A preliminary study of osteochondral regeneration using a scaffold-free three-dimensional construct of porcine adipose tissue-derived mesenchymal stem cells

Scaffold-free 3D culture systems for stem cell-based tissue regeneration

Recent advances in scaffold-free three-dimensional (3D) culture methods have significantly enhanced the potential of stem cell-based therapies in regenerative medicine. This cutting-edge technology circumvents the use of exogenous biomaterial and prevents its associated complications. The 3D culture system preserves crucial intercellular interactions and extracellular matrix support, closely mimicking natural biological niches. Therefore, stem cells cultured in 3D formats exhibit distinct characteristics, showcasing their capabilities in promoting angiogenesis and immunomodulation. This review aims to elucidate foundational technologies and recent breakthroughs in 3D scaffold-free stem cell engineering, offering comprehensive guidance for researchers to advance this technology across various clinical applications. We first introduce the various sources of stem cells and provide a comparative analysis of two-dimensional (2D) and 3D culture systems. Given the advantages of 3D culture systems, we delve into the specific fabrication and harvesting techniques for cell sheets and spheroids. Furthermore, we explore their applications in pre-clinical studies, particularly in large animal models and clinical trials. We also discuss multidisciplinary strategies to overcome existing limitations such as insufficient efficacy, hostile microenvironments, and the need for scalability and standardization of stem cell-based products.

Bone Regeneration of Rat Critical-Sized Calvarial Defects by the Combination of Photobiomodulation and Adipose-Derived Mesenchymal Stem Cells

Introduction: This study explored the synergistic effects of low-level laser therapy (LLLT) and adipose-derived stem cells (ADSCs) on cranial bone regeneration in rats, addressing the limitations of autogenous grafts and advancing bone tissue engineering with innovative photobiomodulation (PBM) applications. Methods: Sixty Wistar rats were allocated to 5 separate groups randomly; (1) natural bovine bone mineral (NBBM); (2) NBBM+LLLT; (3) NBBM+allogenic ADSCs; (4) NBBM+allogenic ADSCs+LLLT; (5) Only defects. 8-mm calvarial defects were made in each rat in the surgical procedure. A diode laser was applied with the following parameters (continuous mode, power of 100mW, wavelength of 808nm, and 4 J/cm2 energy density) immediately after the procedure and every other day. Bone samples were obtained and assessed histomorphometrically and histologically after staining with hematoxylin and eosin (H&E). Results: Different volumes of bony material were observed in two weeks; 2.94%±1.00 in group 1, 5.1%±1.92 in group 2, 7.11%±2.82 in group 3, 7.34%±2.31 in group 4, and 2.01%±0.83 in group 5 (P<0.05). On the other hand, foreign body residuals were up by 23% in the groups with scaffolding by the end of 2 weeks. Four weeks of observation led to 6.74 %±1.95, 13.24%±1.98, 15.76%±1.19, 15.92%±3.4, and 3.11%±1.00 bone formation in groups 1 to 5, respectively (P<0.05). Generally, the difference between groups 2-4 was not statistically significant based on different types of bone and the extent of inflammation. Conclusion: Bearing in mind the limitations of our research, it was demonstrated that ADSCs in combination with PBM have promising effects on bone tissue regeneration in sizeable bony defects. Furthermore, this study also showed that PBM usage improved the newly regenerated bone quality.

Articular Cartilage Regeneration through Bioassembling Spherical Micro-Cartilage Building Blocks

Articular cartilage lesions are prevalent and affect one out of seven American adults and many young patients. Cartilage is not capable of regeneration on its own. Existing therapeutic approaches for articular cartilage lesions have limitations. Cartilage tissue engineering is a promising approach for regenerating articular neocartilage. Bioassembly is an emerging technology that uses microtissues or micro-precursor tissues as building blocks to construct a macro-tissue. We summarize and highlight the application of bioassembly technology in regenerating articular cartilage. We discuss the advantages of bioassembly and present two types of building blocks: multiple cellular scaffold-free spheroids and cell-laden polymer or hydrogel microspheres. We present techniques for generating building blocks and bioassembly methods, including bioprinting and non-bioprinting techniques. Using a data set of 5069 articles from the last 28 years of literature, we analyzed seven categories of related research, and the year trends are presented. The limitations and future directions of this technology are also discussed.

Cell therapies for chondral defects of the talus: a systematic review

Background

This systematic review investigated the efficacy and safety of surgical procedures augmented with cell therapies for chondral defects of the talus.

Methods

The present systematic review was conducted according to the 2020 PRISMA guidelines. PubMed, Google scholar, Embase, and Scopus databases were accessed in March 2022. All the clinical trials investigating surgical procedures for talar chondral defects augmented with cell therapies were accessed. The outcomes of interest were to investigate whether surgical procedures augmented with cell therapies promoted improvement in patients reported outcomes measures (PROMs) with a tolerable rate of complications.

Results

Data from 477 procedures were retrieved. At a mean follow-up of 34.8 ± 9.7 months, the Visual Analogic Scale (VAS) improved of 4.4/10 (P = 0.002) and the American Orthopaedic Foot and Ankle Score (AOFAS) of 31.1/100 (P = 0.0001) points. No improvement was found in Tegner score (P = 0.4). Few articles reported data on complications. At last follow-up, the rate of reoperation and failure were 0.06% and 0.03%, respectively. No graft delamination or hypertrophy was observed.

Conclusion

The current evidence suggests that cell therapies may be effective and safe to enhance surgical procedures for chondral defects of the talus. These results should be considered within the limitations of the present study. The current literature should be enriched with randomized controlled clinical trials with larger population size and longer follow-up.

Cell Aggregate Assembly through Microengineering for Functional Tissue Emergence

Compared to cell suspensions or monolayers, 3D cell aggregates provide cellular interactions organized in space and heterogeneity that better resume the real organization of native tissues. They represent powerful tools to narrow down the gap between in vitro and in vivo models, thanks to their self-evolving capabilities. Recent strategies have demonstrated their potential as building blocks to generate microtissues. Developing specific methodologies capable of organizing these cell aggregates into 3D architectures and environments has become essential to convert them into functional microtissues adapted for regenerative medicine or pharmaceutical screening purposes. Although the techniques for producing individual cell aggregates have been on the market for over a decade, the methodology for engineering functional tissues starting from them is still a young and quickly evolving field of research. In this review, we first present a panorama of emerging cell aggregates microfabrication and assembly technologies. We further discuss the perspectives opened in the establishment of functional tissues with a specific focus on controlled architecture and heterogeneity to favor cell differentiation and proliferation.

Optimization of a Tricalcium Phosphate-Based Bone Model Using Cell-Sheet Technology to Simulate Bone Disorders

Bone diseases such as osteoporosis, delayed or impaired bone healing, and osteoarthritis still represent a social, financial, and personal burden for affected patients and society. Fully humanized in vitro 3D models of cancellous bone tissue are needed to develop new treatment strategies and meet patient-specific needs. Here, we demonstrate a successful cell-sheet-based process for optimized mesenchymal stromal cell (MSC) seeding on a β-tricalcium phosphate (TCP) scaffold to generate 3D models of cancellous bone tissue. Therefore, we seeded MSCs onto the β-TCP scaffold, induced osteogenic differentiation, and wrapped a single osteogenically induced MSC sheet around the pre-seeded scaffold. Comparing the wrapped with an unwrapped scaffold, we did not detect any differences in cell viability and structural integrity but a higher cell seeding rate with osteoid-like granular structures, an indicator of enhanced calcification. Finally, gene expression analysis showed a reduction in chondrogenic and adipogenic markers, but an increase in osteogenic markers in MSCs seeded on wrapped scaffolds. We conclude from these data that additional wrapping of pre-seeded scaffolds will provide a local niche that enhances osteogenic differentiation while repressing chondrogenic and adipogenic differentiation. This approach will eventually lead to optimized preclinical in vitro 3D models of cancellous bone tissue to develop new treatment strategies.

