Trilayered biomimetic hydrogel scaffolds with dual-differential microenvironment for articular osteochondral defect repair

Commonly, articular osteochondral tissue exists significant differences in physiological architecture, mechanical function, and biological microenvironment. However, the development of biomimetic scaffolds incorporating upper cartilage, middle tidemark-like, and lower subchondral bone layers for precise articular osteochondral repair remains elusive. This study proposed here a novel strategy to construct the trilayered biomimetic hydrogel scaffolds with dual-differential microenvironment of both mechanical and biological factors. The cartilage-specific microenvironment was achieved through the grafting of kartogenin (KGN) into gelatin via p-hydroxyphenylpropionic acid (HPA)-based enzyme crosslinking reaction as the upper cartilage layer. The bone-specific microenvironment was achieved through the grafting of atorvastatin (AT) into gelatin via dual-crosslinked network of both HP-based enzyme crosslinking and glycidyl methacrylate (GMA)-based photo-crosslinking reactions as the lower subchondral bone layer. The introduction of tidemark-like middle layer is conducive to the formation of well-defined cartilage-bone integrated architecture. The in vitro experiments demonstrated the significant mechanical difference of three layers, successful grafting of drugs, good cytocompatibility and tissue-specific induced function. The results of in vivo experiments also confirmed the mechanical difference of the trilayered bionic scaffold and the ability of inducing osteogenesis and chondrogenesis. Furthermore, the articular osteochondral defects were successfully repaired using the trilayered biomimetic hydrogel scaffolds by the activation of endogenous recovery, which offers a promising alternative for future clinical treatment.

Non-viral gene delivery to human mesenchymal stem cells: a practical guide towards cell engineering

In recent decades, human mesenchymal stem cells (hMSCs) have gained momentum in the field of cell therapy for treating cartilage and bone injuries. Despite the tri-lineage multipotency, proliferative properties, and potent immunomodulatory effects of hMSCs, their clinical potential is hindered by donor variations, limiting their use in medical settings. To address this challenge, gene delivery technologies have emerged as a promising approach to modulate the phenotype and commitment of hMSCs towards specific cell lineages, thereby enhancing osteochondral repair strategies. This review provides a comprehensive overview of current non-viral gene delivery approaches used to engineer MSCs, highlighting key factors such as the choice of nucleic acid or delivery vector, transfection strategies, and experimental parameters. Additionally, it outlines various protocols and methods for qualitative and quantitative evaluation of their therapeutic potential as a delivery system in osteochondral regenerative applications. In summary, this technical review offers a practical guide for optimizing non-viral systems in osteochondral regenerative approaches. hMSCs constitute a key target population for gene therapy techniques. Nevertheless, there is a long way to go for their translation into clinical treatments. In this review, we remind the most relevant transfection conditions to be optimized, such as the type of nucleic acid or delivery vector, the transfection strategy, and the experimental parameters to accurately evaluate a delivery system. This survey provides a practical guide to optimizing non-viral systems for osteochondral regenerative approaches.

Implant system for large osteochondral defects

Issues with current treatments for osteochondral defects such as mosaicplasty and autologous chondrocyte implantation (ACI) are lack of donor material, problems associated with donor sites, necessity of second surgical intervention and cell expansion, difficult site preparation and implant fitting to match the surrounding tissue. This study presents the development of a patient specific implant system for focal osteochondral defects that addresses these issues. Using computer aided design and manufacturing techniques, computed tomography scans are utilized to design the implant and templates that facilitate site preparation to allow for precise and easy implantation of the designed perfectly fitting tissue replacement. Functionality of the system and accurate restoration of a defect is demonstrated by digital before/after comparison and with a prototype. With the presented implantation system larger defects in curved joint surfaces can be restored to an optimal shape in an easier procedure than for instance mosaicplasty. The proposed system potentially allows for later replacement of worn implants.

Freeze-casting osteochondral scaffolds: The presence of a nutrient-permeable film between the bone and cartilage defect reduces cartilage regeneration

