51 and 44.145±2.81 % for the subchondral and chondral layers, respectively. The composition analysis by energy dispersive X-ray (EDAX) indicated the various elements of both hydrogels. Also, their mechanical properties indicated that the highest modulus and resistance values corresponded to the biphasic hydrogel as 108.33±5.56 and 721.135±8.21 kPa, despite the same strain value as other groups. Their individual examinations demonstrated the proteoglycan synthesis of the chondral layer and also, the alkaline phosphatase (ALP) activity of the subchondral layer as 13.3±2.2 ng. After 21 days, the cells showed a mineralized surface and a polygonal phenotype, confirming their commitment to bone and cartilage tissues, respectively. Immunostaining of collagen I and II represented greater extracellular matrix (ECM) secretion in the biphasic composite group due to the paracrine effect of the two cell types on each other. For the first time, the ability of this biphasic scaffold to regenerate both tissue types was evaluated and the results showed satisfactory cellular commitment to bone and cartilage tissues. Thus, this scaffold can be considered a new strategy for the preparation of implants for OA.

Manufacture of Bilayered Composite Hydrogels with Strong, Elastic, and Tough Properties for Osteochondral Repair Applications.

Layered composite hydrogels have been considered attractive materials for use in osteochondral repair and regeneration. These hydrogel materials should be mechanically strong, elastic, and tough besides fulfilling some basic requirements such as biocompatibility and biodegradability. A novel type of bilayered composite hydrogel with multi-network structures and well-defined injectability was thus developed for osteochondral tissue engineering using chitosan (CH), hyaluronic acid (HA), silk fibroin (SF), CH nanoparticles (NPs), and amino-functionalized mesoporous bioglass (ABG) NPs. CH was combined with HA and CH NPs to build the chondral phase of the bilayered hydrogel, and CH, SF, and ABG NPs were used together to construct the subchondral phase of the bilayer hydrogel. Rheological measurements showed that the optimally achieved gels assigned to the chondral and subchondral layers had their elastic moduli of around 6.5 and 9.9 kPa, respectively, with elastic modulus/viscous modulus ratios higher than 36, indicating that they behaved like strong gels. Compressive measurements further demonstrated that the bilayered hydrogel with an optimally formulated composition had strong, elastic, and tough characteristics. Cell culture revealed that the bilayered hydrogel had the capacity to support the in-growth of chondrocytes in the chondral phase and osteoblasts in the subchondral phase. Results suggest that the bilayered composite hydrogel can act as an injective biomaterial for osteochondral repair applications.

Engineering large, anatomically shaped osteochondral constructs with robust interfacial shear properties

Despite the prevalence of large (>5 cm2) articular cartilage defects involving underlying bone, current tissue-engineered therapies only address small defects. Tissue-engineered, anatomically shaped, native-like implants may address the need for off-the-shelf, tissue-repairing therapies for large cartilage lesions. This study fabricated an osteochondral construct of translationally relevant geometry with robust functional properties. Scaffold-free, self-assembled neocartilage served as the chondral phase, and porous hydroxyapatite served as the osseous phase of the osteochondral constructs. Constructs in the shape and size of an ovine femoral condyle (31 × 14 mm) were assembled at day 4 (early) or day 10 (late) of neocartilage maturation. Early osteochondral assembly increased the interfacial interdigitation depth by 244%, interdigitation frequency by 438%, interfacial shear modulus by 243-fold, and ultimate interfacial shear strength by 4.9-fold, compared to late assembly. Toward the development of a bioprosthesis for the repair of cartilage lesions encompassing up to an entire condylar surface, this study generated a large, anatomically shaped osteochondral construct with robust interfacial mechanical properties and native-like neocartilage interdigitation.