Implication of Mesenchymal Stem Cells and Their Derivates for Osteochondral Regeneration

Healing of articular cartilage defects presents a challenging issue, due to its regenerative shortcomings. Lacking vascularity and innervation of cartilage and low proliferative potential of chondrocytes are the main reasons for the limited healing potential of articular cartilage. Traditional reparative approaches are limited in their efficiency, hence there is a demand for novel reparative treatments. Mesenchymal stromal cells, preferred for clinical uses, can be readily derived from various sources and have been proven to have a therapeutic effect on cartilage and subchondral bone. Therefore, mesenchymal stromal cells, their derivates, and scaffolds have been utilized in research targeting osteochondral regeneration. The present review aims to comprehensively outline and discuss literature considering this topic published within last 5 years.

Scaffold-free approaches for the fabrication of engineered articular cartilage tissue

Tissue engineered cartilaginous constructs have meet great advances in the past decades as a treatment for osteoarthritis, a degenerative disease affecting people all over the world as the population ages. Scaffold-free tissue engineered constructs are designed and developed in recent years with only cells and cell-derived matrix involved. Scaffold-free tissue constructs do not require cell adherence on exogenous materials and are superior to scaffold-based constructs in (1) relying on only cells to produce matrix, (2) not interfering cell-cell signaling, cell migration or small molecules diffusion after implantation and (3) introducing no exogenous impurities. In this review, three main scaffold-free methodologies for cartilage tissue engineering, the cell sheet technology, the phase transfer cell culture-living hyaline cartilage graft (PTCC-LhCG) system and the cell aggregate-based (bottom-up) methods, were reviewed, covering mold fabrication, decellularization and 3D bioprinting. The recent advances, medical applications, superiority and drawbacks were elaborated in detail.

Osteochondral regeneration of the femoral medial condyle by using a scaffold-free 3D construct of synovial membrane-derived mesenchymal stem cells in horses

Background

Medical interventions for subchondral bone cysts in horses have been extensively studied. This study investigated the regeneration of articular cartilage and subchondral bone with scaffold-free three-dimensional (3D) constructs of equine synovial membrane-derived mesenchymal stem cells (SM-MSCs) isolated from three ponies and expanded until over 1.0 × 107 cells at passage 2 (P2).

Results

SM-MSCs were strongly positive for CD11a/CD18, CD44, and major histocompatibility complex (MHC) class I; moderately positive for CD90, CD105, and MHC class II; and negative for CD34 and CD45 on flow cytometry and differentiated into osteogenic, chondrogenic, and adipogenic lineages in the tri-lineage differentiation assay. After culturing SM-MSCs until P3, we prepared a construct (diameter, 6.3 mm; height, 5.0 mm) comprising approximately 1920 spheroids containing 3.0 × 104 cells each. This construct was confirmed to be positive for type I collagen and negative for type II collagen, Alcian blue, and Safranin-O upon histological analysis and was subsequently implanted into an osteochondral defect (diameter, 6.8 mm; depth, 5.0 mm) at the right femoral medial condyle. The contralateral (left femoral) defect served as the control. At 3 and 6 months after surgery, the radiolucent volume (RV, mm3) of the defects was calculated based on multiplanar reconstruction of computed tomography (CT) images. Magnetic resonance (MR) images were evaluated using a modified two-dimensional MR observation of cartilage repair tissue (MOCART) grading system, while macroscopic (gross) and microscopic histological characteristics were scored according to the International Cartilage Repair Society (ICRS) scale. Compared to the control sites, the implanted defects showed lower RV percentages, better total MOCART scores, higher average gross scores, and higher average histological scores.

Conclusions

Implantation of a scaffold-free 3D-construct of SM-MSCs into an osteochondral defect could regenerate the original structure of the cartilage and subchondral bone over 6 months post-surgery in horses, indicating the potential of this technique in treating equine subchondral bone cysts.

Overcoming the Dependence on Animal Models for Osteoarthritis Therapeutics - The Promises and Prospects of In Vitro Models

Osteoarthritis (OA) is a musculoskeletal disease characterized by progressive degeneration of osteochondral tissues. Current treatment is restricted to the reduction of pain and loss of function of the joint. To better comprehend the OA pathophysiological conditions, several models are employed, however; there is no consensus on a suitable model. In this review, different in vitro models being developed for possible therapeutic intervention of OA are outlined. Herein, various in vitro OA models starting from 2D model, co-culture model, 3D models, dynamic culture model to advanced technologies-based models such as 3D bioprinting, bioassembly, organoids, and organ-on-chip-based models are discussed with their advantages and disadvantages. Besides, different growth factors, cytokines, and chemicals being utilized for induction of OA condition are reviewed in detail. Furthermore, there is focus on scrutinizing different molecular and possible therapeutic targets for better understanding the mechanisms and OA therapeutics. Finally, the underlying challenges associated with in vitro models are discussed followed by future prospective. Taken together, a comprehensive overview of in vitro OA models, factors to induce OA-like conditions, and intricate molecular targets with the potential to develop personalized osteoarthritis therapeutics in the future with clinical translation is provided.

Mesangiogenic Progenitor Cells Are Tissue Specific and Cannot Be Isolated From Adipose Tissue or Umbilical Cord Blood

Mesangiogenic progenitor cells (MPCs) have been isolated from human bone marrow (BM) mononuclear cells. They attracted particular attention for the ability to differentiate into exponentially growing mesenchymal stromal cells while retaining endothelial differentiative potential. MPC power to couple mesengenesis and angiogenesis highlights their tissue regenerative potential and clinical value, with particular reference to musculoskeletal tissues regeneration. BM and adipose tissue represent the most promising adult multipotent cell sources for bone and cartilage repair, although discussion is still open on their respective profitability. Culture determinants, as well as tissues of origin, appeared to strongly affect the regenerative potential of cell preparations, making reliable methods for cell isolation and growth a prerequisite to obtain cell-based medicinal products. Our group had established a definite consistent protocol for MPC culture, and here, we present data showing MPCs to be tissue specific.

Fracture Healing Research-Shift towards In Vitro Modeling?

Fractures are one of the most frequently occurring traumatic events worldwide. Approximately 10% of fractures lead to bone healing disorders, resulting in strain for affected patients and enormous costs for society. In order to shed light into underlying mechanisms of bone regeneration (habitual or disturbed), and to develop new therapeutic strategies, various in vivo, ex vivo and in vitro models can be applied. Undeniably, in vivo models include the systemic and biological situation. However, transferability towards the human patient along with ethical concerns regarding in vivo models have to be considered. Fostered by enormous technical improvements, such as bioreactors, on-a-chip-technologies and bone tissue engineering, sophisticated in vitro models are of rising interest. These models offer the possibility to use human cells from individual donors, complex cell systems and 3D models, therefore bridging the transferability gap, providing a platform for the introduction of personalized precision medicine and finally sparing animals. Facing diverse processes during fracture healing and thus various scientific opportunities, the reliability of results oftentimes depends on the choice of an appropriate model. Hence, we here focus on categorizing available models with respect to the requirements of the scientific approach.