Microfracture treatment that is basically relied on stem cells and growth factors in bone marrow has achieved a certain progress for cartilage repair in clinic. Nevertheless, the neocartilage generated from the microfracture strategy is limited endogenous regeneration and prone to fibrosis due to the influences of cell inflammation and vascular infiltration. To explore the crucial factor for articular cartilage remodeling, here we design a trilaminar osteochondral scaffold with a selective permeable film in middle isolation layer which can prevent stem cells, immune cells, and blood vessels in the bone marrow from invading into the cartilage layer, but allow the nutrients and cytokines to penetrate. Our findings show that the trilaminar scaffold exhibits a good biocompatibility and inflammatory regulation, but the osteochondral repair is far less effective than the control of double-layer scaffold without isolation layer. These results demonstrate that it is not adequate to rely only on nutrients and cytokines to promote reconstruction of articular cartilage, and the various cells in bone marrow are indispensable. Consequently, the current study illustrates that cell infiltration involving stem cells, immune cells and other cells from bone marrow plays a crucial role in articular cartilage remodeling based on the integrated scaffold strategy. STATEMENT OF SIGNIFICANCE: Clinical microfracture treatment plays a certain role on the restoration of injured cartilage, but the regenerative cartilage is prone to be fibrocartilage due to the modulation of bone marrow cells. Herein, we design a trilaminar osteochondral scaffold with a selective permeable film in middle isolation layer. This specific film made of dense electrospun nanofiber can prevent bone marrow cells from invading into the cartilage layer, but allow the nutrients and cytokines to penetrate. Our conclusion is that the cartilage remodeling will be extremely inhibited when the bone marrow cells are blocking. Owing to the diverse cells in bone marrow, we will further explore the influence of each cell type on cartilage repair in our continuous future work.

Knee osteochondritis dissecans-treatment technical aspects

Purpose and objective

Current treatments of different stages of knee osteochondritis Dissecans (OCD) are depending on the age of the patients and the stability of the diseased osteochondral area. The purpose of this paper was to summarize the treatment alternatives in order to simplify the choice for the treating surgeon.

Background and principle results

Osteochondritis dissecans (OCD) of the knee is an idiopathic and local osteochondral abnormality that affects mainly children and adolescents with risk of loosening of osteochondral fragments. A good clinical result can be expected when the physes are still open, when the osteochondritis is small and when the osteochondritis can be assessed as stable by MRI. Unstable OCD lesions most often need to be treated operatively by different fixation methods and when the osteochondral cannot be refixated, different local chondral and osteochondral repairs are available to fill up the defect area to congruity.

Summary and major conclusions

The final choice of which treatment to use is depending on fragment viability and forms. Viable fragments are refixated while poor quality fragments are removed followed by a local biological osteochondral repair. Such osteochondral resurfacing may be single bone marrow stimulation with or without scaffold augmentation or different cell seeded grafts.

Integrated polycaprolactone microsphere-based scaffolds with biomimetic hierarchy and tunable vascularization for osteochondral repair

Osteochondral lesion potentially causes a variety of joint degenerative diseases if it cannot be treated effectively and timely. Microfracture as the conservative surgical choice achieves limited results for the larger defect whereas cartilage patches trigger integrated instability and cartilage fibrosis. To tackle aforementioned issues, here we explore to fabricate an integrated osteochondral scaffold for synergetic regeneration of cartilage and subchondral bone in one system. On the macro level, we fabricated three integrated scaffolds with distinct channel patterns of Non-channel, Consecutive-channel and Inconsecutive-channel via Selective Laser Sintering (SLS). On the micro level, both cartilage zone and subchondral bone zone of integrated scaffold were made of small polycaprolactone (PCL) microspheres and large PCL microspheres, respectively. Our findings showed that Inconsecutive-channel scaffolds possessed integrated hierarchical structure, adaptable compression strength, gradient interconnected porosity. Cartilage zone presented a dense phase for the inhibition of vessel invasion while subchondral bone zone generated a porous phase for the ingrowth of bone and vessel. Both cartilage regeneration and subchondral bone remodeling in the group of Inconsecutive-channel scaffolds have been demonstrated by histological evaluation and immunofluorescence staining in vivo. Consequently, our current work not only achieves an effective and regenerative microsphere scaffold for osteochondral reconstruction, but also provides a feasible methodology to recover injured joint through integrated design with diverse hierarchy. STATEMENT OF SIGNIFICANCE: Recovery of osteochondral lesion highly depends on hierarchical architecture and tunable vascularization in distinct zones. We therefore design a special integrated osteochondral scaffold with inconsecutive channel structure and vascularized modulation. The channel pattern impacts on mechanical strength and the infiltration of bone marrow, and eventually triggers synergetic repair of osteochondral defect. The cartilage zone of integrated scaffolds consisted of small PCL microspheres forms a dense phase for physical restriction of vascularized infiltration whereas the subchondral bone zone made of large PCL microspheres generates porous trabecula-like structure for promoting vascularization. Consequently, the current work indicates both mechanical adaptation and regional vascularized modulation play a pivotal role on osteochondral repair.