3D printing of fibre-reinforced cartilaginous templates for the regeneration of osteochondral defects

Successful osteochondral defect repair requires regenerating the subchondral bone whilst simultaneously promoting the development of an overlying layer of articular cartilage that is resistant to vascularization and endochondral ossification. During skeletal development articular cartilage also functions as a surface growth plate, which postnatally is replaced by a more spatially complex bone-cartilage interface. Motivated by this developmental process, the hypothesis of this study is that bi-phasic, fibre-reinforced cartilaginous templates can regenerate both the articular cartilage and subchondral bone within osteochondral defects created in caprine joints. To engineer mechanically competent implants, we first compared a range of 3D printed fibre networks (PCL, PLA and PLGA) for their capacity to mechanically reinforce alginate hydrogels whilst simultaneously supporting mesenchymal stem cell (MSC) chondrogenesis in vitro. These mechanically reinforced, MSC-laden alginate hydrogels were then used to engineer the endochondral bone forming phase of bi-phasic osteochondral constructs, with the overlying chondral phase consisting of cartilage tissue engineered using a co-culture of infrapatellar fat pad derived stem/stromal cells (FPSCs) and chondrocytes. Following chondrogenic priming and subcutaneous implantation in nude mice, these bi-phasic cartilaginous constructs were found to support the development of vascularised endochondral bone overlaid by phenotypically stable cartilage. These fibre-reinforced, bi-phasic cartilaginous templates were then evaluated in clinically relevant, large animal (caprine) model of osteochondral defect repair. Although the quality of repair was variable from animal-to-animal, in general more hyaline-like cartilage repair was observed after 6 months in animals treated with bi-phasic constructs compared to animals treated with commercial control scaffolds. This variability in the quality of repair points to the need for further improvements in the design of 3D bioprinted implants for joint regeneration. Statement of SignificanceSuccessful osteochondral defect repair requires regenerating the subchondral bone whilst simultaneously promoting the development of an overlying layer of articular cartilage. In this study, we hypothesised that bi-phasic, fibre-reinforced cartilaginous templates could be leveraged to regenerate both the articular cartilage and subchondral bone within osteochondral defects. To this end we used 3D printed fibre networks to mechanically reinforce engineered transient cartilage, which also contained an overlying layer of phenotypically stable cartilage engineered using a co-culture of chondrocytes and stem cells. When chondrogenically primed and implanted into caprine osteochondral defects, these fibre-reinforced bi-phasic cartilaginous grafts were shown to spatially direct tissue development during joint repair. Such developmentally inspired tissue engineering strategies, enabled by advances in biofabrication and 3D printing, could form the basis of new classes of regenerative implants in orthopaedic medicine.

The fiveyear outcome of a clinical feasibility study using a biphasic construct with minced autologous cartilage to repair osteochondral defects in the knee.

Autologous minced cartilage has been used to repair cartilage defects. We have developed a biphasic cylindrical osteochondral construct for such use in human knees, and report the fiveyear post-operative outcomes. Ten patients with symptomatic osteochondral lesion at femoral condyles were treated by replacing pathological tissue with the osteochondral composites, each consisted a DL-poly-lactide-co-glycolide chondral phase and a DL-poly-lactide-co-glycolide/β-tricalcium phosphate osseous phase. A flat chamber between the two phases served as a reservoir to house double-minced (mechanical pulverization and enzymatical dissociation) autologous cartilage graft. The osteochondral lesion was drill-fashioned a pit of identical dimensions as the construct. Graft-laden construct was press fit to the pit. Post-operative outcome was evaluated using Knee Injury and Osteoarthritis Outcome Score (KOOS) up to fiveyears. Regenerated tissue was sampled with arthroscopic needle biopsy for histology at oneyear, and imaged with magnetic resonance at one, three, and fiveyears to evaluate the neocartilage with MOCART chart. Subchondral bone integration was evaluated with computed tomography at three and fiveyears. Nine patients completed the five-year follow-up. Post-operative mean KOOS, except that of the "symptom" subscale, had been significantly higher than pre-operation from oneyear and maintained to fiveyears. The change of MOCRAT scores of the regenerated cartilage paralleled the change of KOOS. The osseous phase remained mineralized during the five-year period, yet did not fully integrate with the host bone. This novel construct for chondrocyte implantation yielded promising mid-term outcome. It repaired the osteochondral lesion with hyaline-like cartilage durable for at least fiveyears.

A Cellularized Biphasic Implant Based on a Bioactive Silk Fibroin Promotes Integration and Tissue Organization during Osteochondral Defect Repair in a Porcine Model.