Human Adipose-Derived Stromal/Stem Cell Culture and Analysis Methods for Adipose Tissue Modeling In Vitro: A Systematic Review

Human adipose-derived stromal/stem cells (hASC) are widely used for in vitro modeling of physiologically relevant human adipose tissue. These models are useful for the development of tissue constructs for soft tissue regeneration and 3-dimensional (3D) microphysiological systems (MPS) for drug discovery. In this systematic review, we report on the current state of hASC culture and assessment methods for adipose tissue engineering using 3D MPS. Our search efforts resulted in the identification of 184 independent records, of which 27 were determined to be most relevant to the goals of the present review. Our results demonstrate a lack of consensus on methods for hASC culture and assessment for the production of physiologically relevant in vitro models of human adipose tissue. Few studies have assessed the impact of different 3D culture conditions on hASC adipogenesis. Additionally, there has been a limited use of assays for characterizing the functionality of adipose tissue in vitro. Results from this study suggest the need for more standardized culture methods and further analysis on in vitro tissue functionality. These will be necessary to validate the utility of 3D MPS as an in vitro model to reduce, refine, and replace in vivo experiments in the drug discovery regulatory process.

Biofabrication and bioprinting using cellular aggregates, microtissues and organoids for the engineering of musculoskeletal tissues

The modest clinical impact of musculoskeletal tissue engineering (TE) can be attributed, at least in part, to a failure to recapitulate the structure, composition and functional properties of the target tissue. This has motivated increased interest in developmentally inspired TE strategies, which seek to recapitulate key events that occur during embryonic and post-natal development, as a means of generating truly biomimetic grafts to replace or regenerate damaged tissues and organs. Such TE strategies can be substantially enabled by emerging biofabrication and bioprinting strategies, and in particular the use of cellular aggregates, microtissues and organoids as 'building blocks' for the development of larger tissues and/or organ precursors. Here, the application of such biological building blocks for the engineering of musculoskeletal tissues, from vascularised bone to zonally organised articular cartilage, will be reviewed. The importance of first scaling-down to later scale-up will be discussed, as this is viewed as a key component of engineering functional grafts using cellular aggregates or microtissues. In the context of engineering anatomically accurate tissues of scale suitable for tissue engineering and regenerative medicine applications, novel bioprinting modalities and their application in controlling the process by which cellular aggregates or microtissues fuse and self-organise will be reviewed. Throughout the paper, we will highlight some of the key challenges facing this emerging field. STATEMENT OF SIGNIFICANCE: The field of bioprinting has grown substantially in recent years, but despite the hype and excitement it has generated, there are relatively few examples of bioprinting strategies producing implants with superior regenerative potential to that achievable with more traditional tissue engineering approaches. This paper provides an up-to-date review of emerging biofabrication and bioprinting strategies which use cellular aggregates and microtissues as 'building blocks' for the development of larger musculoskeletal tissues and/or organ precursors - a field of research that can potentially enable functional regeneration of damaged and diseased tissues. The application of cellular aggregates and microtissues for the engineering of musculoskeletal tissues, from vascularised bone to zonally organised articular cartilage, will be reviewed. In the context of engineering anatomically accurate tissues of scale, novel bioprinting modalities and their application in controlling the process by which cellular aggregates or microtissues self-organise is addressed, as well as key challenges facing this emerging field.

Comparison of Genetically Engineered Immunodeficient Animal Models for Nonclinical Testing of Stem Cell Therapies

For the recovery or replacement of dysfunctional cells and tissue-the goal of stem cell research-successful engraftment of transplanted cells and tissues are essential events. The event is largely dependent on the immune rejection of the recipient; therefore, the immunogenic evaluation of candidate cells or tissues in immunodeficient animals is important. Understanding the immunodeficient system can provide insights into the generation and use of immunodeficient animal models, presenting a unique system to explore the capabilities of the innate immune system. In this review, we summarize various immunodeficient animal model systems with different target genes as valuable tools for biomedical research. There have been numerous immunodeficient models developed by different gene defects, resulting in many different features in phenotype. More important, mice, rats, and other large animals exhibit very different immunological and physiological features in tissue and organs, including genetic background and a representation of human disease conditions. Therefore, the findings from this review may guide researchers to select the most appropriate immunodeficient strain, target gene, and animal species based on the research type, mutant gene effects, and similarity to human immunological features for stem cell research.

Scaffold-Free Cartilage Construct from Infrapatellar Fat Pad Stem Cells for Cartilage Restoration

Once damaged, the articular cartilage has a very limited intrinsic capacity for self-renewal due to its avascular nature. If left untreated, damaged cartilage can lead to progressive degeneration of bone and eventually causes pain. Infrapatellar fat pad adipose-derived mesenchymal stromal cells (IPFP-ASCs) has a potential role for cartilage restoration. However, the therapeutic role for IPFP-ASCs remains to be evaluated in an appropriate osteochondral defect model. Thus, this study aimed to investigate the potential of using a three-dimensional (3D) cartilage construct of IPFP-ASCs as a promising source of cells to restore articular cartilage and to attenuate pain associated with the cartilage defect in an osteochondral defect model. The chondrogenic differentiation potential of the 3D cartilage construct derived from IPFP-ASCs was determined before implantation and postimplantation by gene expression and immunohistochemistry analysis. Pain-related behavior was also assessed by using a weight-bearing test. A significant pain-associated with the osteochondral defect was observed in this model in all groups postinduction; however, this pain can spontaneously resolve within 3 weeks postimplantation regardless of implantation of IPFP-ASCs constructs. The expression of SOX9 and COL2A1 genes in addition to protein expression were strongly expressed in 3D construct IPFP-ASCs. The existence of mature chondrocytes, along with significant (p < 0.05) positive immunostaining for type II collagen and aggrecan, were identified in the implanted site for up to 12 weeks compared with the untreated group, indicating hyaline cartilage regeneration. Taken together, this study demonstrated the successful outcome of osteochondral regeneration with scaffold-free IPFP-ASCs constructs in an osteochondral defect rat model. It provides novel and interesting insights into the current hypothesis that 3D construct IPFP-ASCs may offer potential benefits as an alternative approach to repair the cartilage defect. Impact statement This study provides evidence of using the human 3D scaffold-free infrapatellar fat pad adipose-derived mesenchymal stromal cells (IPFP-ASCs) construct to restore the full-thickness osteochondral defect in a rat model. This study showed that chondrogenic features of the construct could be retained for up to 12 weeks postimplantation. The results of this proof-of-concept study support that human 3D scaffold-free IPFP-ASCs construct has potential benefits in promoting the hyaline-like native cartilage restoration, which may be beneficial as a tissue-specific stem cell for cell-based cartilage therapy. There are several clinical advantages of IPFP-ASC including ease and minimal invasive harvesting, chondrogenic inducible property, and tissue-specific progenitors in the knee.

Expanded mesenchymal stem cell transplantation following marrow stimulation is more effective than marrow stimulation alone in treatment of knee cartilage defect: A systematic review and meta-analysis

BACKGROUND

Articular cartilage defect of the knee is a debilitating disease and marrow stimulation techniques (MST) is typically regarded as the first line of treatment for full thickness cartilage lesions. However, the ability of MST to induce the repair of cartilage defects with fibrocartilage is limited, raising concerns about the durability of the repaired tissue. Mesenchymal stem cells (MSCs) provide an alternative means of treating cartilage defects. Expanded MSCs transplantation following MST has achieved great success in animal studies, but relevant clinical results are still lacking.

HYPOTHESIS

Expanded MSCs transplantation could be an effective adjunctive therapy following MST for knee cartilage defects.

PATIENTS AND METHODS

PubMed, EMBASE, and the Cochrane Library were systematically searched. This investigation considers articles that compare the effectiveness of expanded MSCs transplantation following MST (MSCs/MST) with that of MST alone for treating knee cartilage defects. Data on postoperative clinical outcomes were extracted. In an attempt to analyze trends over time in studies that report repeated measurements, an all time-points meta-analysis (ATM) was undertaken.