3D Bioprinting of Biomimetic Bilayered Scaffold Consisting of Decellularized Extracellular Matrix and Silk Fibroin for Osteochondral Repair

Recently, three-dimensional (3D) bioprinting technology is becoming an appealing approach for osteochondral repair. However, it is challenging to develop a bilayered scaffold with anisotropic structural properties to mimic a native osteochondral tissue. Herein, we developed a bioink consisting of decellularized extracellular matrix and silk fibroin to print the bilayered scaffold. The bilayered scaffold mimics the natural osteochondral tissue by controlling the composition, mechanical properties, and growth factor release in each layer of the scaffold. The in vitro results show that each layer of scaffolds had a suitable mechanical strength and degradation rate. Furthermore, the scaffolds encapsulating transforming growth factor-beta (TGF-β) and bone morphogenetic protein-2 (BMP-2) can act as a controlled release system and promote directed differentiation of bone marrow-derived mesenchymal stem cells. Furthermore, the in vivo experiments suggested that the scaffolds loaded with growth factors promoted osteochondral regeneration in the rabbit knee joint model. Consequently, the biomimetic bilayered scaffold loaded with TGF-β and BMP-2 would be a promising strategy for osteochondral repair.

Bilayered scaffold with 3D printed stiff subchondral bony compartment to provide constant mechanical support for long-term cartilage regeneration

BACKGROUND/OBJECTIVE

We seek to figure out the effect of stable and powerful mechanical microenvironment provided by Ti alloy as a part of subchondral bone scaffold on long-term cartilage regeneration.Methods: we developed a bilayered osteochondral scaffold based on the assumption that a stiff subchondral bony compartment would provide stable mechanical support for cartilage regeneration and enhance subchondral bone regeneration. The subchondral bony compartment was prepared from 3D printed Ti alloy, and the cartilage compartment was created from a freeze-dried collagen sponge, which was reinforced by poly-lactic-co-glycolic acid (PLGA).

RESULTS

In vitro evaluations confirmed the biocompatibility of the scaffold materials, while in vivo evaluations demonstrated that the mechanical support provided by 3D printed Ti alloy layer plays an important role in the long-term regeneration of cartilage by accelerating osteochondral formation and its integration with the adjacent host tissue in osteochondral defect model at rabbit femoral trochlea after 24 weeks.

CONCLUSION

Mechanical support provided by 3D printing Ti alloy promotes cartilage regeneration by promoting subchondral bone regeneration and providing mechanical support platform for cartilage synergistically.

TRANSLATIONAL POTENTIAL STATEMENT

The raw materials used in our double-layer osteochondral scaffolds are all FDA approved materials for clinical use. 3D printed titanium alloy scaffolds can promote bone regeneration and provide mechanical support for cartilage regeneration, which is very suitable for clinical scenes of osteochondral defects. In fact, we are conducting clinical trials based on our scaffolds. We believe that in the near future, the scaffold we designed and developed can be formally applied in clinical practice.

Gellan gum/alginate-based Ca-enriched acellular bilayer hydrogel with robust interface bonding for effective osteochondral repair

The treatment of osteochondral (OC) defects remains challenging because of the lack of economical and feasible therapeutic strategies for OC repair and reconstruction. In this study, we report an integrated bilayer hydrogel with robust interface binding force (40 kPa) by facilitating the diffusion of calcium ions to the secondary crosslink of the bilayer hydrogel, in which gellan gum and sodium alginate acted as the chondral layer, gellan gum and hydroxyapatite acted as subchondral layer. This integrated construct has high cytocompatibility, and can seed with mesenchymal stem cells (MSCs) related to different functional protein expression for cartilage and bone formation, respectively. Furthermore, in the rabbit critical-sized osteochondral defect model (4.0 mm in diameter and 8.0 mm in depth), the calcium enriched hydrogel act as a calcium reservoir, promote neovascularization at week 4, and repair the critical defect at week 8, demonstrating the feasible preparation of an acellular hydrogel for OC repair.

Tissue Engineering Strategies to Increase Osteochondral Regeneration of Stem Cells; a Close Look at Different Modalities

The homeostasis of osteochondral tissue is tightly controlled by articular cartilage chondrocytes and underlying subchondral bone osteoblasts via different internal and external clues. As a correlate, the osteochondral region is frequently exposed to physical forces and mechanical pressure. On this basis, distinct sets of substrates and physicochemical properties of the surrounding matrix affect the regeneration capacity of chondrocytes and osteoblasts. Stem cells are touted as an alternative cell source for the alleviation of osteochondral diseases. These cells appropriately respond to the physicochemical properties of different biomaterials. This review aimed to address some of the essential factors which participate in the chondrogenic and osteogenic capacity of stem cells. Elements consisted of biomechanical forces, electrical fields, and biochemical and physical properties of the extracellular matrix are the major determinant of stem cell differentiation capacity. It is suggested that an additional certain mechanism related to signal-transduction pathways could also mediate the chondro-osteogenic differentiation of stem cells. The discovery of these clues can enable us to modulate the regeneration capacity of stem cells in osteochondral injuries and lead to the improvement of more operative approaches using tissue engineering modalities.