In cartilage tissue engineering, biphasic scaffolds (BSs) have been designed not only to influence the recapitulation of the osteochondral architecture but also to take advantage of the healing ability of bone, promoting the implant’s integration with the surrounding tissue and then bone restoration and cartilage regeneration. This study reports the development and characterization of a BS based on the assembly of a cartilage phase constituted by fibroin biofunctionalyzed with a bovine cartilage matrix, cellularized with differentiated autologous pre-chondrocytes and well attached to a bone phase (decellularized bovine bone) to promote cartilage regeneration in a model of joint damage in pigs. BSs were assembled by fibroin crystallization with methanol, and the mechanical features and histological architectures were evaluated. The scaffolds were cellularized and matured for 12 days, then implanted into an osteochondral defect in a porcine model (n = 4). Three treatments were applied per knee: Group I, monophasic cellular scaffold (single chondral phase); group II (BS), cellularized only in the chondral phase; and in order to study the influence of the cellularization of the bone phase, Group III was cellularized in chondral phases and a bone phase, with autologous osteoblasts being included. After 8 weeks of surgery, the integration and regeneration tissues were analyzed via a histology and immunohistochemistry evaluation. The mechanical assessment showed that the acellular BSs reached a Young’s modulus of 805.01 kPa, similar to native cartilage. In vitro biological studies revealed the chondroinductive ability of the BSs, evidenced by an increase in sulfated glycosaminoglycans and type II collagen, both secreted by the chondrocytes cultured on the scaffold during 28 days. No evidence of adverse or inflammatory reactions was observed in the in vivo trial; however, in Group I, the defects were not reconstructed. In Groups II and III, a good integration of the implant with the surrounding tissue was observed. Defects in group II were fulfilled via hyaline cartilage and normal bone. Group III defects showed fibrous repair tissue. In conclusion, our findings demonstrated the efficacy of a biphasic and bioactive scaffold based on silk fibroin and cellularized only in the chondral phase, which entwined chondroinductive features and a biomechanical capability with an appropriate integration with the surrounding tissue, representing a promising alternative for osteochondral tissue-engineering applications.

Agili-C implant promotes the regenerative capacity of articular cartilage defects in an ex vivo model.

Osteochondral implants are currently adopted for the treatment of symptomatic full-thickness chondral and osteochondral defects. Agili-C™ is a cell-free aragonite-based scaffold which aims to reproduce the original structure and function of the articular joint while directing the growth and regeneration of both cartilage and its underlying subchondral bone. The goal of the present study was to investigate the ex vivo mechanisms of action (MOA) of the Agili-C™ implant in the repair of full-thickness cartilage defects. In particular, we tested whether Agili-C™ implant has the potential to stimulate cartilage ingrowth through chondrocytes migration into the 3D interconnected porous structure of the scaffold, along with maintaining theirviability and phenotype and the deposition of hyaline cartilage matrix. Articular cartilage samples were collected through the Gift of Hope Organ and Tissue Donor Network (Itasca, IL) within 24h from death. For this study, cartilage from a total of 14 donors was used. To model a chondral defect, donut-shaped cartilage explants were prepared from each tissue specimen. The chondral phase of the Agili-C™ implant was placed inside the tissue in full contact and press fit manner. Cartilage explants with the Agili-C™ implant inside were cultured for 60 days. As a control, the same donut-shaped cartilage explants were cultured without Agili-C™, under the same culture conditions. Using fresh human cadaveric articular cartilage tissue in a 60-day culture, it was demonstrated that chondrocytes were able to migrate into the Agili-C™ scaffold and contribute to the deposition of theextracellular matrix (ECM) rich in collagen type II and aggrecan, and lacking collagen type I. Additionally, we were able to show the formation of a layer populated by progenitor-like cells on the articular surface of the implant. The analysis of samples taken from knee and ankle joints of human donors with a wide age range and both genders supports the potential of Agili-C™ scaffold to stimulate cartilage regeneration and repair. Based on these results, the present scaffold can be used in the clinical practice as a one-step procedure to treat full-thickness chondral defects.

A Computational Model of Osteochondral Defect Repair Following Implantation of Stem Cell-Laden Multiphase Scaffolds.