RESULTS

Five randomized controlled trials (RCTs) were included in this study. In a pooled analysis, the MSCs/MST group exhibited statistically significantly better postoperative international knee documentation committee subjective knee form (IKDC score) than the MST alone group during two years of follow-up (trend estimate through ATM, 0.27; 95% CI: 0.006 to 0.54). Lysholm scores were similarly favorable to MSCs/MST. The MSCs/MST group also yielded a statistically significantly higher magnetic resonance observation of cartilage repair tissue (MOCART) score at final follow-up (Mean Difference, 16.42; 95% CI: 4.44 to 28.40). No trial has identified serious adverse effects.

DISCUSSION

This meta-analysis demonstrate that expanded MSCs transplantation is a safe and effective adjunctive therapy. Further RCTs with long-term follow up and cost effectiveness analysis are needed.

LEVEL OF EVIDENCE

I, Systematic review and meta-analysis.

Scaffold-Free Bio-3D Printing Using Spheroids as "Bio-Inks" for Tissue (Re-)Construction and Drug Response Tests

In recent years, scaffold-free bio-3D printing using cell aggregates (spheroids) as "bio-inks" has attracted increasing attention as a method for 3D cell construction. Bio-3D printing uses a technique called the Kenzan method, wherein spheroids are placed one-by-one in a microneedle array (the "Kenzan") using a bio-3D printer. The bio-3D printer is a machine that was developed to perform bio-3D printing automatically. Recently, it has been reported that cell constructs can be produced by a bio-3D printer using spheroids composed of many types of cells and that this can contribute to tissue (re-)construction. This progress report summarizes the production and effectiveness of various cell constructs prepared using bio-3D printers. It also considers the future issues and prospects of various cell constructs obtained by using this method for further development of scaffold-free 3D cell constructions.

Osteochondral regeneration using scaffold-free constructs of adipose tissue-derived mesenchymal stem cells made by a bio three-dimensional printer with a needle-array in rabbits

Osteoarthritis is a major joint disease for which medical interventions have been extensively investigated in humans and animals. In this study, we examined the regeneration of articular cartilage and subchondral bone using a scaffold-free construct consisting of adipose tissue-derived mesenchymal stem cells (AT-MSCs) fabricated using a bio three-dimensional (3D) printer. AT-MSCs were isolated from three rabbits and cultured to a number of sufficient for creation of 3D-printed constructs. One construct consisted of 960 spheroids obtained from 3.5 × 10⁴ autologous AT-MSCs. The construct was then implanted into an osteochondral defect (diameter 4 mm and depth 4 mm) surgically bored into the left femoral trochlear groove of each rabbit. Three months after implantation, healing was assessed by computed tomography, magnetic resonance (MR) imaging, and pathology. MR images were evaluated based on a modified two-dimensional (2D)-magnetic resonance observation of cartilage repair tissue (MOCART) grading system, and gross and microscopic histology were scored according to the International Cartilage Repair Society scale. At the time of imaging, treated defects had become radiopaque, while control defects remained radiolucent. Total 2D-MOCART scores were higher in the implanted defects than in the controls, but not to a statistically significant extent. Similarly, average histological scores were comparable among all groups, although average gross scores were significantly higher in implanted defects than in controls. This is the first demonstration of a scaffold-free 3D-printed construct consisting of autologous AT-MSCs regenerating cartilage and subchondral bone within three months.

Osteochondral Regeneration Using Adipose Tissue-Derived Mesenchymal Stem Cells

Osteoarthritis (OA) is a major joint disease that promotes locomotor deficiency during the middle- to old-age, with the associated disability potentially decreasing quality of life. Recently, surgical strategies to reconstruct both articular cartilage and subchondral bone for OA have been diligently investigated for restoring joint structure and function. Adipose tissue-derived mesenchymal stem cells (AT-MSCs), which maintain pluripotency and self-proliferation ability, have recently received attention as a useful tool to regenerate osteocartilage for OA. In this review, several studies were described related to AT-MSC spheroids, with scaffold and scaffold-free three-dimensional (3D) constructs produced using “mold” or “Kenzan” methods for osteochondral regeneration. First, several examples of articular cartilage regeneration using AT-MSCs were introduced. Second, studies of osteochondral regeneration (not only cartilage but also subchondral bone) using AT-MSCs were described. Third, examples were presented wherein spheroids were produced using AT-MSCs for cartilage regeneration. Fourth, osteochondral regeneration following autologous implantation of AT-MSC scaffold-free 3D constructs, fabricated using the “mold” or “Kenzan” method, was considered. Finally, prospects of osteochondral regeneration by scaffold-free 3D constructs using AT-MSC spheroids were discussed.

Cartilage tissue engineering combining microspheroid building blocks and microneedle arrays

Purpose: Scaffold-free cartilage tissue engineering circumvents issues with scaffold seeding, potential toxicity response, and impaired host integration. However, precisely controlling and maintaining a scaffold-free construct shape have been challenging. We explored the feasibility of microneedle arrays to print tissue using cellular microspheroids as building blocks.Materials and Methods: Human embryonic-derived mesenchymal stem cells or infrapatellar fat pad mesenchymal stem cells were used to create microspheroids of 500 µm in diameter, which were assembled on microneedle arrays in a predefined arrangement using a robotic system under computer vision. Microspheroids on microneedles were cultured to permit fusion into a tissue construct. Infrapatellar fat pad mesenchymal stem cell constructs were either implanted into chondral defects created in human osteoarthritic cartilage explants or maintained on the microneedle array for 3 weeks. Embryonic-derived mesenchymal stem cell constructs were designed to be press-fit into 3 mm subchondral defects in New Zealand White rabbits and maintained for up to 8 weeks to assess retention, early tissue repair, and more mature cartilage regeneration.Results: Microspheroids of both cell types fused together in culture to form neotissues of predefined shape and size. Infrapatellar fat pad mesenchymal stem cell neotissues expressed high levels of chondrogenic genes and integrated with the surrounding osteoarthritic host cartilage. Embryonic-derived mesenchymal stem cell constructs generated chondrogenic neotissue in vivo as early as 2 weeks and more mature tissue by 8 weeks with increased glycosaminoglycan deposition.Conclusions: We constructed defined scaffold-free shapes by bioprinting and fusing microspheroids. Proof of concept was shown in the repair of ex vivo osteoarthritic human cartilage and in vivo rabbit osteochondral (OC) defects.

Cartilage and bone tissue engineering using adipose stromal/stem cells spheroids as building blocks

Scaffold-free techniques in the developmental tissue engineering area are designed to mimic in vivo embryonic processes with the aim of biofabricating, in vitro, tissues with more authentic properties. Cell clusters called spheroids are the basis for scaffold-free tissue engineering. In this review, we explore the use of spheroids from adult mesenchymal stem/stromal cells as a model in the developmental engineering area in order to mimic the developmental stages of cartilage and bone tissues. Spheroids from adult mesenchymal stromal/stem cells lineages recapitulate crucial events in bone and cartilage formation during embryogenesis, and are capable of spontaneously fusing to other spheroids, making them ideal building blocks for bone and cartilage tissue engineering. Here, we discuss data from ours and other labs on the use of adipose stromal/stem cell spheroids in chondrogenesis and osteogenesis in vitro. Overall, recent studies support the notion that spheroids are ideal "building blocks" for tissue engineering by “bottom-up” approaches, which are based on tissue assembly by advanced techniques such as three-dimensional bioprinting. Further studies on the cellular and molecular mechanisms that orchestrate spheroid fusion are now crucial to support continued development of bottom-up tissue engineering approaches such as three-dimensional bioprinting.