Developmental engineering of living implants for deep osteochondral joint surface defects

INTRODUCTION

The repair of deep osteochondral joint surface defects represents a significant unmet clinical need. Importantly, untreated lesions lead to a high rate of osteoarthritis. The current strategies to repair these defects include osteochondral autograft transplantation or "sandwich" strategies combining bone autografts with autologous chondrocyte implantation, with poorly documented long-term outcomes. In this study, we first investigated the capacity of juvenile osteochondral grafts (OCGs) to repair osteochondral defects in skeletally mature rats. With this regenerative model in view, we produced a new biological, bilayered and scaffold-free Tissue Engineered construct (bTEC) for the repair of a deep osteochondral defect of the rat knee.

METHODS

Cylindrical OCGs were excised from the femoral intercondylar groove of the knee of skeletally immature rats (5 weeks) and transplanted into osteochondral defects created in skeletally mature rats (11 weeks). To create bTECs, micromasses (μMasses) of human periosteum-derived progenitor cells (hPDCs) and human articular chondrocytes (hACs) were produced in vitro using previously optimized chemically defined medium formulations containing growth and differentiation factors including bone morphogenetic proteins. These two μMass types were subsequently implanted as bilayered constructs into osteochondral defects in nude rats. At 4 and 16 weeks after surgery, the knees were collected and processed for subsequent 3D imaging analysis and histological evaluation. Micro-computed tomography (μCT), H&E, and Safranin O staining were used to evaluate the degree and quality of tissue repair.

RESULTS

The osteochondral unit of the knee joint in 5 weeks old rats exhibits an immature phenotype, displaying active subchondral bone formation through endochondral ossification and the absence of a tidemark. When transplanted into skeletally mature animals, the immature OCGs resumed their maturation process, i.e., formed new subchondral bone, established the tidemark, and maintained their Safranin O-positive hyaline cartilage at 16 weeks after transplantation. The bTECs (hPDCs + hACs) could partially recapitulate the biology as seen with the immature OCGs, including the formation of the joint surface architecture with typical zonation, ranging from non-mineralized hyaline cartilage in the superficial layers to a progressively mineralized matrix at the interface with a new subchondral bone plate.

CONCLUSIONS

Cell-based TE constructs mimicking immature OCGs and displaying a hierarchically organized structure comprising of different tissue forming units seem an attractive strategy to treat deep osteochondral defects of the knee.

The dual character of exosomes in osteoarthritis: Antagonists and therapeutic agents

Exosomes have gained increasing attention as they participate in cell cross-talk in pathological environments and are functional paracrine factors of therapeutic stem cells. Osteoarthritis (OA) is a common age-related degenerative joint disease, leading to a debilitating lifestyle for sufferers. However, currently no drugs on the market promote cartilage repair, and the patients usually have to undergo arthroplasty in the late stage of OA. Although significant progress has been made in the development of stem cells for the treatment of OA and cartilage injury, problems like immune rejection remain. Recently, increasing evidence has demonstrated that exosomes from the joint microenvironment ("negative" exosomes) could play vital and complicated roles in the progression of OA. Moreover, exosomes from therapeutic cells ("therapeutic" exosomes) have also shown enormous potential for OA therapy/cartilage repair. Here, we first discuss the definition and biological background of exosomes. Then, we critically examine the roles of the "negative" exosomes in OA-affected joint. Then, we will cover the potential of the "therapeutic" exosomes for OA therapy/cartilage repair. Next, the recent progress of tissue engineering with exosomes, especially for OA therapy/cartilage repair, will also be discussed. Finally, the limitations and opportunities of exosome-based OA therapy will be outlined. STATEMENT OF SIGNIFICANCE: As natural extracellular vesicles, exosomes participate in the intercellular communication. On the basis of biological characteristics of exosomes, exosomes have their two sides for osteoarthritis (OA). On the one hand, exosomes in the OA microenvironment are involved in pathology of OA. On the other hand, exosomes from therapeutic cells have the potential as advanced strategies for OA therapy. In addition, the development of tissue engineering technology is beneficial to the exosome-based OA therapy. According to the latest research status, exosomes are of great significance and interest for the personalized and precision treatment of OA in the future, despite the limitations and challenges.