Developing successful tissue engineering strategies requires an understanding of how cells within an implanted scaffold interact with the host environment. The objective of this study was to use a computational mechanobiological model to explore how the design of a cell-laden scaffold influences the spatial formation of cartilage and bone within an osteochondral defect. Tissue differentiation was predicted using a previously developed model, in which cell fate depends on the local oxygen tension and the mechanical environment within a damaged joint. This model was first updated to include a rule through which mature cartilage was resistant to both terminal differentiation and vascularization, and then used to simulate osteochondral defect repair following the implantation of various cell-free and cell-laden scaffolds. While delivery of a cell-free scaffold led to only marginal improvements in joint repair, implantation of a cell-laden bilayered scaffold was predicted to significantly increase cartilage formation in the chondral phase of the scaffold. Despite these improvements, bone still progressed into the chondral regions of these engineered implants by means of endochondral ossification during the later stages of repair. This led to thinning of the cartilage tissue, which in turn resulted in a prediction of increased tissue strain and, eventually, increases in fibrocartilage formation as a result of this altered mechanical stimulus. In contrast to this, the model predicted that implantation of a trilayered scaffold, which included a compact layer to confine angiogenesis to the osseous phase of the defect, further improves joint regeneration. This is achieved by allowing chondrogenically primed mesenchymal stem cells, which are seeded into the chondral phase of the implant, to form stable cartilage, which was ultimately resistant to both vascularization and endochondral ossification. These models provide a framework for exploring how environmental factors impact bone, cartilage, and joint regeneration and can be used to inform the design of new tissue engineering strategies for use in orthopedic medicine.

Composite scaffolds for osteochondral repair obtained by combination of additive manufacturing, leaching processes and hMSC-CM functionalization

Articular repair is a relevant and challenging area for the emerging fields of tissue engineering and biofabrication. The need of significant gradients of properties, for the promotion of osteochondral repair, has led to the development of several families of composite biomaterials and scaffolds, using different effective approaches, although a perfect solution has not yet been found. In this study we present the design, modeling, rapid manufacturing and in vitro testing of a composite scaffold aimed at osteochondral repair. The presented composite scaffold stands out for having a functional gradient of density and stiffness in the bony phase, obtained in titanium by means of computer-aided design combined with additive manufacture using selective laser sintering. The chondral phase is obtained by sugar leaching, using a PDMS matrix and sugar as porogen, and is joined to the bony phase during the polymerization of PDMS, therefore avoiding the use of supporting adhesives or additional intermediate layers. The mechanical performance of the construct is biomimetic and the stiffness values of the bony and chondral phases can be tuned to the desired applications, by means of controlled modifications of different parameters. A human mesenchymal stem cell (h-MSC) conditioned medium (CM) is used for improving scaffold response. Cell culture results provide relevant information regarding the viability of the composite scaffolds used.

Tissue engineering scaled-up, anatomically shaped osteochondral constructs for joint resurfacing.

Arthroplasty is currently the only surgical procedure available to restore joint function following articular cartilage and bone degeneration associated with diseases such as osteoarthritis (OA). A potential alternative to this procedure would be to tissue-engineer a biological implant and use it to replace the entire diseased joint. The objective of this study was therefore to tissue-engineer a scaled-up, anatomically shaped, osteochondral construct suitable for partial or total resurfacing of a diseased joint. To this end it was first demonstrated that a bone marrow derived mesenchymal stem cell seeded alginate hydrogel could support endochondral bone formation in vivo within the osseous component of an osteochondral construct, and furthermore, that a phenotypically stable layer of articular cartilage could be engineered over this bony tissue using a co-culture of chondrocytes and mesenchymal stem cells. Co-culture was found to enhance the in vitro development of the chondral phase of the engineered graft and to dramatically reduce its mineralisation in vivo. In the final part of the study, tissue-engineered grafts (~ 2 cm diameter) mimicking the geometry of medial femorotibial joint prostheses were generated using laser scanning and rapid prototyped moulds. After 8 weeks in vivo, a layer of cartilage remained on the surface of these scaled-up engineered implants, with evidence of mineralisation and bone development in the underlying osseous region of the graft. These findings open up the possibility of a tissue-engineered treatment option for diseases such as OA.

Enhancement of chondrogenic differentiation of rabbit mesenchymal stem cells by oriented nanofiber yarn-collagen type I/hyaluronate hybrid

Cartilage defects cause joint pain and loss of mobility. It is crucial to induce the chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) by both biological and structural signals in cartilage tissue engineering. Sponge-like scaffolds fabricated using native cartilage extracellular matrix components can induce the BMSC differentiation by biological signals and limited structural signals. In this study, an oriented poly(L-lactic acid)-co-poly(ε-caprolactone) P(LLA-CL)/collagen type I (Col-I) nanofiber yarn mesh, fabricated by dynamic liquid electrospinning served as a skeleton for a freeze-dried Col-I/hyaluronate (HA) chondral phase (SPONGE) containing both structural and biological signals to guide BMSC chondrogenic differentiation. In vitro results show that the Yarn Col-I/HA hybrid scaffold (Yarn-CH) promotes orientation, adhesion and proliferation of BMSCs better than SPONGE. Furthermore, BMSCs seeded on the Yarn-CH scaffold demonstrated a large increase in the glycosaminoglycan content and expression of collagen type II following a 21-day culture.