Computational fluid dynamic analysis of bioprinted self-supporting perfused tissue models

Natural tissues are incorporated with vasculature, which is further integrated with a cardiovascular system responsible for driving perfusion of nutrient‐rich oxygenated blood through the vasculature to support cell metabolism within most cell‐dense tissues. Since scaffold‐free biofabricated tissues being developed into clinical implants, research models, and pharmaceutical testing platforms should similarly exhibit perfused tissue‐like structures, we generated a generalizable biofabrication method resulting in self‐supporting perfused (SSuPer) tissue constructs incorporated with perfusible microchannels and integrated with the modular FABRICA perfusion bioreactor. As proof of concept, we perfused an MLO‐A5 osteoblast‐based SSuPer tissue in the FABRICA. Although our resulting SSuPer tissue replicated vascularization and perfusion observed in situ, supported its own weight, and stained positively for mineral using Von Kossa staining, our in vitro results indicated that computational fluid dynamics (CFD) should be used to drive future construct design and flow application before further tissue biofabrication and perfusion. We built a CFD model of the SSuPer tissue integrated in the FABRICA and analyzed flow characteristics (net force, pressure distribution, shear stress, and oxygen distribution) through five SSuPer tissue microchannel patterns in two flow directions and at increasing flow rates. Important flow parameters include flow direction, fully developed flow, and tissue microchannel diameters matched and aligned with bioreactor flow channels. We observed that the SSuPer tissue platform is capable of providing direct perfusion to tissue constructs and proper culture conditions (oxygenation, with controllable shear and flow rates), indicating that our approach can be used to biofabricate tissue representing primary tissues and that we can model the system in silico.

Biomechanical issues of tissue-engineered constructs for articular cartilage regeneration: in vitro and in vivo approaches

BACKGROUND

Given the limited regenerative capacity of injured articular cartilage, the absence of suitable therapeutic options has encouraged tissue-engineering approaches for its regeneration or replacement.

SOURCES OF DATA

Published articles in any language identified in PubMed and Scopus electronic databases up to August 2019 about the in vitro and in vivo properties of cartilage engineered constructs. A total of 64 articles were included following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

AREAS OF AGREEMENT

Regenerated cartilage lacks the biomechanical and biological properties of native articular cartilage.

AREAS OF CONTROVERSY

There are many different approaches about the development of the architecture and the composition of the scaffolds.

GROWING POINTS

Novel tissue engineering strategies focus on the development of cartilaginous biomimetic materials able to repair cartilage lesions in association to cell, trophic factors and gene therapies.

AREAS TIMELY FOR DEVELOPING RESEARCH

A multi-layer design and a zonal organization of the constructs may lead to achieve cartilage regeneration.

A Rabbit Model of Osteochondral Regeneration Using Three-Dimensional Printed Polycaprolactone-Hydroxyapatite Scaffolds Coated with Umbilical Cord Blood Mesenchymal Stem Cells and Chondrocytes

BACKGROUND This study aimed to investigate a rabbit model of osteochondral regeneration using three-dimensional (3-D) printed polycaprolactone-hydroxyapatite (PCL-HA) scaffolds coated with umbilical cord blood mesenchymal stem cells (UCB-MSCs) and chondrocytes. MATERIAL AND METHODS Nine female New Zealand white rabbits were included in the study. The 3-D PCL-HA scaffolds were prepared using fused deposition modeling 3-D printing technology. Seeding cells were prepared by co-culture of rabbit UCB-MSCs and chondrocytes with a ratio of 3: 1. A total of 4×10⁶ cells were seeded on 3-D PCL-HA scaffolds and implanted into rabbits with femoral trochlear defects. After 8 weeks of in vivo implantation, 12 specimens were sampled and examined using histology and scanning electron microscopy (SEM). The International Cartilage Repair Society (ICRS) macroscopic scores and histological results were recorded and compared with those of the unseeded PCL-HA scaffolds. RESULTS Mean ICRS scores for the UCB-MSCs and chondrocyte-seeded PCL-HA scaffolds (group A) were significantly higher than the normal unseeded control (NC) PCL-HA scaffold group (group B) (P<0.05). Histology with safranin-O and fast-green staining showed that the UCB chondrocyte-seeded PCL-HA scaffolds significantly promoted bone and cartilage regeneration. CONCLUSIONS In a rabbit model of osteochondral regeneration using 3-D printed PCL-HA scaffolds, the UCB chondrocyte-seeded PCL-HA scaffold promoted articular cartilage repair when compared with the control or non-seeded PCL-HA scaffolds.

Transplantation of Aggregates of Autologous Synovial Mesenchymal Stem Cells for Treatment of Cartilage Defects in the Femoral Condyle and the Femoral Groove in Microminipigs

BACKGROUND

Previous work has demonstrated that patients with cartilage defects of the knee benefit from arthroscopic transplantation of autologous synovial mesenchymal stem cells (MSCs) in terms of magnetic resonance imaging (MRI), qualitative histologic findings, and Lysholm score. However, the effectiveness was limited by the number of cells obtained, so large-sized defects (>500 mm²) were not investigated. The use of MSC aggregates may enable treatment of larger defects by increasing the number of MSCs adhering to the cartilage defect.

PURPOSE

To investigate whether transplantation of aggregates of autologous synovial MSCs with 2-step surgery could promote articular cartilage regeneration in microminipig osteochondral defects.

STUDY DESIGN

Controlled laboratory study.

METHODS

Synovial MSCs derived from a microminipig were examined for in vitro colony-forming and multidifferentiation abilities. An aggregate of 250,000 synovial MSCs was formed with hanging drop culture, and 16 aggregates (for each defect) were implanted on both osteochondral defects (6 × 6 × 1.5 mm) created in the medial femoral condyle and femoral groove (MSC group). The defects in the contralateral knee were left empty (control group). The knee joints were evaluated at 4 and 12 weeks by macroscopic findings and histology. MRI T1rho mapping images were acquired at 12 weeks. For cell tracking, synovial MSCs were labeled with ferucarbotran before aggregate formation and were observed with MRI at 1 week.

RESULTS

Synovial MSCs showed in vitro colony-forming and multidifferentiation abilities. Regenerative cartilage formation was significantly better in the MSC group than in the control group, as indicated by International Cartilage Repair Society score (macro), modified Wakitani score (histology), and T1rho mapping (biochemical MRI) in the medial condyle at 12 weeks. Implanted cells, labeled with ferucarbotran, were observed in the osteochondral defects at 1 week with MRI. No significant difference was noted in the modified Wakitani score at 4 weeks in the medial condyle and at 4 and 12 weeks in the femoral groove.

CONCLUSION

Transplantation of autologous synovial MSC aggregates promoted articular cartilage regeneration at the medial femoral condyle at 12 weeks in microminipigs.

CLINICAL RELEVANCE

Aggregates of autologous synovial MSCs could expand the indications for cartilage repair with synovial MSCs.