Sustained low-dose dexamethasone delivery via a PLGA microsphere-embedded agarose implant for enhanced osteochondral repair

Articular cartilage defects are a common source of joint pain and dysfunction. We hypothesized that sustained low-dose dexamethasone (DEX) delivery via an acellular osteochondral implant would have a dual pro-anabolic and anti-catabolic effect, both supporting the functional integrity of adjacent graft and host tissue while also attenuating inflammation caused by iatrogenic injury. An acellular agarose hydrogel carrier with embedded DEX-loaded poly(lactic-co-glycolic) acid (PLGA) microspheres (DLMS) was developed to provide sustained release for at least 99 days. The DLMS implant was first evaluated in an in vitro pro-inflammatory model of cartilage degradation. The implant was chondroprotective, as indicated by maintenance of Young's modulus (EY) (p = 0.92) and GAG content (p = 1.0) in the presence of interleukin-1β insult. In a subsequent preliminary in vivo experiment, an osteochondral autograft transfer was performed using a pre-clinical canine model. DLMS implants were press-fit into the autograft donor site and compared to intra-articular DEX injection (INJ) or no DEX (CTL). Functional scores for DLMS animals returned to baseline (p = 0.39), whereas CTL and INJ remained significantly worse at 6 months (p < 0.05). DLMS knees were significantly more likely to have improved OARSI scores for proteoglycan, chondrocyte, and collagen pathology (p < 0.05). However, no significant improvements in synovial fluid cytokine content were observed. In conclusion, utilizing a targeted DLMS implant, we observed in vitro chondroprotection in the presence of IL-1-induced degradation and improved in vivo functional outcomes. These improved outcomes were correlated with superior histological scores but not necessarily a dampened inflammatory response, suggesting a primarily pro-anabolic effect. STATEMENT OF SIGNIFICANCE: Articular cartilage defects are a common source of joint pain and dysfunction. Effective treatment of these injuries may prevent the progression of osteoarthritis and reduce the need for total joint replacement. Dexamethasone, a potent glucocorticoid with concomitant anti-catabolic and pro-anabolic effects on cartilage, may serve as an adjuvant for a variety of repair strategies. Utilizing a dexamethasone-loaded osteochondral implant with controlled release characteristics, we demonstrated in vitro chondroprotection in the presence of IL-1-induced degradation and improved in vivo functional outcomes following osteochondral repair. These improved outcomes were correlated with superior histological cartilage scores and minimal-to-no comorbidity, which is a risk with high dose dexamethasone injections. Using this model of cartilage restoration, we have for the first time shown the application of targeted, low-dose dexamethasone for improved healing in a preclinical model of focal defect repair.

Therapeutic "Tool" in Reconstruction and Regeneration of Tissue Engineering for Osteochondral Repair

Repairing osteochondral defects to restore joint function is a major challenge in regenerative medicine. However, with recent advances in tissue engineering, the development of potential treatments is promising. In recent years, in addition to single-layer scaffolds, double-layer or multilayer scaffolds have been prepared to mimic the structure of articular cartilage and subchondral bone for osteochondral repair. Although there are a range of different cells such as umbilical cord stem cells, bone marrow mesenchyml stem cell, and others that can be used, the availability, ease of preparation, and the osteogenic and chondrogenic capacity of these cells are important factors that will influence its selection for tissue engineering. Furthermore, appropriate cell proliferation and differentiation of these cells is also key for the optimal repair of osteochondral defects. The development of bioreactors has enhanced methods to stimulate the proliferation and differentiation of cells. In this review, we summarize the recent advances in tissue engineering, including the development of layered scaffolds, cells, and bioreactors that have changed the approach towards the development of novel treatments for osteochondral repair.

Beneficial clinical effects but limited tissue quality following osteochondral repair with a cell-free multilayered nano-composite scaffold in the talus

BACKGROUND

The treatment of larger osteochondral lesions of the talus remains an operative challenge. In addition to micro fracturing and osteochondral transplantation one promising strategy could be the operative repair with a cell-free multilayered nano-composite scaffold with the potential to regenerate bone and cartilage in one treatment.

METHODS

In this prospective case series four consecutive patients who suffered from a single osteochondral lesion (≥1.5cm²) on the medial talus were enrolled. The repair potential of the implant was assessed using MRI based biochemical, compositional MR sequences (T2 mapping) as well as semi-quantitative morphological analyses (MOCART score) at 18 months follow-up after the surgery. The clinical outcome was determined at 6-, 12-, 18-, and 24 months follow-up by using the Ankle Disability Index and the AOFAS score.

RESULTS

At 18 months after the surgery, the clinical outcome was significantly improved compared to the preoperative baseline. Global T2 relaxation times of the repair tissue were significantly increased compared to the healthy control cartilage.

CONCLUSIONS

Osteochondral repair with a cell-free, biomimetic scaffold provides good clinical, short-term results. However, biochemical MR imaging provides strong evidence for limited repair tissue quality at 18 months after the implantation.

LEVEL OF EVIDENCE

IV.