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±0.59kPa). In conclusion, the biomimetic PEG/β-TCP scaffolds with interface structure enhanced integration show promising potential application for osteochondral tissue engineering.

Osteochondral regeneration using an oriented nanofiber yarn-collagen type I/hyaluronate hybrid/TCP biphasic scaffold.

Osteochondral defects affect both the articular cartilage and the underlying subchondral bone, but poor osteochondral regeneration is still a daunting challenge. Although the tissue engineering technology provides a promising approach for osteochondral repair, an ideal biphasic scaffold is in high demand with regards to proper biomechanical strength. In this study, an oriented poly(l-lacticacid)-co-poly(ε-caprolactone) P(LLA-CL)/collagen type I(Col-I) nanofiber yarn mesh, fabricated by dynamic liquid electrospinning served as a skeleton for a freeze-dried Col-I/Hhyaluronate (HA) chondral phase (SPONGE) to enhance the mechanical strength of the scaffold. In vitro results show that the Yarn Col-I/HA hybrid scaffold (Yarn-CH) can allow the cell infiltration like sponge scaffolds. Using porous beta-tricalcium phosphate (TCP) as the osseous phase, the Yarn-CH/TCP biphasic scaffold was then assembled by freeze drying. After combination of bone marrow mesenchymal stem cells, the biphasic complex was successfully used to repair the osteochondral defects in a rabbit model with greatly improved repairing scores and compressive modulus.

Evaluation of oriented electrospun fibers for periosteal flap regeneration in biomimetic triphasic osteochondral implant

Osteochondral defects represent a serious clinical problem. Although the cell-scaffold complexes have been reported to be effective for repairing osteochondral defects, a periosteal flap is frequently needed to arrest leakage of the implanted cells into the defect and to contribute to the secretion of cytokines to stimulate cartilage repair. The electrospun mesh mimicking the function of the flap assists tissue regeneration by preventing cell leakage and merits favorable outcomes in the cartilaginous region. In this study, an oriented poly(ε-caprolactone) (PCL) fibrous membrane (OEM) was fabricated by electrospinning as a periosteal scaffold and then freeze-dried with a collagen type I and hyaluronic acid cartilage scaffold (CH) and finally, freeze-dried with a tricalcium phosphate (TCP) bone substratum. Scanning electron microscopic images show obvious microstructure formation of the trilayered scaffolds, and electrospun fibrous membranes have an oriented fibrous network structure for the periosteal phase. Also shown are opened and interconnected pores with well designed three-dimensional structure, able to be bound in the CH (chondral phase) and TCP (osseous phase) scaffolds. In vitro results showed that the OEM can promote the orientation of bone marrow mesenchymal stem cell (BMSCs) and BMSCs can penetrate into the CH and TCP. After successfully combining the BMSCs, the tissue-engineered cartilage which contained the OEM and TCP complex was successfully used to regenerate the osteochondral defects in the rabbit model with greatly improved repair effects.

Repair of large osteochondral defects in a beagle model with a novel type I collagen/glycosaminoglycan-porous titanium biphasic scaffold

The limited repair potential of articular cartilage, which hardly heals after injury or debilitating osteoarthritis, is a clinical challenge. The aim of this work was to develop a novel type I collagen (Col)/glycosaminoglycan (GAGs)-porous titanium biphasic scaffold (CGT) and verify its ability to repair osteochondral defects in an animal model with bone marrow stem cells (bMSCs) in the chondral phase. The biphasic scaffold was composed of Col/GAGs as chondral phasic and porous titanium as subchondral phasic. Twenty-four full-thickness defects through the articular cartilage and into the subchondral bone were prepared by drilling into the surface of the femoral patellar groove. Animals were assigned to one of the three groups: 1) CGT with bMSCs (CGTM), 2) only CGT, and 3) no implantation (control). The defect areas were examined grossly, histologically and by micro-CT. The most satisfied cartilage repairing result was in the CGTM group, while CGT alone was better than the control group. Abundant subchondral bone formation was observed in the CGTM and CGT groups but not the control group. Our findings demonstrate that a composite based on a novel biphasic scaffold combined with bMSCs shows a high potential to repair large osteochondral defects in a canine model.