Spontaneous Age-Related Histopathological Changes in Microminipigs

Microminipigs have become an attractive animal model for toxicology and pharmacology studies and for human disease models, owing to their manageable size. Although there are numerous reports of spontaneous age-related lesions in mice, rats, dogs, and monkeys, those in minipigs are scarce. In the present study, spontaneous age-related histopathological changes were investigated using 37 microminipigs (20 males and 17 females) that were 6 months to 10 years of age. Abnormal deposits of materials were evident in several animals from 6 years of age, and these deposits included amyloid in the renal medulla, thyroid gland, and adrenal gland, hyaline droplets in glomeruli, and fibrillar inclusions in neurons. Arterial sclerosing changes (intimal thickening, intimal proliferation, and medial mineralization) and proliferative lesions (hyperplasia of hepatocytes, follicular cells, Leydig cells, and uterine endometrial glands) were present at 4 years of age and beyond. Renal adenoma, uterine leiomyoma, and Leydig cell tumor were observed in several microminipigs. Moreover, glomerulosclerosis, renal interstitial fibrosis, thymic involution, and adrenocortical cell vacuolation were common in aging microminipigs. Since knowledge of age-related changes is helpful for pathologists, the basic information obtained in this study will be a useful reference for all future toxicity evaluations in microminipigs.

[Current progress of research and use of microminipigs in drug development]

The use of minipigs has been increasing in the areas of pharmacology researches and drug development. The microminipig developed by Fuji Micra Inc. (Shizuoka, Japan) inherits characteristics of other pig strains showing several similarities to humans in anatomy, physiology, omnivorousness and diurnal, but at the same time has several advantages over other pig strains because of its small size which allows easy keeping, handling and dosing, and saving of test substances. The microminipig weighs about 10 kg at the age of 6 months. Canine cages can be used to keep the animal. Swine leukocyte antigens (SLA) are defined in each individual animal which is useful for testing immunological reactions. As there are many similarities in metabolic enzymes and transporters to those in humans, the microminipig is a powerful animal model for toxicokinetic studies. Unfortunately as in other minipigs the microminipig is not appropriate for embryo-fetal development studies of antibody drugs due to its poor placental transfer, but can be used for other reproductive and developmental studies. Repeat dose toxicity, safety pharmacology, immunotoxicity and local tolerance studies should be also other arenas of this animal model.

Osteochondral regeneration using constructs of mesenchymal stem cells made by bio three-dimensional printing in mini-pigs

Osteoarthritis is a major joint disease that has been extensively investigated in humans and in model animals. In this study, we examined the regeneration of articular cartilage and subchondral bone using artificial scaffold-free constructs composed of adipose tissue-derived mesenchymal stem cells (AT-MSCs) created using bio three-dimensional (3D) printing with a needle-array. Printed constructs were implanted into osteochondral defects created in the right femoral trochlear groove of six mini-pigs, using femoral defects created in the left femurs as controls. Repair within the defects was evaluated at 3 and 6 months post-implantation using computed tomography (CT) and magnetic resonance (MR) imaging. The radiolucent volume (RV, mm³ ) in the defects was calculated using multi-planar reconstruction of CT images. MR images were evaluated based on a modified 2D- MOCART (magnetic resonance observation of cartilage repair tissue) grading system. Gross and microscopic pathology were scored according to the ICRS (International Cartilage Repair Society) scale at 6 months after implantation. The percentage RV at 3 months postoperation was significantly lower in the implanted defects than in the controls, whereas total scores based on the MOCART system were significantly higher in the implanted defects as compared with the controls. Although there were no statistical differences in the gross scores, the average histological scores were significantly higher in the implanted defects than in the controls. To our knowledge, this is the first report to suggest that artificial scaffold-free 3D-printed constructs of autologous AT-MSCs can be aid in the osteochondral regeneration in pigs. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1398-1408, 2019.

A pilot study of regenerative therapy by implanting synovium-derived mesenchymal stromal cells in equine osteochondral defect models

Synovium-derived mesenchymal stromal cells (SM-MSCs) from seven Thoroughbreds with naturally occurring intra-articular fracture proliferated to over ten million cells by the second passage. Using three experimental Thoroughbreds, columnar osteochondral defects were made arthroscopically at the bilateral distal radius. Five million allogenic SM-MSCs were implanted into the right defect, and another five million were injected into the right radio-carpal joint (implantation site). No SM-MSCs were implanted into the left defect or the same joint (control site). At 3 and 6 weeks after surgery, ten million autologous SM-MSCs were injected into the right joints. Radiolucent volumes of defects calculated by analysis of postmortem CT images 9 weeks after surgery were decreased in implanted sites compared with control sites in all horses. The average scores for ICRS gross and histopathological grading scales in implanted sites were equal to or higher than those of the controls. These results suggest that allogenic implantation and subsequent autologous injection of SM-MSCs might not obstruct subchondral bone formation in defects.

Analysis of Cell Spheroid Morphological Characteristics Using the Spheroid Morphology Evaluation System

Our research group established a technology for forming three-dimensional cell constructs to regenerate osteochondro cells without scaffolding. The established technology employed spheroids to form cell constructs. We also developed a method for arranging spheroids in arbitrary positions to form cell constructs in complex shapes. However, we could only form cell constructs as expected when the formed spheroids were the appropriate sizes. This study, therefore, aimed to chronologically analyze the spheroid morphological characteristics of rabbit mechanical stem cells using the developed spheroid morphological evaluation system. We set the numbers of cells/wells as 2 × 104, 3 × 104, 4 × 104, 5 × 104, 6 × 104, and 7 × 104 and the passage number as 7. Further, we observed the cultured spheroids every 24 hours after seeding for five days. The analysis enabled us to specify an optimal range for the numbers of cells required to form spheroids with high degrees of circularity. We could also control the formed spheroid sizes by adjusting the cell count and culturing time.

Autologous fat grafting: Latest insights

A recent rise in the use of autologous fat transfer for soft tissue augmentation has paralleled the increasing popularity of liposuction body contouring. This creates a readily available and inexpensive product for lipografting, which is the application of lipoaspirated material. Consistent scientific proof about the long-term viability of the transferred fat is not available. Clinically, there is a reabsorption rate which has been reported to range from 20 to 90%. Results can be unpredictable with overcorrection and regular need for additional interventions. In this review, adipogenesis physiology and the adipogenic cascade from adipose-derived stem cells to adult adipocytes is extensively described to determine various procedures involved in the fat grafting technique. Variables in structure and physiology, adipose tissue harvesting- and processing techniques, and the preservation of fat grafts are taken into account to collect reproducible scientific data to establish standard in vitro and in vivo models for experimental fat grafting. Adequate histological staining for fat tissue, immunohistochemistry and viability assays should be universally used in experiments to be able to produce comparative results. By analysis of the applied methods and comparison to similar experiments, a conclusion concerning the ideal technique to improve clinical outcome is proposed.

•

Adipogenic physiology is described to determine various procedures involved in the fat grafting technique.

•

Clinical studies on fat grafting have confirmed an unpredictable result.

•

After analysis of the literature and despite attempts to eliminate confounding factors, on every step of the fat transfer technique a number of studies with conflicting results exist.

•

Adequate histological staining for fat tissue, immunohistochemistry and viability assays should be universally used in experiments to be able to produce comparative results.

Buccal Fat Pad-Derived Stem Cells in Three-Dimensional Rehabilitation of Large Alveolar Defects: A Report of Two Cases

This case report seeks to describe efficient clinical application of adipose-derived stem cells (AdSCs) originated from buccal fat pad (BFP) in combination with conventional guided bone regeneration as protected healing space for reconstruction of large alveolar defects after extraction of multiple impacted teeth. The first case was a 19-year-old woman with several impacted teeth in the maxillary and mandibular regions, which could not be forced to erupt and were recommended for surgical extraction by the orthodontist. After this procedure, a large bone defect was created, and this space was filled by AdSC loaded natural bovine bone mineral (NBBM), which was protected with lateral ramus cortical plates, microscrews, and collagen membrane. After 6 months of post-guided bone regeneration, the patient received 6 and 7 implant placements, respectively, in the maxilla and mandible. At 10 months postoperatively, radiographic evaluation revealed thorough survival of implants. The second case was a 22-year-old man with the same complaint and large bony defects created after his teeth were extracted. After 6 months of post-guided bone regeneration, he received 4 dental implants in his maxilla and 7 implants in the mandible. At 48 months postoperatively, radiographs showed complete survival of implants. This approach represented a considerable amount of 3-dimensional bone formation in both cases, which enabled us to use dental implant therapy for rehabilitation of the whole dentition. The application of AdSCs isolated from BFP in combination with NBBM can be considered an efficient treatment for bone regeneration in large alveolar bone defects.