Tri-layered composite plug for the repair of osteochondral defects: in vivo study in sheep

Cartilage defects are a source of pain, immobility, and reduced quality of life for patients who have acquired these defects through injury, wear, or disease. The avascular nature of cartilage tissue adds to the complexity of cartilage tissue repair or regeneration efforts. The known limitations of using autografts, allografts, or xenografts further add to this complexity. Autologous chondrocyte implantation or matrix-assisted chondrocyte implantation techniques attempt to introduce cultured cartilage cells to defect areas in the patient, but clinical success with these are impeded by the avascularity of cartilage tissue. Biodegradable, synthetic scaffolds capable of supporting local cells and overcoming the issue of poor vascularization would bypass the issues of current cartilage treatment options. In this study, we propose a biodegradable, tri-layered (poly(glycolic acid) mesh/poly(l-lactic acid)-colorant tidemark layer/collagen Type I and ceramic microparticle-coated poly(l-lactic acid)-poly(ϵ-caprolactone) monolith) osteochondral plug indicated for the repair of cartilage defects. The porous plug allows the continual transport of bone marrow constituents from the subchondral layer to the cartilage defect site for a more effective repair of the area. Assessment of the in vivo performance of the implant was conducted in an ovine model (n = 13). In addition to a control group (no implant), one group received the implant alone (Group A), while another group was supplemented with hyaluronic acid (0.8 mL at 10 mg/mL solution; Group B). Analyses performed on specimens from the in vivo study revealed that the implant achieves cartilage formation within 6 months. No adverse tissue reactions or other complications were reported. Our findings indicate that the porous biocompatible implant seems to be a promising treatment option for the cartilage repair.

A novel aragonite-based scaffold for osteochondral regeneration: early experience on human implants and technical developments

INTRODUCTION

Chondral and osteochondral lesions represent a debilitating disease. Untreated lesions remain a risk factor for more extensive joint damage. The objective of this clinical study is to evaluate safety and early results of an aragonite-based scaffold used for osteochondral unit repair, by analysing both clinical outcome and MRI results, as well as the benefits of the procedure optimization through novel tapered shaped implants.

METHODS

A crystalline aragonite bi-phasic scaffold was implanted in patients affected by focal chondral-osteochondral knee lesions of the condyle and trochlea. Twenty-one patients (17 men, 4 women with a mean age of 31.0 ± 8.6 years) without severe OA received tapered shaped implants for the treatment of 2.5 ±1.7 cm² sized defects. The control group consisted of 76 patients selected according to the same criteria from a database of patients who previously underwent implantation of cylindrical-shaped implants. The clinical outcome of all patients was evaluated with the IKDC subjective score, the Lysholm score, and all 5 KOOS subscales administered preoperatively and at 6 and 12 months after surgery, while MRI evaluation was performed at the 12 month follow-up.

RESULTS

A statistically significant improvement in all clinical scores was documented both in the tapered implants and the cylindrical group. No difference could be detected in the comparison between the improvement obtained with the two implant types, neither in the clinical nor in imaging evaluations. A difference could be detected instead in terms of revision rate, which was lower in the tapered implant group with no implant removal - 0% vs 8/76-10.5% failures in the cylindrical implants.

CONCLUSIONS

This study highlighted both safety and potential of a novel aragonite-based scaffold for the treatment of chondral and osteochondral lesions in humans. A tapered shape relative to the cylindrical shaped implant design, improved the scaffold's safety profile. Tapered scaffolds maintain the clinical improvement observed in cylindrical implants while reducing the postoperative risk of revision surgery. This aragonite-based implant was associated with a significant clinical improvement at the 12 month follow-up. Moreover, MRI findings revealed graft integration with good bone and cartilage formation.

Restore a 9 mm diameter osteochondral defect with gene enhanced tissue engineering followed mosaicplasty in a goat model

Objective

The aim of this study was to evaluate the efficacy of gene enhanced tissue engineering followed mosaicplasty in a goat model.

Methods

An acute cylindrical defect 9 mm in diameter was created in the weight bearing area of the medial femoral condyle in a goat model. Thirty-six medial femoral condyles were divided into 6 groups using different proportion of gene enhanced tissue engineering and mosaicplasty to restore the defects. The specimen received gross and histology observation, which was evaluated by the histological grading scale of O'Driscoll, Keeley and Salter. Transmission electron microscope observation was also performed. Two factors analysis of variance and Student-Newman-Kewls test were used to compare the specimen.

Results

The gross and histology observation revealed that each defects of six groups had different restoration. The scores of the reparative tissue of three groups with gene enhancement were significantly higher than those in other three groups without gene enhancement (p > 0.05).

Conclusion

Gene enhanced tissue engineering followed mosaicplasty could restore a 9 mm diameter osteochondral defects in a goat model effectively. With the reduction of covering area of the graft, the advantages of the combined gene enhanced tissue engineering method can be better reflected.