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.

Fabrication and characterization of a biphasic scaffold for osteochondral tissue engineering

A biphasic scaffold with a stratified structure for osteochondral tissue engineering was developed. The chondral phase was a collagen–chitosan composite. The osseous phase was a composite of bioactive glass and collagen. Collagen integrated in the two respective phases was connected by cross-linking agents. Both layers of the scaffold showed interconnected porous structures. After being immersed into stimulated body fluid, precipitation of spherulitic grains could be found on the surface of the osseous phase and this precipitation was proved to be hydroxyapatite by X-ray diffraction and Fourier transform infrared spectroscopy. Inversion, fluorescence and scanning electron microscopy further confirmed that bone marrow stromal cells could anchor on this scaffold with healthy spreading. As the consequence, this biphasic scaffold may have significant potential as an alternative for osteochondral tissue engineering.

A novel MSC‐seeded triphasic construct for the repair of osteochondral defects

Mesenchymal stem cells (MSC) are increasingly replacing chondrocytes in tissue engineering based research for treatment of osteochondral defects. The aim of this work was to determine whether repair of critical-size chronic osteochondral defects in an ovine model using MSC-seeded triphasic constructs would show results comparable to osteochondral autografting (OATS). Triphasic implants were engineered using a beta-tricalcium phosphate osseous phase, an intermediate activated plasma phase, and a collagen I hydrogel chondral phase. Autologous MSCs were used to seed the implants, with chondrogenic predifferentiation of the cells used in the cartilage phase. Osteochondral defects of 4.0 mm diameter were created bilaterally in ovine knees (n = 10). Six weeks later, half of the lesions were treated with OATS and half with triphasic constructs. The knees were dissected at 6 or 12 months. With the chosen study design we were not able to demonstrate significant differences between the histological scores of both groups. Subcategory analysis of O'Driscoll scores showed superior cartilage bonding in the 6-month triphasic group compared to the autograft group. The 12-month autograft group showed superior cartilage matrix morphology compared to the 12-month triphasic group. Macroscopic and biomechanical analysis showed no significant differences at 12 months. Autologous MSC-seeded triphasic implants showed comparable repair quality to osteochondral autografts in terms of histology and biomechanical testing.

A Hyaluronate–Atelocollagen/β-Tricalcium Phosphate–Hydroxyapatite Biphasic Scaffold for the Repair of Osteochondral Defects: A Porcine Study

The authors had devised a novel biphasic scaffold combining hyaluronic acid and atelocallagen for the chondral phase and combining hydroxyapatite and beta-tricalcium phosphate for the osseous phase. Sixty-four osteochondral defects were created in the knee joints of 16 minipigs to evaluate the effectiveness of this scaffold for repairing cartilage in a large animal model. The defects were divided into five groups according to their treatment: filling with a cell/biphasic scaffold composite (Group I, 16 defects); implanting only the biphasic scaffold (Group II, 16 defects); placing the removed osteochondral fragments back into the defect (Group IIIa, 8 defects); autologous chondrocyte implantation (Group IIIb, 8 defects); leaving the defects empty (Group IV, the negative control). After 5 months, the International Cartilage Repair Society Macroscopic Score was similar in Group I (9.0), Group II (9.1), and Group IIIa (9.1), followed by Group IIIb (7.4) and Group IV (6.2). Except for three defects noted in Group IV, all the defects were filled with cartilaginous or fibrous tissue depending on the groups. The junction to the adjacent native cartilage was detectable in all the groups of minipigs. Microscopically, Group II had the highest score from the International Cartilage Repair Society Visual Histological Assessment Scale. The indentation study showed that the maximum loads and time constant of Group I, II, and IIIa defects were comparable to that of native cartilage, whereas the equilibrium loads of these groups were slightly greater than that of native cartilage. In conclusion, our results suggest that a biphasic osteochondral scaffold with a chondral phase, consisting of hyaluronate and atelocollagen, and an osseous phase, consisting of hydroxyapatite and beta-tricalcium phosphate, is effective for repairing osteochondral defects in a large animal model.