Recent Advances in Tissue Engineering Strategies for the Treatment of Joint Damage

PURPOSE OF REVIEW

While the clinical potential of tissue engineering for treating joint damage has yet to be realized, research and commercialization efforts in the field are geared towards overcoming major obstacles to clinical translation, as well as towards achieving engineered grafts that recapitulate the unique structures, function, and physiology of the joint. In this review, we describe recent advances in technologies aimed at obtaining biomaterials, stem cells, and bioreactors that will enable the development of effective tissue-engineered treatments for repairing joint damage.

RECENT FINDINGS

3D printing of scaffolds is aimed at improving the mechanical structure and microenvironment necessary for bone regeneration within a damaged joint. Advances in our understanding of stem cell biology and cell manufacturing processes are informing translational strategies for the therapeutic use of allogeneic and autologous cells. Finally, bioreactors used in combination with cells and biomaterials are promising strategies for generating large tissue grafts for repairing damaged tissues in pre-clinical models. Together, these advances along with ongoing research directions are making tissue engineering increasingly viable for the treatment of joint damage.

Engineering principles for guiding spheroid function in the regeneration of bone, cartilage, and skin

There is a critical need for strategies that effectively enhance cell viability and post-implantation performance in order to advance cell-based therapies. Spheroids, which are dense cellular aggregates, overcome many current limitations with transplanting individual cells. Compared to individual cells, the aggregation of cells into spheroids results in increased cell viability, together with enhanced proangiogenic, anti-inflammatory, and tissue-forming potential. Furthermore, the transplantation of cells using engineered materials enables localized delivery to the target site while providing an opportunity to guide cell fate in situ, resulting in improved therapeutic outcomes compared to systemic or localized injection. Despite promising early results achieved by freely injecting spheroids into damaged tissues, growing evidence demonstrates the advantages of entrapping spheroids within a biomaterial prior to implantation. This review will highlight the basic characteristics and qualities of spheroids, describe the underlying principles for how biomaterials influence spheroid behavior, with an emphasis on hydrogels, and provide examples of synergistic approaches using spheroids and biomaterials for tissue engineering applications.

Translational Application of Microfluidics and Bioprinting for Stem Cell-Based Cartilage Repair

Cartilage defects can impair the most elementary daily activities and, if not properly treated, can lead to the complete loss of articular function. The limitations of standard treatments for cartilage repair have triggered the development of stem cell-based therapies. In this scenario, the development of efficient cell differentiation protocols and the design of proper biomaterial-based supports to deliver cells to the injury site need to be addressed through basic and applied research to fully exploit the potential of stem cells. Here, we discuss the use of microfluidics and bioprinting approaches for the translation of stem cell-based therapy for cartilage repair in clinics. In particular, we will focus on the optimization of hydrogel-based materials to mimic the articular cartilage triggered by their use as bioinks in 3D bioprinting applications, on the screening of biochemical and biophysical factors through microfluidic devices to enhance stem cell chondrogenesis, and on the use of microfluidic technology to generate implantable constructs with a complex geometry. Finally, we will describe some new bioprinting applications that pave the way to the clinical use of stem cell-based therapies, such as scaffold-free bioprinting and the development of a 3D handheld device for the in situ repair of cartilage defects.

The Synergy of Scaffold-Based and Scaffold-Free Tissue Engineering Strategies

Tissue engineering (TE) is a highly interdisciplinary research field driven by the goal to restore, replace, or regenerate defective tissues. Throughout more than two decades of intense research, different technological approaches, which can be principally categorized into scaffold-based and scaffold-free strategies, have been developed. In this opinion article, we discuss the emergence of a third strategy in TE. This synergetic strategy integrates the advantages of both of these traditional approaches, while being clearly distinct from them. Its characteristic attributes, numerous practical benefits, and recent literature reports supporting our opinion, are discussed in detail.

Stem Cells for Cartilage Repair: Preclinical Studies and Insights in Translational Animal Models and Outcome Measures

Due to the restricted intrinsic capacity of resident chondrocytes to regenerate the lost cartilage postinjury, stem cell-based therapies have been proposed as a novel therapeutic approach for cartilage repair. Moreover, stem cell-based therapies using mesenchymal stem cells (MSCs) or induced pluripotent stem cells (iPSCs) have been used successfully in preclinical and clinical settings. Despite these promising reports, the exact mechanisms underlying stem cell-mediated cartilage repair remain uncertain. Stem cells can contribute to cartilage repair via chondrogenic differentiation, via immunomodulation, or by the production of paracrine factors and extracellular vesicles. But before novel cell-based therapies for cartilage repair can be introduced into the clinic, rigorous testing in preclinical animal models is required. Preclinical models used in regenerative cartilage studies include murine, lapine, caprine, ovine, porcine, canine, and equine models, each associated with its specific advantages and limitations. This review presents a summary of recent in vitro data and from in vivo preclinical studies justifying the use of MSCs and iPSCs in cartilage tissue engineering. Moreover, the advantages and disadvantages of utilizing small and large animals will be discussed, while also describing suitable outcome measures for evaluating cartilage repair.

Xeno-free pre-vascularized spheroids for therapeutic applications

Spheroid culture has gained increasing popularity, arising as a promising tool for regenerative medicine applications. Importantly, spheroids may present advantages over single-cell suspensions in cell-based therapies (CT). Unfortunately, most growth media used for spheroid culture contain animal origin-components, such as fetal bovine serum (FBS). The presence of FBS compromises the safety of CT and presents economic and ethical constraints. SCC (supplement for cell culture) is a novel xeno-free (XF) industrial cell culture supplement, derived from well-controlled pooled human plasma and processed under good manufacturing practice rules. Here, we developed a XF SCC-based formulation for 2D-culture of outgrowth endothelial cells (OEC), and then used it for generating co-culture spheroids of OEC and mesenchymal stem cells (MSC). XF MSC-OEC spheroids were characterized in detail and compared to spheroids cultured in FBS-supplemented medium. XF spheroids presented comparable integrity, size and morphology as the reference culture. The use of both media resulted in spheroids with similar structure, abundant extracellular matrix deposition and specific patterns of OEC distribution and organization. Notably, XF spheroids presented significantly enhanced angiogenic potential, both in vitro (fibrin sprouting assay) and in vivo (CAM assay). These findings are particularly promising in the context of potential therapeutic applications.

Tissue Engineering Strategies for Osteochondral Repair

Tissue engineering strategies have been pushing forward several fields in the range of biomedical research. The musculoskeletal field is not an exception. In fact, tissue engineering has been a great asset in the development of new treatments for osteochondral lesions. Herein, we overview the recent developments in osteochondral tissue engineering. Currently, the treatments applied in a clinical scenario have shown some drawbacks given the difficulty in regenerating a fully functional hyaline cartilage. Among the different strategies designed for osteochondral regeneration, it is possible to identify cell-free strategies, scaffold-free strategies, and advanced strategies, where different materials are combined with cells. Cell-free strategies consist in the development of scaffolds in the attempt to better fulfill the requirements of the cartilage regeneration process. For that, different structures have been designed, from monolayers to multilayered structures, with the intent to mimic the osteochondral architecture. In the case of scaffold-free strategies, they took advantage on the extracellular matrix produced by cells. The last strategy relies in the development of new biomaterials capable of mimicking the extracellular matrix. This way, the cell growth, proliferation, and differentiation at the lesion site are expedited, exploiting the self-regenerative potential of cells and its interaction with biomolecules. Overall, despite the difficulties associated with each approach, tissue engineering has been proven a valuable tool in the regeneration of osteochondral lesions and together with the latest advances in the field, promises to revolutionize personalized therapies.