Successful osteoconduction but limited cartilage tissue quality following osteochondral repair by a cell-free multilayered nano-composite scaffold at the knee

INTRODUCTION

The treatment of larger osteochondral lesions in the knee is still a clinical challenge. One promising strategy to overcome this problem could be surgical repair by using a cell-free multilayered nano-composite scaffold.

METHOD

In this prospective cohort study eight consecutive patients which suffered from a single osteochondral lesion (≥1.5 cm(2)) on the femoral condyle were enrolled. The repair potential of the implant was assessed by using MRI based biochemical MR sequences (T2 mapping) as well as semi-quantitative morphological analyses (MOCART score) at 18 months after the surgery. The clinical outcome was determined at six, 12, 18, and 24 month follow ups by using IKDC, Tegner-Lysholm, and Cincinnati knee scores.

RESULTS

Seven out of eight patients showed a complete integration of the scaffold into the border zone and five out of eight patients excellent or good subchondral ossification of the implant at 18 months following implantation. The surface of the repair tissue was found to be intact in all eight patients. T2 mapping data and the zonal T2 index significantly differed in the repair tissue compared to the healthy control cartilage (P < 0.001) which indicates a limited quality of the repair cartilage. The clinical outcome scores consistently improved during the follow up period without reaching statistical significance.

CONCLUSIONS

Osteochondral repair by implanting the MaioRegen® scaffold provides a successful osteoconduction and filling of the cartilage defect. However there is evidence for a limited repair cartilage tissue quality at 18 months after the surgery.

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.

Repair of osteochondral defects in a rabbit model using a porous hydroxyapatite collagen composite impregnated with bone morphogenetic protein-2

Articular cartilage has a limited capacity for spontaneous repair, and an effective method to repair damaged articular cartilage has not yet been established. The purpose of this study was to evaluate the effect of transplantation of porous hydroxyapatite collagen (HAp/Col) impregnated with bone morphogenetic protein-2 (BMP-2). To evaluate the characteristics of porous HAp/Col as a drug delivery carrier of recombinant human BMP-2 (rhBMP-2), the rhBMP-2 adsorption capacity and release kinetics of porous HAp/Col were analyzed. Porous HAp/Col impregnated with different amounts of rhBMP-2 (0, 5, and 25 μg) was implanted into osteochondral defects generated in the patellar groove of Japanese white rabbits to evaluate the effect on osteochondral defect regeneration. At 3, 6, 12, and 24 weeks after operation, samples were harvested and subjected to micro-computed tomography analysis and histological evaluation of articular cartilage and subchondral bone repair. The adsorption capacity was 329.4 μg of rhBMP-2 per cm(3) of porous HAp/Col. Although 36% of rhBMP-2 was released within 24 h, more than 50% of the rhBMP-2 was retained in the porous HAp/Col through the course of the experiment. Defects treated with 5 μg of rhBMP-2 showed the most extensive subchondral bone repair and the highest histological regeneration score, and differences against the untreated defect group were significant. The histological regeneration score of defects treated with 25 μg of rhBMP-2 increased up to 6 weeks after implantation, but then decreased. Porous HAp/Col, therefore, is an appropriate carrier for rhBMP-2. Implantation of porous HAp/Col impregnated with rhBMP-2 is effective for rigid subchondral bone repair, which is important for the repair of the smooth articular surface.

Strategies for controlled delivery of biologics for cartilage repair

The delivery of biologics is an important component in the treatment of osteoarthritis and the functional restoration of articular cartilage. Numerous factors have been implicated in the cartilage repair process, but the uncontrolled delivery of these factors may not only reduce their full reparative potential but can also cause unwanted morphological effects. It is therefore imperative to consider the type of biologic to be delivered, the method of delivery, and the temporal as well as spatial presentation of the biologic to achieve the desired effect in cartilage repair. Additionally, the delivery of a single factor may not be sufficient in guiding neo-tissue formation, motivating recent research toward the delivery of multiple factors. This review will discuss the roles of various biologics involved in cartilage repair and the different methods of delivery for appropriate healing responses. A number of spatiotemporal strategies will then be emphasized for the controlled delivery of single and multiple bioactive factors in both in vitro and in vivo cartilage tissue engineering applications.

Osteochondral tissue engineering using a biphasic collagen/GAG scaffold containing rhFGF18 or BMP-7 in an ovine model

BACKGROUND

The aim of this study was to investigate the effect of combining rhFGF18 or BMP-7 with a biphasic collagen/GAG osteochondral scaffold (Chondromimetic) on the repair of osteochondral defects in sheep.

METHODS

Osteochondral defects (5.8x6mm) were created in the medial femoral condyle (MFC) and the lateral trochlea sulcus (LTS) of the stifle joint of 24 female sheep. Sheep were randomly assigned to four groups (n = 6); 1) empty defect, 2) scaffold only, 3) scaffold + rhFGF-18 (30 μg) and 4) scaffold + BMP-7 (100 μg). At 6 months the defects underwent non-destructive mechanical testing, gross assessment of repair tissue (ICRS score) and histological analysis (Modified O'Driscoll score).

RESULTS

ICRS repair score: Defects treated with scaffold + rhFGF18 (mean 9.83, 95% CI 8.43-11.23) and scaffold + BMP-7 (10, 9.06-10.94) in the MFC had significantly improved ICRS scores compared to empty defects (4.2, 0-8.80) (p = 0.002). Mechanical properties: BMP-7 treated defects (mean 64.35, 95% CI 56.88-71.82) were significantly less stiff than both the rhFGF18 (mean 84.1, 95% CI 76.8-91.4) and empty defects in the LTS, compared to both contralateral limb (p = 0.003), and the perilesional articular cartilage (p < 0.001).

HISTOLOGY

A statistically significant improvement in the modified O'Driscoll score was observed in the rhFGF18 treated group (mean 16.83, 95% CI 13.65-20.61) compared to the empty defects (mean 9, 95% CI 4.88-13.12) (p = 0.039) in the MFC. Excellent tissue fill, lateral integration and proteoglycan staining was observed. Only the rhFGF18 defects showed pericellular type VI collagen staining with positive type II collagen and reduced positive type I collagen staining. The majority of defects in the control and BMP-7 groups demonstrated fibrocartilagenous repair tissue.

CONCLUSION

Statistically significant improvements in gross repair, mechanical properties and histological score were found over empty defects when Chondromimetic was combined with rhFGF18. These results suggest that rhFGF18 may play a significant role in articular cartilage repair applications.

Osteochondral defect repair using bilayered hydrogels encapsulating both chondrogenically and osteogenically pre-differentiated mesenchymal stem cells in a rabbit model

OBJECTIVE

To investigate the ability of cell-laden bilayered hydrogels encapsulating chondrogenically and osteogenically (OS) pre-differentiated mesenchymal stem cells (MSCs) to effect osteochondral defect repair in a rabbit model. By varying the period of chondrogenic pre-differentiation from 7 (CG7) to 14 days (CG14), the effect of chondrogenic differentiation stage on osteochondral tissue repair was also investigated.

METHODS

Rabbit MSCs were subjected to either chondrogenic or osteogenic pre-differentiation, encapsulated within respective chondral/subchondral layers of a bilayered hydrogel construct, and then implanted into femoral condyle osteochondral defects. Rabbits were randomized into one of four groups (MSC/MSC, MSC/OS, CG7/OS, and CG14/OS; chondral/subchondral) and received two similar constructs bilaterally. Defects were evaluated after 12 weeks.

RESULTS

All groups exhibited similar overall neo-tissue filling. The delivery of OS cells when compared to undifferentiated MSCs in the subchondral construct layer resulted in improvements in neo-cartilage thickness and regularity. However, the addition of CG cells in the chondral layer, with OS cells in the subchondral layer, did not augment tissue repair as influenced by the latter when compared to the control. Instead, CG7/OS implants resulted in more irregular neo-tissue surfaces when compared to MSC/OS implants. Notably, the delivery of CG7 cells, when compared to CG14 cells, with OS cells stimulated morphologically superior cartilage repair. However, neither osteogenic nor chondrogenic pre-differentiation affected detectable changes in subchondral tissue repair.

CONCLUSIONS

Cartilage regeneration in osteochondral defects can be enhanced by MSCs that are chondrogenically and osteogenically pre-differentiated prior to implantation. Longer chondrogenic pre-differentiation periods, however, lead to diminished cartilage repair.

Strategies for osteochondral repair: Focus on scaffolds

Interest in osteochondral repair has been increasing with the growing number of sports-related injuries, accident traumas, and congenital diseases and disorders. Although therapeutic interventions are entering an advanced stage, current surgical procedures are still in their infancy. Unlike other tissues, the osteochondral zone shows a high level of gradient and interfacial tissue organization between bone and cartilage, and thus has unique characteristics related to the ability to resist mechanical compression and restoration. Among the possible therapies, tissue engineering of osteochondral tissues has shown considerable promise where multiple approaches of utilizing cells, scaffolds, and signaling molecules have been pursued. This review focuses particularly on the importance of scaffold design and its role in the success of osteochondral tissue engineering. Biphasic and gradient composition with proper pore configurations are the basic design consideration for scaffolds. Surface modification is an essential technique to improve the scaffold function associated with cell regulation or delivery of signaling molecules. The use of functional scaffolds with a controllable delivery strategy of multiple signaling molecules is also considered a promising therapeutic approach. In this review, we updated the recent advances in scaffolding approaches for osteochondral tissue engineering.