Successful Low-Cost Scaffold-Free Cartilage Tissue Engineering Using Human Cartilage Progenitor Cell Spheroids Formed by Micromolded Nonadhesive Hydrogel

The scaffold-free tissue engineering using spheroids is pointed out as an approach for optimizing the delivery system of cartilage construct. In this study, we aimed to evaluate the micromolded nonadhesive hydrogel (MicroTissues®) for spheroid compaction (2-day culture) and spontaneous chondrogenesis (21-day culture) using cartilage progenitors cells (CPCs) from human nasal septum without chondrogenic stimulus. CPC spheroids showed diameter stability (486 μm ± 65), high percentage of viable cells (88.1 ± 2.1), and low percentage of apoptotic cells (2.3%). After spheroid compaction, the synthesis of TGF-β1, TGF-β2, and TGF-β3 was significantly higher compared to monolayer (p < 0.005). Biomechanical assay revealed that the maximum forces applied to spheroids after chondrogenesis were 2.6 times higher than for those cultured for 2 days. After spontaneous chondrogenesis, CPC spheroids were entirely positive for N-cadherin, collagen type II and type VI, and aggrecan and chondroitin sulfate. Comparing to monolayer, the expression of SOX5 and SOX6 genes analyzed by qPCR was significantly upregulated (p < 0.01). Finally, we observed the capacity of CPC spheroids starting to fuse. To the best of our knowledge, this is the first time in the scientific literature that human CPC spheroids were formed by micromolded nonadhesive hydrogel, achieving a successful scaffold-free cartilage engineering without chondrogenic stimulus (low cost).

Lateral Ramus Cortical Bone Plate in Alveolar Cleft Osteoplasty with Concomitant Use of Buccal Fat Pad Derived Cells and Autogenous Bone: Phase I Clinical Trial

Tissue regeneration has become a promising treatment for craniomaxillofacial bone defects such as alveolar clefts. This study sought to assess the efficacy of lateral ramus cortical plate with buccal fat pad derived mesenchymal stem cells (BFSCs) in treatment of human alveolar cleft defects. Ten patients with unilateral anterior maxillary cleft met the inclusion criteria and were assigned to three treatment groups. First group was treated with anterior iliac crest (AIC) bone and a collagen membrane (AIC group), the second group was treated with lateral ramus cortical bone plate (LRCP) with BFSCs mounted on a natural bovine bone mineral (LRCP+BFSC), and the third group was treated with AIC bone, BFSCs cultured on natural bovine bone mineral, and a collagen membrane (AIC+BFSC). The amount of regenerated bone was measured using cone beam computed tomography 6 months postoperatively. AIC group showed the least amount of new bone formation (70 ± 10.40%). LRCP+BFSC group demonstrated defect closure and higher amounts of new bone formation (75 ± 3.5%) but less than AIC+BFSC (82.5 ± 6.45%), suggesting that use of BFSCs within LRCP cage and AIC may enhance bone regeneration in alveolar cleft bone defects; however, the differences were not statistically significant. This clinical trial was registered at clinicaltrial.gov with NCT02859025 identifier.

Adipose-derived stem cells in orthopaedic pathologies

INTRODUCTION

To examine the current literature regarding the clinical application of adipose-derived stem cells (ADSCs) for the management of orthopaedic pathologies.

SOURCES OF DATA

MEDLINE,SCOPUS, CINAHL and EMBASE (1950 to April 14, 2017) were searched by two independent investigators for articles published in English. Reviews, meta-analyses, expert opinions, case reports, mini case series and editorials were excluded. Furthermore, we excluded animal studies, cadaveric studies and in vitro studies.

AREAS OF AGREEMENT

ADSCs seem to produce excellent clinical results. However, the length and modalities of follow-up in the different conditions are extremely variable. Nevertheless, it appears that the use of adipose-derived stem cells is associated with subjective and objective clinical improvements and minimal complication rates.

AREAS OF CONTROVERSY

None of the studies identified is a randomized double-blinded trial, and most of the selected studies present major limitations, and different methods, confounding the results of our review.

GROWING POINTS

It is necessary to conduct more and better studies to ascertain whether ADSCs really play a role in orthopaedic surgery with particular attention to ADSCs harvesting method, type of administration and the conditions treated.

AREAS TIMELY FOR DEVELOPING RESEARCH

The current literature regarding the use of ADSCs for orthopaedic pathologies is limited. At present, long-term safety is the biggest challenge of ADSCs based regenerative medicine.

LEVEL OF EVIDENCE

Level IV-Study of Level I, II, III, IV.

Osteochondral Regeneration with a Scaffold-Free Three-Dimensional Construct of Adipose Tissue-Derived Mesenchymal Stromal Cells in Pigs

Osteochondral lesion is a major joint disease in humans. Therefore, this study was designed to investigate the regeneration of articular cartilage and subchondral bone, using three-dimensional constructs of autologous adipose tissue-derived mesenchymal stromal cells without any biocompatible scaffolds. Mesenchymal stromal cells were harvested by liposuction from seven pigs, isolated enzymatically, and expanded until construct creation. The pig models had two osteochondral defects (cylindrical defects with a diameter of 5.2 mm and a depth of 5 mm) in one of their patello-femoral grooves. A columnar structure consisting of approximately 770 spheroids of 5 × 10⁴ autologous mesenchymal stromal cells were implanted into one of the defects (implanted defect), while the other defect was not implanted (control). The defects were evaluated pathologically at 6 months (in three pigs) and 12 months (in five pigs) after implantation. At 6 months after surgery, histopathology revealed active endochondral ossification underneath the plump fibrocartilage in the implanted defects, but a deficiency of fibrocartilaginous coverage in the controls. At 12 months after surgery, the fibrocartilage was transforming into hyaline cartilage as thick as the surrounding normal cartilage and the subchondral bone was thickening in the implanted defects. The histological averages of the implanted sites were significantly higher than those in the control sites at both 6 and 12 months after surgery. The implantation of a scaffold-free three-dimensional construct of autologous mesenchymal stromal cells into an osteochondral defect can induce regeneration of hyaline cartilage and subchondral bone structures over a period of 12 months.

Properties of porcine adipose-derived stem cells and their applications in preclinical models

Adipose-derived stem cells represent a reliable adult stem cell source thanks to their abundance, straightforward isolation, and broad differentiation abilities. Consequently, human adipose-derived stem cells (hASCs) have been used in vitro for several innovative cellular therapy and regenerative medicine applications. However, the translation of a novel technology from the laboratory to the clinic requires first to evaluate its safety, feasibility, and potential efficacy through preclinical studies in animals. The anatomy and physiology of pigs and humans are very similar, establishing pigs as an attractive and popular large animal model for preclinical studies. Knowledge of the properties of porcine adipose-derived stem cells (pASCs) used in preclinical studies is critical for their success. While hASCs have been extensively studied this past decade, only a handful of reports relate to pASCs. The aim of this concise review is to summarize the current findings about the isolation of pASCs, their culture, proliferation, and immunophenotype. The differentiation abilities of pASCs and their applications in porcine preclinical models will also be reported.